Low-Gradient Aortic Stenosis: Solving the Conundrum Using Multi-Modality Imaging

Up to 1/3 of patients with both reduced or preserved left ventricular ejection fraction (LVEF), harbor a mean pressure gradient (MPG) < 40 mm Hg (peak velocity (PV) < 4 m/s), suggesting moderate aortic stenosis (AS) and an aortic valve area (AVA) < 1 cm² suggesting severe AS raising uncertainties regarding AS severity and appropriate management. In patients with reduced LVEF, increased transvalvular flow and stroke volume ≥ 20% (i.e. contractile reserve) during low-dose dobutamine echocardiography enables distinguishing patients with “true-severe AS” (severe AS with secondary LV dysfunction, PV ≥ 4 m/s or MPG > 30–40 mm Hg at peak while AVA remains <1 cm²) from patients with “pseudo-severe AS” (moderate AS with associated LV dysfunction due to ischemic or dilated cardiomyopathy, AVA at peak ≥1 cm² with a MPG < 30–40 mm Hg). However, interpretation of dobutamine stress echocardiography is often challenging, and absence of contractile reserve is observed in 20 to 30% of patients. Measurement of the degree of calcification (AVC) using computed tomography is an accurate and flow-independent method for the assessment of AS severity. A score > 1250 AU in women and >2000 UA in men strongly suggest severe AS. Combination of dobutamine echocardiography and AVC scoring enables assessment of AS severity with high confidence. The subset of patients with discordant grading and preserved LVEF is heterogenous and encompasses various conditions. A minority harbor a low flow state related to a reduced myocardial performance, an increased arterial afterload or combination of both. A low flow state is an important prognostic factor but does not provide any information regarding AS severity. Similarly to patients with reduced LVEF, assessment of the degree of AVC seems the best method to differentiate patients with pseudo-severe AS from patients with true severe AS. The latter should be referred for an intervention if symptomatic whereas the optimal management of the former subset remains uncertain.