An underestimation of aortic stenosis severity by continuous wave Doppler may occur due to?

An underestimation of aortic stenosis severity by continuous wave Doppler can occur due to low cardiac output. When cardiac output is diminished, the flow velocity across the aortic valve may be reduced, leading to a lower peak gradient being measured. This happens because the Doppler ultrasound technique relies on the velocity of blood flow to estimate pressure gradients; thus, if the flow is less vigorous, the gradient appearing on the Doppler waveform may not accurately reflect the true severity of the stenosis. Low cardiac output can present a challenge in assessing the functional significance of aortic stenosis, as the reduced flow can mask the actual hemodynamic impact of the narrowed valve, potentially leading to an underestimation of severity.

In contrast, high blood pressure might increase afterload but does not inherently affect the measurement of gradient severity in the same context as flow. A normal cardiac rhythm can indicate stable hemodynamic conditions, but doesn't influence the Doppler readings based on flow dynamics. An increased heart rate could potentially either raise or lower the measured gradient depending on the specific hemodynamics, but it is not a direct cause of underestimation like low cardiac output is.