Characterization of the Heart Rate-Lowering Action of Ivabradine, a Selective I f Current Inhibitor

Effects of Ivabradine on Right Ventricular Systolic Function in Patients With Chronic Obstructive Pulmonary Disease and Cor Pulmonale

Cor pulmonale is a clinical syndrome associated with pulmonary hypertension, frequently complicated by congestive heart failure, commonly caused by chronic obstructive pulmonary disease (COPD). Most patients with cor pulmonale have tachycardia. However, heart rate (HR) reduction represents a primary treatment goal to improve the survival and quality of life in these patients. Ivabradine can selectively slow HR at rest and during exercise. In this prospective study, we tested the hemodynamic effects, invasively determined using right-sided cardiac catheterization, of reducing HR with ivabradine. We selected 18 patients (13 men [72.2%], mean age 67 ± 10 years) with COPD and cor pulmonale, presenting with sinus tachycardia. All patients performed clinical evaluation, electrocardiogram, spirometry, echocardiogram, 6-minute walking distance, and right-sided cardiac catheterization within 1 month of enrollment. All tests were repeated after 6 months of ivabradine treatment (median assumed dose 11.9 mg/die). We noticed a significant decrease of HR (from 98 ± 7 to 77 ± 8 beats/min, p = 0.0001), with a concomitant reduction of the congestion index (from 25.9 ± 5.1 to 19.4 ± 5.7 mm Hg, p = 0.001), and the consequent improvement of the right ventricular systolic performance (right ventricular stroke volume augmented from 56.7 ± 7.9 to 75.2 ± 8.6 ml/beat, p = 0.0001). This allows an improvement in clinical status and exercise tolerance (Borg scale score decreased from 5.2 ± 1.4 to 4.1 ± 1.3, p = 0.01 and the 6-minute walking distance increased to 252 ± 65 to 377 ± 59 m, p = 0.001). In conclusion, HR reduction significantly improves hemodynamic and clinical status of patients with tachycardia affected by COPD and cor pulmonale.

An anchor-tether 'hindered' HCN1 inhibitor is antihyperalgesic in a rat spared nerve injury neuropathic pain model

BACKGROUND

Neuropathic pain impairs quality of life, is widely prevalent, and incurs significant costs. Current pharmacological therapies have poor/no efficacy and significant adverse effects; safe and effective alternatives are needed. Hyperpolarisation-activated cyclic nucleotide-regulated (HCN) channels are causally implicated in some forms of peripherally mediated neuropathic pain. Whilst 2,6-substituted phenols, such as 2,6-di-tert-butylphenol (26DTB-P), selectively inhibit HCN1 gating and are antihyperalgesic, the development of therapeutically tolerable, HCN-selective antihyperalgesics based on their inverse agonist activity requires that such drugs spare the cardiac isoforms and do not cross the blood-brain barrier.

METHODS

In silico molecular dynamics simulation, in vitro electrophysiology, and in vivo rat spared nerve injury methods were used to test whether 'hindered' variants of 26DTB-P (wherein a hydrophilic 'anchor' is attached in the para-position of 26DTB-P via an acyl chain 'tether') had the desired properties.

RESULTS

Molecular dynamics simulation showed that membrane penetration of hindered 26DTB-Ps is controlled by a tethered diol anchor without elimination of head group rotational freedom. In vitro and in vivo analysis showed that BP4L-18:1:1, a variant wherein a diol anchor is attached to 26DTB-P via an 18-carbon tether, is an HCN1 inverse agonist and an orally available antihyperalgesic. With a CNS multiparameter optimisation score of 2.25, a >100-fold lower drug load in the brain vs blood, and an absence of adverse cardiovascular or CNS effects, BP4L-18:1:1 was shown to be poorly CNS penetrant and cardiac sparing.

CONCLUSIONS

These findings provide a proof-of-concept demonstration that anchor-tethered drugs are a new chemotype for treatment of disorders involving membrane targets.

Efficacy and Safety of Ivabradine in Combination with Beta-Blockers in Patients with Stable Angina Pectoris: A Systematic Review and Meta-analysis

INTRODUCTION

Beta-blockers are recommended by the European Society of Cardiology as first-line antianginal therapy for reducing heart rate (HR) and symptoms in patients with chronic coronary syndrome, despite a lack of data showing superiority to other antianginal agents. Most patients with angina pectoris require combination therapy to manage symptoms, with a second-line agent chosen to manage the predominant cardiovascular problem. Ivabradine, a selective sinus node If channel inhibitor shown to reduce HR and protect against anginal symptoms, has previously demonstrated noninferior anti-ischaemic and antianginal efficacy to beta-blockers.

METHODS

This systematic review and meta-analysis assessed the efficacy and safety of ivabradine in patients with stable angina pectoris who remained symptomatic despite receiving beta-blockers. Keyword searches of PubMed, The Cochrane Central Library Register, ClinicalTrials.gov, The World Health Organization International Clinical Trials Registry Platform (ICTRP) and Google Scholar identified studies comparing ivabradine plus beta-blockers with placebo or other first- or second-line antianginal agents in patients with stable angina pectoris. No date limits or language restrictions were applied. Outcomes were evaluated after 1 and 4 months of treatment, including changes in HR, angina attacks, use of short-acting nitrates, quality of life and safety. Risk of bias was evaluated on the basis of recommendations of the Cochrane Handbook for Systematic Reviews of Interventions.

RESULTS

Seven relevant studies were identified (N = 6821). Ivabradine plus a beta-blocker consistently reduced HR, anginal symptoms and short-acting nitrate consumption within 1 month of initiating therapy, with continued reductions for up to 4 months. Furthermore, ivabradine plus beta-blocker therapy was well tolerated, with bradycardia rarely reported (0.1% of patients overall). This study is limited by the inclusion of only two randomised studies, which may lead to result interpretation bias.

CONCLUSIONS

Ivabradine may be valuable for tailoring early antianginal treatment when used in combination with beta-blockers for chronic stable angina inadequately controlled by beta-blockers.

Cardioprotective Function of Green Rooibos (Aspalathus linearis) Extract Supplementation in Ex Vivo Ischemic Prediabetic Rat Hearts

Diabetic patients develop ischemic heart disease and strokes more readily. Following an ischemic event, restoration of blood flow increases oxidative stress resulting in myocardial damage, termed ischemia/reperfusion injury. Aspalathus linearis (rooibos), rich in the antioxidant phenolic compound aspalathin, has been implicated as cardioprotective against ischemia/reperfusion injury with undefined mechanism in control rats. Primarily, the therapeutic potential of Afriplex green rooibos extract to prevent ischemia/reperfusion injury in cardiovascular disease-compromised rats was investigated. Additionally, Afriplex Green rooibos extract's cardioprotective signaling on metabolic markers and stress markers was determined using western blotting. Three hundred male Wistar rats received either 16-wk standard diet or high-caloric diet. During the final 6 wk, half received 60 mg/kg/day Afriplex green rooibos extract, containing 12.48% aspalathin. High-caloric diet increased body weight, body fat, fasting serum triglycerides, and homeostatic model assessment of insulin resistance - indicative of prediabetes. High-caloric diet rats had increased heart mass, infarct size, and decreased heart function. Afriplex green rooibos extract treatment for 6 wk lowered pre-ischemic heart rate, reduced infarct size, and improved heart function pre- and post-ischemia, without significantly affecting biometric parameters. Stabilized high-caloric diet hearts had decreased insulin independence via adenosine monophosphate activated kinase and increased inflammation (p38 mitogen-activated protein kinase), whereas Afriplex green rooibos extract treatment decreased insulin dependence (protein kinase B) and conferred anti-inflammatory effect. After 20 min ischemia, high-caloric diet hearts had upregulated ataxia-telangiectasia mutated kinase decreased insulin independence, and downregulated insulin dependence and glycogen synthase kinase 3 β inhibition. In contrast, Afriplex green rooibos extract supplementation downregulated insulin independence and inhibited extracellular signal-regulated kinase 1 and 2. During reperfusion, all protective signaling was decreased in high-caloric diet, while Afriplex green rooibos extract supplementation reduced oxidative stress (c-Jun N-terminal kinases 1 and 2) and inflammation. Taken together, Afriplex green rooibos extract supplementation for 6 wk preconditioned cardiovascular disease-compromised rat hearts against ischemia/reperfusion injury by lowering inflammation, oxidative stress, and heart rate.

The Role of Ivabradine in Managing Symptomatic Patients with Chronic Coronary Syndromes: A Clinically Oriented Approach

Angina is a significant contributor to disability and impairment in quality of life in patients with chronic coronary syndromes (CCS). An elevated heart rate (HR) may trigger myocardial ischemia by increasing oxygen consumption and decreasing the diastolic time, compromising the coronary flow. HR-lowering strategies offer symptom control and prevent cardiovascular events in subgroups of patients with CCS. However, the best therapeutic approach to achieve the desired HR in patients with CCS can be challenging based on efficacy and tolerability. Guidelines usually propose β-blockers and/or non-dihydropyridine calcium channel blockers (CCB) for angina patients with elevated HR. Nonetheless, there is no clear evidence of greater antianginal efficacy of this strategy versus an alternative HR-lowering agent. Ivabradine reduces the HR by blocking the I_f current in the sinoatrial node without affecting myocardial contractility or vascular tone. The magnitude of the HR reduction by ivabradine is proportional to the initial HR, which decreases the risk of significant bradycardia. Ivabradine increases the diastolic time and the coronary flow reserve to a greater extent than β-blockers and favors collateralization, improving the regional blood flow. We present two clinical cases of patients with symptomatic CCS in whom HR control with ivabradine was fundamental for symptom control and improvement in left ventricular (LV) function. An earlier combination of ivabradine plus β-blockers would have provided more rapid symptom control and improved LV function in the first case. In the second case, the primary mechanism responsible for angina was most likely a coronary vasomotor abnormality, in which the use of β-blockers aggravated the discomfort. The combination of a dihydropyridine CCB plus ivabradine was highly influential in symptom control. Due to its effects beyond HR reduction and good tolerability, ivabradine should be considered an essential ally in managing patients with angina and high HR with or without LV dysfunction.

Translating GWAS-identified loci for cardiac rhythm and rate using an in vivo image- and CRISPR/Cas9-based approach

A meta-analysis of genome-wide association studies (GWAS) identified eight loci that are associated with heart rate variability (HRV), but candidate genes in these loci remain uncharacterized. We developed an image- and CRISPR/Cas9-based pipeline to systematically characterize candidate genes for HRV in live zebrafish embryos. Nine zebrafish orthologues of six human candidate genes were targeted simultaneously in eggs from fish that transgenically express GFP on smooth muscle cells (Tg[acta2:GFP]), to visualize the beating heart. An automated analysis of repeated 30 s recordings of beating atria in 381 live, intact zebrafish embryos at 2 and 5 days post-fertilization highlighted genes that influence HRV (hcn4 and si:dkey-65j6.2 [KIAA1755]); heart rate (rgs6 and hcn4); and the risk of sinoatrial pauses and arrests (hcn4). Exposure to 10 or 25 µM ivabradine—an open channel blocker of HCNs—for 24 h resulted in a dose-dependent higher HRV and lower heart rate at 5 days post-fertilization. Hence, our screen confirmed the role of established genes for heart rate and rhythm (RGS6 and HCN4); showed that ivabradine reduces heart rate and increases HRV in zebrafish embryos, as it does in humans; and highlighted a novel gene that plays a role in HRV (KIAA1755).

Clinical and Electrophysiological Correlates of Incessant Ivabradine-Sensitive Atrial Tachycardia

Background:

Incessant focal atrial tachycardia (FAT), if untreated, can lead to ventricular dysfunction and heart failure (tachycardia-induced cardiomyopathy). Drug therapy of FAT is often difficult and ineffective. The efficacy of ivabradine has not been systematically evaluated in the treatment of FAT.

