Efficacy of a beta-adrenergic receptor antagonist, propranolol, in preventing ischaemic ventricular fibrillation: dependence on heart rate and ischaemia duration

Reduced hepatic bradykinin degradation accounts for cold-induced BAT thermogenesis and WAT browning in male mice

An important role for liver in the regulation of adipose tissue thermogenesis upon cold exposure has been suggested; however, the underlying mechanisms remain incompletely defined. Here, we identify elevated serum bradykinin levels in response to acute cold exposure in male mice. A bolus of anti-bradykinin antibodies reduces body temperature during acute cold exposure, whereas bradykinin has the opposite effect. We demonstrate that bradykinin induces brown adipose tissue thermogenesis and white adipose tissue browning, and bradykinin increases uncoupling protein 1 (UCP1) expression in adipose tissue. The bradykinin B2 receptor (B2R), adrenergic signaling and nitric oxide signaling are involved in regulating bradykinin-increased UCP1 expression. Moreover, acute cold exposure inhibits hepatic prolyl endopeptidase (PREP) activity, causing reduced liver bradykinin degradation and increased serum bradykinin levels. Finally, by blocking the breakdown of bradykinin, angiotensin-converting enzyme inhibitors (ACEIs) increase serum bradykinin levels and induce brown adipose tissue thermogenesis and white adipose tissue browning via B2R. Collectively, our data provide new insights into the mechanisms underlying organ crosstalk in whole-body physiology control during cold exposure and also suggest bradykinin as a possible anti-obesity target.

Hepatic c-Jun regulates glucose metabolism via FGF21 and modulates body temperature through the neural signals

Objective

c-Jun, a prominent member of the activator protein 1 (AP-1) family, is involved in various physiology processes such as cell death and survival. However, a role of hepatic c-Jun in the whole-body metabolism is poorly understood.

Methods

We generated liver-specific c-Jun knock-out (c-jun^△li) mice to investigate the effect of hepatic c-Jun on the whole-body physiology, particularly in blood glucose and body temperature. Primary hepatocytes were also used to explore a direct regulation of c-Jun in gluconeogenesis.

Results

c-jun^△li mice showed higher hepatic gluconeogenic capacity compared with control mice, and similar results were obtained in vitro. In addition, fibroblast growth factor 21 (FGF21) expression was directly inhibited by c-Jun knockdown and adenovirus-mediated hepatic FGF21 over-expression blocked the effect of c-Jun on gluconeogenesis in c-jun^△li mice. Interestingly, c-jun^△li mice also exhibited higher body temperature, with induced thermogenesis and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). Furthermore, the body temperature became comparable between c-jun^△li and control mice at thermoneutral temperature (30 °C). Moreover, the activity of sympathetic nervous system (SNS) was increased in c-jun^△li mice and the higher body temperature was inhibited by beta-adrenergic receptor blocker injection. Finally, the activated SNS and increased body temperature in c-jun^△li mice was most likely caused by the signals from the brain and hepatic vagus nerve, as the expression of c-Fos (the molecular marker of neuronal activation) was changed in several brain areas controlling body temperature and body temperature was decreased by selective hepatic vagotomy.

Conclusions

These data demonstrate a novel function of hepatic c-Jun in the regulation of gluconeogenesis and body temperature via FGF21 and neural signals. Our results also provide novel insights into the organ crosstalk in the regulation of the whole-body physiology.

•

Liver-specific inactivation of c-Jun increased gluconeogenesis via decreasing FGF21 expression.

•

Liver-specific inactivation of c-Jun increased body temperature by promoting thermogenesis in BAT.

•

Hepatic c-Jun modulates body temperature via regulating sympathetic nervous system activity and vagus nerve.

