It is unknown whether late preconditioning (PC) enhances the recovery of left ventricular (LV) function after a
myocardial infarction. Thus 25 conscious rabbits were subjected to a 30-min
coronary occlusion followed by 28 days of reperfusion after PC 24 h earlier with either
ischemia or
nitric oxide donor administration [
S-nitroso-N-acetylpenicillamine (SNAP)]. The recovery of wall thickening (WTh) after reperfusion was significantly improved in the ischemic PC and SNAP PC groups compared with controls, both at rest and during
dobutamine stress. Interestingly, neither
ischemia- nor SNAP-induced late PC attenuated
myocardial stunning from day 1 through day 14.
Infarct size was smaller in the ischemic PC and SNAP PC groups compared with controls. In all groups, WTh at 28 days was positively and linearly related to the percentage of viable tissue in the region underlying the ultrasonic crystal (r = 0.90), indicating that the improvement in LV function after both
ischemia-induced and NO donor-induced late PC can be fully explained by the reduction in
infarct size; a separate effect of late PC on LV remodeling or LV contractility need not be invoked. In conclusion, in conscious rabbits late PC, induced either by
ischemia or pharmacologically, not only limits
infarct size but also enhances the recovery of LV function after
myocardial infarction. This finding has important clinical implications and provides
triphenyltetrazolium chloride-independent evidence that late PC limits myocellular death after sustained
ischemia.