Heart Rate Lowering by Specific and Selective If Current Inhibition with Ivabradine

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Ivabradine for the prevention of inappropriate shocks due to sinus tachycardia in patients with an implanted cardioverter defibrillator

AIMS

Ivabradine is a specific blocker of the pacemaker current (I(f)) used to decrease the sinus rate. Several clinical trials have shown that it is beneficial, with or without concomitant beta-blocker therapy, in patients with stable angina or heart failure. We sought to take advantage of ivabradine's ability to decrease the maximal obtainable sinus rate in order to prevent inappropriate shocks due to sinus tachycardia in patients with an implanted cardioverter defibrillator (ICD).

METHODS AND RESULTS

Prospective open-label series including all our patients with an implanted ICD who, during the course of 2010-2011, received ivabradine with the only purpose of preventing inappropriate ICD shocks for sinus tachycardia. These are patients who received one or more inappropriate shocks for sinus tachycardia or were conceived to be at very high risk for developing such complication. Our series includes five patients who received ivabradine (5-10 mg/day) in addition to their usual beta-blocker therapy. During a follow-up of 14 months no inappropriate shocks due to sinus tachycardia were recorded.

CONCLUSION

It is sensible to recommend ivabradine for the prevention of inappropriate ICD shocks due to sinus tachycardia in carefully selected patients.

Safety and efficacy of oral ivabradine as a heart rate-reducing agent in patients undergoing CT coronary angiography

OBJECTIVE

To investigate the role of oral ivabradine as a heart rate reducing agent in patients undergoing CT coronary angiography (CTCA). Despite the routine use of β-blockers prior to CTCA studies, it is not uncommon to have patients with heart rates persistently above the target range of 65 bpm. Ivabradine is a selective inhibitor of the I(f) current, which primarily contributes to sinus node pacemaker activity, and has no significant direct cardiovascular effects such as reduction of blood pressure, cardiac contractility or impairment of cardiac conduction.

METHODS

We investigated 100 consecutive patients who had been referred for CTCA for the evaluation of suspected coronary artery disease (CAD). Patients were randomised to receive either of the following two pre-medication protocols: oral metorprolol or oral ivabradine.

RESULTS

Ivabradine was significantly more effective than metorprolol in lowering the heart rate; the mean percentage reduction in heart rate with ivabradine vs metorpolol was 23.89+6.95% vs 15.20+4.50%, respectively (p=0.0001). Metoprolol significantly lowered both systolic and diastolic blood pressure while ivabradine did not. The requirement of additional doses to achieve a target heart rate of <65 beats per min was also significantly more frequent with metoprolol.

CONCLUSION

Ivabradine is a potentially attractive alternative to currently used drugs for reduction of heart rate in patients undergoing CTCA.

Heart rate-lowering efficacy and respiratory safety of ivabradine in patients with obstructive airway disease: a randomized, double-blind, placebo-controlled, crossover study

BACKGROUND

There is substantial evidence that heart rate (HR) is a powerful predictor of mortality in both normal individuals and in patients with cardiovascular disease. The use of β-adrenoceptor antagonists (β-blockers) has confirmed the importance of lowering elevated HR in a patient's prognosis. However, these agents can have undesirable adverse effects (AEs) and due to the risk of bronchoconstriction are contraindicated in patients with obstructive airway disease. A selective bradycardic agent, without such undesirable effects, could be of therapeutic interest. Ivabradine, a new I(f) inhibitor that acts specifically on the sino-atrial node, is a pure HR-lowering agent.

OBJECTIVE

The objective of this study was to assess HR-lowering efficacy and respiratory safety of ivabradine in patients with asthma and chronic obstructive pulmonary disease (COPD).

METHODS

This was a randomized, single-center, double-blind, placebo-controlled, crossover trial. Enrolment began in May 2009, and the last patient completed the study in January 2011. The study was conducted in an ambulatory setting. A total of 40 patients completed the study (20 asthmatic patients and 20 COPD patients). Inclusion criteria were: documented diagnosis of asthma or COPD according to international guidelines, age 18-75 years, and mean HR on Holter ECG recording of ≥60 beats/min. Exclusion criteria included disease exacerbation in a previous month or inability to understand instructions on the study procedures. All patients received ivabradine 7.5 mg twice daily for 5 days and placebo twice daily for 5 days in a crossover manner, in one of the two arms of the study, with at least 2 days of washout between treatments. The main outcome measures included the difference in HR between ivabradine and placebo treatment and change in HR in comparison with baseline. Other evaluated outcomes were differences in the peak expiratory flow rate (PEFR), the daily symptom score, rescue medication consumption, and AEs.

