Electrophysiologic and antiarrhythmic effects of AZD1305 in canine pulmonary vein sleeves

Effect of autonomic influences to induce triggered activity in muscular sleeves extending into the coronary sinus of the canine heart and its suppression by ranolazine

INTRODUCTION

Extrasystoles arising from the muscular sleeves associated with the pulmonary veins (PV), superior vena cava (SVC), and coronary sinus (CS) are known to precipitate atrial fibrillation (AF). The late sodium channel current (I_Na ) inhibitor ranolazine has been reported to exert antiarrhythmic effects in canine PV and SVC sleeves by suppressing late phase 3 early and delayed after depolarization (EAD and DAD)-induced triggered activity induced by parasympathetic and/or sympathetic stimulation. The current study was designed to extend our existing knowledge of the electrophysiological and pharmacologic properties of canine CS preparations and assess their response to inhibition of late I_Na following autonomic stimulation.

METHODS

Transmembrane action potentials were recorded from canine superfused CS using standard microelectrode techniques. Acetylcholine (ACh, 1 µM), isoproterenol (Iso, 1 µM), high calcium ([Ca²⁺ ]_o  = 5.4 mM), or a combination were used to induce EADs, DADs, and triggered activity.

RESULTS

Action potentials (AP) recorded from the CS displayed short and long AP durations (APD), with and without phase 4 depolarization (n = 19). Iso induced DAD-mediated triggered activity. The combination of sympathetic and parasympathetic agonists resulted in late phase 3 EAD-induced triggered activity in all CS preparations. Ranolazine (5-10 µM) suppressed late phase 3 EAD- and DAD-induced triggered activity in 8 of 8 preparations. Subthreshold stimulation induced a prominent hyperpolarization that could be suppressed by atropine.

CONCLUSIONS

Our results suggest the important role of parasympathetic innervation in the activity of the CS. Autonomic influences promote DAD- and late phase-3-EAD-mediated triggered activity in canine CS, thus generating extrasystolic activity capable of initiating atrial arrhythmias. Ranolazine effectively suppresses these triggers.

Electrophysiological characteristics of canine superior vena cava sleeve preparations: effect of ranolazine

BACKGROUND

In addition to extrasystoles of pulmonary vein (PV) origin, those arising from the superior vena cava (SVC) can precipitate atrial fibrillation (AF). The present study evaluates the electrophysiological properties of canine SVC sleeve preparations and the effect of ranolazine on late phase 3 early and delayed afterdepolarization (EAD and DAD)-induced triggered activity in SVC sleeves and compares SVC and PV sleeve electrophysiological properties.

METHODS AND RESULTS

Action potentials (APs) were recorded from superfused SVC and PV sleeves using microelectrode techniques. Acetylcholine (1 μmol/L), isoproterenol (1 μmol/L), high calcium ([Ca(2+)](o)=5.4 mmol/L), or a combination were used to induce EADs, DADs, and triggered activity. A marked diversity of action potential characteristics was observed in the SVC sleeve, including action potentials with short and long APs, with and without phase 4 depolarization. Rapid pacing induced hyperpolarization, accentuating the slope of phase 4 depolarization. Phase 4 depolarization and rapid pacing-induced hyperpolarization were reduced or eliminated after atropine (10 μmol/L) or ranolazine (10 μmol/L). APs displaying phase 4 depolarization (n=19) had longer APDs, smaller amplitude and V(max), and a more positive take-off potential than APs lacking phase 4 depolarization (n=15). Ranolazine (5-10 μmol/L) eliminated late phase 3 EAD- and DAD-induced triggered activity as well as isoproterenol-induced automaticity elicited in SVC sleeves. Compared with PV, SVC sleeves display phase 4 depolarization, smaller V(max), and longer APs.

CONCLUSIONS

Autonomic influences promote spontaneous automaticity and triggered activity in SVC sleeves, thus generating extrasystolic activity capable of initiating atrial arrhythmias. Ranolazine can effectively suppress these triggers.

Comparison of electrophysiological and antiarrhythmic effects of vernakalant, ranolazine, and sotalol in canine pulmonary vein sleeve preparations

BACKGROUND

Vernakalant (VER) is a relatively atrial-selective antiarrhythmic drug capable of blocking potassium and sodium currents in a frequency- and voltage-dependent manner. Ranolazine (RAN) is a sodium-channel blocker shown to exert antiarrhythmic effects in pulmonary vein (PV) sleeves. dl-Sotalol (SOT) is a β-blocker commonly used in the rhythm-control treatment of atrial fibrillation. This study evaluated the electrophysiological and antiarrhythmic effects of VER, RAN, and SOT in canine PV sleeve preparations in a blinded fashion.

