Echocardiography in Pediatric and Adult Congenital Heart Disease, 2nd Ed.

22. Hypertrophic Cardiomyopathy

It has become clear that hypertrophic cardiomyopathy is a genetic disease. In fact, it is the most common inherited cardiovascular disorder, afflicting one of every 500 individuals. From a molecular perspective, hypertrophic cardiomyopathy is caused by mutations in at least one of the ten proteins of the cardiac sarcomere. Despite our ever increasing understanding of the molecular etiologies of this complex disorder, the clinical diagnosis of hypertrophic cardiomyopathy remains within the realm of the echocardiographer. The most common clinical manifestation of hypertrophic cardiomyopathy is left ventricular outflow obstruction. However, diastolic heart failure and mitral regurgitation are also prominent features of this disease that can be evaluated with echocardiographic techniques in patients of all ages.

This chapter reviews the common echocardiographic features displayed by patients with hypertrophic cardiomyopathy. We will also outline a classification and examination strategy that will not only detect the presence of the disease, but also assist with planning both medical and surgical therapies. Finally, a review of both the intraoperative and postoperative echocardiographic challenges associated with hypertrophic cardiomyopathy will be presented.

DIAGNOSIS OF AND CLASSIFICATION SYSTEMS FOR HYPERTROPHIC CARDIOMYOPATHY

The diagnosis of hypertrophic cardiomyopathy is made when one detects increased myocardial wall thickness that is not caused by another abnormality, such as hypertension or aortic valve stenosis. The most common manifestation of hypertrophic cardiomyopathy is an asymmetrically thickened ventricular septum (Fig. 22.1). This basal septal thickening narrows the left ventricular outflow tract. Accelerated blood flow within the narrowed left ventricular outflow tract creates a Venturi effect, drawing the mitral valve leaflets and chordal support forward into the subaortic area. This systolic anterior mitral valve motion has become known as “SAM.” This combination of abnormalities leads to one of the hallmarks of this disorder—dynamic left ventricular outflow tract obstruction (Figs. 22.2 and 22.3). The systolic distortion of the mitral valve leaflets can cause significant mitral regurgitation (see Figs. 22.2 and 22.3), increasing the degree of symptoms experienced by the patient.

Echocardiography plays a major role not only in diagnosing this disorder but also in excluding secondary causes of hypertrophy. Diagnoses such as coarctation of the aorta and congenital aortic/subaortic stenosis are readily apparent during routine echocardiographic examinations. In older patients, after years of intense athletic training, two-dimensional echocardiographic findings similar to hypertrophic cardiomyopathy may develop. Features that distinguish the athletic heart from hypertrophic cardiomyopathy are summarized in Table 22.1. Clinical tests other than echocardiography are needed to identify patients with systemic hypertension, pheochromocytoma, renal artery stenosis, and/or other forms of renal disease. Diagnoses that are more difficult to exclude on echocardiographic criteria alone include metabolic and storage diseases (Fig. 22.4). The increases in wall thickness associated with these disorders are not caused by true myocyte hypertrophy but rather are caused by storage of abnormal molecules within the myocardial cell. These disorders require clinical correlation and appropriate metabolic screening for accurate identification.

Figure 22.1. Long-axis anatomy typical of hypertrophic cardiomyopathy. A: Anatomic specimen shows a tremendous increase in left ventricular wall thickness, but the increase in myocardial mass is most prominently displayed in the ventricular septum (asterisk). B:Echocardiographic image displays similar anatomy. The increase in myocardial thickness is less prominent than in the anatomic example, but the basal septum (yellow arrow) is still asymmetrically thickened relative to the posterior left ventricular wall. A, anterior; Ao, aorta; LA, left atrium; LV, left ventricle; S, superior; VS, ventricular septum.

Figure 22.2. Systolic, parasternal long-axis frames demonstrating the left ventricular inflow and outflow tracts of a patient with hypertrophic cardiomyopathy. A: Two-dimensional image shows systolic anterior motion (SAM) of the mitral valve chordal supports (yellow arrow). There was prolonged contact between the chords and the septum beginning in mid-systole and extending through the remainder of ventricular ejection. B: Color flow Doppler image shows not only turbulent flow in the left ventricular outflow tract (as a result of dynamic obstruction), but also an eccentric, posteriorly directed jet of mitral regurgitation (yellow arrow). The dysfunction of the mitral valve is related to the distortion of the leaflets caused by the SAM seen on the left. A, anterior; LA, left atrium; LV, left ventricle; RV, right ventricle; S, superior.