Methods:

The study group consisted of patients with incessant FAT (lasting >24 hours) and structurally normal hearts. Patients with ventricular dysfunction as a consequence of FAT were not excluded. All antiarrhythmic drugs were discontinued at least 5 half-lives before the initiation of ivabradine. Oral ivabradine (adults, 10 mg twice 12 hours apart; pediatric patients: 0.28 mg/kg in 2 divided doses) was initiated in the intensive care unit under continuous electrocardiographic monitoring. A positive response was defined as the termination of tachycardia with the restoration of sinus rhythm or suppression of the tachycardia to <100 beats per minute without termination within 12 hours of initiating ivabradine.

Results:

Twenty-eight patients (mean age, 34.6±21.5 years; women, 60.7%) were included in the study. The most common symptom was palpitation (85.7%) followed by shortness of breath (25%). The mean atrial rate during tachycardia was 170±21 beats per minute, and the mean left ventricular ejection fraction was 54.7±14.3%. Overall, 18 (64.3%) patients responded within 6 hours of the first dose of ivabradine. Thirteen of 18 ivabradine responders subsequently underwent successful catheter ablation. FAT originating in the atrial appendages was a predictor of ivabradine response compared with those arising from other atrial sites ( P =0.046).

Conclusions:

Ivabradine-sensitive atrial tachycardia constitutes 64% of incessant FAT in patients without structural heart disease. Incessant FAT originating in the atrial appendages is more likely to respond to ivabradine than that arising from other atrial sites. Our findings implicate the funny current in the pathogenesis of FAT.

Should heart rate variability be "corrected" for heart rate? Biological, quantitative, and interpretive considerations

Metrics of heart period variability are widely used in the behavioral and biomedical sciences, although somewhat confusingly labeled as heart rate variability (HRV). Despite their wide use, HRV metrics are usually analyzed and interpreted without reference to prevailing levels of cardiac chronotropic state (i.e., mean heart rate or mean heart period). This isolated treatment of HRV metrics is nontrivial. All HRV metrics routinely used in the literature exhibit a known and positive relationship with the mean duration of the interval between two beats (heart period): as the heart period increases, so does its variability. This raises the question of whether HRV metrics should be "corrected" for the mean heart period (or its inverse, the heart rate). Here, we outline biological, quantitative, and interpretive issues engendered by this question. We provide arguments that HRV is neither uniformly nor simply a surrogate for heart period. We also identify knowledge gaps that remain to be satisfactorily addressed with respect to assumptions underlying existing HRV correction approaches. In doing so, we aim to stimulate further progress toward the rigorous use and disciplined interpretation of HRV. We close with provisional guidance on HRV reporting that acknowledges the complex interplay between the mean and variability of the heart period.

Treatment of Angina: Where Are We?

Ischaemic heart disease is a major cause of death and disability worldwide, while angina represents its most common symptom. It is estimated that approximately 9 million patients in the USA suffer from angina and its treatment is challenging, thus the strategy to improve the management of chronic stable angina is a priority. Angina might be the result of different pathologies, ranging from the “classical” obstruction of a large coronary artery to alteration of the microcirculation or coronary artery spasm. Current clinical guidelines recommend antianginal therapy to control symptoms, before considering coronary artery revascularization. In the current guidelines, drugs are classified as being first-choice (beta-blockers, calcium channel blockers, and short-acting nitrates) or second-choice (ivabradine, nicorandil, ranolazine, trimetazidine) treatment, with the recommendation to reserve second-line modifications for patients who have contraindications to first-choice agents, do not tolerate them, or remain symptomatic. However, such a categorical approach is currently questioned. In addition, current guidelines provide few suggestions to guide the choice of drugs more suitable according to the underlying pathology or the patient comorbidities. Several other questions have recently emerged, such as: is there evidence-based data between first- and second-line treatments in terms of prognosis or symptom relief? Actually, it seems that newer antianginal drugs, which are classified as second choice, have more evidence-based clinical data that are more contemporary to support their use than what is available for the first-choice drugs. It follows that actual guidelines are based more on tradition than on evidence and there is a need for new algorithms that are more individualized to patients, their comorbidities, and pathophysiological mechanism of chronic stable angina.

Mechano-chronotropic Unloading During the Acute Phase of Myocardial Infarction Markedly Reduces Infarct Size via the Suppression of Myocardial Oxygen Consumption

The oxygen supply-demand imbalance is the fundamental pathophysiology of myocardial infarction (MI). Reducing myocardial oxygen consumption (MVO₂) in acute MI (AMI) reduces infarct size. Since left ventricular (LV) mechanical work and heart rate are major determinants of MVO₂, we hypothesized that the combination of LV mechanical unloading and chronotropic unloading during AMI can reduce infarct size via synergistic suppression of MVO₂. In a dog model of ischemia-reperfusion, as we predicted, the combination of mechanical unloading by Impella and bradycardic agent, ivabradine (IVA), synergistically reduced MVO₂. This was translated into the striking reduction of infarct size with Impella + IVA administered 60 min after the onset of ischemia compared to no treatment (control) and Impella groups (control 56.3 ± 6.5, Impella 39.9 ± 7.4 and Impella + IVA 23.7 ± 10.6%, p < 0.001). In conclusion, Impella + IVA during AMI reduced infarct size via marked suppression of MVO₂. The mechano-chronotropic unloading may serve as a powerful therapeutic option for AMI.

Role of ivabradine in management of stable angina in patients with different clinical profiles

In chronic stable angina, elevated heart rate contributes to the development of symptoms and signs of myocardial ischaemia by increasing myocardial oxygen demand and reducing diastolic perfusion time. Accordingly, heart rate reduction is a well-known strategy for improving both symptoms of myocardial ischaemia and quality of life (QOL). The heart rate-reducing agent ivabradine, a direct and selective inhibitor of the I_f current, decreases myocardial oxygen consumption while increasing diastolic time, without affecting myocardial contractility or coronary vasomotor tone. Ivabradine is indicated for treatment of stable angina and chronic heart failure (HF). This review examines available evidence regarding the efficacy and safety of ivabradine in stable angina, when used as monotherapy or in combination with beta-blockers, in particular angina subgroups and in patients with stable angina with left ventricular systolic dysfunction (LVSD) or HF. Trials involving more than 45 000 patients receiving treatment with ivabradine have shown that this agent has antianginal and anti-ischaemic effects, regardless of age, sex, severity of angina, revascularisation status or comorbidities. This heart rate-lowering agent might also improve prognosis, reduce hospitalisation rates and improve QOL in angina patients with chronic HF and LVSD.

