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Computational Analyses in Ion Channelopathies

Electrophysiological mechanisms of ventricular arrhythmias in relation to Andersen-Tawil syndrome under conditions of reduced I_K1: a simulation study

Departments of ¹Medicine and ³Physiology and Institutes of ⁴Basic Medical Sciences and ⁵Electrical Engineering, Colleges of Medicine and Engineering, National Cheng Kung University, Tainan, Taiwan; and ²Division of Cardiovascular Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, California

Submitted 14 April 2006 ; accepted in final form 26 June 2006

Patients with Andersen-Tawil syndrome (ATS) mostly have mutations on the KCNJ2 gene, producing loss of function or dominant-negative suppression of the inward rectifier K⁺ channel Kir2.1. However, clinical manifestations of ATS including dysmorphic features, periodic paralysis (hypo-, hyper-, or normokalemic), long QT, and ventricular arrhythmias (VAs) are considerably variable. Using a modified dynamic Luo-Rudy simulation model of cardiac ventricular myocytes, we attempted to elucidate mechanisms of VA in ATS by analyzing effects of the inward rectifier K⁺ channel current (I_K1) on the action potential (AP). During pacing at 1.0 Hz with extracellular K⁺ concentration ([K⁺]_o) at 4.5 mM, a stepwise 10% reduction of Kir2.1 channel conductance progressively prolonged the terminal repolarization phase of the AP along with gradual depolarization of the resting membrane potential (RMP). At 90% reduction, early afterdepolarizations (EADs) became inducible and RMP was depolarized to –52.0 mV (control: –89.8 mV), followed by emergence of spontaneous APs. Both EADs and spontaneous APs were facilitated by a decrease in [K⁺]_o and suppressed by an increase in [K⁺]_o. Simulated -adrenergic stimulation enhanced delayed afterdepolarizations (DADs) and could also facilitate EADs as well as spontaneous APs in the setting of low [K⁺]_o and reduced Kir2.1 channel conductance. In conclusion, the spectrum of VAs in ATS may include 1) triggered activity mediated by EADs and/or DADs and 2) abnormal automaticity manifested as spontaneous APs. These VAs can be aggravated by a decrease in [K⁺]_o and -adrenergic stimulation and may potentially induce torsade de pointes and cause sudden death. In patients with ATS, the hypokalemic form of periodic paralysis should have the highest propensity to VAs, especially during physical activity.

Andersen syndrome; long QT

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