Aortic valve anomalies

More on fetal aortic valvular anomalies evolving to HLHS in the fetal echocardiography section of fetal HLHS

Valvular Aortic Stenosis:

• Often associated with a bicuspid aortic valve (BAV). A critical form is the unicuspid aortic valve, resulting from the fusion of all commissures.

• BAV can be associated with arch anomalies (hypoplasia, coarctation). It can also be associated with ascending aorta dilation (especially if BAV is stenosed). 

• Majority of patients with BAV will remain asymptomatic. 

• Bicuspid Aortic Valve Classification (Sievers Classification):

  • Type 0: Two cusps with no raphe, considered a true bicuspid valve. 

    1. Type 1: One raphe present, fusing two cusps. Type 1 with raphe: Fused commissures, with right-left cusp fusion being the most frequent (3/4 of cases). Further subdivided into: 

       1. 1 L-R: Left and right cusp fusion. (RL fusion (~70–80%))

       2. 1 R-N: Right and non-coronary cusp fusion. 

       3. 1 L-N: Left and non-coronary cusp fusion. 

    2. Type 2: Two raphes present, fusing three cusps.

Aortic valvular stenosis

Patients may present with varying clinical manifestations depending on the severity of stenosis, the patency of the PDA, and the underlying ventricular function.

If the stenosis is critical, and most of the systemic output is PDA-dependent, deoxygenated blood enters the aorta and supplies the ascending arch retrogradely, resulting in uniform desaturation across all sites.

In contrast, a patient with some residual anterograde flow through the aortic valve, though insufficient, and a PDA contributing to descending flow from the pulmonary artery to the aorta will present with pre- and post-ductal saturation differences.

Finally, in a patient with a closing/closed PDA, systemic saturation may appear uniformly "normal" (95–100%), but the infant may appear ashen or gray due to systemic hypoperfusion because of the insufficient cardiac output.

Critical aortic stenosis is defined as systemic hypoperfusion secondary to severe obstruction, necessitating urgent intervention to restore adequate systemic blood flow. This typically involves prostaglandin E1 (PGE1) infusion to maintain or reopen the ductus arteriosus and ensure sufficient systemic perfusion.

In rare cases where the PDA does not reopen or remains insufficiently patent—which is uncommon but possible in late-presenting infants—emergent interventions are required to stabilize the patient and rescue systemic circulation.

Histologically, in an abnormal aortic valve, the wall of the ascending aorta is also abnormal and tends to dilate independently of the degree of aortic valve stenosis. The aortic valve leaflets are doming and open abnormally, with a very small area of opening in the case presented below. There is no laminar flow; instead, a jet of blood accelerates (in the case below posteriorly when looking at the parasternal long axis view), causing turbulent flow, which acoustically manifests as a harsh murmur. This occurs because the entire cardiac output must pass through a narrowed opening. When looking at the suprasternal view, in many of these infants, the ascending aorta is significantly dilated. In the case below, there is no coarctation and a normal isthmus. When we identify an obstruction in the left ventricular outflow tract (LVOT), we must ensure there is no obstruction proximal or distal to the valve—ruling out a hypoplastic arch, mitral stenosis, or coarctation. During fetal life, reduced flow through left-sided structures can result in decreased dimensions.

In the example below, the PDA Doppler is bidirectional. In early systole, the PDA shunts from the pulmonary artery (PA) to the aorta, while in diastole, it shunts from the aorta to the pulmonary artery. This is commonly observed in the first hours of life when pulmonary vascular resistance (PVR) remains high in most babies even without congenital heart defect. The echocardiogram example below was performed on day 2 of life; while PVR could still have been elevated. However, it is more likely that there is a component of diminished filling of the aortic arch, which favors PA-to-aortic arch flow, which could account for lower systemic saturations often seen in these patients (as outlined in the diagrams above).

Regarding the valve, the aortic valve should be assessed in systole, not in diastole. In the case below, when it opens, it does so only at a single commissure and there is also a mild jet of insufficiency, which can vary in severity in cases of valvular aortic stenosis. Again, for the case below, in the five-chamber view, the ventricles appear subjectively thickened, though there is no frank hypertrophy. Ventricular function is within normal limits for both ventricles but many infants could present with severely depressed LV function when the PDA becomes restrictive or closes. The mitral valve dimensions are normal in the case below. The aortic valve is thickened and domed. In systole, it does not fully open.

When color Doppler is applied, there is laminar flow below the valve. However, as soon as the blood reaches the valve, aliasing occurs, displaying a mosaic pattern indicative of turbulent flow. There is laminar flow through the mitral valve, with only trivial, clinically insignificant mitral insufficiency. Doppler signals measure blood velocity across the aortic valve, with a peak gradient of approximately 80-90 mmHg, indicating severe aortic stenosis. This results in left ventricular hypertension and possibly elevated left atrial pressure due to increased left ventricular end-diastolic pressure, which can lead to pulmonary edema—explaining the tachypnea observed in some of these infants.

Peak gradient (systolic) at the level of the ascending aorta is estimated at 87 to 91 mmHg. 

Previous case after balloon dilatation by cardiac catheterization

Case of aortic stenosis and coarctation of the aorta

Parasternal long axis views outlining that the aortic valve is dysplastic and with a stenotic appearance in systole

Case of Functionally unicuspid aortic valve and Aortic Stenosis with LV dysfunction

Post-dilation of the fused bicuspid valve by catheterization

TDI outlining decreased systolic velocities at the level of the septum and of the lateral wall of the LV.