Contractile reserve is maintained during the negative inotropy of coronary arteriography.

Contractile reserve was followed throughout the hemodynamic response to coronary arteriography by measuring the post-etrasystolic potentiation every tenth beat following the injection of 3 ml of Renografin-76 into the left coronary arteries of anesthetized dogs. During sinus beats, both systolic pressure and +dP/dt exhibited the usual biphasic response of negative inotropy for 5-8 seconds, followed by a rebound increase in contractility. However, the myocardium retained the ability to increase contractility following a precisely timed extrasystole. The pattern of hemodynamic response to ionic contrast agents is similar to the response of other interventions that decrease calcium inflow to the myocardial cell. Based upon differences in the electrophysiologic effects of ionic contrast agents, we speculate that excess sodium and meglumine transiently compete with calcium for external binding sites that supply calcium necessary for excitation-contraction coupling.