RESULTS

Ivabradine produced significantly lower mean HR than placebo in both groups of patients: asthma 67.4 ± 8.38 versus 82.85 ± 11.19 beats/min (p < 0.001) and COPD 69.75 ± 8.9 versus 81.05 ± 9.75 beats/min (p < 0.001). Similar results were observed for the minimal HR as well as for the maximal noted HR. In comparision with baseline, ivabradine significantly reduced HR in both groups of studied patients (all p < 0.05), whereas placebo did not have such an effect. No significant difference, in either the asthma or the COPD group, was found between ivabradine and placebo in morning and evening peak expiratory flow rate, peak expiratory flow diurnal variability, daily symptom scores, and rescue medication usage (all p > 0.05). Both treatments were well tolerated. The incidence of AEs was low and generally similar in both periods of treatment, except for visual symptoms during treatment with ivabradine, which was reported by 5% of the patients.

CONCLUSION

Our study demonstrated that selective HR reduction with ivabradine is effective in patients with asthma and COPD, with no alteration in respiratory function or symptoms over the duration of the study. Ivabradine offers an interesting alternative, as an HR-lowering agent, in patients with respiratory disease and contraindications to β-blockers.

CLINICAL TRIAL REGISTRATION

Registered at www.clinicaltrials.gov (NCT01365286).

Is heart rate a treatment target in heart failure?

Clinical and experimental studies confirmed an association between elevated resting heart rate and the risk of mortality in heart failure patients. Importantly, elevated heart rate at rest has been identified as a key finding in heart failure addressing a major treatment target. This review shows that heart rate level at rest and its extent of reduction is a sensitive indicator for successful therapy in heart failure patients demonstrating the specific influence of heart rate reduction on clinical outcome in the analyzed patients. Currently, experimental data provide convincing evidence of a pathophysiological concept of heart rate reduction; nevertheless, transition from experimental results to clinical evidence needs further clarification, especially in patients with diastolic heart failure. Since heart rate can be easily determined during physical examination, decrease in heart rate of patients allows a simple hint on prognosis and efficiency of heart failure therapy.

A low-cost, portable, high-throughput wireless sensor system for phonocardiography applications

This paper presents the design and testing of a wireless sensor system developed using a Microchip PICDEM developer kit to acquire and monitor human heart sounds for phonocardiography applications. This system can serve as a cost-effective option to the recent developments in wireless phonocardiography sensors that have primarily focused on Bluetooth technology. This wireless sensor system has been designed and developed in-house using off-the-shelf components and open source software for remote and mobile applications. The small form factor (3.75 cm × 5 cm × 1 cm), high throughput (6,000 Hz data streaming rate), and low cost ($13 per unit for a 1,000 unit batch) of this wireless sensor system make it particularly attractive for phonocardiography and other sensing applications. The experimental results of sensor signal analysis using several signal characterization techniques suggest that this wireless sensor system can capture both fundamental heart sounds (S1 and S2), and is also capable of capturing abnormal heart sounds (S3 and S4) and heart murmurs without aliasing. The results of a denoising application using Wavelet Transform show that the undesirable noises of sensor signals in the surrounding environment can be reduced dramatically. The exercising experiment results also show that this proposed wireless PCG system can capture heart sounds over different heart conditions simulated by varying heart rates of six subjects over a range of 60–180 Hz through exercise testing.

Funny Current and Cardiac Rhythm: Insights from HCN Knockout and Transgenic Mouse Models

In the adult animal the sinoatrial node (SAN) rhythmically generates a depolarizing wave that propagates to the rest of the heart. However, the SAN is more than a simple clock; it is a clock that adjusts its pace according to the metabolic requirements of the organism. The Hyperpolarization-activated Cyclic Nucleotide-gated channels (HCN1–4) are the structural component of the funny (I_f) channels; in the SAN the I_f current is the main driving electrical force of the diastolic depolarization and the HCN4 is the most abundant isoform. The generation of HCN KO and transgenic mouse models has advanced the understanding of the role of these channels in cardiac excitability. The HCN4 KO models that were first developed allowed either global or cardiac-specific constitutive ablation of HCN4 channels, and resulted in embryonic lethality. A further progress was made with the development of three separate inducible HCN4 KO models; in one model KO was induced globally in the entire organism, in a second, ablation occurred only in HCN4-expressing cells, and finally in a third model KO was confined to cardiac cells. Unexpectedly, the three models yielded different results; similarities and differences among these models will be presented and discussed. The functional effects of HCN2 and HCN3 knockout models and transgenic HCN4 mouse models will also be discussed. In conclusion, HCN KO/transgenic models have allowed to evaluate the functional role of the I_f currents in intact animals as well as in single SAN cells isolated from the same animals. This opportunity is therefore unique since it allows (1) to verify the contribution of specific HCN isoforms to cardiac activity in intact animals, and (2) to compare these results to those obtained in single cell experiments. These combined studies were not possible prior to the development of KO models. Finally, these models represent critical tools to improve our understanding of the molecular basis of some inheritable arrhythmic human pathologies.

