Effects of bidisomide (SC-40230), a new class I antiarrhythmic agent, on ventricular arrhythmias induced by coronary artery occlusion and reperfusion in anesthetized rats; comparison with mexiletine and disopyramide

Characterisation of mexiletine's translational therapeutic index for suppression of ischaemia-induced ventricular fibrillation in the rat isolated heart

The 'translational therapeutic index' (TTI) is a drug's ratio of nonclinical threshold dose (or concentration) for significant benefit versus threshold for adversity. In early nonclinical research, discovery and safety studies are normally undertaken separately. Our aim was to evaluate a novel integrated approach for generating a TTI for drugs intended for prevention of ischaemia-induced ventricular fibrillation (VF). We templated the current best available class 1b antiarrhythmic, mexiletine, using the rat Langendorff preparation. Mexiletine's beneficial effects on the incidence of VF caused by 120 min regional ischaemia were contrasted with its concurrent adverse effects (on several variables) in the same hearts, to generate a TTI. Mexiletine 0.1 and 0.5 µM had no adverse effects, but did not reduce VF incidence. Mexiletine 1 µM reduced VF incidence to 0% but had adverse effects on atrioventricular conduction and ventricular repolarization. Separate studies undertaken using an intraventricular balloon revealed no detrimental effects of mexiletine (1 and 5 µM) on mechanical function, or any benefit against reperfusion-related dysfunction. Mexiletine's TTI was found to be less than two, which accords with its clinical therapeutic index. Although non-cardiac adversity, identifiable from additional in vivo studies, may reduce the TTI further, it cannot increase it. Our experimental approach represents a useful early-stage integrated risk/benefit method that, when TTI is found to be low, would eliminate unsuitable class 1b drugs prior to next stage in vivo work, with mexiletine's TTI defining the gold standard that would need to be bettered.

Rat Models of Ventricular Fibrillation Following Acute Myocardial Infarction

A number of animal models have been designed in order to unravel the underlying mechanisms of acute ischemia-induced arrhythmias and to test compounds and interventions for antiarrhythmic therapy. This is important as acute myocardial infarction (AMI) continues to be the major cause of sudden cardiac death, and we are yet to discover safe and effective treatments of the lethal arrhythmias occurring in the acute setting. Animal models therefore continue to be relevant for our understanding and treatment of acute ischemic arrhythmias. This review discusses the applicability of the rat as a model for ventricular arrhythmias occurring during the acute phase of AMI. It provides a description of models developed, advantages and disadvantages of rats, as well as an overview of the most important interventions investigated and the relevance for human pathophysiology.

Amiodarone for the prevention of reperfusion ventricular fibrillation

OBJECTIVE

The purpose of this study was to evaluate the efficacy of prophylactic single-dose amiodarone administered through the pump circuit before releasing the aortic cross-clamp (ACC) in preventing the occurrence of reperfusion ventricular fibrillation (RVF).

DESIGN

A prospective, randomized double-blind, placebo-controlled efficacy study.

SETTING

A tertiary level teaching hospital.

INTERVENTION

Seventeen patients received 150 mg of amiodarone in 10 mL of normal saline by way of the pump 3 minutes before releasing the ACC, and a control group of 17 patients received 10 mL of normal saline.

MEASUREMENT AND MAIN RESULTS

The primary outcome of the study was the incidence of ventricular fibrillation requiring defibrillation during the 30-minute period after myocardial reperfusion. A large decrease in RVF (65% to 18%) was observed in the amiodarone-treated group with the number needed to treat only 2.1.The myocardial performance in terms of cardiac output was better in the amiodarone group; this could be attributed to the lower incidence of RVF and subsequent direct current shock therapy.

CONCLUSIONS

The observations showed that single-dose prophylactic amiodarone administered through the pump circuit 3 minutes before ACC release was an effective therapy to reduce the incidence of post-ACC release ventricular arrhythmias.

Arrhythmia Models for Drug Research: Classification of Antiarrhythmic Drugs

The aim of this study was to classify antiarrhythmic drugs based on their effectiveness on 6 in vivo arrhythmia models, mainly using dogs. The models were produced by two-stage coronary ligation, digitalis, halothane-adrenaline, programmed electrical stimulation in old myocardial infarction dogs, coronary artery occlusion/reperfusion, or chronic atrioventricular block. Na(+)-channel-blocking drugs suppressed two-stage coronary ligation and digitalis arrhythmias. Ca(2+)-channel blockers and beta-blockers suppressed halothane-adrenaline arrhythmia. Positive inotropic drugs aggravated halothane-adrenaline arrhythmia, but did not aggravate digitalis arrhythmia. K(+)-channel blockers suppressed programmed electrical stimulation induced arrhythmia, but induced torsades de pointes type arrhythmia in chronic atrioventricular block dogs and aggravated halothane-adrenaline arrhythmia. Na(+)/H(+)-exchange blockers suppressed coronary artery occlusion/reperfusion arrhythmias. This classification may be useful for predicting the clinical effectiveness in the preclinical stage of drug development.

