Keywords

Introduction

Congenital obstruction of left ventricular outflow in the adult can occur at any level within the aortic valve (AV) complex; the left ventricular outflow tract (subvalvular stenosis), AV leaflets (valvular stenosis) and aorta (supravalvular stenosis) [1]. In the pediatric population, supra-valvular stenosis typically in association with Williams-Beuren syndrome, may also result in significant outflow obstruction [2]. This chapter will review the echocardiographic diagnosis of congenital anomalies involving subaortic, aortic valve and supravalvular stenosis.

Subaortic Stenosis

Fixed subaortic stenosis may occur in the setting of a discrete, thin fibrous membrane, a discrete fibromuscular collar, or a tunnel-type muscular narrowing of the left ventricular outflow tract (LVOT) [3]. The prevalence of subaortic stenosis in adults with congenital heart disease is estimated to be about 6.5%, with a male-to-female ratio of 2:1 [4]. The fibromuscular collar is most common and is caused by a crescent shaped or circumferential ridge of fibromuscular band in the LVOT (Fig. 13.1, Videos 13.1a and 13.1b). However, the tunnel-type narrowing of the LVOT has been associated with a greater degree of stenosis [1, 5]. Not infrequently these congenital abnormalities may be associated with other congenital abnormalities such as ventricular septal defect and coarctation of the aorta, as well as with a series of lesions such as in Shone’s complex (parachute mitral valve, mitral stenosis, bicuspid aortic valve, and coarctation of the aorta) [1, 6]. Tunnel-type stenosis has been associated with small aortic annulus, small mitral orifice, and asymmetric septal hypertrophy [7]. There has been some controversy over whether this entity is a true congenital disease or an acquired disease. Many studies have suggested that in the setting of the right anatomic and hemodynamic substrate, alterations in basal septal shear stress may stimulate cellular proliferation [6, 8,9,10]. These theories may explain the recurrence of obstruction in patients who have undergone prior surgical resection [11,12,13]. Higher recurrence rates have been reported in patients with tunnel-type stenosis, higher resting pre-operative gradients (>40 mmHg) and a residual post-operative gradient of >10 mmHg.

Fig. 13.1
figure 1

Fixed subaortic stenosis. Left panel. A discrete fibromuscular collar (white arrow) is visualized in the left ventricular outflow tract by tow-dimensional echocardiography. The aortic valve shows a mild regurgitation (Video 13.1a/left). Right panel: volume rendering of a 3DE data set of the left ventricular outflow tract and aortic root allowing an en-face view of the membrane and its orifice (white arrow) from the ventricular perspective (Video 13.1b/right). AV aortic valve, LA left atrium, LV left ventricle, MV mitral valve, RA right atrium, RV right ventricle

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In the setting turbulent systolic flow, trauma to the aortic valve may result in aortic stenosis [14] or aortic regurgitation [4, 12, 15, 16]. LVOT gradients ≥50 mmHg are associated with a higher risk of developing aortic regurgitation [17]. Despite surgical repair, some patients may continue to develop aortic regurgitation. This may be related to a persistent LVOT gradient.

Congenital Aortic Stenosis (AS)

Congenital AS occurs as a unicuspid aortic valve (Fig. 13.2a, Video 13.2a), bicuspid aortic valve (Fig. 13.2b, c, Videos 13.2b and 13.2c), or aortic annular hypoplasia. Rarely, a quadricuspid valve may develop stenosis (Fig. 13.2d, Video 13.2d). The bicuspid aortic valve (BAV) anomaly occurring is 1–2% of the population [18] with male:female prevalence ratio is 3.7:1 [19]. Although BAV is a congenital anomaly, complications associated with this anomaly develop in adulthood making early diagnosis important. A number of different classification systems have been used in the past, most based on the fusion of cusps and orientation or number of the raphe [20,21,22]. Some of these classification systems then identified patients with no raphe as “pure” BAV or type 0 [22] (Fig. 13.2b). A recent classification system identifies just two BAV phenotypes: fusion of the right and left coronary cusps (BAV-AP) (Fig. 13.3, Video 13.3) and fusion of the right or left coronary cusp and non-coronary cusp (BAV-RL, Fig. 13.2c) [23]. These two phenotypes have some support in recent animal studies identifying defective development of different embryological structures [24]. Morphology may provide valuable data regarding risk stratification of BAV patients [23, 25, 26]. Kang et al. showed in a small population of 167 patients, that moderate-to-severe aortic stenosis is more prevalent in patients with BAV-RL (66.2% vs. 46.2% in BAV-AP; p = 0.01), and moderate-to-severe aortic regurgitation in BAV-AP (32.3% vs. 6.8% in BAV-RL; p < 0.0001).

