© 1998 by European Society of Cardiology
Copyright © 1998, European Society of Cardiology
Polymorphic ventricular tachycardias induced by D-sotalol and phenylephrine in canine preparations of atrioventricular block: initiation in the conduction system followed by spatially unstable re-entry
a,c
aDepartment of Pharmacology, Université de Montréal, Montréal, Québec, Canada
bDepartment of Pharmacology, McGill University, Montréal, Québec, Canada
cCentre de Recherche, Hôpital du Sacré-Coeur de Montréal, Montréal, Québec, Canada
* Corresponding author. Centre de Recherche, Hôpital du Sacré-Coeur de Montréal, 5400 boul. Gouin Ouest, Montréal, Québec, H4J 1C5 Canada. Tel.: +1 (514) 338-2222, ext. 3180; Fax: +1 (514) 338-2694; E-mail: cardinal@crhsc.umontreal.ca
Objective: Polymorphic ventricular tachycardias (PVT) occur spontaneously in canine hearts under the combination of D-sotalol (S), bradycardia and phenylephrine (PE). We investigated the hypotheses that: (1) the activation patterns of the initial PVT beats would be consistent with an origin in the ventricular conduction system; and (2) the inhomogeneous 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 as well as from intramural and endocardial sites during PVTs. Electrograms 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 270±43 ms, n=45) (mean±s.d.) occurred when a PE bolus (10–50 µg·kg–1) was injected. The first beat of the PVTs occurred with a coupling interval of several hundred ms to the preceding idioventricular beat (IDV) without any bridging activity and its earliest EPI breakthrough occurred in areas overlying the terminations of the right or left bundle branch. ARI values measured in IDV (295±47 ms) were significantly prolonged prior to PVT (462±92 ms). Prolongation was greater in apical than in basal epicardial areas, and at endocardial than 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 between various regions of the ventricles. Conclusion: Thus, PVTs occurring spontaneously under conditions of delayed repolarisation originate from shifting sites in the ventricular conduction system and re-entrant activity shifting between various regions of the ventricle may occur in later beats of the more sustained arrhythmias.
KEYWORDS Polymorphic ventricular tachycardia; Torsades de pointes; D-Sotalol; Epicardial mapping; Repolarisation intervals; Canine
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