Validation of the Ventricular Gradient Comparing Sinus Beats and Ectopic Beats

Introduction. Wilson assumed that the ventricular gradient (VG) is independent of the ventricular activation order. We sought to validate this tenet by intra-individual comparison of the VG of sinus and ectopic beats, thus assessing both the effects of altered ventricular conduction and of restitution (caused by varying ectopic prematurity). Methods. We studied standard diagnostic ECGs of 118 patients with accidental extrasystoles, who had either normally conducted supraventricular ectopic beats ($SN, N=6$), aberrantly conducted supraventricular ectopic beats ($SA,\ N=20$), or ventricular ectopic beats ($V,\ N=92$). We computed the ventricular gradient vectors of the predominant beat, VGp, of the ectopic beat, VGe, the VG difference vector, VGpe, and compared their sizes. Results. The VGe vectors of the SA and $V$ ectopic beats were significantly larger than the VGp vectors. The VGpe vectors were three times larger than the difference in size of the VGe and VGp vectors, demonstrating differences in the VGp and VGe spatial directions. Ectopic prematurity had no influence on these results. Discussion. Electrotonic interactions during repolarization form the likely explanation of our findings. Because of this electrophysiological mechanism, the concept of a conduction-independent ventricular gradient is untenable and cannot be used in ECG diagnostics.