Pathophysiology
The pathophysiology of rheumatic fever is not yet totally understood. It is thought to result from an abnormal immune response to
M proteins on group A beta-hemolytic streptococcal bacteria. These
antigens can bind to cells in the heart, muscles, and brain. They also
bind with receptors in synovial joints, provoking an autoimmune
response. The resulting immune response to the bacteria also leads
to inflammation in tissues containing these M proteins. Inflammatory lesions develop in connective tissues on the heart, joints, and
skin. The antibodies may remain in the serum for up to 6 months
following the initiating event. Refer to Chapters 11 and 12 for more
information about the immune system and inflammatory response.
Carditis, inflammation of the heart, develops in about 50% of
people with rheumatic fever. The inflammatory process usually involves all three layers of the heart—the pericardium, myocardium,
and endocardium. Aschoff bodies, localized areas of tissue necrosis
surrounded by immune cells, develop in cardiac tissues. Pericardial
and myocardial inflammation tends to be mild and self-limiting. Endocardial inflammation, however, causes swelling and erythema
of valve structures and small vegetative lesions on valve leaflets. As
the inflammatory process resolves, fibrous scarring occurs, causing
deformity.
Rheumatic heart disease (RHD) is a slowly progressive
valvular deformity that may follow acute or repeated attacks of
rheumatic fever. Valve leaflets become rigid and deformed; commissures (openings) fuse, and the chordae tendineae fibrose and
shorten. This results in stenosis or regurgitation of the valve. In
stenosis, a narrowed, fused valve obstructs forward blood flow.
Regurgitation occurs when the valve fails to close properly (an
incompetent valve), allowing blood to flow back through it. Valves
on the left side of the heart are usually affected; the mitral valve is
most frequently involved