Intra-individual comparison of sinus and ectopic beats probing the ventricular gradient's activation dependence
Abstract
Wilson assumed that the ventricular gradient (VG) is independent of the ventricular activation order. This paradigm has often been refuted and was never convincingly corroborated. We sought to validate Wilsonβs concept by intra-individual comparison of the VG of sinus beats and ectopic beats, thus assessing the effects of both altered ventricular conduction (caused by the ectopic focus) and restitution (caused by ectopic prematurity). We studied standard diagnostic ECGs of 118 patients with accidental extrasystoles: normally conducted supraventricular ectopic beats (SN, N = 6) and aberrantly conducted supraventricular ectopic beats (SA, N = 20) or ventricular ectopic beats (V, N = 92). In each patient, we computed the VG vectors of the predominant beat, ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§ξ§, of the ectopic beat, ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§, and of the VG difference vector, ΞππΊππξ¦ξ¨ξ§ξ§ξ§ξ§ξ§ξ§ξ§ξ§, and compared their sizes. |ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§| of the SA and V ectopic beats were significantly larger than |ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§ξ§| (53.7 Β± 25.0 vs. 47.8 Β± 24.6 mVβms, respectively; p < 0.001). |ΞππΊππξ¦ξ¨ξ§ξ§ξ§ξ§ξ§ξ§ξ§ξ§| were three times larger than the difference of |ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§| and |ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§ξ§| (19.94 Β± 9.76 vs. 5.94 mVβms, respectively), demonstrating differences in the ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§ξ§ and ππΊπξ¦ξ¨ξ§ξ§ξ§ξ§ spatial directions. The amount of ectopic prematurity was not correlated with |ΞππΊππξ¦ξ¨ξ§ξ§ξ§ξ§ξ§ξ§ξ§ξ§|, although the larger VG difference vectors were observed for the more premature (<80%) extrasystoles. Electrical restitution properties and electrotonic interactions likely explain our findings. We conclude that the concept of a conduction-independent VG should be tested at equal heart rates and without including premature extrasystoles.
