Aortic Stenosis Severity Assessment

Diagnostic Recommendations

The American College of Cardiology recommends transthoracic echocardiography (TTE) with Doppler as the primary modality for measuring aortic stenosis severity, as it directly quantifies the hemodynamic consequences of the stenosis through velocity and gradient measurements 1, 2
TTE with Doppler directly measures the physiologic impact of aortic stenosis by quantifying peak aortic jet velocity, mean transvalvular pressure gradient, and calculating aortic valve area via the continuity equation—the three primary parameters that define AS severity 1, 3
The high temporal resolution of Doppler echocardiography renders it superior to all other current imaging modalities for interrogating aortic valve physiology 2

The American College of Cardiology/American Heart Association (ACC/AHA) guidelines establish echocardiography as the Class I, Level B recommendation for diagnosis and assessment of AS severity 1
The 2017 ACC Expert Consensus explicitly states that initial assessment and staging of AS severity is best performed by guideline-based diagnosis with TTE 4
TTE is recommended for re-evaluation of asymptomatic patients annually for severe AS, every 1-2 years for moderate AS, and every 3-5 years for mild AS 1

The most common error in TTE assessment is underestimation of disease severity due to non-parallel intercept angle between the ultrasound beam and high-velocity jet—peak velocity must be obtained from multiple acoustic windows (apical, right parasternal, suprasternal, subcostal) 1, 3
LVOT diameter measurement is the single largest source of error because it is squared in the continuity equation, magnifying small measurement errors; it should be measured at the base of the aortic valve cusps or 1-5 mm below 3

Cardiac MRI (CMR) plays a complementary role in assessing LV geometry when TTE has poor acoustic windows, particularly for identifying patterns of late gadolinium enhancement suggesting amyloidosis, sarcoidosis, or hypertrophic cardiomyopathy 2
In patients with low-flow, low-gradient AS where severity remains unclear after comprehensive TTE, aortic valve calcium scoring by CT (not MRI) has been proposed as useful, with >1200 Agatston units (women) or >2000 units (men) confirming severe AS 2, 3