In low-flow low-gradient aortic stenosis with reduced EF, why are the gradients often underestimated?

• A. Reduced LVEF and stroke volume
• B. Increased LV contractility
• C. Lower systemic vascular resistance
• D. Increased LVOT velocity

Answer: (A)

The main idea is that pressure gradients across the aortic valve depend on how much blood is flowing through the valve. In a patient with low-flow, low-gradient aortic stenosis and reduced ejection fraction, the heart’s pumping ability is diminished, so stroke volume and transvalvular flow are reduced. Because the Doppler-derived gradient uses velocity across the valve (and velocity is a function of flow), slower flow yields lower velocities and a smaller mean gradient. This makes a severely narrowed valve appear less severe than it truly is. To determine true severity, clinicians look at the valve area (AVA) and may perform tests that increase flow, such as dobutamine or exercise stress echocardiography. If increasing flow reveals a persistently small AVA and a higher gradient, it confirms true severe stenosis; if the AVA enlarges and gradients don’t rise, the stenosis may be pseudo-severe due to low flow rather than fixed severe narrowing.