POLYMORPHIC VENTRICULAR TACHYCARDIAS INDUCED BY D-SOTALOL AND PHENYLEPHRINE IN CANINE PREPARATIONS OF ATRIOVENTRICULAR-BLOCK - INITIATION IN THE CONDUCTION SYSTEM FOLLOWED BY SPATIALLY UNSTABLE REENTRY

Objective: Polymorphic ventricular tachycardias (PVT) occur spontaneou sly in canine hearts under the combination of D-sotalol (S), bradycard ia and phenylephrine (PE). We investigated the hypotheses that: (1) th e activation patterns of the initial PVT beats would be consistent wit h an origin in the ventricular conduction system; and (2) the inhomoge neous prolongation of repolarisation intervals can provide refractory barriers for re-entrant activity. Methods: Unipolar electrograms were recorded from 127 epicardial (EPI) sites with a sock electrode array a s well as from intramural and endocardial sites during PVTs. Electrogr ams were analysed to generate isochronal maps and measure the spatial distribution of activation-recovery intervals (ARI). Results: Under S (9.9-14.5 mg l(-1)), spontaneously terminating PVTs (cycle length of 2 70 +/- 43 ms, n = 45) (mean +/- s.d.) occurred when a PE bolus (10-50 mu g . kg(-1)) was injected. The first beat of the PVTs occurred with a coupling interval of several hundred ms to the preceding idioventric ular beat (IDV) without any bridging activity and its earliest EPI bre akthrough occurred in areas overlying the terminations of the right or left bundle branch. ARI values measured in IDV (295 +/- 47 ms) were s ignificantly prolonged prior to PVT (462 +/- 92 ms). Prolongation was greater in apical than in basal epicardial areas, and at endocardial t han epicardial sites (to > 500 ms). Maximum delays > 200 ms developed in the regions of marked ARI prolongation and, in later beats, circus movement re-entry occurred around refractory barriers, shifting betwee n various regions of the ventricles. Conclusion: Thus, PVTs occurring spontaneously under conditions of delayed repolarisation originate fro m shifting sites in the ventricular conduction system and re-entrant a ctivity shifting between various regions of the ventricle may occur in later beats of the more sustained arrhythmias. (C) 1998 Elsevier Scie nce B.V. All rights reserved.