Dissimilarities in the electrophysiological abnormalities of lateral border and central infarct zone cells after healing of myocardial infarction in cats.

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Abstract
The characteristics of an electrophysiological border zone detected after healing of experimental myocardial infarction in cats were studied. Isolated left ventricles (32) were studied in tissue bath 2-7 mo. after distal left coronary artery ligation. Action potentials were recorded from endocardial ventricular muscle cells in normal, lateral border and central infarct zones. Action potential duration was prolonged in central infarct zone cells, while action potentials of lateral border zone cells had the shortest duration. Ventricular muscle cells in the border zone also had lower resting potential, action potential amplitude and .ovrhdot.Vmax. Slowly rising action potentials (.ovrhdot.Vmax .ltoreq. 20 V/s) were noted in central infarct zone cells, but more consistently in border zone cells. Functional refractory period of cells in central infarct zone was significantly longer than that recorded from border and normal zone cells. Postrepolarization refractoriness occurred in the majority of border zone cells. Failure of a border zone cell to respond to a premature stimulus during repetitive activity was observed in 10 of the 22 preparations in which repetitive activity could be induced. When the coupling interval between driving and premature stimuli was shortened, border zone cells were first to fail to be excited by the premature stimulus. Apparently, conduction was impaired in the border zone, whereas normal conduction was still possible in central infarct and normal areas. The electrophysiological abnormalities in the endocardial lateral border zone cells of the healed myocardial infarction appear to be the most severe, and the border zone may play an important role in chronic electrophysiological instability observed both in situ and in vitro.