New advances in class III antiarrhythmic drug therapy

Efficacy and safety of ibutilide for chemical cardioversion of atrial fibrillation and atrial flutter in cancer patients

BACKGROUND

Atrial fibrillation and atrial flutter (AF/AFL) are the most common arrhythmias encountered in clinical practice. Rate versus rhythm control remains a difficult decision, especially in the acute setting. Ibutilide is a class III antiarrhythmic indicated for pharmacological cardioversion of recent-onset AF/AFL. At the University of Texas MD Anderson Cancer Center, restoration of sinus rhythm is desirable because many patients have contraindications to anticoagulation. In addition, most are on multiple medications that prolong the QT interval; therefore, the objective of this study was to establish the safety and efficacy of ibutilide.

METHODS

This was a retrospective chart review of 81 patients who were identified via the pharmacy database as receiving ibutilide for AF/AFL from January 2002 to May 2006. Outcomes including cardioversion rates and effects on the QT interval were recorded.

RESULTS

Ibutilide use was associated with successful cardioversion in 75% of patients. Out of 81 patients, 68 patients (84%) were on at least 1 medication that prolonged the QT interval at the time of ibutilide administration. However, no significant changes in the corrected QT interval pre and post ibutilide cardioversion were noted in any group of patients.

CONCLUSIONS

Overall, ibutilide is safe and effective in cancer patients when used for acute cardioversion of AF/AFL. Despite the use of multiple medications that can potentially prolong the QT interval, no patient experienced serious life-threatening rhythm disturbances or significant QT prolongation during ibutilide administration.

Sotalol as adjunctive therapy to implantable cardioverter-defibrillators in heart failure patients

The number of heart failure patients with implantable cardioverter-defibrillators is rising. Common issues encountered in this population are high defibrillation thresholds and inappropriate shocks. In order to resolve these problems, the addition of a class III antiarrhythmic such as sotalol is often considered. Given the emerging issue of polypharmacy and medication compliance in the heart failure population, the question of the efficacy of sotalol in reducing inappropriate shocks, defibrillation thresholds, and its ability to replace conventional beta-blockers is often raised. Current literature review suggests that sotalol is a useful adjunct to the contemporary heart failure regimen. It has the ability to reduce inappropriate shocks and defibrillation thresholds, but appears not to fully reproduce the pleiotropic beneficial effects of the beta-blockers more commonly employed for their mortality/remodeling benefits in heart failure patients.

Intravenous amiodarone treatment in horses with chronic atrial fibrillation

Six horses without underlying cardiac disease were presented because of atrial fibrillation of between 5 and 12 months duration. These horses received an intravenous amiodarone treatment of 5mg/kg/h for 1 h followed by 0.83mg/kg/h for 23h and subsequently 1.9mg/kg/h for 30h. During treatment, clinical signs were monitored and a surface ECG and an intra-atrial electrogram were recorded. Infusion was discontinued when sinus rhythm or side effects occurred. Four horses successfully cardioverted, of which one showed symptoms of hind limb weakness and weight shifting. Two horses did not cardiovert and showed similar side effects. In all horses, side effects disappeared within 6h after termination of treatment. Cardiac side effects, such as pro-arrhythmia, were not seen in any of the horses. Total bilirubin slightly increased in three horses and normalised within four days. It was concluded that amiodarone has the potential to treat naturally occurring chronic atrial fibrillation in horses, although further research is needed to refine the infusion protocol.

Cardiovascular and electrocardiographic effects of the dopamine receptor agonists ropinirole, apomorphine, and PNU-142774E in conscious beagle dogs

