Potential Proarrhythmic Effects of Biventricular Pacing
Jeffrey M. Fish, DVM*,
Josep Brugada, MD and
Charles Antzelevitch, PhD, FACC*,*
* Masonic Medical Research Laboratory, Utica, New York
Thorax Institute, Hospital Clinic, University of Barcelona, Barcelona, Spain
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Figure 1 Preferential prolongation of M-cell action potential in response to a slowing of stimulation rate. Transmembrane recordings obtained from tissue slices isolated from epicardial (Epi), M, and endocardial (Endo) regions of the canine right and left ventricles at basic cycle lengths (BCLs) of 300, 1,000, 2,000, and 5,000 ms. Modified and reprinted, with permission, from Sicouri et al. (8).
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Figure 2 Mathematical simulation of effects of epicardial versus endocardial pacing on QT interval, T peak–T end (Tp-Te), and TDR. (Top) Homogeneous myocardium. QT interval, T peak–T end, and TDR are unchanged when pacing site is shifted from endocardium (Endo) (left) to epicardium (Epi) (right) (basic cycle length = 2,000 ms). (Bottom) Heterogeneous myocardium. QT interval, T peak–T end, and TDR all increase after reversal of direction of activation of the transmural cable. Modified and reprinted, with permission, from Fish et al. (5).
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Figure 3 Effect of reversal of transmural sequence of activation in canine LV wedge preparation. Epicardial (Epi), endocardial (Endo), and M-cell action potentials and a transmural electrocardiogram were simultaneously recorded during endocardial (A) and epicardial (B) pacing at a basic cycle length of 2,000 ms. All numbers are in milliseconds. ECG = electrocardiogram; other abbreviations as in Figure 2. Modified and reprinted, with permission, from Fish et al. (5).
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Figure 4 Cisapride (0.2 µmol/l) permits induction of torsades de pointes during epicardial (Epi) but not endocardial stimulation. Epicardial and M-cell action potentials and a transmural electrocardiogram were simultaneously recorded during endocardial (A) and epicardial (B) pacing of the canine left ventricular wedge preparation at a basic cycle length of 2,000 ms. A polymorphic ventricular tachycardia was induced by an extrastimulus delivered to epicardium at an S1-S2 interval of 204 ms (C). ECG = electrocardiogram; other abbreviations as in Figure 2. Modified and reprinted, with permission, from Fish et al. (5).
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Figure 5 A shift from endocardial to epicardial pacing prolongs QT (A) and transmural dispersion of repolarization (B) and permits propagation of early afterdepolarizations (EADs) in an arterially perfused rabbit left-ventricular wedge preparation. Dofetilide (5 nmol/l) led to the appearance of phase 2 EADs in endocardium (Endo). The EADs failed to propagate across the ventricular wall during endocardial pacing (A), but succeeded during epicardial (Epi) pacing, generating R-on-T extrasystoles (B). ECG = electrocardiogram. Modified and reprinted, with permission, from Medina-Ravell et al. (4). Abbreviations as in Figure 3.
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Figure 6 A 12-lead electrocardiogram recorded from a 72-year-old man with dilated cardiomyopathy. The patient was paced at a cycle length of 600 ms from either the endocardium (Endo) or an epicardial (Epi) site immediately across the lateral aspect of the left ventricular free wall. During endocardial pacing (left), the QT interval in lead V6 was 444 ms and the T peak–T end interval was 142 ms. Pacing from the epicardium increased these values to 454 ms and 178 ms, respectively, and augmented and widened the T-wave.
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Figure 7 Pacing site-dependent changes in QT interval, R-on-T ventricular extrasystoles, and the onset of torsades de pointes (TdP). Right ventricular endocardial pacing (RVEndoP; RR interval of 840 ms) yielded a QT interval of 485 ms and a T peak–T end interval of 92 ms. After switching to left ventricular epicardial pacing (LVEpiP; mode VOO), the QT interval increased to 580 ms and T peak–T end to 133 ms. Ventricular extrasystoles appeared at the 46th beat of LVEpiP (B) and initiated one episode of TdP after the 55th beat (C). The TdP was terminated by an implantable cardioverter-defibrillator shock. Modified and reprinted, with permission, from Medina-Ravell et al. (4).
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