Patients presenting with normal contractility and increased left ventricular wall thickness, analysis of myocardial deformation can be very helpful. Those with hypertrophic cardiomyopathy will generally display a reduction in systolic longitudinal fiber shortening (“less negative” longitudinal strain values) in the regions of most prominent myocardial thickening (see Chapter 4 and Fig. 22.5). In contrast, the patient with secondary hypertrophy and normal systolic function due to other disorders or athletic training will demonstrate normal strain values, even in the thickened segments. It is thought that the myofiber disarray associated with hypertrophic cardiomyopathy is responsible for this deviation from the normal pattern of deformation.

Figure 22.3. Hypertrophic cardiomyopathy: images from the cardiac apex. Left: Images are oriented in a four-chamber format, but the plane of sound has been angled anteriorly, allowing visualization of the left ventricular outflow tract. Right: Images are displayed in an apical, long-axis format, also demonstrating the left ventricular inflow and outflow tracts. Top left: Diastolic frame, which demonstrates the asymmetric, basal ventricular septal thickening that is common with hypertrophic cardiomyopathy. Top right: Systolic frame, which demonstrates the systolic anterior motion of the mitral apparatus, as well as septal contact indicating significant obstruction. Bottom: Two color flow Doppler images demonstrate the primary physiologic consequences of this disorder. The early systolic frame (bottom left) shows narrowing of the left ventricular outflow tract between the hypertrophied septum and the deviated mitral apparatus (yellow arrow). The color flow signal displays turbulence and aliasing at this level, indicating outflow tract obstruction extending at least to this level. The image on the bottom right was taken later in systole. The distortion of the mitral valve associated with systolic anterior motion results in inadequate coaptation and late systolic regurgitation. This series of events has been referred to as the “eject, obstruct, leak” phenomenon and can be seen in virtually all patients with the obstructive form of hypertrophic cardiomyopathy. L, left; LA, left atrium; LV, left ventricle; P, posterior; RV, right ventricle; S, superior.

In the normal heart, the ventricular septum and posterior left ventricular wall have similar thicknesses. The normal ventricular septum has a concave curvature, relative to the left ventricular cavity. This curvature is altered in the presence of hypertrophic cardiomyopathy. Patients with hypertrophic cardiomyopathy have been classified based on either this curvature (Fig. 22.6) or the distribution of left ventricular hypertrophy (Fig. 22.7). Both systems are valid. The type of curvature present seems to be related to the presence of an identifiable genetic mutation. Knowing the pattern of hypertrophy present identifies patients who are likely to have or develop obstruction and the surgical approach that may be most beneficial. Classic asymmetric septal hypertrophy (both basal and diffuse), and mid-ventricular hypertrophy usually show reversed septal curvatures and dynamic outflow obstruction, which can be relieved by transaortic myectomy and myotomy. Some patients with sigmoid curves also have typical dynamic outflow obstruction and are effectively treated by surgical interventions. The most severe subset of patients with reversed septal curvatures develops biventricular outflow obstruction. Those with significant biventricular outflow gradients face the greatest risk for sudden, unexpected mortality.

Cases with diffuse, concentric hypertrophy, or hypertrophy that is isolated to the ventricular free wall, usually have a neutral curve and do not manifest obstruction. These morphologies tend to present with diastolic dysfunction and symptoms suggestive of pulmonary venous congestion. As a result, surgical therapy offers little benefit, and medical therapy is the mainstay of treatment for these patients.

Patients with apical hypertrophy have a variable septal curvature, manifest intracavitary gradients, but not develop true outflow tract obstruction. Diastolic dysfunction is often their primary clinical problem. When the severity of hypertrophy compromises the size of the “functional” left ventricular cavity, apical myectomy designed to increase cavity size (and therefore diastolic filling) can reduce symptoms in this group.

Figure 22.4. Parasternal long- and short-axis images of the left ventricle demonstrate diffuse thickening of the myocardium. The examination was performed in a neonate with no family history of cardiomyopathy. The appearance of these images is similar to the diffuse, nonobstructive form of hypertrophic cardiomyopathy. However, the increased thickness of the myocardium is not caused by hypertrophy in this case, but rather it is secondary to accumulation of glycogen within the myocardial cells. This child was found to have type II glycogen storage disease (Pompe disease). This type of case serves to remind one that echocardiography detects increased wall thickness rather than true hypertrophy and that a diagnosis of hypertrophic cardiomyopathy can only be made after other causes of increased myocardial wall thickness have been excluded. Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle.

