An 18-year-old woman is referred to a cardiologist after a heart murmur is discovered during a routine checkup. The patient is healthy and has no symptoms. Medical history is unremarkable. She runs daily and wants to start actively training for a half marathon. The patient is concerned that the murmur is a sign of heart disease. She has no family history of sudden cardiac death. Auscultation reveals a midsystolic click followed by a short late-systolic murmur at the cardiac apex. The murmur disappears with squatting. This patient's condition is most likely related to an abnormality involving which of the following tissues?
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The presence of a midsystolic click followed by a systolic murmur at the cardiac apex that disappears with squatting is most consistent with mitral valve prolapse (MVP). The click is caused by sudden tensing of the chordae tendineae as they are pulled taut by the ballooning valve leaflets, and the murmur results from regurgitation of blood due to malalignment of the valve margins with prolapse.
During systole, there is a critical left ventricular (LV) size at which prolapse occurs; therefore, maneuvers that change LV end-diastolic volume affect the timing of the click and murmur. Squatting increases venous return and LV volume, increasing the tension and decreasing the slack in the mitral valve apparatus. Because the ventricular walls have farther to travel to reach the critical LV size at which prolapse occurs, prolapse occurs later in systole or not at all.
Primary MVP is most commonly a sporadic disorder and is characterized by myxomatous degeneration (ie, pathologic deterioration of the connective tissue) affecting the mitral valve leaflets and chordae tendineae. Secondary MVP is associated with inherited connective tissue disorders, including Marfan or Ehlers-Danlos syndrome and osteogenesis imperfecta.
(Choice A) Hypertrophic cardiomyopathy (HCM) presents with a systolic murmur at the left sternal border that decreases in intensity with squatting (due to increased LV volume and decreased outflow tract obstruction). A midsystolic click is not heard with HCM.
(Choice C) Coronary artery disease can cause myocardial ischemia or infarction leading to papillary muscle dysfunction and acute mitral regurgitation. In such patients, squatting from a standing position increases murmur intensity due to a higher blood volume of regurgitation. In addition, such a murmur is not preceded by a midsystolic click.
(Choice D) Endomyocardial fibrosis and endocardial fibroelastosis are disorders that affect the endocardium and are not associated with MVP.
(Choice E) Pericardial disease may infrequently result in cardiac tamponade or constrictive pericarditis. Pericarditis may produce a friction rub; however, it is not associated with a cardiac murmur.
Educational objective:
Mitral valve prolapse is most often caused by defects in connective tissue proteins that predispose to myxomatous degeneration of the mitral leaflets and chordae tendineae. Cardiac auscultation typically reveals a midsystolic click followed by a mitral regurgitation murmur; the click and murmur occur later in systole or disappear completely with maneuvers (eg, squatting) that increase left ventricular end-diastolic volume.