Mechanisms of stretch-induced electro-anatomical remodeling and atrial arrhythmogenesis

Atrial fibrillation (AF) is the most common cardiac rhythm disorder, often occurring in the setting of atrial distension and elevated myocardialstretch. While various mechano-electrochemical signal transduction pathways have been linked to AF development and progression, the underlying molecular mechanisms remain poorly understood, hampering AF therapies. In this review, we describe different aspects of stretch-induced electro-anatomical remodeling as seen in animal models and in patients with AF. Specifically, we focus on cellular and molecular mechanisms that are responsible for mechano-electrochemical signal transduction and the development of ectopic beats triggering AF from pulmonary veins, the most common source of paroxysmal AF. Furthermore, we describe structural changes caused by stretch occurring before and shortly after the onset of AF as well as during AF progression, contributing to longstanding forms of AF. We also propose mechanical stretch as a new dimension to the concept "AF begets AF", in addition to underlying diseases. Finally, we discuss the mechanisms of these electro-anatomical alterations in a search for potential therapeutic strategies and the development of novel antiarrhythmic drugs targeted at the components of mechano-electrochemical signal transduction not only in cardiac myocytes, but also in cardiac non-myocyte cells.

Antiarrhythmic Effect of Ranolazine in Combination with Selective NCX-Inhibition in an Experimental Model of Atrial Fibrillation

The aim of this study was to investigate the effects of a combination of ranolazine with different selective inhibitors of the Na⁺/Ca²⁺-exchanger (NCX) in an established experimental model of atrial fibrillation (AF). Eighteen hearts of New Zealand white rabbits were retrogradely perfused. Atrial catheters were used to record monophasic action potentials (aPRR). Hearts were paced at three different cycle lengths. Thereby, atrial action potential durations (aAPD₉₀), atrial effective refractory periods (aERP) and atrial post-repolarization refractoriness were obtained. Isoproterenol and acetylcholine were employed to increase the occurrence of AF. Thereafter, the hearts were assigned to two groups (n = 9 each group) and additionally perfused with a combination of 10 µM ranolazine and 1 µM of the selective NCX-inhibitor ORM-10103 (group A: Rano-ORM) or 10 µM ranolazine and 1 µM of another NCX-inhibitor, SEA0400 (group B: Rano-SEA). The infusion of Iso/ACh led to a shortening of aAPD₉₀, aERP, aPRR and the occurrence of AF episodes was significantly increased. Additional perfusion with ranolazine and ORM-10103 (group A) significantly prolonged the refractory periods and aPRR and AF episodes were effectively reduced. In group B, Rano-SEA led to a slight decrease in aAPD₉₀ while aERP and aPRR were prolonged. The occurrence of AF episodes was consecutively reduced. To our knowledge, this is the first study investigating the effect of ranolazine combined with different selective NCX-inhibitors in an isolated whole-heart model of AF. Both combinations prolonged aERP and aPRR and thereby suppressed the induction of AF.

Action Potential Triangulation Explains Acute Proarrhythmic Effect of Aliskiren in a Whole-Heart Model of Atrial Fibrillation

Recent experimental studies showed a protective effect of the renin inhibitor aliskiren regarding atrial structural remodeling. Purpose of this study was to assess acute electrophysiologic effects of aliskiren in a whole-heart model of atrial fibrillation (AF) and to investigate its impact on the ventricle. Twelve rabbit hearts were excised, retrogradely perfused, and paced at different cycle lengths. To enhance atrial vulnerability, a combination of acetylcholine (ACh) and isoproterenol (Iso) was infused and significantly reduced atrial action potential duration (aAPD₉₀) and atrial effective refractory period (aERP). Additional infusion of aliskiren prolonged aAPD₉₀ but did not alter aERP. A triangulation of action potential with ACh/Iso and a further triangulation after treatment with aliskiren were noted. Vulnerability to AF was tested by employing trains of burst pacing. Administration of ACh/Iso provoked more episodes of AF (baseline: 26 episodes, Iso/Ach: 48 episodes). Additional treatment with aliskiren induced AF significantly more often (108 episodes). Another nine hearts were perfused with aliskiren to examine its ventricular effects. Infusion with aliskiren abbreviated ventricular APD₉₀ and ERP. Utilizing programmed ventricular stimulation, a trend towards more ventricular arrhythmias in aliskiren-treated hearts was observed. Though aliskiren did not reduce aAPD₉₀ or aERP, acute treatment with aliskiren promoted AF. Triangulation of atrial action potentials, which is an established risk factor for ventricular proarrhythmia, may contribute to the increased atrial vulnerability. This effect may interfere with its recently demonstrated beneficial properties in atrial remodeling. Of note, aliskiren might have a proarrhythmic effect on the ventricular level.

