Morphologic abnormalities of the left ventricular (LV) outflow tract generally result in one or more of the following pathophysiologic states: obstruction, regurgitation, and aneurysmal dilation of the proximal aorta. Obstruction is the most prevalent problem, whereas the other two are rare in children. Known generally as aortic stenosis (AS), LV outflow tract obstruction occurs in approximately 5 per 10,000 live births, represents 5% to 8% of all congenital heart diseases, and usually ranks as the sixth or seventh most common lesion. Among all patients with LV outflow tract obstruction, valvar AS is the most common subgroup (with a frequency of 60% to 75%), followed by subvalvar AS (8% to 30%) and supravalvar AS (1% to 2%). In addition, a bicuspid aortic valve (AoV) with or without stenosis occurs in up to 2% of the general population, thereby representing the most common congenital heart lesion.
LV outflow tract obstruction is associated with a pressure-overloaded left ventricle, often accompanied by progressive LV hypertrophy and fibrosis. Patients with LV outflow tract obstruction generally present with a systolic murmur whose frequency and intensity are determined by the degree of obstruction. Occasionally, a systolic click is heard in the setting of an abnormal AoV. Symptoms in children with LV outflow tract obstruction are rare, although severe obstruction can be associated with syncope, chest pain, and/or exercise intolerance. Very rarely, older children with significant obstruction will present with signs of congestive heart failure as severe LV hypertrophy results in progressive diastolic and systolic dysfunction. Many patients with the rare subgroup of supravalvar AS also have Williams syndrome with its characteristic features of infantile hypercalcemia, failure to thrive, elfin-like facial abnormalities, and mental retardation. The electrocardiogram may show increased left-sided voltages with ST-T wave changes consistent with LV hypertrophy. The heart is generally normal in size on the chest radiograph, although the ascending aorta may be dilated.
Significant LV outflow tract obstruction in the newborn period often involves severe LV dysfunction, mitral regurgitation, and increased left-to-right shunting across the foramen ovale, all contributing to compromised cardiac output. These infants generally present with signs and symptoms of congestive heart failure and shock. In cases of critical AS, cardiac output across the LV outflow tract is inadequate, and ductal patency must be maintained with prostaglandin E1 infusion so that the right-to-left flow across the ductus augments cardiac output for sufficient tissue oxygen delivery. The electrocardiogram may show increased right-sided and/or left-sided voltages with ST-T wave changes. The heart is usually enlarged on the chest radiograph, and pulmonary edema may be present.
Aortic regurgitation (AR) is associated with a volume-overloaded left ventricle. In contrast to the ventricular hypertrophy which results from pressure overload, volume overload results in ventricular dilation with compensatory hypertrophy (compensated AR). However, the heart’s ability to sustain hypertrophy eventually fails (decompensated AR) and LV wall stress increases, eventually leading to irreversible ventricular dysfunction and poor contractility. A diastolic murmur is generally heard on physical examination. Significant AR is usually associated with a hyperdynamic LV impulse and prominent peripheral pulses. These patients may begin to show signs and symptoms of congestive heart failure. The electrocardiogram will usually show increased left-sided voltages with ST-T wave changes, and cardiomegaly may be seen on the chest radiograph.
Aneurysmal dilation of the aortic root and/or ascending aorta is generally discovered because of its association with a bicuspid AoV, or a specific genetic syndrome or disease prompts a clinician to perform an echocardiogram or another diagnostic study. Rarely, a pediatric patient with aneurysmal dilation of the ascending aorta has an aortic dissection or rupture and presents with acute chest or abdominal pain, shock, or sudden death. Occasionally, a sinus of Valsalva aneurysm can rupture without catastrophic results, resulting primarily in a significant left-to-right shunt from the aorta into a right-sided chamber with consequent congestive heart failure. The chest radiograph generally shows the enlarged aortic root or ascending aorta, and cardiomegaly may be present in the setting of significant left-to-right shunting.
The normal LV outflow tract can be divided into three anatomic segments: the subaortic region, the AoV, and the proximal aorta (Fig. 14.1). In utero, the conus or infundibulum represents the subarterial muscular chamber separating the atrioventricular valve from the corresponding semilunar valve in both the right ventricular (RV) and LV outflow tracts. In normal fetal hearts, the subaortic conus regresses, resulting in varying degrees of fibrous continuity between the mitral valve (MV) and the AoV (Fig. 14.2). The area of fibrous continuity is often referred to as the mitral-aortic intervalvular fibrosa, a structure that originates from the primordial left ventriculoinfundibular fold and can be elongated in cases of subvalvar AS and tetralogy of Fallot. It is usually measured as the shortest distance from the anterior mitral leaflet to the base of the noncoronary or left coronary leaflet of the AoV. Within the LV outflow tract, the anterior mitral leaflet represents the posterior boundary of the subaortic region and the muscular ventricular septum represents the anterior boundary (see Fig. 14.2).
Figure 14.1. The anatomic segments of the left ventricular outflow tract. Includes the subaortic region (SubAo, asterisk), the aortic valve (AoV), and the ascending aorta (AAo), as depicted in (A) an illustration, (B) a pathology specimen, and (C) an apical long-axis view. AR, aortic root. (B, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
The normal AoV is a three-dimensional structure that involves three leaflets attached to the aortic root and supporting ventricular muscle in a semilunar or crown-like fashion (see Figs. 14-1B and 14-2A). The leaflets are separated by three commissures, which are lines of apposition between the leaflets extending from the center of the valve to the periphery (Fig. 14.3) (Video 14.1) and from the area of the ventriculoarterial junction to the sinotubular junction (the junction between the aortic root and proximal ascending aorta). An important and somewhat problematic issue in AoV morphology is the concept of the “aortic annulus,” a diagnostician construct that does not correspond to a true anatomic structure. Although an anatomic ventriculoarterial junction can usually be identified pathologically, the basal attachments of the semilunar leaflets actually extend beyond this ring into the supporting ventricular muscle (see Fig. 14.2), thereby confounding the use of the most proximal or basal attachment of the semilunar valve leaflets to define the “aortic annulus” (Fig. 14.4). In other words, the “aortic annulus” is not synonymous with the anatomic ventriculoarterial junction along the LV outflow tract. In addition, this ventriculoarterial ring does not fully support the AoV because the leaflets are attached or hinged within the entire aortic root up to the level of the sinotubular junction.
Figure 14.2. Fibrous continuity between the mitral valve and the aortic valve. A: Pathology specimen showing the anatomic ventriculoarterial junction (asterisk). B: Parasternal long-axis view. AML, anterior mitral leaflet; AoV, aortic valve; IVS, interventricular septum; LA, left atrium; LV, left ventricle. (A, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
The components of the proximal aorta include the aortic root and ascending aorta, structures that meet at the sinotubular junction (see Fig. 14.4). Because the sinotubular junction represents the most distal attachments of the AoV leaflets within the aortic root, it may be somewhat confusing to label an anomaly at the sinotubular junction a supravalvar anomaly because it often involves the distal segment of the AoV. Nevertheless, the walls of the aortic root and the ascending aorta are composed primarily of vascular smooth muscle cells and extracellular matrix proteins secreted by the cells. The most common component of the aortic wall is elastin, a protein that now appears to play a significant role in the morphogenesis and homeostasis of the arterial vessel walls. In addition, it appears to be involved in the development of supravalvar obstruction and aneurysmal dilation of the proximal aorta.
Figure 14.3. Cross-sectional view of the aortic valve with three leaflets separated by three commissures. Depicted in (A) an illustration, (B) a pathology specimen, and (C) a three-dimensional echocardiographic image. LCL, left coronary leaflet; NCL, noncoronary leaflet; PV, pulmonary valve; RCL, right coronary leaflet. (B, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Figure 14.4. Parasternal long-axis view of the proximal aorta. Diameters are measured at the levels of the aortic “annulus” (Ann), aortic root (AR), sinotubular junction (STJ), and ascending aorta (Aao).
