Cancellation of Electrocardiographic Effects During Ventricular Excitation

Theoretical and experimental estimates of the amount of cancellation of electrocardiographic effects of ventricular excitation have been carried out. The theoretical estimate was based on the excitation sequence reported by Scher and consisted of comparing the total length of excitation fronts at several moments in the activation process with a measurement of the uncanceled portions of these fronts. Experimental estimates in 10 dogs were based on the relative areas of spatial magnitude curves during normal ventricular excitation and during stimulation of the ventricular site yielding the largest magnitude curve area. A theoretical estimate of the cancellation to be expected during ventricular stimulation was also carried out. The theoretical estimate of cancellation of electrocardiographic effects during normal ventricular activation was 71 per cent, while the experimental estimates varied from 51 per cent to 80 per cent, with an average of 66 per cent.