A randomized active-controlled study comparing the efficacy and safety of vernakalant to amiodarone in recent-onset atrial fibrillation

Costs and clinical consequences of suboptimal atrial fibrillation management

Atrial fibrillation (AF) places a considerable burden on the US health care system, society, and individual patients due to its associated morbidity, mortality, and reduced health-related quality of life. AF increases the risk of stroke, which often results in lengthy hospital stays, increased disability, and long-term care, all of which impact medical costs. An expected increase in the prevalence of AF and incidence of AF-related stroke underscores the need for optimal management of this disorder. Although AF treatment strategies have been proven effective in clinical trials, data show that patients still receive suboptimal treatment. Adherence to AF treatment guidelines will help to optimize treatment and reduce costs due to AF-associated events; new treatments for AF show promise for future reductions in disease and cost burden due to improved tolerability profiles. Additional research is necessary to compare treatment costs and outcomes of new versus existing agents; an immediate effort to optimize treatment based on existing evidence and guidelines is critical to reducing the burden of AF.

[Atrial fibrillation : new anticoagulants and antiarrhythmic drugs]

Atrial fibrillation is the most common form of arrhythmia and one of the most frequent causes of ischemic stroke. Several new anticoagulants have recently been introduced as alternatives to vitamin-K antagonists for prophylaxis of ischemic stroke and tested in phase-3 studies for efficacy and safety. Identifying patients who will profit in particular from the new anticoagulant therapy is crucial to the clinical application of these drugs. Vernakalant and dronedarone are new antiarrhythmic drugs for rhythm control of atrial fibrillation. However, therapeutic efficacy of the new agents still has to be proven.

Atrial fibrillation

The management of atrial fibrillation has evolved greatly in the past few years, and many areas have had substantial advances or developments. Recognition of the limitations of aspirin and the availability of new oral anticoagulant drugs that overcome the inherent drawbacks associated with warfarin will enable widespread application of effective thromboprophylaxis with oral anticoagulants. The emphasis on stroke risk stratification has shifted towards identification of so-called truly low-risk patients with atrial fibrillation who do not need antithrombotic therapy, whereas oral anticoagulation therapy should be considered in patients with one or more risk factors for stroke. New antiarrhythmic drugs, such as dronedarone and vernakalant, have provided some additional opportunities for rhythm control in atrial fibrillation. However, the management of the disorder is increasingly driven by symptoms. The availability of non-pharmacological approaches, such as ablation, has allowed additional options for the management of atrial fibrillation in patients who are unsuitable for or intolerant of drug approaches.

Examining the safety of amiodarone

INTRODUCTION

Amiodarone is the most widely used antiarrhythmic agent, with demonstrated effectiveness against all the spectrum of cardiac tachyarrhythmias. The risk of adverse effects acts as a limiting factor to its utilization especially in the long term. This article systematically reviews the published evidence on amiodarone versus placebo to examine its safety as an antiarrhythmic drug.

AREAS COVERED

Authors collected data on adverse effects reported in 49 randomized placebo-controlled trials with amiodarone. Adverse effects were classified according to the organ/system involved. Pooled estimates of the number needed to treat (NNT) and to harm (NNH) versus placebo were calculated.

EXPERT OPINION

Amiodarone is effective for both the acute conversion of atrial fibrillation (AF) (11 trials, NNT = 4 at 24 h; p = 0.003) and the prevention of postoperative AF (18 trials, NNT = 8; p < 0.001), although with an increased risk of bradycardia, hypotension, nausea or phlebitis (pooled NNH = 4; p < 0.001). Amiodarone administration for the maintenance of sinus rhythm has a favorable net clinical benefit (pooled NNT = 3; p < 0.001 versus pooled NNH for either thyroid toxicity, gastrointestinal discomfort, skin toxicity or eye toxicity = 11; p < 0.001). Treatment with amiodarone for the prophylaxis of sudden cardiac death has less favorable net clinical benefit (15 trials, NNT = 38; p < 0.001 versus NNH for either thyroid toxicity, hepatic toxicity, pulmonary toxicity or bradycardia = 14; p < 0.001). Amiodarone treatment in this setting should be used in only selected cases.

