Effect of ranolazine on ventricular repolarization in class III antiarrhythmic drug-treated rabbits.

Ranolazine exhibits a synergistic effect in combination with class III drugs to suppress atrial fibrillation. To investigate whether a combination therapy affects repolarization and provokes ventricular tachyarrhythmias (VT) in a sensitive model of proarrhythmia. Thirty-seven rabbits were assigned to 3 groups and fed with amiodarone (50 mg/kg/d; n = 10) or dronedarone (50 mg/kg/d; n = 10) over a period of 6 weeks. A third group was used as control (n = 17). After obtaining baseline data in Langendorff-perfused control hearts, sotalol (100 μM) was administered in this group. Thereafter, ranolazine (10 μM) was additionally infused on top of amiodarone, dronedarone, or sotalol. Chronic treatment with amiodarone or dronedarone as well as sotalol significantly increased action potential duration at 90% repolarization (APD(90)). Additional treatment with ranolazine further increased APD(90) in amiodarone- and dronedarone-pretreated hearts but not in sotalol-treated hearts. Ranolazine increased postrepolarization refractoriness as compared with amiodarone or dronedarone alone owing to a marked effect on the refractory period. In contrast to amiodarone and dronedarone, acute application of sotalol increased dispersion of repolarization (P < .05). Additional treatment with ranolazine did not further increase spatial or temporal dispersion. After lowering extracellular [K(+)] in bradycardic hearts, no proarrhythmia occurred in amiodarone- or dronedarone-treated hearts whereas 11 of 17 sotalol-treated hearts showed early afterdepolarizations and subsequent polymorphic VT. Additional treatment with ranolazine reduced the number of VT episodes in sotalol-treated hearts and did not cause proarrhythmia in combination with amiodarone or dronedarone. Application of ranolazine on top of class III drugs does not cause proarrhythmia despite a marked effect on ventricular repolarization. The effect of ranolazine on the repolarization reserve is associated with the lack of effect on early afterdepolarizations and dispersion of repolarization.

Frommeyer G ，Kaiser D ，Uphaus T ，Kaese S ，Osada N ，Rajamani S ，Belardinelli L ，Breithardt G ，Eckardt L ，Milberg P ... -  《-》

Antiarrhythmic effect of ranolazine in combination with class III drugs in an experimental whole-heart model of atrial fibrillation.

Ranolazine is evaluated for antiarrhythmic therapy of atrial fibrillation (AF). The electrophysiologic mechanisms of ranolazine in combination with class III drugs were studied in an isolated whole-heart model of stretch-related AF. Thirty rabbits were fed with amiodarone (50 mg/kg/day, n = 10), dronedarone (50 mg/kg/day, n = 10), or placebo (n = 10) for 6 weeks. Subsequently, in isolated hearts, AF was induced by high-rate atrial pacing and acute atrial dilatation. In placebo-treated hearts, d,l-sotalol (50 μM) was acutely administered. Ranolazine (10 μM) was additionally infused in all groups. Chronic amiodarone (+26 ± 7 ms, P < 0.05) or dronedarone (+22 ± 4 ms, P < 0.05) as well as acute application of d,l-sotalol (+20 ± 3 ms, P < 0.05) increased atrial action potential duration (aAPD90 ). Additional treatment with ranolazine did not significantly change aAPD90 (P = ns). Class III drugs did not affect interatrial conduction time, while ranolazine significantly increased it (amiodarone group: +15 ± 3 ms, dronedarone group: +11 ± 3 ms, sotalol group: +15 ± 6 ms; P < 0.05 each). Ranolazine led to an additional increase in atrial effective refractory period (aERP), thus leading to an enhanced atrial postrepolarization refractoriness (aPRR, +17 ± 6 ms, +21 ± 4 ms and +16 ± 8 ms, P < 0.05, respectively). Acute atrial dilatation increased AF incidence compared with baseline. Amiodarone-pretreated hearts showed a lower incidence of AF. Additional infusion of ranolazine further diminished AF. Dronedarone or acute infusion of sotalol did not significantly suppress AF, while additional treatment with ranolazine in these groups also reduced AF incidence. In this study, ranolazine on top of class III antiarrhythmic therapy had a beneficial effect. The increase in interatrial conduction time and marked atrial aPRR suppressed AF. These results shed further light on a potential therapeutic benefit of ranolazine on top of conventional antiarrhythmic therapy for rhythm control in AF.

