Structural determinants of ivabradine block of the open pore of HCN4.

HCN1-4 channels are the molecular determinants of the If/Ih current that crucially regulates cardiac and neuronal cell excitability. HCN dysfunctions lead to sinoatrial block (HCN4), epilepsy (HCN1), and chronic pain (HCN2), widespread medical conditions awaiting subtype-specific treatments. Here, we address the problem by solving the cryo-EM structure of HCN4 in complex with ivabradine, to date the only HCN-specific drug on the market. Our data show ivabradine bound inside the open pore at 3 Å resolution. The structure unambiguously proves that Y507 and I511 on S6 are the molecular determinants of ivabradine binding to the inner cavity, while F510, pointing outside the pore, indirectly contributes to the block by controlling Y507. Cysteine 479, unique to the HCN selectivity filter (SF), accelerates the kinetics of block. Molecular dynamics simulations further reveal that ivabradine blocks the permeating ion inside the SF by electrostatic repulsion, a mechanism previously proposed for quaternary ammonium ions.

A gain-of-function HCN4 mutant in the HCN domain is responsible for inappropriate sinus tachycardia in a Spanish family.

In a family with inappropriate sinus tachycardia (IST), we identified a mutation (p.V240M) of the hyperpolarization-activated cyclic nucleotide-gated type 4 (HCN4) channel, which contributes to the pacemaker current (If) in human sinoatrial node cells. Here, we clinically study fifteen family members and functionally analyze the p.V240M variant. Macroscopic (IHCN4) and single-channel currents were recorded using patch-clamp in cells expressing human native (WT) and/or p.V240M HCN4 channels. All p.V240M mutation carriers exhibited IST that was accompanied by cardiomyopathy in adults. IHCN4 generated by p.V240M channels either alone or in combination with WT was significantly greater than that generated by WT channels alone. The variant, which lies in the N-terminal HCN domain, increased the single-channel conductance and opening frequency and probability of HCN4 channels. Conversely, it did not modify the channel sensitivity for cAMP and ivabradine or the level of expression at the membrane. Treatment with ivabradine based on functional data reversed the IST and the cardiomyopathy of the carriers. In computer simulations, the p.V240M gain-of-function variant increases If and beating rate and thus explains the IST of the carriers. The results demonstrate the importance of the unique HCN domain in HCN4, which stabilizes the channels in the closed state.

Detection of retinal dysfunction induced by HCN channel inhibitors using multistep light stimulus and long-duration light stimulus ERG in rats.

Ivabradine, a hyperpolarization-activated cyclic nucleotide-gated (HCN) channel inhibitor, has been reported to induce photosensitivity-related visual disturbances such as phosphene in humans. Ivabradine-induced visual disturbances are caused by inhibition of HCN channels in the retina, and the mechanisms have been verified using HCN channel knockout mice and electroretinography (ERG). However, in rats, classical ERG using single flash light stimulus with standard analyses of waveform amplitude and latency has not revealed abnormal retinal function after administration of ivabradine. To verify whether retinal dysfunction after ivabradine administration was detectable in rats, we performed ERG using multistep flash light stimulation at the time when plasma concentration of ivabradine was high. Furthermore, the mechanism of the change in the waveform that appeared after the b-wave was investigated. Ivabradine and cilobradine, a selective HCN channel inhibitor, were administered subcutaneously to rats at 4-40 mg/kg as a single dose, and flash or long-duration ERG recordings at each light stimulus luminance were conducted 1.5 h after administration. Plasma and retinal concentrations of both compounds were measured immediately after the ERG recordings. In the flash ERG, prolongation of a- and/or b-wave latencies were detected at each light stimulus, and dose-dependent waveform changes after the b-wave were recorded at the specific light stimulus luminance for both compounds. These ERG changes increased in response to increasing plasma and retinal concentrations for both ivabradine and cilobradine. In the long-duration light stimulus ERG, a change in the waveform of the b-wave trough and attenuation of the c-wave were recorded, suggesting that the feedback control in the photoreceptor cells may be inhibited. This study revealed that the retinal dysfunction by HCN channel inhibitors in rats can be detected by multistep light stimulus ERG. Additionally, we identified that the inhibition of feedback current and the sustained responses in the photoreceptor cells cause the retinal dysfunction of HCN channel inhibitors in rats.