ABNORMAL ANATOMY AND COMMON ASSOCIATIONS
Valvar Aortic Stenosis
Etiologies for valvar AS are listed in Table 14.1. The most common abnormality of AoV morphology is the bicuspid AoV, in which two of the three leaflets are fused or one of the commissures between adjacent leaflets is underdeveloped (also known as a raphe) (Fig. 14.5) (Video 14.2). A true bicuspid AoV with only two leaflets is a rare phenomenon. In most cases of a bicuspid AoV, the size of the combined leaflet (secondary to fusion or underdevelopment of a commissure) is larger than the unaffected leaflet, although it is rarely exactly twice the size of the unaffected leaflet. This latter finding suggests that the lesion is a developmental problem of the entire valve rather than simple fusion of two of the three leaflets. Among all patients with a bicuspid AoV, fusion or underdevelopment occurs most commonly at the intercoronary commissure between the right and left coronary leaflets (with a frequency of 70% to 86%) followed by the commissure between the right and noncoronary leaflets (12% to 28%) and the commissure between the left and noncoronary leaflets (very rare) (Fig. 14.6) (Video 14.3). In addition, the rate of AS progression appears to be higher with underdevelopment of the intercoronary commissure. Common associations with a bicuspid AoV include aortic coarctation (which occurs more frequently with intercoronary commissural underdevelopment) or interrupted aortic arch, subvalvar AS, ventricular septal defect (VSD), coronary anomalies (such as a displaced coronary ostium or a shortened left coronary artery), Turner syndrome, aortic dilation or aneurysm formation (with the increased risk for aortic dissection and rupture) (Fig. 14.7) (Video 14.4), and endocarditis (Fig. 14.8, Table 14.2) (Video 14.5).
Figure 14.5. Bicuspid aortic valve with fusion or underdevelopment of the intercoronary commissure (asterisks). Depicted in (A) a pathology specimen and (B) a parasternal short-axis view. NCL, noncoronary leaflet. (A, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Figure 14.6. Bicuspid aortic valve. A: Illustration of the three subtypes of a bicuspid aortic valve and their relative frequencies. B: Parasternal short-axis view of a bicuspid aortic valve with fusion or underdevelopment of the commissure between the right coronary and noncoronary leaflets. LCL, left coronary leaflet; NCL, noncoronary leaflet; RCL, right coronary leaflet.
Figure 14.7. Parasternal long-axis view of a bicuspid aortic valve with a dilated ascending aorta. AAo, ascending aorta; BAV, bicuspid aortic valve.
The most common AoV morphology in neonatal valvar AS is a unicuspid unicommissural AoV where the only open commissure is located between the left and noncoronary leaflets; in addition, a small eccentric valvar orifice is usually seen (Fig. 14.9) (Video 14.6). Occasionally, the leaflets are thickened and poorly formed with decreased mobility (Fig. 14.10) (Video 14.7). These cases are often associated with a small aortic root and ascending aorta. The left ventricle may be small and hypertrophied with endocardial fibroelastosis (see Fig. 14.9E), or it may be dilated with poor systolic function, mitral regurgitation, and left atrial dilation.
Subvalvar Aortic Stenosis
Because subvalvar AS is rarely diagnosed in utero or in the newborn period, many have suggested that this lesion is an acquired heart disease rather than a congenital one. Nevertheless, it is a progressive disease whose postoperative recurrence rate is as high as 33%. The mechanisms for the development of subvalvar AS, as suggested by Cape and colleagues, are listed in Table 14.3. The associated LV outflow tract morphologic abnormalities include a small aortic annulus and root, a steep aortoseptal angle, abnormal LV muscle bundles, a prominent anterolateral muscle bundle of Moulaert, elongation of the mitral-aortic intervalvular fibrosa, MV pathology, and protrusion of aneurysmal tricuspid valve tissue or membranous septum into the LV outflow tract. Subvalvar AS can occur in isolation or with several common associations (Table 14.4).
Figure 14.8. Bicuspid aortic valve with endocarditis involving a vegetation adherent to the valve (asterisk) as well as a leftward posterior aortic root abscess (hashed). Depicted in (A) a parasternal long-axis view and (B) a three-dimensional echocardiographic short-axis view. AR, aortic root; LV, left ventricle.
In the absence of a VSD or other cardiac associations, subvalvar AS most frequently presents as a discrete fibrous or fibromuscular shelf extending from the ventricular septum just below the AoV (Fig. 14.11) (Video 14.8). Occasionally, the shelf extends to the anterior mitral leaflet in a diaphragmatic fashion (Fig. 14.12) (Video 14.9). Rarely the muscular component is so extensive that it creates a tunnel-like LV outflow tract with significant subaortic obstruction (Fig. 14.13) (Video 14.10). This is distinct from the more diffusely hypertrophied ventricular septum and dynamic subaortic obstruction associated with hypertrophic cardiomyopathy.
In the presence of a VSD, the most significant type of subaortic obstruction results from posterior deviation of the conal or infundibular septum (Fig. 14.14) (Video 14.11). This lesion is often associated with aortic coarctation or an interrupted aortic arch. Another type of potential subvalvar AS with a VSD involves the presence of an endocardial fold or a fibromuscular ridge at the crest of the muscular septum (Fig. 14.15) (Video 14.12). Last, abnormal MV attachments to the ventricular septum, particularly in the setting of unrepaired or repaired atrioventricular canal defects, can also cause subaortic obstruction (Fig. 14.16) (Video 14.13).
An important and not uncommon association with subvalvar AS involves the development of AR, which can progress in children and result in the need for early surgical intervention (Fig. 14.17) (Video 14.13B). The mechanism for AR presumably involves AoV damage secondary to the high-velocity jet coursing through the subaortic region. In addition, the abnormal fibromuscular tissue in subvalvar AS may be continuous with the base of the AoV, potentially disrupting the normal support for the AoV leaflets. It is important to note, however, that AR associated with subvalvar AS in adults is not usually a progressive problem and does not necessarily suggest a need for surgical intervention.
Supravalvar Aortic Stenosis
Although supravalvar AS is usually associated with Williams syndrome, it can also present as an autosomal dominant lesion in a familial form or as a sporadic idiopathic disorder. Supravalvar AS is in fact an elastin arteriopathy resulting from the mutation or deletion of the elastin gene on chromosome 7. There are three anatomic subtypes of supravalvar AS: the hourglass type, which is the most common subtype and frequently involves dilation of the aortic root and the ascending aorta distal to the narrowing (Fig. 14.18) (Video 14.14); the diaphragmatic or membranous type (Fig. 14.19) (Video 14.15); and the tubular type, which is quite rare and involves diffuse hypoplasia of the ascending aorta (Table 14.5). Common associations include abnormalities of the AoV, the coronary arteries (e.g., coronary artery dilation, intrinsic coronary thickening and ostial stenosis, and ostial occlusion or entrapment by a tethered AoV leaflet) (Fig. 14.20), aortic arch branches, and branch pulmonary arteries (Table 14.6).
Figure 14.9. Unicuspid unicommissural aortic valve. The only open commissure is located between the left coronary and noncoronary leaflets (asterisks); the aortic valve leaflets are abnormally thickened; and the left ventricle is small with endocardial fibroelastosis, as depicted in (A) a cross-sectional illustration of the aortic valve, (B) a pathology specimen, (C) a parasternal short-axis view, (D) a parasternal long-axis view, and (E) an apical four-chamber view. Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle. (B, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Aortic regurgitation (AR), defined somewhat loosely as diastolic flow from the aorta into the left ventricle, is rare in childhood, especially in isolation. Congenital etiologies for functional AR include a stenotic or nonstenotic bicuspid AoV (Fig. 14.21) (Video 14.16); other abnormalities of AoV leaflet or commissural morphology; an aortico-LV tunnel (Fig. 14.22) (Video 14.17); absence of one or more AoV leaflets; a fibrous band between an AoV leaflet and the aortic root wall; a coronary-cameral fistula into the left ventricle; and a ruptured left sinus of Valsalva aneurysm into the left ventricle (Table 14.7). Other associations with AR include a membranous VSD or a doubly-committed subarterial VSD with AoV prolapse into the defect secondary to the Venturi phenomenon (Fig. 14.23) (Video 14.18), subvalvar AS, neonatal Marfan syndrome with concurrent aortic root dilation, repaired truncus arteriosus, and tetralogy of Fallot (Table 14.8). In addition, AR occurs commonly with a ruptured sinus of Valsalva aneurysm, secondary to disruption of the normal AoV leaflet support within the aortic root (Fig. 14.24) (Video 14.19). Acquired etiologies include endocarditis (Fig. 14.25) (Video 14.20), rheumatic fever, and surgical valvotomy or transcatheter balloon valvotomy for valvar AS (Fig. 14.26, Table 14.9) (Video 14.21).
Figure 14.10. Thickened and dysplastic aortic valve leaflets. Depicted in (A) a transesophageal view along a plane oriented at approximately 120 degrees, (B) a three-dimensional short-axis view, and (C) an intraoperative photograph.