Frommeyer G ，Milberg P ，Uphaus T ，Kaiser D ，Kaese S ，Breithardt G ，Eckardt L ... -  《-》

New insights into the beneficial electrophysiologic profile of ranolazine in heart failure: prevention of ventricular fibrillation with increased postrepolarization refractoriness and without drug-induced proarrhythmia.

Ranolazine inhibits late Na(+) and K(+) currents. Earlier studies have reported an antiarrhythmic effect. The aim of the present study was to understand whether ranolazine could still preserve its antiarrhythmic properties in the settings of chronic heart failure (CHF). In 12 female rabbits, CHF was induced by 4 weeks of rapid ventricular pacing leading to a decrease in ejection fraction. Twelve rabbits underwent sham operation. Isolated hearts were Langendorff perfused and demonstrated a significant QT prolongation after induction of heart failure. Ranolazine caused a concentration-dependent (10 and 30 μmol/L) increase of action potential duration (APD(90)) in sham-operated and failing hearts. Eight endo- and epicardial monophasic action potentials revealed a nonsignificant increase in spatial and temporal dispersion of repolarization. The increase in APD(90) was accompanied by a greater increase in refractory period, resulting in a significant increase in postrepolarization refractoriness in sham-operated (+29 ms and +55 ms; P < .01) and failing (+22 ms and +30 ms; P < .05) hearts. In control conditions, programmed ventricular stimulation and a burst pacing protocol led to ventricular fibrillation (VF) in 5 of the 12 sham-operated (6 episodes) and in 7 of the 12 failing (18 episodes) hearts. In the presence of ranolazine, VF was inducible in only 2 of 12 failing hearts (5 episodes). In the presence of low [K(+)], only 1 ranolazine-treated sham-operated heart developed early afterdepolarizations and ventricular tachyarrhythmias despite significant QT prolongation. Ranolazine decreases inducibility of VF in the presence of a significant increase in postrepolarization refractoriness. This antiarrhythmic effect in the intact heart is preserved in CHF and is not associated with drug-induced proarrhythmia.

Frommeyer G ，Rajamani S ，Grundmann F ，Stypmann J ，Osada N ，Breithardt G ，Belardinelli L ，Eckardt L ，Milberg P ... -  《-》

Electrophysiological profile of vernakalant in an experimental whole-heart model: the absence of proarrhythmia despite significant effect on myocardial repolarization.

The most recent European Society of Cardiology (ESC) update on atrial fibrillation has introduced vernakalant (VER) for pharmacological cardioversion of atrial fibrillation. The aim of the present study was to investigate the safety profile of VER in a sensitive model of proarrhythmia. In 36 Langendorff-perfused rabbit hearts, VER (10, 30 µM, n = 12); ranolazine (RAN, 10, 30 µM, n = 12), or sotalol (SOT, 50; 100 µM, n = 12) were infused after obtaining baseline data. Monophasic action potentials and a 12-lead electrocardiogram showed a significant QT prolongation after application of VER as compared with baseline (10 µM: +25 ms, 30 µM: +50 ms, P < 0.05) accompanied by an increase of action potential duration (APD). The increase in APD90 was accompanied by a more marked increase in effective refractory period (ERP) leading to a significant increase in post-repolarization refractoriness (PRR, 10 µM: +30 ms, 30 µM: +36 ms, P < 0.05). Vernakalant did not affect the dispersion of repolarization. Lowered potassium concentration in bradycardic hearts did not provoke early afterdepolarizations (EADs) or polymorphic ventricular tachycardia (pVT). Comparable results were obtained with RAN. Hundred micromolars of SOT led to an increase in QT interval (+49 ms) and APD90 combined with an increased ERP and PRR (+23 ms). In contrast to VER, 100 µM SOT led to a significant increase in dispersion of repolarization and to the occurrence of EAD in 10 of 12 and pVT in 8 of 12 hearts. In the present study, application of VER and SOT led to a comparable prolongation of myocardial repolarization. Both drugs increased the PRR. However, VER neither affect the dispersion of repolarization nor induce EAD and therefore did not cause proarrhythmia.

Frommeyer G ，Milberg P ，Clauss C ，Schmidt M ，Ramtin S ，Kaese S ，Grundmann F ，Grotthoff JS ，Pott C ，Eckardt L ... -  《-》

Electrophysiologic profile of dronedarone on the ventricular level: beneficial effect on postrepolarization refractoriness in the presence of rapid phase 3 repolarization.

Milberg P ，Frommeyer G ，Uphaus T ，Kaiser D ，Osada N ，Breithardt G ，Eckardt L ... -  《-》