Anti-Ischemic Effects of Ivabradine, a Selective Heart Rate-Reducing Agent, in Exercise-Induced Myocardial Ischemia in Pigs

Ivabradine ameliorates cardiomyopathy progression in a Duchenne muscular dystrophy model rat

Duchenne muscular dystrophy (DMD) is an X-linked recessive myopathy caused by dystrophin mutations. Inevitable progressive cardiomyopathy is a current leading cause of premature death although respiratory management has improved the prognosis of patients with DMD. Recent evidence shows that reducing the heart rate is expected as one of the promising strategies for heart failure treatment, but administering a sufficient dose of β-blocker for patients with DMD with tachycardia is difficult because of their low blood pressure (BP). Thus, this study aimed to clarify the role of ivabradine, which suppresses cardiac sinus node pacemakers without decreasing BP, in ameliorating cardiomyopathy progression in a rat model with DMD. A trans-oral single ivabradine administration demonstrated a declined dose-dependent heart rate without any significant BP reduction. Trans-gastric repeated administrations of 5 mg/kg of ivabradine twice a day for 3 months showed ameliorated cardiomyopathy in DMD rats based on echocardiography and histopathological observations (left ventricular dysfunction, right ventricular dysfunction, and myocardial fibrosis) as compared with vehicle administration.Our finding indicates that ivabradine is expected as another treatment choice for patients with DMD having tachycardia.

Ivabradine protects rats against myocardial infarction through reinforcing autophagy via inhibiting PI3K/AKT/mTOR/p70S6K pathway

Ivabradine (Iva), a heart rate reducing agent that specifically inhibits the pacemaker I(f) ionic current, has been demonstrated to be cardioprotective in many cardiovascular diseases. Autophagy is an evolutionarily conserved metabolic process that regulates cardiac homeostasis. This study is aimed to explore whether autophagy is functionally involved in the cardioprotective effect of Iva in a rat model of myocardial infarction (MI). We observed that Iva treatment (po, 10 mg/kg/day) showed significant recovery on the hemodynamics parameters in MI rats, including left ventricular systolic pressure, left ventricular end diastolic pressure, and maximal ascending/descending rate of left ventricular pressure. Also, Iva treatment dramatically decreased infarct size, inhibited myocardial apoptosis, and reduced the levels of pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 in MI rats. Moreover, Iva treatment enhanced autophagy and inhibited PI3K/AKT/mTOR/p70S6K pathway in MI rats. Simultaneously, we observed that autophagy enhancer rapamycin (ip, 10 mg/kg/day) showed similar cardioprotective effects with Iva. Furthermore, we observed that addition of autophagy inhibitor 3-methyladenine (ip, 10 mg/kg/day) counteracted the therapeutic effect of Iva, addressing that Iva attenuated post-MI cardiac injury by enhancing autophagy. In summary, these findings demonstrated that Iva attenuated MI in rats by enhancing autophagy, and PI3K/AKT/mTOR/p70S6K pathway might be involved in the process. Autophagy activation by Iva may be a potential therapeutic strategy for the treatment of MI.

Ivabradine for the Treatment of Cardiovascular Diseases

Higher heart rate (HR) is independently related to worse outcomes in various cardiac diseases, including hypertension, coronary artery disease, and heart failure (HF). HR is determined by the pacemaker activity of cells within the sinoatrial node. The hyperpolarization-activated cyclic nucleotide-gated (HCN) 4 channel, one of 4 HCN isoforms, generates the I_f current and plays an important role in the regulation of pacemaker activity in the sinoatrial node. Ivabradine is a novel and only available HCN inhibitor, which can reduce HR and has been approved for stable angina and chronic HF in many countries other than Japan. In this review, we summarize the current knowledge of the HCN4 channel and ivabradine, including the function of HCN4 in cardiac pacemaking, the mechanism of action of I_f inhibition by ivabradine, and the pharmacological and clinical effects of ivabradine in cardiac diseases as HF, coronary artery disease, and atrial fibrillation.

The Clinical Use of Ivabradine

The clinical use of ivabradine has and continues to evolve along channels that are predicated on its mechanism of action. It selectively inhibits the funny current (I_f) in sinoatrial nodal tissue, resulting in a decrease in the rate of diastolic depolarization and, consequently, the heart rate, a mechanism that is distinct from those of other negative chronotropic agents. Thus, it has been evaluated and is used in select patients with systolic heart failure and chronic stable angina without clinically significant adverse effects. Although not approved for other indications, ivabradine has also shown promise in the management of inappropriate sinus tachycardia. Here, the authors review the mechanism of action of ivabradine and salient studies that have led to its current clinical indications and use.

Ivabradine in Patients with Stable Coronary Artery Disease: A Rationale for Use in Addition to and Beyond Percutaneous Coronary Intervention

Heart rate is an established prognostic marker for longevity and is an important contributor in the pathophysiology of various cardiovascular diseases, including ischemic heart disease and heart failure. Most ischemic episodes are triggered by an increase in heart rate, which causes an imbalance between myocardial oxygen delivery and consumption. In addition, increased heart rate is a modifiable risk factor for chronic heart failure. Ivabradine, an inhibitor of I_f ion channels, is an approved second-line anti-ischemic drug for the treatment of angina. Ivabradine has been shown to decrease the risk of hospitalization in patients with chronic heart failure who were previously treated with β-blockers, renin-angiotensin system blockers or mineralocorticoid receptor antagonists. This review describes the rationale for the pathophysiological and clinical use of ivabradine as an anti-ischemic agent in patients with stable coronary disease and highlights its benefits and drawbacks compared with other first- and second-line anti-anginal drugs. The review also highlights the role of ivabradine as a treatment for patients with high-risk coronary artery disease in whom first-line anti-anginal drugs are insufficient or inadequate and percutaneous coronary intervention is contraindicated or revascularization is incomplete or unsuitable.

Reversing dobutamine-induced tachycardia using ivabradine increases stroke volume with neutral effect on cardiac energetics in left ventricular post-ischaemia dysfunction

AIM

Compensatory tachycardia can potentially be deleterious in acute heart failure. In this study, we tested a therapeutic strategy of combined inotropic support (dobutamine) and selective heart rate (HR) reduction through administration of ivabradine.

