Investigational Anti-Atrial Fibrillation Pharmacology and Mechanisms by Which Antiarrhythmics Terminate the Arrhythmia: Where Are We in 2020?

Atrial hiPSC-CM as a Pharmacologic Model to Evaluate Anti-AF Drugs: Some Lessons From I Kur

ABSTRACT

Human induced pluripotent stem cells (hiPSC) and atrial hiPSC-derived cardiomyocytes (hiPSC-CM) have entered the arena of preclinical atrial fibrillation research. A central question is whether they reproduce the physiologic contribution of atrial selective potassium currents (such as the ultrarapid potassium current, I Kur ) to repolarization. Of note, 2 studies in single atrial hiPSC-CM reported prolongation of action potential duration by I Kur block indicating that I Kur might in fact represent a valuable target for the treatment of human atrial fibrillation. However, the results and interpretation are at odds with the literature on I Kur block in human atria and the results of clinical studies. We believe that the discrepancies indicate that experiments in single atrial CM (both adult atrial CM and atrial hiPSC-CM) might be misleading. Under particular experimental conditions, atrial hiPSC-CMs may not closely resemble the electrophysiology of the human atrium. Therefore, we recapitulate here methodological issues evaluating potential value of the I Kur as an antiarrhythmic target when investigated in animal models, in human atrial tissues, and finally in atrial hiPSC-CM.

The Efficacy of I Na Block to Cardiovert Atrial Fibrillation Is Enhanced by Inhibition of I K1

ABSTRACT

There is a need for more efficient pharmacological cardioversion of atrial fibrillation (AF). We tested the hypothesis that inhibition of I K1 significantly enhances the efficacy of I Na block to depress atrial excitability and to cardiovert AF. The study was conducted in canine isolated arterially perfused right atrial preparations with rim of ventricular tissue. AF was induced in the presence of acetylcholine (ACh; 0.5 µM). BaCl 2 (10 µM) was used to inhibit I K1 and flecainide (1.5 µM) to block I Na . Sustained AF (>45 minutes) was recorded in 100% atria (5/5) in the presence of ACh alone. Flecainide cardioverted AF in 50% of atria (4/8), BaCl 2 in 0% (0/5), and their combination in 100% (5/5). AF cardioversion occurred in 15 ± 9 minutes with flecainide alone (n = 4) and in 8 ± 9 minutes with the combination (n = 5). Following drug-induced AF cardioversion, AF was inducible in 4/4 atria with flecainide alone (≤5 minutes duration) and in 2/5 atria with the combination (≤30 seconds duration). Atrial excitability was significantly more depressed by combined versus monotherapies. There was little to no effect on ventricular excitability under any condition tested. Thus, inhibition of I K1 significantly enhances the efficacy of flecainide to depress atrial excitability and to cardiovert AF in our experimental setting. A combination of I Na and I K1 inhibition may be an effective approach for cardioversion of AF.

Mechanisms of Chemical Atrial Defibrillation by Flecainide and Ibutilide

BACKGROUND

Effective and safe pharmacological approaches for atrial defibrillation offer several potential advantages over techniques like ablation. Pharmacological therapy is noninvasive, involving no risk associated with the procedure or resulting complications. Moreover, acute drug intervention with existing drugs is likely to be low cost and broadly accessible, thereby addressing a central tenet of health equity.

OBJECTIVES

This study aims to investigate ibutilide-mediated action potential prolongation to promote use-dependent effects of flecainide on Na+ channels by reducing the diastolic interval and, consequently, drug unbinding to reduce action potential excitability in atrial tissue and terminate re-entrant arrhythmia.

METHODS

Here we utilize a modeling and simulation approach to predict the specific combinations of sodium- and potassium-channel blocking drugs to chemically terminate atrial re-entry.

RESULTS

Computational modeling and simulation show that acute application of flecainide and ibutilide is a promising example of drug repurposing that may constitute a promising combination for chemical atrial defibrillation.

CONCLUSIONS

We predict the drug concentrations that promote efficacy of flecainide and ibutilide used in combination for atrial chemical defibrillation. We also predict the potential safety pharmacology impact of this drug combination on ventricular electrophysiology.

Targeting the Substrate for Atrial Fibrillation: JACC Review Topic of the Week

The identification of the pulmonary veins as a trigger source for atrial fibrillation (AF) has established pulmonary vein isolation (PVI) as a key target for AF ablation. However, PVI alone does not prevent recurrent AF in many patients, and numerous additional ablation strategies have failed to improve on PVI outcomes. This therapeutic limitation may be due, in part, to a failure to identify and intervene specifically on the pro-fibrillatory substrate within the atria and pulmonary veins. In this review paper, we highlight several emerging approaches with clinical potential that target atrial cardiomyopathy-the underlying anatomic, electrical, and/or autonomic disease affecting the atrium-in various stages of practice and investigation. In particular, we consider the evolving roles of risk factor modification, targeting of epicardial adipose tissue, tissue fibrosis, oxidative stress, and the inflammasome, along with aggressive early anti-AF therapy in AF management. Attention to combatting substrate development promises to improve outcomes in AF.

Effect of Flecainide and Ibutilide Alone and in Combination to Terminate and Prevent Recurrence of Atrial Fibrillation

BACKGROUND

There is a need for improved approaches to rhythm control therapy of atrial fibrillation (AF).

METHODS

The effectiveness of flecainide (1.5 µmol/L) and ibutilide (20 nmol/L), alone and in combination, to cardiovert and prevent AF recurrence was studied in canine-isolated coronary-perfused right atrioventricular preparations. We also examined the safety of the combination of flecainide (1.5 µmol/L) and ibutilide (50 nmol/L) using canine left ventricular wedge preparations.

RESULTS

Sustained AF (>1 hour) was inducible in 100%, 60%, 20%, and 0% of atria in the presence of acetylcholine alone, acetylcholine+ibutilide, acetylcholine+flecainide, and acetylcholine+ibutilide+flecainide, respectively. When used alone, flecainide and ibutilide cardioverted sustained AF in 40% and 20% of atria, respectively, but in 100% of atria when used in combination. Ibutilide prolonged atrial and ventricular effective refractory period by 15% and 8%, respectively, at a cycle length of 500 ms (P<0.05 for both). Flecainide increased the effective refractory period in atria by 27% (P<0.01) but by only 2% in the ventricles. The combination of the 2 drugs lengthened the effective refractory period by 42% in atria (P<0.01) but by only 7% (P<0.05) in the ventricles. In left ventricular wedges, ibutilide prolonged QT and Tpeak-Tend intervals by 25 and 55%, respectively (P<0.05 for both; cycle length, 2000 ms). The addition of flecainide (1.5 µmol/L) partially reversed these effects (P<0.05 for both parameters versus ibutilide alone). Torsades de Pointes score was relatively high with ibutilide alone and low with the drug combination.

CONCLUSIONS

In our experimental model, a combination of flecainide and ibutilide significantly improves cardioversion and prevents the recurrence of AF compared with monotherapies with little to no risk for the development of long-QT-mediated ventricular proarrhythmia.

Mild elevation of extracellular potassium greatly potentiates the effect of sodium channel block to cardiovert atrial fibrillation: The Lankenau approach

BACKGROUND

Cardioversion of atrial fibrillation (AF) is a common clinical necessity, and there is a need for more effective and safe options for acute cardioversion of AF.

OBJECTIVE

The purpose of this study was to test the hypothesis that the efficacy and time course of AF cardioversion by sodium channel current (INa) block can be improved by mild elevation of extracellular potassium ([K+]0).

METHODS

Using a canine acetylcholine (ACh)-mediated AF model (isolated coronary-perfused right atrial preparations with a rim of right ventricle), we evaluated the ability of flecainide to suppress AF in the presence of [K+]0 ranging from 3 to 8 mM.

RESULTS

At [K+]0 of 4 mM (baseline), persistent AF (>1 hour) was induced in 5 of 5 atria in the presence of 0.5 μM ACh. Flecainide alone (1.5 μM) cardioverted 3 of 6 atria at 4 mM [K+]0, 1 of 6 atria at 3 mM [K+]0, 5 of 5 atria at 5 mM and 6 mM [K+]0, and 4 of 4 atria at 8 mM [K+]0. In the absence of flecainide, an increase in [K+]0 from 4 mM to 5, 6, and 8 mM terminated AF in 0 of 5, 2 of 6, and 4 of 4 atria, respectively. The time to conversion was also abbreviated by elevation of [K+]0. After AF termination with flecainide plus elevated [K+]0, AF was either not inducible or brief (<100 seconds). Combined flecainide and elevated [K+]0 (6 mM) caused an atrial preferential depression of excitability.

CONCLUSION

Our findings suggest that a combination of INa block accompanied by mild elevation of serum potassium may be a novel approach to more effectively, rapidly, and safely cardiovert AF and prevent its recurrence in the short term.

Advances in basic and translational research in atrial fibrillation

Atrial fibrillation (AF) is a very common cardiac arrhythmia with an estimated prevalence of 33.5 million patients globally. It is associated with an increased risk of death, stroke and peripheral embolism. Although genetic studies have identified a growing number of genes associated with AF, the definitive impact of these genetic findings is yet to be established. Several mechanisms, including electrical, structural and neural remodelling of atrial tissue, have been proposed to contribute to the development of AF. Despite over a century of exploration, the molecular and cellular mechanisms underlying AF have not been fully established. Current antiarrhythmic drugs are associated with a significant rate of adverse events and management of AF using ablation is not optimal, especially in cases of persistent AF. This review discusses recent advances in our understanding and management of AF, including new concepts of epidemiology, genetics and pathophysiological mechanisms. We review the current status of antiarrhythmic drug therapy for AF, new potential agents, as well as mechanism-based AF ablation. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Atrial Fibrillation Induced by Anticancer Drugs and Underling Mechanisms

ABSTRACT

Cancer therapy has made major progress in the past several decades, but treatments are often accompanied by significant side effects. Arrhythmias are a widespread complication of some antineoplastic drugs, with atrial fibrillation (AF) being the most often encountered drug-associated arrhythmia. Preexisting AF risk factors are commonly present in cancer patients who develop drug-associated AF, and active cancer itself may cause or promote AF. Although anticancer drugs may induce AF in cancer patients without AF risk factors, it appears that most drug-associated AF develop when cancer drugs add or aggravate precancer-existing and/or cancer-related pro-AF factors/alterations, additively or synergistically producing AF. Abnormalities in intracellular calcium activity seem to be involved in the generation of anticancer drug-induced AF. In cancer survivors with cancer therapy-induced cardiomyopathy, AF often occurs, with most of the arrhythmias likely to develop secondary to the cardiomyopathy. AF may lead to modification or even cessation of cancer therapy. The management of AF in patients with cancer is currently conducted largely based on pragmatic assumptions. This review briefly discusses AF caused by anticancer drugs and the underlying mechanisms.

Molecular Insights in Atrial Fibrillation Pathogenesis and Therapeutics: A Narrative Review

The prevalence of atrial fibrillation (AF) is bound to increase globally in the following years, affecting the quality of life of millions of people, increasing mortality and morbidity, and beleaguering health care systems. Increasingly effective therapeutic options against AF are the constantly evolving electroanatomic substrate mapping systems of the left atrium (LA) and ablation catheter technologies. Yet, a prerequisite for better long-term success rates is the understanding of AF pathogenesis and maintenance. LA electrical and anatomical remodeling remains in the epicenter of current research for novel diagnostic and treatment modalities. On a molecular level, electrical remodeling lies on impaired calcium handling, enhanced inwardly rectifying potassium currents, and gap junction perturbations. In addition, a wide array of profibrotic stimuli activates fibroblast to an increased extracellular matrix turnover via various intermediaries. Concomitant dysregulation of the autonomic nervous system and the humoral function of increased epicardial adipose tissue (EAT) are established mediators in the pathophysiology of AF. Local atrial lymphomononuclear cells infiltrate and increased inflammasome activity accelerate and perpetuate arrhythmia substrate. Finally, impaired intracellular protein metabolism, excessive oxidative stress, and mitochondrial dysfunction deplete atrial cardiomyocyte ATP and promote arrhythmogenesis. These overlapping cellular and molecular alterations hinder us from distinguishing the cause from the effect in AF pathogenesis. Yet, a plethora of therapeutic modalities target these molecular perturbations and hold promise in combating the AF burden. Namely, atrial selective ion channel inhibitors, AF gene therapy, anti-fibrotic agents, AF drug repurposing, immunomodulators, and indirect cardiac neuromodulation are discussed here.