Bidirectional flow of the funny current (If) during the pacemaking cycle in murine sinoatrial node myocytes.

Sinoatrial node myocytes (SAMs) act as cardiac pacemaker cells by firing spontaneous action potentials (APs) that initiate each heartbeat. The funny current (If) is critical for the generation of these spontaneous APs; however, its precise role during the pacemaking cycle remains unresolved. Here, we used the AP-clamp technique to quantify If during the cardiac cycle in mouse SAMs. We found that If is persistently active throughout the sinoatrial AP, with surprisingly little voltage-dependent gating. As a consequence, it carries both inward and outward current around its reversal potential of -30 mV. Despite operating at only 2 to 5% of its maximal conductance, If carries a substantial fraction of both depolarizing and repolarizing net charge movement during the firing cycle. We also show that ß-adrenergic receptor stimulation increases the percentage of net depolarizing charge moved by If, consistent with a contribution of If to the fight-or-flight increase in heart rate. These properties were confirmed by heterologously expressed HCN4 channels and by mathematical models of If Modeling further suggested that the slow rates of activation and deactivation of the HCN4 isoform underlie the persistent activity of If during the sinoatrial AP. These results establish a new conceptual framework for the role of If in pacemaking, in which it operates at a very small fraction of maximal activation but nevertheless drives membrane potential oscillations in SAMs by providing substantial driving force in both inward and outward directions.

Ivabradine for congenital ectopic tachycardia in newborn.

INTRODUCTION: Congenital junctional ectopic tachycardia is a rare arrhythmia that occurs in patients without previous cardiac surgery. In this report, we wanted to present a 6-hour-old newborn with congenital junctional ectopic tachycardia resistant to conventional anti-arrhythmic medications, who was successfully treated with ivabradine and amiadarone combination. CASE: A six-hour-old newborn girl was hospitalised in neonatal ICU because transient tachypnoea of the newborn. She was tachycardic, and supraventricular tachycardia was noticed. There was no answer to the adenosine esmolol treatment; even synchronised direct cardioversion intravenous amiodarone was started. Junctional ectopic tachycardia was diagnosed. We have added propranolol to the treatment and followed patient for 2 days. On the fourth day, junctional ectopic tachycardia rhythm still persisted; therefore, ivabradine treatment was added to the treatment. On the following day, the heart rhythm was slowed to 110/min, and propranolol was stopped; intravenous amiodarone treatment was changed to the oral form. The rhythm turned into sinus; two days after starting ivabradine and oral amiodarone. CONCLUSION: Tachyarrhythmia originating in the atrioventricular node and atrioventricular junction including the bundle of His complex are junctional ectopic tachycardia. Congenital junctional ectopic tachycardia is rare, and it is mostly resistant to the conventional treatment.Ivabradine is a new anti-arrhythmic agent, used extensively to decrease sinus rate in the treatment of cardiac failure. Ivabradine may be an option for the resistant congenital ectopic tachycardia.

Ivabradine Alleviates Experimental Autoimmune Myocarditis-Mediated Myocardial Injury.

Ivabradine (IVA) reduces heart rate by inhibiting hyperpolarization-activated cyclic nucleotide-gated channels (HCNs), which play a role in the promotion of pacemaker activity in cardiac sinoatrial node cells. HCNs are highly expressed in neural and myocardial tissues and are involved in the modulation of inflammatory neuropathic pain. However, whether IVA exerts any effect on myocardial inflammation in the pathogenesis of heart failure is unclear. We employed single-cell RNA sequencing (scRNA-seq) in porcine cardiac myosin-induced experimental autoimmune myocarditis rat model to determine the effects and mechanisms of IVA. Lewis rats (n = 32) were randomly divided into the normal, control, high-dose-IVA, and low-dose-IVA groups. Heart rate and blood pressure were measured on days 0 and 21, respectively. Echocardiography was performed on day 22, and inflammation of the myocardium was evaluated via histopathological examination. Western blot was employed to detect the expression of HCN1-4, MinK-related protein 1 (MiRP1), matrix metalloproteinase 2 (MMP-2), MMP-9, and transforming growth factor-ß (TGF-ß). Furthermore, enzyme-linked immunosorbent assay was performed to measure serum IL-1, IL-6, and TNF-α. The relative mRNA levels of collagen I, collagen III, and α-smooth muscle actin (α-SMA) were determined via qRT-PCR. We found that IVA reduced the total number of cells infiltrated into the myocardium, particularly in the subset of fibroblasts, endocardia, and monocytes. IVA administration ameliorated cardiac inflammation and reduced collagen production. Results of the echocardiography indicated that left ventricular internal diameter at end-systole LVIDs increased whereas left ventricular ejection fraction and left ventricular fractional shortening decreased in the control group. IVA improved cardiac performance. The expression of HCN4 and MiRP1 protein and the level of serum IL-1, IL-6, and TNF-α were decreased by IVA treatment. In conclusion, HCNs and the helper proteins were increased in the profile of myocardial inflammation. HCNs may be involved in the regulation of myocardial inflammation by inhibiting immune cell infiltration. Our findings can contribute to the development of IVA-based combination therapies for the future treatment of cardiac inflammation and heart failure.

