Antianginal and antiischemic effects of ivabradine, an I(f) inhibitor, in stable angina: a randomized, double-blind, multicentered, placebo-controlled trial

Genesis and regulation of the heart automaticity

The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca(2+) signaling are necessary for the proper setting of the pacemaker mechanism. Here, we review the current knowledge on the cellular mechanisms underlying the generation and regulation of cardiac automaticity. We discuss evidence on the functional role of different families of ion channels in cardiac pacemaking and review recent results obtained on genetically engineered mouse strains displaying dysfunction in heart automaticity. Beside ion channels, intracellular Ca(2+) release has been indicated as an important mechanism for promoting automaticity at rest as well as for acceleration of the heart rate under sympathetic nerve input. The potential links between the activity of ion channels and Ca(2+) release will be discussed with the aim to propose an integrated framework of the mechanism of automaticity.

Effects of ivabradine on allograft function and exercise performance in heart transplant recipients with permanent sinus tachycardia

Aim of this retrospective analysis was to evaluate the effects of ivabradine given primarily as a heart rate-lowering agent on allograft function and cardiopulmonary performance in heart transplant recipients with permanent sinus tachycardia. Starting May 2006, 26 heart transplant recipients with permanent sinus tachycardia received ivabradine (5 mg bid). It was discontinued early in 3 patients (11.5%) due to adverse events. In the remaining 23 patients, resting heart rate (HR) was significantly lowered from 106.3 +/- 9.1 to 82.2 +/- 6.3 bpm after 3 weeks of treatment. The effect remained constant during the remaining treatment period, whereas resting blood pressure was not affected. After 12 weeks of ivabradine treatment, the corrected QT interval was significantly reduced into the range seen in normal individuals. Left ventricular (LV) end-diastolic posterior wall thickness, LV mass and LV mass index were also found to have decreased significantly. There was a trend to improvement of cardiopulmonary performance and LV ejection fraction, both of which did not reach statistical significance, however. It may be concluded that ivabradine successfully reduced the resting HR of heart transplant recipients with sinus tachycardia without negatively influencing the blood pressure. The definitive impact of ivabradine on LV mass regression and cardiopulmonary performance require further prospective, randomized and controlled trials.

Ivabradine: the evidence of its therapeutic impact in angina

INTRODUCTION

Stable angina pectoris (SAP) is a widely prevalent disease affecting 30 000 to 40 000 per million people in Europe and the US. SAP is associated with reductions in quality of life and ability to work, and increased use of healthcare resources. Ivabradine is a drug with a unique therapeutic target, the I(f) current of the sinus node, developed for the treatment of cardiovascular diseases including SAP. It has an exclusive heart rate reducing effect, without any negative effect on left ventricular function or coronary vasodilatation.

AIMS

The aim of this paper is to review the evidence concerning the use of ivabradine in the treatment of SAP.

EVIDENCE REVIEW

Ivabradine is an effective antianginal and antiischemic drug, not inferior to the beta blocker atenolol and the calcium channel antagonist (CCA) amlodipine. It decreases the frequency of angina attacks and increases the time to anginal symptoms during exercise. Because of its exclusive chronotropic effect, ivabradine is not associated with the typical adverse reactions associated with beta blockers or other antianginal drugs.

CLINICAL VALUE

Clinical evidence shows that ivabradine is a very good antiischemic and antianginal agent, being as effective as beta blockade and CCA therapy in controlling myocardial ischemia and symptoms of stable angina. Ongoing studies will determine the potential of ivabradine to improve morbidity and mortality in coronary artery disease and heart failure.

Absence of respiratory effects with ivabradine in patients with asthma

AIM

beta-Blockers are commonly prescribed for stable angina and are recommended as initial therapy. However, beta-blockers are contraindicated in patients with obstructive airway disease because of a risk of bronchoconstriction. Ivabradine is a specific heart rate-lowering agent that acts via I(f) pacemaker channels in the sinoatrial node with no beta-adrenoreceptor activity. Ivabradine has been recently approved for the treatment of stable angina. This study assessed the effects of repeated administration of ivabradine on lung function in patients with asthma.

