The Bicuspid Aortic Valve
Section snippets
History
The earliest description of the BAV has been attributed to Leonardo da Vinci who over 400 years ago sketched the bicuspid variant of the aortic valve (Fig 1).1
In 1844, Paget brought to attention the propensity of the BAV to develop disease and in 1858 Peacock noted the tendency of these valves to develop obstructive lesions initially, with subsequent incompetence.2 The clinical significance of the BAV was also emphasized by Osler in 1886 when he described 18 cases of BAV with a predilection of
Embryology
The semilunar valves originate from mesenchymal outgrowths known as cardiac cushions located along the ventricular outflow tract of the primary heart tube (Fig 1).
Several investigators have shed light upon the processes involved in the development of BAV. Sans-Coma and colleagues were able to study the embryology of BAV development by studying Syrian hamsters that had a high prevalence of BAV following systematic inbreeding.9 Their histologic assessments of hamster embryos revealed that the
Bicuspid Aortic Valve Anatomy, Variants, and Pathologic Features
The anatomy of the BAV usually includes unequal cusp size (due to fusion of two cusps leading to one larger cusp), the presence of a central raphe (usually in the center of the larger of the two cusps), and smooth cusp margins (Fig 2). The raphe or fibrous ridge is the site of congenital fusion of the two components of the conjoined cusps and is identifiable in most BAV patients.19 Of interest, pathologic examination of raphe has shown that they do not contain valve tissue.20
John S. Child, MD:
Prevalence
Prior to the development of noninvasive imaging, autopsy studies provided the earliest information regarding the prevalence of BAV in the general population. The findings of the necropsy studies investigating the prevalence of BAV are summarized in Table 1.34
In one of the earliest studies, Osler noted seven cases of normal-appearing BAVs in 800 necropsy studies giving a prevalence of 1.3%.35 Lewis and Grant noted that in a series of 215 consecutive autopsies the prevalence of BAV was 1.39%.36
Genetics of the Bicuspid Aortic Valve
The earliest studies suggesting that BAV was the consequence of an underlying genetic abnormality were case reports describing familial clustering of BAV and reports of BAVs in monozygotic twins.40, 41, 42, 43, 44 Subsequently, other authors sought to evaluate the relatives of patients with BAV to investigate the prevalence of BAV in the family members of affected patients. In the study by Emanuel and coworkers, 41 families with a family member having surgically proven BAV were studied.45 Six
The Bicuspid Aortic Valve and Associated Congenital Cardiovascular Lesions
While the BAV is usually an isolated defect, 20% and possibly up to 50% of subjects with BAV have additional congenital cardiovascular malformations. The presence of a BAV can account for a significant degree of the morbidity associated with these associated syndromes.
Congenital Coronary Anatomic Variants
Congenital coronary anomalies have been variably described in association with BAV. There appears to be a predilection towards left coronary artery dominance in BAV subjects (24 to 57%). Additionally, the length of the left main coronary artery has been described as generally shorter when compared with TAVs.68, 69, 70 However this was not confirmed in a subsequent large autopsy series.71 A number of other isolated congenital coronary artery anomalies have been reported in the presence of BAV.72
Physical Examination
A great majority of patients with a BAV are asymptomatic. The initial diagnosis is often suspected when a systolic ejection click or murmur is noted on routine physical exam. Younger patients often have an early ejection sound followed by a systolic ejection murmur. In adults, the auscultatory findings depend on the degree of stenosis or regurgitation present. A functionally normal BAV will have an ejection sound followed by an early peaking systolic flow murmur. The ejection sound is a
Chest Radiography
The plain film chest x-ray may provide significant clues as to the presence of BAV as well as any subsequent hemodynamic consequence. With the stenotic BAV, the lung fields are usually clear and the pulmonary arteries are normal. Frequently, aortic root dilation is noted; however, this does not correlate with the functional state of the bicuspid valve.50 Aortic valve calcification may be detected on the plain film and is best seen on the lateral projection.78 In general, calcification is a
Echocardiogram (2D, M-mode, and Doppler)
The distinctive echocardiographic features of the BAV include systolic doming and an eccentric valve closure in the parasternal long-axis views and the demonstration of a single commissural line in diastole with the characteristic two cusps and two commissures in the parasternal short-axis views (Fig 6). Additional short-axis features that support this diagnosis include leaflet redundancy, presence of a raphe, and eccentric valve closure.79, 80
Particular care must be taken to assess the valve
Transesophageal Echocardiogram
Despite improved sensitivity and specificity of the transthoracic echocardiograms, in up to 25% of patients the morphology of the aortic valve cannot be determined by transthoracic echocardiography. A transesophageal echocardiography (TEE) may be useful in such cases for diagnosis of BAV. A recent study demonstrated the sensitivity and specificity of multiplane technique in assessing aortic valve morphology (BAV versus TAV) was 87 and 91%, respectively.84 Furthermore, TEE can be very useful in
Magnetic Resonance Imaging (MRI)/Computed Tomography (CT)
Cardiovascular magnetic resonance imaging (MRI) is a very useful adjunct to standard echocardiography and catheter-based techniques for the diagnosis and evaluation of BAV. MRI likely has both a high diagnostic sensitivity and a high diagnostic specificity when compared with standard echocardiography though little data exist in this regard. Additionally, MRI appears to correlate well with both echocardiographic and invasive catheter-based techniques for evaluation of stenotic and regurgitant
