A post hoc analysis of the PALLAS trial suggested life-threatening interactions of digitalis and dronedarone. Thus, there is concern about an interplay between digitalis and other drugs that influence cardiac electrophysiology. We therefore investigated the interaction between digitalis and flecainide or ranolazine. Twenty-five rabbit hearts were Langendorff-perfused and treated with flecainide (2 µM, 12 hearts) or ranolazine (10 µM, 13 hearts). Infusion of flecainide prolonged mean action potential duration [APD90, from 153 ms (interquartile range (IQR): 29.7 ms) to 159 ms (IQR: 24.9 ms, p = 0.04)] and effective refractory period [ERP, 170 ms (IQR: 40 ms) vs. 200 ms (IQR: 32.5 ms, p < 0.01)]. Administration of ranolazine prolonged APD90 [144 ms (IQR: 34.3 ms)) vs. 157 ms (IQR: 31.2 ms, p < 0.01)] and ERP [180 ms (IQR: 40 ms) vs. 200 ms (IQR: 30 ms, p < 0.01)]. Additional infusion of the digitalis glycoside ouabain (0.2 µM) abbreviated APD90 and ERP in both groups (flecainide: APD90: to 128 ms (IQR: 19 ms), ERP: to 170 ms (IQR: 20 ms), p < 0.01 each; ranolazine: APD90: to 141 ms (IQR: 40 ms), ERP: to 160 ms (IQR: 30 ms), p < 0.01 each). Ventricular vulnerability was assessed by a pacing protocol employing premature extra stimuli and burst stimulation. No proarrhythmic effect was observed with flecainide (1 vs. 3 episodes at baseline) or ranolazine (3 vs. 11 episodes at baseline). However, further infusion of ouabain had a proarrhythmic effect for both drugs (flecainide: 15 episodes, p = 0.04; ranolazine: 21 episodes, p = 0.09). Concomitant treatment of the sodium channel blockers flecainide or ranolazine with digitalis seems to be proarrhythmic. Abbreviation of repolarization and refractoriness that can facilitate re-entry was found as underlying mechanism.
Keywords: Digitalis; Flecainide; Ranolazine; Sudden cardiac death; Ventricular arrhythmias.