Ischemic preconditioning and myocardial hypothermia in rabbits with prolonged coronary artery occlusion

This study tests whether combining regional hypothermia and ischemic preconditioning (IP) provides greater myocardial protection during prolonged coronary artery occlusion (CAO) than either intervention alone, and whether increasing the duration of IP from 5 to 7 min extends the window of protection to include a 2-h CAO. Anesthetized rabbits were randomized to four groups (n = 8 rabbits/group): control (C), hypothermia alone (H), IP alone for two 7-min episodes (IP7), and IP plus hypothermia (H + IP7). To compare differences in IP for 5 versus 7 min, additional rabbits (n = 6) received one 5-min episode of ischemia (IP5). All rabbits got 2 h of CAO and 3 h of reperfusion. In comparison with the infarct size in the control group (72 +/- 4% of the risk zone), infarct size was significantly reduced in H (50 +/- 7%), IP7 (49 +/- 5%), and H + IP7 (42 +/- 6%) (all P < 0.05 vs. control group). IP5 failed to confer protection (67 +/- 5% of the risk zone). Therefore, IP can protect against a 2-h CAO if the IP regimen is increased from 5 to 7 min. The combination therapy significantly improved regional myocardial blood flow in the previously ischemic region to a greater extent than either treatment alone.