Ivabradine reduced ventricular rate in patients with non-paroxysmal atrial fibrillation

PR Interval as a Novel Therapeutic Target of Ivabradine Therapy-Prognostic Impact of Ivabradine-Induced PR Prolongation in Heart Failure Patients

BACKGROUND

Ivabradine reduces heart rate by inhibiting the "funny current" expressed on the sinoatrial node and improves mortality and morbidity in patients with systolic heart failure and sinus tachycardia. The funny current is known to be expressed also on the atrioventricular node according to experimental studies. However, the impact of ivabradine on PR interval remained unknown.

METHODS

Patients with a left ventricular ejection fraction of less than 50% who received 1 month of ivabradine were screened. Electrocardiographic and echocardiographic data, particularly concerning heart rate, the PR interval, and trans-mitral flow pattern, were collected at baseline and 1-month follow-up. The primary endpoint was defined as the composite of cardiovascular death and hospital readmission for worsening heart failure following ivabradine administration.

RESULTS

In the cohort of 29 enrolled patients (median age: 66 years, 62% male), the median baseline heart rate was 86 beats per minute and the median PR interval was 168 milliseconds. Following ivabradine administration, a significant decrease of 20 beats per minute in the heart rate and a significant increase of 24 milliseconds in the PR interval were observed. The truncated interval of the A-wave, detected in the trans-mitral flow, consistently demonstrated a negative correlation with the PR interval both before and after the administration of ivabradine. During a median of 1.8 years of follow-up, six patients reached the primary endpoint. A combination of heart rate reduction and PR prolongation following ivabradine administration, both of which were independent factors associated with the primary endpoint (p < 0.05 for both), was associated with greater freedom from the primary endpoint compared with either/neither of them (p = 0.002).

CONCLUSIONS

Ivabradine seems to prolong PR interval, which is a novel surrogate marker of favorable clinical outcomes in patients with systolic heart failure. This effect may be associated with the dynamics of the trans-mitral flow pattern, in conjunction with heart rate and the PR interval. Clinical implications of PR interval-guided ivabradine therapy remains the future concern.

A pilot study evaluating the role of ivabradine for rate control in patients with rheumatic atrial fibrillation

OBJECTIVES

Ivabradine may have a role in rate control of atrial fibrillation (AF) due to effects on HCN channels in AV node. We studied role of Ivabradine in rate control of rheumatic AF.

METHODS

80 patients, rheumatic AF, HR > 100 bpm (age 47 ± 11 yrs, AF duration 6.8 ± 2.9 years, rate 131 ± 16 bpm) on maximally tolerated ββ or CCB's, randomized to Ivabradine or escalated ββ/CCB. Ivabradine started @ 2.5 mg BD; increased to 5 mg BD if inadequate response at 1 week (failure to decrease HR < 10% vs baseline). After Holter at 1 month, dose escalated to 7.5 mg BD if needed.

RESULTS

Ivabradine resulted in significantly lower HR (81 ± 10 vs 99 ± 9) at 3 months and 6 months (79 ± 8 vs 94 ± 8, p < 0.001). Absolute reduction in HR: 56 ± 15 vs 31 ± 14 bpm and % change in HR: 41 ± 7 vs 24 ± 9%, both p < 0.00001). At 6 months, Ivabradine group had. 1Significantly lower NT Pro BNP (1168 vs 1314 pg/ml), higher 6 min walk distance (410 ± 47 vs 349 ± 54 m, all p < 0.001) 2Better symptom class (EHRA score 1: asymptomatic 84% vs 40%), improvement >1 EHRA class; baseline 60% vs 17% 3Better LA Strain (22.8 ± 2.8% vs 20.6 ± 2.5%) Ivabradine was well tolerated and there was no drug withdrawal.

CONCLUSION

Our data suggest that Ivabradine can be an option for rate control in rheumatic AF.

Ivabradine for controlling heart rate in permanent atrial fibrillation: A translational clinical trial

BACKGROUND

Pharmacological options for rate control in atrial fibrillation are scarce. Ivabradine was postulated to reduce the ventricular rate in this setting.