Figure 22.5. These three panels display apical long-axis myocardial strain curves from three different teenagers with increased left ventricular mass. A was taken during an examination of a 17-year-old student athlete, who was referred for sports participation approval. Although his wall thicknesses were greater than expected, the deformation pattern observed in all myocardial segments was normal. This is consistent with athletic training (not cardiomyopathy) being responsible for the increase in mass. B was taken during an examination of a 14-year-old during screening due to a family history of hypertrophic cardiomyopathy. Although she had no outflow obstruction, her septal deformation or strain (bluered, and lavender curves) is significantly reduced. This implies an abnormality of the myocardium and is consistent with a diagnosis of nonobstructive hypertrophic cardiomyopathy. She was subsequently found to carry the same mutation associated with hypertrophic cardiomyopathy as her relatives. C was taken during an examination of a 15-year-old boy with severe hypertrophic cardiomyopathy in preparation for septal myectomy and defibrillator placement. Note that in his case, the pattern of basal septal deformation is actually “paradoxical.” In other words, the septum immediately adjacent to the aortic annulus (red curve) is actually lengthening (positive strain value) during systole. Only the inferior segment (adjacent to the mitral annulus) shows a normal strain pattern (yellow curve). All of the other segments show the reduced deformation (shortening) that is associated with hypertrophic cardiomyopathy.

ECHOCARDIOGRAPHIC IMAGING IN HYPERTROPHIC CARDIOMYOPATHY

A complete surface echocardiographic evaluation of the patient with hypertrophic cardiomyopathy should include a description of (a) the pattern and severity of myocardial thickening present, (b) the presence and nature of left and/or right ventricular outflow obstruction, (c) the nature of the mitral valve distortion and severity of the resulting regurgitation, (d) the size of the left atrium (shown to be associated with the clinical disease burden), (e) left ventricular diastolic filling, and (f) the pulmonary arterial pressure.

The typical anatomy of obstructive hypertrophic cardiomyopathy is often most easily recognized in the parasternal long-axis views. There is often a prominent basal septal bulge present and the distortion of the mitral support structures can be easily appreciated (see Figs. 22.1 and 22.2). Apical four-chamber and long-axis views can reveal the same findings (see Fig. 22.3) and are better suited for some Doppler echocardiographic interrogations. The magnitude of septal thickening has been associated with the incidence of sudden death. Patients with diastolic septal thicknesses greater than 30 mm have an increased risk of sudden death events, while such events rarely occur if the septal diameter is less than 19 mm. This thickness is best assessed using parasternal two-dimensional scans (Fig. 22.1). These scans allow the examiner to determine the point of maximal diastolic thickness and to avoid inclusion of the right ventricular papillary muscles in the measurement. Systolic ventricular contraction is usually normal or hyperdynamic in this disorder. Systolic ventricular dysfunction is only seen in the most advanced stages of this disease, after years of obstruction and progressive myocardial fibrosis. In contrast, diastolic dysfunction is present in nearly all patients with hypertrophic cardiomyopathy. The associated elevations in left atrial and ventricular diastolic pressures contribute significantly to patients’ symptoms.

Figure 22.6. Variety of septal curvatures that can exist in patients with hypertrophic cardiomyopathy. By far the most common morphology seen in childhood is the reversed septal curve. Any of these patterns can be associated with outflow obstruction. Diastolic dysfunction also occurs in all of these groups but tends to be most severe in those with neutral septal curves or the apical variant of hypertrophic cardiomyopathy (HCM).

Parasternal long-axis views also provide a unique insight into surgical planning. When obstruction is present, the examiner should define the distance between the anatomic aortic valve annulus and the point of contact between the mitral apparatus and the ventricular septum that is farthest from the aortic valve. This distance represents the minimum extent to which a septal myectomy should be performed (Fig. 22.8). Early surgical therapy, first proposed by Morrow, created a single trough in the hypertrophied ventricular septum, allowing an unobstructed channel for ejection (Fig. 22.9). In many patients, the obstructive zone involves the papillary muscles themselves. In these cases, an extended septal myectomy is required (Fig. 22.10) to provide adequate enlargement of the outflow tract. In patients with a small aortic annulus or obstructions extending deep into the ventricle (beyond the mid-papillary muscle level), a combination of transaortic and apical myectomies may be necessary (Fig. 22.11).

Figure 22.7. Shape of the ventricular septum in patients with hypertrophic cardiomyopathy. Top: Patients with these septal geometries often develop significant, dynamic outflow obstruction. The obstruction seen in these three morphologies will usually be effectively treated with transaortic, extended septal myectomy. Bottom: Combined transaortic and transapical approaches may be necessary when the hypertrophy is more diffuse. In the rare patient in whom apical hypertrophy limits ventricular diastolic filling, transapical myectomy may increase the diastolic filling potential.

The diffuse, nonobstructive, and apical form of hypertrophic cardiomyopathy requires multiple planes of imaging for confident recognition. The ventricular walls are concentrically thickened. No accelerated color flow Doppler signals will be seen during systole, and the mitral apparatus will move normally. The prominent diastolic dysfunction associated with this type of myopathy will usually cause significant left atrial enlargement.