Efficacy and Tolerability of Ivabradine for Cardiomyopathy in Patients with Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is an intractable X-linked myopathy caused by dystrophin gene mutations. Patients with DMD suffer from progressive muscle weakness, inevitable cardiomyopathy, increased heart rate (HR), and decreased blood pressure (BP). The aim of this study was to clarify the efficacy and tolerability of ivabradine treatment for DMD cardiomyopathy.A retrospective analysis was performed in 11 patients with DMD, who received ivabradine treatment for more than 1 year. Clinical results were analyzed before (baseline), 6 months after, and 12 months after the ivabradine administration.The initial ivabradine dose was 2.0 ± 1.2 mg/day and the final dose was 5.6 ± 4.0 mg/day. The baseline BP was 95/64 mmHg. A non-significant BP decrease to 90/57 mmHg was observed at 1 month but it recovered to 97/62 mmHg at 12 months after ivabradine administration. The baseline HR was 93 ± 6 bpm and it decreased to 74 ± 12 bpm at 6 months (P = 0.011), and to 77 ± 10 bpm at 12 months (P = 0.008). A linear correlation (y = 2.2x + 5.1) was also observed between the ivabradine dose (x mg/day) and HR decrease (y bpm). The baseline LVEF was 38 ± 12% and it significantly increased to 42 ± 9% at 6 months (P = 0.011) and to 41 ± 11% at 12 months (P = 0.038). Only 1 patient with the lowest BMI of 11.0 kg/m2 and BP of 79/58 mmHg discontinued ivabradine treatment at 6 months, while 1-year administration was well-tolerated in the other 10 patients.Ivabradine decreased HR and increased LVEF without lowering BP, suggesting it can be a treatment option for DMD cardiomyopathy.

Clinical Implications of Ivabradine in the Contemporary Era.

Ivabradine is a recently introduced inhibitor of the If ion channel, which exhibits the capacity to reduce heart rate while preserving hemodynamic stability. At present, ivabradine finds its clinical indication in patients suffering from heart failure with reduced ejection fraction and maintaining a relative sinus rhythm refractory to beta-blockers. To optimize heart rate control, it is recommended to pursue an aggressive up-titration of ivabradine. This approach may ameliorate tachycardia-induced hypotension by incrementally enhancing cardiac output and allow further up-titration of agents aimed at ameliorating heart failure, such as beta-blockers. Both the modulation of heart rate itself and the up-titration of agents targeting heart failure lead to cardiac reverse remodeling, consequently culminating in a subsequent reduction in mortality and morbidity. A novel overlap theory that our team proposed recently has emerged in recent times. Under trans-mitral Doppler echocardiography, the E-wave and A-wave closely juxtapose one another without any overlapping at the optimal heart rate. Employing echocardiography-guided ivabradine for heart-rate modulation to minimize the overlap between the E-wave and A-wave appears to confer substantial benefits to patients with heart failure. This approach facilitates superior cardiac reverse remodeling and yields more favorable clinical outcomes when compared to those patients who do not receive echocardiography-guided care. The next pertinent issue revolves around the potential expansion of ivabradine's clinical indications to encompass a broader spectrum of diseases. It is imperative to acknowledge that ivabradine may not yield clinically significant benefits in patients afflicted by heart failure with preserved ejection fraction, acute heart failure, sepsis, or stable angina. An important fact yet to be explored is the clinical applicability of ivabradine in patients with atrial fibrillation, a concern that beckons future investigation. In this review, the concept of overlap theory it introduced, along with its application to expand the indication of ivabradine and the overlap theory-guided optimal ivabradine therapy.

