A 52-year-old woman from Delhi presents with a holosystolic murmur best heard at the left lower sternal border, radiating to the axilla. She has a history of myocardial infarction 8 years ago. Echocardiography confirms severe mitral regurgitation. What is the most common cause of chronic mitral regurgitation in developed countries?

## Most Common Cause of Chronic Mitral Regurgitation in Developed Countries **Key Point:** Myxomatous degeneration of the mitral valve (mitral valve prolapse, MVP) is the most common cause of chronic mitral regurgitation in developed countries, accounting for 50–60% of cases requiring surgical intervention. **High-Yield:** The epidemiology of mitral regurgitation differs significantly between developed and developing nations: - **Developed countries:** MVP (myxomatous degeneration) > dilated cardiomyopathy > RHD - **Developing countries (India):** RHD > dilated cardiomyopathy > MVP ### Pathophysiology of MVP-Related Mitral Regurgitation 1. **Myxomatous degeneration:** Abnormal collagen and proteoglycan accumulation in valve leaflets 2. **Valve prolapse:** Leaflet billows into left atrium during systole 3. **Chordal rupture:** Progressive elongation or rupture of chordae tendinae 4. **Progressive MR:** Increasing severity over decades; may require surgery ### Comparison of Mitral Regurgitation Etiologies | Cause | Frequency (Developed) | Frequency (India) | Mechanism | Progression | | --- | --- | --- | --- | --- | | **MVP (myxomatous)** | 50–60% | 5–10% | Leaflet degeneration + chordal rupture | Slow, over years | | **Dilated cardiomyopathy** | 20–25% | 15–20% | Annular dilatation + papillary muscle displacement | Variable | | **Rheumatic heart disease** | 10–15% | 60–70% | Commissural fusion + leaflet thickening | Chronic | | **Infective endocarditis** | 5–10% | 10–15% | Vegetation + leaflet perforation | Acute to subacute | **Clinical Pearl:** MVP-related MR has characteristic features: - **Murmur timing:** Holosystolic (pansystolic) when severe; late systolic when mild - **Associated findings:** Midsystolic click, tall thin habitus, connective tissue disorders (Marfan, Ehlers-Danlos) - **Echo findings:** Leaflet prolapse >2 mm above mitral annulus plane; chordal rupture visible - **Natural history:** 1–2% per year progress to severe MR requiring surgery **Mnemonic — MVP Associations (MASS):** - **M**arfan syndrome - **A**nxiety, palpitations (benign) - **S**traight back syndrome, scoliosis - **S**ystemic lupus erythematosus **Warning:** Do not confuse MVP with RHD. MVP presents with a **click + late systolic murmur** in mild disease; RHD presents with **holosystolic murmur** from the start. MVP is associated with tall, thin habitus and connective tissue disorders; RHD is associated with history of ARF and atrial fibrillation. **Tip:** The question stem mentions "myocardial infarction 8 years ago" as a red herring. While post-MI papillary muscle dysfunction can cause MR, the most common cause of chronic MR in the general developed population is still MVP, not post-MI MR. [cite:Harrison 21e Ch 298]