Evaluation of Aortic Stenosis: an Update—Including Low-Flow States, Myocardial Mechanics, and Stress Testing

peer reviewedDegenerative aortic stenosis (AS) is one of the most frequent valvular heart diseases in Western countries. Echocardiography plays a central role in the evaluation and management of patients with AS. To overcome the inherent inconsistencies between the echocardiographic parameters defining severe AS and to unify concepts, a new classification based on the interplay between flow and gradients has recently been adopted. Outcome studies of asymptomatic patients with preserved left ventricular ejection fraction (LVEF), as classified by this new approach, have shown that low-flow (LF) states are associated with poor outcome, that the classical normal-flow/high-gradient pattern has an intermediate outcome, while normal-flow/low-gradient severe AS seems to have an outcome comparable to moderate AS and such patients do not benefit from aortic valve replacement. Patients with LF/low-gradient severe AS with preserved LVEF, also known as "paradoxical LF/low-gradient AS," have the worst outcome and benefit greatly from surgical or percutaneous valve replacement, provided that severity is proven. In patients with LF/low-gradient and depressed LVEF, dobutamine stress echocardiography has an important role to distinguish severe from pseudo-severe AS and to assess surgical risk. Assessment of aortic valve calcium score, as well as computation of projected effective orifice aortic area at normal trans-valvular flow rates, has proved to be very useful to distinguish severe from pseudo-severe AS in LF/low-gradient AS with both reduced and preserved LVEF. Asymptomatic patients with normal flow/gradient should be submitted to an exercise test; exercise echocardiography can identify patients at increased risk when mean gradient increases by >18-20 mmHg and/or pulmonary arterial hypertension develops during exercise