Effect of ivabradine on structural and functional changes of myocardium and NT-proBNP levels in patients with stable coronary heart disease after coronary stenting.

OBJECTIVE: Aim: To investigate the effect of ivabradine on the hemodynamics and contractility of the myocardium and the features of NT-pro-BNP production in patients with stable ischemic heart disease after endovascular revascularization of the myocardium depending on the number of affected coronary arteries during 12 months of therapy. PATIENTS AND METHODS: Materials and Methods: The object of the study was 120 patients with stable coronary artery disease: angina pectoris of functional class III with heart failure IIA FC III with preserved and moderately reduced ejection fraction of the left ventricle, who underwent coronary artery stenting. The examined patients were randomized according to the number of affected coronary vessels and the method of treatment. RESULTS: Results: Ivabradine in patients with stable ischemic heart disease after 12 months of therapy had a significant beneficial effect on the structural and functional parameters of the myocardium (contributed to the reverse remodeling of the left ventricle), which did not depend on the number of stented coronary arteries (p<0.05). In patients with stented one coronary artery, all structural and functional indicators of the heart after 12 months of treatment reached the values of practically healthy individuals from the control group. The use of ivabradine in patients with stable ischemic heart disease with heart failure with preserved and intermediate ejection fraction of the left ventricle after coronary stenting made it possible to ensure the correction of a number of clinical and pathogenetic links of the disease, which generally contributed to the improvement of metric and volumetric parameters of the heart. CONCLUSION: Conclusions: Ivabradine made it possible to significantly increase the effectiveness of standard therapy, which was manifested by a faster recovery of the geometry and contractility of the left ventricle. Therefore, the use of ivabradine along with standard therapy was appropriate for such a contingent of patients. The management of patients with stable coronary heart disease should combine adequate (surgical and pharmacological) treatment of the underlying disease, further individual medication correction of symptoms and circulatory disorders inherent in coronary heart disease and heart failure.

Sex-specific differences in the efficacy of heart failure therapies: a meta-analysis of 84,818 patients.

Women have been historically underrepresented in clinical trials of heart failure (HF). We aimed to assess for sex differences in patient characteristics and the efficacy of guideline-directed medical therapy (GDMT) in HF. Systematic literature search for randomized controlled trials (RCTs) of GDMT reporting cardiovascular outcomes by sex in patients with HF. The primary outcome was the composite of cardiovascular death and hospitalization for HF. Risk ratios (RR) with 95% confidence intervals (CI) were pooled using inverse variance weighting and random effects meta-analysis. Twenty-six RCTs totaling 84,818 participants (27% women) were included. Women with HF were older, had higher New York Heart Association (NYHA) class, more hypertension and obesity, and higher mean left ventricular ejection fraction compared to men. There was evidence for most GDMT in reducing the primary outcome in women with HF with reduced ejection fraction (HFrEF) (angiotensin-converting enzyme inhibitors/angiotensin-receptor blocker [RR 0.86, 95% CI 0.75-0.97], angiotensin-receptor blocker/neprilysin inhibitor (ARNI) [RR 0.77, 95% CI 0.62-0.94], beta-blocker [RR 0.67, 95% CI 0.51-0.89], ivabradine [RR 0.74, 95% CI 0.60-0.91], and sodium-glucose cotransporter-2 (SGLT2) inhibitors [RR 0.66, 95% CI 0.54-0.81]) and a non-significant trend for benefit with mineralocorticoid-receptor-antagonist (MRA) [RR 0.77, 95% CI 0.52-1.16]). Compared to men with HFrEF, GDMT reduced the primary outcome in women to a similar degree across all drug classes (ratio of RR 1.05, 95% CI 0.96-1.14). Despite differences in baseline characteristics and an underrepresentation of women in HF clinical trials, GDMT are as efficacious in women as compared to men in reducing cardiovascular events in HF.

Ivabradine in a 15-day-old male neonate with refractory focal atrial tachycardia.

Ivabradine is used to reduce heart rate in children with chronic heart failure and dilated cardiomyopathy, it has recently been used off-label to treat tachyarrhythmias such as ectopic atrial tachycardia and junctional ectopic tachycardia (JET) in children. We report a successful ivabradine experience in a male neonate with refractory focal atrial tachycardia (FAT).

