Influence of systemic hypothermia on systolic and diastolic functionalrecovery after continuous warm antegrade blood cardioplegia

Experimental observations in our laboratory indicate that myocardialrecovery is similar following warm or cold antegrade blood cardioplegiawhen the core temperature is maintained at 37 degrees C. To determine theeffects of hypothermia on myocardial recovery, 15 adult mongrel dogs wererandomized to normothermic or hypothermic bypass (28 degrees C) during 60min of continuous warm antegrade blood cardioplegia. The hypothermic groupwas rewarmed after releasing the aortic cross-clamp and bypass wasdiscontinued at 30 min in both groups. Myocardial recovery was assessed at60, 90, and 120 min after the arrest. Core temperature was maintained inthe normothermic group but gradually decreased after bypass in thehypothermic group, reaching a low of 33.8 +/− 1 degrees C at 120 min.Myocardial functional recovery was preserved after normothermic bypass. Thedecrease in core temperature, however, that was observed after systemichypothermia, was paralleled by significant decreases in the maximum rate ofleft ventricular pressure rise (dp/dt), the maximum elastance of the leftventricle, and preload recruitable stroke work. Diastolic functiondecreased slightly, but not significantly, during reperfusion followingsystemic hypothermia but was unaltered after normothermic bypass.Myocardial oxygen consumption was unchanged in both groups. Myocardialultrastructure was preserved after normothermic bypass. In contrast, cellular oedema and mild ultrastructural changes were evident aftersystemic hypothermia. We therefore conclude that the use of systemichypothermia during bypass is associated with lower core temperatures duringearly recovery which results in impaired functional recovery.