METHODS

In an open-chest pig model (n = 12) with left ventricular (LV) post-ischaemia dysfunction, cardiac function was assessed by LV pressure catheter and sonometric crystals. Coronary flow and blood samples from the coronary sinus were used to measure myocardial oxygen consumption (MVO2 ). LV energetics was assessed by comparing MVO2 with cardiac work at a wide range of workloads.

RESULTS

In the post-ischaemia heart, dobutamine (5 μg kg(-1)  min(-1) ) increased cardiac output (CO) by increasing HR from 102 ± 21 to 131 ± 16 bpm (beats per min; P < 0.05). Adding ivabradine (0.5 mg kg(-1) ) slowed HR back to 100 ± 9 bpm and increased stroke volume from 30 ± 5 to 36 ± 5 mL (P < 0.05) by prolonging diastolic filling time and increasing end-diastolic dimensions. Adding ivabradine had no adverse effects on CO, mean arterial pressure and cardiac efficiency. Similar findings on efficiency and LV function were also seen using an ex vivo working mouse heart protocol.

CONCLUSIONS

A combined infusion of dobutamine and ivabradine had a neutral effect on post-ischaemia LV efficiency and increased left ventricular output without an increase in HR.

The effects of ivabradine on left atrial electromechanical function in patients with systolic heart failure

AIM

Heart rate (HR) reduction with ivabradine improves left ventricle filling by the prolongation of the diastolic time and increases stroke volume. But, it remains unclear what ivabradine's effect is on atrial conduction time and atrial mechanical functions. The aim of our study was to evaluate in stable outpatients with systolic heart failure (HF) the 3 months effect of ivabradine on atrial conduction time and mechanical functions.

METHOD

We evaluated prospectively 43 (31 males, 12 females) patients with HF. Before and after treatment, all patients were evaluated by transthoracic M mode, two dimensional (2D), pulsed-wave (PW), continuous wave (CW), color flow and tissue Doppler imaging (TDI), and LA volumes were obtained apical four-chamber views by a disc's method. LA maximum volume (Vmax) at the end-systolic phase, LA minimum volume (Vmin) at the end-diastolic phase, and LA volume before atrial systole (Vp) were evaluated. The LA function parameters were calculated as follows: LA passive emptying volume = Vmax - Vp; LA passive emptying fraction = [(Vmax - Vp)/Vmax] × 100%, LA active emptying volume = Vp - Vmin; LA active emptying fraction = [(Vp - Vmin)/Vp] × 100%.

RESULTS

Thirty men and 13 women with mean ± SD age of 63.9 ± 10.1 years were included in this study. Resting heart rate was significantly reduced after ivabradine treatment. There were no significantly difference in LVEF, and E/A before and after ivabradine treatment. LA diameter and Vmin were similar before and after ivabradine treatment (p = 0.793 and p = 0.284). However, Vmax and Vp were significantly decreased after ivabradine treatment (p = 0.040 and p = 0.012). Moreover, LA active emptying volume and LA active emptying fraction were significantly decreased after ivabradine treatment (p = 0.030 and p = 0.008). The PA lateral, septal, and tricuspid durations were significantly reduced after ivabradine treatment (p < 0.001, p < 0.001, and p = 0.002, respectively). Interatrial electromechanical delay and right intra-atrial electromechanical delay were significantly decreased after ivabradine treatment (33.7 ± 12.7 vs 26.2 ± 10.1, p = 0.001; and 14.1 ± 6.1 vs 9.2 ± 6.8, p < 0.001).

CONCLUSIONS

The present study demonstrated that adding ivabradine to the standard therapy reduced HR and improves significantly LA electrical and mechanical functions in systolic HF patients.

Ivabradine: A Unique and Intriguing Medication for Treating Cardiovascular Disease

There has been much research linking elevated resting heart rate to cardiovascular morbidity and mortality. Based on these findings, a lower resting heart rate would be of theoretical benefit in patients with cardiovascular disease. From a pathophysiologic perspective, a lower resting heart rate would be of particular benefit in patients with ischemic heart disease and/or heart failure. Although β-blockers and nondihydropyridine calcium channel blockers are effective at lowering heart rate, they have many other pharmacologic effects that may not be desirable in some patients, such as negative inotropy. Ivabradine is a drug designed to lower heart rate without any other demonstrable pharmacologic effects; in other words, a pure heart rate-lowering drug. It functions by blocking the hyperpolarization-activated cyclic nucleotide gated channels (f-channels) specific for the sinoatrial node and disrupting If ion current flow. This effectively prolongs diastolic depolarization and slows firing in the sinoatrial node, which lowers heart rate. The effects of ivabradine are most pronounced at higher heart rates (use-dependence), which is important in minimizing the development of symptomatic bradycardia. Clinical trials have demonstrated ivabradine to be an effective antianginal drug both alone and in combination with β-blocker therapy, although it has not been shown to produce a demonstrable effect on reducing major adverse cardiovascular events. In patients with heart failure, ivabradine has demonstrated many hemodynamic benefits, but its effect on clinical outcomes have been mixed and dependent on baseline heart rate, ie, the drug may be of benefit with higher baseline heart rates, but detrimental with low baseline heart rates. The adverse effects of ivabradine are not uncommon, but are rarely severe and include visual disturbances, bradycardia, and atrial fibrillation. Although ivabradine is a very interesting new agent, its variable benefits in large-scale clinical trials leave its exact place in therapy still somewhat nebulous. Unanswered questions include which patient populations would benefit most from this drug, and which concomitant medications would produce the best clinical outcomes when used with ivabradine.

Pleiotropic, heart rate-independent cardioprotection by ivabradine

BACKGROUND AND PURPOSE

In pigs, ivabradine reduces infarct size even when given only at reperfusion and in the absence of heart rate reduction. The mechanism of this non-heart rate-related cardioprotection is unknown. Hence, in the present study we assessed the pleiotropic action of ivabradine in more detail.

