New Antiarrhythmic Drugs for Prevention of Atrial Fibrillation

Recent Advances in the Pharmacological Management of Atrial Fibrillation

Atrial fibrillation (AF) is a highly prevalent cardiac arrhythmia that leads to hospitalizations for complications and adverse events each year. Despite significant improvement in our therapeutic approaches in the past decade, management of AF remains a difficult task. Novel therapies have failed to terminate AF and prevent its recurrence, and patients with AF continue to have thromboembolic complications. With the increasingly aging population and associated conditions, the prevalence of AF is expected to progressively increase, becoming a public health problem. Most patients with AF have multiple comorbidities and are of advanced age, making long-term anticoagulation challenging. This article provides an overview of the current pharmacological therapies for the management of AF, with particular emphasis on the emerging agents.

Efficacy and safety of dronedarone in patients previously treated with other antiarrhythmic agents

BACKGROUND

Currently available antiarrhythmic drugs (AADs) for the prevention of atrial fibrillation (AF)/atrial flutter (AFL) suffer from incomplete efficacy and poor tolerability.

HYPOTHESIS

Dronedarone could represent an effective and safe option in patients previously treated with AADs, especially class Ic AADs and sotalol.

METHODS

Retrospective analysis of 2 double-blind, parallel-group trials (EURIDIS [European Trial in Atrial Fibrillation or Flutter Patients Receiving Dronedarone for the Maintenance of Sinus Rhythm] and ADONIS [American-Australian-African Trial With Dronedarone in Atrial Fibrillation or Flutter Patients for the Maintenance of Sinus Rhythm]) comparing the efficacy and safety of dronedarone with placebo over 12 months. The primary end point was AF/AFL recurrence in patients previously treated with another AAD that was discontinued for whatever reason prior to randomization.

RESULTS

In patients previously treated with any AADs, dronedarone decreased the risk of AF recurrence by 30.4% vs placebo (hazard ratio [HR]: 0.70; 95% confidence interval [CI]: 0.59-0.82; P < 0.001). In patients previously treated with a class Ic agent, dronedarone decreased the risk of recurrence by 31.4% (HR: 0.69; 95% CI: 0.53-0.89; P = 0.004), whereas in patients previously treated with sotalol, dronedarone showed a trend toward a decrease of risk of recurrence (HR: 0.86; 95% CI: 0.67-1.11; P = 0.244). Dronedarone was equally effective irrespective of whether class Ic or sotalol were stopped for lack of efficacy or adverse events (AEs). Discontinuation rates were similar in the 2 groups (55.9% vs 43.1%), as were incidence of AEs and serious AEs.

CONCLUSIONS

Dronedarone seems to be effective in preventing AF recurrences in patients without permanent AF previously treated with other AADs, even if those were discontinued for lack of efficacy. Dronedarone appears to be well tolerated even in patients who already had tolerability issues with AADs.

Impact of aldosterone antagonists on the substrate for atrial fibrillation: aldosterone promotes oxidative stress and atrial structural/electrical remodeling

Atrial fibrillation (AF), the most common cardiac arrhythmia, is an electrocardiographic description of a condition with multiple and complex underlying mechanisms. Oxidative stress is an important driver of structural remodeling that creates a substrate for AF. Oxidant radicals may promote increase of atrial oxidative damage, electrical and structural remodeling, and atrial inflammation. AF and other cardiovascular morbidities activate angiotensin (Ang-II)-dependent and independent cascades. A key component of the renin-angiotensin-aldosterone system (RAAS) is the mineralocorticoid aldosterone. Recent studies provide evidence of myocardial aldosterone synthesis. Aldosterone promotes cardiac oxidative stress, inflammation and structural/electrical remodeling via multiple mechanisms. In HF patients, aldosterone production is enhanced. In patients and in experimental HF and AF models, aldosterone receptor antagonists have favorable influences on cardiac remodeling and oxidative stress. Therapeutic approaches that seek to reduce AF burden by modulating the aldosterone system are likely beneficial but underutilized.