METHODS

Transmembrane action potentials were recorded from canine superfused PV sleeve preparations exposed to VER (n = 6), RAN (n = 6), and SOT (n = 6). Delayed afterdepolarizations were induced in the presence of isoproterenol and high-calcium concentrations by periods of rapid pacing.

RESULTS

In PV sleeves, VER, RAN, and SOT (3-30 μM) produced small (10-15 ms) increases in action potential duration. The effective refractory period, diastolic threshold of excitation, and the shortest S(1)-S(1) cycle length permitting 1:1 activation were significantly increased by VER and RAN in a rate- and concentration-dependent manner. VER and RAN significantly reduced V(max) in a concentration- and rate-dependent manner. SOT did not significantly affect the effective refractory period, V(max), diastolic threshold of excitation, or the shortest S(1)-S(1) cycle length permitting 1:1 activation. All 3 agents (3-30 μM) suppressed delayed afterdepolarization-mediated triggered activity induced by isoproterenol and high calcium.

CONCLUSIONS

In canine PV sleeves, the effects of VER and RAN were similar and largely characterized by concentration- and rate-dependent depression of sodium-channel-mediated parameters, which were largely unaffected by SOT. All 3 agents demonstrated an ability to effectively suppress delayed afterdepolarization-induced triggers of atrial arrhythmia.

Reduced ventricular proarrhythmic potential of the novel combined ion-channel blocker AZD1305 versus dofetilide in dogs with remodeled hearts

BACKGROUND

AZD1305 is an investigational antiarrhythmic agent for management of atrial fibrillation. It blocks various cardiac ion currents at different potencies and has atrial-predominant electrophysiological effects. We investigated the electrophysiological and proarrhythmic effects of AZD1305 versus dofetilide in dogs with chronic complete atrioventricular block and myocardial hypertrophic remodeling.

METHODS AND RESULTS

AZD1305 was administered to anesthetized mongrel dogs before and >2 weeks after the induction of atrioventricular block and ventricular and atrial electrophysiological parameters were assessed. In all dogs, the selective I(Kr) blocker dofetilide was used to examine susceptibility to acquired torsades de pointes in chronic atrioventricular block and for comparison. At normal sinus rhythm, AZD1305 increased QT and RR intervals from 290±7 to 397±15 ms (+37%, P<0.0001) and from 603±22 to 778±32 ms (+29%, P=0.002), respectively. In the same animals at chronic atrioventricular block, AZD1305 increased the QT interval from 535±28 to 747±36 ms (+40%, P<0.0001), similar to the QT prolongation by dofetilide (511±22 to 703±45 ms [+38%, P<0.0001]). AZD1305 slightly slowed the idioventricular rhythm. Whereas all (n=14) chronic atrioventricular block animals exhibited torsades de pointes on dofetilide, the arrhythmia was induced in only 4 of 11 dogs after AZD1305. Beat-to-beat variability of left-ventricular monophasic-action-potential duration increased after dofetilide (2.3±0.2 to 6.3±0.7 ms; P<0.0001) but not after AZD1305 (2.8±0.3 to 3.7±0.3 ms; P=0.20) despite similar left-ventricular monophasic-action-potential duration prolongations.

CONCLUSIONS

Despite causing similar degrees of repolarization delay as the selective I(Kr) blocker dofetilide, the combined ion-channel blocker AZD1305 induces less repolarization instability and has a lower ventricular proarrhythmic potential in the remodeled dog heart.

Searching for new cardiovascular drugs: towards improved systems for drug screening?

INTRODUCTION

The pharmaceutical industry urgently needs new ways of profiling the safety and efficacy of new cardiovascular (CV) drugs and more effectively transitioning these compounds through the stages of CV drug screening. This article reviews new technologies and methodological innovations and assesses whether these frameworks offer improved solutions to the problems facing the contemporary CV drug development.

AREAS COVERED

The article comprises literature derived from a systematic search (from 2000 onwards) using the US patent office and ESP@CENET search engines as well as through multiple Boolean terms. The article focuses on patents relating to technologies and resources and categorises the patents according to their niche in the CV drug screening landscape.

