Quantitative fine structural changes in dog heart following cardiopulmonary bypass

Abstract

Quantitative analysis of electron micrographs was performed on cardiac biopsies obtained before and approximately I h following hypothermic cardiopulmonary bypass at 28°C. During bypass the myocardium was exposed to 5, 20 and 30 min of ischemia. Alterations in mitochondrial structure were seen after only 5 min of myocardial ischemia and consisted of end-to-end fusion of these organelles. In the control biopsies, mitochondrial volume fraction ( V vi ) was 0.25, but after 5 min of aortic occlusion it increased to 0.38; after 20 min it was 0.40 and some mitochondria were mildly swollen. After 30 min, V vi was 0.31 and some giant mitochondria were disrupted. The reduction in V vi at 30 min may have been due to the appearance of a new population of small spherical mitochondria. Function studies were done before and after bypass. Mean maximal left ventricular power after 5, 20 and 30 min of myocardial ischemia at 27°C was decreased to 86, 68 and 59%, respectively, of that observed before bypass. This study shows that disruption of myocardial organelles occurs following 20 to 30 min of hypothermic ischemia, corresponding with the moderate decrease in maximal LVP at 30 min.