Pacing within the Ischemic Area Significantly Decreases the Left Ventricular Ejection Fraction during Experimental Acute Myocardial Infarction

Methods: In 12 anesthetized pigs, epicardial LV pacing at the apex or lateral wall, or at both sites simultaneously, was performed before and after left anterior descending (LAD) ligation. Data concerning LV function were obtained by two-dimensional echo during spontaneous sinus rhythm (SR) and during pacing before and 15, 45, 60, and 90 minutes after LAD ligation. Results: Before ligation of the LAD, pacing at the lateral wall (48.04 +/- 6.25%) or both sites (45.71 +/- 6.31%) reduced the LV ejection fraction (EF) significantly (P < 0.01) in comparison to SR (55.44 +/- 4.10%). However, during pacing at the apex (50.19 +/- 6.50%), the reduction was not significant. After LAD ligation, the EF during lateral pacing (43.02 +/- 7.71%) was significantly higher than during apical pacing (38.78 +/- 8.26%, P < 0.04) but was not significantly different from that during dual-site pacing (41.65 +/- 8.69%). Conclusions: Pacing within the ischemic LV apical zone after LAD ligation impairs left ventricular ejection fraction, as compared with pacing the nonischemic LV lateral wall, and should therefore be avoided in clinical settings where the LV pacing site may be chosen. (PACE 2011; 63-71).