Management of atrial fibrillation: translating clinical trial data into clinical practice

Atrial fibrillation is a supraventricular tachyarrhythmia with significant consequences in terms of morbidity and mortality. In light of the limitations of available pharmacologic treatment options (suboptimal efficacy plus safety and tolerability issues), atrial fibrillation management should be individualized based on patient characteristics and comorbidities that could influence response to specific management approaches. The importance of adequate anticoagulation should not be overlooked. This review provides a practical guide for primary care physicians, internists, and cardiologists on current management strategies for atrial fibrillation, based on recent guidelines and current clinical data.

Optimizing the management of atrial fibrillation: focus on current guidelines and the impact of new agents on future recommendations

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia encountered in everyday clinical practice. It affects ~2.3 million individuals in the United States, and the prevalence is expected to increase ~2.5-fold over the next 40 years. Atrial fibrillation accounts for more than 2 million hospitalizations each year and contributes to nearly 67 000 deaths. Our understanding of the pathophysiology of AF has increased dramatically over the past few decades. Recent treatment guidelines have heightened our awareness of the challenges involved in the treatment of AF and provided useful recommendations for its diagnosis and management. Because AF is usually associated with multiple comorbid conditions, greater emphasis must be placed on individualizing treatment. This review focuses on current treatment guidelines for patients with AF, assessing the benefits and shortcomings of current pharmacologic options and discussing new agents and trials that may provide better opportunities to improve and individualize patient management.

Recent advances in pharmacotherapy of atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia associated with increased morbidity and mortality. Efficacy and safety of currently employed antiarrhythmic drugs (AADs) continue to be less optimal in AF. Development of newer AADs has recently been made possible through a greater understanding of electro-pathophysiology of AF. Highly specific drugs acting on atria are currently being explored, although there is little data available on effectiveness of atrial specific agents in maintaining sinus rhythm. Combining AADs and non-AADs such as angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may increase effectiveness of AADs in patients with AF. Controlled clinical trials are required to precisely define the efficacy of single agents versus various combinations in maintaining sinus rhythm in patients with AF. This review describes some of the most promising therapeutic approaches that may overcome some of the limitations of drugs used at present for the management of AF.

Cardioversion for atrial fibrillation: treatment options and advances

Atrial fibrillation (AF) is associated with significant morbidity and mortality. There are two basic approaches to managing AF: slowing the ventricular rate, while allowing the arrhythmia to continue (the rate-control approach), and restoring and maintaining sinus rhythm (the rhythm-control approach) with antiarrhythmic drugs (AADs) and/or ablation, electrical cardioversion (CV), if needed, or both. Strategy trials comparing rate and rhythm control have found no survival advantage of one approach over the other, but other considerations, such as symptom reduction, often necessitate pursuit of rhythm control. Electrical, or direct current, CV is a widely used and effective method for termination of nonparoxysmal AF, although its success can be affected by patient- and technique-related variables. Pharmacological CV options also exist and are preferable in specific circumstances. Both pharmacological and electrical CV are associated with the risk of proarrhythmia. Many AADs are under development for both CV and maintenance of sinus rhythm. Some are atrioselective, such as vernakalant, and target ion channels in the atria, with little or no effects in the ventricle. Vernakalant, currently under Food and Drug Administration review, appears to offer a safer profile than current CV agents and is likely to expand the role of pharmacological CV. Other new AADs that provide increased efficacy or safety while maintaining normal sinus rhythm may also be better than current drugs; if so, rate-rhythm comparisons will differ from those of previous studies. In conclusion, further trials should clarify the long-term safety profiles of new atrioselective agents and other investigational drugs and define their role in the treatment of AF.