EXPERIMENTAL APPROACH

Anaesthetized mice were pretreated with ivabradine (1.7 mg · kg(-1) i.v.) or placebo (control) before a cycle of coronary occlusion/reperfusion (30/120 min ± left atrial pacing). Infarct size was determined. Isolated ventricular cardiomyocytes were exposed to simulated ischaemia/reperfusion (60/5 min) in the absence and presence of ivabradine, viability was then quantified and intra- and extracellular reactive oxygen species (ROS) formation was detected. Mitochondria were isolated from mouse hearts and exposed to simulated ischaemia/reperfusion (6/3 min) in glutamate/malate- and ADP-containing buffer in the absence and presence of ivabradine respectively. Mitochondrial respiration, extramitochondrial ROS, mitochondrial ATP production and calcium retention capacity (CRC) were assessed.

KEY RESULTS

Ivabradine decreased infarct size even with atrial pacing. Cardiomyocyte viability after simulated ischaemia/reperfusion was better preserved with ivabradine, the accumulation of intra- and extracellular ROS decreased in parallel. Mitochondrial complex I respiration was not different without/with ivabradine, but ivabradine significantly inhibited the accumulation of extramitochondrial ROS, increased mitochondrial ATP production and increased CRC.

CONCLUSION AND IMPLICATIONS

Ivabradine reduces infarct size independently of a reduction in heart rate and improves ventricular cardiomyocyte viability, possibly by reducing mitochondrial ROS formation, increasing ATP production and CRC.

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.

Rationale, design, and baseline characteristics of the Study assessInG the morbidity-mortality beNefits of the If inhibitor ivabradine in patients with coronarY artery disease (SIGNIFY trial): a randomized, double-blind, placebo-controlled trial of ivabradine in patients with stable coronary artery disease without clinical heart failure

BACKGROUND

Elevated heart rate in stable coronary artery disease (CAD) is associated with worse outcomes, particularly increased risk of myocardial infarction. Heart rate reduction with the If inhibitor ivabradine confers symptomatic benefits in angina pectoris and reduces coronary events in patients with stable CAD and left ventricular (LV) systolic dysfunction, with a resting heart rate of ≥70 beats/min. The SIGNIFY trial is testing the hypothesis that heart rate reduction using ivabradine reduces mortality and cardiovascular events in patients with stable CAD, but without clinical heart failure.

METHODS

The SIGNIFY trial is a randomized, double-blind, parallel-group, placebo-controlled, event-driven study in patients with stable CAD (1,139 centers, 51 countries). Participants are 55 years or older, with stable CAD and an LV ejection fraction >40%, in sinus rhythm, with a baseline resting heart rate of ≥70 beats/min, and with at least 1 additional cardiovascular risk factor. At inclusion, patients receive ivabradine 7.5 mg twice a day or matching placebo, which is adjusted at every visit to a heart rate target of 60 beats/min. Participants should receive the best possible background treatment for stable CAD. The primary end point is a composite of cardiovascular death or nonfatal myocardial infarction.

RESULTS

Recruitment lasted from October 2009 to April 2012. The SIGNIFY trial has recruited 19,102 patients (age 65.0 ± 7.2 years, resting heart rate 77.2 ± 7.0 beats/min, 72% male) with no evidence for LV dysfunction (ejection fraction 56.5% ± 8.6%).

CONCLUSION

The SIGNIFY trial will shed further light on the role of heart rate lowering with ivabradine in patients with stable CAD without clinical heart failure. The study is expected to end in 2014.

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.

Heart rate: a forgotten link in coronary artery disease?

A considerable body of evidence indicates that elevated resting heart rate is an independent, modifiable risk factor for cardiovascular events and mortality in patients with coronary artery disease. Elevated heart rate can produce adverse effects in several ways. Firstly, myocardial oxygen consumption is increased at high heart rates, but the time available for myocardial perfusion is reduced, increasing the likelihood of myocardial ischemia. Secondly, exposure of the large elastic arteries to cyclical stretch is increased at high heart rates. This effect can increase the rate at which components of the arterial wall deteriorate. Elastin fibers, which have an extremely slow rate of turnover in adult life, might be particularly vulnerable. Thirdly, elevated heart rate can predispose the myocardium to arrhythmias, and favor the development and progression of coronary atherosclerosis, by adversely affecting the balance between systolic and diastolic flow. Comparisons of the effects of the specific heart-rate-lowering drug ivabradine with those of β-blockers could help clarify the pathophysiological effects of elevated heart rate. Effective heart rate control among patients with coronary artery disease is uncommon in clinical practice, representing a missed therapeutic opportunity.

Heart rate reduction with ivabradine prevents the global phenotype of left ventricular remodeling

The aim of this study was to investigate the effect of chronic heart rate (HR) reduction with the hyperpolarization-activated current inhibitor ivabradine on the global phenotype of left ventricular (LV) remodeling in a ligated rat model. Seven days after coronary artery ligation, Wistar rats received ivabradine (10 mg·kg−1·day−1 administered in drinking water) [myocardial infarction + ivabradine (MI+IVA), n = 22] or vehicle only (drinking water) (MI, n = 20) for 90 days. A sham group ( n = 20) was included for model validation. MI+IVA rats had 12% lower HR ( P < 0.01), improved LV volumes, 15% higher LV ejection fraction (LVEF, P < 0.01) than MI rats, and 33% reductions in both plasma atrial natriuretic peptide (ANP, P = 0.052) and cardiac hydroxyproline. Using patch-clamp, action potential duration was reduced and transient outward current density increased ( P < 0.05). Cardiac energy metabolism was also improved (+33% creatine phosphate, P < 0.001; +15% ATP; and +9% energy charge, P < 0.05). Significant correlations were found between HR and parameters of cardiac metabolism, ANP, and LVEF (all P < 0.05). The HR-reducing properties of ivabradine prevent changes in the global phenotype of LV remodeling in the rat, optimize energy consumption, and avoid electrophysiological and structural remodeling.