Cardiac Mechano-Electric Coupling: Acute Effects of Mechanical Stimulation on Heart Rate and Rhythm

The heart is vital for biological function in almost all chordates, including humans. It beats continually throughout our life, supplying the body with oxygen and nutrients while removing waste products. If it stops, so does life. The heartbeat involves precise coordination of the activity of billions of individual cells, as well as their swift and well-coordinated adaption to changes in physiological demand. Much of the vital control of cardiac function occurs at the level of individual cardiac muscle cells, including acute beat-by-beat feedback from the local mechanical environment to electrical activity (as opposed to longer term changes in gene expression and functional or structural remodeling). This process is known as mechano-electric coupling (MEC). In the current review, we present evidence for, and implications of, MEC in health and disease in human; summarize our understanding of MEC effects gained from whole animal, organ, tissue, and cell studies; identify potential molecular mediators of MEC responses; and demonstrate the power of computational modeling in developing a more comprehensive understanding of ‟what makes the heart tick.ˮ.

Histone deacetylase inhibition by Entinostat for the prevention of electrical and structural remodeling in heart failure

Background

The development of heart failure is accompanied by complex changes in cardiac electrophysiology and functional properties of cardiomyocytes and fibroblasts. Histone deacetylase (HDAC) inhibitors hold great promise for the pharmaceutical therapy of several malignant diseases. Here, we describe novel effects of the class I HDAC inhibitor Entinostat on electrical and structural remodeling in an in vivo model of pacing induced heart failure.

Methods

Rabbits were implanted a pacemaker system, subjected to rapid ventricular pacing and treated with Entinostat or placebo, respectively. Following stimulation, rabbit hearts were explanted and subsequently subjected to electrophysiological studies and further immunohistological analyses of left ventricles.

Results

In vivo, rapid ventricular stimulation caused a significant prolongation of monophasic action potential duration compared to sham hearts (from 173 ± 26 ms to 250 ± 41 ms; cycle length 900 ms; p < 0.05) and an increased incidence of Early afterdepolarisations (+ 150%), while treatment with Entinostat in failing hearts could partially prevent this effect (from 250 ± 41 ms to 170 ± 53 ms, p < 0.05; reduction in EAD by 50%). Entinostat treatment partially restored KCNH2 and Cav1.3 gene expressions in failing hearts, and inhibited the development of cardiac fibrosis in vivo.

Conclusion

In a rabbit model of heart failure, Entinostat diminishes heart failure related prolongation of repolarization and partially restores KCNH2 and Cav1.3 expression. In addition, Entinostat exerts antifibrotic properties both in vitro and in vivo. Thus, Entinostat might be an interesting candidate for the pharmaceutical therapy of heart failure directed against structural and electrical remodeling.

Electronic supplementary material

The online version of this article (10.1186/s40360-019-0294-x) contains supplementary material, which is available to authorized users.

Antiarrhythmic Effects of Combining Dofetilide and Ranolazine in a Model of Acutely Induced Atrial Fibrillation in Horses

Supplemental Digital Content is Available in the Text.

Background:

Antiarrhythmic compounds against atrial fibrillation (AF) often have reduced efficacy and may display cardiac and/or noncardiac toxicity. Efficacy can be improved by combining 2 compounds with distinct mechanisms, and it may be possible to use lower doses of each compound, thereby reducing the likelihood of adverse side effects. The purpose of this study was to investigate whether the effective doses of dofetilide and ranolazine can be reduced if the drugs are combined.

Methods:

Dofetilide, ranolazine, and a combination of these were administered in 4 incremental dosing regimens to horses with acutely pacing-induced AF. Time to cardioversion, atrial effective refractory period, and AF vulnerability and duration were assessed.

