How do we reconcile echocardiography, computed tomography, and hybrid imaging in assessing discordant grading of aortic stenosis severity?

Up to 40% of patients with aortic stenosis (AS) present with a “discordant grading” usually referred to as “low-gradient AS.” This article presents a step-by-step integrative approach overview of the utility, limitations, and complementary role of the different imaging modalities for the assessment of AS severity with a special emphasis on the reconciliation of discordant grading. The first step is to confirm the validity of echocardiographic measures of AS severity. For example, hybrid imaging can combine left ventricular outflow tract area measured by 3-dimensional echocardiography or contrast enhanced multidetector row computed tomography with flow velocities measured by Doppler. The next step is to differentiate severe from non-severe AS with the use of low-dose dobutamine stress echocardiography, especially in patients with low left ventricular ejection fraction, low-flow, low-gradient AS. Aortic valve calcium scoring measured by noncontrast multidetector row computed tomography is preferred in patients with low-gradient AS and preserved left ventricular ejection fraction as well as in those with inconclusive results with dobutamine stress echocardiography