Redefining Heart Valve Disease: The Battle Over Atrial Functional Mitral Regurgitation Guidelines

Introduction and Context

For decades, clinicians viewed mitral regurgitation (MR)—the leaking of the heart’s mitral valve—through two primary lenses: primary (organic) disease of the valve leaflets themselves, or secondary (functional) disease caused by dysfunction of the left ventricle. However, a third entity has recently taken center stage: Atrial Functional Mitral Regurgitation (AfMR). Unlike traditional functional MR, which stems from heart failure and a weakened left ventricle, AfMR is driven by the enlargement of the left atrium and the mitral annulus, often as a result of long-standing atrial fibrillation (AF) or heart failure with preserved ejection fraction (HFpEF).

Despite its growing recognition, AfMR has been plagued by a lack of diagnostic consensus. Different medical societies have proposed varying criteria, leading to confusion in clinical practice regarding how to identify, grade, and treat these patients. This discrepancy reached a peak with the release of conflicting definitions from a Journal of the American College of Cardiology (JACC) Expert Consensus and the European Society of Cardiology (ESC) Valve Guidelines. A recent landmark study by Koschatko et al. (2026) has finally put these definitions to the test, evaluating their robustness in predicting patient outcomes and their ability to capture the true phenotype of the disease.