[Heart rate and rate control : Prognostic value in cardiovascular diseases]

Resting heart rate represents a cardiovascular risk indicator and an important target of therapy in chronic heart failure and potentially in coronary artery disease. Clinical and experimental evidence suggests that sustained elevation of heart rate - independent of the underlying trigger - plays a causal role in the pathogenesis of vascular disease. Results of the SHIFT trial support the importance of heart-rate reduction with ivabradine for improvement of clinical outcomes in heart failure and confirm the role of heart rate as a risk factor for patients with severe left ventricular dysfunction. Results of the BEAUTIFUL trial show that patients with ischemic heart disease and a heart rate above 70 bpm exhibit an adverse prognosis concerning coronary events.

The biological effects of ivabradine in cardiovascular disease

A large number of studies in healthy and asymptomatic subjects, as well as patients with already established cardiovascular disease (CAD) have demonstrated that heart rate (HR) is a very important and major independent cardiovascular risk factor for prognosis. Lowering heart rate reduces cardiac work, thereby diminishing myocardial oxygen demand. Several experimental studies in animals, including dogs and pigs, have clarified the beneficial effects of ivabradine associated with HR lowering. Ivabradine is a selective inhibitor of the hyperpolarisation activated cyclic-nucleotide-gated funny current (If) involved in pacemaker generation and responsiveness of the sino-atrial node (SAN), which result in HR reduction with no other apparent direct cardiovascular effects. Several studies show that ivabradine substantially and significantly reduces major risks associated with heart failure when added to guideline-based and evidence-based treatment. However the biological effect of ivabradine have yet to be studied. This effects can appear directly on myocardium or on a systemic level improving endothelial function and modulating immune cell migration. Indeed ivabradine is an 'open-channel' blocker of human hyperpolarization-activated cyclic nucleotide gated channels of type-4 (hHCN4), and a 'closed-channel' blocker of mouse HCN1 channels in a dose-dependent manner. At endothelial level ivabradine decreased monocyte chemotactin protein-1 mRNA expression and exerted a potent anti-oxidative effect through reduction of vascular NADPH oxidase activity. Finally, on an immune level, ivabradine inhibits the chemokine-induced migration of CD4-positive lymphocytes. In this review, we discuss the biological effects of ivabradine and highlight its effects on CAD.

HCN channels and heart rate

Hyperpolarization and Cyclic Nucleotide (HCN) -gated channels represent the molecular correlates of the "funny" pacemaker current (I(f)), a current activated by hyperpolarization and considered able to influence the sinus node function in generating cardiac impulses. HCN channels are a family of six transmembrane domain, single pore-loop, hyperpolarization activated, non-selective cation channels. This channel family comprises four members: HCN1-4, but there is a general agreement to consider HCN4 as the main isoform able to control heart rate. This review aims to summarize advanced insights into the structure, function and cellular regulation of HCN channels in order to better understand the role of such channels in regulating heart rate and heart function in normal and pathological conditions. Therefore, we evaluated the possible therapeutic application of the selective HCN channels blockers in heart rate control.

Ca2+-activated adenylyl cyclase 1 introduces Ca2+-dependence to beta-adrenergic stimulation of HCN2 current

