Effect of varying ventricular function by extrasystolic potentiation on closure of the mitral valve.

Abstract Mitral regurgitant indexes were measured by roentgen videodensitometry in anesthetized dogs without thoracotomy before, during and after extrasystolic potentiation of ventricular contraction while the atria and ventricles were driven in normal temporal sequence simultaneously or in such a way as to induce atrial fibrillation. Small amounts of mitral reflux were observed with simultaneous atrial and ventricular driving and with atrial fibrillation in the control measurements before initiation of extrasystolic potentiation. Reflux became negligible during extrasystolic potentiation and increased beyond control levels after termination of extrasystolic potentiation. The amounts of reflux could be related to variations in ventricular function before, during and after extrasystolic potentiation. When reflux was observed with simultaneous atrial and ventricular driving or atrial fibrillation, it occurred at the onset of systole. It was probably determined by the size of the ventricle before the onset of systole, the inotropic state and the rate of pressure development in the ventricle during systole. During extrasystolic potentiation of ventricular contraction, reflux was negligible and independent of the mode of atrial driving.

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