To confirm recent in vitro findings, we examined the cardiovascular and electrocardiographic (ECG) effects of the dopamine receptor agonists ropinirole, apomorphine, and PNU-142774E in conscious dogs. Intravenous (i.v.) infusions of ropinirole totaling 20 microg/kg maximally reduced mean arterial pressure (MAP; -16 mm Hg) and the ECG PR interval (-13 milliseconds) and increased heart rate (HR; +29 b/min) and QTc length (+33 ms) at a peak plasma drug concentration (p[drug]) of 3.5 ng/ml. I.V. PNU-142774E was better tolerated through 66 microg/kg and a maximal p[drug] of 5.9 ng/ml with negligible cardiovascular changes and mild QTc reduction (13 ms). Apomorphine (25 microg/kg i.v.) was intermediate to ropinirole and PNU-142774E for emesis and peak changes in MAP (-6 mm Hg), HR (+24 b/min), and QTc (+15 milliseconds) at a mean p[drug] of 3.4 ng/ml. By comparison, the class III antiarrhythmic trecetilide (2.0 mg/kg bolus) increased QTc (+58 ms) without affecting mean arterial pressure or heart rate. This study establishes that in conscious dogs, the selective dopamine receptor agonist PNU-142774E has fewer cardiovascular and emetic effects than ropinirole and apomorphine and supports prior in vitro findings that ropinirole and apomorphine but not the PNU-142774E imidazoquinolin analog sumanirole reduces the delayed rectifier current in HERG transfected cells.

Synthesis and biological evaluation of benzopyran analogues bearing class III antiarrhythmic pharmacophores

We have synthesized a series of compounds combining the hydroxy-benzopyran ring of vitamin E with the methylsulfonylaminophenyl group of class III antiarrhythmic drugs, connected through tertiary amine moieties. Evaluation of the antiarrhythmic and antioxidant activity of the new compounds was carried out on isolated rat heart preparations using the non-recirculating Langendorff mode. The new analogues were present, at 10 microM concentration, during ischemia and reperfusion. Selected compounds were further studied by a conventional microelectrode method in order to get insight into their cellular mode of action. The most active compound, N-[4-[2-[[2-(3,4-dihydro-6-hydroxy-2,2,7,8-tetramethyl-2H-1-benzopyran-5-yl)ethyl] methylamine]ethyl]phenyl]methanesulfonamide (19a), reduces premature beats, prolongs QT and QRS intervals during ischemia and reperfusion, and reduces MDA content, leading to a fast recovery of the heart. In addition, it exhibits moderate class III antiarrhythmic action.

Long QT syndrome: reduced repolarization reserve and the genetic link

Marked QT prolongation and torsades de pointes can occur not only in the congenital long QT syndromes (LQTSs) but also as a consequence of environmental stimuli, notably administration of certain drugs. A key feature of this 'acquired' form of the LQTS has been its unpredictable nature. That is, although risk factors have been identified in series of patients, they have not been terribly useful in addressing risk in an individual patient. Normal cardiac repolarization depends critically on the interplay of multiple ion currents, and these provide some redundancy, or 'reserve', to protect against excessive QT prolongation by drugs. We have proposed that lesions in these repolarizing mechanisms can remain subclinical but nevertheless increase risk on drug exposure, and have termed this situation 'reduced repolarization reserve'. The evidence in support of this concept is presented, and the known and potential contributions by genetic variants to risk is examined. Assessing variability in susceptibility to acquired LQTS provides a framework for analysis of other complex gene-environment interactions.