Previous observations show that β-adrenergic modulation of pacemaker current (I(f)) in sinoatrial node (SAN) cells is impaired by disruption of normal Ca(2+)-homeostasis with ryanodine or BAPTA. Recently, the presence of Ca(2+)-activated adenylyl cyclase (AC) 1 was reported in SAN, and was proposed as a possible mechanism of Ca(2+)-dependence of β-adrenergic modulation. However, direct evidence that pacemaker (HCN) channels can be regulated by Ca(2+)-activated AC and that such regulation introduces Ca(2+) dependence, is lacking. Here we co-expressed AC1 or AC6 with HCN2 in neonatal rat ventricular myocytes, which lack AC1. Although both isoforms have equivalent expression level and ability to interact with HCN2, only AC1 increases intracellular cAMP content, accelerates spontaneous beating rate and modifies HCN2 biophysics. Measured HCN2 current in the AC1 group activated ~10mV more positive than in GFP or AC6. The β-adrenergic agonist isoproterenol induced a further positive shift under control conditions, but failed to do so after pretreatment with the Ca(2+) chelator BAPTA. In the AC6 group, isoproterenol shifted the HCN2 activation relation to a similar extent in the absence and presence of BAPTA. Thus, AC1 but not AC6 over-expression introduces Ca(2+)-sensitivity to the β-adrenergic response of HCN2. These results demonstrate physical and functional interaction between AC isoforms and the HCN2 pacemaker channel and support a key role of Ca(2+) activated AC1 as a molecular mechanism in Ca(2+)-dependent modulation of β-adrenergic response of heart rate.

Heart rate reduction as a therapeutic goal: focus on primary prevention

Recently published studies have demonstrated a direct link between heart rate (HR) and prognosis across various populations and clinical groups, including elderly people, patients with arterial hypertension, myocardial infarction, and coronary artery stenting, overweight patients, or even young people with relatively low cardiovascular risk levels. HR is considered as an additional independent risk factor (RF) of cardiovascular disease (CVD). However, thus far, pharmaceutical HR reduction has been demonstrated to improve prognosis only in patients with coronary heart disease or chronic heart failure. The results in CVD-free patients have been contradictory. The review discusses the potential of different HR-reducing therapeutic regimens, as a part of primary CVD prevention.

Treatment of stable angina pectoris

Management of stable angina pectoris includes antianginal medications, medications to prevent progression of atherosclerosis, and aggressive treatment of causative risk factors. Antianginal medications commonly used include nitrates, beta-blockers, calcium channel blockers, and ranolazine. Antiplatelet agents, statins, and angiotensin-converting enzyme inhibitors are used in patients with these problems to prevent progression of atherosclerosis and/or premature cardiovascular death. Aggressive risk factor control with diet; exercise; treatment of diabetes, hypertension, and dyslipidemia; and strategies to stop smoking and reduce weight should be a part of treatment strategy in all patients. Patients with stable angina who have symptoms refractory to medical treatment usually require coronary angiography, followed by either percutaneous or surgical revascularization. Recent mechanical techniques for the treatment of refractory angina include transmyocardial laser revascularization, enhanced external counterpulsation, and spinal cord stimulation.

Ivabradine in combination with beta-blocker improves symptoms and quality of life in patients with stable angina pectoris: results from the ADDITIONS study

AIM

Several clinical trials have demonstrated the antianginal and anti-ischemic efficacy of ivabradine in combination with beta-blocker in patients with stable angina pectoris. The ADDITIONS (PrActical Daily efficacy anD safety of Procoralan(®) In combinaTION with betablockerS) study evaluated the efficacy, safety, and tolerability of ivabradine added to beta-blocker, and its effect on angina symptoms and quality of life in routine clinical practice.

METHODS

This non-interventional, multicenter, prospective study included 2,330 patients with stable angina pectoris treated with a flexible dose of ivabradine twice daily in addition to beta-blocker for 4 months. The parameters recorded included heart rate, number of angina attacks, nitrate consumption, tolerance, and quality of life.

RESULTS

After 4 months ivabradine (mean dose 12.37 ± 2.95 mg/day) reduced heart rate by 19.4 ± 11.4 to 65.6 ± 8.2 bpm (p < 0.0001). The number of angina attacks was reduced by 1.4 ± 1.9 per week (p < 0.0001), and nitrate consumption by 1.9 ± 2.9 U per week (p < 0.0001). At baseline (i.e., on beta-blocker), half of the patients (51%) were classified as Canadian Cardiovascular Society (CCS) grade II; 29% were CCS grade I. After 4 months' treatment with ivabradine, most of the patients were CCS grade I (68%). The EQ-5D index improved by 0.17 ± 0.23 (p < 0.0001). The overall efficacy of ivabradine was considered by the physicians as "very good" (61%) or "good" (36%) in most patients. Suspected adverse drug reactions were documented in 14 patients; none were severe.

CONCLUSION

In daily clinical practice, combining ivabradine with beta-blocker not only reduces heart rate, number of angina attacks, and nitrate consumption, but also improves the quality of life in patients with stable angina pectoris.