Figure 14.11. Subaortic fibromuscular ridge (asterisks). Depicted in (A) a pathology specimen, (B) an apical long-axis view, and (C) a parasternal long-axis view. Ao, aorta; LA, left atrium; LV, left ventricle. (A, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Aneurysm of the Proximal Aorta
Most aortic root aneurysms involve the right sinus of Valsalva, followed by the noncoronary sinus and then the left sinus (Fig. 14.27) (Video 14.22). Aneurysm formation in the aortic root and aneurysmal dilation of the ascending aorta (see Fig. 14.7) (Video 14.4) occur when structural weakness and thinning of the aortic wall result from smooth muscle cell loss and extracellular matrix disruption. Elastin production and maintenance appear to be as important in the development of aortic aneurysms as in the arteriopathy associated with supravalvar AS. For example, Marfan syndrome results from mutations in the fibrillin gene on chromosome 15. The fibrillin protein is necessary in the formation of elastin and other components of the extracellular matrix. In addition, it may inhibit the availability and effects of the cytokine transforming growth factor-β and endogenous matrix metalloproteinases, both of which are thought to be involved in the degradation of elastin and other components of the extracellular matrix. Common associations with aneurysmal dilation of the proximal aorta include Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlos syndrome, Turner syndrome, a bicuspid AoV, systemic hypertension, and coarctation (Table 14.10). It is important to recognize that the term “poststenotic dilation” of the aorta is no longer appropriate in light of the intrinsic aortopathy associated with valvar AS. In addition, the degree of aortic dilation does not usually correlate to the severity of the stenosis.
APPROACH TO TRANSTHORACIC ECHOCARDIOGRAPHY
Valvar Aortic Stenosis
The transthoracic echocardiogram of a patient with valvar AS must include evaluation of several key features (Table 14.11).
Leaflet and Commissural Morphology
The number and relative sizes of the leaflets and commissures are best evaluated with cross-sectional views of the AoV in parasternal short-axis views. The raphe of a fused or underdeveloped commissure is usually difficult to distinguish from a normal commissure when the AoV is viewed in its closed position during diastole. However, during systole when the AoV is open, the affected commissure remains visible as an echogenic line from the leaflet edge to the aortic wall. Occasionally, there is only partial underdevelopment of a commissure such that the separation between two leaflets occurs but does not extend to the aortic wall (Fig. 14.28) (Video 14.23). When fusion or underdevelopment occurs at the intercoronary commissure in a bicuspid AoV, the AoV opening during systole has a horizontal orientation in parasternal short-axis views (see Fig. 14.5B) (Video 14.2C). In contrast, fusion or underdevelopment of the commissure between the right and noncoronary leaflets results in a more vertical orientation of the AoV opening in the same views (see Fig. 14.6B) (Video 14.3B). In a unicuspid or unicommissural AoV, the opening is usually slit-like in appearance and almost always located at the commissure between the left and noncoronary leaflets (see Fig. 14.9) (Video 14.6A). Acommissural valves usually have a more centrally located orifice. Apical and parasternal long-axis views are very useful in characterizing the AoV leaflets. They may be thickened, and the degree of thickening may vary along the length of the leaflet with thicker edges giving it a “lumpy” appearance (see Figs. 14.9D and 10A) (Videos 14.3A, 14.6B, and 14.7A). In addition, the leaflets usually dome in systole, secondary to the restrictive lateral mobility caused by incomplete commissural separation along the distal zone of apposition (which is located more distally near the sinotubular junction).
Figure 14.12. Subaortic fibromuscular shelf extending to the anterior mitral leaflet (asterisks). Depicted in (A) a parasternal long-axis view, (B) a three-dimensional long-axis view, and (C) a three-dimensional short-axis view with display of the crescentic shelf adjacent to the anterior mitral leaflet and the diaphragm-like obstruction along the subaortic region. AML, anterior mitral leaflet; Ao, aorta; IVS, interventricular septum; LA, left atrium; LV, left ventricle; RV, right ventricle.
Degree of Obstruction
Continuous-wave Doppler interrogation across the AoV is best performed in apical, right sternal border, and suprasternal views and can provide information regarding the maximum instantaneous gradient and the mean gradient across the AoV. Every effort should be made to align the Doppler beam with the high-velocity jet across the stenotic AoV. It is well known that discrepancies usually occur between the maximum instantaneous gradient measured by echocardiography and the peak-to-peak gradient measured by catheterization, with the former measurement almost always higher than the latter one. These discrepancies result partly from a phenomenon called pressure recovery. Echocardiographic assessment of maximum instantaneous gradients occurs at the vena contracta, the volume of space in the aorta immediately distal to a stenotic AoV where blood flow velocity, kinetic energy, and the pressure drop are highest (Fig. 14.29). The flow velocity normally decreases farther downstream as kinetic energy is converted back to potential energy and pressure is recovered (thereby decreasing the pressure difference between the subaortic region and the more distal ascending aorta). Because the peak-to-peak gradient involves direct pressure measurement more distally in the ascending aorta, pressure recovery may or may not play a role in the arterial pressure. In cases of severe stenosis, the high-velocity jet extends farther into the ascending aorta, and pressure recovery is less influential; in this situation, the discrepancies are less pronounced. On the contrary, the extent of the high-velocity jet is relatively short and pressure recovery occurs more proximally in the ascending aorta with mild stenosis, and the discrepancies in this situation become more apparent.
Figure 14.13. Marked septal hypertrophy along the left ventricular outflow tract resulting in significant subaortic stenosis. Depicted in (A) a pathology specimen and (B) a parasternal long-axis view. Ao, aorta; LA, left atrium; LV, left ventricle. (A, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Figure 14.14. Conoventricular septal defect and posterior deviation of the conal septum into the subaortic region. Depicted in (A) a pathology specimen and (B) an apical long-axis view. Ao, aorta; CS, conal septum; LV, left ventricle; RV, right ventricle. (A, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Figure 14.15. Apical long-axis view. Ventricular septal defect (VSD), a fibrous ridge at the crest of the ventricular septum (asterisk), and significant aortic overriding. Ao, aorta; LV, left ventricle; RV, right ventricle.
Figure 14.16. Repaired transitional atrioventricular canal defect. Residual cleft mitral valve and subaortic stenosis secondary to the septal attachments of the cleft mitral valve (asterisks), as depicted in (A) a subcostal short-axis view, (B) an apical long-axis view, and (C) an apical long-axis view with color mapping. Ao, aorta; LV, left ventricle; RV, right ventricle.
Figure 14.17. Apical long-axis view. Color Doppler from the patient in Figure 14.16 showing mild aortic regurgitation. Septal attachments of the cleft mitral valve (asterisk). Ao, aorta; LV, left ventricle.
Because determination of the degree of valvar AS and the thresholds for intervention are based primarily on catheterization data using peak-to-peak gradients, these discrepancies have confounded the use of echocardiographic data in clinical decision making for these patients. Many prefer the use of Doppler mean gradients to classify valvar AS because these values correlate more closely with catheterization-derived mean gradients. Others accept the limitations associated with using maximum instantaneous gradients, and they use thresholds of 25 to 30 mm Hg to distinguish mild from moderate stenosis and 50 to 60 mm Hg to distinguish moderate from severe stenosis. A recent study by Vlahos and colleagues reveals that catheterization-derived peak-to-peak gradients are overestimated by maximum Doppler gradients and underestimated by mean Doppler gradients from apical and high parasternal views. A maximum Doppler gradient from high parasternal windows less than 55 mm Hg predicts no intervention, whereas predictors of intervention include a maximum Doppler gradient from high parasternal windows greater than 90 mm Hg, a mean Doppler gradient from apical windows greater than 50 mm Hg, and an average of the maximum Doppler gradients from the two views greater than 70 mm Hg. The study concludes that the best predictor of the catheterization-derived gradient is likely an average of the maximum Doppler gradients from apical and high parasternal views.
Figure 14.18. Hourglass type of supravalvar aortic stenosis. High origin of the right coronary artery (asterisk), as depicted in (A) a pathology specimen and (B) a right sternal border long-axis view. AAo, ascending aorta; AoV, aortic valve. (A, With permission from Prof. Robert H. Anderson, Institute of Child Health, London, United Kingdom.)
Figure 14.19. Diaphragmatic type of supravalvar aortic stenosis (asterisk). Depicted in a parasternal long-axis view without and with color Doppler. AAo, ascending aorta; AoV, aortic valve, STJ, sinotubular junction.
An important determinant of the measured AoV gradient is the amount of transvalvar flow. Cases of significant valvar AS are often associated with severe LV dysfunction, which in turn results in decreased cardiac output, decreased transvalvar flow, and a decreased maximum instantaneous gradient across the AoV despite the severity of the obstruction (Video 14.24). In these situations, Doppler mean gradients tend to be less affected by transvalvar flow than maximum instantaneous gradients.