Results:

Of 8 horses, 6 cardioverted to sinus rhythm after infusion with a combination of 0.889 μg/kg dofetilide and 0.104 mg/kg ranolazine. Two horses cardioverted with 0.104 mg/kg ranolazine alone, and 3 cardioverted with 0.889 μg/kg dofetilide alone. The combination therapy decreased AF vulnerability (P < 0.05) and AF duration (P < 0.05). No change in atrial effective refractory period was detected with any of the drugs.

Conclusions:

The combination of dofetilide and ranolazine showed increased antiarrhythmic effects on acutely induced AF in horses, affecting time to cardioversion, AF vulnerability, and AF duration.

Impact of ranolazine on ventricular arrhythmias - A systematic review

Ranolazine is a new medication for the treatment of refractory angina. However, except its anti-anginal properties, it has been found to act as an anti-arrhythmic. The aim of our systematic review is to present the existing data about the impact of ranolazine in ventricular arrhythmias. We searched MEDLINE and Cochrane databases as well clinicaltrials.gov until September 1, 2017 to find all studies (clinical trials, observational studies, case reports/series) reported data about the impact of ranolazine in ventricular arrhythmias. Our search revealed 14 studies (3 clinical trials, 2 observational studies, 8 case reports, 1 case series). These data reported a beneficial impact of ranolazine in ventricular tachycardia/fibrillation, premature ventricular beats, and ICD interventions in different clinical settings. The existing data highlight the anti-arrhythmic properties of ranolazine in ventricular arrhythmias.

Effective suppression of atrial fibrillation by the antihistaminic agent antazoline: First experimental insights into a novel antiarrhythmic agent

INTRODUCTION

The antihistaminic antazoline (ANT) was reported to be highly effective and safe for rapid conversion of atrial fibrillation (AF). We therefore analyzed underlying mechanisms in an experimental whole-heart model.

METHODS AND RESULTS

Isolated and retrogradely perfused rabbit hearts underwent a standardized protocol employing atrial burst pacing-induced AF in five of 20 hearts under baseline conditions (seven episodes). Thereafter, a combination of acetylcholine and isoproterenol was employed to enhance AF occurrence. Two monophasic action potential recordings on the left- and two on the right atrial epicardium showed a decrease in atrial action potential duration (aAPD, -25 msec, P<.05) and atrial effective refractory period (aERP; -52 msec, P<.01) after infusion of acetylcholine (1 μmol/L) and isoproterenol (1 μmol/L). This led to induction of AF in 14 of 20 hearts (145 episodes). Simultaneous infusion of ANT (20 μmol/L) led to a complete suppression of AF in all inducible hearts. Treatment with ANT also led to a significant increase in aAPD (+41 msec, P<.01) and aERP (+74 msec, P<.05), leading to a marked increase in atrial postrepolarization refractoriness (aPRR, +33 msec, P<.01). Results were compared to 13 rabbits treated with flecainide. Flecainide induced a significant increase in aPRR and resulted in induction of AF in seven of 13 hearts (51 episodes) while 11 of 13 hearts were inducible with acetylcholine and isoproterenol (93 episodes).

CONCLUSION

Administration of ANT was highly effective in suppressing AF. The antiarrhythmic effect could be explained by a significant increase in postrepolarization refractoriness as a result of a more marked increase in aERP as compared with aAPD.

Role of ranolazine in the prevention and treatment of atrial fibrillation: A meta-analysis of randomized clinical trials

BACKGROUND

Randomized controlled trials (RCTs) on the use of ranolazine (RN) for prevention and cardioversion of atrial fibrillation (AF) have yielded conflicting results.

OBJECTIVE

The purpose of this study was to conduct a meta-analysis of RCTs to examine the potential role of RN in the prevention and cardioversion of AF.

METHODS

PubMed and EMBASE were searched until June 2016. Of 484 initially identified studies, 8 RCTs were finally analyzed.