OBJECTIVES

The objectives of this study were to evaluate the mechanism of inhibition of atrioventricular conduction produced by ivabradine and to determine its efficacy and safety in atrial fibrillation.

METHODS

The effects of ivabradine on atrioventricular node and ventricular cells were studied by in vitro whole-cell patch-clamp experiments and mathematical simulation of human action potentials. In parallel, a multicenter, randomized, open-label, phase III clinical trial compared ivabradine with digoxin for uncontrolled permanent atrial fibrillation despite β-blocker or calcium channel blocker treatment.

RESULTS

Ivabradine 1 μM inhibited "funny" current and rapidly activating delayed rectifier potassium channel current by 28.9% and 22.8%, respectively (P < .05). The sodium channel current and L-type calcium channel current were reduced only at 10 μM. Ivabradine slowed the firing frequency of a modeled human atrioventricular node action potential by 10.6% and induced a minimal prolongation of ventricular action potential. Thirty-five (51.5%) patients were randomized to ivabradine and 33 (49.5%) to digoxin. The mean daytime heart rate decreased by 11.6 beats/min (-11.5%) in the ivabradine arm (P = .02) vs 19.6 (-20.6%) in the digoxin arm (P < .001), although the noninferiority margin of efficacy was not met (Z = -1.95; P = .97). The primary safety end point occurred in 3 patients (8.6%) on ivabradine and in 8 (24.2%) on digoxin (P = .10).

CONCLUSION

Ivabradine produced a moderate rate reduction in patients with permanent atrial fibrillation. The inhibition of funny current in the atrioventricular node seems to be the main mechanism responsible for this reduction. Compared with digoxin, ivabradine was less effective, was better tolerated, and had a similar rate of serious adverse events.

Ivabradine in heart failure patients with reduced ejection fraction and history of paroxysmal atrial fibrillation

Aims

Ivabradine is indicated for heart failure (HF) patients with reduced ejection fraction (HFrEF), but limited data are available with regards to the use of ivabradine in those with a history of paroxysmal atrial fibrillation (AF). To assess the effect of ivabradine in HFrEF patients with paroxysmal AF, we analysed heart failure (HF) hospitalization and mortality from multiple‐centre registry database.

Methods and results

We conducted a multicentre observational matched cohort study, and this study enrolled patient with symptomatic HFrEF from 1 January 2015 to 31 December 2018 who had a history of paroxysmal AF in Chang Gung Memorial Hospital medical database in Taiwan. A total of 2042 patients were eligible for the study, of whom 887 were prescribed with ivabradine and 1115 were not. The primary outcome, including HF hospitalization and cardiovascular death, and individual outcome during the 12 month observation period were analysed after inverse probability of treatment weighting. The ivabradine group had significantly lower mean heart rate after 12 months follow‐up than the non‐ivabradine group (P < 0.05). The primary outcome was significantly higher in the ivabradine group than the non‐ivabradine group after 12 months follow‐up (hazard ratio [HR] = 1.58; 95% confidence interval [CI], 1.26–2.00, P < 0.001). Moreover, the ivabradine group had a significantly higher event rate of HF hospitalization (HR = 1.56; 95% CI, 1.40–1.75, P < 0.001) and HF death (HR = 1.67; 95% CI, 1.14–2.44, P = 0.009) than the non‐ivabradine group.

Conclusions

Ivabradine treatment was associated with an increased risk of HF hospitalization in symptomatic HFrEF patients with a history of paroxysmal AF. Further prospective randomized studies are warranted.

The Bradycardic Agent Ivabradine Acts as an Atypical Inhibitor of Voltage-Gated Sodium Channels

Background and purpose: Ivabradine is clinically administered to lower the heart rate, proposedly by inhibiting hyperpolarization-activated cyclic nucleotide-gated cation channels in the sinoatrial node. Recent evidence suggests that voltage-gated sodium channels (VGSC) are inhibited within the same concentration range. VGSCs are expressed within the sinoatrial node and throughout the conduction system of the heart. A block of these channels thus likely contributes to the established and newly raised clinical indications of ivabradine. We, therefore, investigated the pharmacological action of ivabradine on VGSCs in sufficient detail in order to gain a better understanding of the pro- and anti-arrhythmic effects associated with the administration of this drug.