Ivabradine monotherapy in pediatric patients with focal atrial tachycardia: a single-center study.

This study investigated the efficacy of ivabradine monotherapy in pediatric patients with focal atrial tachycardia (FAT). We prospectively enrolled 12 pediatric patients (7.5 ± 4.5 years; six girls) with FAT who were resistant to conventional antiarrhythmics and received ivabradine as monotherapy. Patients were classified as having tachycardia-induced cardiomyopathy (TIC) if they had a left ventricular ejection fraction (LVEF) of < 50% and a left ventricular end-diastolic dimension (LVDD) z-score of > 2 due to tachycardia. Oral ivabradine was initiated at 0.1 mg/kg every 12 h, increased to 0.2 mg/kg every 12 h if no restoration of stable sinus rhythm was observed after two doses, and discontinued after 48 h if neither rhythm nor heart rate control was observed. Of these patients, six (50%) had incessant atrial tachycardia, and 6 had frequent short episodes of FAT. Six patients were diagnosed with TIC, and their mean LVEF and mean LVDD z-score were 36.2 ± 8.7% (range, 27-48%) and 4.2 ± 1.7 (range, 2.2-7.3), respectively. Finally, six patients achieved either rhythm (n = 3) or heart rate control (n = 3) within 48 h of ivabradine monotherapy. One patient achieved rhythm/heart rate control with ivabradine at a dose of 0.1 mg/kg every 12 h, while the others achieved rhythm/heart rate control at a dose of 0.2 mg/kg every 12 h. Five patients received ivabradine monotherapy for chronic therapy, one (20%) of whom had FAT breakthrough 1 month after discharge, and metoprolol was added. Neither FAT recurrence nor adverse effect (with or without beta-blocker) was observed during a median follow-up of 5 months. CONCLUSION: Ivabradine is well-tolerated and may provide early heart rate control in pediatric FAT and can be considered early, especially in the presence of left ventricular dysfunction. Further investigations are deserved to confirm the optimal dose and long-term efficacy in this population. WHAT IS KNOWN: • Focal atrial tachycardia (FAT) is the most common arrhythmia associated with tachycardia-induced cardiomyopathy (TIC) in children, and the efficacy of conventional antiarrhythmic medications in the treatment of FAT is poor. • Ivabradine is currently the only selective hyperpolarization-activated cyclic nucleotide-gated (HCN) inhibitor, which can effectively low HR without negative effect on blood pressure or inotropy. WHAT IS NEW: • Ivabradine (0.1-0.2 mg/kg every 12 h) can effectively suppress focal atrial tachycardia in 50% of pediatric patients. • Ivabradine provides early control of heart rate and hemodynamic stabilization in children with severe left ventricular dysfunction due to atrial tachycardia within 48 h.

Efficacy of Doppler echocardiography-guided ivabradine therapy.

BACKGROUND: The purpose of this study was to evaluate the advantage of heart rate (HR) modulation using ivabradine referring Doppler echocardiography over the conventional ivabradine therapy without echocardiography guide in patients with systolic heart failure. METHODS: From October 2020, our institute updated the protocol of ivabradine therapy, in which HR was optimized to minimize the overlap between the two left ventricular inflow waves using Doppler echocardiography (echo-guided group). The degree of cardiac reverse remodeling at 3-month follow-up was compared between the echo-guided group and the conventional ivabradine therapy group treated before October 2020. RESULTS: A total of 28 patients (62 years old, 17 men) were included, and 18 patients were from echo-guided group. Left ventricular ejection fraction increased significantly in the echo-guided group (from 41% [28%, 49%] to 55% [37%, 66%], p = 0.007), whereas it remained unchanged in the conventional group (p = 0.333). Systolic blood pressure and the daily dose of carvedilol increased significantly only in the echo-guided group (p = 0.009 and p = 0.001, respectively). CONCLUSIONS: Among those with systolic heart failure, a Doppler echocardiography guide might be a promising therapeutic tool in modulating HR by ivabradine in facilitating reverse remodeling.

Ivabradine in the treatment of non-paroxysmal junctional tachycardia with interference atrioventricular dissociation: A case report.