Relation of Higher Resting Heart Rate to Risk of Cardiovascular Versus Noncardiovascular Death

Higher resting heart rate (RHR) is associated with increased risk of all-cause and cardiovascular mortality, with some reports showing the magnitude of association with all-cause mortality being stronger than that with cardiovascular mortality. This suggests that RHR association with mortality may not be limited to cardiovascular death. We compared the association between RHR with cardiovascular and noncardiovascular mortality in 6,743 participants (mean age 58.7 years, 52% women, 48% non-Hispanic whites) from the Third National Health and Nutrition Examination Survey (NHANES-III) after excluding those on antiarrhythmic drugs or with missing data. RHR data were obtained from standard 12-lead electrocardiogram recorded on the NHANES participants during a physical examination. National Death Index was used to identify the date and cause of death. Multivariable Cox proportional hazards analysis was used to calculate the hazard ratios (HRs) and 95% CIs for cardiovascular mortality and noncardiovascular mortality, separately, associated with 10 beats/min increase in RHR. During a median follow-up of 13.9 years, 906 cardiovascular deaths and 1,306 noncardiovascular deaths occurred. In models adjusted for age, gender, race, hypertension, diabetes, obesity, dyslipidemia, previous cardiovascular disease, smoking, cancer, chronic obstructive airway disease, thyroid disease, and serum creatinine, higher RHR was associated with increased risk of both cardiovascular mortality and noncardiovascular mortality with a relatively similar magnitude of risk (HR 1.19, 95% CI 1.12 to 1.26 and HR 1.23, 95% CI 1.17 to 1.29, respectively). In conclusion, higher RHR is associated with both cardiovascular mortality and noncardiovascular mortality suggesting that RHR is probably a marker of overall well-being rather than a marker of cardiovascular health.

Effect of Resting Heart Rate on All-Cause Mortality and Cardiovascular Events According to Age

OBJECTIVES

To examine whether the association between resting heart rate (RHR) and all-cause mortality and cardiovascular events differs according to age.

DESIGN

Prospective cohort.

SETTING

Community in Beijing, China.

PARTICIPANTS

Individuals aged 40 and older without cardiovascular disease at baseline (N = 6,209).

MEASUREMENTS

Trained investigators interviewed participants using a standard questionnaire to obtain information on demographic characteristics, medical history and lifestyle risk factors in 1991. RHR was evaluated according to quartiles (<72, 72-76, 76-84, ≥84 beats/min). Cox regression models were used to assess the associations between RHR and all-cause mortality and cardiovascular events.

RESULTS

During a mean follow-up of 8.3 years, 840 subjects died, and 676 experienced a cardiovascular event. Higher RHR was significantly associated with all-cause mortality (P trend < .001) and cardiovascular events (P trend = .002) in older (≥60) but not younger (<60) participants (both P trend > .05). There were significant modifying effects of age on the association between RHR and all-cause mortality (P interaction < .001) and cardiovascular events (P interaction =.002). Similar results were observed after exclusion of individuals who died (n = 100) or had a cardiovascular event (n = 45) during the first 2 years of follow-up.

CONCLUSION

High RHR appears to be an independent determinant of all-cause mortality and cardiovascular events in older but not younger individuals.

β-Adrenergic stimulation and rapid pacing mutually promote heterogeneous electrical failure and ventricular fibrillation in the globally ischemic heart

Global ischemia, catecholamine surge, and rapid heart rhythm (RHR) due to ventricular tachycardia or ventricular fibrillation (VF) are the three major factors of sudden cardiac arrest (SCA). Loss of excitability culminating in global electrical failure (asystole) is the major adverse outcome of SCA with increasing prevalence worldwide. The roles of catecholamines and RHR in the electrical failure during SCA remain unclear. We hypothesized that both β-adrenergic stimulation (βAS) and RHR accelerate electrical failure in the globally ischemic heart. We performed optical mapping of the action potential (OAP) in the right ventricular (RV) and left (LV) ventricular epicardium of isolated rabbit hearts subjected to 30-min global ischemia. Hearts were paced at a cycle length of either 300 or 200 ms, and either in the presence or in the absence of β-agonist isoproterenol (30 nM). 2,3-Butanedione monoxime (20 mM) was used to reduce motion artifact. We found that RHR and βAS synergistically accelerated the decline of the OAP upstroke velocity and the progressive expansion of inexcitable regions. Under all conditions, inexcitability developed faster in the LV than in the RV. At the same time, both RHR and βAS shortened the time to VF (TVF) during ischemia. Moreover, the time at which 10% of the mapped LV area became inexcitable strongly correlated with TVF (R(2) = 0 .72, P < 0.0001). We conclude that both βAS and RHR are major factors of electrical depression and failure in the globally ischemic heart and may contribute to adverse outcomes of SCA such as asystole and recurrent/persistent VF.

