Abstract
Recent research on myocardial preservation has emphasized the importance of events occurring early in the reperfusion period, which may be of less importance to myocardial outcome in the neonate. We therefore wished to study the contribution of prolonged postischemic perfusion. This situation may occur during repair of congenital heart defects when in an attempt to reduce the period of aortic cross-clamp, the surgeon completes right-sided repairs on a beating empty heart. We used an isolated working rabbit heart model to compare recovery after various periods of ischemia and postischemic perfusion. After 30 min in the working heart mode, hemodynamic measurements were made. The hearts were then rendered globally ischemie, with the exception of cardioplegia. At the conclusion of the ischemic period, the hearts were returned to the 37°C chamber, and reperfused with buffer. After 30 or 60 min retrograde perfusion, the hearts were converted to the working mode again. The working heart period continued until the heart was no longer able to overcome its afterload ("pump failure"). We recorded the time to this point as survival time. Hearts were divided into four groups: Group I (n = 12), 60 min ischemia, 30 min nonworking perfusion; Group II (n = 11), 90 min ischemia, 30 min nonworking perfusion; Group III (n = 8), 60 min ischemia, 60 min nonworking perfusion; and Group IV (n = 11), 0 min ischemia, 130 min nonworking perfusion. Multivariate analysis showed that four factors influenced survival time: aortic flow, age, left ventricular end-diastolic pressure, and mean aortic pressure. Group II did not vary significantly from Group I, Group III had much shorter survival times and Group IV even poorer survival. Water content did not differ significantly in any group. Our data show a clear disadvantage associated with prolonged postischemic perfusion in the nonworking mode. Recovery is adversely affected much more by increased reperfusion time than by increased cold ischemic time. Thus, not only the early reperfusion period and the composition of the reperfusate, but the duration of the postischemic nonworking perfusion period plays a crucial role in the recovery of neonatal myocardium after an ischemic challenge.
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