Mechanical unloading and infarct size: studies with the heterotopically transplanted rabbit heart

The possibility that unloading the heart during regional ischemia and/or reperfusion may limit infarct size was investigated by inducing regional ischemia in both a heterotopically transplanted heart (unloaded) and the recipient's heart (loaded control). In this way, the extent of myocardial infarction was compared in paired hearts in the same animal under similar experimental conditions. Hearts excised from donor rabbits, were arrested with St. Thomas' Hospital cardioplegic solution and maintained at 15 degrees C for 1 hour during which time they were transplanted into the necks of recipient rabbits. 24 hours later, rabbits were reanesthetized and the left circumflex coronary artery ligated in both the transplanted and the recipient's hearts. After 1 hour of regional ischemia hearts were reperfused for 3 hours. The transplanted heart was paced at 205 beats per minute (bpm) throughout the experiment. Similar values for infarct size were obtained in both the loaded and unloaded hearts (73 +/- 4% vs 75 +/- 6%, respectively). No significant differences were seen in any other parameters. In conclusion, our results suggest that during regional ischemia the amount of work performed by the heart does not appear to be a major factor in determining the ultimate size of an infarct.