Evolving therapies for the management of chronic and acute decompensated heart failure

PURPOSE

The pharmacology, clinical efficacy, and safety profiles of evolving therapies for the management of chronic heart failure (HF) and acute decompensated heart failure (ADHF) are described.

SUMMARY

HF confers a significant financial burden despite the widespread use of traditional guideline-directed medical therapies such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-blockers, and aldosterone receptor antagonists, and the rates of HF-related mortality and hospitalization have remained unacceptably high. In response to a demand for novel pharmacologic agents, several therapeutic compounds have recently gained approval or are currently under review by the Food and Drug Administration. Sacubitril-valsartan has demonstrated benefit in reducing cardiovascular mortality and HF-related hospitalizations in clinical trials, while ivabradine and ferric carboxymaltose have proven efficacious in reducing HF-related hospitalizations. Lastly, the role of serelaxin in ADHF is currently under investigation in an ongoing Phase III study. While large, outcome-driven clinical trials are fundamental in informing the clinical application of these therapeutic agents, careful patient selection is imperative to ensuring similar outcomes postmarketing. In addition, optimization of current guideline-directed medical therapy remains essential as new therapies emerge and are incorporated into guideline recommendations. Additional therapeutic agents currently undergoing investigation include bucindolol hydrochloride, cimaglermin alfa, nitroxyl, omecamtiv mecarbil, TRV027, and ularitide. Clinical practitioners should remain abreast of emerging literature so that new therapeutic entities are optimally applied and positive patient outcomes are achieved.

CONCLUSION

Recently introduced agents for the treatment of patients with HF include sacubitril-valsartan, ivabradine, and ferric carboxymaltose. Additional agents worthy of attention include serelaxin and other therapies currently under investigation.

β-Blockers and ivabradine differentially affect cardiopulmonary function and left ventricular filling index

OBJECTIVE

Patients with left ventricular (LV) diastolic dysfunction are characterized by exertional dyspnoea. Heart rate (HR) reduction by β-blockers can improve exercise tolerance by prolonging LV filling, but their negative inotropic and lusitropic properties can be detrimental in this disease. We tested the effects of administering ivabradine, a HR-lowering drug without impact on cardiac kinetics that may favorably affect diastolic function.

METHODS

Twenty-four patients with coronary artery disease (CAD) and normal LV ejection fraction on chronic β-blocker therapy were included. NT-proBNP serum levels were determined prior to and after cardiopulmonary exercise. β-Blockers were then replaced by ivabradine and patients were re-tested after 6 weeks. Patients were initially classified as having a low (E/e' ≤ 8; n = 11) or high (E/e' > 8; n = 13) LV filling index.

RESULTS

E/e' significantly decreased during ivabradine therapy in patients with high E/e' (10.7 ± 2.9 vs. 8.9 ± 1.7; p < 0.01), whereas no difference occurred in patients with low E/e' (6.4 ± 0.7 vs. 6.5 ± 1.1; p = ns). With ivabradine, patients with high E/e' had an increased oxygen uptake at the anaerobic threshold (from 10.8 ± 1.4 to 11.8 ± 1.9 ml/min/kg; p < 0.05) and a steeper slope of the initial oxygen pulse curve (from 293 ± 109 to 359 ± 117 µl/beat/kg/W; p < 0.05). Moreover, patients with high E/e' had lower NT-proBNP serum levels at rest (169 ± 207 vs. 126 ± 146 pg/ml; p < 0.05) and after exercise (190 ± 256 vs. 136 ± 162 pg/ml; p < 0.05) during ivabradine therapy.

CONCLUSIONS

In patients with CAD and elevated E/e', switching therapy from β-blockers to ivabradine may cause a reduction in LV filling pressures and an improved stroke volume response to exercise.

Ivabradine in combination with Beta-blockers in patients with chronic stable angina after percutaneous coronary intervention

Introduction

The anti-anginal efficacy of ivabradine is well established. We describe a post hoc analysis in the ADDITIONS database to investigate effectiveness and tolerability of ivabradine in combination with beta-blocker in patients with angina who have had a percutaneous coronary intervention (PCI).

Methods

ADDITIONS was a non-interventional, multicenter prospective study including 2,330 patients with stable angina. In addition to beta-blocker, patients were treated with ivabradine in approved dosages for 4 months. We divided the population according to whether they had previously had a PCI or not, and explored the effect of ivabradine on heart rate, number of weekly angina attacks, frequency of nitrate consumption, as well as quality of life (QoL) and tolerability.

Results

Data were available for 2,319 patients, of whom 51.4% had previously had a PCI. There was no difference in the effect of ivabradine on mean heart rate between patients with a previous PCI [64.4 ± 7.6 beats per minute (bpm)] than those without (66.8 ± 8.5 bpm) at 4 months (both P < 0.0001). Similarly, the number of angina attacks decreased from 1.9 ± 2.4 to 0.5 ± 1.5 per week in patients with a previous PCI and 1.5 ± 2.0 to 0.3 ± 1.0 per week in patients without a previous PCI (both P < 0.0001). The frequency of nitrate consumption fell from 2.7 ± 3.7 to 1.0 ± 1.9 per week and 1.8 ± 2.8 to 0.6 ± 1.5 per week (both P < 0.0001) in patients with and without a previous PCI, respectively. There was no difference in the improvements in Canadian Cardiovascular Society class of angina, QoL, and physicians’ assessment of effectiveness and tolerability between patients with a previous PCI and those without.

Conclusion

Ivabradine is an effective and well-tolerated anti-anginal treatment in patients with stable angina after PCI. Ivabradine reduced the frequency of weekly angina attacks and nitrate consumption, led to an improvement in Canadian Cardiovascular Society class and a substantial improvement in the QoL of stable angina patients.