I(f) inhibition in cardiovascular diseases

Heart rate (HR) is determined by the pacemaker activity of cells from the sinoatrial node (SAN), located in the right atria. Spontaneous electrical activity of SAN cells results from a diastolic depolarization (DD). Despite controversy in the exact contribution of funny current (I(f)) in pacemaking, it is a major contributor of DD. I(f) is an inward Na(+)/K(+) current, activated upon hyperpolarization and directly modulated by cyclic adenosine monophosphate. The f-proteins are hyperpolarization-activated cyclic nucleotide-gated channels, HCN4 being the main isoform of SAN. Ivabradine (IVA) decreases DD and inhibits I(f) in a use-dependent manner. Under normal conditions IVA selectively reduces HR and limits exercise-induced tachycardia, in animals and young volunteers. Reduction in HR with IVA both decreases myocardial oxygen consumption and increases its supply due to prolongation of diastolic perfusion time. In animal models and in human with coronary artery disease (CAD), IVA has anti-anginal and anti-ischemic efficacy, equipotent to classical treatments, β-blockers, or calcium channel blockers. As expected from its selectivity for I(f), the drug is safe and well tolerated with minor visual side effects. As a consequence, IVA is the first inhibitor of I(f) approved for the treatment of stable angina. Available clinical data indicate that IVA could improve the management of stable angina in all patients including those treated with β-blockers. As chronic elevation of resting HR is an independent predictor of mortality, pure HR reduction by inhibition of I(f) could, beyond the control of anti-anginal symptoms, improve the prognosis of CAD and heart failure; this therapeutic potential is currently under evaluation with IVA.

Elevated heart rate in cardiovascular diseases: a target for treatment?

Heart rate is a major determinant of myocardial oxygen consumption and of cardiac work, and thus reduction of heart rate may represent an important strategy for the treatment of patients with a wide range of cardiac disorders. In addition, several experimental lines of research point to high heart rate as an important risk factor for atherosclerosis and, thus, pharmacologic heart rate reduction could prevent or retard the development of atherosclerotic plaques and increase survival. Today, in patients with acute or chronic coronary syndromes or with congestive heart failure, reducing heart rate is a generally accepted treatment modality. Up to now, no human study has been performed to demonstrate the efficacy and the risk-benefit ratio of cardiac slowing in patients without cardiac disorders. However, recent retrospective analyses of the INternational VErapamil-SR/trandolapril STudy and the Paris Prospective Study 1 provided promising results. Treatment of high heart rate in healthy subjects appears to be premature, but in clinical conditions such as hypertension or diabetes, the reduction of elevated heart rate appears a desirable additional goal of therapy.

Niflumic acid alters gating of HCN2 pacemaker channels by interaction with the outer region of S4 voltage sensing domains

Niflumic acid, 2-[[3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid (NFA), is a nonsteroidal anti-inflammatory drug that also blocks or modifies the gating of many ion channels. Here, we investigated the effects of NFA on hyperpolarization-activated cyclic nucleotide-gated cation (HCN) pacemaker channels expressed in X. laevis oocytes using site-directed mutagenesis and the two-electrode voltage-clamp technique. Extracellular NFA acted rapidly and caused a slowing of activation and deactivation and a hyperpolarizing shift in the voltage dependence of HCN2 channel activation (-24.5 +/- 1.2 mV at 1 mM). Slowed channel gating and reduction of current magnitude was marked in oocytes treated with NFA, while clamped at 0 mV but minimal in oocytes clamped at -100 mV, indicating the drug preferentially interacts with channels in the closed state. NFA at 0.1 to 3 mM shifted the half-point for channel activation in a concentration-dependent manner, with an EC(50) of 0.54 +/- 0.068 mM and a predicted maximum shift of -38 mV. NFA at 1 mM also reduced maximum HCN2 conductance by approximately 20%, presumably by direct block of the pore. The rapid onset and state-dependence of NFA-induced changes in channel gating suggests an interaction with the extracellular region of the S4 transmembrane helix, the primary voltage-sensing domain of HCN2. Neutralization (by mutation to Gln) of any three of the outer four basic charged residues in S4, but not single mutations, abrogated the NFA-induced shift in channel activation. We conclude that NFA alters HCN2 gating by interacting with the extracellular end of the S4 voltage sensor domains.

Ivabradine induces an increase in ventricular fibrillation threshold during acute myocardial ischemia: an experimental study

BACKGROUND

Tachycardia often facilitates ischemic ventricular fibrillation (VF).

OBJECTIVE

This study assessed the impact of ivabradine (IVA), a selective inhibitor of the cardiac pacemaker If current, on ventricular fibrillation threshold (VFT) during acute myocardial ischemia.

METHODS

The experiments were conducted on a total of 54 domestic pigs. Myocardial ischemia was induced in anesthetized pigs by total 1-minute coronary occlusion at baseline and then on 2 occasions after intravenous administration of saline or 0.5 mg/kg of IVA. VF was triggered by electrical stimuli of increasing intensity at a fixed rate. Heart rate (HR), VFT, monophasic action potential duration, and peak of the time derivative of left ventricular pressure (LV dP/dt max) were monitored on each occasion. The activity of mitochondrial succinodehydrogenase was measured on heart sections.

RESULTS

Compared with controls, IVA induced a 31% reduction in HR, a 2.9-fold increase in VFT, and prevented ischemia-induced monophasic action potential duration shortening (+1 +/- 12 vs. -14 +/- 11 milliseconds) without affecting peak LV dP/dt. This beneficial effect on VFT was mainly due to HR reduction and was accompanied by a significant reduction in the hypoxic area (26% +/- 1% vs. 38% +/- 1%, P < 0.0001).

CONCLUSION

HR reduction and the decrease in myocardial damage induced by IVA protected against primary ischemic VF without altering myocardial contractility.

Review of the If selective channel inhibitor ivabradine in the treatment of chronic stable angina

Coronary heart disease is the major cause of morbidity and mortality in industrialized countries, and its prevalence is predicted to grow as the population ages. Current drugs for chronic stable angina (such as beta-blockers, calcium-channel blockers, long- and short-acting nitrates, and potassium-channel activators) are often effective, either as monotherapy or in combination, but side effects and contraindications may limit their use. The "I(f)" (for "funny") channel, discovered in 1979, is expressed mainly in the membrane of pacemaker cells present in the sinus node, the atrioventricular node, the ventricular conduction pathways, and ventricular myocytes. By determining the slope of diastolic depolarization, which in turn controls action potential frequency, it is a key determinant of heart rate and so provides a new therapeutic target for controlling angina symptoms. A new antiangina drug, ivabradine, has been developed and licensed for clinical use. It exclusively reduces the heart rate by selectively blocking the I(f) channel of the sino-atrial node. As clinical trials have shown it to be remarkably well-tolerated, ivabradine offers an alternative for patients who cannot take, or are intolerant of, beta blockade. This review provides an insight into this new agent, its historical background, mechanism of action, and pathophysiologic basis, and provides up-to-date evidence-based information on its optimum use in stable angina.

