(See also Overview of Cardiac Valvular Disorders.)
Mitral valve prolapse is common; prevalence is 1 to 3% in otherwise normal populations, depending on the echocardiographic criteria used. Women and men are affected equally; onset usually follows the adolescent growth spurt.
Mitral valve prolapse is most often caused by
In myxomatous degeneration, the fibrous collagen layer of the valve thins and mucoid (myxomatous) material accumulates. The chordae become longer and thinner and the valve leaflets enlarge and become rubbery. These changes result in floppy valve leaflets that can balloon back (prolapse) into the left atrium when the left ventricle contracts. Rupture of a degenerate chorda can allow part of the valve leaflet to flail into the atrium, which typically causes severe regurgitation.
Degeneration is usually idiopathic, although it may be inherited in an autosomal dominant or, rarely, in an X-linked recessive fashion. Myxomatous degeneration may also be caused by connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome, adult polycystic kidney disease, osteogenesis imperfecta, pseudoxanthoma elasticum, systemic lupus erythematosus, polyarteritis nodosa) and muscular dystrophies. MVP is more common among patients with Graves disease, hypomastia, von Willebrand disease, sickle cell disease, and rheumatic heart disease.
Myxomatous degeneration may also affect the aortic or tricuspid valve, resulting in aortic or tricuspid prolapse. Primary tricuspid regurgitation is much less common than secondary tricuspid regurgitation due to left ventricular pathology.
Mitral regurgitation (MR) due to mitral valve prolapse may occur in patients with apparently normal mitral valve leaflets (ie, nonmyxomatous) due to ischemic papillary muscle dysfunction or rheumatic chordal rupture. Transient MVP may occur when intravascular volume decreases significantly, as occurs in severe dehydration or sometimes during pregnancy (when the woman is recumbent and the gravid uterus compresses the inferior vena cava, reducing venous return).
Mitral regurgitation is the most common complication of mitral valve prolapse. MR may be acute (due to ruptured chordae tendineae causing flail mitral valve leaflets) or chronic. Sequelae of MVP with MR include heart failure, infective endocarditis, and atrial fibrillation (AF) with thromboembolism. Whether MVP causes stroke or endocarditis independent of MR and AF is unclear.
Most patients with mitral valve prolapse are asymptomatic. Some experience nonspecific symptoms (eg, chest pain, dyspnea, palpitations, dizziness, near syncope, migraines, anxiety) thought to be due to poorly defined associated abnormalities in adrenergic signaling and sensitivity rather than to mitral valve pathology. In about one third of patients, emotional stress precipitates palpitations, which may be a symptom of benign arrhythmias (atrial premature beats, paroxysmal atrial tachycardia, ventricular premature beats, complex ventricular ectopy).
Occasionally, patients present with mitral regurgitation. Rarely, patients present with endocarditis (eg, fever, weight loss, thromboembolic phenomena) or stroke. Sudden death occurs in < 1%, most often resulting from ruptured chordae tendineae and flail mitral valve leaflets. Death due to a ventricular arrhythmia is rare.
Other physical findings associated with but not diagnostic of MVP include hypomastia, pectus excavatum, straight back syndrome, and a narrow anteroposterior chest diameter.
Typically, mitral valve prolapse causes no visible or palpable cardiac signs.
MVP alone often causes a crisp mid-systolic click as the subvalve apparatus abruptly tightens. The click is heard best with the diaphragm of the stethoscope over the left apex when the patient is in the left lateral decubitus position. MVP with MR causes a click with a late-systolic MR murmur. The click moves closer to the 1st heart sound (S1) with maneuvers that decrease left ventricle (LV) size (eg, sitting, standing, Valsalva maneuver); the same maneuvers cause an MR murmur to appear or become louder and last longer. These effects occur because decreasing LV size causes papillary muscles and chordae tendineae to pull together more centrally beneath the valve, resulting in quicker, more forceful prolapse with earlier, more severe regurgitation. Conversely, squatting or isometric handgrip delays the S1 click and shortens the MR murmur.
The systolic click may be confused with the click of congenital aortic stenosis; the latter may be distinguished because it occurs very early in systole and does not move with postural or LV volume changes. Other findings include a systolic honk or whoop, thought to be caused by valvular leaflet vibration; these findings are usually transient and may vary with respiratory phase. An early diastolic opening snap caused by return of the prolapsed valve to its normal position is rarely heard. In some patients, especially children, the findings of MVP may be more noticeable after exertion.
Diagnosis of mitral valve prolapse is suggested clinically and confirmed by echocardiography. Thickened (≥ 5 mm), redundant mitral valve leaflets are thought to indicate more extensive myxomatous degeneration and greater risk of endocarditis and mitral regurgitation.
Mitral valve prolapse is usually benign, but severe myxomatous degeneration of the valve can lead to MR. In patients with severe MR, incidence of LV or left atrium enlargement, arrhythmias (eg, AF), infective endocarditis, stroke, need for valve replacement, and death is about 2 to 4%/year. Men are less likely to have MVP, but those who do are more likely to progress to severe MR.
Mitral valve prolapse does not usually require treatment.
Beta-blockers may be used to relieve symptoms of excess sympathetic tone (eg, palpitations, migraines, dizziness) and to reduce risk of tachyarrhythmias, although no data support this practice. A typical regimen is atenolol 25 to 50 mg orally once a day or propranolol 20 to 40 mg orally twice a day.
Treatment of AF may be required.
Treatment of MR depends on severity and associated left atrial and LV changes.
Antibiotic prophylaxis against endocarditis is no longer recommended. Anticoagulants to prevent thromboembolism are recommended only for patients with AF or prior transient ischemic attack or stroke.
Mitral valve prolapse is most often caused by idiopathic myxomatous degeneration of the mitral valve and chordae tendineae.
Mitral regurgitation (MR) is the most common complication.
Heart sounds often include a sharp, mid-systolic click that occurs earlier with the Valsalva maneuver.
Prognosis is usually benign unless MR develops, in which case there is increased risk of heart failure, atrial fibrillation, stroke, and infective endocarditis.
Treatment is not needed unless significant MR develops.