Degree of Left Ventricular Hypertrophy and Dysfunction
LV hypertrophy suggests significant obstruction in these patients, thereby providing an index for the degree of obstruction. M-mode measurements of LV wall thickness at the septum and along the free wall in parasternal short-axis views can be compared to measurements from normal children with the same age and body surface area (z-score calculations) to determine the degree of LV hypertrophy. LV mass is often used to determine the degree of LV hypertrophy and can be calculated from M-mode measurements of LV thickness or from LV volumetric calculations using various standard two- and three-dimensional echocardiographic methods. Increased LV mass is associated with LV diastolic dysfunction. LV systolic dysfunction, usually presenting as decreased LV shortening or ejection fraction, can also occur, but LV strain analysis may provide an earlier index of LV systolic dysfunction in patients with chronic LV outflow tract obstruction.
Figure 14.20. Transesophageal view along a plane oriented at approximately 120 degrees of supravalvar aortic stenosis. Entrapment of the right coronary artery (RCA) by the aortic valve (AoV). AAo, ascending aorta; LV, left ventricle.
Figure 14.21. Bicuspid aortic valve. A: Parasternal short-axis view of a bicuspid aortic valve involving fusion or underdevelopment of the commissure between the right coronary and noncoronary leaflets (asterisk). B: Parasternal long-axis view with color Doppler showing moderate aortic regurgitation. Ao, aorta; LV, left ventricle.
Figure 14.22. Parasternal long-axis view. Small tunnel from the aorta (Ao) to the left ventricle (LV), causing mild functional aortic regurgitation. LA, left atrium.
Echocardiography presents endocardial fibroelastosis (EFE) as abnormally bright and thick LV endocardium (Fig. 14.30) (Video 14.25). The Congenital Heart Surgeons’ Society has provided a system to grade EFE in the setting of valvar AS in the newborn (Table 14.12).
Ascending Aortic Size
As discussed previously, a bicuspid AoV is often associated with intrinsic ascending aortic dilation (see Fig. 14.7) (Video 14.4). Therefore, measurement of the aortic annulus and root, sinotubular junction, and ascending aorta in parasternal long-axis views should always be performed.
Figure 14.23. Parasternal long-axis view of aortic valve prolapse into a ventricular septal defect (asterisk). Shows distortion of the aortic valve in the area of the defect and mild aortic regurgitation. Ao, aorta; LV, left ventricle; VSD, ventricular septal defect.
Left Atrial Dilation
As the LV diastolic function decreases with progressive LV hypertrophy, left atrial dilation becomes more apparent in subcostal and apical views. Occasionally, restrictive left-to-right flow is seen across a patent foramen ovale, consistent with the increased LV diastolic pressure and left atrial pressure associated with LV diastolic dysfunction.
Neonatal Critical Valvar Aortic Stenosis
Because the LV is often small in neonates with critical valvar AS, an important early decision in their management involves the choice between biventricular repair and univentricular palliation. In an important study published in 1991 by Rhodes and colleagues, a retrospective multivariate analysis was performed on a group of neonates with critical valvar AS to identify the independent predictors of outcome after biventricular repair. The parameters evaluated in their analysis included LV volumes, LV mass, LV long-axis measurements, Doppler gradient, aortic annular diameter, aortic root diameter, transverse aortic arch diameter, MV annular diameter and area, tricuspid valve annular diameter and area, and ejection fraction. They derived an equation to calculate a discriminant score that predicts survival after biventricular repair:
Figure 14.24. Parasternal long-axis view of a ruptured sinus of Valsalva aneurysm into the right atrium (hash). Associated mild aortic regurgitation (asterisk). Ao, aorta; LV, left ventricle; RA, right atrium.
(14.0 × body surface area) + (0.943 × aortic root diameter indexed to body surface area) + (4.78 × LV long-axis–to–heart long-axis ratio) + (0.157 × MV area indexed to body surface area) – 12.03
Scores below –0.35 predicted death after a biventricular repair with 90% accuracy. They also identified four risk factors that predicted 100% mortality after biventricular repair if more than one risk factor was present. These risk factors included LV long-axis–to–heart long-axis ratio of 0.8 or less (Fig. 14.31); aortic root diameter indexed to body surface area of 3.5 cm2/m2 or less (see Fig. 14.4); MV area indexed to body surface area of 4.75 cm2/m2 or less; and LV mass indexed to body surface area of 35 g/ m2 or less (Table 14.13). In addition to the morphometric predictors of survival after biventricular repair for this group of patients, Kovalchin and colleagues identified an important hemodynamic predictor, namely the presence of predominant or total antegrade flow in the ascending aorta and transverse aortic arch by color mapping and Doppler interrogation (Fig. 14.32) (Video 14.26).
Figure 14.25. Bicuspid aortic valve with endocarditis resulting in a flail aortic valve segment. A: Parasternal long-axis view. B: Color Doppler in the same view showing significant aortic regurgitation (asterisk) associated with the flail aortic valve segment. AAo, ascending aorta; LV, left ventricle.
In 2001, the Congenital Heart Surgeons’ Society conducted a multicenter study of this group of patients and identified several risk factors for mortality 5 years after biventricular repair, and these include a high EFE grade, a low aortic root diameter z-score, and a young age at presentation. Risk factors for mortality 5 years after univentricular palliation included a small ascending aorta diameter and moderate or severe tricuspid regurgitation. Risk factors associated with differential survival between the two management approaches included all of the above as well as a low LV length z-score (Table 14.14).
More recently in 2006, Colan and colleagues evaluated the efficacy of the Rhodes score and the Congenital Heart Surgeons’ Society model in predicting outcomes in a larger group of patients undergoing biventricular repair. In this analysis, the Rhodes score predicted outcome accurately in only 76% of the patients. In addition, the Congenital Heart Surgeons’ Society model predicted a survival advantage with univentricular palliation in 58% of these patients. However, over half of this group actually survived a biventricular repair, suggesting that the model may be biased in favor of univentricular palliation for this patient population. The new analysis derived an equation to predict survival after biventricular repair where the discriminant score is equal to (10.98 × body surface area) + (0.56 × AoV annular z-score) + (5.89 × LV long-axis–to–heart long-axis ratio) – 0.79 (if EFE grade ≥2) – 6.78 (see Table 14.13). A threshold score of –0.65 predicted the outcome accurately in 90% of the study patients. Unlike the original Rhodes score, MV area did not play a significant role in this analysis, presumably because all patients with critical valvar AS and MV area z-scores less than –2 underwent univentricular palliation and were therefore not included in the analysis.
Figure 14.26. Valvar aortic stenosis after transcatheter balloon valvotomy with thickened aortic valve leaflets. (A) Apical two-chamber view. (B) Color Doppler in the same view showing moderate aortic regurgitation. Ao, aorta; LV, left ventricle; RV, right ventricle.
In response to the bias that a high-risk biventricular repair may be better than a low-risk univentricular palliation, the Congenital Heart Surgeons’ Society, in turn, refined their approach to this group of patients in a paper published in 2007. In this new analysis, the risk factors for mortality 5 years after biventricular repair included a small minimum LV outflow tract diameter indexed to body surface area, LV dysfunction, a high EFE grade, and a small mid-aortic arch diameter indexed to body surface area. Risk factors for mortality 5 years after univentricular palliation included moderate or severe tricuspid regurgitation, a large VSD, a small MV annular z-score, and a small dominant ventricular length indexed to body surface area (see Table 14.14). A more recent analysis from the Congenital Heart Surgeons’ Society in 2012 revealed that the survival of neonates with critical AS undergoing biventricular repair was dependent on the success of the initial intervention. Risk factors for mortality in this study included an early repeat intervention as well as moderate or severe EFE, LV dysfunction, severe leaflet thickening, functionally unicuspid valves, and subvalvar obstruction. This study suggested that children with these risk factors might have better survival with an early commitment to univentricular palliation.
Figure 14.27. Unruptured aneurysm of the right sinus of Valsalva into the right ventricle (asterisks). Depicted in (A) a parasternal long-axis view and (B) a parasternal short-axis view. AAo, ascending aorta; LA, left atrium; LSV, left sinus of Valsalva; LV, left ventricle; RA, right atrium; RV, right ventricle.
Subvalvar Aortic Stenosis
The transthoracic echocardiogram in a patient with subvalvar AS must include evaluation of several key features (Table 14.15).
