New Threshold for Defining Mild Aortic Stenosis Derived From Velocity-Encoded MRI in 60,000 Individuals

Mild aortic stenosis (AS) is associated with adverse outcomes but is incompletely defined.

The purpose of this study was to examine the epidemiology of AV function measured without clinical indications.

We developed a deep learning model to measure aortic valve (AV) area, peak velocity, and mean gradient in velocity-encoded cardiac magnetic resonance imaging in 62,902 UK Biobank participants. Study findings were externally validated in NEDA (National Echo Database Australia), a clinical cohort of 365,870 people.

From measuring reference ranges of AV function in a healthy subcohort (n = 41,859), we observed a natural boundary between normal and abnormal AV hemodynamics (>95th percentile) that we refer to as "mild AS_proposed": peak velocity >1.65 m/s, mean gradient >4.9 mm Hg, or aortic valve area <2.1 cm² (men) or <1.7 cm² (women). In the full cohort, 3,676 (5.8%) participants met these novel criteria; the HR for a subsequent AV replacement for each severity category was 31.7 (mild AS_proposed), 522.4 (moderate AS), and 3,057.4 (severe AS), all P < 0.001. Over a mean 3.9 years of follow-up, those with mild AS_proposed also had a higher risk of atrial fibrillation (110 events; HR: 1.86; P = 1.4 × 10^-9) and heart failure (70 events; HR: 2.37; P = 5.9 × 10^-11) compared with those without AS. In NEDA, the 101,335 participants with mild AS_proposed identified with echocardiography using the same cardiac magnetic resonance imaging-defined criteria had increased all-cause mortality (HR: 1.25; 95% CI: 1.24-1.27).

We report a large-scale study of AV hemodynamics and identify a population threshold between normal and abnormal AV function. Mild AS, as defined by the proposed criteria, was linked to adverse outcomes in the UK Biobank and in NEDA.