Lange Review Ultrasonography Examination, 4th Edition
Chapter 2. Adult Echocardiography
Mark N. Allen and Carol A. Krebs*
Echocardiography has evolved into a highly specialized field of ultrasound. It originally began with M-mode techniques and developed into two-, three-, and even four-dimensional imaging combined with Doppler and color-flow capabilities. Innovative technical advances, such as transesophageal examinations and contrast agents, added yet further diagnostic capabilities. Echocardiology serves as an ideal noninvasive method to examine cardiac anatomy in the normal as well as abnormal states. The combination of anatomical and functional information provided by echocardiography makes it the diagnostic method of choice in a variety of clinical situations.1
The heart is an extremely complex organ, and echocardiography provides a variety of techniques that can be applied to obtain comprehensive information about a very dynamic organ. When performing an echocardiographic examination, it is important to consider not only the two-dimensional imaging information but also the Doppler and color-flow findings.1 These techniques are performed as an integral part of an echocardiographic examination and should be used to complement one another.
TECHNIQUES AND INSTRUMENTATION
Real-time imaging combined with M-mode and Doppler are the foundation of the basic echocardiographic examination. Electrocardiography (ECG) provides timing for electrical events, which are used in making measurements and calculations. There are specific protocols established by each laboratory that govern the performance and interpretation of the examination. These protocols usually include the guidelines recommended by the American Society of Echocardiography (ASE). The positions are specifically designed for viewing specific heart structures. The structures viewed from the various positions and windows are listed in the following sections.
Left Parasternal Long-Axis View
• Anterior right ventricular free wall
• Right ventricular cavity
• Interventricular septum, including membranous portion
• Left ventricle
• Left ventricular posterior wall
• Mitral valve and apparatus
• Left ventricular outflow tract
• Aortic valve—left and noncoronary cusps
• Aortic root
• Left atrium
• Descending thoracic aorta
• Coronary sinus
Right Ventricular Inflow View
• Obtained by starting in a left parasternal long-axis view and angling anteriorly
• Right atrium
• Right ventricle
• Tricuspid valve and apparatus (chordae tendineae and papillary muscles)
Parasternal Short-Axis View
• Left ventricle—all wall segments
• Aortic valve—all three cusps
• Pulmonic valve
• Tricuspid valve
• Right atrium
• Right ventricle
• Main pulmonary artery (left and right branches)
• Interatrial septum
• Left atrium
Apical Four-Chamber View
• Left ventricle (septal wall, apex, lateral wall)
• Right ventricle
• Left atrium
• Right atrium
• Mitral valve—anterior and posterior leaflets
• Tricuspid valve
• Interatrial and interventricular septae
• Pulmonary veins
Apical Two-Chamber View
• Left ventricle (anterior wall, inferior wall, apex)
• Left atrium and left atrial appendage
• Coronary sinus
• Mitral valve
Apical Long-Axis View
• Left ventricle (septum, posterior wall, apex)
• Left atrium
• Aortic valve
• Ascending aorta
• Mitral valve (both leaflets) and apparatus
• Right ventricle (small portion)
Apical Four-Chamber View with Aorta
• Left ventricle (septal wall, apex, lateral wall)
• Right ventricle
• Left atrium
• Right atrium
• Atrioventricular valves
• Aortic valve
• Ascending aorta/left ventricular (LV) outflow tract
Subcostal Four-Chamber View
• Left ventricle (septal wall, lateral wall)
• Right ventricle
• Left atrium
• Right atrium
• Atrioventricular valves
• Interatrial septum
• Interventricular septum
Subcostal Short-Axis View
• Left ventricle—short axis
• Right ventricle
• Tricuspid valve
• Pulmonic valve
• Right ventricular outflow tract
• Main pulmonary artery
Subcostal Inferior Vena Cava View
• Inferior vena cava
• Hepatic veins
• Right atrium
• Ascending aorta
• Aortic arch
• Descending aorta
• Left common carotid artery
• Left subclavian artery
• Innominate artery
• Right pulmonary artery
Stress and Pharmacologic Examination
Stress echocardiography can be performed using a treadmill, supine or upright bike, and pacing techniques or using such pharmacologic agents as dobutamine, adenosine, or dipyridamole. The combination of echocardiography, ECG, and stress has been used since the 1980s. The use of exercise ECG only is unreliable in such subgroups of patients as women or patients who have a history of myocardial infarction or coronary bypass surgery, as well as in patients on certain medications such as antiarrhythmic agents, diuretics, and antidepressive agents. In addition, exercise ECG is unreliable in patients with certain arrhythmias, such as left bundle branch block or other repolarization abnormalities, and valvular heart disease.
The ischemic cascade is a series of events that take place with an ischemic episode (see Table 2–1).
TABLE 2–1. • Ischemic Cascade
The fact that systolic changes occur before ECG changes and patient symptoms, the addition of imaging techniques to the exercise ECG improves the diagnostic accuracy of the test.
Myocardial ischemia occurs when the regional oxygen supply is insufficient to meet the body’s demand. When the myocardial blood flow reserve becomes inadequate, such as during exercise or inotropic stimulation, it results in ischemia and impaired myocardial function. Coronary artery stenoses may have little or no effect in the resting state but become manifested during stress or exercise. Therefore, evaluation of patients with exercise has become a standard part of the echocardiographic examination.
Exercise echocardiography has evolved as a test ideally suited for the evaluation of patients with coronary artery disease (CAD) or valvular heart disease. It is a cost-effective, reliable tool for detecting the presence, extent, and distribution of coronary stenosis. Echocardiography rapidly detects regional wall motion at rest and after exercise, which allows highly accurate predictions of the extent and distribution of CAD.1 Other capabilities of stress echocardiography include the following:
• Assessment of LV size and ejection fraction
• Identification of thrombus or aneurysm that may have resulted from previous myocardial infarction (MI)
• Identification of other causes of chest pain unrelated to vascular obstruction, such as hypertrophic cardiomyopathy, aortic dissection, or pericardial disease
• The evaluation of valvular heart lesions, especially if used in conjunction with Doppler echocardiography
Indications for stress echocardiography include: (1) screening of new patients for CAD, (2) assessing states before and after intervention, (3) determining prognosis after myocardial infarction, and (4) evaluating hemodynamic significance of valvular heart disease.1
Contraindications include: (1) recent myocardial infarction, (2) unstable angina, (3) potentially life threatening dysrhythmias, (4) acute pericarditis, (5) severe hypertension, (6) acute pulmonary embolism, and (7) critical aortic valve stenosis. Interpretation of the test includes the evaluation of the patient’s blood pressure, ECG, symptoms, and the echocardiographic response to exercise. The LV myocardial segments are divided into three perfusion zones, each dictated by coronary artery anatomy. The left anterior descending artery, or LAD, supplies the anterior, septal, and apex. The left circumflex coronary artery supplies the posterolateral segments but may also supply the inferior segments depending on dominance. The right coronary artery, or posterior descending artery (PDA), supplies the inferior segments.
An exercise echocardiogram is considered positive if any of these three findings are present: (1) there is an exercise-induced wall motion abnormality, (2) there is an increase in LV volume, or (3) there is a decrease in global LV ejection fraction. The greater the wall motion abnormality, the more severe the disease. There are many factors that affect wall motion abnormalities. Perhaps the most important of these include the duration of exercise; the less exercise the patient does, the less likely the patient will achieve an adequate heart rate. A list of false positives and false negatives follows below in Table 2–2.
TABLE 2–2 • False Positives and Negatives
The use of contrast agents has gained widespread use in the field of echocardiography. Their uses range from the evaluation of left and right heart structures and function, enhancements of regurgitant and stenotic lesions, enhanced assessment of pulmonary artery pressures, presence of various shunts such as patent foramen, ASD and VSDs and other shunts, and patency coronary artery perfusion.1
Contrast agents come in many forms from the simplest, such as agitated saline solution, to complex agents composed of perfluorocarbon shells (or other substances) filled with gases. These later forms of contrast agents hold special promise not only in aiding in the identification of cardiac structures and function, but more recently in the evaluation of myocardial perfusion imaging. Currently (at the time of this writing), contrast agents are only approved by the Food and Drug Administration (FDA) in the evaluation of LV opacification and not for the evaluation of myocardial perfusion imaging. Still, research continues in the use of microbubbles to help identify coronary distribution.
Internal contrast or spontaneous echo contrast (SEC) is the discrete reflections in the blood within the cardiac chambers or vessels without the injection of contrast media. SEC is observed when blood becomes echogenic in a region of decreased flow. It is not seen with shear rates greater than 40 seconds. SEC may be seen in normal states as well as abnormal conditions. SEC has the potential to induce embolic events caused by thrombus formation.1 As technology and equipment improve, visualization of SEC may become more prevalent, even in totally healthy patients.
Contrast agents in the form of microbubbles range in size from 0.1 to 8.0 μm. These tiny spheres are strong reflectors of ultrasound but are small enough to pass through the capillary bed. The microbubbles must be small to avoid harmful effects, must remain tiny after injection, and must stay in the circulation long enough to be detected by ultrasound. The reflective property of the microbubbles comes from the material within the bubbles or spheres, which is usually gas or air bodies. Because of the acoustic impedance of the air or gas versus blood, there is a strong signal. Other factors that affect reflective properties are:
• Transmitted frequency
• Microbubble diameter
• Microbubble concentration
• Microbubble survival rate
The microbubble eventually disappears through natural processes of the body. Table 2–3 lists the currently available agents in the United States and their potential uses.
TABLE 2–3 • Microbubble Agents
Transesophageal echocardiography (TEE) is another echocardiographic technique routinely used to evaluate cardiac structure and function. It is performed by a physician with specialized training in TEE performance and interpretation.1 TEE examinations provide complete evaluation of all regions of the heart, including the great vessels. Although it is considered more invasive than a transthoracic or surface echocardiogram, it is a relatively simple procedure tolerated by most patients.
Atrial paced TEE is performed by attaching a flexible silicone-coated pacing catheter to the TEE probe. Pacing is increased incrementally to 85% of patient age predicted maximum heart scale. LV function is monitored by TEE examination at baseline, as well as during and immediately after maximal pacing. This technique has a high sensitivity and specificity for detection of CAD and a high success rate of 90̫100% of patients.1
TEE plus pharmacologic agents is used to assess CAD and has proved to be feasible and accurate. At each stage of dobutamine infusion, it is important to use longitudinal and transverse planes to optimize visualization of all wall segments.
There are several advantages of using TEE, that include the following:
• TEE provides higher resolution than the transthoracic echocardiographic (TTE) exam because of the use of the transesophageal window, that allows the use of higher frequencies. The transducer is mounted on a flexible gastroscope that is sufficient in length to be advanced down the esophagus. It is positioned behind the posterior wall of the left ventricle.