METHODS

In this double-blind, placebo-controlled, crossover study, 20 subjects with asthma received either oral ivabradine 10 mg b.i.d. or placebo for 4.5 days. Forced expiratory volume in 1 s (FEV(1)) and peak expiratory flow rate (PEFR) were designated as the main outcome variable. Diary cards were used to monitor asthma symptoms on a five-point scale, rescue medication usage, and adverse events.

RESULTS

There were no significant differences in mean variation of FEV(1) (ivabradine P = 0.664; placebo P = 0.652) or PEFR (ivabradine P = 0.153; placebo P = 0.356) from baseline following administration of ivabradine. There was also no significant difference in maximum percent variation in FEV(1) or PEF between treatment groups (P = 0.994; FEV(1) and P = 0.704; PEF). On a similar note, there was no significant difference in asthma symptoms or rescue medication usage reported between the two groups. Adverse events were generally mild-to-moderate in intensity and no cardiovascular or serious adverse events were recorded.

CONCLUSIONS

This study confirms that ivabradine does not affect respiratory function or symptoms in patients with asthma and therefore represents a valuable therapeutic alternative to beta-blockers for treating patients with stable angina and asthma.

The funny current: cellular basis for the control of heart rate

The 'funny' (pacemaker, I(f)) current, first described almost 30 years ago in sinoatrial node (SAN) myocytes, is a mixed sodium/potassium inward current, activated on hyperpolarisation in the diastolic range of voltages. 'Funny' (f) channels are activated by intracellular cyclic adenosine monophosphate (cAMP) concentrations according to a mechanism mediating regulation of heart rate by the autonomic nervous system, as well as by voltage hyperpolarisation. Structural subunits of native f-channels are the hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels; of the four HCN isoforms known, HCN4 is the most highly expressed in SAN tissue. The I(f) current is a natural target in the search for drugs aimed specifically at affecting heart rate, given its function in pacemaking. Increased heart rate has a negative influence on clinical outcome in patients with cardiovascular disease, and indeed is also an established risk factor for cardiovascular and all-cause mortality in the general population. Clearly, therefore, independent reduction of heart rate, through inhibition of the I(f) current, appears to be a suitable therapeutic option for patients with ischaemic heart disease.beta-Adrenoceptor antagonists (beta-blockers) reduce intracellular cAMP levels, and a substantial part of their negative chronotropic effect is therefore attributable to a reduction of the I(f) current. However, neither beta-blockers nor Ca(2+) channel antagonists, both of which have traditionally been used to reduce myocardial ischaemia, are 'pure' heart rate-lowering drugs. These agents may, in fact, have adverse cardiovascular and noncardiovascular effects.Conversely, the novel heart rate-reducing agent ivabradine is a specific blocker of f-channels, hence a selective inhibitor of the pacemaker I(f) current in the SAN. Ivabradine slows heart rate by reducing the I(f) current-regulated steepness of the diastolic depolarisation in SAN myocytes, thereby increasing diastolic duration, without altering action potential duration or causing negative inotropy. As such, ivabradine is particularly useful in patients with chronic stable angina pectoris. Further clinical studies are ongoing to evaluate the efficacy of ivabradine in patients with coronary heart disease, left ventricular dysfunction and heart failure. This short article reviews the current state of knowledge of the properties of the 'funny' current in relation to exploitation of the I(f) function in pacemaking generation and modulation for the pharmacological control of heart rate.

Perspectives of I(f) inhibition by ivabradine in cardiology

High heart rates predict cardiovascular morbidity and mortality in the healthy population, in hypertensive patients, and in those with coronary heart disease (CHD) or heart failure. I(f) channel inhibition with ivabradine is an effective approach to reduce heart rate pharmacologically, with the prospect of preventing complications. The antianginal effects of heart rate-lowering with ivabradine have been shown to be similar to those with beta-adrenoceptor antagonists (beta-blockers) in patients with CHD. The BEAUTIfUL and SHIfT trials will provide evidence on whether I(f) channel inhibition with ivabradine is able to reduce mortality and morbidity in patients with CHD with impaired left ventricular function and heart failure. Future perspectives for additional study are potential roles of ivabradine in the treatment of hypertension and atherosclerosis, and their complications. Further clinical and mechanistic studies to clarify the pathophysiological background are needed to fully define the role of heart rate reduction in the broad spectrum of cardiovascular interventions.