Exploring HCN channels as novel drug targets

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have a key role in the control of heart rate and neuronal excitability. Ivabradine is the first compound acting on HCN channels to be clinically approved for the treatment of angina pectoris. HCN channels may offer excellent opportunities for the development of novel anticonvulsant, anaesthetic and analgesic drugs. In support of this idea, some well-established drugs that act on the central nervous system - including lamotrigine, gabapentin and propofol - have been found to modulate HCN channel function. This Review gives an up-to-date summary of compounds acting on HCN channels, and discusses strategies to further explore the potential of these channels for therapeutic intervention.

Cardioprotection by Ivabradine Through Heart Rate Reduction and Beyond

The present review summarizes the experimental and clinical evidence for the anti-ischemic action of the selective bradycardic agent ivabradine. Improvements in myocardial blood flow and contractile function during experimental myocardial ischemia and the clinical anti-anginal effect are largely mediated by heart rate reduction. However, a significant reduction in infarct size by ivabradine persists in the absence of heart rate reduction, and such protection can also be recruited when ivabradine is given only during early reperfusion. The mechanisms for such pleiotropic action of ivabradine remain to be resolved.

[New agents for the therapy of angina pectoris]

There is a renaissance of medical treatment of chronic angina pectoris despite of advances in interventional therapy. New drugs include nicorandil, ivabradine and ranolazine. Nicorandil dilates venous and arterial vessels via relaxation of smooth muscle cells. Since the drug has only recently been approved, the German experience is limited. Ivabradine exerts an anti-anginous effect by selective action on the sinus node with reduction of heart rate. Multiple studies have demonstrated its anti-anginal efficacy, which has also been shown if it was used as an additional therapy to classic anti-anginal treatment. Its use is reasonable as a substitute for beta-blockers or as an "add-on therapy" combined with beta-blockers, if the target heart rate for treatment of angina pectoris has not been reached. Ranolazine delays the late sodium current into the myocytes. Thereby, it improves the diastolic ventricular function and the microcirculation of the myocardium. Several large studies confirmed the anti-anginal efficacy of the drug. Currently it is used if angina pectoris still occurs under a combined treatment with different classic anti-anginal drugs.

Heart rate contributes to the vascular effects of chronic mental stress: effects on endothelial function and ischemic brain injury in mice

BACKGROUND AND PURPOSE

Vascular effects of mental stress are only partially understood. Therefore, we studied effects of chronic stress and heart rate (HR) on endothelial function and cerebral ischemia.

METHODS

129S6/SvEv mice were randomized to the I(f)-channel inhibitor ivabradine (10 mg/kg per day) or vehicle and underwent a chronic stress protocol for 28 days.

RESULTS

Stress increased HR from 514 ± 10 bpm to 570 ± 14 bpm, this was prevented by ivabradine (485 ± 7 bpm). Endothelium-dependent relaxation of aortic rings was impaired in mice exposed to stress. HR reduction restored endothelial function to the level of naive controls. Vascular lipid hydroperoxides were increased to 333% ± 24% and vascular NADPH oxidase activity was upregulated to 223 ± 38% in stressed mice, which was prevented by ivabradine. Stress reduced aortic endothelial nitric oxide synthase mRNA expression to 84% ± 3% and increased AT1 receptor mRNA to 168% ± 18%. Both effects were attenuated by HR reduction. In brain tissue, stress resulted in an upregulation of lipid hydroperoxides to 140% ± 11%, which was attenuated by HR reduction. Ivabradine increased brain capillary density in naive and in stressed mice. Mice exposed to chronic stress before induction of ischemic stroke by transient middle cerebral artery occlusion exhibited increased lesion size (33.7 ± 2.3 mm3 versus 23.9 ± 2.4 mm3). HR reduction led to a marked reduction of the infarct volume to 12.9 ± 3.3 mm3.

CONCLUSIONS

Chronic stress impairs endothelial function and aggravates ischemic brain injury. HR reduction protects from cerebral ischemia via improvement of endothelial function and reduction of oxidative stress. These results identify heart rate as a mediator of vascular effects induced by chronic stress.

