Mechanism of Production of Midsystolic Click in a Prolapsed Mitral Valve

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Abstract
To examine the production mechanism of the midsystolic click in cases of a midsystolic click and a late systolic murmur, the relationship between the click and motion of the mitral apparatus was studied [in a patient] by ultrasono-cardiotomography and the simultaneous recording of phonocardiograms and ultrasono-cardiograms. The systolic click occurred in exact coincidence with the time at which the hump of the echo of the unusual early systolic anterior motion (early SAM) took its backmost position. This coincidence was found when the click was shifted either by postural changes or inhalation of amyl nitrite. The echo source of the early SAM could be attributed to the protrusion into the left ventricular outflow tract of the slakened elongated chordae tendineae in systole. The anterior leaflet moved suddenly to the position of maximal prolapse when the slakened chordae tendineae were stretched taut in midsystole. The midsystolic click occurred when the anterior leaflet prolapsed and the tension exerted on the chordae tendineae was at its maximum.