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.

HCN212-channel biological pacemakers manifesting ventricular tachyarrhythmias are responsive to treatment with I(f) blockade

BACKGROUND

A potential concern about biological pacemakers is their possible malfunction, which might create ventricular tachycardias (VTs).

OBJECTIVE

The purpose of this study was to test our hypothesis that should VTs complicate implantation of HCN-channel-based biological pacemakers, they would be suppressed by inhibitors of the pacemaker current, I(f).

METHODS

We created a chimeric channel (HCN212) containing the N- and C-termini of mouse HCN2 and the transmembrane region of mouse HCN1 and implanted it in HEK293 cells. Forty-eight hours later, in whole-cell patch clamp recordings, mean steady state block induced by 3 microM ivabradine (IVB) showed HCN1 = HCN212 > HCN2 currents. The HCN212 adenoviral construct was then implanted into the canine left bundle branch in 11 dogs. Complete AV block was created via radiofrequency ablation, and a ventricular demand electronic pacemaker was implanted (VVI 45 bpm). Electrocardiogram, 24-hour Holter monitoring, and pacemaker log record check were performed for 11 days.

RESULTS

All dogs developed rapid VT (>120 bpm, maximum rate = 285 +/- 37 bpm) at 0.9 +/- 0.3 days after implantation that persisted through 5 +/- 1 days. IVB, 1 mg/kg over 5 minutes, was administered during rapid VT, and three dogs received a second dose 24 hours later. While VT terminated with IBV in all instances within 3.4 +/- 0.6 minutes, no effect of IVB on sinus rate was noted.

CONCLUSION

We conclude that (1) I(f)-associated tachyarrhythmias-if they occur with HCN-based biological pacemakers-can be controlled with I(f)-inhibiting drugs such as IVB; (2) in vitro, IVB appears to have a greater steady state inhibiting effect on HCN1 and HCN212 isoforms than on HCN4; and (3) VT originating from the HCN212 injection site is suppressed more readily than sinus rhythm. This suggests a selectivity of IVB at the concentration attained for ectopic over HCN4-based pacemaker function. This might confer a therapeutic benefit.

Effect of Long-Term Heart Rate Reduction by If Current Inhibition on Pressure Overload-Induced Heart Failure in Rats

We investigated the effects of long-term heart rate reduction (HRR) on pressure overload-induced heart failure. Pressure overload of the left ventricle was induced in 21-day-old rats by banding the ascending aorta. HRR was induced for 3 months with ivabradine (n = 44), a selective I(f) current inhibitor, at 10 mg/kg/day, starting 14 days after banding. Thirty-six control banded rats and 16 sham-operated rats received standard chow. Banding resulted in severe left ventricular (LV) hypertrophy (+55% versus shams; p < 0.001) and fibrosis, together with a 34% decrease (p < 0.01) in the LV shortening fraction. Heart rate decreased by 19% in ivabradine-treated rats (p < 0.005 versus controls). Stroke volume increased (by 17%; p < 0.01), whereas cardiac output did not change with HRR. In contrast, HRR resulted in 1) a marked increase in LV filling pressure (p < 0.01) and in atrial, lung, and right ventricular weights (38, 30, and 54%, respectively; p < 0.001); 2) a 50% increase in the incidence of pleural/abdominal effusion (p < 0.001); 3) 7 and 26% increases in LV hypertrophy and fibrosis, respectively (p < 0.05); and 4) a 53% increase in the atrial natriuretic peptide mRNA level compared with controls (p < 0.001). After 3 months of treatment, ivabradine withdrawal normalized the heart rate and reduced LV size and LV filling pressure (p < 0.05). In conclusion, pure longstanding HRR showed no beneficial effect on LV dysfunction in a rat model of pressure overload-induced LV hypertrophy, and it seemed to favor adverse LV remodeling and its congestive consequences.

