Myocardial infarction in the guinea pig: cellular electrophysiology

The cellular electrophysiology of left ventricular preparations from guinea pig hearts was studied 1 hour, 24 hours, and 4-6 weeks after myocardial infarction produced by 6-8 single ties of the distal left coronary artery system or after sham operation. Microelectrode recordings were used to monitor cells from the endocardial surface of each preparation in tissue bath. All coronary ligated preparations displayed accelerated spontaneous activity compared to normal and sham operated preparations. Single and multiple premature ventricular depolarizations occurred frequently in coronary ligated and rarely in normal and sham operated preparations. Premature stimuli delivered to areas overlying and bordering the area of infarction, induced short bursts of self-terminating rapid repetitive ventricular activity in 4 of 8 (50%) acute (1-hour), 5 of 9 (55%) subacute (24-hour), and 14 of 20 (70%) healed (4-6-week) infarcted preparations. Such activity could not be induced in normal and sham operated preparations. The preparations with healed infarction were unique in that they demonstrated runs of self-terminating repetitive ventricular activity which occurred spontaneously or was inducible with premature stimulation. Recordings from multiple sites in acute, subacute, and healed preparations revealed a variety of transmembrane action potential abnormalities (i.e., reduced action potential amplitude and resting potential, decreased and increased action potential duration, and depressed maximum rates of phase 0 depolarization) in cells overlying and bordering areas of infarction. Only Purkinje fiber action potentials were recorded over the healed infarcts. These data demonstrate that a spectrum of electrophysiological alterations occur in response to ischemic injury and persist after healing of the injury in this new model of myocardial infarction utilizing the guinea pig.