The Localization of Ventricular Extrasystoles *

The interest in localization of the site of origin of ventricular extrasystoles by study of their electrocardiographic configuration does not arise from a sense of the importance of such a localization in the case of the majority of ventricular extrasystoles observed in man. It is, rather, founded on the recognition in the earliest days of electrocardiography'5 26, 27, 28 that the electrocardiographic configuration of a ventricular extrasystole is to be interpreted in terms of an altered sequence of excitation and recovery in the heart, and that study of the configurations obtained when the sequence of excitation is altered in a predetermined manner by stimulation of chosen localities in the heart should permit inferences to be drawn regarding the location and nature of pathological processes when these are responsible for alterations in the distribution of the cardiac impulse. There is, however, an apparent disagreement over the localizing significance of the various electrocardiographic patterns, which is particularly marked in the case of the so-called "discordant" patterns, in which the major deflections of the QRS portion are oppositely directed in leads I and III.29 The classical interpretation of Lewis, in which an extrasystole wlth a QS1 and an R3 was considered to have a right-sided origin, has been largely supplanted by a diametrically opposite interpretation. Others have held that changes in the position of the heart in the chest and other factors may so alter the configuration of extrasystoles that localization is, for all practical purposes, impossible."2 The apparent difficulties attending the application of experimental results in the dog to'man have brought repeated warnings of the hazards of such attempts.28' 29 At least three factors appear to have contributed to the lack of agreement that at present exists. These are as follows: