## Acute Rheumatic Fever: Valve Pathology ### Most Commonly Affected Valve **Key Point:** The **mitral valve** is affected in >65% of cases of acute rheumatic fever (ARF), followed by aortic valve (30%), and tricuspid valve (10%). Pulmonary valve is rarely involved. ### Characteristic Lesion: Verrucous Vegetations **High-Yield:** The hallmark lesion of acute rheumatic carditis is **verrucous (or marantic) vegetations**—small (1–2 mm), sterile, fibrin-platelet deposits arranged along the **line of valve closure** (atrial surface of mitral leaflets, ventricular surface of aortic leaflets). ### Microscopic Features **Key Point:** These vegetations are composed of: - Fibrin and platelets - Minimal inflammatory infiltrate - No bacterial organisms (sterile—distinguishes from infective endocarditis) ### Progression to Chronic Rheumatic Heart Disease **Clinical Pearl:** Repeated episodes of ARF lead to: 1. Fibrosis and thickening of valve leaflets 2. Commissural fusion (especially mitral commissures) 3. Chordal shortening and calcification 4. Result: Mitral stenosis (most common chronic lesion), aortic regurgitation, or mixed lesions ### Why Not Other Valves? - **Aortic valve:** Affected but less commonly; vegetations are smaller and do not produce stenosis as readily as mitral involvement - **Tricuspid/Pulmonary:** Rarely involved; low-pressure systems less susceptible to the rheumatic process **Mnemonic:** **MAC** — **M**itral most common, **A**ortic second, **C**arditis causes verrucous lesions 
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