Abstract
Experimental observations in our laboratory indicate that myocardial recovery is similar following warm or cold antegrade blood cardioplegia when the core temperature is maintained at 37 degrees C. To determine the effects of hypothermia on myocardial recovery, 15 adult mongrel dogs were randomized to normothermic or hypothermic bypass (28 degrees C) during 60 min of continuous warm antegrade blood cardioplegia. The hypothermic group was rewarmed after releasing the aortic cross-clamp and bypass was discontinued at 30 min in both groups. Myocardial recovery was assessed at 60, 90, and 120 min after the arrest. Core temperature was maintained in the normothermic group but gradually decreased after bypass in the hypothermic group, reaching a low of 33.8 +/- 1 degrees C at 120 min. Myocardial functional recovery was preserved after normothermic bypass. The decrease in core temperature, however, that was observed after systemic hypothermia, was paralleled by significant decreases in the maximum rate of left ventricular pressure rise (dp/dt), the maximum elastance of the left ventricle, and preload recruitable stroke work. Diastolic function decreased slightly, but not significantly, during reperfusion following systemic hypothermia but was unaltered after normothermic bypass. Myocardial oxygen consumption was unchanged in both groups. Myocardial ultrastructure was preserved after normothermic bypass. In contrast, cellular oedema and mild ultrastructural changes were evident after systemic hypothermia. We therefore conclude that the use of systemic hypothermia during bypass is associated with lower core temperatures during early recovery which results in impaired functional recovery.