Mitral Regurgitation Causes and Mechanisms

Primary Mitral Regurgitation

The European Society of Cardiology notes that primary mitral regurgitation results from direct pathology of the mitral valve apparatus itself, with common causes including mitral valve prolapse, Barlow disease, fibroelastic degeneration, and connective tissue disorders 1, 2, 3
Mitral annular calcification is a cause of primary mitral regurgitation, according to the American College of Cardiology 1, 4
Infective endocarditis can cause leaflet perforation, vegetations, or chordal/papillary muscle rupture, leading to primary mitral regurgitation 1
Rheumatic heart disease can cause leaflet thickening and chordal fibrosis, particularly affecting the posterior leaflet, resulting in primary mitral regurgitation 1

The European Society of Cardiology states that secondary mitral regurgitation develops despite structurally normal valve leaflets, resulting from dysfunction of surrounding cardiac structures, such as ischemic heart disease and dilated cardiomyopathy 1, 2
Ischemic heart disease can cause left ventricular remodeling, papillary muscle displacement, and leaflet tethering, leading to secondary mitral regurgitation 1
Dilated cardiomyopathy can cause symmetric tethering pattern with both leaflets exhibiting reduced systolic motion, resulting in secondary mitral regurgitation 1
Severe left atrial dilation can cause pure annular dilation, termed "atrial functional MR", according to the American College of Cardiology 4

Carpentier's Functional Classification of Mechanisms helps identify the underlying cause, with types including normal leaflet motion (Type I), excessive leaflet motion (Type II), restricted motion in systole and diastole (Type IIIa), and restricted motion in systole only (Type IIIb) 1, 4
Type IIIb motion is characterized by restricted motion in systole only, often seen in ischemic or non-ischemic cardiomyopathy with leaflet tethering 1, 4

Mixed pathology commonly occurs and should not be overlooked, with examples including untreated primary mitral regurgitation causing irreversible left ventricular dilation, and patients with long-standing secondary mitral regurgitation subsequently rupturing a chord 4
Anterior leaflet override in Type IIIb motion should not be mistaken for prolapse, as the anterior leaflet overrides the severely tethered posterior leaflet but does not move above the annular plane 4