Ivabradine therapy effectiveness in patients with chronic heart failure, Functional Class III

Aim. To assess the effectiveness of ivabradine-including therapy, as well as the effects of ivabradine on regulatoryadaptive status (RAS), in patients with chronic heart failure (CHF), Functional Class (FC) III. Material and methods. The study included 100 patients with FC III CHF and coronary heart disease (CHD) and/ or Stage III arterial hypertension (AH). The participants were previously prescribed a complex treatment regime. After randomisation, Group I included 56 patients (mean age 62,9±1,8 years), who were additionally administered metoprolol succinate extended-release (mean dose 59,1±4,5 mg/day). Group II (n=44; mean age 59,4±1,3 years) was additionally administered an If channel inhibitor ivabradine, when beta-adrenoblocker (BAB) therapy was not possible. At baseline and 6 months later, participants underwent treadmill test (with VO2max assessment), echocardiography, 24-hour blood pressure monitoring, and the measurement of plasma levels of N-terminal probrain natriuretic peptide (NT-proBNP). RAS status was qualitatively assessed in a cardio-respiratory synchronism test. Results. Ivabradine-including therapy improved myocardial structure and function, increased exercise capacity, and demonstrated positive effects on plasma NT-proBNP levels, VO2мах during treadmill test, and RAS status.

Conclusion. Ivabradine could be an alternative medication when BAB therapy is not possible in patients with FC III CHF and CHD and/or Stage III AH.

New drugs vs. old concepts: a fresh look at antiarrhythmics

Common arrhythmias, particularly atrial fibrillation (AF) and ventricular tachycardia/fibrillation (VT/VF) are a major public health concern. Classic antiarrhythmic (AA) drugs for AF are of limited effectiveness, and pose the risk of life-threatening VT/VF. For VT/VF, implantable cardiac defibrillators appear to be the unique, yet unsatisfactory, solution. Very few AA drugs have been successful in the last few decades, due to safety concerns or limited benefits in comparison to existing therapy. The Vaughan-Williams classification (one drug for one molecular target) appears too restrictive in light of current knowledge of molecular and cellular mechanisms. New AA drugs such as atrial-specific and/or multichannel blockers, upstream therapy and anti-remodeling drugs, are emerging. We focus on the cellular mechanisms related to abnormal Na⁺ and Ca²⁺ handling in AF, heart failure, and inherited arrhythmias, and on novel strategies aimed at normalizing ionic homeostasis. Drugs that prevent excessive Na⁺ entry (ranolazine) and aberrant diastolic Ca²⁺ release via the ryanodine receptor RyR2 (rycals, dantrolene, and flecainide) exhibit very interesting antiarrhythmic properties. These drugs act by normalizing, rather than blocking, channel activity. Ranolazine preferentially blocks abnormal persistent (vs. normal peak) Na⁺ currents, with minimal effects on normal channel function (cell excitability, and conduction). A similar "normalization" concept also applies to RyR2 stabilizers, which only prevent aberrant opening and diastolic Ca²⁺ leakage in diseased tissues, with no effect on normal function during systole. The different mechanisms of action of AA drugs may increase the therapeutic options available for the safe treatment of arrhythmias in a wide variety of pathophysiological situations.

Safety of ivabradine in patients with coronary artery disease and left ventricular systolic dysfunction (from the BEAUTIFUL Holter Substudy)

The BEAUTIFUL Holter substudy explored the cardiac safety of the I(f) inhibitor ivabradine in patients with stable coronary artery disease and left ventricular systolic dysfunction receiving optimal background therapy. The Holter substudy included 840 patients (ivabradine 5 or 7.5 mg/day, n = 421; placebo, n = 419), and the safety set consisted of 807 patients (ivabradine, n = 408; placebo, n = 399). Ambulatory 24-hour electrocardiographic Holter monitoring was performed at baseline and after 1 month and 6 months. There were no relevant between-group differences in baseline characteristics; 93% were receiving concomitant β blocker. Treatment with ivabradine was associated with a decrease in 24-hour heart rate of 6.3 ± 9.5 beats/min at last assessment versus no change with placebo (0.4 ± 7.2 beats/min, p <0.001, between-group difference), with a greater decrease in waking heart rate with ivabradine than during sleep (6.8 ± 10.4 vs 5.2 ± 8.9 beats/min, respectively, at last visit). Incidence of episodes of heart rate <30 beats/min during waking hours or during sleep was ≤1% in the 2 groups. Although there were more patients with heart rates <40 or <50 beats/min with ivabradine than with placebo (awake 12% vs 4% for <40 beats/min and 68% vs 36% for <50 beats/min, respectively; asleep 22% vs 5% for <40 beats/min and 77% vs 50% for <50 beats/min, respectively), there was no between-group difference in episode severity. There was no increase in incidence of conduction and rhythm disturbances. In conclusion, our results confirm that ivabradine significantly lowers heart rate without raising concern for cardiac safety. Our observations strongly support the safety of combining ivabradine with β blockers in patients with coronary artery disease.

