Moderate gradient severe aortic stenosis: diagnosis, prognosis and therapy

Abstract

Aortic stenosis (AS) is defined as severe in the presence of: mean gradient ≥40 mmHg, peak aortic velocity ≥4 m/s, and aortic valve area (AVA) ≤1 cm² (or an indexed AVA ≤0.6 cm²/m²). However, up to 40% of patients have a discrepancy between gradient and AVA, i.e. AVA ≤1 cm² (indicating severe AS) and a moderate gradient: >20 and <40 mmHg (typical of moderate stenosis). This condition is called 'low-gradient AS' and includes very heterogeneous clinical entities, with different pathophysiological mechanisms. The diagnostic tools needed to discriminate the different low-gradient AS phenotypes include colour-Doppler echocardiography, dobutamine stress echocardiography, computed tomography scan for the definition of the calcium score, and recently magnetic resonance imaging. The prognostic impact of low-gradient AS is heterogeneous. Classical low-flow low-gradient AS [reduced left ventricular ejection fraction (LVEF)] has the worst prognosis, followed by paradoxical low-flow low-gradient AS (preserved LVEF). Conversely, normal-flow low-gradient AS is associated with a better prognosis. The indications of the guidelines recommend surgical or percutaneous treatment, depending on the risk and comorbidities of the individual patient, both for patients with classic low-flow low-gradient AS and for those with paradoxical low-flow low-gradient AS.

Keywords: Aortic valve replacement; Calcium score; Low-flow low-gradient; Severe aortic stenosis; TAVI.

Figure 1

Diagnostic flow chart. AS, aortic stenosis; AU, Agaston unit; AVA, aortic valve area; DES, dobutamine stress echocardiography; LF-LG, low-flow low-gradient; LVEF, left ventricular ejection fraction; LVOT, left ventricular outflow tract; NF-LF, normal-flow low-gradient; SVI, stroke volume index. ^aWithout significant gradient increase. ^bWith a significant increase in the gradient.