Mechanism of Obstruction
The mechanism of the subaortic obstruction is best evaluated in apical and parasternal long-axis views, particularly if the stenosis results from a fibromuscular ridge (see Fig. 14.11) (Video 14.8), an endocardial fold at the crest of the muscular septum (see Fig. 14.15) (Video 14.12), or a diffuse muscular narrowing along the LV outflow tract (see Fig. 14.13) (Video 14.10). These views are also useful when the conal septum is deviated into the subaortic region (see Fig. 14.14) (Video 14.11) or if the MV is involved (see Fig. 14.16) (Video 14.13), although subcostal long-axis and short-axis views are also quite informative. Parasternal short-axis views can be useful in characterizing fibromuscular ridges that extend to the anterior mitral leaflet, although three-dimensional echocardiography may provide a better representation of this type of subvalvar AS (see Fig. 14.12C) (Video 14.9B).
Figure 14.28. Parasternal short-axis view of partial fusion or underdevelopment of the commissure between the right coronary and noncoronary leaflets (asterisk).
Figure 14.29. Illustration of the vena contracta, the narrowest segment of the high-velocity jet coursing across a stenotic aortic valve during ventricular contraction. AAo, ascending aorta; LV, left ventricle.
Location of Obstruction
The distance from the fibromuscular ridge to the AoV leaflets can usually be measured in parasternal long-axis and apical views (see Fig. 14.11). It is especially important to evaluate any continuity between the fibromuscular ridge and the AoV leaflets because surgical resection may involve disruption of the normal supporting structures of the AoV.
Figure 14.30. Parasternal long-axis view of endocardial fibroelastosis involving a left ventricular papillary muscle group and some left ventricular endocardial segments (Grade 2). Ao, aorta; LA, left atrium; LV, left ventricle.
Degree of Obstruction
The Doppler-derived maximum instantaneous gradient across the LV outflow tract is best measured in apical, right sternal border, and suprasternal views. Thresholds for surgical intervention for subvalvar AS are generally lower than those for valvar AS because of the progressive nature of this anomaly. In fact, the degree of obstruction along the subaortic region may increase fairly quickly over a short period of time in children, thereby necessitating periodic echocardiographic follow-up of the gradient every 6 to 12 months in some patients. Beyond adolescence, however, patients with mild subvalvar AS usually do not develop worsening obstruction.
Figure 14.31. Apical four-chamber view of critical aortic stenosis with mild left ventricular hypoplasia depicting the left ventricular long-axis length (green line) and the heart long-axis length (red line).
Similar to the progression of the degree of obstruction along the LV outflow tract, AR can appear suddenly and worsen fairly quickly in children with subvalvar AS. In contrast, AR is not usually a progressive association in adults with subvalvar AS.
The initial echocardiogram of any patient with subvalvar AS should always exclude the presence of a VSD, a MV anomaly, and partial or complete obstruction along the aortic arch. Because a double-chamber or divided right ventricle can develop in the setting of subvalvar AS and a VSD, the right ventricular outflow tract should always be evaluated in the follow-up echocardiograms of this group of patients.
Several reports have been published identifying morphometric and hemodynamic parameters related to the development and progression of subvalvar AS. In 1993, Kleinert and colleagues compared patients with isolated subvalvar AS as well as patients with a VSD or aortic coarctation who developed subvalvar AS after their initial presentation to a normal control population. In their analysis, they identified several morphometric predictors of the development of fixed subvalvar AS, and these included a wide mitral-aortic separation (elongated intervalvular fibrosa), exaggerated aortic override (see Fig. 14.15), and a steep aortoseptal angle (Fig. 14.33, Table 14.16). In the same year, Geva and colleagues looked specifically at patients with an interrupted aortic arch and VSD, a group of patients whose LV outflow tract is often small. Because of the left-to-right flow across the VSD and the right-to-left flow across the patent ductus arteriosus, there is often decreased flow across the LV outflow tract, and turbulence may not be seen along this area despite the presence of significant subvalvar AS (Fig. 14.34) (Video 14.11). Their analysis revealed that the best predictor of the development of postoperative subvalvar AS in these patients was the LV outflow tract cross-sectional area divided by body surface area, with a threshold value of 0.7 cm2/m2. In 1998, Bezold and colleagues performed a multivariate analysis of patients with simple discrete subvalvar AS for whom echocardiographic follow-up was available 1 year or longer after presentation. They found that the best predictors of significantly progressive subvalvar AS included the distance from the fibromuscular ridge to the AoV indexed to the square root of the body surface area, involvement of the anterior MV leaflet, and the initial Doppler gradient (Table 14.17). More recently in 2007, Geva and colleagues identified several independent predictors of reoperation after surgical resection of discrete subvalvar AS, and these include a distance between the fibromuscular ridge and the AoV less than 6 mm, a maximum Doppler gradient of 60 mm Hg or greater, and involvement of the AoV or MV with the need for surgical peeling (Table 14.18).
Figure 14.32. Critical aortic stenosis with hypoplasia of the ascending aorta and a large patent ductus arteriosus. A: Suprasternal long-axis view. B: Color Doppler in the same view depicting reversal of flow in the transverse aortic arch. AAo, ascending aorta; Dao, descending aorta; DTA, distal transverse aortic arch; PDA, patent ductus arteriosus.
Supravalvar Aortic Stenosis
In the setting of supravalvar AS, the aortic root and ascending aorta are best evaluated in apical, parasternal long-axis, and right sternal border views (see Fig. 14.18) (Video 14.14). The diameters at the levels of the aortic annulus, aortic root, sinotubular junction, and ascending aorta should be measured in parasternal long-axis views (see Fig. 14.4), and z-scores should be calculated. Echocardiographic assessment of the hourglass type of supravalvar AS usually reveals a z-score discrepancy between the sinotubular junction and ascending aorta diameters, often with values less than –2 for the former. The rare tubular supravalvar AS is usually associated with low concordant z-score values for both the sinotubular junction and ascending aorta diameters. The AoV morphology should be carefully evaluated because AoV disease along with diffuse tubular hypoplasia of the ascending aorta correlates strongly with death and reoperations in these patients. Continuous-wave Doppler interrogation to calculate the maximum instantaneous gradient along the aortic outflow tract should be performed in apical, right sternal border, and suprasternal views. Because obstruction can occur at more than one level in patients with supravalvar AS, pulsed-wave Doppler interrogation should also be performed along the various segments of the aortic outflow tract. Spontaneous improvement rarely occurs and the degree of obstruction often worsens over time, so patients with supravalvar AS should be evaluated by echocardiography every year.
Figure 14.33. Parasternal long-axis view of significant muscular subaortic stenosis depicting a steep aortoseptal angle. Ao, aorta; LA, left atrium; LV, left ventricle.
Figure 14.34. Color Doppler in an apical two-chamber view of a ventricular septal defect and posterior deviation of the conal septum into the subaortic region. Depicting laminar flow along the subaortic region despite significant subaortic obstruction. Ao, aorta; CS, conal septum; LV, left ventricle; RV, right ventricle; VSD, ventricular septal defect.
The coronary arteries (including the coronary ostia) should be carefully assessed in parasternal short-axis views, especially given the higher incidence of coronary artery dilation, ostial stenosis, and coronary entrapment in patients with supravalvar AS (see Figs. 14.18 and 14.20). The aortic arch should be carefully evaluated in suprasternal long-axis and short-axis views because aortic coarctation and proximal stenosis of aortic arch branches may occur, particularly in the setting of Williams syndrome. Peripheral pulmonary artery stenosis is also frequently seen in Williams syndrome, although spontaneous improvement of the obstruction along the branch pulmonary arteries can occur. The branch pulmonary arteries are usually best evaluated in parasternal short-axis views, although occasionally suprasternal short-axis and apical views can delineate the stenotic segments along the branch pulmonary arteries.
When AR is present, echocardiography should determine the etiology and identify any of the common associations. AoV morphology is best evaluated in parasternal short-axis and long-axis views. An aortico-LV tunnel or a ruptured sinus of Valsalva aneurysm is best seen in subcostal, apical, and parasternal views (see Fig. 14.22) (Video 14.17). These views are also useful when the AoV prolapses into a VSD, although the parasternal long-axis view usually provides the best display of the AoV leaflet distortion in the area of the VSD flow (see Fig. 14.23) (Video 14.18). As discussed previously, subvalvar AS is best evaluated in apical and parasternal views, and color mapping can sometimes depict exactly how the high-velocity jet across the subaortic region can damage the AoV (see Fig. 14.17) (Video 14.13B).
Echocardiographic determination of the severity of AR usually involves characterization of the regurgitant jet, measurement of Doppler-derived parameters, and assessment of LV size and function (Table 14.19).
