Importance of heart rate in determining beta-blocker efficacy in acute and long-term acute myocardial infarction intervention trials

Use of beta-blockers and effects on heart rate and blood pressure post-acute coronary syndromes: are we on target?

BACKGROUND

beta-blockers have been shown to benefit patients after myocardial infarction by decreasing mortality, sudden cardiac death, and reinfarction. Although beta-blockers are recommended for all patients with acute coronary syndromes (ACS) without contraindications, a target heart rate (HR) is recommended only for patients with unstable angina/non ST-elevation myocardial infarction. A contemporary series documenting trends in beta-blocker usage and achieved HR and blood pressures (BP) is not available. The study objectives were to monitor trends in HR and BP in relation to beta-blocker use in a contemporary series of patients with ACS.

METHODS

In this observational study, 300 consecutive patients with proven ACS had HR and BP values collected hourly from admission until hospital discharge and averaged at multiple intervals throughout hospital stay. Data on baseline demographic characteristics, beta-blocker doses, and titration schedules, procedures performed, cardiac regimens, concurrent medical issues, and contraindications to therapy were collected.

RESULTS

Only 5.3% achieved an average HR of 50 to 60 beat/min throughout the hospital stay. Overall, the average HR was 74 beat/min and average BP was 115/64 mm Hg. Admission daily doses of metoprolol averaged 58 mg compared to discharge daily doses of 88 mg; only 52% of patients had dosage increases.

CONCLUSIONS

Although effective levels of BP were maintained during hospitalization for an ACS, target HRs were generally not achieved. Future studies are needed to determine the relationship between treatment objectives and clinical outcomes in the present era of ACS management.

Heart rate, autonomic markers, and cardiac mortality

Heart rate is a precisely regulated variable, which plays a critical role in health and disease. Numerous epidemiologic studies and large post-myocardial infarction trials have provided evidence that elevated resting heart rate is an independent risk factor for cardiac mortality. This body of knowledge has prompted the development and evaluation of negative chronotropic agents, prototypically the I(f) inhibitor Ivabradine. The present review addresses several fundamental questions: (1) How is heart rate regulated at the integrative, cellular, and molecular levels? (2) How are autonomic tone and reflexes measured clinically, and what is the prognostic utility of these parameters? (3) What mechanisms are responsible for the cardiovascular pathology associated with elevated heart rates? (4) Does reducing heart rate independent of effects on other factors protect against cardiovascular events?

Impact of a pure reduction in heart rate for the treatment of left ventricular dysfunction: clinical benefits of ivabradine in the BEAUTIFUL trial

Ivabradine is an I(f) current inhibitor, that has documented antianginal efficacy. The BEAUTIFUL trial tested ivabradine against placebo in a large population of 10,917 patients in sinus rhythm, with coronary artery disease and left ventricular dysfunction, defined as left ventricular ejection fraction < or =35%. Overall, there was no impact of ivabradine on the primary end-point of the trial (cardiovascular mortality, hospitalisation for myocardial infarction, new onset or worsening heart failure). In the placebo arm of the trial, baseline heart rate > or = 70 bpm was associated with an increased risk of cardiovascular mortality, myocardial infarction, heart failure and coronary revascularisation. In the subgroup of patients with a baseline heart rate > or =70 bpm, treatment with ivabradine resulted in a significant, 36% reduction in the risk of myocardial infarction and a 20% reduction in the need for coronary revascularisation. Ivabradine was well tolerated, with an increased rate of treatment discontinuation, mainly due to bradycardia, compared with placebo. Because of its safety and efficacy to control angina, ivabradine should be considered first-line antianginal treatment in coronary artery disease patients with left ventricular dysfunction and increased heart rate, already receiving beta-blocker therapy or in whom these medications are not tolerated.

[Heart rate reduction: beneficial effects in heart failure and post-infarcted myocardium]

Heart rate (HR) is an independent predicting factor of cardiovascular events in patients with advanced heart failure. Clinical trials conducted with beta-blockers have demonstrated that reduction of HR is a fundamental mechanism to explain the reduction of morbidity-mortality in such a disease. Trials conducted with ivabradine, the first selective inhibitor of the I(f) current in cardiac pacemaker cells, have also clearly confirmed that reduction of HR lead to powerful and sustained favourable effects in patients with cardiac failure and post-infarcted myocardial diseases. These effects are not only due to the reduction of the risk factors associated with myocardial ischemia but also to the reduction of cardiac and perivascular fibrosis associated with the remodelling process at the ventricular level. Although the mechanisms associated with reduction of HR following administration of beta-blockers and ivabradine are to a large extent similar, others like their effects on post-systolic contraction are totally opposed. So, new clinical trials are necessary to know whether it is possible to substitute these drugs or conversely to associate them for an optimal therapeutic strategy in patients with advanced heart failure and post-infarcted myocardium.