Heart rate in the pathophysiology of coronary blood flow and myocardial ischaemia: benefit from selective bradycardic agents

Starting out from a brief description of the determinants of coronary blood flow (perfusion, pressure, extravascular compression, autoregulation, metabolic regulation, endothelium-mediated regulation and neurohumoral regulation) the present review highlights the overwhelming importance of metabolic regulation such that coronary blood flow is increased at increased heart rate under physiological circumstances and the overwhelming importance of extravascular compression such that coronary blood flow is decreased at increased heart rate through reduction of diastolic duration in the presence of severe coronary stenoses. The review goes on to characterize the role of heart rate in the redistribution of regional myocardial blood flow between a normal coronary vascular tree with preserved autoregulation and a poststenotic vasculature with exhausted coronary reserve. When flow is normalized by heart rate, there is a consistent close relationship of regional myocardial blood flow and contractile function for each single cardiac cycle no matter whether or not there is a coronary stenosis and what the actual blood flow is. beta-Blockade improves both flow and function along this relationship. When the heart rate reduction associated with beta-blockade is prevented by pacing, alpha-adrenergic coronary vasoconstriction is unmasked and both flow and function are deteriorated. Selective heart rate reduction, however, improves both flow and function without any residual negative effect such as unmasked alpha-adrenergic coronary vasoconstriction or negative inotropic action.

Selective and specific I(f) inhibition: new perspectives for the treatment of stable angina

Ivabradine is the first selective and specific inhibitor of the I(f) current (the cardiac pacemaker 'funny' current), and provides pure heart rate reduction without altering myocardial contractility, the cardiac conduction system or coronary vascular resistance. Clinical proof of the antianginal efficacy and tolerability of ivabradine comes from the largest clinical development programme that has ever been performed in stable angina, involving more than 5000 patients. Ivabradine was shown to be as effective as well-established reference antianginal drugs, such as beta-blockers and calcium antagonists. It is well tolerated and is free of the most commonly observed side effects of currently prescribed antianginal drugs. It offers clear therapeutic benefits for a whole range of patients with stable angina, including those with contraindications or intolerance to beta-blockers.

The heart rate-lowering agent ivabradine inhibits the pacemaker current I(f) in human atrial myocytes

INTRODUCTION

It has been speculated that pacemaker current (I(f)) in human atria could play a role in causing ectopic atrial automaticity. Ivabradine is a novel selective and specific I(f) inhibitor in the sinus node that reduces heart rate without any negative inotropic effect. The aim of the study was to explore possible effects of ivabradine on I(f) in atrial myocytes.

METHODS AND RESULTS

Using patch-clamp technique, we studied effects of ivabradine on I(f) present in atrial myocytes isolated from human right appendages of patients undergoing cardiac surgery. The identification of HCN isoforms was obtained by means of multiplex single-cell RT-PCR. Ivabradine induced a marked concentration and use-dependent I(f) inhibition with an IC50 at steady state of 2.9 microM. Time constant of block development (Tau(on)) decreases with the increase in the ivabradine concentration. Use-dependent inhibition induced by ivabradine (3 microM) was not modified in the presence of cAMP (10 microM) in the pipette solution. Multiplex single-cell RT-PCR indicates that the major HCN gene subtype detected in atria was HCN2. HCN4 is detected weakly and HCN1 is not significantly detected.

CONCLUSIONS

Ivabradine inhibits I(f) current in the nonpacemaker cell with characteristics similar to those described previously in rabbit sinus node cells, but revealed a lesser sensitivity for I(f) recorded in human atrial cell than hHCN4 subunits considered as the major contributors to native f-channels in human sinoatrial node. A potential protection of atrial arrhythmias by ivabradine is discussed.

Antianginal efficacy and safety of ivabradine compared with amlodipine in patients with stable effort angina pectoris: a 3-month randomised, double-blind, multicentre, noninferiority trial

BACKGROUND AND OBJECTIVE

Current medical therapies for the symptoms of angina pectoris aim to improve oxygen supply and reduce oxygen demand in the myocardium. Not all patients respond to current antianginal monotherapy, or even combination therapy, and a new class of antianginal drug that complements existing therapies would be useful. This study was undertaken to compare the antianginal and anti-ischaemic effects of the novel heart-rate-lowering agent ivabradine and of the calcium channel antagonist amlodipine.

PATIENTS AND METHODS

Patients with a >/=3-month history of chronic, stable effort-induced angina were randomised to receive ivabradine 7.5mg (n = 400) or 10mg (n = 391) twice daily or amlodipine 10mg once daily (n = 404) for a 3-month, double-blind period. Bicycle exercise tolerance tests were performed at baseline and monthly intervals. The primary efficacy criterion was the change from baseline in total exercise duration after 3 months of treatment. Secondary efficacy criteria included changes in time to angina onset and time to 1mm ST-segment depression, rate-pressure product at trough drug activity, as well as short-acting nitrate use and anginal attack frequency (as recorded in patient diaries).

RESULTS

At 3 months, total exercise duration was improved by 27.6 +/- 91.7, 21.7 +/- 94.5 and 31.2 +/- 92.0 seconds with ivabradine 7.5 and 10mg and amlodipine, respectively, both ivabradine groups were comparable to amlodipine (p-value for noninferiority < 0.001). Similar results were observed for time to angina onset and time to 1mm ST-segment depression. Heart rate decreased significantly by 11-13 beats/min at rest and by 12-15 beats/min at peak of exercise with ivabradine but not amlodipine, and rate-pressure product decreased more with ivabradine than amlodipine (p-value vs amlodipine <0.001, at rest and at peak of exercise). Anginal attack frequency and short-acting nitrate use decreased substantially in all treatment groups with no significant difference between treatment groups. The most frequent adverse events were visual symptoms and sinus bradycardia with ivabradine (0.8% and 0.4% withdrawals, respectively) and peripheral oedema with amlodipine (1.5% withdrawals).