The length and area of the regurgitant jet as characterized by color mapping in apical views have been proposed as indices for AR severity. However, these measurements generally do not correlate well with the severity of the AR, particularly because the Coanda effect tends to alter the shape and extent of a regurgitant jet when it courses along a surface such as the ventricular septum or anterior mitral leaflet. As in valvar AS, the vena contracta in AR represents the smallest area of the regurgitant jet at or below the AoV. The width or diameter of the vena contracta measured in parasternal long-axis views may correlate better with AR severity in adults (Fig. 14.35), though the ratio of the vena contracta diameter to the LV outflow tract diameter (also measured in parasternal long-axis views) may be a more appropriate index for children. According to a 2003 report from the American Society of Echocardiography Task Force on Valvular Regurgitation, a vena contracta width greater than 6 mm and a ratio greater than 65% correspond to severe AR. Others have suggested using the area of the vena contracta or proximal regurgitant jet as measured in parasternal short-axis views as a more accurate determinant of severity, particularly because the regurgitant orifice is frequently not circular. Another method that calculates the effective regurgitant orifice area by using the proximal isovelocity surface areas (PISA) is quite complicated and therefore rarely used.
Abnormal diastolic reversal of flow in the abdominal aortic Doppler pattern is often used as a simple indicator of moderate AR, with holodiastolic reversal representing severe AR (Fig. 14.36). A more accurate assessment may be obtained by calculating the ratio of the velocity time integrals of the diastolic reverse flow and the systolic forward flow, and ratios greater than 35% generally represent severe AR. A study by Beroukhim and colleagues revealed that a regression model using the vena contracta area as well as the velocity time integral ratio appears to be an even better index or AR severity. Continuous-wave Doppler assessment of the AR jet deceleration over time also provides some quantitation for AR severity. The most commonly used indices include deceleration rate (calculated as the slope from the peak regurgitant velocity to the velocity at end diastole) and pressure half-time (defined as the time from peak regurgitant velocity to half the peak value) (Fig. 14.37). A deceleration rate greater than 3.5 m/s2and a pressure half-time less than 250 ms generally represent severe AR. However, both indices can be significantly affected by abnormal systemic vascular resistance and LV compliance. For example, a stiff left ventricle will have a higher deceleration rate and a lower pressure half-time than a more compliant left ventricle with the same degree of AR. In addition, the higher heart rates in children tend to decrease the reproducibility and reliability of these measurements. Other Doppler-derived indices for regurgitant volume or regurgitant fraction as calculated from the total forward flow across the AoV and the MV are also quite complicated and therefore rarely used.
Figure 14.35. Color Doppler in a parasternal long-axis view of moderate aortic regurgitation depicting measurement of the width of the vena contracta. Ao, aorta; LA, left atrium; LV, left ventricle.
Figure 14.36. Holodiastolic reversal of flow in the abdominal aortic Doppler signal indicating severe aortic regurgitation.
Figure 14.37. Measurement of the deceleration rate and pressure half-time by continuous-wave Doppler interrogation for severe aortic regurgitation.
Left Ventricular Size and Function
According to a 2006 report from the American College of Cardiology and American Heart Association Task Force on Practice Guidelines, the recommended LV size thresholds for intervention in asymptomatic adults with significant AR include an end-diastolic diameter of 75 mm and an end-systolic diameter of 55 mm. There are, however, no significant data showing that end-diastolic diameter is an independent risk factor for irreversible LV dysfunction in patients with severe AR. On the other hand, the preoperative LV end-systolic diameter has been shown to predict LV recovery after surgical intervention, and a LV end-systolic diameter z-score greater than 4.5 appears to increase the risk for postoperative problems, persistent LV dysfunction, and death. Because the goal is to intervene before irreversible LV dysfunction ensues, an understanding of myocardial mechanics may provide some insight into the development of LV dysfunction in these patients. Decompensated AR occurs when there is inadequate hypertrophy with a consequent increase in peak systolic and end-systolic wall stress, a measure of afterload. This, in turn, affects load-dependent indices of LV function such as shortening fraction and ejection fraction, initially without any significant effect on intrinsic myocardial contractility. It appears that irreversible LV dysfunction occurs after myocardial contractility diminishes, suggesting that echocardiographic measures of contractility or afterload-adjusted ejection fraction might provide better guidelines for the timing of intervention.
Aneurysm of the Proximal Aorta
The aortic root and ascending aortic diameters are usually measured in parasternal long-axis views (see Fig. 14.4), and calculation of the corresponding z-scores provides an easy index to identify aneurysmal dilation of these structures. Occasionally, aneurysmal dilation of the aortic root results in a windsock deformity of one of the sinuses of Valsalva, although sinus of Valsalva aneurysms may also present sporadically without preexisting aortic root dilation (see Fig. 14.27) (Video 14.22). Parasternal long-axis and short-axis images usually present the best views for evaluating the extent and effects of these aneurysms. If an aneurysm does not rupture, it can extend into one of the right or left heart chambers, sometimes causing problems such as right ventricular outflow tract obstruction or disruption of the tricuspid or mitral valve. Color flow Doppler in most views will depict the associated problems with a ruptured sinus of Valsalva aneurysm (Fig. 14.38) (Video 14.27), including the effective left-to-right shunt resulting from a ruptured aneurysm into a right heart chamber or pulmonary artery, the functional AR resulting from a ruptured aneurysm into the left ventricle, and the continuous high-velocity jet resulting from a ruptured aneurysm into the left atrium.
Rarely, aneurysmal dilation of the ascending aorta resulting from the intrinsic aortopathy of diseases such as Marfan syndrome, Loeys-Dietz syndrome, and Turner syndrome is associated with aortic dissection and catastrophic rupture. Parasternal, right sternal border, and suprasternal views may display the characteristic parallel lines of the dissection along the ascending aorta wall, and occasionally color Doppler will show the connection between the dissection and the aortic lumen (Fig. 14.39) (Video 14.28). Because dissection generally occurs in adolescents or adults with poor echocardiographic windows, transthoracic imaging may be inadequate. In addition, artifacts may falsely suggest the presence of a dissection in patients at risk (Fig.14.40). In these cases, transesophageal echocardiography or computed tomography may be necessary to make or confirm the diagnosis.
Figure 14.38. Ruptured sinus of Valsalva aneurysm into the right atrium (asterisks). Depicted in (A) an intraoperative photograph from the ascending aorta, (B) an intraoperative photograph from the right atrium showing the jet of blood coursing through the rupture, (C) a parasternal long-axis view, (D)a parasternal short-axis view, and (E) an abdominal aortic Doppler pattern with holodiastolic reversal of flow. Ao, aorta; LA, left atrium; RA, right atrium; RV, right ventricle; TV, tricuspid valve.
Figure 14.39. Aortic dissection along the posterior aspect of the aortic root and ascending aorta in a Marfan patient with marked aortic dilation. A: Parasternal long-axis view. B: Parasternal short-axis view. AAo, ascending aorta; Ao, aorta; LA, left atrium; LV, left ventricle.
Although aortic atresia is the most common LV outflow tract abnormality seen in utero by echocardiography, this lesion will not be discussed because it usually results in a hypoplastic left heart syndrome or some variation thereof and requires a staged univentricular surgical approach. Among 2136 fetal cardiac diagnoses reported by Sharland and Allan in 2000, valvar AS represented almost 3% of the group, ranking as the 11th most common diagnosis. Subvalvar AS, supravalvar AS, and isolated AR are extremely rare diagnoses. Occasionally a fetus that appears to have significant AR actually has an aortico-LV tunnel, and this lesion is usually associated with LV dilation, LV dysfunction, and aortic root dilation.
Figure 14.40. Marfan patient with marked aortic dilation and chest pain showing possible dissection (asterisks). A: Parasternal long-axis view. B: Subcostal long-axis view. Computed tomography did not reveal any aortic dissection. AAo, ascending aorta; Dao, descending aorta.
Some of the echocardiographic features of a fetus with significant or critical valvar AS include a left-to-right shunt across the patent foramen ovale (in contrast to the usual right-to-left shunt seen in normal fetuses) (Fig. 14.41) (Video 14.29); significant mitral regurgitation (Fig. 14.42) (Video 14.30); a dilated LV with poor systolic function (Fig. 14.43) (Video 14.31); echogenic LV papillary muscle groups and endocardium; thickened AoV leaflets with turbulent flow (if the LV function is still preserved); hypoplasia of the ascending aorta; and retrograde flow along the aortic arch (Fig. 14.44, Table 14.20) (Video 14.32). The altered hemodynamics in fetuses with significant LV outflow tract obstruction involves abnormal redistribution of blood flow to the right atrium and RV, which, in turn, can reduce the growth rate of left heart structures such as the LV and aorta. Consequently, a fetus with significant valvar AS may develop hypoplastic left heart syndrome wherein the LV is unable to support the systemic circulation (Fig. 14.45) (Video 14.33).
