Beneficial effects of potassium cardioplegia during intermittent aortic cross-clamping and reperfusion

Aortic cross-clamping is an essential adjunct to a variety of cardiac surgical procedures requiring a quiet flaccid heart and avoidance of systemic air embolism. The consequences of excluding the heart from perfusion, oxygen, and substrate are time dependent and lead ultimately to irreversible damage of the myocardium. The goal of complete preservation of myocardial function and metabolism during ischemia has not been realized even with the best clinically applicable techniques. The present study was designed to evaluate the effects of sequential aortic cross-clamping interrupted by reperfusion similar to that used in clinical practice. The advantages of induced cardiac arrest with potassium chloride solution at the onset of aortic cross-clamping were assessed in a second group of animals. A total of 27 mongrel dogs supported by normothermic cardiopulmonary bypass was subjected to four aortic cross-clamp periods interrupted by 5-min reper-fusion periods. The study included an evaluation of left ventricular performance using an isovolumic balloon technique and an assessment of myocardial metabolism using “stop-freeze” biopsies and biochemical assay for ATP, ADP, AMP, and creatine phosphate. The data demonstrate that repeated induction of ischemic arrest results in profound depletion of adenine nucleo-tides and severe depression of contractility. Using potassium-induced cardiac arrest, normal contractile function is preserved along with conservation of adenine nucleo-tides, suggesting that even at normothermia, preservation of the heart during ischemia can be achieved.