Heart rate and cardiovascular protection

Recent large epidemiological studies have confirmed that an elevated resting heart rate is an independent predictor of cardiovascular and overall mortality in the general population as well as in patients with hypertension, coronary heart disease and chronic heart failure. Pathophysiological studies indicate that a higher heart rate has detrimental effects that favor myocardial ischemia, ventricular arrhythmias, as well as an increase in vascular oxidative stress, endothelial dysfunction and atherosclerosis progression. Benefits of heart rate lowering drugs, such as beta-blockers and ivabradine, in reducing overall and cardiovascular-related mortality, have been demonstrated particularly in patients with coronary heart disease and heart failure. However, despite these evidences, resting heart rate is still an overlooked cardiovascular risk factor.

Selective heart rate reduction with ivabradine slows ischaemia-induced electrophysiological changes and reduces ischaemia-reperfusion-induced ventricular arrhythmias

Heart rates during ischaemia and reperfusion are possible determinants of reperfusion arrhythmias. We used ivabradine, a selective I_f current inhibitor, to assess the effects of heart rate reduction (HRR) during ischaemia–reperfusion on reperfusion ventricular arrhythmias and assessed potential anti-arrhythmic mechanisms by optical mapping. Five groups of rat hearts were subjected to regional ischaemia by left anterior descending artery occlusion for 8 min followed by 10 min of reperfusion: (1) Control n = 10; (2) 1 μM of ivabradine perfusion n = 10; (3) 1 μM of ivabradine + 5 Hz atrial pacing throughout ischaemia–reperfusion n = 5; (4) 1 μM of ivabradine + 5 Hz pacing only at reperfusion; (5) 100 μM of ivabradine was used as a 1 ml bolus upon reperfusion. For optical mapping, 10 hearts (ivabradine n = 5; 5 Hz pacing n = 5) were subjected to global ischaemia whilst transmembrane voltage transients were recorded. Epicardial activation was mapped, and the rate of development of ischaemia-induced electrophysiological changes was assessed. HRR observed in the ivabradine group during both ischaemia (195 ± 11 bpm vs. control 272 ± 14 bpm, p < 0.05) and at reperfusion (168 ± 13 bpm vs. 276 ± 14 bpm, p < 0.05) was associated with reduced reperfusion ventricular fibrillation (VF) incidence (20% vs. 90%, p < 0.05). Pacing throughout ischaemia–reperfusion abolished the protective effects of ivabradine (100% VF), whereas pacing at reperfusion only partially attenuated this effect (40% VF). Ivabradine, given as a bolus at reperfusion, did not significantly affect VF incidence (80% VF). Optical mapping experiments showed a delay to ischaemia-induced conduction slowing (time to 50% conduction slowing: 10.2 ± 1.3 min vs. 5.1 ± 0.7 min, p < 0.05) and to loss of electrical excitability in ivabradine-perfused hearts (27.7 ± 4.3 min vs. 14.5 ± 0.6 min, p < 0.05). Ivabradine administered throughout ischaemia and reperfusion reduced reperfusion VF incidence through HRR. Heart rate during ischaemia is a major determinant of reperfusion arrhythmias. Heart rate at reperfusion alone was not a determinant of reperfusion VF, as neither a bolus of ivabradine nor pacing immediately prior to reperfusion significantly altered reperfusion VF incidence. This anti-arrhythmic effect of heart rate reduction during ischaemia may reflect slower development of ischaemia-induced electrophysiological changes.

Trimetazidine demonstrated cardioprotective effects through mitochondrial pathway in a model of acute coronary ischemia

Myocardial ischemia affects mitochondrial function leading to ionic imbalance and susceptibility to ventricular fibrillation. Trimetazidine (TMZ), a metabolic agent, is clinically used as an anti-anginal therapy. This study was conducted to compare the effect of TMZ 20 mg immediate release (IR) and TMZ 35 mg modified release (MR), two bioequivalent marketed formulations of TMZ, on cardioprotection during acute ischemia in pigs. A 4-day oral treatment with TMZ 20 mg IR (800 mg, tid) or TMZ 35 mg MR (1,400 mg, bid) had no effect on ventricular fibrillation threshold (VFT) prior to ischemia but significantly prevented the decrease in VFT observed in placebo-treated groups after a 1-min left anterior descending coronary artery occlusion. This effect occurred without modifying cardiac hemodynamic and conduction parameters. In both TMZ-treated groups, a significant reduction of the ischemic area as well as a protection of cardiomyocytes were observed. Cardiac enzymatic activity (phosphorylase, succinate dehydrogenase, ATPase) was increased in TMZ-treated groups. Both formulations preserved mitochondrial structure and improved mitochondrial function as demonstrated by a twofold increase of oxidative phosphorylation, by a reduction of reactive oxygen species (ROS) production (>30 %) and by a trend to increase the mitochondrial calcium retention capacity. In this model of ischemia, both TMZ formulations, leading to equivalent TMZ plasma exposures, demonstrated similar cardioprotective effects. This protection could be attributed to a preservation of mitochondrial structure and function, which plays a central role in ATP and ROS production and consequently could be considered as a target of cardioprotection.