Elevated heart rate: a "new" cardiovascular risk factor?

A number of epidemiologic studies and several experimental lines of research point to high heart rate as a main risk factor for cardiovascular disease. However, translating research into clinical practice has been a challenge throughout medical history. From the present symposium, it appears clear that this is particularly the case for heart rate. The complex nature of atherogenesis makes it difficult to establish the role of a putative risk factor because of the correlations and complex interactions among factors. The pathogenetic mechanisms for the connection of resting heart rate with atherosclerosis and cardiovascular morbidity have been elaborated extensively in the chapter papers of this symposium, suggesting that there is a causal relationship between heart rate and cardiovascular mortality. The benefit of heart rate reduction has been proved in patients with coronary artery disease or congestive heart failure. Until now it has been difficult to determine whether modulation of heart rate is beneficial also in patients free of cardiac diseases. This concern, however, does not in any fashion suggest that health care professionals should pay less attention to this clinical variable. The impressive amount of available epidemiologic data show support for the continued effort to raise awareness of the clinical importance of resting heart rate among health care professionals.

Heart rate in coronary syndromes and heart failure

In the past 2 decades, there have been growing evidences that resting heart rate might be a marker of risk or even a risk factor for cardiovascular morbidity and mortality. This article reviews current evidences concerning the relation between heart rate and patients' outcome in different clinical settings such as acute coronary syndromes, left ventricular systolic dysfunction, and heart failure. The relationship between resting heart rate and the development of coronary artery disease, as well as all-cause and cardiovascular mortality, has been found to be strong, graded, and independent from other risk factors. Several lines of research indicate that heart rate plays an important role in the pathophysiology of atherosclerosis and in the clinical manifestations of coronary artery disease and that it is an independent prognostic factor in all coronary syndromes. The prognostic value of elevated heart rate in patients with heart failure has been tested in several clinical trials evaluating pharmacologic heart rate-lowering agents (eg, beta-blockers). It is difficult to determine which percentage of the clinical benefit obtained with beta-blockers is related to induced bradycardia because cardiac slowing is only one of the effects of these drugs. In the BEAUTIFUL trial, a subgroup analysis conducted in patients with resting HR more than 70 beats per minute showed that treatment with ivabradine was able to improve outcome. According to the results presented in this review, we can conclude that heart rate is a predictor of death in both stable coronary artery disease and acute coronary syndromes. Elevated heart rate is also able to negatively predict clinical outcomes in patients with heart failure. However, it is still unclear if heart rate reduction per se can improve prognosis.

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

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

The Secondary Prevention of myocardial infarction by drug treatment; excluding lipid lowering agents

About 10% of survivors of an acute myocardial infarction will die in the following year. Thereafter the risk declines but reinfarction is still an important cause of mortality and morbidity. The post infarction trials have clearly shown that the best proven agents to mitigate this toll are aspirin, beta adrenoceptor blockers, and verapamil (but not other calcium blockers, except diltiazem for non Q wave infarction). In the context of hypertension treatment these post infarction trials may have important lessons for drug selection and ancillary treatment since the majority of subjects will ultimately die of ischaemic heart disease. Although the newer agents such as ACE and renin inhibitors, newer calcium channel blockers and alpha blockers have many promising properties in terms of risk factor reduction, no convincing mortality data exists; it is needed. This review will deal with the known effects (both good and bad) of antihypertensive agents and will also review other drug strategies relevant to the hypertensive patient. It will also point out large areas of ignorance.

