Effect of propranolol on left ventricular work in aortic stenosis.

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Abstract
The changes in left ventricular work produced by propranolol were measured in 6 patients with severe aortic stenosis. Left ventricular volume was obtained by thermodilution using a thermocouple with a fast response. Possible errors in the therm odilution method are discussed. A significant reduction in heart rate and cardiac output was found after propranolol, and the mean ventricular ejection was reduced. There was a significant increase in the thermodilution ratio, indicating an increase in left ventricular end-diastolic volume, and left ventricular end-diastolic pressure tended to rise after propranolol. Force-time per min. was selected as the best index of left ventricular work as it is sensitive to changes in ventricular volume and in the duration of systole. By this criterion there was no change in left ventricular work after propranolol. The mean circumferential shortening rate was consistently reduced, and this change probably leads to a lower myocardial O2 consumption. The primary effect of propranolol is to reduce the velocity of myocardial contraction. The fall in cardiac output and the increase in left ventricular end-diastolic volume and pressure after propranolol in these patients indicate that sympathetic nervous activity plays an important part in the response of the left ventricle to aortic stenosis.