Rate-dependent effects of vernakalant in the isolated non-remodeled canine left atria are primarily due to block of the sodium channel: comparison with ranolazine and dl-sotalol

BACKGROUND

Several clinical trials have shown that vernakalant is effective in terminating recent onset atrial fibrillation (AF). The electrophysiological actions of vernakalant are not fully understood.

METHODS AND RESULTS

Here we report the results of a blinded study comparing the in vitro canine atrial electrophysiological effects of vernakalant, ranolazine, and dl-sotalol. Action potential durations (APD(50,75,90)), effective refractory period (ERP), post repolarization refractoriness (PRR), maximum rate of rise of the action potential (AP) upstroke (V(max)), diastolic threshold of excitation (DTE), conduction time (CT), and the shortest S(1)-S(1) permitting 1:1 activation (S(1)-S(1)) were measured using standard stimulation and microelectrode recording techniques in isolated normal, non-remodeled canine arterially perfused left atrial preparations. Vernakalant caused variable but slight prolongation of APD(90) (P=not significant), but significant prolongation of APD(50) at 30 μmol/L and rapid rates. In contrast, ranolazine and dl-sotalol produced consistent concentration- and reverse rate-dependent prolongation of APD(90). Vernakalant and ranolazine caused rate-dependent, whereas dl-sotalol caused reverse rate-dependent, prolongation of ERP. Significant rate-dependent PRR developed with vernakalant and ranolazine, but not with dl-sotalol. Other sodium channel-mediated parameters (ie, V(max), CT, DTE, and S(1)-S(1)) also were depressed significantly by vernakalant and ranolazine, but not by dl-sotalol. Only vernakalant elevated AP plateau voltage, consistent with blockade of ultrarapid delayed rectified potassium current and transient outward potassium current.

CONCLUSIONS

In isolated canine left atria, the effects of vernakalant and ranolazine were characterized by use-dependent inhibition of sodium channel-mediated parameters, and those of dl-sotalol by reverse rate-dependent prolongation of APD(90) and ERP. This suggests that during the rapid activation rates of AF, the I(Na) blocking action of the mixed ion channel blocker vernakalant takes prominence. This mechanism may explain vernakalant's anti-AF efficacy.

Lone atrial fibrillation: where are we now?

There is a growing pandemic of atrial fibrillation (AF), affecting nearly 2% of the general adult population. Atrial fibrillation is commonly associated with structural heart disease, and AF itself causes a sequence of complex processes of electrical, contractile, and structural remodeling of the atrial myocardium, which facilitate further AF progression. Nonetheless, AF may also affect individuals aged ≤ 65 years who have no evidence of associated cardiopulmonary or other disease, including hypertension; this is otherwise referred to as "lone" AF and is considered to have a generally favorable prognosis. The true prevalence of lone AF is unknown. Growing insights into the diversity of numerous mechanisms involved in the pathogenesis of AF, including acute atrial stretch, structural and electrophysiological alterations, systemic inflammation, oxidative stress, autonomic imbalance, genetic predisposition, and many others, and increasing recognition of novel risk factors for AF, including obesity, metabolic syndrome, subclinical atherosclerosis, sleep apnea, alcohol consumption, and endurance sports, suggest that apparently lone AF might not be so "lone" in many patients, which could have important prognostic and therapeutic implications. In this article, we summarize the current knowledge of epidemiology, etiopathogenesis, and pathophysiology of so-called lone AF and discuss the issues of long-term prognosis and management of patients who have an apparently lone AF.

Update on the clinical management of atrial fibrillation: guidelines and beyond

In clinical practice, atrial fibrillation (AF) is the most commonly encountered arrhythmia. With the aging of the US population, the number of patients with AF that physicians encounter will increase. Atrial fibrillation management involves a combination of rate- and rhythm-control strategies with thromboprophylaxis, a complicated endeavor given side effect profiles of treatments, patient comorbidities, and anticoagulation treatment requirements. Early treatment discontinuation and poor compliance with anticoagulation treatment are frequent and result in increased mortality, a 5-fold increased risk of ischemic stroke, decreased health-related quality of life, and decreased exercise capacity. In 2006, the American College of Cardiology/American Heart Association/European Society of Cardiology (ACC/AHA/ESC) provided guidelines for the management of patients with AF. Recently, the ACC Foundation, AHA, and Heart Rhythm Society released updates to these guidelines (January and February 2011). This article aims to assist physicians in improving the management of patients with AF by focusing on the main components of therapy as reflected in the guidelines, and by providing an update on new US Food and Drug Administration-approved treatments.