Long-Term Safety and Efficacy of Ivabradine in Patients with Chronic Stable Angina

OBJECTIVE

To assess the long-term safety and antianginal efficacy of two doses of ivabradine, a novel selective and specific inhibitor of the sinus node I(f) current.

METHODS

In a randomized double-blind, parallel-group study 386 patients with chronic stable angina were randomized to either ivabradine 5 mg b.i.d. (n = 198, group 1) or ivabradine 7.5 mg b.i.d. (n = 188, group 2) for 12 months. Concomitant medication included antithrombotic agents, lipid-lowering agents, long-acting nitrates and dihydropyridine calcium antagonists. Safety was assessed on the basis of reported adverse events at 1, 3, 6, 9 and 12 months. Antianginal efficacy was based on the reduction in the weekly number of angina attacks and in the consumption of short-acting nitrates from month 0 (baseline) to month 12.

RESULTS

Ivabradine was well tolerated. Phosphene-like mild transient visual symptoms were the most frequently reported adverse events but led to treatment withdrawal in only 4 patients. Resting heart rate was reduced by 9 bpm in group 1 and 12 bpm in group 2. Sinus bradycardia caused treatment withdrawal in only three cases. The QTc (Bazett) interval did not increase. At month 12 relative to month 0 there was a significant reduction in the number of angina attacks per week.

CONCLUSION

Ivabradine at the recommended doses of 5 and 7.5 mg b.i.d. was well tolerated and demonstrated antianginal efficacy in patients with documented coronary artery disease treated with concomitant antianginal medications.

Ranolazine in patients with coronary artery disease

Traditional anti-anginal agents such as beta-blockers and nitrates improve symptoms of cardiac ischemia by affecting either blood pressure or heart rates. Despite aggressive therapy, many patients suffer persistent angina, and optimal therapy is limited by intolerance to traditional agents. Ranolazine, a novel anti-anginal agent that is approved for use in the US, is felt to improve ischemic symptoms by reducing myocardial cellular sodium and calcium overload via inhibition of the late sodium current (I(Na)) of the cardiac action potential. Several Phase-III trials in patients with chronic angina have demonstrated that ranolazine improves exercise tolerance and reduces ischemic symptoms as compared with placebo. In the largest evaluation of ranolazine, the MERLIN-TIMI 36 trial (Metabolic Efficiency with Ranolazine for Less Ischemia in non ST elevation acute coronary syndrome), ranolazine did not reduce the risk of death or recurrent myocardial infarction in patients with non-ST-elevation acute coronary syndromes, but it did improve ischemic symptoms over the subsequent year of therapy. Thus, ranolazine offers clinicians a new therapy in the long-term treatment of patients with chronic angina.

Ranolazine in patients with angina and coronary artery disease

The optimal management of coronary artery disease is based on achieving two parallel objectives: 1) prevention of major cardiovascular events, and 2) resolution of symptoms. Traditional antianginal agents improve ischemic symptoms by reducing myocardial oxygen demand through modulation of heart rate, preload, and/or afterload. Ranolazine is a novel antianginal agent believed to relieve ischemia by reducing myocardial cellular sodium and calcium overload via inhibition of the late sodium current of the cardiac action potential. In three randomized double-blind trials in selected patients with chronic angina, ranolazine prolonged exercise duration and reduced symptoms when compared with placebo when given as either monotherapy or in combination with traditional antianginal pharmacotherapy. When evaluated in patients with non-ST-elevation acute coronary syndromes, ranolazine reduced recurrent ischemia but did not significantly reduce the risk of death or myocardial infarction at 1 year. Ranolazine complements traditional antianginal agents and offers clinicians a new option in the long-term treatment of patients with angina.