• TEE provides additional viewing of structures that are often not seen well on the TTE exam in technically difficult studies. These structures include the posterior cardiac structures such as the aorta, atria, left atrial appendage, and cardiac valves.
• TEE provides “off-axis planes” in addition to the standard planes, which often provides a clearer view of the anatomy or anomalies.
There are contraindications to performing the TEE examination. These include: esophageal tumors or tumors of the mouth, esophageal stenosis or strictures, diverticulum, esophageal varices, perforated viscus, gastric volvulus or perforation, active gastrointestinal tract bleeding, and patient refusal or unwillingness to cooperate.1 Occasionally, the TEE probe cannot be easily passed and should never be forced.
Table 2–4 lists the indications for TEE.
TABLE 2–4 • Indications for TEE
To become proficient in the techniques of echocardiography, a thorough understanding of cardiac anatomy is essential. One must know the normal structures and be able to recognize normal variants from pathologic states. One must also understand the anatomic orientation of the heart within the chest cavity.
The heart is a cone-shaped, hollow, fibromuscular organ located in the middle mediastinum between the lungs and the pleurae. It has a base, apex, and multiple surfaces and borders. It is enclosed within the pericardium. The pericardium is made of fibrous and serosal components. The fibrous pericardium is the tough outer sac that completely surrounds the heart but does not adhere to it. The serosal component is the inner layer, which has two components. The visceral, or epicardial, layer adheres to the surface of the heart and makes up the epicardium and the serosal pericardium, which is the outer or parietal layer. The serosal pericardium lines the inside surface of the fibrous pericardium. Within the serosal layers is a thin film of pericardial fluid. The purpose of the pericardium is to (1) reduce friction with cardiac movement; (2) allow the heart to move freely with each beat, facilitating ejection and volume changes; (3) contain the heart within the mediastinum, especially during trauma; and (4) serve as a barrier to infection.1
The average adult heart measures approximately 12 cm from the apex to the base, 8–9 cm transversely in the broadest diameter, and 6 cm anterior–posterior. The weight varies in males ranging from 280–340 g and in females from 230–280 g. Cardiac weight is approximately 0.45% of total body weight in men and 0.40% of total body weight in women.1,2
The heart is divided into four chambers: two atria and two ventricles. The external surface contains numerous grooves and sulci. The coronary or atrioventricular groove separates the atria from the ventricles and contains the main trunk of the coronary arteries and coronary sinus. The interventricular groove separates the right and left ventricles. The anterior interventricular groove runs on the anterior surface and contains the descending branch of the left coronary artery. The posterior interventricular groove lies on the diaphragmatic surface of the heart and contains the posterior interventricular descending coronary artery and the middle cardiac vein. The interatrial grooves separate the atria. The interatrial grooves are shallow and less prominent than the other grooves. The interatrial, atrioventricular, and posterior interventricular grooves meet and form the crux of the heart. The terminal groove or sulcus terminalis demarcates the true atrium and the venous component of the right atrium. These external grooves are filled with fatty tissue that varies with overall body fat and increases with age.1
There are basically two important types of heart valves: the semilunar and the atrioventricular. Semilunar valves are the aortic and the pulmonary. Atrioventricular valves are the tricuspid and the mitral.
Numerous pathologies can affect the heart in the adult. These disease states can cause a variety of primary as well as secondary anatomical changes in the heart. Knowing what these changes are greatly enhances the echocardiographic examination. Once the student has an understanding of the heart anatomy, the echocardiographic images are better understood. The basic two-dimensional echocardiographic views are illustrated in Figs. 2–1 to 2–8. These figures are from the American Society of Echocardiography and are the accepted nomenclature for two-dimensional imaging.
FIGURE 2–1. Parasternal long-axis view of the heart demonstrating the method of subdividing the myocardial walls along the long axis (L) into three regions of equal length using the left ventricular papillary muscles as landmarks. (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–2. Apical four-chamber view of the heart demonstrating the method of subdividing the myocardial walls into three regions using the left ventricular papillary muscles as landmarks. (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–3. Apical long-axis view of the heart demonstrating the method of subdividing the myocardial walls into three regions of equal length. (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–4. The functional and anatomic left ventricular outflow tracts of the heart are diagrammed in the upper panel (A), whereas the functional and anatomic right ventricular outflow tract is illustrated in the bottom panel (B). (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–5. Diagram of the heart (A) and the short-axis views of the basal region (B), midventricular region (C), and apical region (D). (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–6. Short-axis view of the basal region of the heart demonstrating the method of subdividing the myocardial walls into segments using a coordinate system consisting of eight lines that are 45° apart. With this system, the left ventricular free wall (LVFW) is divided into five segments, whereas the ventricular septum (VS) and right ventricular free walls (RVFW) are subdivided into three segments each. (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–7. Short-axis view of the midventricular region of the heart demonstrating the method of subdividing the myocardial walls into segments using a coordinate system consisting of eight lines that are 45° apart. With this system, the left ventricular free wall (LVFW) is divided into five segments, whereas the ventricular septum (VS) and right ventricular free walls (RVFW) are subdivided into three segments each. (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
FIGURE 2–8. Short-axis view of the apical region of the heart demonstrating the method of subdividing the myocardial walls into segments using a coordinate system consisting of four lines that are 90° apart. With this system, the left ventricular free wall (LVFW) is subdivided into three segments, whereas the ventricular septum and right ventricular free wall (FW) are subdivided into one segment each. (Reproduced with permission from Henry WL, DeMaria A, Feigenbaum H, et al: Report of the American Society of Echocardiography Committee on Nomenclature and Standards: Identification of myocardial wall segments. November, 1982: 1–15.)
Anatomy. The left ventricle is the largest cardiac chamber, accounting for 75% of the heart mass. It consists of two papillary muscles, has trabeculations in the apex, and a smooth-walled basal area. Its end-diastolic diameter is 3.6–5.6 cm, and its end-systolic diameter is 2.3–4.0 cm. Normal fractional shortening (difference between diastolic and systolic diameters is:
Normal LV wall thickness in diastole ranges from 0.6–1.1 cm.
Hemodynamics. The ventricle receives oxygenated blood from the left atrium and pumps it through the aortic valve to the body by way of arteries, arterioles, and capillaries. Its systolic pressure is 100–120 mm Hg.
Echocardiographic Views. Almost all the standard views allow visualization of at least part of the left ventricle. The apical views allow examination of the apex, which can be difficult to see in other views. The maximum internal dimensions are seen at end systole and should be taken at the peak posterior motion of the interventricular septum (see Table 2–5).
TABLE 2–5 • TEE Left Ventricle Examination
Anatomy. The left atrium is a smooth-walled sac, the walls of which are thicker than those of the right atrium. The chamber receives four pulmonary veins: two (sometimes three) on the right and two (sometimes one) on the left. The interatrial septum divides the left and right atria. It is thinnest in its central portion, the fossa, and varies in thickness elsewhere due to fat deposits. These normally increase with age. The left auricle, or left atrial appendage, arises from the upper anterior part of the left atrium and contains small pectinate muscles. The average dimension of the chamber in the adult is 29–38 mm.
Hemodynamics. The mean pressure in the left atrium ranges from 1 to 10 mm Hg. Oxygenated blood flows from the lungs and enters the atrium through the pulmonary veins. As left atrial pressure increases over that of the left ventricle, the mitral valve opens, and blood then passes through the mitral valve and enters the left ventricle.
Echocardiographic Views. Maximal dimensions should be measured at end-systole. Measurements may be made from the leading edge of the posterior wall of the aorta to the leading edge of the posterior wall of the left atrium. This chamber is best seen from the parasternal long- and short-axis views; however, it also can be seen from the apical and subcostal views. In the left parasternal long-axis view, the descending aorta can be seen from running posteriorly to the left atrium. Care must be given when measuring the diameter of the left atrium so that the descending aorta is not included in the measurement because this will give an erroneous left atrial diameter. The left atrial appendage can be seen from the transthoracic two-chamber and parasternal short-axis views.
TEE can also be used to evaluate this area and is typically carefully evaluated in patients where the source of embolus is a consideration or when patients may be scheduled for cardioversion.
Anatomy. The right atrium has two parts: an anterior portion and a posterior portion. The two portions are separated by a ridge of muscle called the crista terminalis. This area is typically not well seen from the transthoracic approach.
The smooth-walled posterior portion of the atrium is derived from the embryonic sinus venosus and receives the inferior and superior vena cavae. Guarding the opening (ostium) of the inferior vena cava is a thin fold of tissue called the eustachian valve, which is sometimes large and complex and forms a network of tissues known as the network of Chiari. The coronary sinus also enters the right atrium anteriorly to the inferior vena cava. The coronary sinus also can be guarded by a thin fold of tissue called the Thebesian valve.
The anterior portion, that represents the embryonic right atrium, is extremely thin and is trabeculated. The right atrial appendage, or right auricle, arises from the superior portion of the right atrium and contains pectinate muscle. The dimensions of the right atrium in adults range from 26 to 34 mm.
Hemodynamics. Deoxygenated blood from the body, head, and heart flows into the right atrium through the inferior vena cava, the superior vena cava, and the coronary sinus, respectively. When pressures in the right atrium increase above the pressures in the right ventricle, the tricuspid valve opens, allowing the blood to flow forward into the right ventricle. Mean pressures in this chamber range from 0 to 8 mm Hg.
Echocardiographic Views. Apical views are best for assessing the right atrium. Others include the subcostal and, to a lesser extent, the parasternal short-axis views.
Anatomy. The right ventricle is divided into a posterior inferior inflow portion and an anterior superior outflow portion. The inflow portion contains the tricuspid valve and is heavily trabeculated. The outflow portion, also called the infundibulum, gives rise to the pulmonary trunk. The subpulmonic area is smooth walled.
The right ventricle contains numerous papillary muscles that anchor the tricuspid valve. The ventricle contains numerous bands of muscle. One band, the moderator band, is readily seen in the apex of the ventricle by two-dimensional imaging. Internal diameters range from 7 to 26 mm.
Hemodynamics. Systolic pressures range from 15 to 30 mm Hg, and diastolic pressures range from 0 to 8 mm Hg.
Echocardiographic Views. The right ventricle is seen best from the apical and subcostal views. It also can be seen from the left parasternal long- and short-axis views and right ventricular inflow view.
