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PA26.{5,7} | Rheumatic Heart Disease & Infective Endocarditis — SDL Guide (Part 2)

Pancarditis — Pathology of Acute Rheumatic Heart Disease

Diagram of acute rheumatic pancarditis showing inflamed pericardium, myocardium with Aschoff body, valvular verrucae, and MacCallum plaque in the left atrium. — **Panel A:** Semi-cutaway heart showing fibrinous pericarditis, myocarditis with Aschoff bodies, endocarditis, mitral valve involvement, and aortic valve involvement.. **Panel B:** Magnified mitral valve atrial surface showing 1-2 mm warty verrucae along the line of valve closure, representing fibrin over inflamed denuded endothelium.. **Panel C:** Microscopic Aschoff body showing central fibrinoid necrosis, Anitschkow cells, lymphocytes, macrophages, and interstitial oedema.. **Panel D:** Opened left atrium showing MacCallum plaque on the posterior left atrial wall at the mitral regurgitant jet impact zone..

ARF causes pancarditis — inflammation of all three layers of the heart. The endocarditis component causes the clinically significant lasting damage.

Pericarditis:
• Fibrinous or serofibrinous exudate — 'bread-and-butter' appearance on gross examination
• Resolves completely; rarely progresses to constrictive pericarditis

Myocarditis:
• Pathognomonic lesion: the Aschoff body
• Interstitial oedema and Aschoff bodies throughout myocardium

Endocarditis:
• Small, warty verrucae (1–2 mm) along the lines of valve closure — most commonly the mitral valve, followed by the aortic valve
• Verrucae represent areas of fibrin deposition over inflamed, denuded endothelium
• These are NOT destructive at this stage — but they set the stage for chronic scarring

MacCallum's plaque: Irregular roughened plaque on the posterior left atrial wall at the jet-stream impact zone of mitral regurgitation — formed by organisation of endocardial inflammation; pathognomonic of rheumatic disease

Remember: in ARF, the inflammation is exudative and reversible in pericardium and joints, but the endocardial and myocardial changes set in motion a chronic fibrotic process in the valves.

The Aschoff Body — Pathognomonic Lesion of Rheumatic Fever

Medical diagram showing an Aschoff body in myocardium with central fibrinoid necrosis, Anitschkov cells, Aschoff giant cells, perivascular myocardial distribution, and clinical correlation with rheumatic fever. — **Panel A:** High-power H&E-style Aschoff body in myocardium showing central fibrinoid necrosis, Anitschkov cells, caterpillar/owl-eye nuclei, multinucleated Aschoff giant cells, lymphocytes, plasma cells, myocardial fibers, and nearby blood vessel.. **Panel B:** Magnified Anitschkov cell morphology showing central wavy chromatin bar, caterpillar nucleus, and owl-eye appearance on cross-section.. **Panel C:** Heart wall schematic showing Aschoff bodies concentrated in myocardium, especially perivascularly, with valves shown separately to emphasize poor correlation with valvular damage.. **Panel D:** Clinical correlation strip showing bread-and-butter pericarditis, friction rub in a child with fever and joint pains, ASO titre prompt, and endomyocardial biopsy confirmation..

The Aschoff body is the hallmark microscopic lesion of rheumatic myocarditis. It is a granuloma-like lesion consisting of:

Central zone of fibrinoid necrosis — eosinophilic, amorphous material (denatured collagen + fibrin)
Anitschkov cells (also called Aschoff cells): large, activated macrophages with a characteristic nucleus — the chromatin is arranged in a central wavy bar resembling a caterpillar (owl-eye or caterpillar nucleus on cross-section). These are pathognomonic — no other disease produces them.
Aschoff giant cells: multinucleate forms of Anitschkov cells
Peripheral lymphocytes and plasma cells

Aschoff bodies are most numerous in the myocardium, particularly around blood vessels. They heal by fibrosis over months to years, leaving small scars.