The thickened segments of myocardium in patients with apical hypertrophic cardiomyopathy are often not visible from the parasternal window (Fig. 22.12). Apical four-chamber and long-axis scans will demonstrate obliteration of the apical portion of the left ventricular cavity by hypertrophied muscle (Fig. 22.13). High-velocity flow signals can be found in the left ventricular apex. These systolic flow accelerations are directed toward the mid-ventricular cavity, but the true outflow tract is usually widely patent. The potential left ventricular diastolic volume is often reduced in these patients, further compounding the diastolic dysfunction associated with this form of cardiomyopathy. In select cases, transapical resection of the inner myocardial segments may be helpful, increasing the potential diastolic ventricular stroke volume in these patients.

Figure 22.8. Impact of echocardiography on surgical planning. This parasternal long-axis image shows the relationship between the hypertrophied segment of basal ventricular septum and the aortic valve. The plane of the aortic valve annulus is indicated by the white arrow.The yellow arrow shows the point at which ventricular septal thickness decreases. This point is beyond the septal contact lesion and is approximately at the same level as the heads of the papillary muscles. This morphology and spatial relationship should be defined on the preoperative echocardiogram. The distance between the aortic annulus and the yellow arrow is approximately 4 cm. This information assists the surgeon in planning the “depth” of an adequate septal myectomy and in deciding whether such depth can be achieved by a standard transaortic approach. These assessments should be obtained both during the preoperative transthoracic examination and with transesophageal echocardiography in the operating theater. Ao, aorta; LA, left atrium.

Figure 22.9. Anatomic relationships of the left ventricular outflow tract in typical hypertrophic cardiomyopathy with prominent basal hypertrophy and dynamic obstruction. The white horizontal line on the ventricular septum represents the fibrotic contact lesion associated with systolic anterior motion of the mitral valve. Bottom right inset: An example of an early septal myectomy. In essence, a long trough was created in the outflow of ventricular septal myocardium. This trough allowed left ventricular ejection, even though significant portions of the left ventricular outflow tract were still compromised.

Left atrial size has become increasingly recognized as an accurate barometer of disease burden in many forms of adult cardiac disease. It has recently been shown that left atrial volume has a similar association to disease severity in children and adolescents with hypertrophic cardiomyopathy. This is not surprising given the fact that the obstruction and diastolic dysfunction associated with hypertrophic cardiomyopathy lead to elevations in diastolic filling pressures, and mitral regurgitation, both potent stimuli for left atrial distention.

Figure 22.10. Areas targeted by an extended septal myectomy for hypertrophic cardiomyopathy. Left (dotted lines): Areas in which myocardium is resected to increase the area available for left ventricular outflow. Right: The ventricular septum after such a myectomy. In comparison to the technique originally used (Fig. 22.8), this approach is much more likely to completely relieve left ventricular hypertension and has a much lower incidence of late recurrence of obstruction.

DOPPLER ECHOCARDIOGRAPHY

Doppler echocardiography plays a major role in the evaluation of patients with hypertrophic cardiomyopathy. Color flow Doppler demonstrates and localizes the turbulence associated with dynamic outflow obstruction (see Figs. 22.2 and 22.3). Mitral regurgitation can be detected and quantified as previously described. Continuous-wave Doppler allows quantitation of obstructive flow velocities and determination of ventricular-to-atrial pressure gradients. Pulsed-wave and tissue Doppler techniques enhance the assessment of left ventricular filling abnormalities.

Figure 22.11. Apical echocardiographic images of a patient with prominent basal and mid-ventricular hypertrophy caused by hypertrophic cardiomyopathy. The area of thickened septum (A) extends beyond the true midpoint of the papillary muscles and the obstruction originates deep in the ventricular cavity (B, white arrow). When this is the case, a combined transaortic and transapical approach may be required to adequately relieve the obstruction. L, left; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; S, superior; Ao, aorta.

Figure 22.12. A 15-year-old patient with apical hypertrophic cardiomyopathy. Both ventricles showed evidence of diastolic dysfunction, as evidenced by the severe biatrial enlargement seen in these images. A: The parasternal long-axis image on the left does not reveal significantly increased wall thicknesses. B: The typical four-chamber view suggests prominent apical walls, primarily because of the tapering shape of the ventricular cavity. These images highlight the difficulties in making this diagnosis. When images are particularly challenging, contrast imaging can improve image definition at the apex. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Dynamic left ventricular outflow tract obstruction is the physiologic hallmark of the “obstructive” forms of hypertrophic cardiomyopathy. The reduction in left ventricular outflow tract diameter associated with septal hypertrophy and systolic anterior mitral valve motion results in a late-peaking left ventricular–to–aortic gradient and Doppler flow signal. Continuous-wave Doppler velocities provide convenient quantitation of these gradients. The Doppler signals associated with this obstruction are usually recorded from the apical transducer position. However, right parasternal and suprasternal positions may also provide good acoustic windows.