Dronedarone: an amiodarone analogue

Of the antiarrhythmic drugs in current use, amiodarone is one of the most effective and is associated with a comparatively low risk of drug-induced pro-arrhythmia, probably due to its multiple pharmacological actions on cardiac ion channels and receptors. However, amiodarone is associated with significant extra-cardiac side effects and this has driven development of amiodarone analogues. These analogues include short acting analogues (e.g., AT-2001) with similar acute effects to amiodarone, the thyroid receptor antagonist KB-130015 and dronedarone. Dronedarone, (SR-33589; Sanofi-Synthelabo), is a non-iodinated amiodarone derivative that inhibits Na +, K + and Ca 2+ currents. It is a potent inhibitor of the acetylcholine-activated K + current from atrial and sinoatrial nodal tissue, and inhibits the rapid delayed rectifier more potently than slow and inward rectifier K + currents and inhibits L-type calcium current. Dronedarone is an antagonist at alpha- and beta-adrenoceptors and unlike amiodarone, has little effect at thyroid receptors. Dronedarone is more potent than amiodarone in inhibiting arrhythmias and death in animal models of ischaemia- and reperfusion-induced arrhythmias. In the Dronedarone Atrial Fibrillation Study After Electrical Cardioversion (DAFNE) clinical trial, dronedarone 800 mg/day appeared to be effective and safe for the prevention of atrial fibrillation relapses after cardioversion. The Antiarrhythmic Trial with Dronedarone in Moderate-to-Severe Congestive Heart Failure Evaluating Morbidity Decrease (ANDROMEDA) trial was stopped due to a potential increased risk of death in the dronedarone group. Trials of dronedarone in the maintenance of sinus rhythm in patients with atrial fibrillation and a safety and tolerability study in patients with an implantable cardioverter defibrillator are ongoing. Further experimental and clinical studies are required before we have a definitive answer to whether dronedarone has advantages over amiodarone and other amiodarone analogues.

Antiarrhythmic drug therapy of atrial fibrillation

In the post-AFFIRM era, treatment of AF has become the treatment of symptoms. In some patients, this will be simple rate control, but there remain a significant cohort of patients in whom rate control alone does not give acceptable symptom relief. In this group, antiarrhythmic therapy still has a role, and the AFFIRM trial indicates that this therapeutic strategy is without significant deleterious effect on mortality. The choice of antiarrhythmic agent must be individualized according to underlying cardiac pathologies and comorbidities, however. Most recently, the introduction of dofetilide has widened the therapeutic options in patients with severe heart disease, and the Canadian Trial of Atrial Fibrillation indicated the superior efficacy of amiodarone at low doses. The release/ development of newer Class III antiarrhythmic agents may offer hope for the benefits of amiodarone without the serious adverse effects with long-term therapy.

Differential recovery of action potential duration and HERG currents from the effects of two methanesulfonamide class III antiarrhythmic agents, KCB-328 and dofetilide

A novel pure class III antiarrhythmic agent, 1-(2-amino-4-methanesulfonamidophenoxy)-2-[N-(3,4-dimethoxyphen-ethyl)-N-methylamino]ethane hydrochloride (KCB-328) prolongs action potential duration (APD) by blocking the rapid component delayed rectifier K+ current (IKr). However, KCB-328 manifests little of the reverse frequency dependence (RFD) that is a general characteristic of class III antiarrhythmic agents. We have studied the onset and recovery kinetics of KCB-328 and dofetilide on APD in guinea-pig papillary muscle and on human ether-a-go-go-related gene (HERG) channel, which encodes IKr, expressed in Xenopus oocytes. KCB-328 (1 microM) and dofetilide (0.1 microM) progressively increased the duration of post-rest AP at 1-Hz stimulation, with onset time constants of 6.4 +/- 0.6 seconds and 20.7 +/- 1.8 seconds, respectively. With a 100-second resting period, the effect of KCB-328 recovered by 70% with a time constant of 13.2 +/- 4.2 seconds, whereas that of dofetilide recovered only by 25%. Both drugs blocked activated HERG channels in a biexponential decay fashion, with faster time constants for KCB-328 (3 microM) than for dofetilide (0.3 microM). After a 300-second resting period, HERG current inhibited by KCB-328 was recovered more at depolarized membrane potentials than at hyperpolarized ones, with a time constant of 179.9 seconds during the rest at -60 mV. In contrast, recovery after dofetilide was negligible at all voltages tested. These results suggest that KCB-328 binds to IKr at a preferentially open state in a use-dependent manner, but that KCB-328 unbinds from the resting state more readily than dofetilide. The less striking RFD of KCB-328 than of dofetilide might be related to the faster recovery from its effect on IKr.