Resting heart rate in cardiovascular disease

The importance of resting heart rate (HR) as a prognostic factor and potential therapeutic target is not yet generally accepted. Recent large epidemiologic studies have confirmed earlier studies that showed resting HR to be an independent predictor of cardiovascular and all-cause mortality in men and women with and without diagnosed cardiovascular disease. Clinical trial data suggest that HR reduction itself is an important mechanism of benefit of beta-blockers and other heart-rate lowering drugs used after acute myocardial infarction, in chronic heart failure, and in stable angina pectoris. Pathophysiological studies indicate that a relatively high HR has direct detrimental effects on the progression of coronary atherosclerosis, on the occurrence of myocardial ischemia and ventricular arrhythmias, and on left ventricular function. Studies have found a continuous increase in risk with HR above 60 beats/min. Although it may be difficult to define an optimal HR for a given individual, it seems desirable to maintain resting HR substantially below the traditionally defined tachycardia threshold of 90 or 100 beats/min. These findings suggest that the potential role of HR and its modulation should be considered in future cardiovascular guidance documents.

The role of pacemaker currents in neuropathic pain

Hyperpolarization-activated cation nonselective cyclic nucleotide-gated (HCN) channels mediate pacemaker currents that control basic rhythmic processes including heartbeat. Alterations in HCN channel expression or function have been described in both epilepsy and cardiac arrhythmias. Recent evidence suggests that pacemaker currents may also play an important role in ectopic neuronal activity that manifests as neuropathic pain. Pacemaker currents are subject to endogenous regulation by cyclic nucleotides, pH and perhaps phosphorylation. In addition, a number of neuromodulators with known roles in pain affect current density and kinetics. The pharmacology of a number of drugs that are commonly used to treat neuropathic pain includes effects on pacemaker currents. Altered pacemaker currents in injured tissues may be an important mechanism underlying neuropathic pain, and drugs that modulate these currents may offer new therapeutic options.

Lack of pharmacokinetic interaction between omeprazole or lansoprazole and ivabradine in healthy volunteers: an open-label, randomized, crossover, pharmacokinetic interaction clinical trial

The effects of omeprazole and lansoprazole (CYP3A4 inhibitors) on the pharmacokinetics of a single dose of ivabradine (metabolized via CYP3A4) and its active metabolite (S18982) were assessed. Pharmacodynamics and safety were secondary objectives. An open-label, randomized, crossover, phase I, pharmacokinetic interaction design was used. Volunteers received a single oral dose of ivabradine (10 mg), were randomized to receive either omeprazole (40 mg) or lansoprazole (60 mg) for 5 days, and were administered an ivabradine dose on the sixth day. Crossover was performed after washout. Pharmacokinetic parameters for ivabradine did not vary significantly after omeprazole (C(max): 45.0 +/- 36.6 vs 42.7 +/- 27.6 ng/mL, P = .98; AUC: 128 +/- 87 vs 126 +/- 63 ng/mL, P = .82) or lansoprazole administration (C(max): 45.0 +/- 36.6 vs 41.3 +/- 29.4 ng/mL, P = .70; AUC: 128 +/- 87 vs 123 +/- 50, P = .73). Analyses of S18982 pharmacokinetic parameters showed similar results. Coadministration of either omeprazole or lansoprazole did not significantly affect the pharmacokinetics of a single dose of ivabradine. No pharmacodynamic interaction or safety concerns were evidenced.

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.

Novel therapeutic approaches to treating chronic angina in the setting of chronic ischemic heart disease

Pharmacologic therapy to alleviate symptoms in chronic angina has been enhanced by the recent approval of several novel compounds that complement the traditional approach using beta-adrenergic blocking drugs, calcium antagonists, and long-acting nitrates. In the United States, ranolazine, a drug that inhibits late I(Na), was approved for patients with chronic angina that remain symptomatic on beta-blockers, calcium antagonists, or long-acting nitrates, on the basis of an acceptable safety profile and efficacy in several randomized placebo controlled studies. A slight increase in the QT interval is observed (<10 ms on average) at the maximum approved dose of 1,000 mg twice daily. Therefore, an ECG should be acquired at baseline and during follow-up, and the drug should not be used in patients with QT prolongation or those who are on QT prolonging drugs unless longer term randomized outcome data demonstrates no excess risk. The MERLIN trial of non-ST-elevation acute coronary syndrome (NSTE ACS) randomized 6,560 patients to assess the potential benefit of ranolazine in reducing the composite endpoint of cardiovascular death, myocardial infarction, and recurrent ischemia, with results expected in 2007. In Europe, ivabradine, a drug that inhibits the hyperpolarization-activated mixed sodium/potassium inward I(f) current, which slows the rest and exercise heart rate, was approved in 2005. Ivabradine at a dose of 10 mg twice daily has been shown to have similar efficacy to amlodipine 10 mg once daily or atenolol 100 mg once daily in alleviating chronic angina symptoms. In this review, several other novel investigational approaches are presented and patient selection considerations for the most recent approved drugs for chronic angina are discussed.

