Mitral Stenosis, Acute Rheumatic Fever & Rheumatic Heart Disease

Acute rheumatic fever (ARF) is an acute multisystem inflammatory disease that arises as a sequel to a Strep pyogenes or group A streptococcal pharyngitis infection, not from skin or other types of group A strep infections. This disorder primarily targets the mitral valve within the heart. ARF is particularly prevalent in underdeveloped countries and frequently afflicts children aged between 5 and 15 years, usually surfacing about 2-3 weeks post the initial strep pharyngitis.

The underpinning mechanism causing cardiac damage in ARF is a type II hypersensitivity reaction, which is antibody-mediated. These autoantibodies, formed by molecular mimicry, react adversely with the heart tissues. For diagnosing ARF, clinicians employ the JONES criteria: ‘Joints’ signifies the common presentation of ARF as migratory polyarthritis, particularly affecting large joints like elbows, knees, and ankles; ‘O’ stands for myocarditis, a severe complication of ARF and the predominant cause of mortality; ‘Nodules’ pertain to subcutaneous nodules that exhibit central fibrinoid necrosis, usually forming on the extensor surfaces of the forearm; ‘Erythema marginatum’ describes a distinctive rash that consists of hive-like, C-shaped erythematous areas; ‘Sydenham chorea’ delineates the rapid, uncontrolled movements that affect the entire musculature. This presentation may not be immediate but can appear anywhere from 1 to 8 months post-infection.

The cardiac implications of ARF are vast, manifesting as pancarditis, which affects the pericardium, myocardium, and endocardium. Both pericarditis and myocarditis are common outcomes, with the latter being especially perilous, often leading to acute heart failure marked by pulmonary and peripheral edema in younger patients. Moreover, ARF can also cause endocarditis, specifically a valvulitis, which results in fibrinoid necrosis and sterile verrucous vegetations, most commonly on the mitral valve leaflet closure.

Cardiac involvement arises due to a type II hypersensitivity reaction, with autoantibodies formed via molecular mimicry. This damage frequently targets the mitral valve, leading to mitral regurgitation and, less commonly, aortic regurgitation. Clinically, ARF often presents with a harsh holosystolic murmur over the apex that radiates to the left axilla, indicative of mitral regurgitation. Histologically, Aschoff bodies are the characteristic granulomatous findings, and within these granulomas, Anitschkow (‘caterpillar’) cells—activated macrophages with slender, ribbon-like nuclei—can be detected. For diagnostic purposes, antistreptolysin-O and anti-DNase B titers can be leveraged to identify a prior streptococcal infection, even if cultures might be negative at the time of patient presentation.

Penicillin is the treatment of choice for ARF, with some patients requiring prolonged therapy, contingent upon the severity of carditis. A significant risk lies in subsequent group A streptococcal infections, as they can incite recurrent episodes of ARF, exacerbating symptoms and ultimately progressing to chronic rheumatic heart disease (RHD).

Chronic RHD may surface years later due to continued damage and repair processes. Years of inflammation and scarring most commonly causes mitral stenosis, though aortic stenosis is also possible. These stenosis can result in left atrial (LA) dilation, subsequently leading to atrial fibrillation, blood stasis, and mural thrombus formation. Such mural thrombi in the dilated LA may embolize, precipitating an ischemic stroke. Furthermore, a dilated LA can compress the left recurrent laryngeal nerve, causing chronic cough or hoarseness, and the esophagus, leading to dysphagia & regurgitation.

Mitral stenosis results in increased LA and symptoms of left heart failure, such as pulmonary edema. The classic clinical presentation includes a mid-diastolic rumbling murmur, preceded by an opening snap. The the closer the opening snap is to the S2 heart sound, the greater the severity of mitral stenosis. Annular calcification is another less common cause of mitral stenosis, particularly in older individuals.