Ivabradine: beyond heart rate control

Chronic stable angina pectoris (CSAP) usually occurs in patients with coronary artery disease (CAD) that affects one or more large epicardial arteries. It results when myocardial perfusion is insufficient to meet cardiac metabolic demand. Elevated heart rate (HR) is an important factor in the development of myocardial ischemia and angina pectoris. The pharmacologic agents most commonly administered in the treatment of CSAP are beta-blockers and calcium channel blockers (CCBs). However, the use of beta-blockers is limited by poor compliance related to contraindications and comorbidities, especially in elderly patients. Ivabradine is a new selective HR-lowering agent that selectively inhibits the pacemaker current I (f) in the sinus atrial node. In several randomized controlled trials, ivabradine 5-10 mg twice daily has demonstrated equivalent anti-ischemic and anti-anginal activity to beta-blockers and CCBs, with a good safety and tolerability profile. Although ivabradine has been shown not to improve cardiac outcomes in patients with stable CAD and left ventricular systolic dysfunction, it may be used to reduce the incidence of CAD outcomes in a subgroup of patients with HR > or =70 bpm. The aim of this short review is to summarize the use of ivabradine in the treatment of CSAP, and its potential utility in atherosclerosis, primitive and dilatative cardiomyopathy, and arrhythmias, such as postural tachycardia syndrome and inappropriate sinus tachycardia, where exclusive lowering of elevated HR may prove beneficial.

Heart rate as a treatable cardiovascular risk factor

BACKGROUND

Although several epidemiological studies demonstrate the association between resting heart rate (HR) and cardiovascular morbidity and mortality, an elevated HR remains a neglected cardiovascular risk factor.

SOURCES OF DATA

This review summarizes the results of published studies on the relationship between elevated HR and cardiovascular risk.

AREAS OF AGREEMENT

The role of HR in myocardial ischaemia in coronary patients is well known. Experimental data and clinical observations support the importance of HR in the pathophysiology of atherosclerosis and plaque rupture. A large body of evidence points to high resting HR as a risk factor for mortality in various populations, including coronary patients.

AREAS OF CONTROVERSY

HR reduction is suggested to be a mechanism explaining the prognostic benefit of beta-blockers after myocardial infarction or in heart failure patients. However, it was unclear whether HR reduction per se directly affects cardiovascular prognosis. Treatment with ivabradine, a pure HR-reducing agent, provides an opportunity to assess the effects of selectively lowering HR without altering other aspects of cardiac function.

GROWING POINTS

The results of the recent Morbidity-Mortality Evaluation of the I(f) Inhibitor Ivabradine in Patients with Coronary Disease and Left Ventricular Dysfunction study underline the importance of HR reduction in the management of stable coronary artery disease. The prospective analysis of data from the placebo arm demonstrated that elevated resting HR (>or=70 bpm) is a strong independent predictor of clinical outcomes. Consistent with these data, ivabradine significantly improved coronary outcomes in patients with a HR of 70 bpm or more. AREAS TIMELY FOR DEVELOPMENT: These data support the importance of HR in the management of stable coronary artery disease to assess prognosis and to guide optimal therapy.

Heart rate, lifespan, and mortality risk

An increasing body of scientific research and observational evidence indicates that resting heart rate (HR) is inversely related to the lifespan among homeothermic mammals and within individual species. In numerous human studies with patients stratified by resting HR, increased HR is universally associated with greater risk of death. The correlation between HR and maximum lifespan seems to be due to both basal metabolic rate and cardiovascular-related mortality risk. Both intrinsic and extrinsic factors are already postulated to determine how the biological clock works, through regulating and modulating the processes such as protein oxidation, free radical production, inflammation and telomere shortening. Given the remarkable correlation between HR and lifespan, resting HR should be seriously considered as another possible cap on maximum lifespan. Future research is needed to determine whether deliberate cardiac slowing, through methods like lifestyle modification, pharmacological intervention, or medical devices, can decelerate biological clock of aging, reduce cardiovascular mortality and increase maximum lifespan in humans in general.