Cellular mechanisms underlying the pharmacological induction of phosphenes

Visual sensations evoked by stimuli other than luminance changes are called phosphenes. Phosphenes may be an early symptom in a variety of diseases of the retina or of the visual pathways, but healthy individuals may perceive them as well. Phosphene-like phenomena are perhaps the most common side effect reported in clinical pharmacology. Ivabradine, a novel anti-anginal drug that reduces heart-rate by inhibiting the hyperpolarization activated current expressed in cardiac sinoatrial node cells (I(f)) induces phosphenes in some patients. One hypothesis is that ivabradine interacts with the visual system by inhibiting hyperpolarization-activated current in retinal cells (Ih). An Ih current with properties similar to cardiac I(f) has been reported in retinal neurones. Under normal circumstances most of the random fluctuations generated within the retinal circuits do not reach the level of conscious perception because they are filtered out. Presumably, filtering occurs mostly within the retina and one serious candidate for this action is the ability of Ih to act as a negative-feedback mechanism. Ih activation in the membrane of visual cells causes dampening of responses to slow noisy inputs thus tuning the visual system to perceptually more relevant signals of higher frequency. Ih inhibition, by altering at the retinal synapses the filtering of signals generated by thermal breakdown of rhodopsin or other fluctuations, is expected to increase the probability of phosphene occurrence. It is the purpose of the present paper to outline and discuss the features of the visual system and the pharmacological conditions relevant to phosphene perception.

The pacemaker current: from basics to the clinics

Activation of the pacemaker ("funny," I(f)) current during diastole is the main process underlying generation of the diastolic depolarization and spontaneous activity of cardiac pacemaker cells. I(f) modulation by autonomic transmitters is responsible for the chronotropic regulation of heart rate. Given its role in pacemaking, I(f) has been a major target of investigation aimed to exploit its rate-controlling function in a clinical perspective. In this short review, we describe some of the most recent clinically relevant applications of the concept of I(f)-based pacemaking.

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.

[Heart rate reduction as a therapeutic strategy: novel options]

Elevated heart rate is associated with increased cardiovascular mortality. Heart rate reduction optimises myocardial oxygen consumption and decreases angina pectoris symptoms. Thus, heart rate control is an important therapeutic strategy in coronary artery disease and, for example, chronic heart failure. The pacemaker current I(f) plays a central role in determining spontaneous activity of the sinus node. Ivabradine, a selective inhibitor of the I(f) channel, reduces heart rate without any effect on cardiac contractility and without lowering blood pressure. While beta-blockers remain the first choice for heart rate reduction, in cases of adverse effects ivabradine may be used to treat stable angina pectoris. Studies evaluating possible further uses, for example in heart failure or after acute myocardial infarction, are still warranted.

Rationale and design of a randomized, double-blind, placebo-controlled trial of ivabradine in patients with stable coronary artery disease and left ventricular systolic dysfunction: the morBidity-mortality EvAlUaTion of the I(f) inhibitor ivabradine in patients with coronary disease and left ventricULar dysfunction (BEAUTIFUL) study

BACKGROUND

Raised resting heart rate (HR) is associated with increased cardiovascular and total mortality. Ivabradine is a new specific HR-reducing agent, which has been shown to have antianginal and anti-ischemic properties in patients with stable angina. Because patients with coronary artery disease and left ventricular dysfunction are at high risk of cardiac events and death, we hypothesized that they could derive particular benefit from a specific HR-lowering agent such as ivabradine.

