Ryanodine-receptor inhibition by dantrolene effectively suppresses ventricular arrhythmias in an ex vivo model of long-QT syndrome.

AIMS: A significant antiarrhythmic potential of ryanodine receptor inhibition was reported in experimental studies. The aim of the present study was to assess potential antiarrhythmic effects of dantrolene in an experimental whole-heart model of drug-induced long-QT syndrome (LQTS). METHODS: In 12 isolated rabbit hearts, long-QT-2-syndrome was simulated by infusion of erythromycin (300 µM). Twelve rabbit hearts were treated with veratridine (0.5 µM) to mimic long-QT-3-syndrome. RESULTS: Monophasic action potentials and ECG showed a significant prolongation of QT-interval (+71 ms, P < 0.01) and action potential duration (APD, +43 ms, P < 0.01) after infusion of erythromycin as compared with baseline. Similar results were obtained in veratridine-treated hearts (QT-interval: +43 ms, P < 0.01; APD: +36 ms, P < 0.01). Both erythromycin (+36 ms, P < 0.05) and veratridine (+38 ms) significantly increased dispersion of repolarization. Additional infusion of dantrolene (20 µM) did not significantly alter QT-interval and APD but resulted in a significant reduction of dispersion of repolarization (erythromycin group: -33 ms, P < 0.05; veratridine group: -29 ms, P < 0.05). Lowering of potassium concentration resulted in the occurrence of early afterdepolarizations (EAD) and polymorphic ventricular tachycardia (VT) in 9 of 12 erythromycin-treated hearts (175 episodes) and 8 of 12 veratridine-treated hearts (66 episodes). Additional infusion of dantrolene significantly reduced occurrence of polymorphic VT and resulted in occurrence of EAD and polymorphic VT in 1 of 12 erythromycin-treated hearts (18 episodes) and 1 of 12 veratridine-treated hearts (3 episodes). CONCLUSION: Inhibition of the ryanodine receptor by dantrolene significantly reduced occurrence of polymorphic VT in drug-induced LQTS. A significant reduction of spatial dispersion of repolarization represents a major antiarrhythmic mechanism. These results imply that dantrolene may represent a promising antiarrhythmic option in drug-induced LQTS.

Colchicine Increases Ventricular Vulnerability in an Experimental Whole-Heart Model.

The traditional gout medication colchicine has been reported to effectively prevent atrial fibrillation recurrence after atrial fibrillation ablation or cardiac surgery in a few clinical trials. Severe adverse events have not yet been reported. The aim of the present study was to assess possible direct electrophysiological effects in an experimental whole-heart model. Ten rabbit hearts were isolated and Langendorff-perfused. Thereafter, colchicine was administered in two concentrations (1 and 3 µM). Eight endo- and epicardial monophasic action potentials and a 12-lead ECG showed a stable QT interval and action potential duration during colchicine infusion. Furthermore, there was no significant increase in dispersion of repolarization. However, colchicine induced a dose-dependent significant decrease of effective refractory period (ERP; 1 µM: -19 ms, 3 µM: -22 ms; p < 0.05). In the present study, acute infusion of colchicine in isolated rabbit hearts resulted in a reduction of ERP in the presence of a stable myocardial repolarization. This led to a significantly elevated inducibility of ventricular fibrillation. In 4 of 10 hearts, incessant ventricular fibrillation occurred. These results suggest a pro-arrhythmic or toxic effect of colchicine and underline that further clinical studies on potential adverse effects should be conducted before the drug can be recommended for routine use after atrial fibrillation ablation.