Low-dose estrogen therapy does not change postexercise hypotension, sympathetic nerve activity reduction, and vasodilation in healthy postmenopausal women

The aim of this study was to determine whether estrogen therapy enhances postexercise muscle sympathetic nerve activity (MSNA) decrease and vasodilation, resulting in a greater postexercise hypotension. Eighteen postmenopausal women received oral estrogen therapy (ET; n = 9, 1 mg/day) or placebo ( n = 9) for 6 mo. They then participated in one 45-min exercise session (cycle ergometer at 50% of oxygen uptake peak) and one 45-min control session (seated rest) in random order. Blood pressure (BP, oscillometry), heart rate (HR), MSNA (microneurography), forearm blood flow (FBF, plethysmography), and forearm vascular resistance (FVR) were measured 60 min later. FVR was calculated. Data were analyzed using a two-way ANOVA. Although postexercise physiological responses were unaltered, HR was significantly lower in the ET group than in the placebo group (59 ± 2 vs. 71 ± 2 beats/min, P < 0.01). In both groups, exercise produced significant decreases in systolic BP (145 ± 3 vs. 154 ± 3 mmHg, P = 0.01), diastolic BP (71 ± 3 vs. 75 ± 2 mmHg, P = 0.04), mean BP (89 ± 2 vs. 93 ± 2 mmHg, P = 0.02), MSNA (29 ± 2 vs. 35 ± 1 bursts/min, P < 0.01), and FVR (33 ± 4 vs. 55 ± 10 units, P = 0.01), whereas it increased FBF (2.7 ± 0.4 vs. 1.6 ± 0.2 ml·min−1·100 ml−1, P = 0.02) and did not change HR (64 ± 2 vs. 65 ± 2 beats/min, P = 0.3). Although ET did not change postexercise BP, HR, MSNA, FBF, or FVR responses, it reduced absolute HR values at baseline and after exercise.

Nighttime heart rate and survival in depressed patients post acute myocardial infarction

OBJECTIVES

To determine if: 1) depressed patients with a recent acute myocardial infarction (AMI) have higher nighttime heart rate (HR) than nondepressed patients, and 2) elevated nighttime HR is associated with decreased survival post AMI. Depression is a risk factor for mortality post AMI. It is also associated with sleep disturbances and with elevated HR, which may be more pronounced at night. Resting and 24-hour HR have been found to predict mortality in patient and community samples.

METHODS

Ambulatory electrocardiographic data were obtained from 333 depressed patients and 383 nondepressed patients with recent AMI. They were followed for up to 30 months (median = 24 months).

RESULTS

Depressed patients had higher nighttime HR (70.7 +/- 0.7 versus 67.7 +/- 0.6 beats per minute (bpm); p = .001), and daytime HR (76.4 +/- 0.7 versus 74.2 +/- 0.6 bpm; p = .02) than nondepressed patients, even after adjusting for potential confounds. Depression (hazard ratio (Haz R) = 2.19; p = .02) and nighttime HR (Haz R = 1.03; p = .004), but not daytime HR, predicted survival after adjusting for other major predictors and for each other. The interaction between nighttime HR and depression on survival approached, but did not achieve, significance (p = .08).

CONCLUSIONS

Mean day and nighttime HR values are higher in depressed patients than in nondepressed patients post AMI. Depression and elevated nighttime HR, but not daytime HR, are independent predictors of survival in these patients. Although depressed patients have a higher nighttime HR than nondepressed patients, nighttime HR predicts mortality in both depressed and nondepressed patients.

Assessment of autonomic function in cardiovascular disease: physiological basis and prognostic implications

Certain abnormalities of autonomic function in the setting of structural cardiovascular disease have been associated with an adverse prognosis. Various markers of autonomic activity have received increased attention as methods for identifying patients at risk for sudden death. Both the sympathetic and the parasympathetic limbs can be characterized by tonic levels of activity, which are modulated by, and respond reflexively to, physiological changes. Heart rate provides an index of the net effects of autonomic tone on the sinus node, and carries prognostic significance. Heart rate variability, though related to heart rate, assesses modulation of autonomic control of heart rate and carries additional prognostic information, which in some cases is more powerful than heart rate alone. Heart rate recovery after exercise represents the changes in autonomic tone that occur immediately after cessation of exercise. This index has also been shown to have prognostic significance. Autonomic evaluation during exercise and recovery may be important prognostically, because these are high-risk periods for sudden death, and the autonomic changes that occur with exercise could modulate this high risk. These markers provide related, but not redundant information about different aspects of autonomic effects on the sinus node.

Resting heart rate: a modifiable prognostic indicator of cardiovascular risk and outcomes?