Electronic supplementary material

The online version of this article (doi:10.1007/s12325-015-0182-8) contains supplementary material, which is available to authorized users.

From beat rate variability in induced pluripotent stem cell-derived pacemaker cells to heart rate variability in human subjects

BACKGROUND

We previously reported that induced pluripotent stem cell-derived cardiomyocytes manifest beat rate variability (BRV) resembling heart rate variability (HRV) in the human sinoatrial node. We now hypothesized the BRV-HRV continuum originates in pacemaker cells.

OBJECTIVE

To investigate whether cellular BRV is a source of HRV dynamics, we hypothesized 3 levels of interaction among different cardiomyocyte entities: (1) single pacemaker cells, (2) networks of electrically coupled pacemaker cells, and (3) the in situ sinoatrial node.

METHODS

We measured BRV/HRV properties in single pacemaker cells, induced pluripotent stem cell-derived contracting embryoid bodies (EBs), and electrocardiograms from the same individual.

RESULTS

Pronounced BRV/HRV was present at all 3 levels. The coefficient of variance of interbeat intervals and Poincaré plot indices SD1 and SD2 for single cells were 20 times greater than those for EBs (P < .05) and the in situ heart (the latter two were similar; P > .05). We also compared BRV magnitude among single cells, small EBs (~5-10 cells), and larger EBs (>10 cells): BRV indices progressively increased with the decrease in the cell number (P < .05). Disrupting intracellular Ca(2+) handling markedly augmented BRV magnitude, revealing a unique bimodal firing pattern, suggesting that intracellular mechanisms contribute to BRV/HRV and the fractal behavior of heart rhythm.

CONCLUSION

The decreased BRV magnitude in transitioning from the single cell to the EB suggests that the HRV of in situ hearts originates from the summation and integration of multiple cell-based oscillators. Hence, complex interactions among multiple pacemaker cells and intracellular Ca(2+) handling determine HRV in humans and cardiomyocyte networks.

Ivabradine: a new rate-limiting therapy for coronary artery disease and heart failure

Ivabradine is a new bradycardic agent acting on the I f channels of sinoatrial nodal cells to decrease the rate of diastolic depolarization and thus heart rate. The benefit of ivabradine over other negatively chronotropic agents is its absence of negative inotropy. Effective management of coronary artery disease, in terms of reducing morbidity and mortality, is reliant on controlling heart rate. Ivabradine has been shown to safely and effectively reduce heart rate without compromising cardiac function in patients with coronary artery disease and more recently in patients with heart failure and raised heart rate. Furthermore, ivabradine has been shown to have a favourable side-effect profile compared with alternative bradycardic agents. This article reviews the evidence for ivabradine in coronary artery disease and heart failure and compares its safety with alternative bradycardic agents for these conditions.

Safety of intravenous ivabradine in acute ST-segment elevation myocardial infarction patients treated with primary percutaneous coronary intervention: a randomized, placebo-controlled, double-blind, pilot study

AIMS

Rapid heart rate lowering may be attractive in acute ST-segment elevation myocardial infarction (STEMI). Accordingly we studied the effect of intravenous ivabradine on heart rate in this setting.

METHODS AND RESULTS

This was a multicenter randomized double-blind placebo-controlled trial: patients aged 40-80 years were randomized after successful primary percutaneous coronary intervention (PCI) performed within 6 h of STEMI symptom onset. Patients were in sinus rhythm and with heart rate >80 bpm and systolic blood pressure >90 mm Hg. They were randomly assigned (2:1 ratio) to intravenous ivabradine (n=82) (5 mg bolus over 30 s, followed by 5 mg infusion over 8 h) or matching placebo (n=42). The primary outcome measure was heart rate and blood pressure. In both groups, heart rate was reduced over 8 h, with a faster and more marked decrease on ivabradine than placebo (22.2 ± 1.3 vs 8.9 ± 1.8 bpm, p<0.0001). After treatment discontinuation, heart rate was similar in both groups. Throughout the study, there was no difference in blood pressure between groups. There was no difference in cardiac biomarkers (creatine kinase (CK-MB), troponin T and troponin I). On echocardiography performed at baseline and post treatment (median 1.16 days), final left ventricular volumes were lower in the ivabradine group both for left ventricular end-diastolic volume (LVEDV) (87.1 ± 28.2 vs 117.8 ± 21.4 ml, p=0.01) and left ventricular end-systolic volume (LVESV) (42.5 ± 19.0 versus 59.1 ± 11.3 ml, p=0.03) without differences in volume change or left ventricular ejection fraction.

CONCLUSION

This pilot study shows that intravenous ivabradine may be used safely to slow the heart rate in STEMI. Further studies are needed to characterize its effect on infarct size, left ventricular function and clinical outcomes in this population.

Heart rate reduction with ivabradine in patients with acute decompensated systolic heart failure

INTRODUCTION

In patients with acute decompensated systolic heart failure (ADSHF) high resting heart rate (HR) could be either a compensatory mechanism or contribute to worsening heart failure. The aim of this study was to evaluate, in patients with ADSHF and resting HR >70 bpm, the early (within 24 h) and late (at discharge) effects of oral administration of ivabradine on HR reduction.

METHODS

Ten consecutive patients with ADSHF, left ventricular ejection fraction <40 % and HR >70 bpm, without other acute conditions or inotropic therapy, began open-label treatment with oral ivabradine according to a pre-established Heart Failure Unit protocol. We obtained clinical and laboratory data at four periods: admission (T0), immediately before initiation of ivabradine (T2), 24 h after initiation of ivabradine (T3), and at discharge (T4).

RESULTS

Ivabradine was administered in 60 % of the patients before the second day. HR decreased 10.7 ± 7.2 bpm at T3 (p < 0.001) and 16.3 ± 8.2 bpm at T4 (p = 0.002). The systolic blood pressure decreased at T3 (p = 0.012), returning to baseline values at T4. There was no change in diastolic and mean blood pressure. New York Heart Association (NYHA) class improvement by two levels was associated with lower HR at T4 (p = 0.033). HR and N-terminal pro-brain natriuretic peptide (Nt-ProBNP) at baseline correlated significantly [Spearman correlation coefficient (rs) = 0.789, p = 0.013]. Total Nt-ProBNP reduction correlated with the HR before (r = 0.762, p = 0.028) and after (T3: r = 0.647, p = 0.083; T4: r = 0.738, p = 0.037) ivabradine addition.

