Comparison of intermittent warm and cold blood perfusion during hypothermic myocardial preservation on functional and metabolic recovery

Numerous techniques are used to maintain intraoperative heart viability. Th e studies presented here evaluated heart function and metabolism after Vari ous periods of preservation up to 4 hours with intermittent warm and cold b lood perfusion. Using a heterotopic heart model cooled to 10 degreesC and m aintained for 1, 2, 3, and 4 hours, various preservation techniques were co mpared. Changes in myocardial metabolism were determined from substrate upt akes and biopsy samples of the left ventricular muscle for high-energy phos phates. Preservation techniques included: (1) sustained hypothermia, (2) 1 or 2 hours of sustained warm blood perfusion with fibrillation, (3) intermi ttent cold blood perfusion during 2, 3, and 4 hours of preservation, (4) in termittent warm blood perfusion during 2, 3, and 4 hours of preservation an d (5) a control group (no preservation). Normothermic fibrillation had no e ffect on postpreservation functional or metabolic parameters. Sustained hyp othermia reduced functional recovery proportional to the length of ischemia . The cold intermittent procedures maintained function and metabolism bette r than sustained hypothermia, while warm intermittent preservation maintain ed function and metabolism at control levels throughout the recovery period for all preservation techniques. Changes in ATP mirrored the functional ch anges. Creatine phosphate (CP) was markedly reduced during heart isolation and preservation and exceeded the control by 100% during reperfusion. For o perative procedures of 2 hours or less, functional and metabolic recovery w as not affected by the various preservation methods applied. Warm intermitt ent perfusion during hypothermic preservation offered the best protection f or the myocardium. The warming cycles during hypothermia may provide some d egree of preconditioning and protect the myocardium during reperfusion.