Abstract
The ischemic myocardial contraction of dog was induced under the long time duration of normothermic aortic occlusion. In order to evaluate the myocardial damage and the occurring time of ischemic myocardial contraction (IMC), the influence of the electrical ventricular fibrillation (EVF) and the myocardial ultrastructural findings were studied.
The results were obtained as follows.
1. Under normothermic aortic occlusion with EVF for 30 minutes, the IMC was occurred. The IMC spread gradually out and finaly caused the irreversible myocardial damage, and the normal cardiac function could not been maintained even if the heart was resuscitated. The IMC could be also induced under the same condition without EVF, but the occurring time was fairly delayed. These results suggest that the duration of fibrillating time is the major factor for induction of IMC rather than the duration of aortic cross clamping time.
2. It has been reported that left ventricular vents is effctive for protection from myocardial damage, however in our experiments the vents was not effective for occurring time of IMC.
3. Both mild hypothermia and washing out of coronary blood after aortic occlusion were effective to delay the occurring time of IMC.
4. By electron microscopy, the main findings of ischemic myocardium were mitochondrial degeneration which showed clearing of the matrix with fragmentation of creste, amorphous matrix densities, disruption of membranes and edema. In our series observation, these changes were found after 20 minutes of aortic occlusion in ventricular fibrillating heart, however they were showed scarcely even after 60 minutes in ventricular fibrillating heart which is maintained coronary perfusion.
5. After resuscitation, the myocardial fine structure seemed to be aggravated gradually in following 24 hours, thereafter markedly improved in additional 24 hours.
From these results, it is considered that the safe duration of aortic cross clamping must be restricted within 30 minutes and the myocardial structural changes are recovered in 48 hours afterresuscitation at normothermia.