The Doppler signal of dynamic left ventricular outflow obstruction shows a characteristic “dagger-shape” profile (Fig. 22.14). The curved upstroke is a consequence of the gradually increasing severity of obstruction caused by progressive thickening of the outflow septum and mitral systolic anterior motion during systole. The late-peaking nature of this obstruction causes left ventricular and aortic pressures to be maximal at nearly the same time. As a result, the maximum instantaneous Doppler gradient is usually closely correlated with the peak-to-peak gradient measured at cardiac catheterization. This situation is distinctly different from what is seen in more fixed obstructions, like aortic valve stenosis, in which the mean Doppler gradient best reflects the pressure drop across the stenotic valve.

In some patients, the left ventricular outflow tract Doppler signal is difficult to separate from the mitral regurgitation flow profile. In these cases, the left ventricular outflow gradient can be estimated by using the maximum mitral regurgitant velocity to determine the peak left ventricular pressure (Fig. 22.15). The regurgitant velocity is converted to a left ventricular–to–left atrial pressure difference with the simplified Bernoulli equation (4V2). The patient’s systolic blood pressure can then be subtracted from that gradient, providing a value for the left ventricular to aortic gradient (Fig. 22.16). Accuracy of this type of gradient determination is increased if one adds an estimate of left atrial pressure to the Doppler predicted ventricular-to-atrial gradient. Alternatively, the left ventricular outflow signal can be obtained from an alternative acoustic window, such as the suprasternal notch or high right parasternal areas (see Fig. 22.16).

Figure 22.13. Same patient shown in Figure 22.12. Top left: The apical four-chamber view depicts the reduction in apical cavity size associated with this disorder. Top middle: Focused imaging, in the apical long-axis projection, revealed prominent apical hypertrophy, especially involving the posterior wall (yellow arrow). Top right: Oblique, parasternal long-axis view oriented more toward the cardiac apex than normal. Unlike the standard long-axis image shown in Figure 22.11, this view reveals the tremendously hypertrophied apical myocardium that is characteristic of this disorder. The color flow image and continuous-wave Doppler signal (bottom) document the intracavitary gradients that are common in this morphology. The obstruction in abnormal systolic flow is limited to the cardiac apex (bottom left,yellow arrow). Although the apical velocities reach nearly 5 m/s, most of the left ventricular cavity is not obstructed during systole, because the outflow septum is of normal thickness and there is no systolic anterior motion present. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 22.14. Continuous-wave Doppler signals from a patient with classic, dynamic left ventricular outflow obstruction caused by hypertrophic cardiomyopathy. A: Late-peaking, “dagger”-shaped signal (arrow). The systolic upstroke is concave to the left. This is a manifestation of progressive narrowing in the left ventricular outflow area caused by hyperdynamic contraction. B: Mitral regurgitation signal reached a maximum velocity of 6.6 m/s. Occasionally, these two signals are difficult to separate in space. This is not surprising because the obstruction and regurgitation both originate from the point of contact between the septum and mitral valve tissue. When completely separated signals cannot be recorded, the left ventricular outflow gradient can be estimated by measurement of the maximal mitral regurgitation velocity. This velocity can be converted to a value representing the maximum left ventricular–to–left atrial pressure difference by Bernoulli’s equation (4V2). The example shown in Figure 22.13 would suggest a left ventricular–to–left atrial gradient of 172 mm Hg. The left atrium was enlarged and diastolic function was abnormal. As a result, we assumed the left atrial pressure to be 15 mm Hg, predicting a left ventricular maximal systolic pressure of 187 mm Hg. The patient’s blood pressure was 105 mm Hg as measured by an arm cuff. These two values would suggest a left ventricular outflow gradient of 82 mm Hg. This correlates relatively well with the velocity of the outflow Doppler signal, which could be separated from the regurgitant flow in this case. This signal reached 4.3 m/s, suggesting a maximum instantaneous gradient of 74 mm Hg between the left ventricle and the aorta. CW, continuous-wave; LV, left ventricular.

Evaluation of the mitral valve assists in defining the clinical burden of the disease. Even the patient with severe outflow obstruction often has no symptoms, if the mitral valve remains relatively competent. However, when the mitral valve is significantly distorted, mitral regurgitation will occur. As the volume of regurgitation increases, so does the size of the left atrium. The mitral regurgitation increases the left atrial and pulmonary venous pressures. These changes are associated with reduced exercise tolerance and exertional dyspnea.

