Are Atrial-Selective Drugs Superior to Currently Available Antiarrhythmic Drugs Used in the Treatment of Atrial Fibrillation?

Current pharmacologic strategies for the management of atrial fibrillation (AF) include use of

1) sodium channel blockers, which are contraindicated in patients with coronary artery or tructural heart disease because of their potent effect to slow conduction in the ventricles,

2) potassium channel blockers, which predispose to acquired long QT and Torsade de Pointes arrhythmias because of their potent effect to prolong ventricular repolarization, and

3) mixed ion channel blockers such as amiodarone, which are associated with multi-organ toxicity.Accordingly, recent studies have focused on agents that selectively affect the atria but not the ventricles.

Several atrial-selective approaches have been proposed for the management of AF, including inhibition of the atrial-specific ultrarapid delayed rectified potassium current (I_Kur), acetylcholine-regulated inward rectifying potassium current (I_K-ACh), or connexin-40 (Cx40).

All three are largely exclusive to atria.Recent studies have proposed that an atrial-selective depression of sodium channel-dependent parameters with agents such as ranolazine may be an alternative approach capable of effectively suppressing AF without increasing susceptibility to ventricular arrhythmias.

Clinical evidence for Cx40 modulation or I_K-ACh inhibition are lacking at this time. The available data suggest that atrial-selective approaches involving a combination of I_Na, I_Kur, I_Kr, and, erhaps, I_to block may be more effective in the management of AF than pure IKur or I_Na block. The anti-AF efficacy of the atrial-selective/predominant agents appears to be similar to that of conventionally used anti-AF agents,with the major difference being that the latter are associated with ventricular arrhythmogenesis and extracardiac toxicity.