New approaches to atrial fibrillation management: a critical review of a rapidly evolving field

Atrial fibrillation (AF) is the most common cardiac arrhythmia, the prevalence of which is increasing with the aging of the population. Because of its clinical importance and the lack of highly satisfactory management approaches, AF is the subject of active clinical and research efforts. This paper reviews recent and on-going developments in pharmacological and non-drug management of AF. The ideal therapeutic goal for AF is the production and maintenance of sinus rhythm. Comparative studies suggest that available class I and III drugs have comparable and modest efficacy for sinus rhythm maintenance. Amiodarone, with actions of all antiarrhythmic classes, has recently been shown to have clearly superior efficacy compared with other available drugs. Newer agents are in development, but their advantages are as yet unclear and appear limited. A potentially interesting approach is the prescription of drugs upon the occurrence of an attack, rather than on a continuous basis. Recent insights into AF mechanisms may permit therapy to prevent development of the AF substrate. An alternative to sinus rhythm maintenance is a rate control approach, with no attempt to prevent AF. Drugs to effect rate control include digitalis, beta-blockers and calcium channel antagonists. Digitalis has limited value for control of exercise heart rate and for paroxysmal AF, but is particularly well suited for patients with concomitant AF and congestive heart failure. AV-nodal ablation and pacing is an effective alternative for rate control but leaves the patient pacemaker dependent. The relative merits of rate versus rhythm control are being evaluated in ongoing trials, preliminary results of which indicate no statistically significant differences in primary endpoints but highlight the risks of rhythm control therapy. In patients requiring pacemakers, physiological pacing (dual chamber devices or atrial pacing) has an advantage over purely ventricular pacemakers in AF prevention. Newer pacing modalities that produce more synchronised atrial activation, as well as pacemakers that prevent excessive atrial rate swings, show promise in AF prevention and may soon see wider use. The usefulness of automatic atrial defibrillators is presently limited by discomfort during shocks. Targeted destruction of pulmonary vein foci by radiofrequency catheter ablation suppresses paroxysmal AF. Efficacy in persistent AF is lower and still under study. Problems include potential recurrence in other veins and a small but nontrivial risk of pulmonary vein stenosis. Surgical division of the atria into zones with limited electrical connection, the MAZE procedure, is highly effective in AF prevention but is a major intervention that is not applicable to most patients. In conclusion, significant advances are being made in the management of patients with AF but much more work remains to be done.

Risk of proarrhythmia with class III antiarrhythmic agents: sex-based differences and other issues

Although men have a higher risk of atrial fibrillation compared with women, the absolute number of women with atrial fibrillation is greater. Congestive heart failure increases the risk of developing atrial fibrillation in women more than in men, and the prognosis for women with atrial fibrillation is worse than for men. The longer baseline corrected QT interval in women is well known. The mechanism is likely the result of increased circulating androgens, causing the QT interval to shorten in men after puberty. Female sex is associated with an increased risk of torsades de pointes in the setting of potassium antagonists. Class III antiarrhythmic drugs are frequently used for the treatment of atrial fibrillation in heart failure patients because of their neutral effect on mortality and their tolerance by patients with low ejection fractions. Although amiodarone and azimilide carry a low potential for producing torsades de pointes compared with sotalol and dofetilide, the prevalence of torsades de pointes in women is at least twice that in men for all these drugs. Careful monitoring of the QT interval and potassium level, as well as control of congestive heart failure, can help reduce the risk of proarrhythmia. Avoidance of polypharmacy with other potassium antagonists and unmonitored drug formulation changes are important in the management of all patients taking class III agents, but they are particularly crucial in women with additional risk factors for torsades de pointes.

Dronerarone acts as a selective inhibitor of 3,5,3'-triiodothyronine binding to thyroid hormone receptor-alpha1: in vitro and in vivo evidence

