Effects of pacing location on coronary circulation in dogs.

Abstract

In 13 open-chest dogs, the right atrium and various ventricular sites (i.e., the inflow and outflow tracts and apex of the right ventricle, apex and lateral wall of the left ventricle) were stimulated electrically at a given rate, ranging from 140-210/min. Coronary circulation and cardiodynamics in response to ventricular pacing were compared with those to right atrial pacing at equivalent heart rate. Stimulation of the ventricle except lateral wall of the left ventricle produced no significant changes in coronary sinus blood flow and myocardial O2 consumption despite decreased blood pressure and cardiac output. The minor change of coronary sinus blood flow was related to the decrease in coronary vascular resistance. O2 content of coronary sinus blood decreased during ventricular pacing, while arterial O2 saturation remained constant. The response of coronary circulation to ventricular pacing did not differ essentially at faster and slower heart rates. When stimuli were applied to the ventricular surface, the relatively constant myocardial O2 consumption in the presence of lowered cardiac performance was attributed to the asynchrony of fractionate contractions of the ventricular muscle.