Valvular Disease and Hemodynamics in Rheumatic Fever
Rheumatic fever is characterized by primary involvement of the heart valves, most commonly leading to stenosis of the left atrioventricular orifice (mitral stenosis). This valvular defect triggers a distinct pathogenetic chain of hemodynamic disturbances.
Initially, progressive dilatation of the left atrium occurs as it attempts to pump blood through the narrowed orifice. Subsequently, venous congestion develops in the pulmonary circulation. Chronic blood flow disruption causes remodeling of the pulmonary parenchyma and vascular bed, resulting in brown induration of the lungs. Furthermore, blood stasis within the dilated left atrial cavity promotes thrombus formation.
The myocardium itself undergoes staged alterations during the development of the valvular defect:
- Compensation stage: Right ventricular hypertrophy and concentric myocardial hypertrophy are observed.
- Decompensation stage: Due to myogenic dilatation (expansion) of the heart chambers, hypertrophy transitions into eccentric hypertrophy.
Morphological Forms of Rheumatic Myocarditis
Myocarditis (inflammation of the myocardium) in rheumatic fever presents in three main morphological forms, which differ in severity and prognosis.
- Nodular (granulomatous) myocarditis. Its primary feature is the formation of specific rheumatic granulomas within the perivascular stroma. These granulomas can be in various phases of development. Surrounding cardiomyocytes undergo protein or fatty degeneration, potentially progressing to micro-necrosis. The outcome of this form is diffuse fine-focal cardiosclerosis, leaving small oval or spindle-shaped perivascular scars in the myocardium.
- Diffuse interstitial exudative myocarditis. This form has significant clinical importance as it frequently develops in children. Clinically, it manifests as severe heart failure. Grossly, the heart is altered: the chambers are markedly dilated, and the myocardium appears flabby and pale. Microscopic examination reveals marked vascular congestion. The entire interstitium is edematous with serous exudate and densely infiltrated by lymphocytes, histiocytes, and band neutrophils. Muscle fibers are separated, showing marked degenerative changes and foci of necrosis. The process terminates in diffuse cardiosclerosis—a continuous proliferation of connective tissue forming thin layers between groups of muscle fibers.
- Focal interstitial exudative myocarditis. This form typically occurs during latent (subclinical) rheumatic fever. It is characterized by minor foci of lymphohistiocytic infiltration with a small admixture of band neutrophils in the interstitium. Degeneration and necrosis of cardiomyocytes are also focal. The expected outcome is focal cardiosclerosis.
Rheumatic Pericarditis
Pericarditis is inflammation of the outer membrane of the heart. In rheumatic fever, the inflammatory process can be serous, serous-fibrinous, or fibrinous.
The most striking macroscopic picture is seen in fibrinous inflammation. Massive fibrin strands are deposited on the epicardial surface, giving the heart a characteristic shaggy appearance, known as a "cor villosum" (hairy heart).
Further evolution of the process involves the organization of the deposited exudate. Fibrin strands are invaded by granulation tissue, leading to the formation of adhesions (synechiae) between the pericardial layers. In severe cases, complete obliteration of the pericardial cavity occurs. Ultimately, the connective tissue undergoes calcification (calcium salt deposition), forming a rigid, inelastic framework around the myocardium—resulting in an "armor heart" (cor armoratum).