Dronedarone (Dron), without iodine, was developed as an alternative to the iodine-containing antiarrhythmic drug amiodarone (AM). AM acts, via its major metabolite desethylamiodarone, in vitro and in vivo as a thyroid hormone receptor alpha(1) (TRalpha(1)) and TRbeta(1) antagonist. Here we investigate whether Dron and/or its metabolite debutyldronedarone inhibit T(3) binding to TRalpha(1) and TRbeta(1) in vitro and whether dronedarone behaves similarly to amiodarone in vivo. In vitro, Dron had a inhibitory effect of 14% on the binding of T(3) to TRalpha(1), but not on TRbeta(1). Desethylamiodarone inhibited T(3) binding to TRalpha(1) and TRbeta(1) equally. Debutyldronedarone inhibited T(3) binding to TRalpha(1) by 77%, but to TRbeta(1) by only 25%. In vivo, AM increased plasma TSH and rT(3), and decreased T(3). Dron decreased T(4) and T(3), rT(3) did not change, and TSH fell slightly. Plasma total cholesterol was increased by AM, but remained unchanged in Dron-treated animals. TRbeta(1)-dependent liver low density lipoprotein receptor protein and type 1 deiodinase activities decreased in AM-treated, but not in Dron-treated, animals. TRalpha(1)-mediated lengthening of the QTc interval was present in both AM- and Dron-treated animals. The in vitro and in vivo findings suggest that dronedarone via its metabolite debutyldronedarone acts as a TRalpha(1)-selective inhibitor.

[Recent findings on the dromotropic actions of the class III antiarrhythmic agents]

Class III antiarrhythmic agents have been considered to lengthen the myocardial effective refractory period (ERP) without any significant effects on the conduction velocity. However, recent investigations have clarified the positive or negative dromotropic effects of these agents. Amiodarone, a representative class III agent, exerts negative dromotropism by suppressing the fast sodium current responsible for conduction in acute administration (class I effects). Chronic amiodarone causes prolongation of ERP (class III effects), which is sometimes associated with negative dromotropism based on the alteration of passive or active membrane properties. Sotalol shows neither significant positive nor negative dromotropism under the normoxic condition, whereas this agent is reported to exert positive dromotropism mediated by the cAMP-dependent facilitation of gap junctional electrical coupling under the hypoxic condition. Some pure class III agents such as nifekalant are suspected to elicit 'apparent' positive dromotropism in the premature impulse propagation. This is explained by the right and upward shift of the strength-interval curve, which theoretically transforms the graded premature response to the all-or-none response. Although the clinical relevancy of these phenomena remains to be investigated, such variable dromotropism of the individual class III agent may contribute to the better understanding and development of antiarrhythmic agents.

A Benefit-Risk Assessment of Class III Antiarrhythmic Agents

With beta-blockers as the exception, increasing doubt is emerging on the value of antiarrhythmic drug therapy following a series of trials that have either shown no mortality benefit or even an excess mortality. Vaughan Williams class I drugs are generally avoided in patients with structural heart disease, and class IV drugs are avoided in heart failure. Unfortunately, arrhythmias are a growing problem due to an increase in the incidence of atrial fibrillation and sudden death. The population is becoming older and more patients survive for a longer time period with congestive heart failure, which again increases the frequency of both supraventricular as well as ventricular arrhythmias. Class III antiarrhythmic drugs act by blocking repolarising currents and thereby prolong the effective refractory period of the myocardium. This is believed to facilitate termination of re-entry tachyarrhythmias. This class of drugs is developed for treatment of both supraventricular and ventricular arrhythmias. Amiodarone, sotalol, dofetilide, and ibutilide are examples of class III drugs that are currently available. Amiodarone and sotalol have other antiarrhythmic properties in addition to pure class III action, which differentiates them from the others. However, all have potential serious adverse events. Proarrhythmia, especially torsade de pointes, is a common problem making the benefit-risk ratio of these drugs a key question. Class III drugs have been evaluated in different settings: primary and secondary prevention of ventricular arrhythmias and in treatment of atrial fibrillation or flutter. Based on existing evidence there is no routine indication for antiarrhythmic drug therapy other than beta-blockers in patients at high risk of sudden death. Subgroup analyses of trials with amiodarone and dofetilide suggest that patients with atrial fibrillation may have a mortality reduction with these drugs. However, this needs to be tested in a prospective trial. Similarly, subgroups that will benefit from prophylactic treatment with class III antiarrhythmic drugs may be found based on QT-intervals or - in the future - from genetic testing. Class III drugs are effective in converting atrial fibrillation to sinus rhythm and for the maintenance of sinus rhythm after conversion. This is currently by far the most important indication for this class of drugs. As defined by recent guidelines, amiodarone and dofetilide have their place as second-line therapy except for patients with heart failure where they are first line therapy being the only drugs where the safety has been documented for this group of high risk patients.

