Myocardial protective effect of hypoxic preconditioning with double cardiopulmonary bypass in canine hearts

Abstract

Objective To investigate the myocardial protective effect of hypoxic preconditioning in thein vivo canine hearts.Methods Healthy beagle dogs were randomly divided into two groups:the hypoxic preconditioning group (HPC group,n =8) and the control group (C group,n =8).The dog model of the double cardiopulmonary bypass (systemic and coronary circulation) was established after chest opening under general anesthesia.In HPC group,dog hearts were perfused by the coronary circulation and subjected to hypoxic preconditioning (3 min of hypoxia followed by 5 min of reoxygenation,repeated 3 times).The animals in C group were not subjected to hypoxic preconditioning.Both groups underwent cold cardioplegia perfusion through coronary circulation to induce cardiac arrest.At 60 min after cardiopulmonary bypass,we observed one-time rebeat rate,the incidence of arrhythmia and electric defibrillation times.At 30 min after rebeating,the left anterior descending coronary arteries were ligated with suture at the lower 1/3.The myocardial infarction area size was observed 60 min later,and samples were taken for examination by electron microscopy.At T1 (before operation),T2 (before cardiopulmonary bypass),T3 (immediately after the rebeat),and T4 (30 min after the ligation of left anterior descending coronary),the troponin and myocardial enzymes spectrum were measured.Cardiac function and myocardial structure were also observed in both groups.Results Myocardial enzymes at T3 were higher in HPC group than in C group (P ＜ 0.05),and myocardial enzymes and troponin at T4 were significantly lower in HPC group (P ＜ 0.05).As compared with C group,one-time rebeat rate and defibrillation times were significantly reduced in HPC group (7/8 vs.4/8 and 1/8 vs.5/8,P＜0.05).The infarct area size was significantly smaller in HPC group than in C group [(15.37 ± 1.64) ％ vs.(29.77 ± 3.38) ％,P ＜ 0.05],and electron microscopy revealed that the damage of mitochondrial structure and edema of cardiomyocytes were significantly reduced in HPC group as compared with C group.Conclusion Hypoxia preconditioning of the whole heart in vivo had protective effect on myocardia.It could improve the tolerance of myocardia to hypoxic injury. Key words: Hypoxic preconditioning; Cardiopulmonary bypass; Myocardial protection