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Figure 6 Polymorphic ventricular tachycardia displaying features of Torsade de Pointes (TdP) in the LQT2 (A) and the LQT3 (B) models of arterially-perfused canine left ventricular wedge preparations. Each trace shows action potentials simultaneously recorded from M and epicardial (Epi) cells together with a transmural ECG. The preparation was paced from the endocardial surface at a BCL of 1,000 or 2,000 msec (S1). A: Spontaneous TdP induced in the LQT2 (d-Sotalol) model. The long episode of TdP (fourth group) was preceded by salvos of three consecutive beats (first group) and an isolated ventricular premature beat (third group), similar to the clinical experience. B: Stimulation-induced TdP in the LQT3 (ATX-II) model. ATX-II produced very significant dispersion of repolarization (first grouping). A single extrastimulus (S2) applied to the epicardial surface initiated TdP (second grouping). LQT1, 2 = long QT syndrome 1, 2.
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