Safety considerations in the pharmacological management of atrial fibrillation

The pharmacological management of atrial fibrillation (AF) requires careful consideration from a safety perspective. This article focuses primarily on maintenance therapy using antiarrhythmic drugs (AADs). The foremost safety issue for AADs is the propensity of class IA and III agents to cause torsade de pointes arrhythmias. Class IA drugs, particularly quinidine, can induce torsade de pointes at low or subtherapeutic doses, but higher doses are not necessarily associated with an increased incidence. 'Pure' class III drugs such as dofetilide induce torsade de pointes in a dose-related manner, but some class III agents with more complex actions such as amiodarone have a markedly lower potential to cause this arrhythmia. The risk of torsade de pointes precludes the use of class IA and 'pure' class III agents in patients with left ventricular hypertrophy and bradycardia. Class IC agents may cause sustained monomorphic ventricular tachycardias and are generally precluded in ischaemic and structural heart disease. Advanced heart failure patients may be treated with amiodarone or dofetilide, but most other AADs are unsuitable. The most important extracardiac toxicities occurring with AADs are those of amiodarone. Drug interactions are a significant safety issue in the management of AF, including pharmacokinetic interactions in which plasma levels of the AAD are raised - increasing the risk of proarrhythmia - and concomitant use of drugs that prolong the QT interval. Notwithstanding these considerations, most patients with AF can be considered for rhythm control, provided there is adequate pre-treatment assessment and protocols for initiation, dosing and monitoring are followed with care.

Drug therapy for atrial fibrillation

Atrial fibrillation (AF) is the most frequently diagnosed arrhythmia. Prevalence increases with age, and the overall incidence is expected to increase as the population continues to age. Choice of pharmacologic therapy for atrial fibrillation depends on whether or not the goal of treatment is maintaining sinus rhythm or tolerating atrial fibrillation with adequate control of ventricular rates. New antiarrhythmic drugs are being tested in clinical trials. Drugs that target remodeling and inflammation are being tested for their use as prevention of AF or as adjunctive therapy.

Emerging adenosine receptor agonists

Adenosine receptors (ARs) are a four-member subfamily of G protein-coupled receptors and are major targets of caffeine and theophylline. There are four subtypes of ARs, designated as A1, A2A, A2B and A3. Selective agonists are now available for all four subtypes. Over a dozen of these selective agonists are now in clinical trials for various conditions, although none has received regulatory approval except for the endogenous AR agonist adenosine itself. A1AR agonists are in clinical trials for cardiac arrhythmias and neuropathic pain. A2AAR agonists are now in trials for myocardial perfusion imaging and as anti-inflammatory agents. A2BAR agonists are under preclinical scrutiny for potential treatment of cardiac ischemia. A3AR agonists are in clinical trials for the treatment of rheumatoid arthritis and colorectal cancer. The present review will mainly cover the agonists that are presently in clinical trials for various conditions and only a brief introduction will be given to major chemical classes of AR agonists presently under investigation.

Management of atrial fibrillation

Atrial fibrillation is the most common sustained cardiac rhythm disorder, and confers a substantial mortality and morbidity from stroke, thromboembolism, heart failure, and impaired quality of life. With the increasingly elderly population in the developed world, as well as improvements in the management of myocardial infarction and heart failure, the prevalence of atrial fibrillation is increasing, resulting in a major public-health problem. This Review aims to provide an overview on the modern management of atrial fibrillation, with particular emphasis on pharmacological and non-pharmacological approaches. Irrespective of a rate-control or rhythm-control strategy, stroke prevention with appropriate thromboprophylaxis still remains central to the management of this common arrhythmia. Electrophysiological approaches could hold some promise for a curative approach in atrial fibrillation.

Regional and tissue specific transcript signatures of ion channel genes in the non-diseased human heart

