The Efficacy of I Na Block to Cardiovert Atrial Fibrillation Is Enhanced by Inhibition of I K1

There is a need for more efficient pharmacological cardioversion of atrial fibrillation (AF). We tested the hypothesis that inhibition of I K1 significantly enhances the efficacy of I Na block to depress atrial excitability and to cardiovert AF. The study was conducted in canine isolated arterially perfused right atrial preparations with rim of ventricular tissue. AF was induced in the presence of acetylcholine (ACh; 0.5 µM). BaCl 2 (10 µM) was used to inhibit I K1 and flecainide (1.5 µM) to block I Na . Sustained AF (>45 minutes) was recorded in 100% atria (5/5) in the presence of ACh alone. Flecainide cardioverted AF in 50% of atria (4/8), BaCl 2 in 0% (0/5), and their combination in 100% (5/5). AF cardioversion occurred in 15 ± 9 minutes with flecainide alone (n = 4) and in 8 ± 9 minutes with the combination (n = 5). Following drug-induced AF cardioversion, AF was inducible in 4/4 atria with flecainide alone (≤5 minutes duration) and in 2/5 atria with the combination (≤30 seconds duration). Atrial excitability was significantly more depressed by combined versus monotherapies. There was little to no effect on ventricular excitability under any condition tested. Thus, inhibition of I K1 significantly enhances the efficacy of flecainide to depress atrial excitability and to cardiovert AF in our experimental setting. A combination of I Na and I K1 inhibition may be an effective approach for cardioversion of AF.