A 52-year-old man with a history of rheumatic mitral stenosis presents with fever, fatigue, and a new diastolic murmur. Blood cultures grow Streptococcus viridans. Which is the most common valve affected in infective endocarditis in patients with underlying rheumatic heart disease?

Explanation

## Valve Involvement in Infective Endocarditis **Key Point:** The mitral valve is the most commonly affected valve in infective endocarditis overall, accounting for approximately 65–70% of cases. In patients with pre-existing rheumatic heart disease, the mitral valve is involved in >80% of endocarditis cases. ### Frequency of Valve Involvement by Clinical Context | Valve | Overall Frequency | In Rheumatic Heart Disease | In IVDU | Key Features | |---|---|---|---|---| | **Mitral** | 65–70% | >80% | 20–30% | Most common; left-sided; subacute course | | **Aortic** | 25–30% | 15–20% | 10–20% | Left-sided; acute presentation; aortic regurgitation | | **Tricuspid** | 5–10% | <5% | 50–60% | Right-sided; septic pulmonary emboli | | **Pulmonary** | <1% | Rare | Rare | Extremely rare; usually with congenital disease | **Clinical Pearl:** The **mitral valve is affected 10 times more often than the tricuspid valve** in native valve endocarditis. However, in IV drug users, the tricuspid valve is preferentially infected (right heart), making it the exception to the rule. **High-Yield:** Rheumatic heart disease creates a **substrate for bacterial seeding** — the abnormal valve surface (stenotic, regurgitant, or both) has turbulent flow and endothelial damage, making it vulnerable to infection. The mitral valve is the most commonly damaged valve in rheumatic heart disease, so it is also the most common site of endocarditis in this population. ### Pathophysiology: Why Mitral Valve? 1. **Highest pressure gradient** across the mitral valve during systole → turbulent flow 2. **Largest surface area** among left-sided valves 3. **Most common site of rheumatic damage** in RHD 4. **Endothelial injury** from chronic valve disease creates a nidus for bacterial adhesion **Mnemonic:** **Left > Right** (left-sided valves [mitral, aortic] >> right-sided valves [tricuspid, pulmonary] in native valve endocarditis, EXCEPT in IVDU where tricuspid dominates)