Fig. 13.2
figure 2

Congenital abnormalities of the aortic valve. Volume rendered en face views of the valve from the aortic perspective. (a) Transesophageal 3DE acquisition of unicuspid aortic valve (Video 13.2a); (b) transthoracic 3DE acquisition of a pure bicuspid aortic valve with typical fish mouth opening appearance (Video 13.2b); (c) transthoracic 3DE acquisition of a bicuspid aortic valve with calcified rafe between the left and the non-coronary cusps (Video 13.2c); (d) transesophageal acquisition of a quadricuspid aortic valve (Video 13.2d)

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Fig. 13.3
figure 3

Volume rendered image of a bicuspid valve with rafe (white arrow) between the right and left coronary cusps. The 3DE data set has been acquired from transesophageal approach and the valve is seen en face from the aorta perspective (Video 13.3). L left coronary cusp, NC non-coronary cusp, R right coronary cusp

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In addition, the association with BAV and dilatation of the ascending aorta has been well-established [27,28,29]. Aortopathy type (0–3), type 0, normal aorta; type 1, dilated aortic root; type 2, aortic enlargement involving the tubular portion of the ascending aorta; and type 3, diffuse involvement of both the entire ascending aorta and the transverse aortic arch. Some authors have suggested that the aortic abnormality is unrelated to the valvular pathology [27, 29] and thus a primary anomaly associated with this entity. More recent studies using advanced imaging techniques have suggested that regional wall stress in the setting of eccentric outflow patterns contributes to the pattern of aortic dilatation [30,31,32,33]. Overall outcomes for BAV are related not only to valvular pathology (stenosis or regurgitation) but also to aortopathy. Tzemos et al. [25] identified the following cardiac event risk factors: age >30 years, moderate or severe aortic stenosis, and moderate or severe aortic incompetence. Although fatal events are rare, surgical intervention is not uncommon. Most surgical procedures involve aortic valve and aortic root replacements with the 25-year rate of aortic surgery as high as 25% [25, 34, 35].

Although valvular disease may present in the fourth and fifth decades, in a series of operatively excised, stenotic aortic valves (isolated aortic valve surgery) from 932 patients (mean age of 70 ± 12 years) 54% of patients had congenital abnormalities commonly BAV, with the median age at surgery of 67 years [36]. Another series of excised aortic stenosis valves in patients greater than 80 years of age showed a prevalence of bicuspid aortic valve in 22% [37]. Importantly, although current transcatheter aortic valve devices are designed for use in tricuspid aortic valves, numerous case reports and two reports of transcatheter aortic valve (TAVR) in a series of BAV patients have shown that, compared to matched trileaflet aortic valve patients, there was no difference in acute procedural success, valve hemodynamics, or short-term survival [38, 39].

Echocardiography remains the most validated imaging modality for the diagnosis, phenotyping, and hemodynamic assessment of BAV dysfunction and the initial assessment of the thoracic aorta. With conventional echocardiography, the diagnosis is typically made using the short-axis views of the valve. Although in diastole, the raphe may be mistaken for a commissure, particularly in calcified valves, in systole in the short-axis view there is a typical “fish-mouth” appearance of valve opening and absence of opening at the raphe. In patients with good-quality transthoracic images who do not have dense BAV calcification, diagnostic sensitivity and specificity are >70% and >90%, respectively [40, 41]. However, diagnostic uncertainty may remain in 10–15% of patients after echocardiogram [35]. Particularly in the setting of calcification, color Doppler in systole may be helpful in distinguishing immobile trileaflet aortic valves without commissural fusion from bicuspid valves with fusion. Diagnostic and phenotyping accuracy can be significantly improved with the use of higher-resolution imaging techniques such as transesophageal echocardiography (TEE) and 3DE imaging [42,43,44,45]. Using longitudinal cut-planes of 3DE data sets of the aortic root, the presence or absence of interleaflet triangles (the anatomical landmark for the diagnosis of BAV) can be diagnosed (Fig. 13.4, Videos 13.4a and 13.4b). 3DE has also been utilized to quantify BAV function. For stenotic valves, direct planimetry of the orifice [46,47,48,49] has been validated. Machida et al. in fact showed that in the bicuspid AS group, the planimetered aortic valve area (AVA) by 3D TEE significantly correlated with AVA calculated by the Doppler continuity equation (r = 0.83, mean difference 0.10 ± 0.18 cm2, P < 0.001), whereas AVA by two-dimensional TEE did not (r = 0.42, mean difference 0.48 ± 0.32 cm2, P = 0.066) [49].

