The pressure events of the cardiac cycle in the dog: Mitral valve lesions

Abstract

1. 1. Simultaneous pressure pulses from the left atrium, left ventricle, and aorta were recorded from 39 dogs with acutely produced isolated mitral stenosis, isolated mitral insufficiency, and combined mitral stenosis and insufficiency. 2. 2. Isolated mitral insufficiency was characterized by increased prominence of the v wave and widening of the pulse pressure of the left atrial curve. The slope of the isometric contraction phase of the left ventricle did not change appreciably until myocardial depression and shock ensued. 3. 3. In mitral stenosis, magnification of the a wave of left atrial contraction occurred. An elevated atrioventricular pressure gradient appeared during the filling phase of the left ventricle. The end-diastolic pressure of the left ventricle fell in response to the acute restriction of mitral flow. 4. 4. The acute superimposition of mitral stenosis on pre-existing mitral insufficiency markedly narrowed the left atrial pulse pressure and obscured the prominence of the late systolic v wave seen in isolated mitral insufficiency. 5. 5. The mechanism of opening and closure of the mitral valves was discussed and an explanation offered for the accentuated first sound and opening snap found in mitral stenosis. 6. 6. Aortic compression in a dog with mitral insufficiency caused a far greater rise in left atrial pressure than in a normal dog.