Experimental Approach: Ivabradine was tested on VGSCs in native cardiomyocytes isolated from mouse ventricles and the His-Purkinje system and on human Na_v1.5 in a heterologous expression system. We investigated the mechanism of channel inhibition by determining its voltage-, frequency-, state-, and temperature-dependence, complemented by a molecular drug docking to the recent Na_v1.5 cryoEM structure. Automated patch-clamp experiments were used to investigate ivabradine-mediated changes in Na_v1.5 inactivation parameters and inhibition of different VGSC isoforms.

Key results: Ivabradine inhibited VGSCs in a voltage- and frequency-dependent manner, but did not alter voltage-dependence of activation and fast inactivation, nor recovery from fast inactivation. Cardiac (Na_v1.5), neuronal (Na_v1.2), and skeletal muscle (Na_v1.4) VGSC isoforms were inhibited by ivabradine within the same concentration range, as were sodium currents in native cardiomyocytes isolated from the ventricles and the His-Purkinje system. Molecular drug docking suggested an interaction of ivabradine with the classical local anesthetic binding site.

Conclusion and Implications: Ivabradine acts as an atypical inhibitor of VGSCs. Inhibition of VGSCs likely contributes to the heart rate lowering effect of ivabradine, in particular at higher stimulation frequencies and depolarized membrane potentials, and to the observed slowing of intra-cardiac conduction. Inhibition of VGSCs in native cardiomyocytes and across channel isoforms may provide a potential basis for the anti-arrhythmic potential as observed upon administration of ivabradine.

A case report of ivabradine used for heart rate control of atrial fibrillation in acute decompensated heart failure

Background

Achieving pharmacologic rate control in patients with atrial fibrillation (AF) with rapid ventricular response (RVR) can be tricky when the patient’s underlying cardiac function is decreased. We present a case illustrating how ivabradine can be useful in this clinical scenario.

Case summary

A 95-year-old woman with a history of systolic heart failure (HF) presented with acute decompensated HF in AF with RVR. Beta blockade and calcium channel blockade were avoided given her cardiac history, and diuresis with high doses of furosemide was ineffective. Her ventricular response slowed with ivabradine, allowing for rapid decongestion and a safe discharge home.

Discussion

Ivabradine acts on the I_f current of cardiac pacemaker cells to slow heart rate (HR), and it currently carries a class IIa recommendation to reduce the risk of HF hospitalization and cardiac death in patients with left ventricular ejection fraction ≤35% and a symptomatic HR ≥70 b.p.m. Although current recommendations are for patients in sinus rhythm, ivabradine has a theoretical benefit in patients with AF given its mechanism of action. Because it does not negatively affect inotropy or blood pressure, ivabradine was used in our patient with a good clinical outcome. Our case provides an example of ivabradine’s usefulness in patients with AF in RVR with a history of depressed systolic function.

Ivabradine and Atrial Fibrillation: A Meta-analysis of Randomized Controlled Trials

ABSTRACT

This was a meta-analysis of randomized control trials (RCTs) to evaluate the effect of ivabradine on the risk of atrial fibrillation (AF) as well as its effect on the ventricular rate in patients with AF. The PubMed, EMBASE, Cochrane Controlled Trials Register, and other databases were searched for RCTs of ivabradine. Thirteen trials with 37,533 patients met the inclusion criteria. The incidence of AF was significantly higher in the ivabradine treatment group than in the control group (odds ratio (OR), 1.23; 95% confidence interval (CI), 1.08-1.41), although it was reduced after cardiac surgery (OR, 0.70; 95% CI, 0.23-2.12). Regarding left ventricular ejection fraction (LVEF), ivabradine increased the risk of AF in both LVEF >40% (OR, 1.42; 95% CI, 1.24 to 1.63) and LVEF ≤40% subgroups (OR, 1.16; 95% CI, 0.98-1.37). The risk of AF was increased by both small and large cumulative doses of ivabradine (small cumulative dose: OR, 3.00; 95% CI, 0.48 to 18.93; large cumulative dose: OR, 1.05; 95% CI, 0.83-1.34). Furthermore, ivabradine may reduce the ventricular rate in patients with AF. In conclusion, we found that both large and small cumulative doses of ivabradine were associated with an increased incidence of AF, and the effect was more marked in the LVEF >40% subgroup. Nevertheless, ivabradine therapy is beneficial for the prevention of post-operative AF. Furthermore, ivabradine may be effective in controlling the ventricular rate in patients with AF, although more RCTs are needed to support this conclusion.