A growing body of evidence from clinical trials and epidemiological studies has identified elevated resting heart rate as a predictor of clinical events. Proof of direct cause and effect is limited, because current drugs that lower heart rate (eg, beta-blockers) have multiple mechanisms of action. A new class of drug, selective I(f) inhibitors, is under investigation as a 'pure' heart rate-reducing medication and will help confirm if there is a causal link between elevated heart rate and cardiovascular outcomes. The present paper reviews the evidence for elevated heart rate as a cardiovascular risk factor and some of the current clinical trials testing this hypothesis.

Post-myocardial infarction beta-blocker therapy: the bradycardia conundrum. Rationale and design for the Pacemaker & beta-blocker therapy post-MI (PACE-MI) trial

Multiple clinical trials have demonstrated beta-blockers improving survival after myocardial infarction (MI). Patients with "bradycardia-related" contraindications to beta-blockers, such as those with asymptomatic bradycardia or AV conduction abnormalities, have been excluded from clinical trials of beta-blockers and continue to be excluded from post-MI beta-blocker therapy in routine clinical practice. These patients tend to be elderly and have a high 1-year mortality. If beta-blockers provide benefit to the post-MI patient independent of their heart rate-lowering effect, then these patients could benefit substantially from initiation of beta-blocker therapy. However, in this particular group of patients, beta-blockers can be safely initiated only if more severe or significant bradycardia can be prevented by pacemaker implantation. It is unclear whether adverse effects related to pacemaker implantation could also negate some or all of the hypothesized benefit of beta-blocker therapy. Although beta-blockers are particularly effective in the elderly, the benefit of beta-blocker therapy in patients with bradycardia-related contraindications to beta-blockers has not been established. The PACE-MI trial is a randomized controlled trial that will address whether beta-blocker therapy enabled by pacemaker implantation is superior to no beta-blocker and no pacemaker therapy after MI in patients with rhythm contraindications to beta-blockers or in those who have developed symptomatic bradycardia due to beta-blockers. The trial will randomize 1124 patients to standard therapy (not to include beta-blockers as patients must have a contraindication to be enrolled) or standard therapy plus pacemaker implantation and beta-blocker. The primary end point is the composite end point of total mortality plus nonfatal reinfarction.

Factors affecting heart rate as measured at home among treated hypertensive patients: the Japan home versus office blood pressure measurement evaluation (J-HOME) study

We previously reported that a resting heart rate measured at home (home HR) of >or=70 beats per minute was a powerful predictor of the risk of cardiovascular disease mortality, and identified factors affecting home HR in the general Japanese population. The present study examines factors affecting home HR in hypertensive patients treated with antihypertensive medications. Home HR was measured using a home blood pressure (BP) device. Information about the characteristics of the patients was collected using questionnaires administered by a physician. Among 3,400 patients, 3,086 measured home HR both in the morning and evening. The mean values of home HR in the morning and evening were 67.2+/-9.1 and 69.6+/-9.2 beats per minute, respectively. Multivariate linear regression analysis showed that lower age, diabetes mellitus, habitual smoking, higher diastolic BP, and the lack of beta-blocker or angiotensin-converting enzyme inhibitor use were determinants of elevated morning or evening home HR. These results suggest that adequate control of risk factors for cardiovascular disease such as smoking and diabetes mellitus or use of heart rate-lowering agents might help to decrease home HR in treated hypertensive patients.

European guidelines on cardiovascular disease prevention in clinical practice: executive summary. Fourth Joint Task Force of the European Society of Cardiology and other societies on cardiovascular disease prevention in clinical practice (constituted by representatives of nine societies and by invited experts)

Other experts who contributed to parts of the guidelines: Edmond Walma, Schoonhoven (The Netherlands), Tony Fitzgerald, Dublin (Ireland), Marie Therese Cooney, Dublin (Ireland), Alexandra Dudina, Dublin (Ireland) European Society of Cardiology (ESC) Committee for Practice Guidelines (CPG):, Alec Vahanian (Chairperson) (France), John Camm (UK), Raffaele De Caterina (Italy), Veronica Dean (France), Kenneth Dickstein (Norway), Christian Funck-Brentano (France), Gerasimos Filippatos (Greece), Irene Hellemans (The Netherlands), Steen Dalby Kristensen (Denmark), Keith McGregor (France), Udo Sechtem (Germany), Sigmund Silber (Germany), Michal Tendera (Poland), Petr Widimsky (Czech Republic), José Luis Zamorano (Spain)

