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 p rotection in open heart operations. Methods. The effect of preconditio ning before ischemia and cardioplegia was investigated in Langendorff- perfused rat hearts in the following groups. First, group 1 received t wo episodes of 3-minute ischemia and 5-minute reperfusion before 25 mi nutes 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 we re preconditioned as described, before 3.5, 4, or 5 hours of cold (6 d egrees to 8 degrees C) St. Thomas' II cardioplegia and 1 hour of reper fusion (37 degrees C). Groups 4, 6, and 8 were cardioplegic controls t o 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 i schemia-induced increase of left ventricular end-diastolic pressure (3 +/- 1 versus 17 +/- 4 mm Hg: p < 0.01) (mean +/- standard error of th e 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 ve rsus 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. C onclusions. Ischemic preconditioning improved postischemic cardiac fun ction after warm global ischemia, but did not protect cold cardioplegi c hearts, perhaps because of the time span used.