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.

Regulation of sinus node pacemaking and atrioventricular node conduction by HCN channels in health and disease

The funny current, I_f, was first recorded in the heart 40 or more years ago by Dario DiFrancesco and others. Since then, we have learnt that I_f plays an important role in pacemaking in the sinus node, the innate pacemaker of the heart, and more recently evidence has accumulated to show that I_f may play an important role in action potential conduction through the atrioventricular (AV) node. Evidence has also accumulated to show that regulation of the transcription and translation of the underlying Hcn genes plays an important role in the regulation of sinus node pacemaking and AV node conduction under normal physiological conditions - in athletes, during the circadian rhythm, in pregnancy, and during postnatal development - as well as pathological states - ageing, heart failure, pulmonary hypertension, diabetes and atrial fibrillation. There may be yet more pathological conditions involving changes in the expression of the Hcn genes. Here, we review the role of I_f and the underlying HCN channels in physiological and pathological changes of the sinus and AV nodes and we begin to explore the signalling pathways (microRNAs, transcription factors, GIRK4, the autonomic nervous system and inflammation) involved in this regulation. This review is dedicated to Dario DiFrancesco on his retirement.

Beyond Heart Failure and Ischemic Heart Disease: A Scoping Review of Novel Uses of Ivabradine in Adults

Ivabradine lowers heart rate by inhibiting the hyperpolarization-activated current in pacemaker cells, and its use for the treatment of heart failure (HF) and ischemic heart disease (IHD) is well described. Ivabradine may be an attractive treatment option for other conditions for which a reduction in heart rate is desirable but less is known about its role in these settings. The primary objective was to perform a scoping review summarizing the literature evaluating novel uses for ivabradine other than HF and IHD in adults. PubMed and EMBASE were searched for articles for all dates through September 2019. Search strategies combined terms generic, commercial/trade, and international names for ivabradine. Manual search of references was also performed to identify additional articles. Studies were included if they were published in English, evaluated the efficacy of ivabradine for indications other than HF or IHD in patients aged 18 years or older, and the primary outcome included clinically relevant end points. Articles were screened first by title and abstract followed by full-text screening of the remaining articles. After removal of duplicates, 1807 records were screened for inclusion and 84 studies were included in this scoping review. Novel uses of ivabradine were reported for various tachyarrhythmias, valvular heart disease, premedication for coronary computed tomography angiography, perioperative risk reduction, sepsis with and without multi-organ dysfunction syndrome, cor pulmonale, reactive airway disease, and erectile dysfunction. This scoping review identified several potential novel uses for ivabradine in adults. This review may help to identify existing gaps where further research is needed to elucidate the role of ivabradine for indications beyond HF and IHD.

Pharmacological management of atrial fibrillation in patients with heart failure with reduced ejection fraction: review of current knowledge and future directions

Introduction: Both heart failure with reduced ejection fraction (HFrEF) and atrial fibrillation (AF) independently cause significant morbidity and mortality. The two conditions commonly coexist and AF in the setting of HFrEF is associated with worse mortality, hospitalizations, and quality of life compared to HFrEF without AF. Despite the large burden of these conditions, there is no clear optimal management strategy for when they occur together.Areas covered: This review focuses on the pharmacological management of AF in HFrEF. Studies were identified through PubMed search of relevant keywords. The authors review key clinical trials that have influenced management strategies and guidelines. The authors focus on the classes of drugs used to treat AF for both rate and rhythm control strategies including beta-blockers, digoxin, amiodarone, and dofetilide. Additionally, the authors discuss select non-antiarrhythmic medications that affect AF in HFrEF. The authors highlight the strengths and weakness of the data supporting the use of these medications and suggest future directions.Expert opinion: The pharmacological treatment of AF in HFrEF will need further refinement alongside the emerging role of catheter ablation. Novel HF medications and antiarrhythmics offer new tools to prevent the development of AF, as well as for rate and rhythm control strategies.