Ivabradine reduces the heart rate by selectively inhibiting the If current of the sinoatrial node, mainly for the treatment of chronic heart failure with decreased left ventricular systolic function and inappropriate sinus tachycardia, but the inhibitory effect on the atrioventricular node is rarely reported. The patient was admitted to hospital mainly because of intermittent chest pain for 7 years, which worsened for 10 days. Admission electrocardiogram (ECG) considered sinus tachycardia, with QS wave and T wave inversion in II, III, aVF, V3 R-V5 R, V4 -V9 leads, and non-paroxysmal junctional tachycardia (NPJT) with interference atrioventricular dissociation. After treatment with ivabradine the ECG returned to normal conduction sequence. NPJT with interference atrioventricular dissociation is a fairly rare electrocardiographic phenomenon. This case reports for the first time that ivabradine is used in the treatment of NPJT with interference atrioventricular dissociation. It is speculated that ivabradine has a potential inhibitory effect on the atrioventricular node.

Ivabradine curbs isoproterenol-induced kidney fibrosis.

This study investigated whether chronic isoproterenol administration could induce kidney alterations and whether ivabradine, a heart rate (HR)-reducing substance exerting cardiovascular protection, is able to attenuate potential kidney damage. Twenty-eight Wistar rats were divided into non-diseased controls, rats treated with ivabradine, rats treated with isoproterenol, and rats treated with isoproterenol plus ivabradine. Six weeks of isoproterenol administration was associated with decreased systolic blood pressure (SBP) (by 25%) and glomerular, tubulointerstitial and vascular/perivascular fibrosis due to enhanced type I collagen volume (7-, 8-, and 4-fold, respectively). Ivabradine reduced HR (by 15%), partly prevented SBP decline (by 10%) and site-specifically mitigated kidney fibrosis by decreasing type I collagen volume in all three sites investigated (by 69, 58, and 67%, respectively) and the ratio of type I collagen-to-type III collagen in glomerular and vascular/perivascular sites (by 79 and 73%, respectively). We conclude that ivabradine exerts protection against kidney remodelling in isoproterenol-induced kidney damage.

Successful use of ivabradine in a 10-year-old patient with graft failure after heart transplantation.

We encountered a paediatric case of graft failure due to antibody-mediated rejection after heart transplantation in which ivabradine was effective. Inappropriate sinus tachycardia in denervated transplanted hearts is a good indication for ivabradine administration as beta-blockers have a limited efficacy. To our knowledge, this is the first report on the effectiveness of ivabradine in a paediatric heart transplant rejection case.

Successful treatment of the focal ectopic atrial tachycardia in an infant with a single dose of ivabradin.

We report on a 12-month-old boy with an ectopic atrial tachycardia successfully treated with the ivabradine that acts on cardiac pacemaker cells by selectively inhibiting the If channel. The patient was diagnosed with supraventricular tachycardia in another centre, and multi-drug therapy was unsuccessful to restore sinus ryhthm, so he was sent to our hospital for catheter ablation. We stopped the medications the patient was taking and started using ivabradine. Sinus rhythm was restored 2 hours after ivabradine treatment was started.

Therapeutic Use and Molecular Aspects of Ivabradine in Cardiac Remodeling: A Review.

Cardiac remodeling can cause ventricular dysfunction and progress to heart failure, a cardiovascular disease that claims many lives globally. Ivabradine, a funny channel (If) inhibitor, is used in patients with chronic heart failure as an adjunct to other heart failure medications. This review aims to gather updated information regarding the therapeutic use and mechanism of action of ivabradine in heart failure. The drug reduces elevated resting heart rate, which is linked to increased morbidity and mortality in patients with heart failure. Its use is associated with improved cardiac function, structure, and quality of life in the patients. Ivabradine exerts several pleiotropic effects, including an antiremodeling property, which are independent of its principal heart-rate-reducing effects. Its suppressive effects on cardiac remodeling have been demonstrated in animal models of cardiac remodeling and heart failure. It reduces myocardial fibrosis, apoptosis, inflammation, and oxidative stress as well as increases autophagy in the animals. It also modulates myocardial calcium homeostasis, neurohumoral systems, and energy metabolism. However, its role in improving heart failure remains unclear. Therefore, elucidating its molecular mechanisms is imperative and would aid in the design of future studies.

Synergy between Membrane Currents Prevents Severe Bradycardia in Mouse Sinoatrial Node Tissue.

