Effects of sodium nitroprusside and phenylephrine on coronary dynamics in patients with normal left ventricular function.

Abstract

The effects of sodium nitroprusside alone and in combination with phenylephrine were studied during cardiac catheterization in 10 patients with normal left ventricular function. Nitroprusside was infused to reduce mean arterial pressure in 5 patients with the heart rate free (group 1) and in 5 with the heart rate fixed by atrial pacing (group 2). In group 1 nitroprusside increased heart rate and reduced left ventricular filling pressure and stroke volume. Mean coronary sinus flow increased from 168-187 ml/min; mean myocardial O2 extraction fell from 65-58%. Mean myocardial O2-consumption was unchanged. In group 2 nitroprusside reduced left ventricular filling pressure and stroke volume. Mean coronary sinus flow fell from 154-121 ml/min while myocardial O2 extraction remained unchanged. Mean myocardial O2 consumption fell from 17-13 ml/min. Phenylephrine restored mean arterial pressure with associated bradycardia in group 1. Left ventricular filling pressure and stroke volume were restored in both groups. In group 1 phenylephrine produced no further changes in mean coronary sinus flow or myocardial O2 extraction. In group 2 phenylephrine increased mean coronary sinus flow from 121-173 ml/min and increased mean myocardial O2 consumption from 13-19 ml/min, myocardial O2 extraction remaining constant. Nitroprusside is a coronary vasodilator but this action may be counteracted by changes in heart rate or afterload.