THE CONFIGURATION OF EPICARDIAL AND ENDOCARDIAL EXTRASYSTOLES IN THE CHEST LEADS

Abstract

Epicardial extrasystoles and their endocardial counterparts have been elicited from the right and left ventricles in the dog and their configuration compared in transthoracic leads, leads 4R and 4F, and in Wilson''s central terminal lead. When the stimulating electrodes were carefully aligned with the transthoracic leads or were immediately subjacent to the exploring electrode in the chest leads, no differences were found between endocardial and epicardial extrasystoles, the initial deflections of both showing a simple QS complex. When the stimulating electrodes were not in line with the transthoracic leads or were not directly beneath the exploring electrode in the chest leads, endocardial and epicardial extrasystoles showed one or another of the following configurations: both epicardial and endocardial extrasystoles showed a simple QS complex; both epicardial and endocardial extrasystoles showed R waves preceding S; the endocardial extrasystole alone showed an RS configuration, while the epicardial extrasystole showed a simple QS wave; the epicardial extra-systole showed an RS, while the endocardial extrasystole showed a simple QS wave; and extrasystoles (endocardial, epicardial or both) which arose early in the cycle showed a simple QS, while later extrasystoles showed an RS. These results are interpreted to mean that the electrocardiogram, as recorded by limb and chest leads, does not reveal the existence of currents associated with the conduction of excitation from the endocardium to the epicardium.