CONCLUSIONS

In patients with stable angina, ivabradine has comparable efficacy to amlodipine in improving exercise tolerance, a superior effect on the reduction of rate-pressure product (a surrogate marker of myocardial oxygen consumption) and similar safety.

Antianginal Efficacy and Safety of Ivabradine Compared with Amlodipine in Patients with Stable Effort Angina Pectoris

BACKGROUND AND OBJECTIVE

Current medical therapies for the symptoms of angina pectoris aim to improve oxygen supply and reduce oxygen demand in the myocardium. Not all patients respond to current antianginal monotherapy, or even combination therapy, and a new class of antianginal drug that complements existing therapies would be useful. This study was undertaken to compare the antianginal and anti-ischaemic effects of the novel heart-rate-lowering agent ivabradine and of the calcium channel antagonist amlodipine.

PATIENTS AND METHODS

Patients with a >/=3-month history of chronic, stable effort-induced angina were randomised to receive ivabradine 7.5mg (n = 400) or 10mg (n = 391) twice daily or amlodipine 10mg once daily (n = 404) for a 3-month, double-blind period. Bicycle exercise tolerance tests were performed at baseline and monthly intervals. The primary efficacy criterion was the change from baseline in total exercise duration after 3 months of treatment. Secondary efficacy criteria included changes in time to angina onset and time to 1mm ST-segment depression, rate-pressure product at trough drug activity, as well as short-acting nitrate use and anginal attack frequency (as recorded in patient diaries).

RESULTS

At 3 months, total exercise duration was improved by 27.6 +/- 91.7, 21.7 +/- 94.5 and 31.2 +/- 92.0 seconds with ivabradine 7.5 and 10mg and amlodipine, respectively, both ivabradine groups were comparable to amlodipine (p-value for noninferiority < 0.001). Similar results were observed for time to angina onset and time to 1mm ST-segment depression. Heart rate decreased significantly by 11-13 beats/min at rest and by 12-15 beats/min at peak of exercise with ivabradine but not amlodipine, and rate-pressure product decreased more with ivabradine than amlodipine (p-value vs amlodipine <0.001, at rest and at peak of exercise). Anginal attack frequency and short-acting nitrate use decreased substantially in all treatment groups with no significant difference between treatment groups. The most frequent adverse events were visual symptoms and sinus bradycardia with ivabradine (0.8% and 0.4% withdrawals, respectively) and peripheral oedema with amlodipine (1.5% withdrawals).

CONCLUSIONS

In patients with stable angina, ivabradine has comparable efficacy to amlodipine in improving exercise tolerance, a superior effect on the reduction of rate-pressure product (a surrogate marker of myocardial oxygen consumption) and similar safety.

Heart rate reduction by inhibition of If or by beta-blockade has different effects on postsystolic wall thickening

BACKGROUND AND PURPOSE

Postsystolic wall thickening (PSWT) is part of thickening that occurs after end-systole and represents wasted effort as it does not contribute to ejection. The effects of antianginal drugs on PSWT remain to be established. We compared the effects on PSWT of two agents that reduce heart rate, the beta-blocker atenolol and the selective inhibitor of If current, ivabradine.

EXPERIMENTAL APPROACH

Six dogs were prepared to measure wall thickening by sonomicrometry in the conscious state, at rest and during exercise, after administration of saline, atenolol (1 mg.kg-1) or ivabradine (1 mg.kg-1).

KEY RESULTS

Atenolol and ivabradine similarly reduced heart rate vs saline at rest (about 10-20%) and during exercise (about 30%). Atenolol but not ivabradine decreased dP/dtmax. Concomitantly, PSWT increased with atenolol vs saline at rest (0.35+/-0.07 vs 0.21+/-0.03 mm, respectively) and during exercise (0.30+/-0.04 vs 0.15+/-0.04 mm, respectively). In contrast, ivabradine did not alter PSWT. Importantly, atenolol but not ivabradine increased the ratio of postsystolic to systolic wall thickening by 80+/-23%. This enhanced thickening during diastole with atenolol was accompanied by impeded isovolumic relaxation of the left ventricle, as illustrated by the significant correlation between the isovolumic relaxation time constant tau and the postsystolic to systolic wall thickening ratio. None of these effects of atenolol were abolished when heart rate was controlled with atrial pacing.

CONCLUSION AND IMPLICATIONS

For a similar heart rate reduction at rest and during exercise, ivabradine, but not atenolol, did not alter PSWT and preserved the part of thickening contributing to ejection.

Use-dependent inhibition of hHCN4 by ivabradine and relationship with reduction in pacemaker activity

BACKGROUND AND PURPOSE

Ivabradine, a specific and use-dependent I(f) inhibitor, exerts anti-ischaemic activity purely by reducing heart rate. The aim of this work was to characterize its effect on the predominant HCN channel isoform expressed in human sino-atrial nodes (hSAN), to determine its kinetics in HCN channels from multicellular preparations and rate-dependency of its action.

EXPERIMENTAL APPROACH

RT-PCR analysis of the four HCN channel isoforms was carried out on RNAs from hSAN. Patch-clamp and intracellular recordings were obtained from CHO cells stably expressing hHCN4 and isolated SAN, respectively. Beating rate of rat isolated atria was followed using a transducer.

KEY RESULTS

hHCN4 mRNAs were predominant in hSAN. Ivabradine induced a time-dependent inhibition of hHCN4 with an IC(50) of 0.5 microM. In rabbit SAN, ivabradine progressively reduced the frequency of action potentials: by 10% after 3 h at 0.1 microM, by 14% after 2 h at 0.3 microM and by 17% after 1.5 h at 1 microM. After 3h, ivabradine reduced the beating rate of rat right atria with an IC(30) of 0.2 microM. The onset of action of ivabradine was use-dependent rather than time-dependent with slower effects than caesium, an extracellular I (f) blocker. Ivabradine 3 microM decreased the frequency of action potentials in SAN from guinea-pig, rabbit and pig by 33%, 21% and 15% at 40 min, respectively.

