The Ultrastructural Study on Myocardial Protection During Experimental Cardiopulmonary B ypass

Abstract

It was aimed in the present investigation to observe the fine structural changes in the myocardium of a 2 -hour period of the selective continuous coronary perfusion with cold blood of low flow rate after the cross-clamping of the aorta as compared with those of the selective continuous coronary perfusion with cold Ringer-lactate solution and of the topical cooling with cold physiological saline solution, using normal adult dogs as well as dogs with experimentally produced left ventricular hypertrophy.
Twenty adult mongrel dogs, weighing 12 to 15 kilograms, and 10 mongrel dogs with left ventricular hypertrophy produced by banding of the ascending aorta were subjected to total body perfusion.
In the group of cold blood coronary perfusion, the structural integrity was well preserved during the cooling and even after weaning from the bypass. At the end of a 2 -hour period of the coronary perfusion, the myocardium was essentially normal in all its inner and outer layers, although mitochondria were slightly swollen with a mild decrease in stainable glycogen. Mitochondria were sharply demarcated and the cristae within mitochondria were clear and distinct. Neither clumping nor margination of the nuclear chromatin was demonstrated.
These findings were almost the same as those in the group of cold Ringer-lactate coronary perfusion. The ultrastructure of myocardium at a 2 -hour period of the aortic cross-clampin g in the group of topical cooling, showed distinct abnomality. Particulary, in the inner layer of the myocardium, swelling, clearing and destruction of mitochondria with margination of nuclear chromatin were significant. These findings tended to aggravate at the rewarming period after the release of the aortic cross-clamping or during the recovery period. These morphological changes were more severe in dogs with left ventricular hypertrophy.
Peroxidase in dogs with left ventricular hypertrophy, was injected into the coronary artery immediately before releasing of aortic cross-clamping to evaluate its distribution in the myocardium and its uptake to the endothelium of capillary. In the group of cold blood coronary perfusion, peroxidase could be observed in the endothelium in all areas of the myocardium. On the contrary, in the group of topical cooling, peroxidase was hardly demonstrated in the endothelium of the endocardium, although it was observed in the outer layer of the myocardium. Moreover, peroxidase could be observed not only in the endothelia, but also in the intercellular space based on changes in permiability.
These results clearly show ed that the protection afforded by means of topical cooling for the ischemic myocardium was doubtful in dogs with normal heart, and more doubtful in the case of dogs with left ventricular hypertrophy.
It was the conclusion from the results obtained in the present investigation that the coronary perfusion with cold blood of low flow rate was the choice of the method of myocardial protection for open heart surgery.