Background: Enhanced late inward Na current (INa-L) modulates action potential duration (APD) and plays a key role in the genesis of early afterdepolarizations (EADs) and delayed afterdepolarizations (DADs) and triggered activity.
Objective: The purpose of this study was to define the influence of selective block of INa-L on EAD- and DAD-mediated triggered ventricular tachycardia (VT) and ventricular fibrillation (VF) in intact hearts using (GS967), a selective and potent (IC50 = 0.13 ± 0.01 μM) blocker of INa-L.
Methods: VT/VF were induced either by local aconitine injection (50 μg) in the left ventricular muscle of adult (3-4 months) male rats (N = 21) or by arterial perfusion of 0.1 mM hydrogen peroxide (H2O2) in aged male rats (24-26 months, N = 16). The left ventricular epicardial surface of the isolated-perfused hearts was optically mapped using fluorescent voltage-sensitive dye, and microelectrode recordings of action potentials were made adjacent to the aconitine injection site. The suppressive and preventive effects of GS967 (1 μM) against EAD/DAD-mediated VT/VF were then determined.
Results: Aconitine induced VT in all 13 hearts studied. Activation map (N = 6) showed that the VT was initiated by a focal activity arising from the aconitine injection site (cycle length [CL] 84 ± 12) that degenerated to VF (CL 52 ± 8 ms) within a few seconds. VF was maintained by multifocal activity with occasional incomplete reentrant wavefronts. Administration of GS967 suppressed the VT/VF in 10 of 13 hearts (P < .001). Preexposure to GS967 for 15 minutes before aconitine injection prevented initiation of VT/VF in 5 of 8 additional hearts (P < .02). VF reoccurred within 10 minutes on washout of GS967. Microelectrode recordings (N = 7) showed that VT/VF was initiated by EAD- and DAD-mediated triggered activity at CL of 86 ± 14 ms (NS from VT CL) that preceded the VF. GS967 shortened APD, flattened the slope of the dynamic APD restitution curve, and reduced APD dispersion from 42 ± 12 ms to 8 ± 3 ms (P < .01). H2O2 perfusion in eight fibrotic aged hearts promoted EAD-mediated focal VT/VF, which was suppressed by GS967 in five hearts (P < .02).
Conclusion: The selective INa-L blocker GS967 effectively suppresses and prevents aconitine and oxidative stress-induced EADs, DADs, and focal VT/VF. Suppression of EADs, DADs, and reduction of APD dispersion make GS967 a potentially useful antiarrhythmic drug in conditions of enhanced INa-L.
Keywords: Aconitine; Early afterdepolarization; Late I(Na); Late afterdepolarization; Optical mapping; Oxidative stress; Ventricular fibrillation; Ventricular tachycardia.
Copyright © 2014 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.