Effect of Four Crystalloid Cardioplegias on Immature Rabbit Hearts During Global Ischaemia

ObjectiveControversy surrounds the reported beneficial effects of crystalloid cardioplegic solutions in the immature myocardium. In the present study, we investigated the efficacy of four clinical cardioplegic solutions in the immature myocardium to determine if cardioplegic protection could be demonstrated and, if yes, the relative efficacy of the four solutions.MethodsIsolated, working hearts (n = 6 per group) from neonatal rabbits (age, 7-14 days) were perfused aerobically (37° C) for 15 minutes in the Langendorff mode and 30 minutes in the working mode before a 2- minute infusion of one of four cardioplegic solutions: the modified St. Thomas' Hospital no. 1 cardioplegic solution, Tyers solution, Bretschneider solution or Roe solution. Hearts were then rendered globally ischaemic for 120 minutes at 14° C before reperfusion for 15 minutes in the Langendorff mode and 30 minutes in the working mode. The post-ischaemic recovery of cardiac function and leakage of myocardial enzymes (GOT, CK, CK-MB, LDH, LDH1) were compared with results in noncardioplegic control hearts.ResultsGood protection was observed with modified St. Thomas' Hospital and Tyers solutions: post-ischaemic recovery of cardiac output was increased from 80.43 ± 3.62% in the noncardioplegic group to 85.19 ± 3.12% and 70.66 ± 3.48% in the St. Thomas' Hospital and Tyers groups (p < 0.05), respectively. In contrast, no obvious protection was observed with either the Bretschneider or Roe solutions: cardiac output recovered to 45.08 ± 3.16% and 30.06 ± 2.59%, respectively. Post-ischaemic CK leakage was 19.83 ± 2.14 IU/mL and 21.17 ± 2.32 IU/mL in the St. Thomas' Hospital and Tyers groups (p > 0.05). In the Bretschneider group, CK leakage increased to 30.00 ± 3.16 IU/mL (p < 0.01 vs. noncardioplegic control hearts), and in the Roe group, CK leakage was 31.00 ± 5.10 IU/mL (p < 0.05 vs. cardioplegic-free hearts). Post-ischaemic ATP was 1.98 ± 0.54 μmol/g dry weight and 1.35 ± 0.39 μmol/g dry weight in the St. Thomas' Hospital and Tyers groups (p < 0.01 vs. noncardioplegic control group), respectively. In the Bretschneider group, ATP decreased to 0.91 ± 0.16 μmol/g-dry weight (p < 0.05 vs. noncardioplegic control hearts), and in the Roe group to 0.88 ± 0.10 μmol/g-dry weight (p < 0.01 vs. cardioplegic-free hearts).ConclusionIn conclusion, cardioplegic protection can be achieved in the immature rabbit myocardium with both St. Thomas' Hospital and Tyers solutions, but acalcaemic solutions such as Bretschneider and Roe solutions increased damage. The reported lack of cardioplegic efficacy in the immature myocardium may, therefore, reflect the choice of cardioplegic solution rather than a greater vulnerability to injury in the neonatal heart.