Advances in cardiac electrophysiology and pacing

Significant advances have been made in the management of cardiac arrhythmias. New technology has enhanced the ability to understand and treat a variety of tachycardias. Excitement and caution surround ablative approaches for atrial fibrillation. The role of ICDs and class III antiarrhythmic drugs in the management of patients at risk for sudden cardiac death has been clarified. A new indication for cardiac pacing is evolving as a supplemental treatment for patients with refractory congestive heart failure. These and other advances provide numerous exciting options for management of cardiac patients.

Evaluation and management of atrial fibrillation

Atrial fibrillation is a common cardiac arrhythmia with significant sequela. The goals of treating atrial fibrillation are rate control, prevention of thromboembolism, and maintenance of sinus rhythm. The epidemiology and pathophysiology of atrial fibrillation is reviewed, as well as strategies and recommendations for achieving therapeutic goals. The authors also review investigational therapeutic options using nonpharmacologic modalities.

Cardiac arrhythmias: drugs and devices

This review focuses on the important role played by the various types of remedial therapy in the prevention and treatment of perioperative cardiac arrhythmias. It discusses the new concepts of arrhythmogenesis and pro-arrhythmia; the long QT interval syndrome; newer, more selective class 3 antiarrhythmic drugs; cardiac rhythm management devices; drugs or devices used as prophylaxis for postoperative atrial arrhythmias; intravenous amiodarone for destabilizing ventricular arrhythmias; and preoperative potassium imbalance.

Amiodarone therapy for sustained ventricular tachycardia after myocardial infarction: long-term follow-up, risk assessment and predictive value of programmed ventricular stimulation

We determine the value of the programmed ventricular stimulation (PVS) and of clinical, angiographic and electrophysiologic variables in assessing the long-term risk of arrhythmia recurrence in a group of coronary artery diseased patients presenting with a first episode of monomorphic sustained ventricular tachycardia (VT) treated with amiodarone. Mortality and arrhythmia recurrence rates were retrospectively assessed in 55 consecutive patients with previous myocardial infarction presenting with a first VT episode. Results of left heart catheterization, echocardiography and time-domain signal-averaging were collected. Patients underwent PVS after amiodarone oral loading and were classified according to inducibility before being all discharged on amiodarone (200 mg daily). The mean follow-up was 42+/-31 months. Total and cardiac mortality rates were 29% (16 patients) and 23% (13 patients) respectively. Sudden death (SD) occurred in nine patients (16%). VT recurred in 13 patients (23%). Sustained monomorphic VT was inducible in 40 patients (72%) after amiodarone loading. Neither total mortality (10/40 vs. 6/15) nor cardiac mortality (3/40 vs. 1/15) were significantly different between inducible and non-inducible patients. Recurrent VT rate was 27% (11/40 patients) for the inducible group and 13% (2/15 patients) for the non-inducible group (NS). SD occurred in 6/40 inducible patients (15%) and in 2/15 non-inducible patients (13%) (NS). Arrhythmic events occurred in 42% (17/40) inducible patients vs. 26% (4/15) non-inducible patients (P=0.07). Parameters correlated with outcome were ejection fraction (EF) (5 SD/11 patients with EF <0.3 vs. 4/44 with EF >0.3, P=0.003), mitral insufficiency (MI) (4 SD/10 patients with MI vs. 4/44 patients without MI, P=0.004) and age (65+/-9 years for patients with VT recurrence vs. 58+/-9, P=0.02). Although the risk stratification can be improved, reliable and safe long-term prediction of recurrence of malignant ventricular arrhythmia in individual patients cannot be made. Consequently, the systematic implantation of a cardioverter-defibrillator in case of a first episode of sustained VT occurring in coronary artery disease patients should be further debated.