Heart rate: a forgotten link in coronary artery disease?

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

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

BACKGROUND

Tachycardia often facilitates ischemic ventricular fibrillation (VF).

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Beta-blocker use and the changing epidemiology of out-of-hospital cardiac arrest rhythms

BACKGROUND

The incidence of ventricular fibrillation (VF) as the presenting rhythm in out-of-hospital cardiac arrest (OHCA) is declining, whereas pulseless electrical activity (PEA) is increasing. This changing epidemiology has occurred concomitant with an increase in beta-blocker use.

AIMS

The aim of this study was to measure the association of beta-blocker use among prehospital cardiac arrest patients with PEA versus VF as presenting rhythm.

MATERIALS AND METHODS

In this retrospective cohort study, records of all OHCA patients presenting to a single municipal hospital between 1 January 2001 and 31 December 2006 were reviewed. Age, sex, race, first documented rhythm, estimated down time, presence of bystander CPR, return of spontaneous circulation, beta-blocker use, and comorbid illnesses were noted. A Mantel-Haenzel chi-square was computed to describe the association between beta-blocker use and PEA, compared to beta-blocker use and VF. A sensitivity analysis was also performed to account for missing data, misclassification of beta-blocker use, misclassification of initial rhythm, confounding by unknown factors, and random error.

RESULTS

After exclusion of patients with asystole and patients in whom beta-blocker use was unclear/unknown, a cohort of 179 arrests was evaluated. The odds ratio for beta-blocker use among PEA versus VF patients was 3.7 (95% CI 1.9-7.2), and probabilistic adjustment for exposure and outcome misclassification, confounding, and random error increased the odds ratio to 5.0 (95% CI 1.1-31.0).

CONCLUSIONS

There appears to be an association between beta-blockers and the changing epidemiology of arrest rhythms, which may account for the increasing incidence of PEA and concomitant decrease in VF.

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.

Role of the Posterior Papillary Muscle and Purkinje Potentials in the Mechanism of Ventricular Fibrillation in Open Chest Dogs and Swine: Effects of Catheter Ablation

BACKGROUND

Papillary muscle (PM) ablation may terminate ventricular fibrillation (VF) in rabbit hearts. Whether or not PM ablation prevents ventricular fibrillation (VF) induction in large animals is unknown.

METHODS

We performed noncontact endocardial mapping and/or high-density epicardial mapping during VF in 12 dogs and 16 swine and tested the effects of posterior PM (PPM) ablation on VF inducibility.

RESULTS

During VF in progressive global ischemia (3 swine and 2 dogs), the highest dominant frequency (DF) was near PPM. The majority of the reentrant wavefronts during a propranolol infusion (swine) were anchored to the PPM. Purkinje potentials onset were recorded on the PPM both during sinus rhythm and during VF. Radiofrequency (RF) ablation of the endocardium on the PPM with a linear extension of the ablation line from the PPM to the mitral valve annulus and then the left ventricular apex in 7 dogs reduced the VF inducibility from 100% at baseline to 22% after ablation (P < 0.0001). RF applications to the anterolateral wall of dogs (n = 3) did not prevent VF induction. The application of RF energy near the PPM frequently initiated VF in swine (n = 7), preventing subsequent testing of VF inducibility.

CONCLUSION

In dogs and swine, the highest DF and majority of reentrant wavefronts during VF with acute global ischemia or during a propranolol infusion were located on the PPM. RF ablation targeted at the PPM reduced the inducibility of VF in normal dogs. However, the same ablation provoked incessant VF in swine, preventing subsequent testing of VF inducibility.

