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Rheumatic Mitral Stenosis
Worldwide, rheumatic heart disease (RHD) is the predominant cause of mitral stenosis (MS) but is rare in developed countries. Most cases of rheumatic mitral stenosis (RMS) in developed countries are found among immigrants from less developed parts of the world where the prevalence of rheumatic fever may be as high as 150 cases per 100,000 people. Acute rheumatic fever is triggered by rheumatogenic group A β-hemolytic Streptococcus pyogenes infection, typically pharyngitis (“strep throat”). RMS may be considered an autoimmune disease triggered by streptococcal infection mediated by cross-reactivity between the streptococcal M antigen (mucoid surface protein) and human epitopes in the heart, skin, and connective and nerve tissues. The index streptococcal infection and subsequent reinfections trigger lifelong progressive fibrosis and calcifications leading to MS. In this chapter, we concentrate on transthoracic (TTE) and transesophageal echocardiographic (TEE) analysis of mitral valve morphology and secondary cardiac changes in RMS.
Cause of Mitral Stenosis
MS may result from a variety of congenital and acquired conditions. Worldwide, rheumatic heart disease is the predominant cause of MS but is rare in developed countries.
Nonrheumatic Mitral Stenosis
Congenital MS is very rare (∼1% of all patients with MS) and may be caused by cor triatriatum, a supravalvular mitral ring, or a parachute mitral valve (typically as a part of the Shone syndrome). Nonrheumatic causes of acquired MS include lupus erythematosus, carcinoid, rheumatoid arthritis, radiation valvulitis, and age-related degenerative mitral annular calcifications. They are all rare except for mitral annular calcification, which is becoming the leading cause of acquired MS in developed countries.
Rheumatic Mitral Stenosis
The disease typically starts in childhood with a bout of acute rheumatic fever and is followed by lifelong progressive valvular damage. Acute rheumatic fever is triggered by rheumatogenic group A β-hemolytic Streptococcus pyogenes infection, typically pharyngitis (“strep throat”). Rheumatic heart disease may be considered an autoimmune disease triggered by streptococcal infection mediated by cross-reactivity between the streptococcal M antigen (mucoid surface protein) and human epitopes in the heart, skin, and connective and nerve tissues. Streptococci do not invade and are not present in the affected tissues. The index streptococcal infection and subsequent reinfections trigger lifelong progressive fibrosis and calcifications.
Clinically, acute rheumatic fever is characterized by five major findings: (1) pancarditis (endocarditis, myocarditis, and pericarditis), (2) migrating arthritis of large joints, (3) subcutaneous nodules, (4) skin rash (erythema marginatum), and (5) Sydenham chorea (random rapid dancelike movements of the face and the extremities). Minor (nonspecific) signs of inflammation include fever, leukocytosis, and an elevated erythrocyte sedimentation rate.
The so-called Jones criteria (first published in 1944) are used to establish the clinical diagnosis of acute rheumatic fever. In addition to evidence of a recent group A β-hemolytic streptococcal infection (such as antistreptococcal antibody titers), two major criteria or one major criterion plus two minor criteria are required for the diagnosis.
Although any cardiac valve may be involved, the mitral valve is virtually always affected, and MS with or without concomitant mitral regurgitation (MR) is the predominant chronic form. MS results primarily from commissural fusion along leaflet edges, with an additional contribution from chordal fusion and shortening. In general, leaflet thickening and calcification proceed from the leaflet tips toward the leaflet bases. This contrasts with MS caused by age-related mitral annular calcification, in which the process starts at the base of the posterior mitral leaflet.
Epidemiology
The prevalence of acute rheumatic fever and RMS reflects the overall socioeconomic development and access to medical care. Because of introduction of antistreptococcal antibiotics and improvement in living standard, the incidence of rheumatic fever has declined dramatically since World War II in developed countries to fewer than 1 case to 100,000 people. Most cases of RMS in developed countries are found among immigrants from less developed parts of the world where the prevalence of rheumatic fever may be as high as 150 cases per 100,000 people.
In developed countries, MS becomes symptomatic 20 to 30 years after the onset of rheumatic fever. In contrast, RMS progresses more rapidly in developing countries and may be observed even in children and adolescents because of frequent streptococcal reinfections.
Rheumatic fever occurs exclusively in humans because there are no known animal reservoirs. Acute rheumatic fever affects both sexes equally, but women are at least twice as likely as men to develop RMS. This may reflect the generally higher prevalence of autoimmune disorders in women compared with men.
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