FUNCTIONAL AND ULTRASTRUCTURAL ALTERATIONS OF CANINE MYOCARDIUM SUBJECTED TO VERY BRIEF CORONARY OCCLUSIONS

The effects of very brief and recurrent coronary occlusions on myocard ial regional shortening and its ultrastructure have been analysed Ultr asonic crystals were implanted in the left ventricular subendocardium of 23 anaesthetized dogs with the thorax open, to measure the shorteni ng fractions of an ischaemic and a control segment. Twenty 2 min total occlusions were provoked in the left anterior descending coronary art ery, with 3 min recovery intervals (reperfusion) between occlusions. T he shortening fraction decreased progressively,vith each occlusion, re aching a value 18.9% lower than the basal after the last ischaemic epi sode (P<0.05); 32.3% after 4 h of reperfusion (P<0.01), and 28.6% afte r 24 h (P<0.01). Qualitative and quantitative ultrastructural analysis showed an increase in the mitochondrial volume of the ischaemic tissu e (158% vs control, P<0.001) with significant damage to the cell compo nents (7.7-fold increases vs control mitochondria). These results show that when the myocardium is subjected to very brief and repeated coro nary occlusions, there is progressive deterioration of systolic functi on with structural alterations, mainly at the mitochondrial level. The se modifications ale still observable 24 h after the end of ischaemic stimulation and could be the cause of transitory and/or chronic systol ic dysfunctions in the absence of previous heart attack.