Anatomy. The aorta arises from the base of the heart and enters the superior mediastinum, where it almost reaches the sternum, then courses obliquely backward and to the left over the left bronchus. It then becomes the descending aorta and courses downward anterior to and slightly left of the vertebral column. The aorta is highly elastic and has three layers: (1) a thin inner layer called the tunica intima, (2) a thick middle layer called the tunica media, and (3) a thin outer layer called the tunica adventitia. The diameter of the aortic root measures 2.5–3.3 cm.
Hemodynamics. Maximal velocities of blood flow in adults are 1.0–0.7 m/s.
Echocardiographic Views. The aortic root is seen from the parasternal views. A good portion of the ascending aortic arch can be seen by beginning with the transducer in a standard left parasternal long-axis view and sliding the probe up an intercostal space. The ascending aorta, aortic arch, and descending aorta can be seen from the suprasternal view. As was mentioned earlier, part of the descending aorta also can be seen behind the left atrium in the long-axis view. The subcostal views allow visualization of the aortic root and valve.
Main Pulmonary Artery
Anatomy. The main pulmonary artery is located superior to and originates from the right ventricle. Immediately after leaving the pericardium, it bifurcates into a right pulmonary artery and a left pulmonary artery that enter the right and left lung, respectively.
Hemodynamics. This artery delivers deoxygenated blood from the right ventricle to the lungs. Flow velocities range from 0.6 to 0.9 m/s.
Echocardiographic Views. The artery is best seen from the parasternal short-axis view.
Anatomy. The mitral valve is an atrioventricular valve. It is located between the left atrium and the left ventricle and it is a thick yellow-white membrane that originates at the annulus fibrosus, a fibrous ring that surrounds the orifice of the valve. The valve has an anterior leaflet and a posterior leaflet, both of which have sawtooth-like edges. Both leaflets are attached to papillary muscles by chordae tendineae. The surface on the atrial side of the valve is smooth, whereas the surface on the ventricular side is irregular the normal mitral valve area is 4–6 cm2.
Hemodynamics. Flow velocities across the valve range from 9.6 to 1.3 m/s. The valve’s function is to prevent backflow of blood from the left ventricle into the left atrium.
Echocardiographic Views. The mitral valve is best seen from the long- and short-axis parasternal views and the apical view. Doppler measurements are best obtained from the apical four- and two-chamber views.
Anatomy. The aortic valve consists of three pocket-shaped, thin, smooth cusps named according to their location in relation to the coronary arteries. The cusp near the left coronary artery is the left coronary cusp, the cusp near the right coronary artery is the right coronary cusp, and the cusp that is not near a coronary artery is the noncoronary cusp. Because of its lunar, or half-moon shape, the aortic valve is referred to as semilunar. The normal aortic valve area is 3–4 cm2.
Hemodynamics. The function of the aortic valve is to prevent backflow of blood from the aorta into the left ventricle. The velocity of flow ranges from 1.0 to 1.7 m/s.
Echocardiographic Views. The valve is best seen from the parasternal views. It also can be seen from the apical four-chamber view with anterior angulation. The best Doppler measurements are obtained from the apical four-chamber view with anterior angulation, from the right parasternal window, and from the suprasternal view.
Anatomy. The tricuspid valve is an atrioventricular valve. It is located between the right atrium and ventricle. The atrial side is smooth, whereas the ventricular side is irregular. As in the mitral valve, it is a thick yellow-white membrane that originates at the annulus fibrosus, a fibrous ring that surrounds the orifice of the valve. The valve has three leaflets—anterior, posterior, and medial—all of which are sawtooth-like in appearance. Each leaflet is attached to papillary muscles by chordae tendineae.
Hemodynamics. The function of this valve is to prevent backflow of blood from the right ventricle to the right atrium. The velocity of flow ranges from 0.3 to 0.7 m/s.
Echocardiographic Views. The valve is best seen from the parasternal short-axis, parasternal four-chamber, apical four-chamber, and subcostal views. Measurements are best obtained in the parasternal four-chamber view. The best Doppler measurements are taken from the parasternal short-axis and apical four-chamber views.
Anatomy. The pulmonic valve consists of three thin, smooth pocket S-shaped cusps. Because of its shape, this valve, like the aortic valve, is called semilunar.
Hemodynamics. The function of this valve is to prevent backflow of blood from the main pulmonary artery to the right ventricle. The velocity of flow ranges from 9.6–0.9 m/s.
Echocardiographic Views. The pulmonic valve is best seen from the parasternal short-axis view. The best Doppler recordings are taken from the left parasternal short axis.
The heart functions as a pump to distribute blood to the body. In order for blood to be adequately distributed, the blood pressure must be maintained. Pressure and flow are controlled by a complex control mechanism that responds to the metabolic requirements of the body.
There are two fluid pumps within the heart, one on the right and one on the left, lying side by side. The right side supplies the pulmonary circulation. From the lungs, blood returns to the left side and ultimately supplies the body via the systemic circulation. The volume pumped by both sides is equal to ensure normal circulation of flow. The blood is pumped from the ventricles during systole and received during diastole, the relaxation phase. The cardiac cycle includes all of the electrical and mechanical events that occur during the cycle of one heartbeat (see Fig. 2–9). Each side of the heart has specific characteristics and functions, which are listed below.
FIGURE 2–9. Events of the cardiac cycle.
RIGHT HEART CHARACTERISTICS AND FUNCTIONS
• Blood returns to the right atrium from the superior and inferior vena cava.
• Right heart supplies the pulmonary circulation.
• Normal pressure in the right ventricle is approximately 22 mm Hg.
• Blood returning to the right heart has a lower oxygen saturation (75%).
• Contains the tricuspid valve which closes during right ventricular systole and contained blood in right ventricle is propelled out of right ventricle outflow tract through the open semilunar pulmonic valve to the pulmonic circulation.
LEFT HEART CHARACTERISTICS AND FUNCTIONS
• Left ventricular pressure is approximately 120 mm Hg.
• Blood pumped from the left ventricle has a high oxygen saturation (95–100%).
• Left atrium receives blood from the lungs through the pulmonary veins in the back of the left atrium.
• During left atrial systole, the mitral valve opens and allows blood in the left atrium to be propelled into the left ventricle. When ventricular systole occurs, the mitral valve closes and blood is propelled out of the left ventricle through the outflow tract.
The blood supply to the heart is derived from the right and left coronary arteries and their respective tributaries (see Fig. 2–10).
FIGURE 2–10. Anatomic drawing of the heart and vessels.
CONDUCTION SYSTEM OF THE HEART/INTRINSIC INNERVATION OF THE HEART
The conduction system of the heart is responsible for the initiation, propagation, and coordination of the heartbeat. Fig. 2–11 demonstrates this system.
FIGURE 2–11. Intrinsic conduction system of the heart.
The sinoatrial node (SA) is also called the pacemaker of the heart. It provides the bursts of electrical impulses that are conducted throughout the walls of the heart. The activation conduction is from the sinoatrial node to the atrioventricular (AV) node, where it is slows and delays. The impulse is conducted to the ventricles by way of the atrioventricular bundle and the right and left bundle branches. It becomes continuous with the fibers of the Purkinje network. The ventricles contract and blood is ejected to the pulmonic and systemic circulation. The heart contains its own intrinsic conduction system; however, its rate is modified by the autonomic nervous system. Fibers from both the sympathetic and the parasympathetic nervous systems are received by the heart. Sympathetic nervous system fibers are received by the atria via the right and left vagus nerves, which contribute to the control of the sinoatrial and atrioventricular nodes. The parasympathetic nerves are derived from the vagus and come off in the neck as vagal cardiac nerves. They connect to the sinoatrial node. Stimulation of the parasympathetic nervous system fibers to the heart causes the following:
• Decrease in the heart rate
• Retardation of transmission between the atria and ventricles
• Decrease in the force of contraction
• Decrease in conduction rate of the nodes and atria
The sympathetic and parasympathetic nervous systems have opposite effects on the heart. The reflex center for both is in the medulla oblongata.
DISEASES AFFECTING THE VALVES
Anomalies or diseases of the valves can be divided into two main categories. Valve anomalies that occur in fetal development are known as congenital anomalies. Valve anomalies that develop after fetal development or in the adult stages are referred to as acquired valve disease. This latter category can be further divided into rheumatic and nonrheumatic heart disease.
Mitral Valve Disease
Stenosis. Mitral valve stenosis results primarily from rheumatic disease. The valves may not become involved for many decades following rheumatic fever. Congenital mitral stenosis can occur but is extremely rare.
M-mode findings include (1) a flattened E-D slope (reduced diastolic filling), (2) anterior motion of the posterior leaflet, (3) thickened leaflets, and (4) an absent A wave in the absence of atrial fibrillation. Two-dimensional imaging also indicates thickening and shows doming of the leaflets in diastole.
Doppler measurements reveal a reduced rate of decrease in diastolic flow (reduced diastolic slope), a higher than normal peak velocity of flow, and spectral broadening on Doppler display. Secondary findings and complications include left atrial dilatation, pulmonary hypertension, a left atrial clot, and an exaggerated diastolic dip of the interventricular septum.3 Color Doppler shows turbulent LV inflow.
Stenosis-Severity of Mitral Stenosis (Valve Area)
Regurgitation. Mitral regurgitation (shunting back and forth of blood) can occur as a result of mitral annular calcification, rheumatic mitral disease, flail mitral valve leaflet, conditions that may stretch the mitral annulus, such as cardiomyopathies, myocardial infarction, mitral valve vegetations or other masses on the mitral valve or within the left atrium, papillary dysfunction, and mitral valve prolapse. The hallmark sign of regurgitation is a systolic murmur, most often maximal over the LV apex.
M-mode findings include (1) increased size of the left atrium, (2) exaggerated motion of the interventricular septum, (3) pulsations of the left atrial wall, and (4) preclosure of the aortic valve during systole. The first three findings are the result of volume overload.
Two-dimensional imaging reveals an increase in the size of the left atrium and exaggerated motion of the interventricular septum—all of which are the result of volume overload. In addition, pulsations of the left atrial wall and preclosure of the aortic valve during systole are observed.
Doppler may be used to evaluate the regurgitant fraction. Color Doppler displays the turbulent jet in the left atrium and is useful for estimating the severity of regurgitation.
Prolapse. (Protrusion or buckling of the mitral leaflets into the left atrium in systole.) The classic clinical findings in mitral valve prolapse are a systolic click (a sound that corresponds with the posterior displacement of the mitral valve leaflet into the left atrium) and a late systolic murmur (a sound that corresponds with the resulting mitral regurgitation that often occurs because of the prolapsing leaflets).
M-mode findings include late systolic posterior displacement of the anterior and posterior leaflets and anterior motion of the mitral valve in early systole. To achieve the best views for making the diagnosis, the ultrasound beam should be perpendicular to the valve from the parasternal windows. The two-dimensional findings reveal that the valve is bowing into the left atrium and, in many cases, thickened.
