A Comparison of Intermittent and Continuous Arrest for Prolonged Hypothermic Cardioplegia

A study was carried out to evaluate the best method of myocardial preservation in the pig-heart model. Two techniques for employing hypothermic potassium cardioplegia during prolonged ischemic arrest were compared. One entailed three one-hour periods of arrest interrupted with 30-minute intervals of reperfusion (intermittent arrest), and the other involved a single period of continuous hypothermic cardioplegic arrest (continuous arrest) of three hours' duration. In order to evaluate intermittent versus continuous cardioplegic arrest, prearrest and postarrest contractility, compliance, myocardial perfusion, and left ventricular adenosine triphosphate (ATP) and creatine phosphate (CP) levels were compared in 28 animals.The results show significant deterioration in myocardial contractility and compliance following three-hour cardioplegic arrest whether the arrest was intermittent or continuous. However, there were significant differences between the two groups studied. The animal having continuous arrest had less functional impairment than the animal having intermittent arrest. Myocardial perfusion 30 minutes following continuous arrest returned to prearrest levels whereas there was significant depression in perfusion in the group with intermittent arrest. This represented severe coronary vasoconstriction. The ATP level after completion of arrest is significantly higher in the group having continuous arrest and remains higher throughout the final reperfusion period.On the basis of these studies, it is thought that intermittent reperfusion may lead to a reperfusion injury, which is primarily reflected in decreased perfusion, contractility, and compliance. While hypothermic potassium cardioplegia does not optimally protect the myocardium during prolonged (three hour) ischemic arrest, the alternative of intermittent arrest provides poorer myocardial preservation.