Effects of electrical pacing to the preischemic rate during rewarming after hypothermic ischemia in the rat heart.

The effects of electrical pacing during the early reperfusion following hypothermic global ischemia (60 min, at 25 degrees C) was studied in the isolated working rat heart model. The hearts were divided into three groups. Hearts in Group I (n = 8) were control without hypothermia, ischemia or pacing. Hearts in Group II (n = 16) were paced with ventricular rate at 300 beats/min with 1 mVolt for 10 min during the Langendorff mode after an initial 5 min of reperfusion. Hearts in Group III (n = 14) were not paced. The recovery of aortic flow (both absolute and percent) was significantly better in Group II than in Group III, but was significantly lower in both groups than in control. No significant differences were noted, however, in heart rate, aortic pressure or coronary flow between Group II and III. In contrast, the tissue concentration of adenosine triphosphate (ATP) in Groups II and III decreased significantly by the end of reperfusion relative to Group I, but no difference in ATP existed between Group II and III. Myocardial ATP concentrations did not correlate with percent recovery of aortic flow. The myocardial concentration of calcium in Groups II and III increased by the end of reperfusion as compared with Group I, but no difference in calcium existed between Group II and III. The myocardial concentration of calcium demonstrated a significant correlation with percent recovery of aortic flow (r = 0.71, n = 30, p < 0.005). Our results indicate that an electrical pacing during early reperfusion in the myocardium improves functional recovery of aortic flow.