An Experimental Study of Electrocardiogram and Vecrtorcardiogram on the Localization of the Site of Origin of Ventricular Extrasystoles

Abstract

There have been many reports of studies done on the localization of the site of origin of ventricular extrasystoles by means of electrocardiograms or vectorcardiograms. However, in the previous reports which were based on clinical cases, the site of origin were merely assumed, and the results obtained by animal experiments were difficult to apply to humans because of the difference in the leads used, and the discrepancy of heart-torso relationship between humans and animals. Moreover, there have been no papers which investigated the possible sites of origin in more detail, such as a focus in the subepicardium or in the subendocardium within the same myocardial region. Methods: Langendorf perfusion was done. The perfused canine heart was situated and held in a desired position with a holder within a hollow elliptic cylinder made of acryl resin filled with a Tyrode solution. The ratio between the major and minor axes of the cylinder was almost the same as that in an average human thorax. The position of the perfused heart was kept carefully in relation of that of the human heart and thorax. From the silver wire electrodes through the wall of the cylinder, a set of 12 leads ECG, and a Frank lead VCG were recorded. The heart was driven at a rate of 60-70 per minute through a bipolar electrode placed in the area near the sinus node. Also the electrodes, to elicit a ventricular extrasystole, were fixed firmly in place at each locus of the myocardium. Within a 500-600 msec delay after the pacing, a stimulus with a strength of less than 2-4 times the resting threshold was given to each site of the ventricles to elicit a ventricular extrasystole. Ventricular extrasystoles were elicited at the following ten sites: subepicardium and subendocardium at the conus area of the right ventricle; subepicardium and subendocardium at the anterolateral aspect of the free wall of the right ventricle; subepicardium and subendocardium at the basilar area of the left ventricle ; and the right side and left side of the interventricular septum. Twenty-eight dogs were used for these experiments. Results: In the case of the stimulation of the basilar portion of the left ventricle, the direction of the major QRS deflection was upward in leads III, VR, V1, V2, and V3, and downward in leads I, VL, V5, and V6. On the stimulation of the subepicardial focus, the QRS pattern showed a slow upward incline, and a delta wave pattern was recognized. On the other hand, on stimulation of the subendocardial focus, the initial portion of the QRS showed a sudden upward rise. In VCG the spatial maximal QRS vector pointed to the right, anterior, inferior.