METHODS

BEAUTIFUL is a multicenter, randomized, international, double-blind placebo-controlled trial to evaluate the superiority of ivabradine over placebo in reducing cardiovascular events in patients with stable coronary artery disease and left ventricular systolic dysfunction (ejection fraction < or = 39%). The primary end point is the composite of cardiovascular mortality and hospital admission for acute myocardial infarction or new onset or worsening of heart failure. This event-driven study will randomize 9650 patients and continue until 950 primary end points have occurred, providing 90% power to detect a 19% reduction in relative risk. In approximately 660 centers, men and women aged > or = 55 years if nondiabetic and > or = 18 years if diabetic are randomized to placebo or oral ivabradine (5 mg twice daily for 2 weeks then target dose of 7.5 mg twice daily). Follow-up is expected to last between 18 and 36 months.

RESULTS

The first patient was randomized in January 2005.

CONCLUSION

BEAUTIFUL will be the first major outcome trial of a specific HR-reducing agent. The study results are expected in 2008.

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.

Current strategies for the prevention of angina in patients with stable coronary artery disease

PURPOSE OF REVIEW

Angina pectoris affects at least 6.6 million people in the US and approximately 400,000 new cases of stable angina occur each year. Angina may be one of the first signs of ischemic heart disease, although it is likely not causally related to the likelihood of plaque rupture leading to an acute coronary syndrome. Modalities for treatment of angina should be used maximally to improve quality of life and decrease cardiovascular morbidity and mortality. The current recommended pharmacologic and invasive approaches, as well as novel therapies, are reviewed.

RECENT FINDINGS

Antiischemic agents, including beta-blockers, nitrates and calcium channel blockers, remain the mainstay in the prevention of angina. Revascularization via percutaneous interventions or coronary bypass surgery are appropriate in specific cases or when medical treatment fails. Noninvasive treatment options for refractory angina, metabolic agents, and vasodilator therapies are adding to the armamentarium to prevent and treat angina.

SUMMARY

A multifaceted approach is optimal to address the prevention of angina. Once angina is recognized, there are many modalities that lessen the incidence of daily life-induced and exercise-induced angina and ischemia. Angina management is best addressed by pharmacologic and lifestyle interventions.

The heterogeneous spectrum of the long QT syndrome

The long QT syndrome affects predominantly younger people who demonstrate structurally normal hearts. The underlying defect in the long QT syndrome seems to be genetic mutations in the cardiac ionic channels responsible for generating action potentials. Genetic linkage mapping has identified six genes (designated LQT1-6) associated with the Romano-Ward syndrome; two of these genes (LQT1, LQT5) are associated with the Jervell and Lange-Nielsen syndrome. All of these genes encode potassium channels with the exception of LQT3, which encodes a sodium channel. Mutations affecting these channels will lead to a derangement in ionic flows across the cytoplasmic membranes of cardiac cells, thereby leading to prolongation of the cardiac action potential and lengthening of the QT interval on the surface electrocardiogram. Long QT syndrome is a cause of death in young, otherwise healthy individuals. The heterogeneity of the long QT syndrome also makes prognosis and risk stratification difficult. In patients with long QT syndrome genotypes 1 and 2, as well as during slower heart rates, men exhibited shorter mean QTc interval durations than did women; thus, women possess a predilection for developing torsades de pointes. In female probands with the congenital long QT syndrome, the postpartum period appears to confer a significant risk for experiencing a cardiac event. The study determined that certain combinations, such as exhibiting a QTc of 500ms or more, along with the presence of LQT1, LQT2, and LQT3 (with male gender), conferred a 50% or greater risk of a first cardiac event. Based on the observation that physical exertion and emotional stress are significant triggers for cardiac events in the setting of congenital long QT syndrome (specifically the LQT1 and LQT2 genotypes), avoidance of competitive sports seems to be a prudent lifestyle modification. This heterogeneity stems from the presence of different mutations in the genes that encode cardiac ion channels. The triggering events, prognosis, and risk stratification of the patient with long QT syndrome appear to be influenced by the underlying genotype. The primary treatment of congenital long QT syndrome, i.e., beta-blockade therapy with internal cardioverter defibrillator therapy, appears to be useful in a subset of patients.

