AUTHOR=Wang Sufen , Rodríguez-Mañero Moisés , Ibarra-Cortez Sergio H. , Kreidieh Bahij , Valderrábano Laura , Hemam Majd , Tavares Liliana , Blanco Elvin , Valderrábano Miguel
TITLE=NS5806 Induces Electromechanically Discordant Alternans and Arrhythmogenic Voltage-Calcium Dynamics in the Isolated Intact Rabbit Heart
JOURNAL=Frontiers in Physiology
VOLUME=10
YEAR=2019
URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.01509
DOI=10.3389/fphys.2019.01509
ISSN=1664-042X
ABSTRACT=Background: NS5806 activates the transient outward potassium current Ito, and has been claimed to reproduce Brugada Syndrome (BrS) in ventricular wedge preparations. Ito modulates excitation-contraction coupling, which is critical in alternans dynamics. We explored NS5806-arrhythmogenic effects in the intact whole heart and its impact on alternans.
Methods: Langendorff-perfused rabbit hearts (n = 20) underwent optical AP and Ca mapping during pacing at decremental cycle lengths (CL). Spontaneous arrhythmias and pacing-induced alternans was characterized at baseline (BL), after perfusing with NS5806, before and after adding verapamil (VP), and SEA0400 (SEA, n = 5 each), to modulate Ca-current and Na-Ca exchange, the main AP-Ca coupling mechanisms.
Results: NS5806 induced BrS-like ECG features in 6 out of 20 hearts. NS5806 prolonged steady-state (3 Hz) action potential duration (APD) by 16.8%, Ca decay constant by 34%, and decreased conduction velocity (CV) by 52.6%. After NS5806 infusion, spontaneous ventricular ectopy (VE) and AP/Ca alternans occurred. Pacing-induced alternans during NS5806 infusion occurred at longer CL and were AP/Ca discordant from its onset. Spatially discordant alternans after NS5806 infusion had non-propagation-driven nodal line distribution. No spontaneous phase-2 reentry occurred. Under NS5806 + VP, alternans became AP/Ca concordant and only induced in two out of five; NS5806 + SEA did not affect alternans but suppressed spontaneous ectopy.
Conclusions: NS5806 disrupts AP-Ca coupling and leads to Ca-driven, AP/Ca-discordant alternans and VE. Despite BrS-like ECG features, no spontaneous sustained arrhythmias or phase-2 reentry occurred. NS5806 does not fully reproduce BrS in the intact rabbit heart.