MITRAL VALVE PROLAPSE
Mitral valve prolapse is classically characterized by a mid-systolic click, with or without a late apical sys-tolic murmur on auscultation. It is a relatively com-mon abnormality that is present in up to 1% to 2.5% of the general population. The diagnosis is based on auscultatory findings and is confirmed by echocar-diography, which shows systolic prolapse of mitral valve leaflets into the left atrium. Patients with the murmur often have some element of mitral regurgi-tation. The posterior mitral leaflet is more commonly affected than the anterior leaflet. The mitral annulus may also be dilated. Pathologically, most patients have redundancy or some myxomatous degenera-tion of the valve leaflets. Most cases of mitral valve prolapse are sporadic or familial, affecting otherwise normal persons. A high incidence of mitral valve prolapse is found in patients with connective tissue disorders (particularly Marfan syndrome).
The overwhelming majority of patients with mitral valve prolapse are asymptomatic, but in a small percentage of patients, the myxomatous degen-eration is progressive. Manifestations, when they occur, can include chest pains, arrhythmias, embolic events, florid mitral regurgitation, infective endocar-ditis, and, rarely, sudden death. The diagnosis can be made preoperatively by auscultation of the charac-teristic click, but must be confirmed by echocardiog-raphy. The prolapse is accentuated by maneuvers that decrease ventricular volume (preload). Both atrial and ventricular arrhythmias are common. Although bradyarrhythmias have been reported, paroxysmal supraventricular tachycardia is the most commonly encountered sustained arrhythmia. An increased incidence of abnormal AV bypass tracts is reported in patients with mitral valve prolapse.
Most patients have a normal life span. About 15% develop progressive mitral regurgitation. A smaller percentage develops embolic phenomena or infective endocarditis. Patients with both a click and a systolic murmur seem to be at greater risk of developing complications. Anticoagulation or anti-platelet agents may be used for patients with a his-tory of emboli, whereas β-adrenergic blocking drugs are commonly used for arrhythmias.
The management of these patients is based on their clinical course. Most patients are asymptomatic and do not require special care. Ventricular arrhyth-mias may occur intraoperatively, particularly fol-lowing sympathetic stimulation, and will generally respond to lidocaine or β-adrenergic blocking agents. Mitral regurgitation caused by prolapse is generally exacerbated by decreases in ventricular size. Hypovolemia and factors that increase ven-tricular emptying or decrease afterload should be avoided. Vasopressors with pure α-adrenergic agonist activity (such as phenylephrine) may be preferable to those that are primarily β-adrenergic agonists (ephedrine).
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