Aggressive approach and outcome in patients presenting atrial fibrillation and hypertension

AIM

Aggressive approach in patients presenting atrial fibrillation (AF) and hypertension could result in improving rhythm control and reducing admission.

METHODS

Out of 3475 patients presenting AF, those with hypertension (n=1739, 52%) underwent standard (n=591, group 1, years 2004-2005) or aggressive pharmacological and electrical approach (n=1148, group 2, years 2006-2009). Overall, in 1071 patients AF duration was less than 48 h. Primary endpoint was rhythm conversion; secondary endpoints were modalities of rhythm conversion and reduction of admissions.

RESULTS

At univariate and multivariate analyses, AF lasting less than 48 h, absence of comorbidities and younger age were independent predictors of sinus rhythm; conversely, lack of sinus rhythm, older age, AF lasting more than 48 h and comorbidities were independent predictors of hospitalization. Overall, 55% of patients achieved sinus rhythm in group 1 versus 62% in group 2 (p=0.018). Interestingly, in patients with AF lasting less than 48 h, 89% achieved sinus rhythm, more likely by class 1C than by class III antiarrhythmic drugs (p<0.001). Overall reduction of admission accounts for 60%; 50% of patients need admission in group 1 versus 29% in group 2 (p<0.001).

CONCLUSIONS

Aggressive pharmacological and electrical approach in patients presenting AF and hypertension significantly improved rhythm conversion overall up to 62%. Patients with AF lasting less than 48 h eventually achieved sinus rhythm up to 89%, mostly by class IC antiarrhythmic drugs. Admissions eventually reduced up to 60%.

A Randomized, Placebo-Controlled Study of Vernakalant (Oral) for the Prevention of Atrial Fibrillation Recurrence After Cardioversion

Background—

Vernakalant, a relatively atrial-selective antiarrhythmic drug, has previously demonstrated efficacy for the acute conversion of atrial fibrillation (AF) to sinus rhythm. This study was designed to determine the most appropriate oral dose of vernakalant for the prevention of AF recurrence postcardioversion.

Methods and Results—

Patients with nonpermanent AF were randomized to 150, 300, or 500 mg vernakalant or placebo twice daily for up to 90 days. The efficacy analysis was conducted on 605 of 735 patients who entered the maintenance phase on day 3 after cardioversion. The time to the first recurrence of symptomatic sustained AF was significantly longer in the 500 mg vernakalant group, with a median of >90 days versus 29 days in the placebo group (hazard ratio, 0.735; P =0.0275). No significant effect was seen at the lower doses. The percent of patients in sinus rhythm at day 90 was 41%, 39%, and 49% in the 150-mg (n=147), 300-mg (n=148), and 500-mg (n=150) vernakalant groups, respectively, compared with 36% in the placebo group (n=160). There were no vernakalant-related proarrhythmic events. Related serious adverse events occurred in 2 patients in the 150-mg vernakalant group and in 1 patient in each of the other groups.

Conclusions—

Vernakalant, 500 mg twice daily, appears to be effective and safe for the prevention of AF recurrence after cardioversion. The absence of proarrhythmia and favorable safety profile is an important finding for the drug.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00526136.

Update on the management of atrial fibrillation: anticoagulation and medical therapy

2010 saw the introduction of dabigatran (Pradaxa; Boehringer Ingelheim Pharmaceuticals, Ridgefield, CT), following US Food and Drug Administration approval, into daily clinical practice in the United States as an alternative to Coumadin (Bristol-Myers-Squibb, New York, NY) therapy. Dronedarone (Multaq; Sanofi-Aventis, Bridgewater, NJ), originally approved for use in the United States in 2009, has seen further widespread deployment in contemporary clinical practice. Intravenous vernakalant (Cardiome Pharm, Vancouver, B.C., Canada; Merck & Co., Whitehouse Station, NJ) is being considered for approval in the United States and may serve as an alternative to current agents for safe and efficacious acute conversion from atrial fibrillation. We focus primarily on new information concerning these and other antiarrhythmic drug and anticoagulation therapies. We provide brief updates of recently published articles along with our perspective on how they will likely alter clinical practice now and in the future.

