Comparison of the Effects of Na⁺ and K⁺ Channel Blockers on the Electrophysiological Properties of the Pulmonary Veins in Patients with Atrial Fibrillation

Introduction: We assessed the effects of pilsicainide, a pure Na + channel blocker, and nifekalant, a pure rapid delayed rectifier potassium current (IKr) blocker, on the electrophysiological characteristics within the pulmonary vein (PV) and at the PV‐left atrial (LA) junction. Methods and Results: We used a basket catheter for PV mapping in 38 patients with paroxysmal atrial fibrillation (AF). Programmed stimulation was performed in the distal PV and PV‐LA junction before and after the infusion of pilsicainide (1 mg/kg; n = 24) or nifekalant (0.3 mg/kg; n = 14). Both drugs significantly prolonged the effective refractory period (ERP) of the distal PV and PV‐LA junction. Pilsicainide significantly decreased the ERP heterogeneity of the PV and PV‐LA junction (36 ± 43 vs. 9 ± 60 ms, P < 0:05). In contrast, nifekalant significantly increased the ERP heterogeneity of the PV and PV‐LA junction (from 38 ± 34 to 60 ± 46 ms, P < 0:01). Pilsicainide significantly prolonged the conduction time (S1‐A1) from the distal PV to the PV‐LA junction (from 42 ± 12 to 63 ± 26 ms, P < 0:001), whereas this did not change with nifekalant. Conclusions: In AF patients, pilsicainide has antiarrhythmic effects mainly on the distal PV by modifying the ERP and conduction properties. In contrast, nifekalant has antiarrhythmic effects mainly on the PV‐LA junction by modifying the ERP.