Bradycardia is initiated by the sinoatrial node (SAN), which is regulated by a coupled-clock system. Due to the clock coupling, reduction in the 'funny' current (If), which affects SAN automaticity, can be compensated, thus preventing severe bradycardia. We hypothesize that this fail-safe system is an inherent feature of SAN pacemaker cells and is driven by synergy between If and other ion channels. This work aimed to characterize the connection between membrane currents and their underlying mechanisms in SAN cells. SAN tissues were isolated from C57BL mice and Ca2+ signaling was measured in pacemaker cells within them. A computational model of SAN cells was used to understand the interactions between cell components. Beat interval (BI) was prolonged by 54 ± 18% (N = 16) and 30 ± 9% (N = 21) in response to If blockade, by ivabradine, or sodium current (INa) blockade, by tetrodotoxin, respectively. Combined drug application had a synergistic effect, manifested by a BI prolonged by 143 ± 25% (N = 18). A prolongation in the local Ca2+ release period, which reports on the level of crosstalk within the coupled-clock system, was measured and correlated with the prolongation in BI. The computational model predicted that INa increases in response to If blockade and that this connection is mediated by changes in T and L-type Ca2+ channels.

Ivabradine for the Prevention of Anthracycline-Induced Cardiotoxicity in Female Patients with Primarily Breast Cancer: A Prospective, Randomized, Open-Label Clinical Trial.

Background and Objectives: Cancer therapy containing anthracyclines is associated with cancer-treatment-related cardiac dysfunction and heart failure (HF). Conventional cardioprotective medications can be frequently complicated by their blood-pressure-lowering effect. Recently, elevated resting heart rate was shown to independently predict mortality in patients with cancer. As a heart rate-lowering drug without affecting blood pressure, ivabradine could present an alternative management of anthracyclines-induced cardiotoxicity. Materials and Methods: This study aimed to investigate the probable protective effects of ivabradine in cancer patients with elevated heart rate (>75 beats per minute) undergoing anthracycline chemotherapy. Patients referred by oncologists for baseline cardiovascular risk stratification before anthracycline chemotherapy who met the inclusion criteria and had no exclusion criteria were randomly assigned to one of two strategies: ivabradine 5 mg twice a day (intervention group) or controls. Electrocardiogram, transthoracic echocardiogram with global longitudinal strain (GLS), troponin I (Tn I), and N-terminal natriuretic pro-peptide (NT-proBNP) were performed at baseline, after two and four cycles of chemotherapy and at six months of follow-up. The primary endpoint was the prevention of a >15% reduction in GLS. Secondary endpoints were effects of ivabradine on Tn I, NT-proBNP, left ventricular (LV) systolic and diastolic dysfunction, right ventricle dysfunction, and myocardial work indices. Results: A total of 48 patients were enrolled in the study; 21 were randomly assigned to the ivabradine group and 27 to the control group. Reduced GLS was detected 2.9 times less often in patients receiving ivabradine than in the control group, but this change was non-significant (OR [95% CI] = 2.9 [0.544, 16.274], p = 0.208). The incidence of troponin I elevation was four times higher in the control group (OR [95% CI] = 4.0 [1.136, 14.085], p = 0.031). There was no significant change in NT-proBNP between groups, but the increase in NT-proBNP was almost 12% higher in the control group (OR [95% CI] = 1.117 [0.347, 3.594], p = 0.853). LV diastolic dysfunction was found 2.7 times more frequently in the controls (OR [95% CI] = 2.71 [0.49, 15.10], p = 0.254). Patients in the ivabradine group were less likely to be diagnosed with mild asymptomatic CTRCD during the study (p = 0.045). No differences in right ventricle function were noted. A significant difference was found between the groups in global constructive work and global work index at six months in favour of the ivabradine group (p = 0.014 and p = 0.025). Ivabradine had no adverse effects on intracardiac conduction, ventricular repolarization, or blood pressure. However, visual side effects (phosphenes) were reported in 14.3% of patients. Conclusions: Ivabradine is a safe, well-tolerated drug that has shown possible cardioprotective properties reducing the incidence of mild asymptomatic cancer-therapy-induced cardiac dysfunction, characterised by a new rise in troponin concentrations and diminished myocardial performance in anthracycline-treated women with breast cancer and increased heart rate. However, more extensive multicentre trials are needed to provide more robust evidence.