Deep bradycardia and heart block caused by inducible cardiac-specific knockout of the pacemaker channel gene Hcn4

Cardiac pacemaking generation and modulation rely on the coordinated activity of several processes. Although a wealth of evidence indicates a relevant role of the I(f) ("funny," or pacemaker) current, whose molecular constituents are the hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels and particularly HCN4, work with mice where Hcn genes were knocked out, or functionally modified, has challenged this view. However, no previous studies used a cardiac-specific promoter to induce HCN4 ablation in adult mice. We report here that, in an inducible and cardiac-specific HCN4 knockout (ciHCN4-KO) mouse model, ablation of HCN4 consistently leads to progressive development of severe bradycardia (∼50% reduction of original rate) and AV block, eventually leading to heart arrest and death in about 5 d. In vitro analysis of sinoatrial node (SAN) myocytes isolated from ciHCN4-KO mice at the mean time of death revealed a strong reduction of both the I(f) current (by ∼70%) and of the spontaneous rate (by ∼60%). In agreement with functional results, immunofluorescence and Western blot analysis showed reduced expression of HCN4 protein in SAN tissue and cells. In ciHCN4-KO animals, the residual I(f) was normally sensitive to β-adrenergic receptor (β-AR) modulation, and the permanence of rate response to β-AR stimulation was observed both in vivo and in vitro. Our data show that cardiac HCN4 channels are essential for normal heart impulse generation and conduction in adult mice and support the notion that dysfunctional HCN4 channels can be a direct cause of rhythm disorders. This work contributes to identifying the molecular mechanism responsible for cardiac pacemaking.

Evaluation of aggressive heart rate reduction in patients with stable angina

BACKGROUND

There is a strong correlation between heart rate and myocardial ischemia, cardiovascular diseases, and life expectancy in general; however, heart rate has been neglected as an important risk factor as well as a therapeutic opportunity.

PURPOSE

To investigate the effect of aggressive heart rate reduction (50 ⩽ HR ⩽ 60 bpm) on anti-ischemic and anti-anginal efficacy, left ventricular function, exercise tolerance and quality of life in patients with stable coronary artery disease with or without left ventricular dysfunction during 4 months.

METHODS

A total of 159 patients presented with stable CAD without clinical heart failure symptoms were included in a open-label, non-comparative, prospective clinical study between June 2009 to February 2010 in King Abdul Aziz Specialist Hospital, Taif, KSA, Al Hayah National Hospital, Khamis Mushyt, KSA and Critical care department, Cairo University, Egypt. All included patients were, in addition to the ant ischemic treatment, subjected to aggressive heart rate control starting by beta blocker titrated to the maximum dose as tolerated, then Ivabradine added if the target heart rate is not achieved or rate control started by Ivabradine if beta blockers are contraindicated. Exercise treadmill test (ETT) to assess exercise capacity using time to 1 mm ST-segment depression in milliseconds, ejection fraction (EF) assessed by transthoracic echocardiography and frequency of angina attacks and the use of sublingual nitroglycerin per week during the last week were evaluated during a follow-up for 4 months. The patients were divided into two groups, group-I (patients achieved a resting heart rate between 50 and 60 bpm with heart rate reduction treatment) and group-II (patients with resting HR >60 bpm in spite of maximum treatment for heart rate reduction).

RESULTS

The resting heart rate was significantly reduced from 77.98 ± 8.7 at baseline to 60.68 ± 4.34 bpm after 4 months of treatment, P < 0.001. The frequency of angina pectoris attacks had been significantly reduced from 2.14 ± 1.27 to 0.48 ± 0.58 attacks per week, P < 0.001 and the highest significant reduction was observed with group-I. Also, the frequency of use sublingual nitrate therapy was significantly reduced from 1.38 ± 1.1 tablet per week at the last week before the study to 0.12 ± 0.33 tablet per week during the last week after 4 months of treatment, P < 0.001 and the reduction was more significantly with group-I. Exercise treadmill test demonstrated statistically significant increase in the time to 1 mm ST-segment depression from 357.36 ± 66.73 at baseline to 387.96 ± 65.19 ms. after 4 months with P < 0.001. The degree of improvement was significantly higher for group-I (from 358.06 ± 68.81 at baseline to 391.71 ± 69.01 after 4 months with P < 0.001) than that of group-II (from 356.11 ± 64.8 at baseline to 381.27 ± 59.08 after 4 months with P < 0.001). Ejection fraction showed a statistically significant increase from 59.76 ± 6.86 at baseline to 61.04 ± 5.35 after 4 months with P < 0.001.

CONCLUSION

This study indicates that heart rate reduction has been associated with an improvement in quality of life in patients with stable coronary artery disease, presenting new opportunities for treatment.