Several studies have attempted to identify the predictors of LV hypoplasia in fetuses with critical valvar AS. In 1995, Hornberger and colleagues identified several predictors of postnatal LV hypoplasia. These include the mid-trimester MV diameter z-score, mid-trimester ascending aorta diameter z-score, and decreased growth rate of left heart structures (Table 14.21). In 2002, Rychik and colleagues demonstrated that a ratio of LV length to RV length greater than 0.75 predicted LV adequacy for a biventricular circulation after birth. More recently in 2006, Mäkikallio and colleagues evaluated 43 fetuses that were diagnosed with valvar AS at less than 30 weeks gestation and had normal LV size at presentation. In their analyses, the best predictors of progression to hypoplastic left heart syndrome included retrograde flow along the aortic arch, a left-to-right shunt across the patent foramen ovale, a monophasic MV inflow Doppler pattern, and LV dysfunction (see Table 14.21). These studies have become especially relevant with the advent of fetal cardiac interventions such as transcatheter balloon aortic valvotomy for fetal valvar AS. This strategy involves in utero relief of the LV outflow tract obstruction to restore nearly normal distribution of blood between the right and left sides of the heart, thereby preventing growth retardation of the LV and progression to hypoplastic left heart syndrome. In 2004, Tworetzky and colleagues reported technically successful balloon valvotomy for 14 of 20 fetuses that had valvar AS and a potential risk for developing LV hypoplasia. More recently in 2007, Tierney and colleagues reported that technically successful balloon valvotomy improved LV systolic function and left heart Doppler indices.
Figure 14.41. Four-chamber view of fetal aortic stenosis with a left-to-right shunt across the patent foramen ovale. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
Figure 14.42. Four-chamber view of fetal aortic stenosis with significant mitral regurgitation. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
Figure 14.43. Left ventricular outflow tract view of fetal aortic stenosis at 22 weeks gestation with significant left ventricular dilation and dysfunction. Ao, aorta; LV, left ventricle.
Figure 14.44. Arch view of fetal aortic stenosis with retrograde flow in the transverse aortic arch by color Doppler. AAo, ascending aorta; Dao, descending aorta.
Because few patients with LV outflow tract abnormalities undergo surgical intervention during infancy or early childhood, many of these patients have limited transthoracic windows at the time of their operation. Transesophageal echocardiography can be quite useful in further delineating the abnormal anatomy associated with LV outflow tract obstructive lesions, AR or its functional variants, and diseases of the aortic root and ascending aorta, thereby providing the surgeon and cardiologist increased information in the operating room. Some of the anatomic features for which transesophageal echocardiography can provide improved images are listed in Table 14.22. Although multiple gastroesophageal locations and image planes should be used during a transesophageal study to evaluate these features, several views are particularly useful in patients with LV outflow tract abnormalities: high and mid-level transesophageal views in a horizontal plane (at 0 degrees) can provide useful information regarding the AoV morphology; low transesophageal and transgastric views in a horizontal plane can provide information regarding MV morphology as well as LV function before and after the operation; a mid-level transesophageal view at approximately 120-degree image plane usually provides long-axis images of the subaortic region and its relationship to the aorta, similar to the parasternal long-axis view in transthoracic imaging (see Figs. 14.10A and 14.20) (Video 14.7A); and a transgastric view in a vertical plane (at 90 degrees) or a deep transgastric view in a horizontal plane often provide an accurate means to measure the degree of LV outflow tract obstruction by continuous-wave Doppler interrogation (Fig. 14.46) (Video 14.34).
Figure 14.45. Four-chamber view of the same fetal aortic stenosis as shown in Figure 14.42 at 33 weeks gestation, now with left ventricular hypoplasia. LA, left atrium; LV, left ventricle; RV, right ventricle.
POSTOPERATIVE AND POSTINTERVENTIONAL ECHOCARDIOGRAPHY
Techniques in postoperative and postinterventional echocardiography are similar to preoperative approaches and should include assessment of the following parameters (Table 14.23).
Residual Left Ventricular Outflow Tract Obstruction
Valvar AS, particularly when it presents in the first year of life, is a chronic problem that usually requires multiple “palliative” interventions during the individual’s lifetime. The absence of a residual gradient immediately after a surgical or transcatheter valvotomy does not necessarily preclude recurrence and progression of residual valvar AS in the future. Therefore, follow-up echocardiograms should be performed serially in these patients. Because subvalvar AS is a progressive disease, recurrence after surgical resection is also common, particularly because resection may not correct the intrinsic abnormality in LV outflow tract morphology nor address the genetic predisposition that are both believed to cause subvalvar AS. Serial follow-up echocardiograms should also be performed for these patients, regardless of the absence of postoperative subaortic obstruction.
Figure 14.46. Long-axis transesophageal view from the transgastric position of supravalvar aortic stenosis. This provides an acceptable angle for Doppler interrogation to assess the degree of obstruction. AAo, ascending aorta; LV, left ventricle.
Residual or Postintervention Aortic Regurgitation
AR is seen frequently in patients who have undergone surgical or transcatheter valvotomy for valvar AS, and these patients should undergo serial follow-up echocardiograms. In a 2007 report by Pasquali and colleagues, patients with valvar AS who have undergone the Ross procedure (which involves aortic valve and root replacement with the patient’s native pulmonary valve and root and placement of a homograft from the right ventricle to the pulmonary artery) (Video 14.35) are at risk for progressive neo-AR, particularly if the patient previously underwent a VSD repair or an AoV replacement. If the AoV has been significantly damaged by the high-velocity jet associated with subvalvar AS or because of chronic prolapse into a VSD, significant residual AR may be present postoperatively, and the clinical and echocardiographic guidelines for future intervention apply to these patients.
Left Ventricular Size and Function
LV hypertrophy may persist after surgical or transcatheter valvotomy for valvar AS, especially if there is residual LV outflow tract obstruction. As discussed previously, LV dysfunction may or may not improve after surgical intervention for AR, depending on whether the intervention is undertaken before irreversible myocardial damage occurs. Therefore, the usual methods for assessing LV size and function should be included in the follow-up protocol for all patients who have undergone intervention for AS or AR.
Size of the Proximal Aorta
Aortic dilation may occur even after plication or size reduction of the proximal aorta because the etiology in most cases is an intrinsic aortopathy that can affect any remaining aortic tissue after surgery. Therefore, these patients should also undergo serial follow-up echocardiograms. In addition, the 2007 paper by Pasquali and colleagues on mid-term follow-up after the Ross procedure also reported that the neoaortic root size in these patients increased significantly out of proportion to somatic growth.
Prosthetic Aortic Valve Function
Occasionally, the intervention for a patient with significant LV outflow tract obstruction or AR involves AoV replacement with a prosthetic AoV. The most commonly used prosthetic AoV in many centers is the St. Jude valve, a metallic valve ring to which two hemidisc leaflets are hinged at both ends of a bisecting line across the ring (blood flows through the ring on either side of this bisecting line). Echocardiographic follow-up is often difficult because the patients are usually older with poor transthoracic echocardiographic windows. In addition, acoustic interference from the prosthetic valve ring can obscure assessment of the hemidisc leaflets as well as any structure on the other side of the ring from the echocardiographic probe. Nevertheless, every effort should be made to assure full symmetric mobility of the prosthetic hemidisc leaflets. Occasionally transesophageal echocardiography may be used if limited information is available by transthoracic echocardiography (Fig. 14.47) (Video 14.36). Doppler interrogation of the flow across a prosthetic valve almost always results in a maximum instantaneous gradient that overestimates the peak-to-peak gradients measured in the catheterization laboratory because the pressure recovery effects are significantly increased with prosthetic valves, especially for the smaller ones used in children. For example, the normal maximum instantaneous gradient across a 19-mm St. Jude prosthesis in the aortic position may be as high as 30 to 50 mm Hg by continuous-wave Doppler interrogation without significant obstruction across the prosthetic valve. Color flow mapping will usually show trivial AR associated with the hemidisc leaflets, a normal finding for a St. Jude prosthetic valve (Fig. 14.48) (Video 14.37). Echocardiographic assessment should distinguish this finding from the pathologic paravalvular leaks, which are localized outside the prosthetic valve ring and usually represent disruption of the normal connection between the prosthetic valve ring and the surrounding tissue.