CONCLUSIONS AND IMPLICATIONS

The use-dependent inhibition of hHCN4 current by ivabradine probably contributes to its slow developing effect in isolated SAN and right atria and to its increased effectiveness in species with rapid SAN activity.

Comparative effects of ivabradine, a selective heart rate-lowering agent, and propranolol on systemic and cardiac haemodynamics at rest and during exercise

AIM

To compare in humans the effects of ivabradine and propranolol on cardiac and systemic haemodynamics at rest, during tilt and exercise.

METHODS

Nine healthy volunteers randomly received single oral doses of ivabradine (Iva, 30 mg), propranolol (Propra, 40 mg) or placebo (Plac) during a double-blind cross-over study. Doses were selected to be equipotent in heart rate (HR) reduction. HR, systolic and diastolic blood pressure (SBP, DBP), cardiac index (CI, bioimpedance), rate pressure product (RPP), plasma epinephrine (E) and norepinephrine (NE), were measured at rest at baseline, before and after two tilt and exercise tests, started 2 and 5 h after drug intake. Heart rate variability (low to high frequency ratio LF/HF) was evaluated at rest and at 5 th minute of tilt.

RESULTS

At rest, HR and RPP decreased similarly with Iva and Propra (both P < 0.01). During tilt, HR increased less with Iva than Propra (P < 0.01), LF/HF decreased after Iva (P < 0.03), SBP and mean blood pressure decreased after Propra (both P < 0.01), RPP decreased similarly after Iva and Propra (both P < 0.01) and CI decreased to a greater extent with Propra than with Iva or Plac (both P < 0.04). During exercise, Iva and Propra similarly decreased HR (both P < 0.01) and RPP (P < 0.01).

CONCLUSIONS

These results demonstrate that for a similar decrease in HR at rest and during sympathetic stimulation, acute administration of ivabradine, a selective heart rate-lowering agent, decreased myocardial oxygen demand to the same extent as a reference beta-blocker, propranolol, but without evidence of depressant effect on cardiac function.

Characterization of hyperpolarization-activated current (Ih) in dorsal root ganglion neurons innervating rat urinary bladder

Afferent pathways innervating the urinary bladder consist of myelinated Adelta-fibers and unmyelinated C-fibers. Normal voiding is dependent on mechanoceptive Adelta-fiber bladder afferents that respond to bladder distention. However, the mechanisms for controlling the excitability of Adelta-fiber bladder afferents are not fully understood. We therefore used whole cell patch-clamp techniques to investigate the properties of hyperpolarization-activated, cyclic nucleotide-gated (HCN) currents (I(h)) in dorsal root ganglion (DRG) neurons innervating the urinary bladder of rats. The neurons were identified by axonal tracing with a fluorescent dye, Fast Blue, injected into the bladder wall. Hyperpolarizing voltage step pulses from -40 to -130 mV produced voltage- and time-dependent inward I(h) currents in bladder afferent neurons. The amplitude and current density of I(h) at a holding potential of -130 mV was significantly larger in medium-sized bladder afferent neurons (diameter: 37.8 +/- 0.3 microm), a small portion (19%) of which were sensitive to capsaicin (1 microM), than in uniformly capsaicin-sensitive small-sized (27.6 +/- 0.5 microm) bladder neurons. In medium-sized bladder neurons, a selective HCN channel inhibitor, ZD7288, dose-dependently inhibited I(h) currents. ZD7288 (10 microM) also increased the time constant of the slow depolarization phase of spike after-hyperpolarization from 91.8 to 233.0 ms. These results indicate that I(h) currents are predominantly expressed in medium-sized bladder afferent neurons innervating the bladder and that inhibition of I(h) currents delayed recovery from the spike after-hyperpolarization. Thus, it is assumed that I(h) currents could control excitability of mechanoceptive Adelta-fiber bladder afferent neurons, which are usually capsaicin-insensitive and larger in size than capsaicin-sensitive C-fiber bladder afferent neurons.

[The discovery of the selective If current inhibitor ivabradine (Procoralan): a new therapeutic approach to ischemic heart disease]

Coronary artery disease is still a major cause of morbidity and mortality in the industrialized countries and its prevalence is predicted to grow with the current aging of the population in these countries. In spite of the rapid pace of progress and increasing use of myocardial revascularization procedures, in particular percutaneous coronary interventions, the medical treatment of coronary artery disease has lost none of its relevance in the majority of patients, though conventional drugs have their limitations and the pharmacological approach to ischemic heart disease needs to be improved in terms of efficacy and tolerance to ensure better prevention of mortality and improvement in quality of life. Since increased heart rate plays a major role in coronary artery disease, not only as a trigger of most ischemic episodes, but also as an independent predictor of mortality, inhibition of the pacemaker If current in view of inducing a direct and selective decrease in heart rate represents an ideal conceptual target and an attractive therapeutic approach to coronary artery disease. The screening of original benzocycloalkane compounds at the Servier Research Institute resulted in the selection of ivabradine (Procoralan) for clinical development. Preclinical data showed that ivabradine inhibits the If current originating in the sinus node, induces a selective reduction in heart rate both at rest and during exercise, preserves myocardial contractility, atrioventricular conduction and ventricular repolarization and prevents exercise-induced myocardial ischemia as effectively as a b-blocker while offering better protection of regional myocardial contractility. These data were confirmed in humans, in particular the anti-ischemic efficacy of ivabradine, at least as effective as that of a b-blocker in patients with stable angina. Large ongoing clinical trials are seeking to assess the therapeutic value of ivabradine in ischemic heart failure and its potential for improving the prognosis of coronary artery disease by reducing mortality and the occurrence of major cardiovascular events.

