High cardioplegic perfusion pressure entails reduced myocardial recovery

The cardioplegic solution is often given at high flow and pressure following aortic clamping clamping to ensure rapid diastolic arrest. With standard setup in clinical practice, it is easy to exceed 200 mmHg in the aortic root. To investigate whether cardioplegic solution delivery pressure has an influence on myocardial protection, intermittent infusions of crystalloid cardioplegia were given at two different pressures using an in vivo pig model.

Fourteen pigs (48-57 kg) were put on cardiopulmonary bypass, aorta-clamped (2 h) and 500 ml St. Thomas' cardioplegia (4 degrees C) was delivered antegradely at either 75 mmHg (group 1, n = 7) or 175 mmHg (group 2, n = 7) pressure via 9-F aortic root cardioplegic needle. Every 20 min, 100 ml cardioplegic were delivered at either one of the two pressures. After 2 h, the aorta was unclamped and the hearts reperfused. Attempts were made to wean pigs from bypass following 20 min reperfusion or, if they were failing, after 40 min. If failing once again, the pigs were reperfused for the last 20 min on the heart-lung machine.

Hearts in group 1 (n = 7) needed significantly longer time to stop after aortic clamping (38 +/- 9 s) than did group 2 hearts (n = 7) (21 +/- 5 s) (P = 0.043). In group 1, all pigs were weaned from bypass, whereas in group 2 only 2 out of 7 pigs were able to sustain circulation without cardiopulmonary bypass (P = 0.01), and then with lower hemodynamic performances. At the end of cardiac arrest, group 1 had significantly higher adenosine triphosphate (19.4 +/- 1.1 mumol/g dry weight and 15.05 +/- 1.8 mumol/g dry weight, respectively) (P = 0.05) and significantly lesser fall in energy charge than group 2 (0.02 +/- 0.01 and 0.05 +/- 0.02, respectively) (P = 0.05). Also at the end of reperfusion, group 1 had significantly higher adenosine triphosphate (16.54 +/- 1.4 mumol/g dry weight and 12.53 +/- 0.95 mumol/g dry weight, respectively) (P = 0.016) than group 2.

Despite a swifter diastolic cardiac arrest, the high cardioplegic solution delivery pressure caused significantly poorer postischemic recovery than a moderate pressure with the same amount of cardioplegic solution.