Fig. 13.4
figure 4

Anatomical diagnosis of bicuspid aortic valve. Left panel, anatomical specimen of the aortic root showing the aortic cusps, coronary ostia (white arrows) and interleaflet triangles (white dashed triangles). Central panel, volume rendered 3DE cut plane of the aortic root showing the left main ostia (white arrow) and the interleaflet triangle between the left and non-coronary cusps (Video 13.4a). Right panel, volume rendered 3DE cut plane of the aortic root showing the right coronary ostia (white arrow) and the rafe (yellow arrow) between the left and the right coronary cusps (Video 13.4b)

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Particularly in the setting of concomitant subvalvular stenosis when the continuity equation may be erroneous, direct planimetry of the AVA may be the primary means of quantifying valvular stenosis. Acquisition of the 3D volume to accurately assess valvular morphology and function requires using the higher volume rate, thus smallest volume that images the entire aortic valve and proximal aortic root (Fig. 13.5, Videos 13.5a and 13.5b). The orientation of the valve may vary significantly depending on the number of cusps and the size, shape and orientation of the aortic root which is the main advantage of using 3D imaging to assess the aortic valve. Because longitudinal, lateral and elevational resolution are different, structures most perpendicular to the insonation beam will have the best linear definition. Thus acquiring 3DE volumes from multiple imaging planes is always recommended. For transthoracic imaging, acquire a user-defined volume from both parasternal long-axis and short-axis views as well as from both apical 5-chamber and 3-chamber views. Similarly, mid-esophageal TEE volumes should be acquired from short-axis view (~60°) and long-axis (~120°) views as well as transgastric 5-chamber (~0°) and 3-chamber views (~120°).

Fig 13.5
figure 5

Assessment of the relative stenosis severity of subaortic (M) and aortic (AV) stenosis using transthoracic 3DE. By proper cropping of the 3E data set both the subaortic membrane (M, Video 13.5a/M) and the aortic valve (Video 13.5b/A) can be seen en face and the residual anatomical orifice area of both subaortic (M) and aortic (AV) stenoses can be planimetered. LA left atrium, LV left ventricle

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Once the 3D volume has been acquired, the standard orientation of the aortic valve on TTE is with the right coronary cusp in the near field. From the aortic side, the left coronary cusp is in the far field and to the right with the noncoronary cusp in the far field and to the left. From the ventricular side, the left coronary cusp is in the far field and to the left with the noncoronary cusp in the far field and to the right (see also Chap. 12). On TEE however the image is flipped with the right coronary cusp in the far field. From the aortic side, the left coronary cusp is in the near field and to the right with the noncoronary cusp in the near field and to the left. From the ventricular side, the left coronary cusp is in the near field and to the left with the noncoronary cusp in the near field and to the right. Planimetry of the orifice may be performed either on volume rendered images or using multi-planar reconstruction, first ensuring that the cropping plane is positioned at the level of the smallest orifice (Fig. 13.5).

Supravalvular Aortic Stenosis

Supravalvular aortic stenosis is the most common cardiac finding associated with Williams-Beuren syndrome (also known simply as Williams syndrome), and is rarely seen outside of this patient population [2]. This syndrome is a result of a deletion on the long arm of chromosome 7 and affects the encoding of the elastin protein and causing major systemic arteries to become rigid. It typically presents in childhood with a number of phenotypic abnormalities, including a distinct facial appearance, developmental delay, behavioral changes, and hypercalcemia. Other common cardiac anomalies include hypoplasia of the aortic arch and pulmonary artery stenosis. Less common associated cardiac anomalies include: coarctation of the aorta, ventricular septal defect, patent ductus, subaortic stenosis, and hypertrophic cardiomyopathy. The stenosis occurs at the sinotubular junction, distal to the coronary ostia, resulting in abnormal flow within the coronaries. In the setting of significant outflow obstruction severe left ventricular hypertrophy may occur. These patients are at high risk for sudden death and surgical intervention is usually required. Echocardiography remains the initial diagnostic modality for supravalvular stenosis [50] however the constellation of cardiac anomalies may be best evaluated by computed tomography [51]. Newborns with supravalvular aortic stenosis should be followed for rapid progression. Although right ventricular outflow obstruction may regress in some patients, supravalvular aortic stenosis may develop in others with right ventricular outflow obstruction. Patients with right ventricular outflow obstruction (at the valvular, supravalvular, or peripheral pulmonary arterial level) should be evaluated carefully for development of supravalvular aortic stenosis at follow-up [52].