Flail Leaflet. The most common cause of flail leaflet is rupture of the chordae tendineae, which often occurs secondarily to myocardial infarction. Rupture of papillary muscle is a less common etiology.
M-mode findings indicate coarse diastolic fluttering and systolic fluttering of the leaflet and visualization of part of the leaflet in the left atrium. Two-dimensional imaging indicates protrusion of the flail leaflet into the left atrium, non-coaptation of the two leaflets, and a systolic and coarse diastolic motion of the flail leaflet. Doppler measurements indicate harsh, turbulent mitral regurgitation.
Annular Calcification. Mitral annular calcification results from the deposition of calcium in the annulus of the mitral valve. This is normally associated with aging. This condition can be caused by mitral regurgitation, conduction abnormalities, aging, or obstruction of the LV outflow (LVOF) tract.
M-mode findings reveal high-density echoes between the valve and the posterior wall of the left ventricle. Two-dimensional imaging reveals high-density bright echoes between the valve and the posterior wall of the left ventricle.
Aortic Valve Disease
Stenosis (versus Sclerosis). The cause of stenosis of the aortic valve can be congenital, the result of rheumatic heart disease, or degeneration. Degenerative disease is the most common cause of aortic valve stenosis. Clinical symptoms include chest pain, shortness of breath, and syncope. These symptoms do not present until the aortic valve stenosis becomes moderate to severe. Patients with aortic valve stenosis often present with a harsh systolic murmur heard at the right sternal border, which often radiates to the carotids.
The normal aortic valve has three leaflets. In congenital or rheumatic stenosis, the body of the cusps may appear to be thin and pliable, but the cusp tips are tethered, resulting in a systolic doming effect that is best seen in the early systole from a left parasternal or apical long-axis view. In degenerative stenosis, the cusps frequently appear to be bright reflectors with little or no discernable cusp separation. Because of the increased pressure from the valve stenosis, the walls of the left ventricle become thickened or hypertrophied.
M-mode findings indicate thickened cusps and restricted excursion of the cusps to <1.5 cm. Continuous-wave Doppler is used in the apical long-axis or apical “five”-chamber views to evaluate the velocity across the valve. The peak instantaneous and mean aortic gradients are recorded. The continuity equation is commonly used to evaluate the severity of the aortic valve stenosis by calculating the valve area. This equation is based on the principle of “conservation of mass.” All blood flow going across the LVOT must be equal to the blood flow across the aortic valve. By determining the flow in the LVOT, the flow in the aortic valve can also be determined. This is measured by calculating the velocity integral of flow in the LVOT and at the aortic valve leaflet tips. The diameter of the LVOT is also measured to obtain a cross-sectional area. The continuity equation is as follows: Flow 1 = Flow 2, where Flow 1 = LVOT VTI × LVOT CSA and Flow 2 = AV VTI × AV CSA. The aortic valve area, or AVA, is calculated by dividing LVOT VTI × LVOT CSA by AV VTI. It is important to note that the LVOT VTI is obtained using pulsed-wave Doppler, whereas the AV VTI is obtained using continuous wave Doppler. The LVOT diameter is a two-dimensional measurement. Current equipment normally performs this calculation for the user, but an understanding of these principles is important. The normal aortic valve area is 2.5–4.5 cm2. The normal diameter of the LVOT ranges from 1.8 to 2.4 cm with an LVOT VTI of 18–22 cm (see Table 2–6). Color Doppler can also be used to help identify aortic valve stenosis by demonstrating turbulent flow in the ascending aorta.
TABLE 2–6 • Criteria Range for Aortic Valve Stenosis
Parasternal Long- and Short-Axis Views. These views can be used to help evaluate the aortic valve cusps, making measurements of the LV walls in M-mode or two-dimensional planes. The diameter of the LVOT is usually taken from a left parasternal long-axis view, although the apical long-axis view may also be used.
Apical Views. The apical views are used to obtain Doppler measurements across the valve because the blood flow is parallel to the sound beam and, therefore, well suited to obtain maximal and accurate blood velocities.
Regurgitation. The effects of regurgitation on atria, ventricles, and cardiac vessels result in dilatation of the left ventricle. The condition can be caused by any one of the following: congenital (bicuspid cusp), rheumatic heart disease (the most common cause in adults), or degeneration of the leaflet caused by infection or aortic dilatation (Marfan syndrome).
M-mode findings reveal fluttering of the interventricular septum and diastolic fluttering of the mitral valve. Two-dimensional imaging indicates fine diastolic fluttering of the aortic valve, diastolic fluttering of the mitral valve, and fluttering of the interventricular septum. Spectral Doppler studies reveal diastolic flow, which appears above the baseline when in an apical position.
Tricuspid Valve Diseases
Stenosis. Stenosis of the tricuspid valve is most often caused by rheumatic heart disease. It can be caused by other conditions, which include systemic lupus erythematosus (SLE), carcinoid heart disease, Löffler’s endocarditis, metastatic melanoma, and congenital heart disease.1 In stenotic disease of the tricuspid valve, the effects on atria, ventricles, and vessels cause dilatation of the right atrium.
M-mode findings indicate a reduced diastolic slope and thickening and decreased separation of the leaflets. Two-dimensional imaging reveals the most specific finding, systolic doming, as well as thickening of the leaflets. In Doppler measurements, the sample is placed in the right ventricle, and the results indicate turbulent diastolic flow and slowed reduction in the velocity of flow during diastole.
Doppler is used to qualify and quantitate the severity of stenosis.
Regurgitation. Regurgitation is a common abnormality associated with the tricuspid valve in adults.1 The primary cause of regurgitation is secondary to pulmonary hypertension. In rare cases, the condition can be caused by rheumatic heart disease, prolapse of the valve, or carcinoid heart disease. A secondary effect is dilatation of the right atrium and ventricle. Continuous-wave Doppler is used to measure the velocity of the regurgitant jet. Pulmonary artery pressure may be calculated by adding the pressure gradient across the tricuspid valve to right atrial pressure (normally 5–10 mm Hg). Generally, a TR (tricuspid valve regurgitation) velocity at 3 m/s or greater indicates pulmonary hypertension.
M-mode findings indicate a dilated right ventricle and anterior motion of the interventricular septum during isovolumetric contraction. Two-dimensional imaging reveals incomplete closure and diastolic fluttering of the leaflets, ruptured chordae, dilatation of the right ventricle, and flattening of the interventricular septum. With Doppler measurements, turbulent flow can be detected in the right atrium during systole.
Pulmonic Valve Disease
Stenosis. The causes of pulmonic valve disease are atherosclerosis, infections, endocarditis, and papillary fibroma. This disease is extremely rare in adults. Continuous-wave Doppler reveals velocities greater than 2 m/s in the main pulmonary artery. Color Doppler reveals turbulent flow distal to the pulmonic valve.
Regurgitation. M-mode findings reveal fluttering of the tricuspid leaflets, and Doppler measurements reveal early diastolic high-velocity, turbulent flow. The cause can be pulmonary hypertension or bacterial endocarditis or secondary to pulmonary valvotomy.
Endocarditis is an inflammation of the endocardium characterized by vegetations on the surface and in the endocardium.1
Types. Endocarditis can be caused by either bacteria or vegetation (fungus-like growth) and, depending on the infecting organism, is classified as acute or subacute. Although the disease can occur in the endocardium of the heart, the infection usually affects the endocardium in specific valves and is more likely to affect the left heart than the right. Infection of the tricuspid and pulmonic valves is usually the result of intravenous (IV) drug abuse.
Bacterial Endocarditis. Predisposing factors for bacterial endocarditis include dental procedures, tonsilloadenoidectomy, cirrhosis, drug addiction, surgery, and burns. Infectious endocarditis is mainly caused by two groups of bacteria: staphylococci and streptococci.1
Nonbacterial Endocarditis. Among the nonbacterial forms of the disease are SLE and fungal (mycotic), nonbacterial thrombotic, Löffler’s, marantic, and Libman-Sacks endocarditis. The most common manifestation of SLE is vegetation. Although this nonbacterial form of endocarditis primarily involves the mitral valve, it also can affect the mural endocardium. The mycotic form of the disease is usually subacute and can be caused by a variety of fungi—most commonly Candida, Aspergillus, and Histoplasma. In the thrombotic form of nonbacterial endocarditis, the vegetation consists of fibrin and other blood elements.
Löffler’s endocarditis is characterized by a marked increase of eosinophils. It primarily affects men in their forties who live in temperate climates. The disease affects both ventricles equally. Thickening of the inflow portions of the ventricles and the apices can be observed, as can formation of mural thrombi. Hemodynamically, diastolic filling is impaired because of increased stiffness of the heart. Atrioventricular valve regurgitation is a typical finding.
In the marantic form of the disease, the vegetation is nondestructive and sterile. It occurs in patients with malignant tumors and primarily affects the valves on the left side of the heart. Embolus is the most serious complication.
Libman–Sacks endocarditis is characterized by vegetation or verrucae on the echocardium.
Hemodynamic Mechanisms. One common cause of subacute infectious endocarditis occurs when a high velocity jet consistently hits a surface. Damage results when blood from a high-pressure area flows to a low-pressure area; this is called the Venturi effect. The site where vegetation has formed will usually be in the low-pressure area. When the mitral valve is involved and mitral regurgitation is present, the atrial side of the leaflets is the susceptible area. In this case, the high-pressure area is the ventricle, and because the mitral leaflets fail to coapt, the low-pressure area is the atrial side of the leaflets. The atrial wall that bears the brunt of the regurgitation also may become infected.
When the aortic valve is involved and aortic insufficiency is present, the aorta is the high-pressure area, and the ventricle is the low-pressure area. Vegetations tend to form on the ventricular side of the aortic cusps because the cusps do not close completely in aortic regurgitation. The section of the ventricular wall hit by the regurgitant jet also may be damaged.
In ventricular septal defects (VSDs), the high-pressure area is the left ventricle in left-to-right shunting and the low-pressure area is the right ventricular side of the defect. The right ventricular wall directly across from the defect also can suffer damage and become prone to vegetation.
The presence of a mass on any valve leads to a diagnosis of infection caused by vegetation. However, echocardiography cannot differentiate between a new and an old infection. M-mode patterns indicate shaggy echoes on the infected valve and detect 52% of vegetations. TEE is the imaging modality of choice.
Aortic Valve. Vegetation is seen best in diastole and is attached to the ventricular side of the cusps. This condition can cause reduced cardiac output and acute aortic regurgitation. The best views for two-dimensional imaging are the left parasternal long and short axes.
