Normothermic cardioplegia prevents intracellular calcium accumulation during cardioplegic arrest and reperfusion

Development of intracellular calcium overloading is to be a primary factor in cellular injury during myocardial reperfusion. We studied the effects of different temperatures during continuously perfused cardioplegic arrest on the changes of intracellular calcium concentration ([Ca2+]i) level in isolated rat hearts. Rat hearts were perfused by the Langendorff technique with Krebs-Henseleit bicarbonate (KHB) buffer. The [Ca2+]i was monitored by loading the heart with fura-2 acetoxymethyl ester and by using a [Ca2+]i analyzer. [Ca2+]i was calculated by determining the maximal and minimal fluorescent intensity for each heart. The hearts (n = 6 in each group) were subjected to cardioplegic arrest by continuous perfusion of oxygenated crystalloid K+ (15 mEq/L) cardioplegic solution (CPS) at different temperatures (4 degrees C, 20 degrees C, 28 degrees C, 37 degrees C) for 120 minutes, followed by 30 minutes of normothermic KHB buffer reperfusion. A fifth group received continuous perfusion as a control with 37 degrees C KHB buffer. The baseline values of [Ca2+]i were comparable in all experimental groups. In hearts perfused with 4 degrees C CPS, [Ca2+]i increased significantly during reperfusion (from 221 +/- 24 nmol/L [mean +/- SEM] at baseline to 341 +/- 19 at the end of reperfusion, P < .05). CPS perfusion at 20 degrees C also induced significant Ca2+ overloading during reperfusion, but not as much as in the 4 degrees C group. No significant [Ca2+]i increase occurred at 28 degrees C or 37 degrees C. Continuous cardioplegic perfusion at lower temperatures (ie, 4 degrees C or 20 degrees C) induces Ca2+ overloading during reperfusion, which is detrimental to the optimal recovery of ventricular performance, while normothermic cardioplegic perfusion prevents the development of Ca2+ accumulation. These results provide experimental evidence for a detrimental effect of prolonged hypothermic continuous cardioplegia.