Last updated on:September 9th, 2021
Mitral regurgitation can be categorized as organic or functional, depending on the architecture of the valve and remainder of the heart. Organic mitral regurgitation refers to disease of the valves themselves—e.g., after rheumatic heart disease or infective endocarditis. The remainder of the heart is often structurally normal initially; but remodeling then occurs to compensate for the valvular dysfunction. Functional mitral regurgitation is where the valve's architecture is normal, but has been distorted by remodeling of the surrounding heart muscle, resulting in regurgitation. Ischemic heart disease is the most common culprit.
Patients with mitral regurgitation are initially asymptomatic, as the heart can maintain sufficient cardiac output for a prolonged period. However, despite the lack of symptoms, a dysfunctional mitral valve reduces the heart's efficiency and triggers remodeling. Over time, this leads to heart failure and conduction abnormalities.
Symptoms of heart failure
Symptoms of heart failure include exertional dyspnea, paroxysmal nocturnal dyspnea, orthopnea, and peripheral edema. In mitral regurgitation, the effective output of the heart is reduced because a proportion of the ejection fraction is expelled back into the left atrium. To maintain the circulating volume, dilation of the left ventricle occurs, in as per Starling's law. Once the left ventricle has dilated beyond a certain point, progressive systolic dysfunction results; this culminates in overt heart failure. Dilation may also worsen the mitral regurgitation by distorting the ventricular architecture.
Symptoms of infective endocarditis
Symptoms of infective endocarditis include fever, weight loss, lethargy and night sweats. Septic embolization may result in infections in atypical locations (e.g., discitis or cerebral abscesses). Infective endocarditis is a complication of organic mitral regurgitation, with the structurally abnormal valves conferring an increased risk of bacterial colonization. Note that the absolute risk of infective endocarditis is still small.
Symptoms of atrial fibrillation
Atrial fibrillation is often seen as a complication of mitral regurgitation. When it develops it can present as palpitations; an acute reduction in exercise tolerance, due to the switch from sinus rhythm to fibrillation; or as chest pain, due to the increased heart rate causing reduced myocardial perfusion. This is a result of the progressive left atrial remodeling that occurs in chronic mitral regurgitation.
Past rheumatic fever
Rheumatic heart disease is a consequence of rheumatic fever, an autoimmune complication of group A streptococcus infection. The autoimmune response causes inflammation of the cardiac valves, with the mitral valve often affected. Mitral regurgitation may result.
Family history of mitral valve prolapse
Mitral valve prolapse is a known cause of mitral regurgitation. In this condition, changes in elasticity result in prolapse of one or more valvular leaflets into the left atrium during systole. This can progress into overt mitral regurgitation over time; chordal rupture can also occur. Mitral valve prolapse has been shown to have a genetic component; it is also linked to several connective tissue disorders.
History of connective tissue disorders
Individuals with connective tissue disorders such as Ehlers-Danlos syndrome and Marfan syndrome have an increased incidence of mitral valve prolapse; this predisposes them to developing mitral regurgitation.
History of infective endocarditis
Infective endocarditis involving the mitral valve is a known cause of mitral regurgitation. This tends to occur due to rupture of the chordae tendineae that maintain the valve's structure. Note that most cases tend to present acutely and severely. However, in others, the valve's architecture is altered only slightly; it may be years before symptoms appear.
Other risk factors
Other risk factors include congenital heart disease, previous myocardial infarction, longstanding hypertension, past irradiation of the chest, renal dysfunction, the use of drugs known to cause valvular heart disease (e.g., ergotamine, cabergoline, etc.), older age, and female gender.