Mitral Valve. Predisposing factors to vegetational infection of the mitral valve include mitral valve prolapse, rheumatic valvulitis, and dysfunction of the papillary muscles with secondary mitral regurgitation and mitral annular calcification. Infection occurs most commonly on the atrial side of the leaflet.
The best views include the left parasternal short and long axes; the apical two- and four-chamber views also can be used. Vegetations as small as 2 mm in diameter are detectable or can be as large as 40 mm in diameter. Whereas M-mode imaging detects 14–65% of the vegetation, two-dimensional imaging detects 43–100%. Differential diagnoses include myomas, lipomas, and fibromas.
Tricuspid or Pulmonic Valve. Infections of the tricuspid or pulmonic valves are usually caused by intravenous (IV) drug abuse. Such infections are less common than left-sided infections; however, when they occur on the tricuspid valve, the infections can become larger than is typical of left-sided infections. They rarely occur on the pulmonic valve.
Types. Two types of prosthetic valves are available: mechanical and bioprosthetic. The mechanical types are ball-in-cage, disc-in-cage, and tilting-disc valves. The Starr–Edwards valve is the most common ball-in-cage type. The best view for observing excursion of the ball is the apical view when in the mitral and aortic positions. The disc-in-cage valve has less excursion than the ball-in-cage type. The most common type of tilting-disc valve is the Bjork–Shiley, which consists of one disc that tilts. The less common St. Jude valve contains two tilting discs.
All bioprosthetic valves are made from biological tissue, which include heterografts or xenografts (porcine tissue or bovine pericardial tissue), homografts (human cryopreserved from autopsy), and allografts (patient’s own tissue).1 The most common bioprosthetic valve is the xenograft. A porcine heterograft is the most commonly used tissue; porcine pericardial tissue also can be used. Human homografts and fascia lata tissue are sometimes used as valves.
Malfunctions. The following factors cause both types of prosthetic valves to malfunction: thrombi, regurgitation, stenosis, dehiscence, and vegetation.
Thrombi. Blood clots, the most common cause of valve malfunction, reduce the effective orifice and impair motion of the ball, disc, or leaflet tissue. Their major complication is the potential for an embolus. Two-dimensional imaging is the echocardiographic technique of choice for detecting the presence of a clot. The limitation of the technique is the masking effect produced by the highly reflective nature of the prosthetic valves. In the Bjork–Shiley mitral prosthesis, there is a rounding to the E point on M-mode.
Regurgitation. Regurgitation can occur through the valve or around the sewing ring. Doppler echocardiography is the procedure of choice for detecting the problem. When masking is a problem from apical views, color Doppler is especially useful. Color-flow Doppler not only allows spatial orientation but also demonstrates the direction of blood jets. Secondary echocardiographic findings for aortic prosthetic regurgitation include: (1) fluttering of the mitral valve, (2) fluttering of the interventricular septum, and (3) evidence of volume overload in the left ventricle. Doppler echocardiography also is a procedure of choice for detecting paravalvular leaks with a high degree of sensitivity and specificity. In the Bjork–Shiley mitral valve, an early diastolic bump is noted by M-mode and two-dimensional imaging.
Stenosis. All prosthetic valves have some degree of obstruction. Doppler echocardiography can detect a valve with moderate to severe stenosis.
Dehiscence. In dehiscence, the valve becomes detached from its sewing bed. Disruption of suture lines securing the prosthesis to the sewing ring is usually the cause. The result is severe regurgitation, heart failure, or both, which can be detected by a Doppler examination. Two-dimensional imaging demonstrates an unusual rocking motion away from its normal excursion. Cinefluoroscopy can be helpful in assessing abnormal rocking motion.
Vegetation. As was mentioned earlier, vegetation is difficult to assess with echocardiographic techniques because it is often masked by the highly reflective properties of the prosthesis. These infections are usually found on bioprosthetic valves, are extremely mobile, and are more common in the aortic than in the mitral position.
Degeneration. Degeneration is most common in the bioprosthetic valves and usually occurs as a result of calcification of the area where the valve is joined to the surrounding tissue.
DISEASES AFFECTING THE PERICARDIUM
The pericardium is composed of two layers. The inner layer is a serous membrane called the visceral pericardium, which is attached to the surface of the heart. This layer folds back upon itself to form an outer fibrous layer called the parietal pericardium. Between the two layers is the pericardial space, which is filled with a thin layer of fluid throughout. The functions of the pericardium are to (1) fix the heart anatomically1, (2) prevent excessive motion during changes in body position, (3) reduce friction between the heart and other organs, (4) provide a barrier against infection, and (5) help maintain hydrostatic forces on the heart. Pericardial disease can be caused by any one of the following: malignant disease that spreads to the pericardium, pericarditis, acute infarction, cardiac perforation during diagnostic procedures, radiation therapy, SLE, or postcardiac surgery.
In the normal pericardium, the pressure within the pericardial space is similar to that in the intrapleural pressure and lower than the right and LV diastolic pressures. Increased intrapericardial pressure depends on three factors: the volume of the effusion, the rate at which fluid accumulates, and the characteristics of the pericardium. The normal intrapericardial space contains 15–50 mL of fluid, and it can tolerate the slow addition of as much as 1–2 L of fluid without increasing the intrapericardial pressure. However, if the fluid is added rapidly, the intrapericardial pressure increases dramatically.
Pericardial effusion can be diagnosed using M-mode and two-dimensional techniques. Three diagnostic criteria can be used: (1) posterior echo-free space, (2) obliteration of echofree space at the left atrioventricular groove, and (3) decreased motion of the posterior pericardial motion.
Cardiac tamponade results when intrapericardial pressures increase. This problem is characterized by increased intracardiac pressures, impaired diastolic filling of the ventricles, and reduced stroke volume. The following echocardiographic findings are associated with cardiac tamponade:
• Increased dimensions of the right ventricle during inspiration
• Decreased mitral diastolic slope (E–F)
• Decreased end-diastolic dimension of the right atrium or ventricle
• Posterior motion of the anterior wall of the right ventricle
• Collapse of the right ventricular free wall
• Diastolic collapse of the right atrial wall
• Increased flow velocities across the tricuspid pulmonic valve during inspiration
Several findings can create a false-positive diagnosis of pericardial effusion:
• Epicardial fat located on the anterior wall
• Misinterpretation of normal cardiac structures such as the descending aorta or coronary sinus
• Other abnormal cardiac or noncardiac structures
• Confusion of pleural effusions with pericardial effusions
Pericardial effusion can be differentiated from pleural effusion in several ways. First, in pericardial effusion, a large amount of fluid can collect posterior to the heart without any anterior collection. Second, pericardial effusion tapers as it approaches the left atrium; a pleural effusion does not. Third, if both types of effusion occur simultaneously, a thin echogenic line should be noted between the two collections of fluid. And fourth, the descending aorta lies posterior to a pericardial effusion, whereas it lies anterior to a pleural effusion.
Pericarditis comes in two forms: acute and constrictive. In acute pericarditis, the pericardium is inflamed. This form of the disease has a variety of etiologies: idiopathic causes, viruses, uremia, bacterial infections, acute myocardial infarction, tuberculosis, malignancies, and trauma. Echocardiography reveals thickening of the pericardium, with or without pericardial effusion.
In constrictive disease, the pericardium thickens and restricts diastolic filling of the heart chambers. As in the acute form, it has a variety of causes: tuberculosis, hemodialysis used to treat chronic renal failure, connective tissue disorders (e.g., SLE, rheumatoid arthritis), metastatic infiltration, radiation therapy to the mediastinum, fungal or parasitic infections, and complications of surgery. Echocardiographic findings may include:
• Thickened pericardium
• Flattening of the LV wall in mid and late systole
• A rapid mitral valve E–F slope
• Exaggerated anterior motion of the interventricular septum
• Mid-diastolic premature opening of the pulmonic valve
• Inspiratory dilatation of hepatic veins and the inferior vena cava
• Inspiratory leftward motion of the interatrial and interventricular septa
DISEASES AFFECTING THE MYOCARDIUM
The term cardiomyopathy is used to describe a variety of cardiac diseases that affect the myocardium. Cardiomyopathies have been classified into three categories: (1) hypertrophic, which may or may not obstruct the LV outflow tract, (2) dilated, and (3) restrictive. The classification depends on the anatomical characteristics of the LV cavity as well as systolic ejection and diastolic-filling properties of the left ventricle.
Hypertrophic cardiomyopathy is characterized by concentric or asymmetric LV hypertrophy, which results in an increase in LV mass, with normal or reduced dimensions of the LV cavity. Normal systolic function usually is preserved. Although asymmetric hypertrophy can occur anywhere within the left ventricle, the most common site is the proximal portion of the ventricular septum near the outflow tract. Asymmetric septal hypertrophy can be diagnosed when the ratio of septal thickness to posterior wall thickness is 1.3:1.0. When asymmetric hypertrophy is present, obstruction most frequently occurs. Concentric hypertrophy may or may not lead to obstruction. A number of names are used to describe the obstructive forms of cardiomyopathy, including idiopathic hypertrophic subaortic stenosis, muscular subaortic stenosis, asymmetric septal hypertrophy, and hypertrophic obstructive cardiomyopathy.
Several echocardiographic findings, when found in conjunction, are highly specific for the diagnosis of obstructive cardiomyopathy. M-mode and two-dimensional findings include systolic anterior motion of the mitral valve, asymmetric septal hypertrophy, premature midsystolic closure of the aortic valve, septal hypokinesis, and anterior displacement (and its size) of the mitral valve. The left ventricle may be small to normal in size. Doppler examination reveals a decreased E wave to mitral flow with an exaggerated A wave. These findings suggest a decrease in diastolic compliance and an increase in LV end-diastolic pressures. In aortic flow, there is a midsystolic reduction of velocity. Fifty percent of patients demonstrate regurgitation in the mitral valve. Pulsed-wave Doppler is used to determine the obstructed area. At rest, systolic anterior motion of the mitral valve may not be demonstrated. Because this motion is a diagnostic indication for this disease, provocative maneuvers are used to bring it out. Such techniques include the Valsalva maneuver and amyl nitrate and IV isoproterenol administration.
Dilated cardiomyopathy is characterized by globally reduced systolic function, with an ejection fraction of less than 40%, increased end-systolic and end-diastolic volumes, and, eventually, congestive heart failure. M-mode findings include increased end-diastolic and end-systolic dimensions of the left ventricle, reduced septal and posterior wall excursion, increased E point-to-septal separation, decreased aortic root movement, and a structurally normal aortic valve that opens slowly and drifts closed during systole because of reduced cardiac output. The principal two-dimensional echocardiographic findings include LV dilatation and dysfunction, abnormal closure of the mitral valve, and dilatation of the left atrium. The abnormal closure of the aortic valve also is noted. Mitral regurgitation is a frequent Doppler finding in dilated cardiomyopathy. Hemodynamically, the left ventricle demonstrates signs of increased diastolic pressure in the left ventricle and decreased compliance. The walls of the left ventricle are normal in size. The right heart also may become enlarged as a result of the increased diastolic pressures in the left heart. The most common complication of dilated cardiomyopathy is the formation of thrombi and a potential cardiac source of emboli.
