| Abstrakt: |
This study tests the hypothesis that multidose, hypocalcemic aspartate/glutamate–enriched blood cardioplegia provides safe and effective protection during prolonged aortic clamping of immature hearts. Of 17 puppies (6 to 8 weeks of age, 3 to 5 kg) placed on vented cardiopulmonary bypass, five were subjected to 60 minutes of 37° C global ischemia without cardioplegic protection and seven underwent 120 minutes of aortic clamping with 4° C multidose aspartate/glutamate–enriched blood cardioplegia ([Ca++] = 0.2 mmol/L), preceded and followed by 37° C blood cardioplegic induction and reperfusion. Five puppies underwent blood cardioplegic perfusion for 10 minutes without intervening ischemia to assess the effect of the cardioplegic solution and the delivery techniques. Left ventricular performance was assessed 30 minutes after bypass was discontinued (Starling function curves). Hearts were studied for high–energy phosphates and tissue amino acids. One hour of normothermic ischemia resulted in profound functional depression, with peak stroke work index only 43% of control (0.7 ± 0.1 versus 1.7 ± 0.2 gm × m/kg, p < 0.05). There was 70% depletion of adenosine triphosphate (7.6 ± 1 versus control 20.3 ± 1 μmol/gm dry weight, p < 0.05) and 75% glutamate loss (6.6 ± 1 versus control 26.4 ± 3 μmol/gm, p < 0.05). In contrast, after 2 hours of aortic clamping with multidose blood cardioplegia preceded and followed by 37° C blood cardioplegia, there was complete recovery of left ventricular function (peak stroke work index 1.6 ± 0.2 gm × m/kg) and maintenance of adenosine triphosphates, glutamate, and aspartate levels at or above control levels adenosine triphosphate 18 + 2 μmol/gm, aspartate 21 ± 1 versus control 2 μmol/gm, and glutamate 25.4 ± 2 μmol/gm). Puppy hearts receiving blood cardioplegic perfusion without ischemia had complete recovery of control stroke work index. We conclude that methods of myocardial protection used in adults, with amino acid–enriched, reduced-calcium blood cardioplegia, can be applied safely to the neonatal heart and allow for complete functional and metabolic recovery after prolonged aortic clamping. |