CONCLUSION

In the present cohort of patients with ADSHF and HR >70 bpm, the selective reduction of HR with oral ivabradine was safe and efficient.

Selective and specific inhibition of If with ivabradine for the treatment of coronary artery disease or heart failure

Heart rate is an important contributor in the pathophysiology of both coronary artery disease (CAD) and heart failure (HF). Ivabradine is an anti-anginal and anti-ischaemic agent, which selectively and specifically inhibits the I_f current in the sino-atrial node and provides pure heart rate reduction without altering other cardiac parameters, including conduction, and without directly affecting other haemodynamic parameters. It is approved for the treatment of CAD and HF. This article summarises the pharmacological properties, pharmacokinetics, clinical efficacy and tolerability of ivabradine in the treatment of CAD and HF, and presents evidence demonstrating that the pharmacological and clinical properties and clinical efficacy of ivabradine make it an important therapeutic choice for patients with stable CAD or HF. The positive effect of ivabradine on angina pectoris symptoms and its ability to reduce myocardial ischemia make it an important agent in the management of patients with stable CAD or chronic HF. Further studies are underway to add to the already robust evidence of ivabradine for the prevention of cardiovascular events in patients with CAD but without clinical HF. The SIGNIFY (Study assessInG the morbidity–mortality beNefits of the I_f inhibitor ivabradine in patients with coronarY artery disease) trial includes patients with stable CAD and an LVEF above 40 %, with no clinical sign of HF, and is investigating the long-term effects (over a period of 48 months) of ivabradine in a large study population. So far, this study has included more than 19,000 patients from 51 countries.

Ivabradine therapy to unmask heart rate-independent effects of β-blockers on pulse wave reflections

BACKGROUND

Prior studies suggest that β-blockers lead to increased pulse wave reflections, thereby negating the blood pressure lowering effects on cardiovascular mortality. Parts of these effects may be induced by the heart rate reduction under β-blockade. The aim of this study was to unmask heart rate-independent effects of β-blockade on pulse wave reflections by switching therapy from β-blockers to ivabradine, an I f channel inhibitor without impact on systemic hemodynamics.

METHODS

14 male patients (age 61 ± 3 years, LVEF 62 ± 1 %) with arterial hypertension and coronary artery disease (CAD) under chronic β-blocker therapy at moderate dosage and additional renin-angiotensin system-blocking therapy were included. We determined radial augmentation index (rAI) by radial applanation tonometry in patients under β-blockade both at rest and during early recovery after exercise. β-Blockers were then replaced by ivabradine. Six weeks later, patients were re-tested at rest and after exercise under ivabradine therapy.

RESULTS

Mean heart rate (68 ± 3 vs. 63 ± 3 bpm; p = ns) and resting mean arterial pressure (98 ± 2 vs. 98 ± 2 mmHg; p = ns) were not different between β-blocker or ivabradine therapy, respectively. The rAI remained unchanged after switching therapy from β-blocker to ivabradine (86 ± 2 vs. 84 ± 4 %; p = ns). Post exercise, the rAI revealed an identical decrease in both groups (-7.2 ± 2.4 vs. -5.4 ± 2.5 %, p = ns). The increase in heart rate between resting conditions and early recovery post exercise was inversely correlated with the decrease of rAI under β-blockade (r = -0.70; p < 0.01) and showed a trend towards correlation under ivabradine (r = -0.52; p = 0.07).

CONCLUSION

In men at the age of 60 years and CAD, β-blockade does not exert heart rate-independent, pleiotropic effects on peripheral pulse wave reflections, both at rest or after exercise. Our results fit well within recent studies, demonstrating the fundamental influence of heart rate on rAI.

Impaired signaling intrinsic to sinoatrial node pacemaker cells affects heart rate variability during cardiac disease

The normal heart beat intervals are neither strictly stationary nor completely random, and continuously shift from one period to another. Decoding the ECG identifies this "hidden" information that imparts inherent complexity to the heart-beating interval time series. Loss of this complexity in cardiovascular disease is manifested as a reduction in heart rate variability (HRV) and this reduction correlates with an increase in both morbidity and mortality. Because HRV measurements are noninvasive and easy to perform, they have emerged as an important tool in cardiology. However, the identities of specific mechanisms that underline the changes in HRV that occur in cardiovascular diseases remain largely unknown. Changes in HRV have mainly been interpreted on a neural basis, ie due to changes in autonomic impulses to the heart: sympathetic activity decreases both the average heart beat interval and HRV, and parasympathetic activity increases both. It has now become clear, however, that the heart rate and HRV are also determined by intrinsic properties of the pacemaker cells that comprise the sinoatrial node, and the responses of these properties to autonomic receptor stimulation. Here we review how changes in the properties of coupled-clock mechanisms intrinsic to pacemaker cells that comprise the sinoatrial node and their impaired response to autonomic receptor stimulation are implicated in the changes of HRV observed in heart diseases.

An evaluation of the pharmacokinetics and pharmacodynamics of ivabradine for the treatment of heart failure

INTRODUCTION

Ivabradine is a new heart-rate-lowering drug; the aim of this review was to analyze its role in heart failure (HF).

AREAS COVERED

This systematic review on the role of ivabradine in HF is based on material searched and obtained through Pubmed and Medline up to September 2013.

EXPERT OPINION

Heart rate (HR) is a risk factor in patients with HF, and its reduction is considered an important goal of therapy. The BEAUTIFUL trial demonstrated the benefits of ivabradine on prognosis (only on ischemic endpoints) in patients with coronary artery disease (CAD) and left ventricular systolic dysfunction (LVSD) and HR ≥ 60 bpm. In the SHIFT trial, which enrolled patients with LVSD, HF and HR ≥ 70 bpm, ivabradine administration (on top of guideline-based therapy, including β-blockers [BB]) was associated with a reduction of cardiovascular death and hospitalizations for HF, but BB were underutilized. Further studies are needed to test the efficacy of ivabradine in CAD patients with high HR and to shed light on the comparison between ivabradine and a more aggressive therapy with higher doses of BB in HF patients.