Dilated cardiomyopathies can be the result of a familiar or X-linked cardiomyopathy, pregnancy, systemic hypertension, ingestion of toxic agents such as alcohol or other drugs, and a variety of viral infections. They also can be of an unknown cause, or idiopathic. This form of cardiomyopathy also can be found in severe CAD.
Restrictive cardiomyopathy falls into two categories: endomyocardial fibrosis and infiltrative myocardial disease, which includes amyloidosis, sarcoidosis, hematochromatosis, Pompe’s disease, and Fabry’s disease. The characteristic feature of restrictive cardiomyopathy is increased resistance to LV filling. The associated cardiac findings include elevated diastolic pressure in the left ventricle, hypertension and enlargement of the left atrium, and secondary pulmonary hypertension. The echocardiographic features include an increase in the thickness and mass of the LV wall, a small-to-normal-sized LV cavity, normal systolic function, and pericardial effusion. Restrictive cardiomyopathies are most common in East Africa; they account for only 5% of noncoronary cardiomyopathies in the Western world.
Endomyocardial fibrosis involves formation of fibrotic sheets of tissue in the subendocardium. These sheets vary in thickness and result in increased stiffness of the ventricles. The bright reflective characteristic of this tissue is easily seen with two-dimensional echocardiography. Other characteristic echocardiographic findings include a normal-sized left ventricle, increased thickness of the LV wall, thrombus, and left atrial enlargement, which usually occurs because of elevated diastolic pressure of the left ventricle. The right heart is normal in size, with mildly reduced systolic function and increased wall dimensions. Tricuspid regurgitation is present because of the pulmonary hypertension that occurs as a result of elevated pressures in the left heart.
There are two basic varieties of endomyocardial fibrosis. One form, found primarily in temperate regions, results from hypereosinophilia and is, therefore, termed hypereosinophilic syndrome. This syndrome, also referred to as Loffler’s endocarditis parietalis fibroplastic or Loffler’s endocarditis, mainly affects men in their 40s and is characterized by increased eosinophils of more than 1,500/mm.4 The second form, obliterative endomyocardial fibrosis,4occurs primarily in subtropical climates and is especially common in Uganda and Nigeria. It accounts for 10–20% of all cardiac deaths in those countries. Large pericardial effusions are typical in this cardiomyopathy.
The importance of diastolic function has become apparent over recent years. Many patients with symptoms of congestive heart failure (shortness of breath, edema) have normal systolic function. The inability of the left ventricle to relax properly can result in diastolic heart failure. This is often seen in patients with hypertrophic cardiomyopathies and similar conditions. Doppler echocardiography is the diagnostic tool of choice for evaluating diastolic function.
Myxomas. Myxomas are neoplasms that arise from the endocardial tissue and typically arise from the left atrium.1 They are the most common type of benign tumor, accounting for 30–50% of all benign tumors. Three times as many females as males are affected, and 90% of the tumors are found in the atria: 75–86% are found in the left atrium; 9–20% in the right atrium; and 5–11% in the right atrium or left ventricle but rarely in both atria. Ninety percent of myxomas are pedunculated; the most common site of attachment is the interatrial septum near the fossa ovalis. This tumor may be hereditary (autosomal dominant).
M-mode findings reveal echoes behind the anterior leaflet of the mitral valve. Two-dimensional imaging reveals an echogenic mass in the affected chamber. The echo may be brightly echogenic to sonolucent because of hemorrhage or necrosis.
The clinical findings include the following: symptoms similar to those of mitral valve disease, embolic phenomena, no symptoms, symptoms similar to those of tricuspid valve disease, sudden death, pericarditis, myocardial infarction, symptoms similar to pulmonic valve disease, and a fever of unknown origin.
Rhabdomyomas. Rhabdomyoma is a benign tumor derived from striated muscle most commonly associated with tuberous sclerosis. It is also called myocardial hamartoma, and the most common cardiac tumor found in infants and children. In 90% of the cases, multiple rhabdomyomas are involved. The tumor is yellow gray in appearance, ranges from 1 mm to several centimeters in diameter, and most commonly involves the ventricles. Large tumors may lead to intracavitary obstruction resulting in death.
Lipomas. Lipomas are benign tumors usually containing mature fat cells. They are the second most common benign tumors of the heart. They affect people of all ages and are found equally often in males and females. Most of these tumors are sessile. Fifty percent are located in the subendocardium, and 25% are intramuscular. The most common sites are the left ventricle, right atrium, and interatrial septum.
Fibromas. Fibromas occur in the connective tissue and contain fibrous connective tissue. They are usually well circumscribed and the second most common benign tumors found predominantly in children (most of whom are younger than 10 years of age). Almost all of these tumors occur in the ventricular myocardium. On the echocardiogram, they typically present as large masses within the interventricular system.
Angiomas. Angiomas are extremely rare. They may occur in any part of the heart.5
Teratomas. Teratomas are extremely rare and occur more often in children. They contain all three germ cell layers. They are found most frequently in the right heart but also can occur in the interatrial or interventricular septum.5
Primary Cardiac Tumors. Angiosarcomas usually occur in adults and are twice as common in men than in women. They are the fourth most common primary tumors but the most common malignant cardiac tumors. They are soft tissue tumors of the blood vessels and are usually found in the right atrium; the most common site is the interatrial septum. Other primary cardiac tumors are rhabdomyosarcomas, fibrosarcomas, lymphosarcomas, and sarcomas of the pulmonary artery.
Secondary Metastatic Tumors. Metastatic and secondary tumors usually invade the right heart and are far more common than primary tumors. Usually they are clinically silent. However, they can cause superior vena cava syndrome because of obstruction, supraventricular arrhythmias, myocardial infarction, cardiomegaly, congestive heart failure, or nonbacterial endocarditis, bronchogenic carcinomas, breast carcinomas, malignant melanomas, and leukemias. Spread of these tumors varies. Bronchogenic carcinomas spread via the lymphatic channels, and metastases of malignant melanomas spread through the blood. Usually metastases involve the pericardium or the myocardium.5
Left Ventricular Thrombi. Thrombi of the left ventricle occur in myocardial infarctions, LV aneurysms, and cardiomyopathies. They usually form in the apex of the ventricle. Two-dimensional imaging can diagnose clots with 90% sensitivity and specificity. Echocardiography reveals that the clot has distinct margins, is usually located near an akinetic or dyskinetic area, and may protrude within the ventricle or move with the adjacent wall. Protruding thrombi tend to be more echo dense than mural thrombi, whereas mural thrombi have a layered appearance and are often echolucent along the endocardial border.
Thrombi form within the first 4 days after an infarction and occur in 30% of all anterior wall infarctions; they rarely occur in inferior wall infarctions. If they do not dissolve spontaneously, they may disappear with the use of anticoagulants.
Left Atrial Thrombi. Thrombi usually form in the left atrium in the presence of mitral valve disease (stenosis), an enlarged left atrium, and atrial fibrillation—conditions that predispose to blood stasis. The most common site is the atrial appendage. The echocardiographic appearance of these thrombi varies. In many cases, they are attached to the atrial wall and can be round or ovoid in shape. Their borders are often well defined, they demonstrate mobility, and their texture is uniform. Occasionally, a thrombus appears as a flat immobile mass or as a free-floating ball.
Thrombi of the Right Heart. Most thrombi form in the right heart in the presence of right ventricular infarction, cardiomyopathies, or cor pulmonale. They usually are immobile, heterogeneous sessile masses. In addition, secondary thrombi may occur. Their source is embolization from deep-vein thrombosis. Echocardiography typically reveals a long, serpentine, apparently free-floating mass with no obvious site of attachment. Patients are at a much higher risk for an embolus when the thrombus in any area of the heart is protruding or free floating.
Other Cardiac Masses. Because a number of foreign objects can mimic a thrombus, one must be aware of their presence and location. For example, right-heart catheters are often seen in both the right atrium and the right ventricle. These appear as highly reflective linear echoes.
Normal cardiac structures also can mimic intracardiac masses. The moderator band seen in the apex of the right ventricle appears as a thick muscular band extending from the free wall of the right ventricle to the interventricular septum. Occasionally, a prominent eustachian valve can be seen in the right atrium at the junction of the inferior vena cava. It appears as a thin, long, mobile structure in the right atrium, which also may contain thin filamentous structures known as the Chiari network that is a remnant of embryonic structures. The left ventricle also may contain long thin fibers known as false tendons or ectopic chordae tendineae. These filamentous structures traverse the left ventricle and typically are brightly reflective structures of no clinical significance.
DISEASES OF THE AORTA
The aorta is considered dilated when its diameter is >37 mm. The average diameter of the adult aorta is 33–37 mm. M-mode measurements of the aorta should be taken at the level of the aortic annulus and the sinus of Valsalva. Aortic dilatation is seen most frequently in patients with annuloaortic ectasia or Marfan syndrome. In these patients, the medial layer of the aorta weakens, and the aorta dilates. The dilatation occurs not only in the wall of the aorta, but in the aortic annulus as well. This often leads to aortic insufficiency because the cusps of the aorta are unable to coapt during closure. Two-dimensional echocardiography can easily detect a dilated aorta.
An aortic aneurysm can occur anywhere along the thoracic aorta. The most common sites are the arch and descending aorta, with most occurring just beyond the left subclavian artery. Aneurysms of the thoracic aorta often extend into the abdominal aorta. There are several types of aneurysms, that include; saccular (sack-like dilatation), fusiform (spindle-shaped aneurysm), and dissecting (separation of the arterial wall creating a false and true lumen).
A dissecting aortic aneurysm results from intimal tears of the aortic wall. The driving force of the blood destroys the media further and strips the intimal layer from the adventitial layer. Aortic dissections are classified according to the area and extent of the intimal tear. Type I tears extend from the ascending aorta and continue beyond the arch. Type II tears also begin a few centimeters from the aortic valve but are confined to the ascending aorta. Type III tears begin in the descending aorta, usually just distal to the origin of the left subclavian artery. More than 90% of patients with dissecting aneurysms experience severe pain. Dissections occur twice as often in men as in women and usually in the sixth and seventh decade of life. M-mode findings reveal extra linear echoes within the aorta. Two-dimensional imaging is the echocardiographic tool of choice. Two-dimensional imaging allows visualization of the intimal flap, which divides the true lumen of the aorta from the false lumen. Color-flow Doppler can be invaluable in localizing the site of intraluminal communication. Other echocardiographic evidence for dissection includes aortic regurgitation—the most commonly noted complication. Doppler is useful for detecting disturbed flow patterns in the LV outflow tract. The left ventricle may become enlarged because of volume overload from the aortic regurgitation; pericardial effusion can be noted, and left pleural effusion also may be noted. The diagnosis of dissection should be made when an intima flap is seen in more than one view.
