Progressive mechanical impairment associated with progressive but reversible electrocardiographic ischaemic changes during repeated brief coronary artery occlusion in pigs.
Epicardial and endocardial electrograms, myocardial metabolism, left ventricular pressure, and regional myocardial tension were studied during 15 min coronary occlusions followed by 45 min reperfusion in the in situ pig heart to evaluate their reproducibility and the possibility of a cumulative effect. Two coronary occlusions were performed in 27 animals, three in 21, and four in nine. Throughout the different occlusions there was a progressive increase in peak TQ-ST segment shift, a progressively higher incidence of ST segment alternans, and an increasing prolongation of the ventricular activation time. Regional myocardial tension in the ischaemic area, measured in eight pigs, declined progressively after each occlusion-reperfusion cycle, whereas it failed to change in four sham experiments. Nevertheless, complete electrical recovery ensued after each reperfusion and was progressively quicker throughout the four reperfusions. In addition, lactate production due to ischaemia returned to extraction after each reperfusion when studied in eight pigs undergoing three occlusion-reperfusion cycles. It is concluded that multiple coronary occlusions in pigs causes (a) a progressive deterioration in contractility and (b) a progressive but reversible deterioration in the electrically changes. These findings may explain the impaired segmental wall motion seen in some patients with recurrent angina at rest and no evidence of infarction. In this model, the electrical and metabolic recovery after each reperfusion probably indicates that the gross ischaemic alterations were reversed but that a minor though probably increasing degree of tissue necrosis may have been present.