Differences in prolonged ischemia length using ischemic preconditioning in the rabbit heart. Tolerable limitation time for surgically induced myocardial ischemia during normothermic cardiac operation

BACKGROUND: To determine the effect of the tolerable limitation time of prolonged ischemia after ischemic preconditioning on postischemic functional recovery and infarct size reduction in the rabbit heart. METHODS: White rabbits (n=30) were used for Langendorff perfusion. Control hearts were perfused at 37 degrees C for 180 min; 30 min global ischemia hearts (30GI) received 30 min global ischemia and 120 min reperfusion; IPC+30GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 30 min global ischemia; 20 min global ischemia hearts (20GI) received 20 min global ischemia and 120 min reperfusion; IPC+20GI hearts received 5 min zero flow global ischemia and 5 min reperfusion prior to 20 min global ischemia. RESULTS: Infarct size in the 30GI hearts was 33.5+/-4.0% and 1.7+/-0.5% in the control hearts. The 20GI hearts and IPC+30GI hearts decreased infarct size, as compared with the 30GI hearts (13.0+/-1.8% and 16.6+/-1.7%, respectively; p<0.001, 20GI vs 30GI; p<0.01, IPC+30GI vs 30GI; p>0.05, 20GI vs IPC+30GI) but did not enhance postischemic functional recovery. The IPC+20GI hearts (3.5+/-0.6%) significantly decreased infarct size as compared with the 20GI hearts (p<0.05, IPC+20GI vs 20GI), and there was no significant difference between the IPC+20GI and the control hearts (p>0.05), but the IPC+20GI hearts did not enhance postischemic functional recovery. CONCLUSIONS: A 20 min ischemia may be the tolerable limitation time of prolonged ischemia after ischemic preconditioning in an isolated rabbit heart model.