The advantages of normocalcemic continuous warm cardioplegia over low calcemic cardioplegia in myocardial protection.

The effects of changing the calcium content of a continuous warm hyperkalemic crystalloid cardioplegia (CWCP) were investigated in an isolated rat heart preparation. The hearts were divided into eight groups of six each. A control group consisted of fresh nonarrested hearts and the remaining seven groups consisted of hearts perfused with continuous hyperkalemic (20 mM) modified Krebs-Henseleit bicarbonate buffer solution with calcium concentrations of 0.1, 0.3, 0.5, 1.0, 1.5, 2.0, or 2.5 mM, for either 180 or 240 min at 37 degrees C. In the hearts arrested for 180 min, there were no significant differences in postarrest cardiac functions between the control group and any of the groups perfused with calcium concentrations of 0.5 mM or more. With a calcium concentration of 0.1 mM, the calcium paradox was provoked. The change in the calcium content of CWCP perfused for 240 min significantly affected myocardial protection. Maximum aortic flow recovery, of 74.7% +/- 2.7%, and minimum CK release, of 15.7 +/- 2.4 IU/15 min/g dry weight, were observed in hearts perfused with a calcium concentration of 1.5 mM. The calcium paradox occurred even at a calcium concentration of 0.3 mM; therefore, normal calcium concentrations should be maintained in cardiac surgery to prevent cardiac injury.