Aortic Stenosis (AS)

Aortic stenosis (AS) is a very common valvular disease that impacts approximately 9 million people worldwide. A narrowing of the valve opening restricts blood flow from the left ventricle into systemic circulation. Echocardiography plays a vital role in monitoring the progression of systolic and diastolic dysfunction, transvalvular gradients, and pulmonary hypertension in these cases.

The continuity equation is used to calculate the aortic valve area; it assumes that the flow of blood is constant throughout the heart's outflow tract. This means that any narrowing of the aortic valve will cause an increase in the velocity of the blood across the valve to maintain the same volume of flow. The aortic valve area (AVA) is a critical parameter in diagnosing and assessing aortic stenosis.

The Continuity Equation is key in these cases:

A1​V1​=A2​V2​

A1​ = Area of the left ventricular outflow tract (LVOT) just before the aortic valve

V1​ = Velocity of blood flow in the LVOT (measured by pulsed-wave Doppler)

A2 = Aortic valve area (AVA), the area that we are solving for

V2 = Velocity of blood flow across the aortic valve (measured by continuous-wave Doppler)

Key Measurements

A1 Left Ventricular Outflow Tract (LVOT) Diameter: a linear dimension performed in the parasternal long axis view measured 0.3-1.0cm from the leaflet insertion point.

V1 Pulsed Wave Doppler of the LVOT: performed in the apical 5-chamber view to assess the flow at the same location you measured the diameter. This waveform is traced in what we call a velocity-time integral (VTI).

V2 Continuous Wave Doppler of the aortic valve: performed in the apical 5-chamber view to assess the peak velocity through the stenotic valve and the transvalvular gradient. This VTI is traced as well.

Scanning Tips

  • As the valve thickens, blood flow velocity increases. For accurate Doppler readings, align the Doppler beam parallel to flow. A clear 2D image and color Doppler help pinpoint the flow path.

  • Assess the aortic valve from multiple windows—parasternal, apical, suprasternal, subcostal, and right parasternal—using both the standard and Pedoff probes.

  • Early-peaking Doppler signals suggest mild stenosis, while late-peaking jets indicate severe stenosis. Always trace the highest velocity. Use the continuity equation to estimate stenosis severity and support clinical decisions.