Aneurysms that occur in the sinus of Valsalva are best seen using two-dimensional imaging. They are observed most easily in the short-axis view during diastole. Rupture usually occurs in the right side of the heart, but it also can occur in the left heart and interventricular septum. Sinus of Valsalva aneurysms can be acquired or congenital in nature.
CONGENITAL HEART DISEASE
Abnormalities of the LV outflow tract are the most common congenital heart disease found in the adult population. Obstruction can occur at the subvalvular, supravalvular, or valvular level. Congenital abnormalities of the aortic valve occur in 1% of the population, with a higher prevalence among males. The most common malformation of the aortic valve is a bicuspid valve. Aortic coarctation, VSD, and isolated pulmonic stenosis are associated with the condition. As the valve ages, it becomes fibrotic and may calcify. By the fourth decade, 50% of all bicuspid aortic valves become stenotic.
Subvalvular stenosis also can occur. There are two types of subvalvular stenosis: discrete and subaortic. In discrete stenosis, a thin membrane obstructs the outflow tract or a more fibromuscular ridge obstructs the flow of blood. Subaortic stenosis, too, is more common in males. Aortic regurgitation is a frequent finding in subaortic stenosis. Discrete subvalvular stenosis is primarily an acquired rather than a congenital problem when it is present in adults.
Supravalvular stenosis also can be classified into two categories. The most frequent supravalvular narrowing is found in the ascending aorta just above the valve. Less frequently, the obstruction involves the ascending aorta, the aortic arch, and the descending aorta. Supravalvular obstruction can be a familial finding, but it also can be sporadic or as a result of rubella infection. When found in association with mental retardation, a diagnosis of Williams syndrome can be made.
Patients with congenital outflow obstruction usually present with LV systolic hypertension and develop concentric LV hypertrophy. The physical examination reveals a harsh systolic ejection murmur over the right parasternal border. Echocardiography has become the diagnostic tool of choice in making this diagnosis. M-mode echocardiography reveals a thickened valve with an eccentric closure line. Normally, the closure line of the aortic valve is centrally located. In a bicuspid aortic valve, however, the closure line is displaced toward either the anterior or the posterior wall of the aorta. Two-dimensional echocardiography reveals systolic doming of the cusps, which is seen in the left parasternal long-axis view. The left parasternal short-axis view reveals the presence of only two cusps. Pulsed-wave Doppler echocardiography can localize the area of obstruction and determine what type of obstruction is present. Continuous-wave Doppler examination allows quantification of peak and mean pressure gradients across the obstruction. Color-flow Doppler examination allows assessment of blood flow direction.
Atrial Septal Defects
Atrial septal defects (ASDs) are the second most common congenital abnormality found in adults. There are three classifications of ASDs, depending on their location: ostium secundum defects, ostium primum defects, and sinus venosus defects. Ostium secundum defects make up 70% of all ASDs found in adults. These are located near the fossa ovalis. Women are three times more likely than men to have this defect. Twenty percent of patients with this type of ASD have mitral valve prolapse. Other associated findings include mitral or pulmonic stenosis and atrial septal aneurysm. When an ASD and mitral stenosis exist simultaneously, the condition is called Lutembacher’s syndrome. In isolated mitral stenosis, the left atrium is dilated because the valve area is reduced. With ASD, the blood can escape across the atrial defect, thereby preserving the size of the left atrium.
Fifteen percent of all ASDs are of the ostium primum type. These defects occur in the region of the ostium primum or the lower portion of the atrial septum. A commonly associated finding is a clefted anterior mitral valve leaflet.
Sinus venosus ASDs account for the other 15%. The defects occur in the upper portion of the atrial septum near the orifice of the inferior vena cava. The most common finding associated with this defect is partial anomalous pulmonary venous drainage.
Two-dimensional and M-mode echocardiography reveal a volume overload in the right heart. Findings indicative of rightsided volume overload include a dilated right ventricle and a flattening of the septum in diastole. Two-dimensional imaging of the atrial septum allows direct visualization and localization of the defect. The views most commonly used to assess the atrial septum include the parasternal short-axis, the apical four-chamber, and the subcostal views. The latter view is the best one for visualizing the atrial septum. In addition to the secondary findings already described, two-dimensional imaging allows direct visualization of the defect. In septal defects, a dropout of echoes is noted in the area of the defect. On echocardiography, the dropout of echoes is characterized by a bright echo perpendicular to the atrial septum. This finding has been described as the T sign.
Doppler echocardiography also can help detect ASDs. In the absence of elevated pressures in the right heart, blood flows from the higher-pressure left ventricle to the lower-pressure right heart. In the subcostal view, a pulsed Doppler sample gate can be placed in the right heart near the atrial septum. The spectral display will reveal turbulent flow toward the transducer in late systole and throughout diastole. Color-flow Doppler allows visualization of the interatrial shunt by superimposing a color coding on a two-dimensional image.
Contrast echocardiography can be used when imaging and Doppler are unable to identify the atrial defect clearly. When used in conjunction with two-dimensional imaging, 92–100% of ASDs can be detected. Contrast agents injected into a vein enter the right heart, which is often highly opacified. In the presence of an ASD, small amounts of contrast material can be seen crossing the atrial septum into the left atrium and to the left ventricle. When the shunt is left to right, which is normally the case, a negative contrast effect can be noted. Contrast enhancement can be increased by having the patient perform the Valsalva maneuver, or cough.
Patent Foramen Ovale
Patent (open) foramen ovale can be found in 27% of older patients. Left-to-right shunting does not normally occur when pressures are normal. A potential complication of the condition is paradoxical embolus.
Ventricular Septal Defects
VSDs are the most common defects found in infants and children. In the adult, ASDs are much more common. VSDs fall into two major classifications: muscular septal defects and membranous defects. Like ASDs, VSDs are classified according to the region involved.
Muscular Septal Defects. Muscular septal defects are entirely surrounded by muscle. Outlet defects occur in the most superior portion of the septum and make up part of the outflow region of the left ventricle. They are also referred to as outflow defects, subpulmonic or infundibular defects, or bulbar defects. These defects are bordered by the trabecular septomarginalis (right ventricular septal band) and the pulmonary valve annulus. Thus, they are the most difficult VSDs to image and are best seen from the subcostal and high parasternal positions.
A special form of outlet defect occurs above the crista supraventricularis. This defect is known as supracristal ventricular defect; it is also referred to as the doubly committed subarterial defect because of its proximity to both semilunar valves. This defect also is best seen from the subcostal and high parasternal positions. Associated findings in this defect include: (1) aortic valve prolapse because of lack of support, usually involving the right coronary cusp, (2) dilatation of the right coronary sinus of Valsalva, and (3) aortic insufficiency. The defect is usually small.
Inlet ventricular defects are bordered superiorly by the tricuspid valve annulus, apically by the tips of the papillary muscles, and anteriorly by the trabecula septomarginalis. They are also referred to as endocardial cushion defects, retrocristal defects, sinus defects, and inflow defects, which can be seen in several planes, including the parasternal, apical, and subcostal views. Because these defects are usually large, they can be confused with a double-inlet ventricle.
Trabecular defects are bordered by the chordal attachments of the papillary muscle to the apex. They extend from the smooth outlet septum to the inlet septum, are heavily trabeculated, and are usually large. They also can be multiple. These defects typically lead to hypertension of the right ventricle and may produce a right-to-left shunt if the pressures in the right heart exceed those in the left. A special type of muscular septal defect that occurs in the muscular septum is characterized by numerous small defects resembling Swiss cheese. This “Swiss cheese” defect occurs primarily in the apex.
Membranous Defects. Membranous septal defects occur in the region bordered by the inlet and outlet septums and the junctions between the right and noncoronary cusps of the aortic valve. This part of the septum is located at the base of the heart. Defects in this area are often referred to as perimembranous because they usually involve part of a surrounding muscular septum. Almost all planes can be used to image these defects, which occur more frequently than the muscular varieties.
Using two-dimensional imaging allows visualization of the septum. When the defect is large, a dropout of echoes is appreciated. In addition, a T artifact is observed. When imaging does not allow localization of the defect, color-flow Doppler can be used. High-velocity turbulent flow usually can be seen as a mosaic color pattern in the area of the jet. Contrast echocardiography also can be used to localize the defect. Agitated solution can be injected into the right heart through a peripheral vein. Even a few bubbles seen entering the left ventricle are indicative of a right-to-left shunt when right-sided pressures are slightly elevated.
Tetralogy of Fallot
In adults, tetralogy of Fallot is the primary congenital disease producing cyanosis. In this condition, four specific findings are noted. The aorta overrides the perimembranous VSD. Infundibular or valvular pulmonic stenosis is present, resulting in right ventricular hypertrophy. M-mode criteria for diagnosing tetralogy of Fallot include a break in the continuity of the anterior wall of the aorta from that of the interventricular septum as well as a narrowing of the right ventricular outflow tract. Two-dimensional imaging, however, allows direct visualization of the cardiac anatomy and is, therefore, the echocardiographic procedure of choice. Imaging often allows visualization of the VSD and gives valuable information about the amount of aortic override. Doppler echocardiography allows quantification of gradients across the obstruction of right ventricular outflow.
Eighty percent of all congenital obstructions of right ventricular outflow occur at the level of the pulmonic valve. The valve is often thickened with fusion of the cusps and can be seen doming in systole. Right ventricular hypertrophy occurs as a result of the increased resistance to flow. Two-dimensional imaging allows visualization of the valve, which usually appears thickened and with reduced excursion.
Persistent Ductus Arteriosus
Persistent ductus arteriosus (PDA) occurs when the ductus fails to close after birth. In utero, communication exists between the pulmonary circulation and the systemic circulation, the purpose of which in fetal circulation is to direct the flow of desaturated blood away from the coronary and cerebral circulation and toward the placenta. The ductus is located near the isthmus of the aorta near the origin of the left subclavian artery; it extends to the left pulmonary artery just beyond the bifurcation. In the absence of elevated pulmonary pressures, blood flows from the aorta to the pulmonary artery. In adults, the most common symptom of a PDA is dyspnea on exertion. In persistent ductus, the increased blood flow to the lungs results in dilatation of the pulmonary arteries, the left atrium and ventricle, and the aorta. If pulmonary pressure increases, the blood flow may reverse and travel from the pulmonary circulation toward the aorta. This condition is known as Eisenmenger’s complex and is characterized by right-to-left shunting.