RESULTS

The analysis of RCTs showed that RN significantly reduced the incidence of AF compared to the control group in various clinical settings, such as after cardiac surgery, in acute coronary syndromes, and post-electrical cardioversion of AF (relative risk [RR] 0.67, 95% confidence interval [CI] 0.52-0.87, Z = 3.06, P = .002). Furthermore, a higher conversion rate of AF from the combined use of RN and amiodarone compared to amiodarone alone (RR 1.23, 95% CI 1.08-1.40, Z = 3.07, P = .002) was clear, with conversion time significantly shorter in RN plus amiodarone compared to the amiodarone group (weighted mean difference [WMD] = -10.38 hours, 95% CI -18.18 to -2.57, Z = 2.61, P = .009).

CONCLUSION

Our meta-analysis suggests that RN may be effective in AF prevention, whereas it potentiates and accelerates the conversion effect of amiodarone of recent-onset AF. Larger RCTs with long-term follow-up in diverse clinical settings are needed to further clarify the impact of RN on AF therapy.

Ranolazine Therapy in Cardiac Arrhythmias

Ranolazine is an antianginal medication originally granted approval by the U.S. Food and Drug Administration for therapeutic use in 2006. Since its introduction into the U.S. market, there have been multiple trials and clinical case reports that demonstrate ranolazine may be effective in the prevention and treatment of both atrial and ventricular arrhythmias, including postoperative atrial fibrillation following coronary artery bypass graft (CABG) surgery. More recently, the combination of dronedarone with ranolazine has demonstrated in initial studies to have a synergistic effect in the reduction of burden of atrial fibrillation. This article will review the basic pharmacology of ranolazine, the studies demonstrating use of ranolazine in atrial and ventricular arrhythmias, the limitations to the use of ranolazine as antiarrhythmic therapy, and explore the synergistic effect with other agents in the suppression of arrhythmias.

Rabbit models of cardiac mechano-electric and mechano-mechanical coupling

Cardiac auto-regulation involves integrated regulatory loops linking electrics and mechanics in the heart. Whereas mechanical activity is usually seen as 'the endpoint' of cardiac auto-regulation, it is important to appreciate that the heart would not function without feed-back from the mechanical environment to cardiac electrical (mechano-electric coupling, MEC) and mechanical (mechano-mechanical coupling, MMC) activity. MEC and MMC contribute to beat-by-beat adaption of cardiac output to physiological demand, and they are involved in various pathological settings, potentially aggravating cardiac dysfunction. Experimental and computational studies using rabbit as a model species have been integral to the development of our current understanding of MEC and MMC. In this paper we review this work, focusing on physiological and pathological implications for cardiac function.

Atrial fibrillation in patients with diabetes: molecular mechanisms and therapeutic perspectives

Atrial fibrillation (AF) remains the most frequent sustained cardiac arrhythmia worldwide and its incidence increases with ageing, cardiovascular risk factors and comorbidities. Prevalence of diabetes mellitus (DM) is growing fast and is assuming pandemic proportions mostly due to overnutrition and sedentary habits. Experimental and clinical evidences suggest that DM and AF are strongly interconnected. The present review addresses in detail new molecular pathways implicated in the etiology of AF and their relevance for mechanism-based therapeutic strategies in this setting. Advances in risk stratification, drug therapy (i.e., novel anticoagulants) and catheter ablation are also described.

The HARMONY Trial: Combined Ranolazine and Dronedarone in the Management of Paroxysmal Atrial Fibrillation: Mechanistic and Therapeutic Synergism

BACKGROUND

Atrial fibrillation (AF) requires arrhythmogenic changes in atrial ion channels/receptors and usually altered atrial structure. AF is commonly treated with antiarrhythmic drugs; the most effective block many ion channels/receptors. Modest efficacy, intolerance, and safety concerns limit current antiarrhythmic drugs. We hypothesized that combining agents with multiple anti-AF mechanisms at reduced individual drug doses might produce synergistic efficacy plus better tolerance/safety.

METHODS AND RESULTS

HARMONY tested midrange ranolazine (750 mg BID) combined with 2 reduced dronedarone doses (150 mg BID and 225 mg BID; chosen to reduce dronedarone's negative inotropic effect-see text below) over 12 weeks in 134 patients with paroxysmal AF and implanted pacemakers where AF burden (AFB) could be continuously assessed. Patients were randomized double-blind to placebo, ranolazine alone (750 mg BID), dronedarone alone (225 mg BID), or one of the combinations. Neither placebo nor either drugs alone significantly reduced AFB. Conversely, ranolazine 750 mg BID/dronedarone 225 mg BID reduced AFB by 59% versus placebo (P=0.008), whereas ranolazine 750 mg BID/dronedarone 150 mg BID reduced AFB by 43% (P=0.072). Both combinations were well tolerated.

