The effect of temperature during extracorporeal circulation on ultrastructure of cardiomyocytes

Introduction

Previous studies have suggested that mild hypothermia (28°C) during extracorporeal circulation (ECC) confers organ protection. The study was conducted to examine whether temperature during ECC influences cardiomyocyte ultrastructure.

Method

Fifteen pigs were randomly assigned to one of three temperature groups (37, 28 and 20°C) during ECC (n = 5 each). ECC time was 120 min and myocardial ischaemia time was 60 min. Cardioplegia was achieved by injecting a crystalloid solution (4°C cold Bretschneider solution, 30 ml/kg) into the aortic root. Flow index was set at 2.7 l/m² per min. Six hours after ECC, myocardial samples were taken from the left ventricle for ultrastructural examination by electron microscopy.

Results

All animals showed intact contractile apparatus, with normal texture of the myofibrils and normal configuration of the Z-bands. Quantitative and structural changes of mitochondria were frequent. Animals from the 37°C group showed marked interstitial oedema and dehiscence of the cytoplasmatic membrane with ruptures, whereas lesser damage to the membrane was observed in the other two groups. The 28°C group showed the least pronounced ultrastructural changes.

Conclusion

These results show that cardiac operations with ECC are associated with ultrastructural lesions of the cardiomyocytes. In this experimental setup, these lesions were most pronounced under normothermic and least pronounced under moderate hypothermic ECC.