Introduction. Wilson postulated that the ventricular gradient (VG) is independent of the cardiac activation order. This concept has been criticized several times, but these studies had small numbers of patients, selective pathology, were mostly done in two dimensions, and did not take restitution effects into account. The purpose of our study was to validate this concept by intra-individual comparison of the VG of sinus beats and ectopic beats, and thus to estimate the effects of altered ventricular conduction and of restitution. 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 sizes op the VGe vectors were significantly larger than those of the VGp vectors in the SA and V ectopic beats. The sizes of the VGpe vectors were three times larger than the difference in size of the VGe and VGp vectors, a manifestation of differences in the spatial directions of then VGp and VGe vectors. Prematurity of the ectopic beats had no influence on these results. Discussion. This outcome can mechanistically be explained by the electrotonic interactions during ventricular repolarization that change with a changing ventricular activation order. Because of this electrophysiological mechanism, the concept of a conduction-independent ventricular gradient as put forward by Wilson is untenable. Therefore, the VG cannot straightforwardly be used in ECG diagnostics.