To determine if the addition of
potassium enhances the myocardial protective effect of intracoronary perfusion
hypothermia during aortic cross-clamping, 50 patients undergoing
aortocoronary bypass grafting were studied in a randomized, prospective, double-blind fashion. Twenty-six patients received a cold
crystalloid solution infused with a handheld syringe into the root of the cross-clamped aorta every 20 minutes, and 24 patients received the same
solution but with 25 mEq/L of
potassium chloride added, infused in a similar manner. Both groups were analyzed by mortality, rate of perioperative
myocardial infarction (electrocardiographic changes, MB-CPK
enzyme release, and preoperative and postoperative gated cardiac blood pool scans), intraoperative hemodynamic changes, intraoperative
lactate determinations, postoperative arrhythmias, and requirement for pressor or intraaortic balloon pump support. One patient in the
potassium cardioplegia group died (massive
pulmonary embolism), and none in the hypothermic perfusion group died. Possible perioperative
myocardial infarction was diagnosed by more than one marker in 4 of 26 patients in the hypothermic perfusion group and 5 of 24 patients in the
potassium group (p = 0.61). There were no differences between the two groups in terms of hemodynamic changes,
lactate production, postoperative arrhythmias, or the need for postoperative hemodynamic support. This study in human beings could not demonstrate a specific protective effect of
potassium, beyond that afforded by myocardial perfusion
hypothermia and wash-out. The data suggest that myocardial
hypothermia, achieved through cold intracoronary arterial perfusion, may be the most important beneficial component of so-called
cardioplegia for attaining effective intraoperative myocardial preservation in human beings.