The various cardiac regions have specific action potential properties appropriate to their electrical specialization, resulting from a specific pattern of ion-channel functional expression. The present study addressed regionally defined differential ion-channel expression in the non-diseased human heart with a genomic approach. High-throughput real-time RT-PCR was used to quantify the expression patterns of 79 ion-channel subunit transcripts and related genes in atria, ventricular epicardium and endocardium, and Purkinje fibres isolated from 15 non-diseased human donor hearts. Two-way non-directed hierarchical clustering separated atria, Purkinje fibre and ventricular compartments, but did not show specific patterns for epicardium versus endocardium, nor left- versus right-sided chambers. Genes that characterized the atria (versus ventricles) included Cx40, Kv1.5 and Kir3.1 as expected, but also Cav1.3, Cav3.1, Cav alpha2 delta2, Nav beta1, TWIK1, TASK1 and HCN4. Only Kir2.1, RyR2, phospholamban and Kv1.4 showed higher expression in the ventricles. The Purkinje fibre expression-portrait (versus ventricle) included stronger expression of Cx40, Kv4.3, Kir3.1, TWIK1, HCN4, ClC6 and CALM1, along with weaker expression of mRNA encoding Cx43, Kir2.1, KChIP2, the pumps/exchangers Na(+),K(+)-ATPase, NCX1, SERCA2, and the Ca(2+)-handling proteins RYR2 and CASQ2. Transcripts that were more strongly expressed in epicardium (versus endocardium) included Cav1.2, KChIP2, SERCA2, CALM3 and calcineurin-alpha. Nav1.5 and Nav beta1 were more strongly expressed in the endocardium. For selected genes, RT-PCR data were confirmed at the protein level. This is the first report of the global portrait of regional ion-channel subunit-gene expression in the non-diseased human heart. Our data point to significant regionally determined ion-channel expression differences, with potentially important implications for understanding regional electrophysiology, arrhythmia mechanisms, and responses to ion-channel blocking drugs. Concordance with previous functional studies suggests that regional regulation of cardiac ion-current expression may be primarily transcriptional.

Design and synthesis of novel isoquinoline-3-nitriles as orally bioavailable Kv1.5 antagonists for the treatment of atrial fibrillation

Novel 3-cyanoisoquinoline Kv1.5 antagonists have been prepared and evaluated in in vitro and in vivo assays for inhibition of the Kv1.5 potassium channel and its associated cardiac potassium current, IKur. Structural modifications of isoquinolinone lead 1 afforded compounds with excellent potency, selectivity, and oral bioavailability.

The role of oxidative stress in the pathogenesis and perpetuation of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice representing a major health hazard. Owing to relative inefficacy and side effects of classic antiarrhythmic drugs, current interest has shifted to treatments that target AF substrate. Accumulating evidence suggests that there is a link between oxidative processes and AF. In atrial myocardium during AF, there is substantial oxidative damage that may contribute to atrial remodeling. Several pathophysiological changes that possibly associated with increased oxidative stress in AF have been proposed. These include changes in gene transcriptional profiles and mitochondrial DNA, increased activity of enzymes such as NAD(P)H oxidase and xanthine oxidase, inflammatory processes, activation of the renin-angiotensin system and others. Moreover, oxidative stress is involved in the pathophysiology of several predisposing factors and cardiovascular disorders that correspondingly associated with AF. Preliminary studies using dietary antioxidants such as vitamin C have shown promising results. More evidence has been obtained from studies examining agents with pleiotropic effects, including antioxidant, such as inhibitors of the renin-angiotensin system, statins, corticosteroids and carvedilol. Further investigations are needed in order to elucidate the impact of oxidative stress on atrial remodeling. The clarification of these processes in the setting of AF may lead to the development of novel therapeutic strategies.

Nonantiarrhythmic drug therapy for atrial fibrillation

Recent studies have begun to elucidate the molecular mechanisms that promote the generation and progressive nature of atrial fibrillation. Evidence from both experimental and clinical investigations has implicated an important role for the renin-angiotensin-aldosterone system, inflammation, and oxidative stress, with data that suggest a potential beneficial effect for angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, aldosterone receptor antagonists, antiinflammatory agents, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), and omega-3 polyunsaturated fatty acids. In addition, compounds that increase gap junctional conductance or that block 5-hydroxytryptamine-4 receptors have also shown promise in the experimental setting. Large-scale, prospective clinical trials will clarify the utility of these new therapeutic approaches to prevent atrial fibrillation in specific clinical settings.