β-blockers and their mortality benefits: underprescribed in heart failure and chronic obstructive pulmonary disease

This article discusses the most recent insights into the actions of β-blockers on the heart and lungs, highlighting that β-blockers should have a place in the treatment of patients with chronic obstructive pulmonary disease (COPD), especially in those with coexisting cardiovascular disease or arterial hypertension. Practical studies clearly show underutilization of β-blockers in patients with heart failure and COPD, which seems to be caused by an unnecessary fear for adverse effects on the lungs, and the ‘outdated’ adverse effects mentioned on instruction leaflets.

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

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

Incremental value and safety of oral ivabradine for heart rate reduction in computed tomography coronary angiography

BACKGROUND

Heart rate (HR) reduction is essential to achieve optimal image quality and diagnostic accuracy with computed tomography coronary angiography (CTCA). Administration of ivabradine could be an attractive alternative to beta-blockade to reduce HR.

METHODS

One-hundred-twenty-three patients referred for CTCA were prospectively enrolled. Patients were divided in two groups depending on the absence or presence of chronic beta-blockade treatment. Within the two groups patients were randomized to either no additional premedication or oral ivabradine for 5 days prior to CTCA. In presence of chronic beta-blockade therapy it was shifted to atenolol 50mg twice a day for 5 days prior to CTCA. HR and blood pressure were assessed at admission (T0), immediately before CTCA (T1) and during CTCA (T2). The target HR was <65 bpm.

RESULTS

Ivabradine significantly reduced HR during CTCA. Mean relative HR reduction was 15% for controls, 12% for chronic beta-blockade, 19% for ivabradine and 24% for both chronic beta-blockade and ivabradine at T2 (p for trend <0.001). The rate of patients who reached the target HR at T2 was 83% in controls, 71% with chronic beta-blockade, 97% with ivabradine and 97% with both (p for trend <0.05). The percentage of patients that needed additional IV beta-blockade at T1 decreased from 69% to 40% with ivabradine and 30% with both (p for trend <0.05).

CONCLUSIONS

Ivabradine is safe and effective in increasing the rate of patients at target HR and in reducing the need for additional IV beta-blockade in patients referred for CTCA.

Impact of ‘‘Off-Label’’ Use of Ivabradine on Exercise Capacity, Gas Exchange, Functional Class, Quality of Life, and Neurohormonal Modulation in Patients With Ischemic Chronic Heart Failure

Background: Epidemiologic studies indicate that elevated heart rate (HR) is an independent risk factor for mortality and morbidity in patients (pts) with chronic heart failure (CHF). Clinical trials with β-blockers suggest that HR reduction is an important mechanism of their benefit in pts with stable CHF. Pharmacologic inhibition of the If current now provides the opportunity of pure HR reduction. The purpose of this study was to evaluate the impact of ‘‘Off-Label’’ use of ivabradine on exercise capacity, gas exchange, functional class, quality of life, and neurohormonal modulation in pts with ischemic CHF. Methods: Between January 2008 and June 2008, a graded maximal exercise test with respiratory gas analysis and an endurance test with constant workload corresponding to 85% of the peak VO2 at the baseline and after 3 months were performed, and at the same times, N-terminal probrain natriuretic peptide (NT-proBNP) levels were also measured, in 60 pts (45 M, 15 F, mean age 52.7 ± 5.3 years), with stable ischemic CHF, New York Heart Association (NYHA) functional classes II (n = 35)—III (n = 25), with left ventricular ejection fraction (LVEF) ≤ 40%, randomized to a ‘‘off-label’’ ivabradine use (n = 30) and a control group (n = 30). Results: The exercise capacity increased from 14.8 ± 2.5 to 28.2 ± 3.5 min (P < .0001) and the peak oxygen consumption tended to improve from 13.5 ± 1.3 to 17.9 ± 2.4 mL/kg per minute (P < .0001) in ivabradine group. Oxygen consumption at the anaerobic threshold (AT) increased from 11.9 ± 1.4 to 15.3 ± 1.4 mL/kg per minute (P < .0001). NTproBNP levels decreased from 2356 ± 2113 pg/mL to 1434 ± 1273 pg/mL (P = .045). No significant differences were found in control group at 3 months. The positive ivabradine effects were also associated with an improvement in the NYHA functional class and quality of life. Conclusion: The ‘‘Off-Label’’ use of ivabradine significantly improves the exercise capacity, gas exchange, functional heart failure class, quality of life, and neurohormonal modulation in pts with ischemic CHF.