Antiarrhythmic Properties of a Prior Oral Loading of Amiodarone in In Vivo Canine Coronary Ligation/Reperfusion-Induced Arrhythmia Model: Comparison With Other Class III Antiarrhythmic Drugs

Amiodarone, which is generally classified as class III antiarrhythmic drug in the Vaughan Williams classification, is widely used for the treatments of refractory arrhythmias. However, we previously reported that intravenous infusion of amiodarone (6.67 mg/kg per hour) did not suppress arrhythmias induced by coronary ligation/reperfusion in dogs. In this study, we examined effects of a prior oral loading of amiodarone on arrhythmias induced by coronary ligation/reperfusion. Sixteen female beagle dogs (8.5 - 12.5 kg) were divided into two groups; one group was given amiodarone (40 mg/kg, orally, n = 8), and the other was given empty gelatin capsules (n = 8) 2 h before the operation. Dogs were anesthetized with pentobarbital and artificially ventilated. The left chest was opened, and the left anterior descending coronary artery was ligated for 30 min and then reperfused. The mean plasma concentration of amiodarone was over 1.3 mug/ml. Although the prior oral loading of amiodarone did not change the QT interval, amiodarone suppressed the number of ectopic beats during coronary ligation and the incidence of ventricular fibrillation during coronary ligation and reperfusion periods (P<0.05 vs control group). In conclusion, a prior oral loading of amiodarone suppressed arrhythmias induced by coronary ligation/reperfusion with a dose that did not prolong the QT interval. This antiarrhythmic property of amiodarone is different from those of the other class III drugs in that antiarrhythmic effects were accompanied by QT prolongation in our all previous studies.

Effects of a Novel Cyclohexane Dicarboximide Derivative, ST-6, on Reperfusion-Induced Arrhythmia in Rats

The present study was designed to determine whether a novel cyclohexane dicarboximide derivative, ST-6, 2-[4-[4-(chlorophenyl)-4-hydroxy-1-piperidinyl]butyl]hexahydro-1H-isoindol-1,3(2H)-dione, prevents reperfusion-induced ventricular arrhythmias. Pentobarbital-anesthetized rats were subjected to left coronary artery occlusion for 4 min followed by 4-min reperfusion, and the incidence of their ventricular arrhythmias was examined. The coronary occlusion of control rats induced ventricular tachycardia and fibrillation, eventually leading to sudden death. The intravenous injection of 0.1 to 2 mg/kg ST-6 prior to the occlusion resulted in a dose-dependent suppression of the ventricular arrhythmias. The suppression of ventricular fibrillation was also observed on the intraperitoneal and intradoudenal administration of 2 to 10 mg/kg ST-6 15 min prior to coronary occlusion. Antiarrhythmic effects of this agent (0.5 mg/kg per min) were compared with those of other antiarrhythmic agents including lidocaine (0.1 mg/kg per min), sematilide (0.3 mg/kg per min), and diltiazem (0.5 mg/kg per min) by administrating the agents from 1 min after the coronary occlusion to the end of 4-min reperfusion. Antiarrhythmic effects of ST-6 were similar in degree to those of lidocaine and diltiazem, whereas no significant prevention by sematilide was seen. The results suggest that ST-6 may be capable of suppressing reperfusion-induced arrhythmias following oral or intravenous administration.

Electrophysiologic effects of an antiarrhythmic agent, bidisomide, on sodium current in isolated rat ventricular myocytes: comparison with mexiletine and disopyramide

The effects of bidisomide, an antiarrhythmic agent, on sodium current (I(Na)) in isolated rat ventricular myocytes were investigated using a whole cell voltage clamp method. Bidisomide blocked I(Na) with a Ki of 214 microM at a holding potential of -140 mV. The blockade of I(Na) was enhanced at a less negative holding potential of -100 mV with a Ki of 21 microM. Bidisomide shifted the steady state inactivation curve to a negative potential direction by 20 mV without a significant change in the slope factor. Bidisomide slowed the time course of recovery of I(Na) at a holding potential of -140 mV with a slow recovery phase. The time constant of recovery phase for bidisomide, disopyramide and mexiletine were 2703, 1858 and 757 ms, respectively. The development of the block of I(Na) consisted of two phases in the presence of bidisomide. The fast and slow time constants were 11 and 648 ms. Bidisomide produced a use-dependent block of I(Na) when the depolarizing pulse was repeated at 1-3 Hz. Our results indicate that bidisomide binds to rat cardiac sodium channels and that the dissociation kinetics of bidisomide from the inactivated sodium channel is slower than that of disopyramide.

