Rheumatic Heart Disease - Pathology

Overview

Rheumatic heart disease (RHD) is the cardiac manifestation of acute rheumatic fever (ARF), an immunologically mediated, multisystem inflammatory disease triggered by Group A beta-hemolytic streptococcal (GAS) pharyngeal infection. It is characterized by inflammation of all three layers of the heart (pancarditis), but valvular scarring produces the most clinically significant, permanent damage.

RHD remains the most important form of acquired heart disease in children and young adults in low-income countries. In high-income countries, its incidence has fallen dramatically due to improved socioeconomic conditions, rapid antibiotic treatment, and declining streptococcal virulence.

Pathogenesis

The characteristic 2-3 week latency between streptococcal infection and symptom onset reflects the time needed to mount an immune response. The core mechanism is molecular mimicry:

Antibodies and CD4+ T cells directed against streptococcal M proteins cross-react with cardiac antigens (myocardial, valvular, and pericardial)
Cross-reactive autoantibodies target: streptococcal carbohydrate epitope (N-acetyl-beta-D-glucosamine / GlcNAc), laminin in valve endothelium, and cardiac myosin
Anti-body binding activates complement and recruits Fc-receptor-bearing neutrophils and macrophages
Cytokine release by stimulated T cells leads to macrophage activation within Aschoff bodies
Streptococci are completely absent from the lesions - confirming the immunological basis
Only 0.3% to 3% of those with streptococcal infection develop RF, implying an underlying genetic susceptibility (HLA class II alleles are implicated; heritability estimated at ~60%)

Morphology: Acute Rheumatic Fever (Pancarditis)

During the acute phase, focal inflammatory lesions are found in all three layers of the heart.

1. The Aschoff Body (Pathognomonic Lesion)

The Aschoff body (also called Aschoff-Geipel body) is the hallmark granulomatous lesion of rheumatic fever, found in the myocardium. It is pathognomonic for this disease.

Composition:

Central zone of fibrinoid necrosis
Surrounding infiltrate of T lymphocytes (primarily), plasma cells
Plump activated macrophages called Anitschkow cells (also called "caterpillar cells")

Anitschkow cells have:

Abundant cytoplasm
Central round-to-ovoid nuclei (occasionally binucleate)
Chromatin condensed into a slender, central, wavy ribbon - classically described as the "caterpillar nucleus" or "owl-eye" nucleus on cross-section

Aschoff body - Braunwald's Heart Disease: Photomicrograph of an Aschoff nodule showing Anitschkow cells (arrows) with caterpillar chromatin, central fibrin, and surrounding mononuclear infiltrate

Aschoff body (Braunwald's Heart Disease): Anitschkow cells (arrows) with their characteristic caterpillar nuclei, surrounded by mononuclear infiltrate. Adjacent myocardial fibers are undergoing destruction.

2. Endocarditis (Most Clinically Important)

Inflammation of the endocardium and left-sided valves causes fibrinoid necrosis within cusps or tendinous cords
Overlying necrotic foci along the lines of closure form small (1-2 mm) verrucae (vegetations)
These are sterile, flat, wartlike deposits - unlike the bulky vegetations of infective endocarditis
MacCallum plaques: irregular subendocardial thickenings in the left atrium, often on the posterior wall, caused by regurgitant jet injury

3. Myocarditis

Diffuse interstitial Aschoff bodies throughout the myocardium
May be sufficiently severe to cause cardiac dilation and functional mitral insufficiency in acute phase

4. Pericarditis

Fibrinous, sometimes with effusion ("bread-and-butter" pericarditis)
Occurs only alongside endocardial inflammation
Generally subsides without permanent damage

Morphology: Chronic Rheumatic Heart Disease

The chronic fibrotic lesions are the predictable consequence of healing and scarring. Clinical manifestations appear years to decades after the initial acute episode. Each recurrence of ARF adds cumulative damage.

Acute and chronic rheumatic heart disease - Robbins Pathology

(A) Acute rheumatic mitral valvulitis: small verrucae along the line of valve closure (arrows), with fibrous thickening and fusion of chordae. (B) Aschoff body: Anitschkow cells with caterpillar chromatin. (C) Chronic mitral stenosis viewed from above: commissural fusion (arrows). (D) Anterior mitral leaflet: neovascularization (arrow). (E) Rheumatic aortic stenosis: thickening and commissural fusion.

Valve Changes

The cardinal anatomic changes in the chronic mitral valve:

Feature	Detail
Leaflet thickening	Progressive fibrosis obliterates normal architecture
Commissural fusion	Leaflets fuse at the edges - most characteristic change
Chordae tendineae	Thickened, shortened, fused
Calcification	Progressive calcification of valvular and subvalvular apparatus
Neovascularization	New vessel ingrowth visible in leaflets
Overall shape	Funnel-shaped valve with domed leaflets; "fish-mouth" orifice

Aschoff bodies are rarely found in chronic RHD surgical specimens or autopsy tissue due to the long interval between the initial insult and development of the deformity.

Valve Frequency of Involvement

Valve	Frequency
Mitral alone	~70% (isolated); ~two-thirds of all chronic RHD
Mitral + Aortic	~25%
Tricuspid	Infrequent, less severe
Pulmonary	Almost always spared

RHD is essentially the only cause of acquired mitral stenosis. Mitral regurgitation is the most common valvular abnormality in RHD overall.

Microscopic Changes (Chronic)

Organization of acute inflammation
Post-inflammatory neovascularization within leaflets
Transmural fibrosis obliterating the normal leaflet architecture
Aschoff bodies absent or rare

Consequences of Chronic RHD

Mitral stenosis - progressive left atrial dilation; normal valve area (4-5 cm²) reduced to ≤1.5 cm² in severe disease
Atrial fibrillation - from left atrial pressure overload and dilation
Mural thrombi - fertile substrate from dilated, fibrillating left atrium; risk of systemic thromboembolism (stroke)
Pulmonary hypertension - from long-standing elevated left atrial pressure transmitted to pulmonary vasculature
Right ventricular hypertrophy/failure - secondary to pulmonary hypertension
Left ventricle - generally normal in pure mitral stenosis
Infective endocarditis - scarred, deformed valves are highly susceptible
Arrhythmias (atrial fibrillation predominates)

Summary Table: Acute vs. Chronic RHD Pathology

Feature	Acute RHD	Chronic RHD
Lesion type	Aschoff bodies, fibrinoid necrosis	Fibrosis, calcification, commissural fusion
Valve vegetations	Small (1-2 mm) verrucae along line of closure	None; replaced by fibrous scar
Aschoff bodies	Present (pathognomonic)	Absent/rare
Chordae tendineae	Mild involvement	Shortened, thickened, fused
Pericardium	Fibrinous pericarditis	Usually no permanent damage
Valve shape	Near normal outline, inflamed	"Fish-mouth" / funnel-shaped stenosis
Left atrium	Mildly affected	Markedly dilated

Sources:

Robbins & Kumar Basic Pathology, Chapter 9 (Valvular Heart Disease)
Robbins, Cotran & Kumar Pathologic Basis of Disease, Chapter 12
Braunwald's Heart Disease, Chapter 81 (Pathologic Features)
Schwartz's Principles of Surgery, 11th Ed., Chapter 21 (Mitral Valve Disease)

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