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

Aortic stenosis (AS) is a significant congenital heart condition characterized by an obstacle at the exit of the left ventricle (LV). When this obstruction is severe and accompanied by left heart failure, it is classified as "critical aortic 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. In aortic valve stenosis, the gradient through the valve is dependent on the dowstream blood pressure. Of course, if the LV is unable to generate sufficient output, the blood pressure will fall and a low gradient may not necessarily mean that the stenosis is less severe.

Patients with aortic valvular stenosis have various degree of left-sided obstruction. When the obstruction is significant, the LV faces high afterload and the LV will dilate. There is increased wall tension, which increases the trans-mural pressure and may impeded coronary perfusion. On top of this, there may be decreased output, limiting flow through the coronary system and further impairing the perfusion of the myocardium. These patients will eventually have significant LV failure when the obstruction is severe. In fetal life, there may be even some degree of endofibroelastosis, as fibrous tissue replaces myocardium that has become ischemic. Aortic stenosis creates a significant and persistent obstacle to blood flow from the left ventricle. This obstruction leads to a substantial increase in pressure within the left ventricle and, subsequently, in the left atrium. Over time, the left ventricle, constantly working against this high pressure, undergoes pathological changes. These include fibrosis and elastosis, where normal myocardial cells are replaced by fibrous tissue. This process compromises the heart's ability to contract effectively, leading to impaired function (hypokinesia). In severe, critical cases of AS, the left ventricle's function can become so compromised that it is unable to adequately perfuse the systemic circulation. In such scenarios, the patent ductus arteriosus (PDA) becomes vital, taking over the supply of blood to the aortic arch and the descending aorta, ensuring systemic circulation.

Clinical findings: The diagnosis of aortic stenosis relies on a comprehensive clinical assessment, which includes saturation, presence or absence of cyanosis, signs of heart failure, heart murmurs, and femoral pulses. Key clinical indicators for aortic stenosis include: 

• Weakly Perceived Peripheral Pulses: Due to the obstruction or a state of low cardiac output. 

• Absence of Differential Tension: Unlike some other aortic pathologies, there is typically no significant difference in blood pressure between the upper and lower limbs. There may be diffuse low blood pressure and/or hypoperfusion because of the low output state

• Signs of Respiratory Distress: Such as polypnea (rapid breathing) and retractions (visible pulling in of the chest wall during breathing). These often signify left heart failure, characterized by increased pressure within the left ventricle and left atrium, leading to post-capillary pulmonary congestion. 

• Systolic Murmur may be present due to the turbulence of flow. Of course, if the LV generates very limited output through the obstruction, there may be not sufficient flow to hear the murmur.

• Differential Saturation: A notable feature can be a saturation of 99% in the upper limbs and 90% in the lower limbs. This differential saturation occurs if the ductus arteriosus remains open (patent) and shunts deoxygenated blood into the aorta after the branching of the left subclavian artery. This can result in the child appearing "pink above and blue below". The degree of left ventricular dysfunction dictates how much the ductus arteriosus contributes to the systemic circulation, thus influencing the extent of saturation difference. It is important to differentiate aortic stenosis from conditions like aortic arch interruption. Unlike aortic arch interruption, aortic stenosis invariably presents with signs of left heart failure due to the constant hyperpressure created by the left-sided obstruction. In contrast, in aortic arch interruption, the left heart often functions normally, without signs of hyperpressure because there is no obstacle increasing the afterload to the LV. 

On echocardiography, there may be "globular" left ventricle, indicating chronic strain and an attempt to compensate by increasing its volume. There may also be some hyperechogenic papillary muscles of the mitral valve, a sign of myocardial ischemia, as these structures are watershed areas of the heart (and signs of subendocardial ischemia can lead to the appearance of "brightness" of structures). Often, this brightness is secondary to edema of the papillary muscles due to ischemia and inflammatoin. A thickened aortic valve that fails to open normally during systole, with the leaflets not fully coapting against the aortic wall can be appreciated. The valve may be dysplastic (abnormal/anomaly) and/or non-triscupid (bicuspid, unicuspid, quadricuspid). Dysplasia refers to abnormal, thickened, or redundant valve leaflets, which can occur regardless of whether the valve is bicuspid or tricuspid. It is essential for visualizing the aortic valve structure and associated coronary arteries. The apical 5 chamber view or the suprasternal ascending aortic view are excellent for measuring the gradient between the left ventricle and the aorta, which directly reflects the severity of the obstruction. It is crucial to consider the child's overall clinical state when interpreting gradients, as low cardiac output can lead to a deceptively low gradient, even in cases of severe stenosis (for example, when there is systemic hypotension). If the aortic valve sits on the RV (transposition), there may be RVOT obstruction due to aortic stenosis. It is important to assess for the concomitant presence of aortic insufficiency and its severity, as this can be prognositc and often present with valvular dysplasia. In neonates with valvar aortic stenosis, severity is typically graded using the peak instantaneous Doppler gradient (from continuous-wave Doppler across the aortic valve), and sometimes the mean gradient. The cut-offs are extrapolated from pediatric and congenital literature, since neonates often present with duct-dependent physiology and additional clinical factors must be weighed. General gradient thresholds for aortic stenosis (coming out of the LV):

• Mild: Peak Doppler gradient < 40 mmHg (mean < 25 mmHg) 

• Moderate: Peak Doppler gradient 40–70 mmHg (mean 25–40 mmHg) 

• Severe: Peak Doppler gradient > 70 mmHg (mean > 40 mmHg)

• In practice, any neonate with duct-dependent systemic circulation and valvar aortic stenosis is managed as “critical,” regardless of Doppler gradient.

Treatment for aortic stenosis involves a range of options, including medication (PGE to maintain the duct), catheter-based interventions, and surgical procedures. The choice of treatment depends on the severity of the stenosis, the child's clinical condition, and the presence of associated cardiac dysfunction. 

• Catheter-Based Intervention (Valvuloplasty): Valvuloplasty is typically reserved for children experiencing severe cardiac failure or cardiogenic shock. The objective is to relieve the obstruction, stabilize the patient by improving cardiac output, reduce left ventricular pressure, and enhance left ventricular function. This intervention is often a bridge to definitive surgical repair. The procedure involves dilating the aortic valve using a balloon catheter. Successful valvuloplasty can lead to a significant improvement in cardiac contraction and a normalization of the ejection fraction.A known risk of valvuloplasty is the creation or worsening of aortic regurgitation (aortic leak). It is important to note that a dysplastic valve is not a contraindication for valvuloplasty; such valves are frequently encountered in critical AS.

• Surgical Intervention (Commissurotomy): Surgical commissurotomy may be indicated as an urgent procedure in children with a very high aortic gradient and left ventricular failure, provided they are not in cardiogenic shock. Operating on a heart in severe failure, which requires stopping it, is exceptionally dangerous. If the left ventricle demonstrates good adaptation to the obstruction and the gradient is well-tolerated, surgery can be delayed (but first it must be confirmed that the duct has closed and that the circulation is not ductal-dependent). This period of delay can extend for a month or longer, with the child undergoing regular monitoring of the gradient and ventricular adaptation. There is no rigid "threshold" gradient (e.g., 40 mmHg) that mandates immediate surgery, as individual patient tolerance varies. 

• The long-term management involves continuous life-long monitoring of valve function (re-stenosis, insufficiency), ventricular adaptation, aortic vessel integrity (dilatation for example) and addressing any emerging complications.

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.