Bicuspid aortic valves are an important and relatively common congenital cardiac anomaly, with an incidence of 1.37% incidence based on a Mayo Clinic series,² and an 0.5% incidence on review of two large databases.⁷ There is a strong male gender preponderance, with a male-to-female ratio of 3 or 4 to 1.⁸ Bicuspid aortic valves may be heritable. In a series of 309 probands and relatives, 74 bicuspid aortic valves were found, for a prevalence of 24% and heritability of 89%.⁹ It is important to recognize bicuspid aortic valves for three reasons:

1. Up to one third will become sufficiently dysfunctional to require replacement. Most bicuspid valves that develop functional disturbance will become stenotic or have mixed aortic stenosis and aortic insufficiency.¹⁰ A congenitally bicuspid aortic valve is the most common underlying cause of aortic stenosis in adults younger than 65 years of age. Development of pure aortic insufficiency is uncommon; if present, it usually is due to infection or cusp prolapse.

2. Bicuspid aortic valves appear to be prone to infection.

3. Associated congenital cardiovascular anomalies and malformations, discussed in the next section, may be life-threatening.

Structural associations or complications of bicuspid aortic valves include aortic associations and shunts.

Aortic associations

• Ascending aortic dilatation/aneurysm independent of the degree of aortic stenosis or aortic insufficiency.¹¹ Over half of younger patients with bicuspid aortic valves have been shown to have one measurement of aortic diameter greater than the 95th age-adjusted percentile, usually of the ascending aorta.¹² Dilation of the ascending aorta may be of aneurysmal severity in the presence of an entirely functional bicuspid aortic valve.

• Coarctation of the aorta.¹³ Most cases of coarctation are associated with bicuspid valves.

• Dissection of the aorta. In younger adult patients with acute aortic dissection, bicuspid valves are associated nearly ten times more frequently than is Marfan syndrome.

Shunts

• Intracardiac shunts (e.g., ventricular septal defect)

• Extra-cardiac shunts (e.g., patent ductus arteriosus)

“Berry aneurysms” of the cerebral vasculature

Ineffective endocarditis

Other defects

Echocardiographic Recognition of Bicuspid Aortic Valves

Two-dimensional (2D) imaging is the most reliable means to identify bicuspid aortic valves by echocardiography. Parasternal long-axis views offer suggestions (e.g., systolic doming; possible downward displacement of a raphe into the LVOT, or “reverse doming”; possible prolapse of a cusp ¹⁵; thickening of leaflets), but actual recognition is achieved through short-axis views that demonstrate the systolic ellipsoid shape (“football” or “fish mouth” shape depending on your recreational interests). Using the criterion of systolic shape, 2D echocardiography is 78% sensitive and 96% specific for the diagnosis of bicuspid aortic valve using the sign of systolic orifice,² according to somewhat dated studies. The inability to clearly image the aortic valve appearance is regularly encountered.¹⁶ It is likely that improved imaging has improved the level of recognition.

M-mode signs are now out of date. Valve thickening and very eccentric closure (>1.5:1) formerly were recognized as signs of a bicuspid valve, but neither was of particular sensitivity or specificity. However, obvious eccentric closure by 2D or M-mode imaging should prompt consideration of a bicuspid valve.

The true bicuspid aortic valve has one (long) commissure, two cusps, and two sinuses of Valsalva. A “functionally” bicuspid valve has a raphae, an incompletely developed commissure that is still fused over part of its length. The residual fusion tends to be thickened. In diastole it may not be distinguishable from a normal commissure. Occasionally, an acquired disease process—especially rheumatic valve disease, but occasionally endocarditis—may result in fusion of a previously functioning commissure, rendering the valve functionally bicuspid.

The Vicissitudes of Aging: Age-Related Changes of the Aortic Valve and Root ¹⁷

The aortic valve seldom retains pristine architecture in older adults. Typically, lesser degrees of thickening and a more echogenic appearance develop as the valve scleroses. Most of this thickening is wear-and-tear injury and response, and occurs most prominently at the line of closure.¹⁷

Bright, thin Lambl’s excrescences (fibrous whiskers) on the free edge and the closure line,¹⁸ which invariably are directed upward into the aorta and do not have mobility, may develop at advanced age. They have no functional consequence or clinical relevance, but may be a source of confusion with respect to endocarditis. Lambl’s excrescences differ in appearance from vegetations in that they are on the aortic side of the leaflets, whereas vegetations are most commonly on the underside. Lambl’s excrescences have little motion independent from the valve, whereas longer vegetations usually have independent motion.

As a result of gradually rising systolic blood pressure through adult life, the diameters of the aortic root and ascending aorta tend to increase. Elongation of the aorta occurs concurrent with age- and hypertension-related diameter increase of the aorta. This elongation often results in a rightward tilt of the root of the aorta with downward protrusion, angling the interventricular septum into a sigmoid shape. Unfolding of the aorta from its normally tight “candy-cane” curvature displaces the aortic root downward into the superior aspects of the atria.

Atheromatous disease may extend into the root and onto the aortic valve, thickening both and often making the appearance more echogenic.