Figure 22.15. Patient in whom the obstructive zone extended for 3.7 cm below the aortic annulus (A). The color Doppler signals (B) depict a situation in which the left ventricular outflow and the mitral regurgitant Doppler signals could not be separated using Doppler examinations from the cardiac apex. The approach described in Figure 22.14 was used to determine the left ventricular outflow gradient (Fig. 22.16). Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle.

Figure 22.16. Same patient shown in Figure 22.15. Middle: Apical long-axis view, with overlapping color flow jets of outflow obstruction and mitral regurgitation. From the apex, separate obstructive and regurgitant signals could not be obtained. Therefore, the examiner concentrated on the mitral regurgitant signal, obtaining the maximum velocity of 8 m/s. The Bernoulli equation predicted that left ventricular systolic pressure was 260 mm Hg greater than the left atrial pressure. The systolic blood pressure was 90 mm Hg, suggesting a gradient of approximately 170 mm Hg between the ventricle and the aorta. Later in the examination, right parasternal imaging revealed the plane in which the outflow jet could be separately evaluated (left). A 6.7-m/s velocity was obtained, suggesting a maximum instantaneous gradient of 180 mm Hg and confirming the extremely severe nature of this obstruction. Ao, aorta; CW, continuous-wave; HCM, hypertrophic cardiomyopathy; LA, left atrium; LV, left ventricle; LVOT, left ventricular outflow tract; MR, mitral regurgitation; RV, right ventricle.

The mitral leaflet distortion caused by systolic anterior motion creates a posteriorly directed regurgitant jet in patients with typical dynamic left ventricular outflow obstruction. Unlike many other diseases associated with mitral regurgitation, the parasternal long-axis image frequently provides parallel alignment for Doppler interrogation of the mitral regurgitation (see Fig. 22.2). Therefore, this view often provides an excellent acoustic window for Doppler interrogation of the mitral regurgitation, either for PISA analysis or for obtaining the maximum continuous-wave Doppler velocity profile.

ASSESSMENT OF DIASTOLIC DYSFUNCTION

Hearts with hypertrophic cardiomyopathy display markedly impaired myocardial relaxation. Left ventricular pressures fall more slowly after aortic valve closure as shown by prolongation of the isovolumic relaxation time and reduction in transmitral early filling velocity. While left ventricular compliance is still relatively normal, atrial contraction will produce significant augmentation of diastolic filling (Fig. 22.17, left). As myocardial fibrosis progresses, left atrial pressures rise and the transmitral Doppler diastolic filling profile shifts to a more restrictive pattern (Fig. 22.17, top right). These changes are also reflected in the pulmonary venous flow signal (Fig. 22.17, bottom right). The amount and duration of flow reversal within the pulmonary vein after atrial contraction are very sensitive markers for elevated diastolic filling pressure, even in children. Early diastolic mitral annular tissue Doppler velocities are reduced in most patients with hypertrophic cardiomyopathy. Comparison of the pulsed-wave Doppler early transmitral diastolic filling velocity with the annular early tissue Doppler velocity (E/E’ ratio) has provided noninvasive insight into pulmonary capillary wedge pressure and exercise tolerance. Larger values of this ratio are associated with more advanced disease.

Figure 22.17. Pulsed-wave Doppler tracings demonstrate the spectrum of diastolic filling patterns seen in patients with hypertrophic cardiomyopathy. A: Mitral inflow signal depicts a classic pattern of abnormal relaxation with a ratio between early and atrial diastolic filling velocity that is less than 1. Mid-diastolic deceleration time is prolonged (260 ms), as is isovolumic relaxation time (not shown). B: Recording represents mitral inflow (top) and pulmonary venous Doppler flow patterns in a patient with restrictive ventricular filling, suggesting significant elevation of diastolic ventricular pressure. The early mitral diastolic filling wave is dominant; deceleration time and atrial filling waves are short; and pulmonary venous atrial reversal velocity and duration are severely increased (yellow arrows). HCM, hypertrophic cardiomyopathy; MV, mitral valve; PV, pulmonary vein.

ROLE OF ECHOCARDIOGRAPHY DURING AND AFTER SURGICAL INTERVENTIONS

Medical and device therapies are important components of the treatment strategies used for patients with hypertrophic cardiomyopathy. However, in young patients with severe obstruction, surgical septal myectomy and myotomy provide significant therapeutic benefits. Adequate relief of the outflow gradient reduces the risk of sudden death, can eliminate mitral regurgitation (often without valve repair or replacement), and can significantly reduce clinical symptoms. Echocardiography should be a routine part of both the intraoperative and postoperative evaluation of these patients. Whether the examination is performed in the operating room or late after surgery, the postoperative evaluation of a patient with hypertrophic cardiomyopathy needs to include assessment of left ventricular outflow obstruction, diastolic ventricular filling, mitral regurgitation, and the unintended consequences of septal myectomy (if any). These unintended consequences may include aortic regurgitation, iatrogenic ventricular septal defect, or mitral valve perforation. Unusual color flows are often seen in the area of a ventricular septal myectomy. These flows are usually secondary to small septal coronary arteries that have been incised during the subaortic resection. These coronary-to-left ventricular communications are benign and can be distinguished from ventricular septal defects by their flow pattern. Ventricular septal defects will have a high-velocity, predominantly systolic flow pattern. The small coronary artery–to–left ventricle communications will usually have exclusively diastolic flow.