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.

Evolving treatment strategies for chronic refractory angina

Chronic refractory angina is a term used to describe patients who, despite optimal medical therapy, have both angina and objective evidence of ischaemia. It is estimated that 5-15% of the 12 million patients with chronic angina in the US meet the criteria for having refractory angina. This review focuses on the following evolving pharmacological therapies for chronic refractory angina: L-arginine, ivabradine, ranolazine, nicorandil and trimetazidine. Evolving devices and invasive procedures including enhanced external counterpulsation, spinal cord stimulation, and transmyocardial revascularisation are also briefly discussed.

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.

Chronic heart rate reduction remodels ion channel transcripts in the mouse sinoatrial node but not in the ventricle

We investigated the effects of chronic and moderate heart rate (HR) reduction on ion channel expression in the mouse sinoatrial node (SAN) and ventricle. Ten-week-old male C57BL/6 mice were treated twice daily with either vehicle or ivabradine at 5 mg/kg given orally during 3 wk. The effects of HR reduction on cardiac electrical activity were investigated in anesthetized mice with serial ECGs and in freely moving mice with telemetric recordings. With the use of high-throughput real-time RT-PCR, the expression of 68 ion channel subunits was evaluated in the SAN and ventricle at the end of the treatment period. In conscious mice, ivabradine induced a mean 16% HR reduction over a 24-h period that was sustained over the 3-wk administration. Other ECG parameters were not modified. Two-way hierarchical clustering analysis of gene expression revealed a separation of ventricles from SANs but no discrimination between treated and untreated ventricles, indicating that HR reduction per se induced limited remodeling in this tissue. In contrast, SAN samples clustered in two groups depending on the treatment. In the SAN from ivabradine-treated mice, the expression of nine ion channel subunits, including Navbeta1 (-25%), Cav3.1 (-29%), Kir6.1 (-28%), Kvbeta2 (-41%), and Kvbeta3 (-30%), was significantly decreased. Eight genes were significantly upregulated, including K+ channel alpha-subunits (Kv1.1, +30%; Kir2.1, +29%; Kir3.1, +41%), hyperpolarization-activated cation channels (HCN2, +24%; HCN4, +52%), and connexin 43 (+26%). We conclude that reducing HR induces a complex remodeling of ion channel expression in the SAN but has little impact on ion channel transcripts in the ventricle.

Efficacy of ivabradine, a new selective If inhibitor, compared with atenolol in patients with chronic stable angina

AIMS

Ivabradine, a new I(f) inhibitor which acts specifically on the pacemaker activity of the sinoatrial node, is a pure heart rate lowering agent. Ivabradine has shown anti-ischaemic and anti-anginal activity in a placebo-controlled trial. The objective of this study was to compare the anti-anginal and anti-ischaemic effects of ivabradine and the beta-blocker atenolol.

METHODS AND RESULTS

In a double-blinded trial, 939 patients with stable angina were randomized to receive ivabradine 5 mg bid for 4 weeks and then either 7.5 or 10 mg bid for 12 weeks or atenolol 50 mg od for 4 weeks and then 100 mg od for 12 weeks. Patients underwent treadmill exercise tests at randomization (M(0)) and after 4 (M(1)) and 16 (M(4)) weeks of therapy. Increases in total exercise duration (TED) at trough at M(4) were 86.8+/-129.0 and 91.7+/-118.8 s with ivabradine 7.5 and 10 mg, respectively and 78.8+/-133.4 s with atenolol 100 mg. Mean differences (SE) when compared with atenolol 100 mg were 10.3 (9.4) and 15.7 (9.5) s in favour of ivabradine 7.5 and 10 mg (P<0.001 for non-inferiority). TED at M(1) improved by 64.2+/-104.0 s with ivabradine 5 mg and by 60.0+/-114.4 s with atenolol 50 mg (P<0.001 for non-inferiority). Non-inferiority of ivabradine was shown at all doses and for all criteria. The number of angina attacks was decreased by two-thirds with both ivabradine and atenolol.

CONCLUSION

Ivabradine is as effective as atenolol in patients with stable angina.