Comparative myocardial protection with calcium-free versus calcium-containing potassium cardioplegic solutions

The present study was designed to determine if the addition of calcium to a potassium cardioplegic solution results in improved myocardial protection during ischemic arrest. An isolated perfused cat heart preparation was used. Hearts were made ischemic for 60 min and then reperfused for 45 min. Four groups were studied with the myocardial temperature during ischemia being maintained at 37°C in one and at 27°C in the remaining three groups. Two of these latter three groups received cardioplegic solutions while one remaining hypothermic group served as a hypothermic control. The cardioplegic solutions differed in that one was a calcium-free moderately hyperkalemic solution while the other contained 2 mM calcium, 16 mM magnesium, and 1 mM procaine in addition to being moderately hyperkalemic. Myocardial gas tensions were monitored by mass spectrometry and isovolumic ventricular function assessed by developed pressure and maximum dP/dt. Hypothermia alone resulted in significantly better recovery of ventricular function than normothermic ischemia. Recovery was further enhanced by the addition of cardioplegia. The best return of left ventricular function was seen in the group which had received the calcium-free cardioplegic solution and this group also developed the least myocardial edema following reperfusion. This study demonstrates that the omission of calcium as well as magnesium and procaine, from a cardioplegic solution, rather than being hazardous, may in fact be beneficial.