Antiarrhythmic and electrophysiological effects of GYKI-16638, a novel N-(phenoxyalkyl)-N-phenylalkylamine, in rabbits

The effect of N-[4-[2-N-methyl-N-[1-methyl-2-(2, 6-dimethylphenoxy)ethylamino]-ethyl]-phenyl]-methanesulfonamide. hydrochloride (GYKI-16638; 0.03 and 0.1 mg/kg, i.v.), a novel antiarrhythmic compound, was assessed and compared to that of D-sotalol (1 and 3 mg/kg, i.v.) on arrhythmias induced by 10 min of coronary artery occlusion and 10 min of reperfusion in anaesthetized rabbits. Also, its cellular electrophysiological effects were studied in rabbit right ventricular papillary muscle preparations and in rabbit single isolated ventricular myocytes. In anaesthetized rabbits, intravenous administration of 0.03 and 0.1 mg/kg GYKI-16638 and 1 and 3 mg/kg D-sotalol significantly increased survival during reperfusion (GYKI-16638: 82% and 77%, D-sotalol: 75% and 83% vs. 18% in controls, P<0.05, respectively). GYKI-16638 (0.1 mg/kg) significantly increased the number of animals that did not develop arrhythmias during reperfusion (46% vs. 0% in controls, P<0.05). In isolated rabbit right ventricular papillary muscle, 2 microM GYKI-16638, at 1 Hz stimulation frequency, lengthened the action potential duration at 50% and 90% repolarization (APD(50-90)) without influencing the resting membrane potential and action potential amplitude (APA). It decreased the maximal rate of depolarization (V(max)) in a use-dependent manner. This effect was statistically significant only at stimulation cycle lengths shorter than 700 ms. The offset kinetics of this V(max) block were relatively rapid, the corresponding time constant for recovery of V(max) was 328.2+/-65.0 ms. In patch-clamp experiments, performed in rabbit ventricular myocytes, 2 microM GYKI-16638 markedly depressed the rapid component of the delayed rectifier outward and moderately decreased the inward rectifier K(+) current without significantly altering the slow component of the delayed rectifier and transient outward K(+) currents. These results suggest that in rabbits, GYKI-16638 has an in vivo antiarrhythmic effect, comparable to that of D-sotalol, which can be best explained by its combined Class I/B and Class III actions.

Treatment of atrial fibrillation and paroxysmal supraventricular tachycardia with bidisomide. The Atrial Fibrillation Investigation with Bidisomide (AFIB) Investigators

BACKGROUND

Atrial fibrillation and paroxysmal supraventricular tachycardia are common disorders of the heart rhythm for which antiarrhythmic drug therapy is commonly prescribed. The Atrial Fibrillation Investigation with Bidisomide (AFIB) study was a randomized, placebo-controlled clinical trial designed to accomplish three goals in a single protocol: (1) to determine the efficacy of the antiarrhythmic drug bidisomide in the treatment of these two arrhythmias; (2) to establish the appropriate dose range for bidisomide; and (3) to detect an adverse mortality effect of bidisomide if one were present in patients with atrial fibrillation.

METHODS AND RESULTS

In this clinical trial, 1227 patients with atrial fibrillation and 187 with paroxysmal supraventricular tachycardia were randomly assigned to bidisomide (200, 400, or 600 mg BID) or placebo; patient groups with each arrhythmia were analyzed separately. Symptomatic recurrences of atrial fibrillation and paroxysmal supraventricular tachycardia were documented with the use of transtelephonic ECG monitoring. The time to the first symptomatic arrhythmia recurrence was measured in each patient and compared among treatment groups. Among the atrial fibrillation patients, there was no significant difference in the time to first symptomatic recurrence between the placebo group and any of the three bidisomide treatment groups; the hazard ratios (placebo:treatment) were 1.19, 1.03, and 1.14 for bidisomide 200, 400, and 600 mg BID, respectively. Among paroxysmal supraventricular tachycardia patients, there was a similar lack of a significant treatment effect; the hazard ratios were 1.30, 1.93, and 1.59 for bidisomide 200, 400, and 600 mg BID, respectively. In the primary safety analysis of mortality, 3 of 493 patients taking placebo died, compared with 9 of 488 patients taking one of the two higher doses of bidisomide (P>.10).

CONCLUSIONS

Bidisomide in the doses tested did not have a clinically important antiarrhythmic effect. The AFIB study provided a novel clinical trial design to test antiarrhythmic drugs for both safety and efficacy.