HYPOXIC PRECONDITIONING ENHANCES FUNCTIONAL RECOVERY AFTER PROLONGED CARDIOPLEGIC ARREST

The purpose of this study was to assess the ability of hypoxic precond itioning to improve myocardial salvage after prolonged hypothermic car dioplegic arrest. Isolated working rat hearts were arrested at 4 degre es C with St. Thomas' Hospital cardioplegic solution and immersion sto red for 4 or 6 hours. Two groups were studied, control and hypoxically preconditioned (HP) hearts. After 4 hours' preservation, aortic now, coronary now, and the first derivative of aortic pressure were 8.7 +/- 1.6 mL/min, 17.8 +/- 1.6 mL/min, and 2,064 +/- 123 mm Hg/s, respectiv ely, in control hearts (n = 11) and 25.7 +/- 2.5 mL/min, 27.1 +/- 2.5 mL/min, and 2,655 +/- 93 mm Hg/s, respectively, in HP hearts (n = 11) (p < 0.05). After 6 hours' preservation, aortic now, coronary flow, an d the first derivative of aortic pressure were 3.5 +/- 1.2 mL/min, 18. 8 +/- 0.4 mL/min, and 1,622 +/- 226 mm Hg/s, respectively, in control hearts (n = 6) and 21.5 +/- 3.2 mL/min, 25.5 +/- 2.3 mL/min, and 2,439 +/- 239 mm Hg/s, respectively, in HP hearts (n = 6) (p < 0.05). After 6 hours' preservation adenine nucleotides and creatine phosphate leve ls were not significantly different between the two groups, but lactat e dehydrogenase release was significantly increased (p < 0.05) in cont rol versus HP hearts (4.66 +/- 0.58 IU/L versus 1.98 +/- 0.28 IU/L). W e conclude that hypoxic preconditioning reduces cellular necrosis and preserves myocardial function after prolonged hypothermic cardioplegic arrest.