Valvular Complications of the Bicuspid Aortic Valve
The valvular complications of the BAV are AS, AR, and IE. Significant valve disease in infancy and children is usually attributed to a stenotic BAV that can be treated via balloon aortic valvuloplasty.32 Later in childhood and into adolescence, AR becomes more frequent. AS will eventually develop in adulthood in the majority of patients due to superimposed leaflet calcification.32
The actual incidence of the complications the BAV varies with the population studied (adult or pediatric) as well as
Pregnancy and the Bicuspid Aortic Valve Patient
Severe left ventricular outflow tract obstruction (symptomatic or not) is poorly tolerated in pregnancy. Likewise, severely regurgitant aortic valve lesions with class III or IV symptoms are associated with significant peripartal risk.99 Clinical deterioration has been described in up to 30% of pregnancies complicated by severe maternal congenital aortic stenosis with a high rate of therapeutic abortions.100 In one large series of pregnancies with congenital AS, cardiovascular complications
Abnormalities of the Aortic Wall Associated with Bicuspid Aortic Valve
The BAV is associated with disorders of the aortic wall, including COA and aortic dissection.107, 108 In addition, aortic root dilation has been recognized to be a relatively frequent complication of the BAV, even when the valve functions “normally.” That is, the BAV may have no evidence of aortic valve stenosis or insufficiency, yet aortic root enlargement or aneurysm is present. Thus, the aortic wall abnormality is entirely independent of any hemodynamically significant valvular disease. In
Coarctation of the Aorta
The BAV is associated with COA.38, 53 While COA is a relatively uncommon disorder, approximately 50% of patients with COA have a BAV.29, 53 Because of the associated hypertension, COA is associated with an increased risk of aortic dissection. However, hypertension is not the only explanation for the increased risk of aortic dissection in COA patients. Inherent abnormalities of the aortic wall also play a role. In the days before surgical correction was available, aortic dissection was the cause
Aortic Dissection
Aortic dissection may complicate the BAV in the absence of COA or hypertension (Fig 10).
In autopsy series of aortic dissection, the BAV is present in approximately 7 to 9% of patients.8, 29 In clinical series of aortic dissection, the BAV is also present in approximately 7% of cases.29 Importantly, BAV is described in 15% of patients with an ascending aortic dissection.9 In the patient with an aortic dissection (particularly an ascending aortic dissection), one must diligently search for the
Aortic Medial Disease, Aortic Root Dilation, and the Bicuspid Aortic Valve
The aortic wall abnormalities that occur with the BAV have led many to theorize the presence of a common underlying developmental defect involving the aortic valve and aortic wall in BAV patients.52, 108, 111 In 1928, Abbott postulated that BAV, COA, and aortic wall thinning and rupture were all related to some form of common developmental abnormality.52 In 1972, McKusick described the BAV as a developmental defect of the vascular tree with variable expression.111 In some cases, the BAV was
Histopathology of Bicuspid Aortic Valve “Aortopathy”
The histologic abnormality underlying aortic root complications in BAV is cystic medial necrosis (CMN).126, 127 Elastic fiber degeneration and fragmentation, noninflammatory smooth muscle cell loss, and accumulation of basophilic ground substance within cell-depleted areas in the media have been demonstrated in the aortic wall of patients with BAV, even without significant aneurysm formation (Fig 15).
David and colleagues observed that the pulmonary autograft tends to dilate in some patients
Aortic Complications Late after Valve Replacement for Bicuspid Aortic Valve
Russo et al added significantly to the literature of BAV and aortic complications by reporting the long-term follow-up after BAV replacement.115 These investigators examined 50 BAV patients who underwent valve replacement between 1975 and 1985 and compared them with age-matched patients who underwent TAV replacement for similar indications. None of the patients had aortic aneurysm reported at the time of surgery. The mean follow-up time was 10 years. In follow-up, the BAV patients had a high
Familial Bicuspid Aortic Valve and Ascending Aortic Aneurysms
The BAV may be hereditary or familial with studies demonstrating the occurrence of a BAV in approximately 9% of first-degree relatives of affected individuals.47 Aneurysms associated with BAV may also be familial. In a landmark study, Dietz and colleagues performed a comprehensive evaluation of multiple pedigrees segregating BAV with ascending aortic aneurysm revealing a high incidence of individuals with ascending aneurysm alone, suggesting that BAV and ascending aortic aneurysm are both
Surgical Treatment of the Bicuspid Aortic Valve
The indications for replacement of a BAV with stenosis or regurgitation are well established and are identical to those for replacement of a diseased TAV.102 However, patients undergoing AVR for BAVs are often younger than those with TAVs, making the decision to implant a mechanical versus bioprosthetic valve more complex. The postoperative gradients and expected longevity of newer generation tissue valves with advanced valve preservation techniques are likely better than those associated with
Recommendations for Management of the Bicuspid Aortic Valve Patient
The BAV is not just a valve disease. As has been reported, there are complex interrelationships between the BAV and intrinsic valvular lesions as well as an important aortopathy which may lead to significant morbidity and mortality. There are several important steps in the long-term management of the patient with a BAV. First, one must be correctly identified as having this lesion by echocardiogram. Once recognized, the patient should be educated about the potential for valve lesion
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Disclosure: The authors have no conflicts of interest associated with this manuscript.