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 ... -  《-》

Divergent electrophysiologic profile of fluconazole and voriconazole in an experimental whole-heart model of proarrhythmia.

In several case reports a prolongation of the QT-interval and even proarrhythmic effects of fluconazole and voriconazole were reported. The aim of the present study was to investigate if application of fluconazole or voriconazole has the potential to provoke polymorphic ventricular tachycardia in a sensitive model of proarrhythmia. In female rabbits, fluconazole (10, 30 and 50 µM, n=6) and voriconazole (10, 30 and 50 µM, n=6) were infused after obtaining baseline data. Eight endocardial and epicardial monophasic action potentials and a simultaneously recorded 12-lead ECG showed a significant QT prolongation after application of fluconazole as compared with baseline (10 µM:+12 ms, 30 µM:+22 ms, 50 µM:+37 ms; P<0.05) accompanied by an increase of action potential duration (APD90). Administration of voriconazole also induced QT prolongation (30 µM:+10 ms, 50 µM:+20 ms, P<0.05). Spatial dispersion of repolarization remained stable in voriconazole-treated hearts while fluconazole induced a significant increase (30 µM:+15 ms, 50 µM:+16 ms; P<0.05). Lowering of potassium concentration in bradycardic AV-blocked hearts did not provoke any early afterdepolarizations (EADs) or polymorphic ventricular tachycardia in voriconazole-treated hearts. Application of fluconazole led to the reproducible induction of EADs in 4 of 6 hearts and polymorphic ventricular tachycardia in 3 of 6 hearts (36 episodes). In the present study, voriconazole demonstrated a safe electrophysiologic profile despite significant QT prolongation. In contrast, fluconazole led to a more marked prolongation of myocardial repolarization combined with a more marked increase of dispersion of repolarization. These results imply that application of fluconazole might be torsadogenic and the QT-interval should be closely monitored.

Frommeyer G ，Fischer C ，Lange PS ，Leitz P ，Fehr M ，Bogossian H ，Milberg P ，Eckardt L ... -  《-》

Reduction of dispersion of repolarization and prolongation of postrepolarization refractoriness explain the antiarrhythmic effects of quinidine in a model of short QT syndrome.

Milberg P ，Tegelkamp R ，Osada N ，Schimpf R ，Wolpert C ，Breithardt G ，Borggrefe M ，Eckardt L ... -  《-》

Sodium channel block by ranolazine in an experimental model of stretch-related atrial fibrillation: prolongation of interatrial conduction time and increase in post-repolarization refractoriness.

Milberg P ，Frommeyer G ，Ghezelbash S ，Rajamani S ，Osada N ，Razvan R ，Belardinelli L ，Breithardt G ，Eckardt L ... -  《-》

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 ... -  《-》