Figure 14.47. Long-axis transesophageal view of a prosthetic aortic valve with symmetric positioning of the prosthetic hemidisc leaflets (asterisks). Ao, aorta; LA, left atrium; LV, left ventricle.
Alternative Imaging Modalities
Because of poor echocardiographic windows in older children and young adults, computed tomography and magnetic resonance imaging can be useful in assessing the caliber of the aortic root and ascending aorta as well as the coronary arteries. In addition, these modalities are quite valuable when aortic dissection is suspected. Magnetic resonance imaging also provides an accurate means to quantify LV size and function. When prosthetic valve dysfunction is suspected, fluoroscopy often provides information that cannot be gleaned from echocardiography because of the obscuring issues discussed previously.
Figure 14.48. Color Doppler in a long-axis transgastric view of a prosthetic aortic valve showing normal trivial intravalvular regurgitation (asterisk) that is not localized outside the prosthetic valve ring. LV, left ventricle.
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1.Which of the following represents the relative prevalence rates of the variants of left-ventricular outflow tract obstruction?
A.Subvalvar > valvar > supravalvar aortic stenosis
B.Supravalvar > valvar > subvalvar aortic stenosis
C.Valvar > subvalvar > supravalvar aortic stenosis
D.Subvalvar > supravalvar > valvar aortic stenosis
E.Supravalvar > subvalvar > valvar aortic stenosis
2.What is the most common aortic valve morphology in neonatal valvar aortic stenosis?
A.Tricuspid aortic valve
B.Bicuspid aortic valve with fusion or underdevelopment of the intercoronary commissure between the right and left coronary leaflets
C.Bicuspid aortic valve with fusion or underdevelopment of the commissure between the left and noncoronary leaflets
D.Bicuspid aortic valve with fusion or underdevelopment of the commissure between the right and noncoronary leaflets
E.Unicuspid unicommissural aortic valve in which the only open commissure is located between the left and noncoronary leaflets
3.Which one of these patients with valvar aortic stenosis is likely to require intervention during cardiac catheterization?
A.Eight-year-old boy with a maximum instantaneous gradient of 70 mm Hg from a high parasternal view and 50 mm Hg from an apical view
B.Three-year-old boy with an average maximum instantaneous gradient from high parasternal and apical views of 75 mm Hg
C.Twelve-year-old girl with a maximum instantaneous gradient of 45 mm Hg from an apical view and 60 mm Hg from a high parasternal view
D.Five-year-old boy with a mean gradient from a high parasternal view of 40 mm Hg
E.Six-year-old girl with a mean gradient from an apical window of 35 mmHg
4.Which one of these abnormalities is more likely to be associated with subvalvar aortic stenosis?
A.Tetralogy of Fallot
B.Coronary ostial stenosis
C.Sinus of Valsalva aneurysm
D.Double-chambered right ventricle
5.What is an important risk factor for mortality in neonates with critical valvar aortic stenosis?
A.Severe mitral regurgitation
B.Intact atrial septum
C.Small patent ductus arteriosus
D.Ascending aortic dilation
E.Severe endocardial fibroelastosis
6.Decompensated aortic regurgitation occurs when there is:
A.inadequate left ventricular hypertrophy.
B.inadequate cardiac output.
C.inadequate left ventricular dilation.
D.more mitral regurgitation than aortic regurgitation.
E.more aortic regurgitation than mitral regurgitation.
7.Which of the following fetal echocardiographic findings suggests critical valvar aortic stenosis?
A.Right-to-left shunting across the patent foramen ovale
B.Premature ductal closure
C.Retrograde flow along the aortic arch
D.Mild mitral regurgitation
E.Ascending aortic diameter Z-score +1
8.Which of the following lesions is associated with proximal aortic dilation?
A.Subvalvar aortic stenosis
D.Congenital rubella infection
9.Which of the following fetal echocardiographic finding predicts progression to hypoplastic left-heart syndrome?
A.Monophasic mitral valve inflow Doppler pattern
B.Aortic annular Z-score
E.Supravalvar aortic stenosis
10.The Ross procedure involves:
A.baffling of the systemic veins to the mitral valve and baffling of the pulmonary veins to the tricuspid valve.
B.pericardial patch augmentation of the aortic arch.
C.direct anastomosis of the proximal branch pulmonary arteries to the right ventricular free wall.
D.aortic root translocation, reconstruction of the left ventricular outflow tract with the translocated aorta, and patch augmentation of the right ventricular outflow tract
E.aortic valve and root replacement with the patient’s native pulmonary valve and root and placement of a homograft from the right ventricle to the pulmonary artery.
1.Answer: C. Among all patients with left-ventricular outflow tract obstruction, valvar aortic stenosis is the most common subgroup (with a frequency of 60% to 75%), followed by subvalvar aortic stenosis (8% to 30%), and supravalvar aortic stenosis (1% to 2%).
2.Answer: E. The most common aortic valve morphology in neonatal valvar aortic stenosis is a unicuspid unicommissural AoV where the only open commissure is located between the left and noncoronary leaflets. The most common abnormality of aortic valve morphology in all ages is the bicuspid aortic valve, in which two of the three leaflets are fused or one of the commissures between adjacent leaflets is underdeveloped. Among all patients with a bicuspid AoV, fusion or underdevelopment occurs most commonly at the intercoronary commissure between the right and left coronary leaflets (with a frequency of 70% to 86%) followed by the commissure between the right and noncoronary leaflets (12% to 28%) and the commissure between the left and noncoronary leaflets (very rare).
3.Answer: B. The specificities of gradient measurements by echocardiogram for intervention are: maximum instantaneous gradient from high paraternal windows more than 90 mm Hg (94%); mean gradient from apical windows more than 50 mm Hg (100%); and average of maximum instantaneous gradient from apical and high parasternal views more than 70 mm Hg (92%).
4.Answer: D. Tetralogy of Fallot is usually associated with aortic root dilation and associated with aortic regurgitation. Coronary ostial stenosis is a common associated anomaly in patients with supravalvar aortic stenosis. Aneurysms of the pulmonary arteries as well as the cerebral vasculature can occur in patients with left outflow tract anomalies, specifically patients with bicuspid aortic valve. Subvalvar aortic stenosis usually is associated with ventricular septal defect and mitral valve abnormalities and aortic arch abnormalities. In the setting of subvalvar aortic stenosis and a ventricular septal defect, a double-chambered or divided right ventricle can develop. Ebstein anomaly is usually associated with an interatrial communication and ventricular septal defects and pulmonary stenosis or atresia.
5.Answer: E. Risk factors for mortality five years after biventricular repair include a high EFE grade, a low aortic root diameter z-score, and a young age at presentation. Risk factors for mortality five years after univentricular palliation include a small ascending aorta diameter and moderate or severe tricuspid regurgitation.
6.Answer: A. Decompensated AR occurs when there is inadequate hypertrophy with a consequent increase in peak-systolic and end-systolic wall stress, a measure of afterload. This, in turn, affects load-dependent indices of LV function such as shortening fraction and ejection fraction, initially without any significant effect on intrinsic myocardial contractility. It appears that irreversible LV dysfunction occurs after myocardial contractility diminishes, suggesting that echocardiographic measures of contractility or afterload-adjusted ejection fraction might provide better guidelines for the timing of intervention.
7.Answer: C. Some of the echocardiographic features of a fetus with significant or critical valvar AS include a left-to-right shunt across the patent foramen ovale (in contrast to the usual right-to-left shunt seen in normal fetuses); significant mitral regurgitation; a dilated left ventricle with poor systolic function; echogenic LV papillary muscle groups and endocardium; thickened AoV leaflets with turbulent flow (if the LV function is still preserved); hypoplasia of the ascending aorta; and retrograde flow along the aortic arch.
8.Answer: C. Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlös syndrome, Turner syndrome, bicuspid aortic valve, systemic hypertension, and aortic coarctation are known be associated with proximal aortic dilation.
9.Answer: A. Monophasic mitral valve inflow Doppler, mitral valve diameter Z-score, ascending aorta diameter Z-score, left ventricular to right ventricular length ratio, retrograde flow along the aortic arch, left-to-right shunt across the foramen ovale, decreased growth rate of left-sided structures and left ventricular dysfunction are all shown to predict hypoplastic left-heart syndrome.
10.Answer: E. The Ross procedure involves aortic valve and root replacement with the patient’s native pulmonary valve and root and placement of a homograft from the right ventricle to the pulmonary artery.