Clinical correlate: Because Aschoff bodies are in the myocardium (not valves), their number does NOT correlate with the degree of valvular damage. Endomyocardial biopsy can confirm active rheumatic carditis even years after the initial episode.

High-power H&E educational diagram of an Aschoff body showing central fibrinoid necrosis, Anitschkow cells with caterpillar and owl-eye nuclei, and peripheral multinucleate Aschoff giant cells. — **Panel A:** High-power H&E Aschoff body with central fibrinoid necrosis, Anitschkow cells, caterpillar nucleus, owl-eye nucleus, multinucleate Aschoff giant cell, myocardial fibers, and lymphocytes.. **Panel B:** Magnified Anitschkow cells demonstrating caterpillar nucleus and owl-eye nucleus with labeled chromatin pattern.. **Panel C:** Contextual myocarditis inset showing an Aschoff body located between myocardial fibers as the pathognomonic lesion of rheumatic myocarditis..

CLINICAL PEARL

The 'bread-and-butter' pericarditis of ARF is a clinical red flag — friction rub on auscultation in a child with fever and joint pains should prompt immediate ASO titre and throat culture. Do not dismiss it as viral — the pericarditis itself resolves, but the concurrent endocarditis is silently starting the valve's 20-year journey to stenosis.

Chronic Rheumatic Heart Disease — Mitral Stenosis

Diagram showing rheumatic mitral stenosis with fish-mouth mitral valve orifice, fibrotic fused leaflets, shortened chordae, valve area thresholds, and downstream haemodynamic effects. — **Panel A:** Gross specimen of rheumatic mitral stenosis showing narrowed fish-mouth/buttonhole orifice, leaflet thickening and fibrosis, anterior and posterior commissural fusion, chordae tendineae thickening and fusion, and late calcification.. **Panel B:** Normal versus stenosed mitral valve area comparison showing normal 4-6 cm², symptomatic stenosis below 2 cm², and severe stenosis below 1 cm².. **Panel C:** Haemodynamic sequence showing fixed narrowed mitral orifice leading to elevated left atrial pressure, left atrial dilatation and hypertrophy, pulmonary venous hypertension, pulmonary arterial hypertension, right ventricular hypertrophy, and right heart failure..

Repeated episodes of ARF cause cumulative valve scarring, leading to chronic rheumatic heart disease (CRHD). The mitral valve is affected in >90% of cases; isolated mitral stenosis accounts for ~25% of all valvular disease.

Gross pathology of rheumatic mitral stenosis:
• Leaflet thickening and fibrosis — due to repeated fibrin deposition and organisation
• Commissural fusion — the leaflet edges fuse along the anterior and posterior commissures, narrowing the orifice
• Chordae tendineae thickening and fusion — the subvalvular apparatus is pulled into the ventricle
• Calcification — late feature; reduces leaflet mobility further
• The result: a fixed, narrowed orifice with the characteristic 'fish-mouth' or 'buttonhole' appearance on gross examination

Normal mitral valve area: 4–6 cm². Symptoms begin when area falls below 2 cm²; severe stenosis: <1 cm².

Haemodynamic consequences:
• Elevated left atrial pressure → left atrial dilatation and hypertrophy
• Pulmonary venous hypertension → breathlessness, orthopnoea, PND
• Progressive pulmonary arterial hypertension → right ventricular hypertrophy and failure

Diagram of rheumatic mitral stenosis showing a fish-mouth mitral orifice, commissural fusion, fibrotic thickened leaflets, and shortened thickened chordae tendineae. — **Panel A:** Left atrial gross view showing fish-mouth/buttonhole mitral orifice, commissural fusion, and leaflet fibrosis.. **Panel B:** Side-by-side superior views comparing normal wide mitral orifice with narrowed stenotic rheumatic mitral orifice and fused commissures.. **Panel C:** Ventricular-side cutaway showing thickened fused mitral leaflets, shortened chordae tendineae, chordal thickening, and papillary muscle..