Future directions in antiarrhythmic drug therapy for atrial fibrillation

Atrial fibrillation is the most commonly sustained cardiac arrhythmia. Drugs currently approved by the US FDA for the treatment of this arrhythmia are imperfect owing to either side effects or limited efficacy. Drug development strategies have focused on two areas: the modification of existing agents – such as Class III drugs aimed at improving their safety and efficacy profile – and targeting newly postulated mechanisms of atrial fibrillation. In this article, we review new drugs currently in development and promising drug strategies for atrial fibrillation prevention and treatment.

Rotigaptide (ZP123) improves atrial conduction slowing in chronic volume overload-induced dilated atria

Chronic atrial dilation is associated with atrial conduction velocity slowing and an increased risk of developing atrial tachyarrhythmias. Rotigaptide (ZP123) is a selective gap junction modifier that increases cardiac gap junctional intercellular communication. We hypothesised that rotigaptide treatment would increase atrial conduction velocity and reduce the inducibility to atrial tachyarrhythmias in a model of chronic volume overload induced chronic atrial dilatation characterized by atrial conduction velocity slowing. Chronic volume overload was created in Japanese white rabbits by arterio-venous shunt formation. Atrial conduction velocity and atrial tachyarrhythmias inducibility were examined in Langendorff-perfused chronic volume overload hearts (n=12) using high-resolution optical mapping before and after treatment with rotigaptide. Moreover, expression levels of atrial gap junction proteins (connexin40 and connexin43) were examined in chronic volume overload hearts (n=6) and compared to sham-operated controls (n=6). Rotigaptide treatment significantly increased atrial conduction velocity in chronic volume overload hearts, however, rotigaptide did not decrease susceptibility to the induction of atrial tachyarrhythmias. Protein expressions of Cx40 and Cx43 were decreased by 32% and 72% (P<0.01), respectively, in chromic volume overload atria compared to control. To conclude, rotigaptide increased atrial conduction velocity in a rabbit model of chromic volume overload induced atrial conduction velocity slowing. The demonstrated effect of rotigaptide on atrial conduction velocity did not prevent atrial tachyarrhythmias inducibility. Whether rotigaptide may possess antiarrhythmic efficacy in other models of atrial fibrillation remains to be determined.

Is Helicobacter pylori a cause of atrial fibrillation?

Inflammation has been implicated in the pathogenesis of cardiovascular diseases. C-reactive protein, a sensitive marker of systemic inflammation, has recently been reported to be significantly higher in patients with atrial fibrillation (AF) compared with a control group with no history of atrial arrhythmia. Elevated C-reactive protein levels in patients with AF reflects an underlying inflammatory process. Histological anomalies in the atria of patients with AF have also been observed. These anomalies may have an inflammatory basis, although it is not known if any structural changes within the atria are a cause or a consequence of the arrhythmia. Ongoing chronic infection(s) has been suggested as a possible cause of the inflammatory process demonstrated in patients with AF. Helicobacter pylori, a Gram-negative bacterium more commonly known for infecting the gastric mucosa and causing peptic ulcers, is a noncardiac factor that has been controversially reported to be associated with cardiovascular diseases. This article gives a brief overview of AF and specifically explores the recent evidence that suggests that Helicobacter pylori infection causes AF.

[New antiarrhythmic drugs for therapy of atrial fibrillation: I. Ion channel blockers]

During the last ten years we have made substantial progress in our understanding of the underlying mechanisms of atrial fibrillation. The high rate associated alterations in electrical and structural properties of the atria, referred to as atrial remodeling, promote the progression of atrial fibrillation. The development of new therapeutic approaches addresses three different directions: (i) prevention of atrial remodeling, especially of structural remodeling; (ii) increase of long-term efficacy of currently used drugs and improvement of their side-effect profile; and (iii) design of atria- and pathology-specific antiarrhythmic drugs without concomitant proarrhythmic effects in the ventricles. The current review outlines the pathophysiology of atrial fibrillation and focuses on electrical remodeling. The properties of new antiarrhythmic drugs for atrial fibrillation are discussed in detail.