Preconditioning improves cardiac function after global ischemia, but not after cold cardioplegia

Background. Ischemic preconditioning reduces infarct size and cardiac dysfunction during reperfusion. Preconditioning may offer myocardial protection in open heart operations. Methods. The effect of preconditioning before ischemia and cardioplegia was investigated in Langendorff-perfused rat hearts in the following groups. First, group 1 received two episodes of 3-minute ischemia and 5-minute reperfusion before 25 minutes of global (37 degrees C) ischemia and 60 minutes of reperfusion. Group 2 served as ischemic controls to group 1. Groups 3, 5, and 7 were preconditioned as described, before 3.5, 4, or 5 hours of cold (6 degrees to 8 degrees C) St. Thomas' II cardioplegia and 1 hour of reperfusion (37 degrees C). Groups 4, 6, and 8 were cardioplegic controls to groups 3, 5, and 7 (n = 17 in groups 1 and 2, and n = 10 in groups 3 to 8). Results. Preconditioning before warm ischemia attenuated the ischemia-induced increase of left ventricular end-diastolic pressure (3 +/- 1 versus 17 +/- 4 mm Hg: p < 0.01) (mean +/- standard error of the mean), the reduction of coronary flow (14 +/- 1 versus 9 +/- 0.5 mL/min; p < 0.001) and heart rate (252 +/- 19 versus 198 +/- 18 beats/min; p < 0.04), and the incidence of ventricular fibrillation (2 of 17 versus 10 of 17 hearts; p < 0.04) at the start of reperfusion. However, preconditioning did not influence postischemic cardiac function or the release of lactate dehydrogenase in any of the cardioplegia groups. Conclusions. Ischemic preconditioning improved postischemic cardiac function after warm global ischemia, but did not protect cold cardioplegic hearts, perhaps because of the time span used.