Ivabradine and AF: Coincidence, Correlation or a New Treatment?

Ivabradine is a heart rate-lowering agent that inhibits pacemaker funny current (If). It has been approved by the European Medicines Agency and the US Food and Drug Administration for patients with stable angina and heart failure (HF). AF is a common issue especially in ischaemic heart disease and HF patients. In contrast to experimental findings and a limited number of clinical trials that demonstrate the emerging role of ivabradine for heart rate control in AF or maintenance of sinus rhythm, there is accumulating contradictory data indicating that there is, in fact, an increased incidence of new-onset AF among people who are taking ivabradine in clinical practice. This article reviews the most recent evidence highlighting the diversity of data in relation to the use of ivabradine and the onset of AF and whether it has a legitimate role in AF treatment and the maintenance of sinus rhythm.

Possibilities of Combination of Beta-blockers and Ivabradine in Patients with Stable Angina Pectoris

Aim. To evaluate the therapeutic efficacy of a combination of ivabradine and beta-blockers (BAB) in patients with stable angina, initially taking only BAB and not reaching the target heart rate (HR) due to the risk of hypotension.

Material and methods. A prospective observational post-registration study was performed at the Research Institute for Complex Issues of Cardiovascular Diseases. The study included 50 patients with stable angina pectoris (diagnosed by coronary angiography in combination with clinical manifestations of angina of functional class II-III according to the Canadian classification) and an initial sinus rhythm with a heart rate of more than 70 beats per minute. These patients have already taken BAB. Heart rate, the number of angina attacks, nitrate intake and quality of life indicators according to the questionnaire were evaluated as criteria for therapeutic efficacy.

Results. Taking the study drug in combination with BAB led to a significant decrease the average heart rate at rest by 20%, as well as after a six-minute walk test (TLC) in most patients (p<0.050), and a decrease in the total number of angina attacks per week from 5 to less than 1 (p<0.050) and the frequency of nitrate intake for the relief of angina attacks from 58% to 20% (p=0.001). Therapy with ivabradine (Bravadin) was well tolerated by patients: there were no adverse events in the observed sample of patients, patients had a high adherence to treatment (100% of the contents of handed out blisters were used). During the 3 months of follow-up, according to the EQ-5D-5L quality of life questionnaire, patients improved their perception of their own health level (p<0.050), the number of patients experiencing mild (p=0.034) and strong (p=0.041) mobility limitations decreased; strong (p=0.024) restriction in self-care, mild (p=0.041) and strong (p=0.024) restriction of daily activities, mild manifestation of pain (p=0.009) and mild anxiety (p=0.027) also were reduced compared with the initial questionnaires.

Conclusion. Ivabradine (Bravadin) in addition to BAB is an effective and safe antianginal therapy for the prevention of angina attacks by reducing the initially high heart rate in patients with angina pectoris of functional class II-III.

Ivabradine for chronic heart rate control in persistent atrial fibrillation. Design of the BRAKE-AF project

INTRODUCTION AND OBJECTIVES

Ivabradine is an inhibitor of the If channel, the main determinant of the pacemaker function of the sinus node. The drug has been approved for the treatment of angina and heart failure. There is some evidence of its role as an inhibitor of atrial-ventricular node (AVN) conduction. The aim of the BRAKE-AF project is to assess ivabradine use for rate control in atrial fibrillation (AF).

METHODS

A multicenter, randomized, parallel, open-label, noninferiority phase III clinical trial will be conducted to compare ivabradine vs digoxin in 232 patients with uncontrolled permanent AF despite beta-blockers or calcium channel blockers. The primary efficacy endpoint is the reduction in daytime heart rate measured by 24-hour Holter monitoring at 3 months. This clinical trial will be supported by an electrophysiological study of the effect of ivabradine on the action potential of the human AVN. To do this, an experimental model will be used with Chinese hamster ovarium cells transfected with the DNA encoding the expression of the t channels involved in this action potential and recording of the ionic currents with patch clamp techniques.