Coarctation of the Aorta
Coarctation is a stricture or contraction of the aorta. Twice as many men as women are likely to have Coarctation of the Aorta. Most patients with this condition are asymptomatic. The coarctation is manifested as LV hypertension. On physical examination, a systolic murmur can be heard. The most common site of narrowing occurs in the thoracic aorta just distal to the left subclavian artery. This condition is often found in association with other congenital abnormalities such as VSD, PDA, a bicuspid aortic valve, and mitral valve abnormalities. It is the most common cardiac malformation found in Turner’s syndrome.
The suprasternal notch offers the best view of the ascending aorta, the arch, and the descending aorta. Direct visualization of the coarctation is possible using two-dimensional imaging. Doppler echocardiography typically reveals increased velocities across the site of coarctation.
Ebstein’s anomaly is characterized by downward displacement of the anterior or septal leaflet of the tricuspid valve into the right ventricle. As a result, the ventricle becomes “atrialized” and loses some of its pumping capacity. Associated findings include secundum-type ASDs, pulmonic stenosis or atresia, VSD, and mitral valve prolapse. Symptoms may not be evident until the patient is between 30 and 40 years of age. The most common complication of this abnormality is failure of the right ventricle.
The M-mode criterion for this anomaly includes visualization of a large tricuspid valve leaflet, simultaneously seen with the anterior leaflet of the mitral leaflet. A delay time in closure of the tricuspid valve of 80 m/s or more to that of closure of the mitral valve is the second M-mode finding. Two-dimensional imaging allows direct visualization of the anatomy. Specific findings in imaging include an apically located tricuspid leaflet and a functionally small right ventricle. Ebstein’s anomaly can be diagnosed if the leaflet is displaced 20 mm or more.
There are two basic types of systemic hypertension: essential or idiopathic and secondary hypertension. Both affect the diastolic and systolic pressure. The classification of blood pressure is shown in Table 2–7.
TABLE 2–7 • Classification of Blood Pressure
The cause of essential hypertension is unknown. Although several mechanisms may come into play, no specific cause has been well described. Secondary hypertension results in high blood pressure associated with any of the following: renal disease, endocrine disease, Coarctation of the Aorta, pregnancy, neurological disorders, acute stress, increased intravascular volume, alcohol and other drug abuse, increased cardiac output, and rigidity of the aorta.
The hemodynamic properties of systemic hypertension, whatever the cause, are similar. Initially cardio output increases, as does fluid volume. This increased fluid volume is transferred to the various organs and tissues. Once tissues receive more blood than they need, the blood vessels that deliver the blood constrict. This is known as vasoconstriction, which is an intrinsic property of such systemic vessels as arterioles, and the bicep increases in size when one does curls, so do the arteries. If this state continues, the vessels continue to exert resistance on the incoming blood (peripheral resistance). As a result, the heartbeats gain greater resistance and the vessel themselves become thicker.
As is the case with any muscle, hypertrophy occurs when stress is exerted. Similar to the bicep increasing in size when one does curls, the heart also increases in size as it is forced to pump blood against increased peripheral resistance. Therefore, the main echocardiographic findings are increased muscle mass of the heart, especially the left ventricle. By M-mode criteria, the walls of the left ventricle are thick. The principal Doppler findings include (1) decreased transmitral E wave, (2) increased A wave, and (3) increased A-to-E-wave ratios.
In normal physiology, the pulmonary blood flow allows passage of blood to the lungs for three basic functions: oxygenation, filtration, and pH balance by excreting carbon dioxide. Blood coming in from the various tissues and organs of the body is directed to the right heart through the superior and inferior vena cavae. Once this deoxygenated blood enters the right atrium, it passes through the tricuspid valve into the right ventricle across the pulmonic valve and into the main pulmonary artery, which bifurcates into a left and right branch and directs blood to the left and right lobes of the lungs. Normally the pulmonary circulation offers little resistance to blood flow. The normal peak systolic pressure ranges from 18 to 25 mm Hg, and the normal diastolic pressure ranges from 6 to 10 mm Hg. Pulmonary artery pressure in excess of 30 mm Hg systolic pressure and 20 mm Hg diastolic pressure represents elevated pulmonary pressures, or pulmonary hypertension.
As with systemic hypertension, pulmonary hypertension has two basic forms: primary and secondary. Primary pulmonary hypertension—also known as idiopathic, essential, or unexplained pulmonary hypertension—has no known discernible cause. Secondary pulmonary hypertension can be the result of any one of the following factors:
• Increased resistance to pulmonary venous drainage
• Elevated LV diastolic pressure
• Left atrial hypertension (mitral stenosis)
• Pulmonary parenchyma disease
• Pulmonary venous obstruction (cor triatriatum or pulmonary veno-occlusive disease
Cor triatriatum is a congenital abnormality in which the common embryonic pulmonary vein is not incorporated into the left atrium. Instead, the pulmonary veins empty into an accessory chamber and communicate with the left atrium through a small opening. The result is obstruction of pulmonary venous flow that simulates mitral stenosis. In pulmonary veno-occlusive disease, the veins and venules of the lung become fibrotic. M-mode findings reveal an absent or decreased A wave in the absence of right ventricular failure: a lack of respiratory variation in the A wave; an extended pre-ejection period; midsystolic closure of the pulmonic valve, also known as midsystolic notch; and reduced ejection time of the right ventricle. Two-dimensional imaging indicates a dilated pulmonary artery and abnormalities in interventricular septal motion.
Doppler measurements reveal the following: a decreased acceleration time, a longer pre-ejection period, a shorter ejection time, and tricuspid regurgitation. The acceleration time is the time interval between the onset of flow and the peak systolic flow. In pulmonary hypertension, the velocity of blood flow increases rapidly and peaks early in systole. This measurement is made by identifying the beginning of the Doppler signal and the peak velocity of the same signal. The time between the two is the acceleration time.
The pre-ejection period is the time interval between the onset of the QRS complex to onset of flow in the pulmonary artery. In pulmonary hypertension, this time period increases.
Ejection time is the time from the onset of flow to the cessation of flow. In pulmonary hypertension, this time period becomes shorter. This measurement is made by taking the time between the beginning and the end of the Doppler signal.
Tricuspid regurgitation occurs in the majority of patients with elevated pressures in the pulmonary artery. Continuouswave Doppler can be used to localize the regurgitant jet and obtain the peak transtricuspid gradient using the modified Bernoulli equation. The peak gradient is the difference in systolic pressure between the right atrium and right ventricle. Estimation of the pulmonary pressures is accomplished by adding the right atrial pressures, which are determined by visual inspection of the jugular venous pulse. A more common way is to add the constant “10” to the peak systolic transtricuspid gradient. When stenosis of the pulmonic valve is present, however, one cannot determine pulmonary artery pressures using the peak transtricuspid regurgitant gradient.
CORONARY ARTERY DISEASE
The normal right and left coronary arteries supply the heart muscle with oxygenated blood (see Table 2–8). The left coronary artery originates from the left coronary sinus of Valsalva, which bifurcates into two branches: the anterior interventricular or descending branch, also known as the left anterior descending branch, and the circumflex branch. The right coronary artery originates from the right coronary sinus of Valsalva.
TABLE 2–8 • Normal Branches of the Coronary Arteries
The coronary anatomy can vary considerably in humans. In 67% of cases, the right coronary artery is the dominant artery. In these cases, this artery supplies the parts of the left ventricle and septum. In 15% of cases, the left coronary artery is the dominant one and supplies blood to all of the left ventricle and septum. In 18% of cases, the two arteries are equal; this situation is called the balanced coronary arterial pattern.
Abnormal Wall Motion
When the blood supply to the heart muscle is interrupted, the muscle is damaged and immediate changes in motion can be observed. The affected area can be identified using the various echocardiographic views. The wall segment should be identified using the American Society of Echocardiography’s recommendation (see the section on Normal Anatomy).6
Complications of Ischemic Heart Disease
Ventricular Aneurysm. One complication of ischemic heart disease is ventricular aneurysm. Although aneurysm can form in any part of the left ventricle, more than 80% form in the apex and are the result of an anterior infarction. Of the 5–10% that form in the posterior wall, nearly half are false aneurysms.
The echocardiographic appearance of aneurysms includes thin walls that do not thicken in systole, a bulging wall, and dyskinetic motion to the affected area.
There are three types of ventricular aneurysms: anatomically true, functionally true, and anatomically false aneurysms. An anatomically true aneurysm is composed of fibrous tissue, may or may not contain a clot, and protrudes during both diastole and systole. Its mouth is wider or as wide as its maximum diameter, and its wall is the former LV wall. An anatomically true aneurysm almost never ruptures once healed. A functionally true aneurysm also consists of fibrous tissue but protrudes only during ventricular systole.
An anatomically false aneurysm always contains a clot. Its mouth is considerably smaller than its maximum diameter, and it protrudes during both systole and diastole and may even expand. Its wall is composed of parietal pericardium. Because a false aneurysm often ruptures, immediate surgery is usually required.
Ventricular Septal Defect. A VSD occurs when a rupture occurs in the septum. Several echocardiographic techniques can be used to make the diagnosis. Two-dimensional imaging allows direct visualization of the defect. With contrast echocardiography with imaging, contrasting material can be seen filling the right ventricle and entering the left ventricle as blood moves back and forth through the defect. Negative contrast effect also can be noted. Doppler measurements can detect turbulent high-velocity signals on the right side of the ventricular septum. The best views include the left parasternal long- and short-axis views and the apical four-chamber view. Color Doppler can demonstrate communication between the left and right ventricles. The color jet appears as a mosaic pattern of high-velocity flow.
Thrombus. Thrombus, the most common complication of infarction, usually occurs in the apex in areas of dyskinesia. It can be laminar, lay close to the wall of the ventricle, or protrude into the cavity and be highly mobile. The diagnosis should be made when the thrombus is seen in several views.
Valve Dysfunction. An infarction is most likely to affect the mitral valve. Mitral regurgitation results if the papillary muscle is ruptured, if it becomes fibrosed, or if the mitral annulus is affected, resulting in incomplete closure of the leaflets.
Right Ventricular Involvement. Involvement of the right ventricle occurs primarily when the infarction is in the inferior wall or when the proximal right coronary artery is obstructed. Echocardiography reveals that the ventricle is dilated and its free wall moves abnormally.
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