Demonstrating absence of systolic anterior motion of the mitral support apparatus is one of the most important components of the postbypass intraoperative echocardiogram. If systolic anterior motion is present, then the dynamic component of the left ventricular outflow tract obstruction has not been relieved. The gradient may be low, but when systolic anterior motion persists, additional interventions are usually required to ensure a good outcome.

Unfortunately, recurrent, symptomatic left ventricular outflow tract obstruction does occur in this disorder. Often this is secondary to the aggressive nature of the underlying disease. However, an incomplete or cautious initial myectomy can also contribute to redeveloping obstruction. Clear definition of the extent of and mechanism causing the obstruction is critical to planning and executing successful reintervention.

The 10-year-old girl illustrated in Figures 22.1822.19, and 22.20 provides a good example of this type of integrated case management. She clearly had extensive septal hypertrophy (see Fig. 22.18). Unfortunately, the first attempt at surgical therapy removed only a small segment of basal myocardium (see Fig. 22.18). The tremendously thickened segments of ventricular septum extended nearly 6.5 cm below the aortic annulus. Figure 22.19 shows a typical, late-peaking left ventricular outflow Doppler signal consistent with severe dynamic obstruction. The color flow Doppler aliases deep within the ventricle, well beyond the previous myectomy. The surface images revealed that the geometry and extent of the septal hypertrophy would not be successfully approached through the patient’s relatively small, but normal, aortic valve annulus (14 mm). These findings predicted that a combined transaortic and transapical approach was required to adequately relieve the obstruction present in this child. The results of this approach are demonstrated in Figures 22.20 and 22.21.

Figure 22.18. “Recurrent” left ventricular outflow obstruction in a 10-year-old with hypertrophic cardiomyopathy and a prior history of subaortic resection. The parasternal long-axis image (top) shows the area of the prior myectomy outlined by the white bracket.Unfortunately, the hypertrophy extends much farther into the ventricular cavity and the septal contact point was at the point indicated by the white arrow. This patient had an initial reduction in gradient after her first operation; however, the hypertrophy was far more extensive than could be addressed by the small myectomy that had been performed. Ao, aorta; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 22.19. Color flow and continuous-wave Doppler findings consistent with severe dynamic obstruction. The color flow Doppler aliases deep within the ventricle, at the mid to papillary muscle level—well beyond the previous myectomy. The continuous-wave Doppler signal has the typical late-peaking morphology and predicts a 66 mm Hg maximum instantaneous outflow gradient. LA, left atrium; LV, left ventricle; LVOT, left ventricular outflow tract; vel, velocity.

Figure 22.20. Comparison of the preoperative (A) and postoperative (B) anatomic findings in the patient described in Figures 22.18 and 22.19. An extensive resection has been performed, allowing an unobstructed passageway between the ventricular cavity and the aorta (asterisk). Despite the large amount of muscle that was removed, the ventricular septum remains quite thick. Ao, aorta; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Figure 22.21. Comparison of the preoperative (A) and postoperative (B) physiology of the patient described in Figures 22.18 and 22.19. The color flow “wavefront” in the left ventricular outflow tract is still aliased (top right). However, systolic velocities only reach the upper limit of normal (1.7 m/s), likely because of the patient’s hyperdynamic postoperative state rather than any residual obstruction. Note that the outflow signal is no longer late-peaking, and does not have the concave upstroke that was seen preoperatively. Ao, aorta; LA, left atrium; LV, left ventricle; LVOT, left ventricular outflow tract; vel, velocity.

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Questions

1.When is hypertrophic cardiomyopathy diagnosed?

A.When dynamic left ventricular outflow tract obstruction is present.

B.When systolic anterior motion of the mitral valve apparatus is detected.

C.When increased myocardial thickness is present, in the absence of another abnormality that could result in hypertrophy.

D.When mitral regurgitation coexists with asymmetrical ventricular septal thickening.

2.Systolic anterior motion of the mitral valve apparatus (SAM) is:

A.associated with mitral stenosis.

B.caused by accelerated blood flow within the left ventricular outflow tract.