Spotlight on intravenous vernakalant in recent-onset atrial fibrillation

Intravenous vernakalant (Brinavess®) is an atrial-repolarization-delaying agent that is currently approved in the EU for the rapid conversion of recent-onset atrial fibrillation to sinus rhythm. Vernakalant blocks atrial-specific potassium and sodium ion channels, prolonging atrial refractory periods and rate-dependently slowing atrial conduction, without promoting ventricular arrhythmia. In pivotal, randomized, phase III trials, intravenous vernakalant 3 mg /kg administered as a 10-minute infusion, followed by a 2 mg/kg 10-minute infusion after 15 minutes if atrial fibrillation persisted, was effective in the rapid termination of recent-onset atrial fibrillation in nonsurgical patients (≥ 3 hours' to ≤ 7 days' duration) and in those with postoperative atrial fibrillation (3-72 hours' duration) following cardiac surgery. Conversion to sinus rhythm occurred rapidly following infusion of vernakalant, with the majority of patients converting after the first dose, and conversion to sinus rhythm was generally associated with a rapid resolution of symptoms. These antiarrhythmic effects of vernakalant were durable, with most responders remaining in sinus rhythm 24 hours after treatment initiation. In nonsurgical patients with recent-onset atrial fibrillation of 3-48 hours' duration, vernakalant was more effective than intravenous amiodarone, with a significantly higher proportion of patients converting to sinus rhythm within the first 90 minutes of treatment. Vernakalant was generally well tolerated in clinical trials, with most adverse events being of mild or moderate severity and not treatment limiting. Increases in QRS or QT intervals were transient, and there was no increased incidence of ventricular arrhythmia observed with vernakalant compared with placebo. Therefore, intravenous vernakalant provides an effective option for the management of recent-onset atrial fibrillation.

Pharmacological management of atrial fibrillation: one, none, one hundred thousand

atrial fibrillation (AF) is associated with a significant burden of morbidity and increased risk of mortality. Antiarrhythmic drug therapy remains a cornerstone to restore and maintain sinus rhythm for patients with paroxysmal and persistent AF based on current guidelines. However, conventional drugs have limited efficacy, present problematic risks of proarrhythmia and cause significant noncardiac organ toxicity. Thus, inadequacies in current therapies for atrial fibrillation have made new drug development crucial. New antiarrhythmic drugs and new anticoagulant agents have changed the current management of AF. This paper summarizes the available evidence regarding the efficacy of medications used for acute management of AF, rhythm and ventricular rate control, and stroke prevention in patients with atrial fibrillation and focuses on the current pharmacological agents.

The pathology and treatment of cardiac arrhythmias: focus on atrial fibrillation

Atrial fibrillation (AF) is the most frequently encountered sustained cardiac arrhythmia in clinical practice and a major cause of morbidity and mortality. Effective treatment of AF still remains an unmet medical need. Treatment of AF is based on drug therapy and ablative strategies. Antiarrhythmic drug therapy is limited by a relatively high recurrence rate and proarrhythmic side effects. Catheter ablation suppresses paroxysmal AF in the majority of patients without structural heart disease but is more difficult to achieve in patients with persistent AF or with concomitant cardiac disease. Stroke is a potentially devastating complication of AF, requiring anticoagulation that harbors the risk of bleeding. In search of novel treatment modalities, targeted pharmacological treatment and gene therapy offer the potential for greater selectivity than conventional small-molecule or interventional approaches. This paper summarizes the current understanding of molecular mechanisms underlying AF. Established drug therapy and interventional treatment of AF is reviewed, and emerging clinical and experimental therapeutic approaches are highlighted.

Biochemistry and biology of mammalian DNA methyltransferases

DNA methylation is a stable but not irreversible epigenetic signal that silences gene expression. It has a variety of important functions in mammals, including control of gene expression, cellular differentiation and development, preservation of chromosomal integrity, parental imprinting and X-chromosome inactivation. In addition, it has been implicated in brain function and the development of the immune system. Somatic alterations in genomic methylation patterns contribute to the etiology of human cancers and ageing. It is tightly interwoven with the modification of histone tails and other epigenetic signals. Here we review our current understanding of the molecular enzymology of the mammalian DNA methyltransferases Dnmt1, Dnmt3a, Dnmt3b and Dnmt2 and the roles of the enzymes in the above-mentioned biological processes.