Ivabradine -- the first selective sinus node I(f) channel inhibitor in the treatment of stable angina

Heart rate, a major determinant of angina in coronary disease, is also an important predictor of cardiovascular mortality. Lowering heart rate is therefore one of the most important therapeutic approaches in the treatment of stable angina pectoris. To date, beta-blockers and some calcium-channel antagonists reduce heart rate, but their use may be limited by adverse reactions or contraindications. Heart rate is determined by spontaneous electrical pacemaker activity in the sinoatrial node controlled by the I(f) current. Ivabradine is the first specific heart rate-lowering agent that has completed clinical development for stable angina pectoris. It is selective for the I(f) current, lowering heart rate at concentrations that do not affect other cardiac ionic currents. Specific heart-rate lowering with ivabradine reduces myocardial oxygen demand, simultaneously improving oxygen supply. Ivabradine has no negative inotropic or lusitropic effects, preserving ventricular contractility, and does not change any major electrophysiological parameters unrelated to heart rate. Randomised clinical studies in patients with stable angina show that ivabradine effectively reduces heart rate, improves exercise capacity and reduces the number of angina attacks. It has superior anti-anginal and anti-ischaemic activity to placebo and is non-inferior to atenolol and amlodipine. Ivabradine therefore offers a valuable approach to lowering heart rate exclusively and provides an attractive alternative to conventional treatment for a wide range of patients with confirmed stable angina.

Drug insight: If inhibitors as specific heart-rate-reducing agents

Heart rate is determined primarily by spontaneously repeating net inward current carried by sodium ions and potassium ions through hyperpolarization-activated cyclic-nucleotide-gated channels. Within the heart, these channels are found most abundantly in sinoatrial cardiomyocytes. The channels open in response to membrane hyperpolarization, modulated by local cAMP concentrations. They permit activation of the I(f) current, which can be blocked specifically by molecules characterized by linked benzazepinone and benzocyclobutane rings, and which are devoid of effects on cardiac conduction, inotropy or peripheral vascular tone. The resulting heart-rate reduction has been effective in angina prevention in clinical trials involving 4,000 patients, using the prototype I(f) inhibitor, ivabradine. No serious adverse events have been attributed to the treatment; the most prominent side-effect is dose-related, always reversible and often transient visual symptoms that seldom result in voluntary drug discontinuation.

Bradycardic and proarrhythmic properties of sinus node inhibitors

Sinus node inhibitors reduce the heart rate presumably by blocking the pacemaker current If in the cardiac conduction system. This pacemaker current is carried by four hyperpolarization-activated, cyclic nucleotide-gated cation (HCN) channels. We tested the potential subtype-specificity of the sinus node inhibitors cilobradine, ivabradine, and zatebradine using cloned HCN channels. All three substances blocked the slow inward current through human HCN1, HCN2, HCN3, and HCN4 channels. There was no subtype-specificity for the steady-state block, with mean IC50 values of 0.99, 2.25, and 1.96 microM for cilobradine, ivabradine, and zatebradine, respectively. Native If, recorded from mouse sinoatrial node cells, was slightly more efficiently blocked by cilobradine (IC50 value of 0.62 microM) than were the HCN currents. The block of I(f) in sinoatrial node cells resulted in slower and dysrhythmic spontaneous action potentials. The in vivo action of these blockers was analyzed using telemetric ECG recordings in mice. Each compound reduced the heart rate dose-dependently from 600 to 200 bpm with ED50 values of 1.2, 4.7, and 1.8 mg/kg for cilobradine, ivabradine, and zatebradine, respectively. beta-Adrenergic stimulation or forced physical activity only partly reversed this bradycardia. In addition to bradycardia, all three drugs induced increasing arrhythmia at concentrations greater than 5 mg/kg for cilobradine, greater than 10 mg/kg for zatebradine, or greater than 15 mg/kg for ivabradine. This dysrhythmic heart rate is characterized by periodic fluctuations of the duration between the T and P wave, resembling a form of sick sinus syndrome in humans. Hence, all available sinus node inhibitors possess an as-yet-unrecognized proarrhythmic potential.

Physiology and pharmacology of the cardiac pacemaker (“funny”) current

First described over a quarter of a century ago, the cardiac pacemaker "funny" (I(f)) current has been extensively characterized since, and its role in cardiac pacemaking has been thoroughly demonstrated. A similar current, termed I(h), was later described in different types of neurons, where it has a variety of functions and contributes to the control of cell excitability and plasticity. I(f) is an inward current activated by both voltage hyperpolarization and intracellular cAMP. In the heart, as well as generating spontaneous activity, f-channels mediate autonomic-dependent modulation of heart rate: beta-adrenergic stimulation accelerates, and vagal stimulation slows, cardiac rate by increasing and decreasing, respectively, the intracellular cAMP concentration and, consequently, the f-channel degree of activation. Four isoforms of hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels have been cloned more recently and shown to be the molecular correlates of native f-channels in the heart and h-channels in the brain. Individual HCN isoforms have kinetic and modulatory properties which differ quantitatively. A comparison of their biophysical properties with those of native pacemaker channels provides insight into the molecular basis of the pacemaker current properties and, together with immunolabelling and other detection techniques, gives information on the pattern of HCN isoform distribution in different tissues. Because of their relevance to cardiac pacemaker activity, f-channels are a natural target of drugs aimed at the pharmacological control of heart rate. Several agents developed for their ability to selectively reduce heart rate act by a specific inhibition of f-channel function; these substances have a potential for the treatment of diseases such as angina and heart failure. In the near future, devices based on the delivery of f-channels in situ, or of a cellular source of f-channels (biological pacemakers), will likely be developed for use in therapies for diseases of heart rhythm with the aim of replacing electronic pacemakers.

[Selection and pharmacological characterisation of Procoralan, a selective inhibitor of the pacemaker If current]

The screening of a series of benzocycloalkane derivatives led to the selection of Procoralan (ivabradine), the first selective inhibitor of the depolarizing If (funny) current of the sinus node, for the treament of myocardial ischaemia. In vitro, this compound reduces the spontaneous beating rate of isolated right rat atria and the firing rate of the action potential of rabbit sinus node preparations. This effect is explained by a reduction in the diastolic depolarisation slope of the action potential and underlies a selective inhibition of the pacemaker If current. In vivo, it induces a selective reduction in heart rate both at rest and during exercise. It preserves myocardial contractility, atrioventricular conduction and ventricular repolarisation duration. Ivabradine exerts a similar anti-ischaemic activity in exercise-induced myocardial ischaemia in pigs to that of a beta-blocker and, furthermore, it limits to a greater extent ischaemic myocardial contractile dysfunction.