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.
Adapted from: Congenital Diseases of the Heart - Abraham M. Rudolph, MD; San Francisco, CA, USA. Third Edition.
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.
Zoom in 2D on the aortic valve. It is thickened and does not open fully. Parasternal short axis view.
Colour box with flow acceleration at the aortic valve opening. The valve does not open fully.
M-mode in the parasternal long axis at the tip of the mitral valve for assessment of shortening fraction, and signs of LV hypertrophy.
M-mode in the parasternal short axis at the tip of the mitral valve for assessment of shortening fraction, and signs of LV hypertrophy.
Another clip in the parasternal long axis view
One may appreciate the degree of ascending aorta dilation in the suprasternal view
Flow acceleration in the ascending aorta. This is a good angle, in the suprasternal view, to appreciate the peak gradient of the aortic stenosis, because of angle of insonation.
Peak gradient (systolic) at the level of the ascending aorta is estimated at 87 to 91 mmHg.
It is important to rule out any associated hypoplastic aortic arch, coarctation and even distal coarctation. Here the flow is seen in the descending aorta.
There is some concern when evaluation the PW-Doppler in the Descending Aorta. There is some subjective low velocities in systole, possibly indicating some compromise to the systemic blood flow in the descending aorta.
Ductus is bidirectional. With some right to left shunting in systole.
Bidirectional PDA by CW-Doppler.
It is important to sweep and tilt in order to follow the trajectory of the flow coming out of the LVOT.
Zoom in the parasternal short axis over the aortic valve area.
By B-mode, one may appreciate some minimal LV hypertrophy, which is usually quite present in the context of long-standing aortic stenosis.
Sweep with colour in the parasternal short axis. There is only minimal (if any) LV hypertrophy.
Apical 4 Chamber with RV focused view. Aortic stenosis may be associated with significant LV systolic and diastolic dysfunction, which may lead to post-capillary pulmonary hypertension and RV dysfunction. As such, it is important to evaluate the biventricular function.
Apical 4 chamber view, LV Focus. One may see that there is adequate systolic contraction.
Acceleration at the level of the aortic valve in the 5 chamber view.
Gradient obtained through the LVOT, estimated at a peak of 81 mmHg.
TDI at the level of the septum.
TAPSE
The valve is seen now with a larger opening at the peak of systole.
One may appreciate the leaftlets of the aortic valve by M-Mode.
Colour flow indicating acceleration at aortic valve.
Flow the the ascending aorta with acceleration starting at the level of the valve. This may be appreciated during the sweep and tilting.
The peak gradient is of 49 mmHg post-dilatation. There is also some degree of aortic insufficiency during diastole.
Measurement of the aorta (ascending, transverse and isthmus)
Right to left PDA gradient in systole
Parasternal short axis view with a sweep outlining: the aortic valve, the LV and the RV (for subjective appreciation of function) and presence of some septal flattening.
M-mode at the level of the parasternal long axis.
Apical 5 chamber view outlining the aortic regurgitation. There is turbulence at the LVOT.
Another clip of the Apical 5 chamber view outlining the aortic regurgitation. There is turbulence at the LVOT.
PW-Doppler in the descending aorta, outlining some retrograde flow possibly secondary to the aortic insufficiency.
Tracing at the LVOT outlining the aortic insufficiency, as well as the LVOT peak gradient of flow during peak of systole (40.83 mmHg).
PW-Doppler in the descending aorta. This was sampled in the pre-ductal area, outlining that some of the holodiastolic retrograde flow is secondary to the aortic insufficiency (rather than from ductal steal)
PDA diameter
Parasternal long axis views outlining that the aortic valve is dysplastic and with a stenotic appearance in systole
Parasternal short axis view outlining the stenotic aortic valve
There is acceleration of flow (from the coarctation) at the area of the ductus arteriosus, which is restrictive.
Coarctation with small arch at the isthmus.
Flow acceleration at the level of the isthmus, outlining an area of coarctation.
View of the aortic valve obtained from the subcostal region.
Post-dilation of the fused bicuspid valve by catheterization
Partially opening Aortic-valve by M-Mode
Severely reduced LV function with fractional shortening of 15%
Peak systolic gradient through the Aortic valve from the suprasternal notch estimated at 65 mmHg
Peak systolic gradient through the Aortic valve from the apical view estimated at 64 mmHg
dp/dt of LV of 768 mmHg/s (detal T 41.67 msec) - Calculator here. This indicates LV dysfunction (Normal > 1200 mmHg/s)
Mean Aortic Gradient of 33 mmhg during systole (stenosis).
Depressed mild to moderate LV function with EF of 42%.
RV-RA velocity gradient indicating a TR of 37 mmHg (incomplete curve), which is slightly increased and possibly secondary to LV diastolic dysfunction and post-capillary obstruction.
Global longituinal strain outlining depressed deformation.
TDI outlining decreased systolic velocities at the level of the septum and of the lateral wall of the LV.