Rheumatic fever is a late inflammatory, nonsuppurative complication of pharyngitis that is caused by group A-hemolytic streptococci.[4] Rheumatic fever results from humoral and cellular-mediated immune responses occurring 1-3 weeks after the onset of streptococcal pharyngitis. Streptococcal proteins display molecular mimicry recognized by the immune system, especially bacterial M-proteins and human cardiac antigens such as myosin[4] and valvular endothelium. Antimyosin antibody recognizes laminin, an extracellular matrix alpha-helix coiled protein, which is part of the valve basement membrane structure.
The valves most affected by rheumatic fever, in order, are the mitral, aortic, tricuspid, and pulmonary valves. In most cases, the mitral valve is involved with 1 or more of the other 3. In acute disease, small thrombi form along the lines of valve closure. In chronic disease, there is thickening and fibrosis of the valve resulting in stenosis, or less commonly, regurgitation.
T-cells that are responsive to the streptococcal M-protein infiltrate the valve through the valvular endothelium, activated by the binding of antistreptococcal carbohydrates with release or tumor necrosis factor (TNF) and interleukins.[5] A study reported that the increased expression of Th17 cell-associated cytokines might play an important role in the pathogenesis and development of rheumatic heart disease.[6] The acute involvement of the heart in rheumatic fever gives rise to pancarditis, with inflammation of the myocardium, pericardium, and endocardium. Carditis occurs in approximately 40-50% of patients on the first attack; however, the severity of acute carditis has been questioned.[7] Pericarditis occurs in 5-10% of patients with rheumatic fever; isolated myocarditis is rare.