CONCLUSIONS

HARMONY showed synergistic AFB reduction by moderate dose ranolazine plus reduced dose dronedarone, with good tolerance/safety, in the population enrolled.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; Unique identifier: NCT01522651.

Effects of ranolazine on torsades de pointes tachycardias in a healthy isolated rabbit heart model

PURPOSE

Torsades de pointes (TdP) tachycardias are triggered, polymorphic ventricular arrhythmias arising from early afterdepolarizations (EADs) and increased dispersion of repolarization. Ranolazine is a new agent which reduces pathologically elevated late INa but also IKr . Aim of this study was to evaluate the effects of ranolazine in a validated isolated Langendorff-perfused rabbit heart model.

METHODS

TdP was reproducibly induced with d-sotalol (10(-4)  mol/L) and low potassium (K) (1.0 mmol/L for 5 min, pacing at CL 1000 ms). In 10 hearts, ECG and 8 epi- and endocardial monophasic action potentials were recorded. Action potential duration (APD) was measured at 90% repolarization and dispersion defined as APD max-min.

RESULTS

D-sotalol prolonged APD90 and increased dispersion of APD90 , simultaneously causing EADs and induction of TdP. The combination of d-sotalol and two concentrations of ranolazine did not increase dispersion of ventricular APD90 as compared to vehicle. Ranolazine at 5 μmol/L did not cause additional induction of EADs and/or TdP but also did not significantly suppress arrhythmogenic triggers. The higher concentration of ranolazine (10 μmol/L) in combination with d-sotalol caused further prolongation of APD90 , at the same time reduction in APD90 dispersion. In parallel, the incidence of EADs was reduced and an antitorsadogenic effect was seen.

CONCLUSIONS

In the healthy isolated rabbit heart (where late INa is not elevated), ranolazine does not cause proarrhythmia but exerts antiarrhythmic effects in a dose-dependent manner against d-sotalol/low K-induced TdP. This finding-despite additional APD prolongation-supports the safety of a combined use of both drugs and merits clinical investigation.

Ranolazine in the treatment of atrial fibrillation: Results of the dose-ranging RAFFAELLO (Ranolazine in Atrial Fibrillation Following An ELectricaL CardiOversion) study

BACKGROUND

Currently available antiarrhythmic agents for the treatment of atrial fibrillation (AF) have important limitations, leaving an unmet need for safe and effective therapy. Ranolazine is an approved antianginal agent with a favorable safety profile and electrophysiologic properties suggesting a potential role in the treatment of AF.

OBJECTIVE

The purpose of this study was to assess the safety and efficacy of ranolazine in the prevention of AF recurrence after successful electrical cardioversion and to ascertain the most appropriate dose of this agent.

METHODS

This prospective, multicenter, randomized, double-blind, placebo-control parallel group phase II dose-ranging trial randomized patients with persistent AF (7 days to 6 months) 2 hours after successful electrical cardioversion to placebo, or ranolazine 375 mg, 500 mg, or 750 mg bid. Patients were monitored daily by transtelephonic ECG. The primary end-point was the time to first AF recurrence.

RESULTS

Of 241 patients randomized, 238 took at least 1 drug dose. Ranolazine proved to be safe and tolerable. No dose of the drug significantly prolonged time to AF recurrence. AF recurred in 56.4%, 56.9%, 41.7%, and 39.7% of patients in the placebo, ranolazine 375 mg, ranolazine 500 mg, and ranolazine 750 mg groups, respectively. The reduction in overall AF recurrence in the combined 500-mg and 750-mg groups was of borderline significance compared to the placebo group (P = .053) and significant compared to 375-mg group (P = .035).

CONCLUSION

No dose of ranolazine significantly prolonged time to AF recurrence. However, the 500-mg and 750 mg-groups combined reduced AF recurrences, suggesting a possible role for this agent in the treatment of AF.