Which of the following is a common cause of acute mitral regurgitation?

• A. Aortic stenosis
• B. Pulmonary hypertension
• C. Flail MV leaflet
• D. Mitral stenosis

Answer: (C)

Acute mitral regurgitation most often results from sudden disruption of the mitral valve’s subvalvular apparatus, especially rupture of chordae tendineae or papillary muscle. When a chord or muscle fails, a portion of the leaflet becomes flail and cannot coapt properly during systole. This flail leaflet plunges into the left atrium with each contraction, producing a rapid, severe regurgitant jet and a sudden rise in left atrial pressure. That abrupt mechanism is why a flail mitral valve leaflet is the most common cause of acute MR.

Other options don’t fit this immediate mechanism. Aortic stenosis affects the aortic valve and doesn’t typically cause sudden mitral regurgitation by itself. Pulmonary hypertension is usually a consequence or a chronic contributor rather than a primary cause of acute MR. Mitral stenosis is a distinct valvular lesion that causes obstruction rather than a sudden collapse of leaflet coaptation leading to acute regurgitation.