EXPERT OPINION

The CV drug pipeline is stalling due to the inability of many contemporary drug screening frameworks to discriminate between safe, efficacious therapy and hazardous off-target effect. Given the current limitations of drug screening frameworks, there is little scope for expanding the CV drug portfolio with newer, safer drugs with improved mechanisms of action. New screening modalities are urgently needed. Searches reveal that there are few examples of truly new technologies and systems in the patent literature. This apparent failure to revamp facets of the CV drug screening process can only perpetuate the inability of current platforms to improve the CV drug pipeline. Consequently, with few exceptions, there is stagnation in pre-clinical assay design that limits the pharmaceutical industry's ability to search for new drugs in new and more effective ways.

Pharmacological cardioversion of atrial fibrillation--a double-blind, randomized, placebo-controlled, multicentre, dose-escalation study of AZD1305 given intravenously

AIM

AZD1305 is a combined ion channel blocker developed for the treatment of atrial fibrillation (AF). The aim of this study was to determine whether AZD1305 was effective in converting AF to sinus rhythm (SR).

METHODS AND RESULTS

Patients with AF episodes of duration 3 h to 3 months were randomized in a 3:1 ratio to receive a maximum 30 min intravenous infusion of AZD1305 or matching placebo. The primary efficacy endpoint was the proportion of patients converting within 90 min of the start of infusion, after which patients who had not converted were to undergo direct current (DC) cardioversion. Four ascending AZD1305 dose groups were assigned sequentially, with dose rates of 50, 100, 130, and 180 mg/h. A total of 171 patients were randomized. Pharmacological conversion was achieved in 0 of 43 patients (0%) in the placebo group, and in 2 of 26 (8%; P= 0.14 vs. placebo), 8 of 45 (18%; P= 0.006), 17 of 45 (38%; P< 0.001), and 6 of 12 patients (50%; P< 0.001) in AZD1305 dose groups 1-4, respectively. Maximum QTcF (QT interval corrected according to Fridericia's formula) generally increased dose-dependently up to a plateau, although there was wide variation between patients. Two patients experienced torsade de pointes (TdP): one patient without symptoms in dose group 3, and one patient requiring DC defibrillation in dose group 4. Both patients recovered without sequelae.

CONCLUSIONS

AZD1305 was effective in converting AF to SR, but was associated with QT prolongation and TdP. The benefit-risk profile was judged as unfavourable and the AZD1305 development programme was discontinued.

CLINICAL TRIAL REGISTRATION

http://clinicaltrials.gov identifier NCT00915356.

Pulmonary Vein Sleeves as a Pharmacologic Model for the Study of Atrial Fibrillation

OBJECTIVES

To review the electrophysiologic effects of antiarrhythmic agents in pulmonary veins (PV) sleeve preparations.

BACKGROUND

Ectopic activity arising from the PV plays a prominent role in the development of atrial fibrillation.

METHODS

Transmembrane action potentials were recorded from canine superfused left superior or inferior PV sleeves using standard microelectrode techniques. Acetylcholine (ACh, 1 μM), isoproterenol (1 μM), high calcium ([Ca2+]o=5.4mM) or a combination was used to induce early or delayed afterdepolarizations (EADs or DADs) and triggered activity.

RESULTS

In canine PV sleeves, ranolazine (10 μM) induced a marked use-dependent decrease in Vmax, a rate-dependent abbreviation of action potential duration (APD), but a rate-dependent increase in effective refractory period due to the development of post-repolarization refractoriness and eliminates rate-dependent delayed and late phase 3 early afterdepolarizations (DADs and EADs)-induced triggered activity induced by high calcium, isoproterenol, acetylcholine of their combination together with rapid pacing. Chronic amiodarone induced a prolongation of APD, a marked decrease in Vmax, and prevented the development of DADs and late phase 3 EADs-induced triggered activity. Combination of ranolazine and chronic amiodarone act synergistically to cause potent use-dependent depression of sodium channel-dependent parameters in PV sleeves but not ventricular tissues.

CONCLUSIONS

The PV sleeve preparation is a useful model for the study of pharmacologic agents for the treatment of atrial fibrillation. The effectiveness of these agents in arrhythmias induced in PV sleeves may indicate an antiarrhythmic action in eliminating the triggers responsible for AF.