The fractal-like complexity of heart rate variability beyond neurotransmitters and autonomic receptors: signaling intrinsic to sinoatrial node pacemaker cells

The heart rate and rhythm are controlled by complex chaotic neural, chemical and hormonal networks which are not strictly regular, but exhibit fluctuations across multiple time scales. A careful assessment of the heart rate variability (HRV) offers clues to this complexity. A reduction in HRV, specifically in advanced age, is associated with increase in morbidity and mortality. Mechanisms that induce this decrease, however, have not been fully elucidated. The classical literature characterizes changes in HRV as a result of changes in the balance of competing influences of the sympathetic and parasympathetic autonomic impulses delivered to the heart. It has now become clear, however, that the heart rate and HRV are also determined by intrinsic properties of the pacemaker cells that comprise sinoatrial node, and that these properties respond to autonomic receptor stimulation in a non-linear mode. That HRV is determined by both the intrinsic properties of pacemaker cells in the sinoatrial node and the competing influences of the two branches of the autonomic neural input to the cells requires an expansion of our perspective about mechanisms that govern HRV in the normal heart, and how HRV changes with aging in health and in heart diseases.

Ivabradine: potential clinical applications in critically ill patients

It has been extensively demonstrated that an elevated heart rate is a modifiable, independent risk factor for cardiovascular events. A high heart rate increases myocardial oxygen consumption and reduces diastolic perfusion time. It can also increase ventricular diastolic pressures and induce ventricular arrhythmias. Critical care patients are prone to develop a stress induced cardiac impairment and consequently an increase in sympathetic tone. This in turn increases heart rate. In this setting, however, heart rate lowering might be difficult because the effects of inotropic drugs could be hindered by heart rate reducing drugs like beta-blockers. Ivabradine is a new selective antagonist of funny channels. It lowers heart rate, reducing the diastolic depolarization slope. Moreover, ivabradine is not active on sympathetic pathways, thus avoiding any interference with inotropic amines. We reviewed the literature available regarding heart rate control in critical care patients, focusing our interest on the use of ivabradine to assess the potential benefits of the drug in this particular setting.

Effects of ivabradine in patients with stable angina receiving β-blockers according to baseline heart rate: an analysis of the ASSOCIATE study

BACKGROUND

Any increase in heart rate (HR) during daily activities above the ischemic threshold may trigger myocardial ischemia. HR reduction with the If inhibitor ivabradine has been demonstrated to confer anti-ischemic and antianginal efficacy in patients with stable angina pectoris. This analysis of the ASSOCIATE trial assessed whether the anti-ischemic efficacy and safety of ivabradine were comparable in patients with baseline resting HRs above and below the median.

METHODS

Patients with chronic stable angina pectoris were randomized to treatment with ivabradine (5 to 7.5mg bid) or placebo for 4 months, in addition to atenolol 50mg od. The effect of treatment on exercise tolerance test parameters was analyzed in two groups according to baseline HR: > 65 bpm (n=418) versus ≤ 65 bpm (n=436) (above and below the median, respectively).

RESULTS

Ivabradine reduced resting HR in both groups with placebo-corrected reductions of -9.1 (95% CI -11.0 to -7.3; >65 bpm group) and -5.9 (95% CI -7.5 to -4.3; ≤ 65 bpm group) (both P<0.001 versus placebo). Ivabradine reduced heart rate at all stages of exercise (all P<0.001). Improvements in exercise capacity (total exercise duration, time to limiting angina, angina onset, and 1-mm ST segment depression, all P<0.05) were recorded in both HR groups. There were no differences between the two groups in terms of safety.

CONCLUSIONS

Ivabradine resulted in significant improvements in exercise capacity relative to placebo in patients with stable angina pectoris receiving beta-blocker therapy whether their resting HR was above or below 65 bpm.

A low resting heart rate at diagnosis predicts favourable long-term outcome in pulmonary arterial and chronic thromboembolic pulmonary hypertension. A prospective observational study

Background

A low resting heart rate (HR) is prognostically favourable in healthy individuals and in patients with left heart disease. In this study we investigated the impact of HR at diagnosis on long-term outcome in patients with differently classified precapillary pulmonary hypertension (pPH).

Methods

pPH patients diagnosed as pulmonary arterial (PAH) or inoperable chronic thromboembolic pulmonary hypertension (CTEPH) were registered and regularly followed at our centre Baseline characteristics and events defined as either death or lung transplantation were noted. The prognostic value of HR was analysed using Kaplan Meier estimates, live tables and Cox regression.

Results

206 patients with PAH (148) and inoperable CTEPH (58) were included. The median HR was 82 bpm. pPH with a HR below 82 bpm had a significantly longer overall event-free survival (2409 vs.1332 days, p = .000). This advantage was similarly found if PAH and CTEPH were analysed separately. Although a lower HR was associated with a better hemodynamic and functional class, HR was a strong and independent prognostic marker for transplant free survival even if corrected for age, sex, hemodynamics and functional status.

Conclusion

We show that resting HR at diagnosis is a strong and independent long-term prognostic marker in PAH and CTEPH. Whether reducing HR by pharmacological agents would improve outcome in pPH has to be assessed by future trials with high attention to safety.

