Protection of the immature myocardium during global ischemia. A comparison of four clinical cardioplegic solutions in the rabbit heart

Controversy surrounds the reported beneficial effects of crystalloid cardioplegic solutions in the immature myocardium. In the present study we have investigated the efficacy of four clinical cardioplegic solutions in the immature myocardium to determine (1) whether cardioplegic protection could be demonstrated and, if so, (2) the relative efficacy of the four solutions. Isolated, working hearts (n = 6 per group) from neonatal rabbits (aged 5 to 8 days) were perfused aerobically (37 degrees C) for 20 minutes before a 2-minute infusion of one of four cardioplegic solutions: The St. Thomas' Hospital No. 2, Tyers, Bretschneider, and Roe solutions. Hearts were then rendered globally ischemic for 50 minutes at 37 degrees C before reperfusion for 15 minutes in the Langendorff mode and 20 minutes in the working mode. The postischemic recovery of cardiac function and leakage of creatine kinase were compared with results in noncardioplegic control hearts. Good protection was observed with the St. Thomas' Hospital and Tyers solutions: The postischemic recovery of cardiac output was increased from 21.2% +/- 12.7% in the cardioplegia-free group to 79.4% +/- 6.2% and 72.9% +/- 4.4%, respectively, in the St. Thomas' Hospital and Tyers groups (p less than 0.01). In contrast, no protection was observed with either the Bretschneider or Rose solutions: Cardiac output recovered to 31.7% +/- 10.3% and 5.1% +/- 3.2%, respectively, in these groups. Postischemic creatine kinase leakage was 72.4 +/- 12.3 and 92.1 +/- 18.6 IU/15 min/gm dry weight in the St. Thomas' Hospital and Tyers groups compared with 125.6 +/- 28.6 IU/15 min/gm dry weight in control hearts (p = no significant difference). In the Bretschneider group, creatine kinase leakage increased to 836.9 +/- 176.8 IU/15 min/gm dry weight (p less than 0.01 versus noncardioplegic control hearts), and with the Roe solution the value was 269.0 +/- 93.0 IU/15 min/gm dry weight (p = no significant difference). In conclusion, cardioplegic protection can be achieved in the immature rabbit myocardium with both St. Thomas' Hospital and Tyers solutions, but acalcemic solutions such as Bretschneider and Roe solutions (which may be effective in the adult heart) increased damage in this preparation. 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.