Effects of ischemia on myocardial function during rapid left ventricular pacing

Coronary artery disease is often accompanied with deterioration in left ventricular function. Left ventricular pacing has been shown to improve cardiac function in chronic heart failure. However, data are limited about left ventricular pacing during acute ischemia. Therefore, we studied the effects of acute myocardial ischemia on myocardial function during left ventricular pacing.

In 8 anesthetized dogs, the left ventricle was rapidly paced (180 bpm) from a basolateral and apicoseptal site during normal perfusion and mild and severe ischemia of the left anterior descending coronary artery. Effects on myocardial function were measured at each level of ischemia before and during pacing.

Significant differences (p < 0.05) between basolateral and apicoseptal pacing were found for segmental shortening (12.1+/-1.6 vs. 10.8+/-1.6%), and QRS duration (77.3+/-4.1 vs. 85.7+/-3.8 ms) at normal coronary perfusion. During mild ischemia, significant differences (p < 0.05) were seen for myocardial contractility dP/dt(max) (1277+/-197 vs. 1158+/-156 mm Hg/s), segmental shortening (10.3+/-1.9 vs. 8.1+/-1.7%), left ventricular end-systolic pressure (76.9+/-7.5 vs. 69.6+/-7.9 mm Hg), and QRS duration, and for myocardial contractility dP/dt(max) (1033+/-209 vs. 917+/-207 mm Hg/s) and left ventricular end-systolic pressure (69.2+/-13.5 vs. 62.2+/-15.0 mm Hg) during severe ischemia. There were no significant differences in coronary blood flow during pacing from both sites.

During acute myocardial ischemia, depression of left ventricular function was lowest, when pacing from a left ventricular basolateral site. The effects of rapid left ventricular pacing were amplified by reduced coronary perfusion pressures. The choice of pacing site did not relevantly influence coronary blood flow.