Document reviewers: Irene Hellemans (CPG Review Coordinator) (The Netherlands), Attila Altiner (Germany), Enzo Bonora (Italy), Paul N. Durrington (UK), Robert Fagard (Belgium), Simona Giampaoli(Italy), Harry Hemingway (UK), Jan Hakansson (Sweden), Sverre Erik Kjeldsen (Norway), Mogens Lytken Larsen (Denmark), Giuseppe Mancia (Italy), Athanasios J. Manolis (Greece), Kristina Orth-Gomer (Sweden), Terje Pedersen (Norway), Mike Rayner (UK), Lars Ryden (Sweden), Mario Sammut (Malta), Neil Schneiderman (USA), Anton F. Stalenhoef (The Netherlands), Lale Tokgözoglu (Turkey), Olov Wiklund (Sweden), Antonis Zampelas (Greece)

Control of home heart rate and home blood pressure levels in treated patients with hypertension: the J-HOME study

OBJECTIVE

Recently, it was found that resting heart rate (HR) measured at home (home HR), as well as self-measured blood pressure (BP) at home (home BP), was a strong predictor of the risk of cardiovascular disease mortality in the general Japanese population. It was also reported that home BP levels were not adequately controlled in hypertensive patients. Little information, however, is available on the current status of home HR control in treated patients with hypertension. The objective of this study was to examine the current status of home HR control and home BP control among treated patients with hypertension.

METHODS

Home HR and BP were measured using a self-monitored BP measuring device. Morning home HR and BP were obtained in 3183 patients and evening home HR and BP were obtained in 3106 patients. On the basis of an earlier study, we defined a home HR value of >or=70 beats/min as 'high home HR'.

RESULTS

The mean home HR value was 67.2+/-9.1 beats/min in the morning and 69.6+/-9.2 beats/min in the evening. Of the 3183 patients, 35.7% had a high home HR in the morning and 46.7% of the 3106 patients had a high home HR in the evening. The prevalence of patients with a high home HR and a controlled home BP (<135/85 mmHg) was 11.3% in the morning and 24.2% in the evening.

CONCLUSION

Resting home HR control and home BP control were inadequate.

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.

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.

Estimation of microinhomogeneity of conduction impairment by wavelet analysis during early phase of myocardial ischemia in pigs

Ventricular fibrillation (VF) is most frequent in the very early phase in acute coronary occlusion, and is triggered by the re-entrant mechanism in this phase. An inhomogeneous conduction in the ischemic myocardium would be substrates for re-entry. The aim of this study was to examine the relationship between the severity of irregularities of the QRS complex and VF. Eleven pigs were analyzed, and the heart was fixed in the pericardial cradle. Ag-AgCl bipolar electrodes were fixed on the epicardium in ischemic and non-ischemic regions. The proximal portion of the left anterior descending coronary artery was occluded for one hour. Electrocardiograms (ECGs) were continuously recorded on a magnetic tape, and wavelet analysis was performed on signal-averaged ECG (25 beats) every 60 sec after the experiment. The number of local maxima (N) and the duration between the first and the last local maximum (D) were automatically measured. N and D significantly increased in the ischemic area, but not in the non-ischemic area. N and D increased approximately twofold just before the occurrence of VF in 8 fibrillated pigs (p<0.01, each). There were significant positive linear relationships between the rate of increase in N and D to VF and basal heart rate before coronary occlusion (r=0.90, p <0.01 in N, r=0.84, p <0.01 in D at 160 Hz). These results suggest that there would be a threshold inhomogeneous conduction for the occurrence of VF and an increase in heart rate would accelerate the inhomogeneous conduction in acute myocardial ischemia.

[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.

[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.

La fréquence cardiaque, facteur pronostique majeur du risque cardiovasculaire

The prognostic value of heart rate (HR) was analysed based on the reports from the literature in the general population and in patients with coronary artery disease (CAD). Multivariate analyses showed that elevated resting HR was found to be an independent predictor of total and cardiovascular mortality. The behaviour of HR during exercise testing was predictive of sudden death. The beneficial effects of betablockers in post-infarction patients are well established. Calcium channel blockers that increase resting HR are associated with a deleterious effect on mortality. Therefore, resting HR should not be overlooked in risk stratification of CAD patients. Reduction of resting HR should be viewed as an attractive therapeutic target in CAD patients.