The "funny" current (I(f)) inhibition by ivabradine at membrane potentials encompassing spontaneous depolarization in pacemaker cells

Recent clinical trials have shown that ivabradine (IVA), a drug that inhibits the funny current (I(f)) in isolated sinoatrial nodal cells (SANC), decreases heart rate and reduces morbidity and mortality in patients with cardiovascular diseases. While IVA inhibits I(f), this effect has been reported at essentially unphysiological voltages, i.e., those more negative than the spontaneous diastolic depolarization (DD) between action potentials (APs). We tested the relative potency of IVA to block I(f) over a wide range of membrane potentials, including those that encompass DD governing to the SANC spontaneous firing rate. A clinically relevant IVA concentration of 3 μM to single, isolated rabbit SANC slowed the spontaneous AP firing rate by 15%. During voltage clamp the maximal I(f) was 18 ± 3 pA/pF (at -120 mV) and the maximal I(f) reduction by IVA was 60 ± 8% observed at -92 ± 4 mV. At the maximal diastolic depolarization (~-60 mV) I(f) amplitude was only -2.9 ± 0.4 pA/pF, and was reduced by only 41 ± 6% by IVA. Thus, I(f) amplitude and its inhibition by IVA at physiologically relevant membrane potentials are substantially less than that at unphysiological (hyperpolarized) membrane potentials. This novel finding more accurately describes how IVA affects SANC function and is of direct relevance to numerical modeling of SANC automaticity.

Pharmacodynamic effects of ivabradine, a negative chronotropic agent, in healthy cats

OBJECTIVE

To determine the pharmacodynamic effects of oral ivabradine in cats.

ANIMALS

Eight healthy, adult domestic short hair cats.

METHODS

Each cat underwent four study periods of 24 h, receiving either one dose of placebo or ivabradine (0.1 mg/kg, 0.3 mg/kg, and 0.5 mg/kg) in a single-blind randomized crossover study. Clinical tolerance was assessed hourly for the first 8 h, at 12 h, and at the end of the 24-h study period. Heart rate and blood pressure were monitored continuously for 18-24 h via radiotelemetry after each treatment. Response to stress (acoustic startle) was studied before (t = 0) and after treatment (t = 4 h). Statistical comparisons were made using a linear mixed models and 1-way and 2-way repeated measures ANOVA.

RESULTS

Heart rate (min(-1)) decreased significantly (P < 0.05) in a dose-dependent manner with peak negative chronotropic effects observed 3 h after ivabradine (mean ± SD; placebo, 144 ± 20; ivabradine 0.1 mg/kg, 133 ± 22; ivabradine 0.3 mg/kg, 112 ± 20; and ivabradine 0.5 mg/kg, 104 ± 11). Heart rate (min(-1)) was still reduced (P < 0.05) 12 h after ivabradine (0.3 mg/kg; 128 ± 18 and 0.5 mg/kg; 124 ± 16) compared to placebo (141 ± 21). The tachycardic response to acoustic startle was significantly (P < 0.01) blunted at all 3 doses of ivabradine. Myocardial oxygen consumption estimated by the rate-pressure product was significantly reduced (P < 0.05) for all doses of ivabradine. No effect of ivabradine on systolic, diastolic, and mean blood pressure was identified and no clinically discernable side effects were observed.

CONCLUSION

These findings indicate that a single oral dose of ivabradine predictably lowers heart rate, blunts the chronotropic response to stress, and is clinically well tolerated in healthy cats. This makes ivabradine potentially interesting in the treatment of feline heart disease where ischemia is of pathophysiologic importance.

Innovation in coronary artery disease and heart failure: clinical benefits of pure heart rate reduction with ivabradine

The link between elevated heart rate and cardiovascular events is established in healthy individuals and in patients with cardiovascular disease. The new agent, ivabradine, specifically and selectively inhibits the I(f) current, with the sole action of heart rate reduction, with no impact on any other cardiac parameters. The benefits of "pure" heart rate reduction with ivabradine have been the focus of one of the largest clinical development programs ever performed, involving >20,000 individuals. Ivabradine has anti-ischemic and antianginal efficacy in monotherapy, as well as in combination with other antianginals, such as beta-blockers, and is safe and well tolerated. Two major morbidity-mortality trials, BEAUTIFUL and SHIFT, showed that heart rate reduction with ivabradine dramatically improves prognosis in patients with coronary artery disease and left ventricular dysfunction, symptomatic angina, or chronic heart failure. The development of ivabradine represents a clear innovation in the management of cardiovascular disease.

[Ivabradine in coronary heart disease: experimental and clinical pharmacology]

The present paper reviews clinical evidence underlining the role of ivabradine in the management of patient with ischemic heart disease. Reduction in heart rate mediated by this selective I(f) current inhibitor has been associated with anti-ischemic efficacy without any effect on haemodynamic or myocardial contractility. The antianginal efficacy of ivabradine is similar or superior to that of conventional anti-ischemic agents. Moreover combination therapy with ivabradine provides substantial benefit in patients already receiving beta-blocker. Prognostic efficacy of ivabradine is evaluated in a large program of studies, among which BEAUTIFUL in coronary patients with left ventricular dysfunction. The SIGNIFY study is ongoing in stable coronary patients without ventricular dysfunction. Furthermore the SHIFT trial will evaluate ivabradine benefits in heart failure patients, whatever the origin, ischemic or not.

Pacemaker activity of the human sinoatrial node: role of the hyperpolarization-activated current, I(f)

The mechanism of primary, spontaneous cardiac pacemaker activity of the sinoatrial node (SAN) has extensively been studied in several animal species, but is virtually unexplored in man. Understanding the mechanisms of human SAN pacemaker activity is important for developing new therapeutic approaches for controlling the heart rate in the sick sinus syndrome and in diseased myocardium. Here we review the functional role of the hyperpolarization-activated 'funny' current, I(f), in human SAN pacemaker activity. Despite the many animal studies performed over the years, the contribution of I(f) to pacemaker activity is still controversial and not fully established. However, recent clinical data on mutations in the I(f) encoding HCN4 gene, which is thought to be the most abundant isoform of the HCN gene family in SAN, suggest a functional role of I(f) in human pacemaker activity. These clinical findings are supported by recent experimental data from single isolated human SAN cells that provide direct evidence that I(f) contributes to human SAN pacemaker activity. Therefore, controlling heart rate in clinical practice via I(f) blockers offers a valuable approach to lowering heart rate and provides an attractive alternative to conventional treatment for a wide range of patients with confirmed stable angina, while upregulation or artificial expression of I(f) may relieve disease-causing bradycardias.