RESULTS

New data will be obtained on the effect of ivabradine on the human AVN and its safety and efficacy in patients with permanent AF.

CONCLUSIONS

The results of the BRAKE-AF project might allow inclusion of ivabradine within the limited arsenal of drugs currently available for rate control in AF.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov. Identifier: NCT03718273.

HCN4 Gene Polymorphisms Are Associated With Occurrence of Tachycardia-Induced Cardiomyopathy in Patients With Atrial Fibrillation

BACKGROUND

Tachycardia-induced cardiomyopathy (TIC) is a reversible cardiomyopathy induced by tachyarrhythmia, and the genetic background of the TIC is not well understood. The hyperpolarization-activated cyclic nucleotide-gated channel gene HCN4 is highly expressed in the conduction system where it is involved in heart rate control. We speculated that the HCN4 gene is associated with TIC.

METHODS

We enrolled 930 Japanese patients with atrial fibrillation (AF) for screening, 350 Japanese patients with AF for replication, and 1635 non-AF controls. In the screening AF set, we compared HCN4 single-nucleotide polymorphism genotypes between AF subjects with TIC (TIC, n=73) and without TIC (non-TIC, n=857). Of 17 HCN4 gene-tag single-nucleotide polymorphisms, rs7172796, rs2680344, rs7164883, rs11631816, and rs12905211 were significantly associated with TIC. Among them, only rs7164883 was independently associated with TIC after conditional analysis (TIC versus non-TIC: minor allele frequency, 26.0% versus 9.7%; P=1.62×10^-9; odds ratio=3.2).

RESULTS

We confirmed this association of HCN4 single-nucleotide polymorphism rs7164883 with TIC in the replication set (TIC=41 and non-TIC=309; minor allele frequency, 28% versus 9.9%; P=1.94×10^-6; odds ratio=3.6). The minor allele frequency of rs7164883 was similar in patients with AF and non-AF controls (11% versus 10.9%; P=0.908).

CONCLUSIONS

The HCN4 gene single-nucleotide polymorphism rs7164883 may be a new genetic marker for TIC in patients with AF.

Ivabradine Reduces Digitalis-induced Ventricular Arrhythmias

The I_(f) channel inhibitor ivabradine is recommended for treatment of heart failure but also affects potassium currents and thereby prolongs ventricular repolarization. The aim of this study was to examine the electrophysiological effects of ivabradine on digitalis-induced ventricular arrhythmias. Thirteen rabbit hearts were isolated and Langendorff-perfused. After obtaining baseline data, the digitalis glycoside ouabain was infused (0.2 μM). Monophasic action potentials and ECG showed a significant abbreviation of QT interval (-34 ms, p < 0.05) and action potential duration (APD₉₀ ; -27 ms, p < 0.05). The shortening of ventricular repolarization was accompanied by a reduction in effective refractory period (ERP; -27 ms, p < 0.05). Thereafter, hearts were additionally treated with ivabradine (5 μM). Of note, this did not exert significant effects on QT interval (-4 ms, p = ns) or APD₉₀ (-15 ms, p = ns) but resulted in an increase in ERP (+17 ms, p < 0.05). This led to a significant increase in post-repolarization refractoriness (PRR, +32 ms, p < 0.01) as compared with sole ouabain treatment. Under baseline conditions, ventricular fibrillation (VF) was inducible by a standardized pacing protocol including programmed stimulation and burst stimulation in four of 13 hearts (31%; 15 episodes). After application of 0.2 μM ouabain, eight of 13 hearts were inducible (62%, 49 episodes). Additional infusion of 5 μM ivabradine led to a significant suppression of VF. Only four episodes could be induced in two of 13 hearts (15%). In this study, ivabradine reduced digitalis-induced ventricular arrhythmias. Ivabradine did not affect ventricular repolarization in the presence of digitalis treatment but demonstrated potent anti-arrhythmic properties based on an increase in both ERP and PRR. The study further characterizes the beneficial electrophysiological profile of ivabradine.