C.only seen in patients with severe left ventricular outflow obstruction.

D.associated with elevated ventricular diastolic pressure.

3.Myocardial strain (deformation) is:

A.reduced in patients with HCM.

B.normal in patients with HCM.

C.increased in patients with HCM.

D.not helpful in patients with HCM.

4.Diastolic dysfunction is the primary manifestation of which subtype of HCM?

A.Reversed septal curve

B.Sigmoidal septal curve

C.Biventricular

D.Apical

5.Patients with HCM and biventricular outflow obstruction represent:

A.the most common form of HCM.

B.a subtype of HCM with a reduced risk for sudden death events.

C.a subtype of HCM with an increased risk for sudden death events.

D.a subtype of HCM that usually does not require surgical treatment.

6.Which of the following ventricular septal wall thicknesses is associated with an increased risk of sudden death in HCM patients?

A.12 mm

B.19 mm

C.24 mm

D.35 mm

7.Doppler signals from the left ventricular outflow tract of patients with obstructive HCM show which of the following patterns?

A.Early peaking systolic velocity profile

B.Late peaking systolic velocity profile

C.Notched systolic velocity profile

D.Downsloping systolic velocity profile

8.Which of the following Doppler gradients is used to predict the left ventricular outflow “peak-to-peak” systolic gradient?

A.The maximum instantaneous systolic outflow gradient

B.The mean systolic outflow gradient

C.The maximum instantaneous mitral regurgitation gradient (systolic left ventricular to left atrial gradient)

D.The mean mitral regurgitation gradient (systolic left ventricular to left atrial gradient)

9.Which of the following is not associated with an increased left ventricular diastolic filling pressure?

A.Prolonged pulmonary venous atrial flow reversal duration

B.Prolonged mitral inflow deceleration time

C.Increased left atrial volume

D.Increased early mitral inflow Doppler to septal annular tissue Doppler velocity ratio

10.The presence of postoperative systolic anterior motion of the mitral apparatus (SAM) is associated with:

A.persistence of mitral regurgitation.

B.absence of mitral regurgitation.

C.persistence of dynamic left ventricular outflow tract obstruction.

D.absence of dynamic left ventricular outflow tract obstruction.

Answers

1.Answer: C. Options A, C and D can occur in a variety of pathologic conditions, not just HCM. HCM is characterized by myocardial thickening (hypertrophy) in the absence of another identifiable cause (such as hypertension, aortic stenosis or other disorders).

2.Answer: B. The Venturi effect associated with accelerated flow stream from the dynamic left ventricular outflow obstruction draws the mitral apparatus anteriorly into the subaortic area – actually worsening the obstruction. SAM can be seen in patients with all degrees of obstruction, is not related to mitral stenosis (in fact MS is rare in HCM), and is not related to diastolic filling pressure.

3.Answer: A. Strain (myocardial deformation) is reduced in HCM patients, especially in the thickest segments. It is helpful in separating HCM patients from those with other causes of myocardial thickening, because hypertrophied segments that are not due to HCM will display normal strain values.

4.Answer: D. Apical HCM rarely has significant outflow obstruction and is not only associated with thickened myocardium, but also with prominent reductions in chamber compliance and potential volume. These result in significant diastolic abnormalities. The other forms of HCM listed may also show diastolic dysfunction, but have outflow obstruction as their primary manifestation.

5.Answer: C. Biventricular outflow obstruction is actually a rare form of HCM and it has been shown to have an increased risk for sudden death events (even compared to other HCM subgroups). Surgical treatment is often required and relief of outflow gradients may improve survival.

6.Answer: D. Patients with maximal septal diastolic thicknesses in excess of 30 mm are thought to have an increased risk of sudden death events.

7.Answer: B. The outflow obstruction seen in HCM increases as myocardial contraction progresses during systole. Therefore, the degree of obstruction is greater in the later portion of the systolic ejection period.

8.Answer: A. Due to the late peaking nature of the obstruction, the peak LV and aortic pressures occur at almost the same time and therefore the maximum instantaneous Doppler gradient obtained in the LVOT most closely reflects the pressure difference between the LV and the aorta. The mean gradient will understate the difference somewhat, and mitral regurgitation gradients reflect the difference between the LV and the LA, not the outflow gradient.

9.Answer: B. Prolonged deceleration time is a sign of early diastolic dysfunction and is usually present before filling pressures increase. The other three options are all associated with increased filling pressure.

10.Answer: C. SAM is caused by the accelerated flow seen with dynamic outflow obstruction. Postoperative SAM is a reliable marker for persistent or recurrent obstruction. If obstruction is absent, then SAM will be absent. Patients with significant SAM may also have mitral regurgitation, but MR may occur even in the absence of SAM.