Background: The aim of this study was to compare the protective effects of continuous warm blood cardioplegia (CWBC) and intermittent warm blood cardioplegia (IWBC) in an experimental model of blood-perfused, isolated rabbit heart.
Methods: In the CWBC group, cardiac arrest was induced by continuous infusion of blood cardioplegia (10 mEq/L KCl) followed by 30 minutes of reperfusion with blood. In the IWBC group, after 5 minutes of perfusion with blood cardioplegia (10 mEq/L KCl), coronary flow was abolished for 10 minutes, followed by reperfusion with blood cardioplegia for 5 minutes. This sequence was repeated three times for a total period of 45 minutes. Finally the hearts were reperfused for 30 minutes with blood.
Results: Infusion of potassium induced a marked increase in coronary perfusion pressure (from 50 +/- 3 to 98 +/- 1 mm Hg; p < 0.01), which remained elevated throughout in the CWBC group, whereas in the IWBC group, it dropped to 0 during each no-flow period. In both groups, cardioplegia resulted in a significant reduction in oxygen consumption (from 5.5 +/- 0.2 to 0.6 +/- 0.03 mL O2.min-1.100 g-1 wet wt; p < 0.01). During CWBC, glucose extraction was significantly reduced (from 152 +/- 10 to 64 +/- 18 micrograms.min-1.g-1 wet wt; p < 0.01). Free fatty acid uptake and creatine kinase and lactate release were not affected. During IWBC, in contrast, a transient but significant release of creatine kinase (from 643 +/- 254 to 2,234 +/- 296 mU.min-1.g-1 wet wt; p < 0.01) and lactate (from 63 +/- 22 to 374 +/- 32 micrograms.min-1.g-1 wet wt; p < 0.01) occurred after each period of ischemia. Despite these metabolic differences, both cardioplegic procedures allowed a prompt and complete recovery of mechanical function and tissue content of high-energy phosphates.
Conclusions: Both CWBC and IWBC exert optimal protection in the isolated blood perfused rabbit heart. Thus, IWBC can be safely used to improve visualization of the surgical field.