Heart Rate Reduction: A Potential Target for the Treatment of Myocardial Ischaemia

Because most of myocardial perfusion takes place during diastole, reducing the heart rate is likely to have anti-ischaemic effects. The present paper reviews the role of heart rate in relation to coronary artery disease outcome, as well as ways to reduce heart rate in the clinical setting. Nonpharmacological intervention, and particularly exercise training, has a definite effect on both heart rate reduction and the prevention of myocardial ischaemia. The protective role of beta-blockers after acute myocardial infarction is amply documented; their anti-ischaemic efficacy appears to be attributable to their effect on heart rate, but also to their role in cardiac inotropism. Recently, the If (funny) current inhibitor ivabradine, which has a potent heart rate reduction effect without any haemodynamic effect has demonstrated anti-ischaemic efficacy in a randomised trial versus placebo, as well as in trials where it showed an effect similar to that of the conventional anti-ischaemic agents amlodipine and atenolol. In addition, such an agent, which does not influence myocardial contractility, might be particularly valuable in the setting of myocardial stunning or acute left ventricular failure at the acute stage of myocardial infarction. However, only future studies will determine whether isolated heart rate reduction will have the same protective efficacy as that of beta-blocking agents in secondary prevention after myocardial infarction.

Differential effects of sarcolemmal and mitochondrial K(ATP) channels activated by 17 beta-estradiol on reperfusion arrhythmias and infarct sizes in canine hearts

We have demonstrated the effects of estrogen on modulation of ATP-sensitive K(+) channels; however, the subcellular location of these channels is unknown. The purpose of the present study was to investigate the role of the sarcolemmal and mitochondrial ATP-sensitive K(+) channels in a canine model of myocardial infarction after stimulation with 17 beta-estradiol. Anesthetized dogs were subjected to 60 min of the left anterior descending coronary artery occlusion followed by 3 h of reperfusion. Infarct size was markedly reduced in estradiol-treated dogs compared with controls (14 +/- 6 versus 42 +/- 6%, P < 0.0001), indicating the effective dose of estradiol administrated. Pretreatment with the mitochondrial ATP-sensitive K(+) channel antagonist 5-hydroxydecanoate completely abolished estradiol-induced cardioprotection. The sarcolemmal ATP-sensitive K(+) channel antagonist 1-15-12-(5-chloro-o-anisamido)ethyl-methoxyphenyl)sulfonyl-3-methylthiourea (HMR 1098) did not significantly attenuate estradiol-induced infarct size limitation. In addition, estradiol administration significantly reduced the incidence and duration of reperfusion-induced ventricular tachycardia and ventricular fibrillation. Although 5-hydroxydecanoate alone caused no significant effect on the incidence of reperfusion arrhythmias in the presence or absence of estradiol, the administration of HMR 1098 abolished estrogen-induced improvement of reperfusion arrhythmias. Pretreatment with the estrogen-receptor antagonist faslodex (ICI 182,780) did not alter estrogen-induced infarct-limiting and antiarrhythmic effects. These results demonstrate that estrogen is cardioprotective against infarct sizes and fatal reperfusion arrhythmias by different ATP-sensitive K(+) channels for an estrogen receptor-independent mechanism. The infarct size-limiting and antiarrhythmic effects of estrogen were abolished by 5-hydroxydecanoate and HMR 1098, suggesting that the effects may result from activation of the mitochondrial and sarcolemmal ATP-sensitive K(+) channels, respectively.

Salutary antiarrhythmic effect of combining a K channel blocker and a beta-blocker in a canine model of 7-day-old myocardial infarction

We sought to examine whether the antiarrhythmic effect of E4031 (E), or I(Kr) channel blocker, is affected by beta-adrenergic stimulation using isoproterenol (Iso) or by beta-adrenergic blockade (betaB) using, ONO1101, in a canine myocardial infarction model. Electrophysiologic studies were performed in 10 dogs with 7-day-old myocardial infarctions. Local QT intervals were measured at 47 sites on the infarcted myocardium using a mapping electrode. QT dispersion (QTd), as defined by the coefficient of variation of QT intervals, was obtained. Inducibility of ventricular arrhythmias was examined by programmed stimulation. These procedures were repeated during administration of E, E + Iso, and E + betaB. The effect of prolonging local QT intervals by E was counteracted by Iso, and was accentuated by betaB. The amount of prolongation was dependent on the baseline QT intervals, and QTd showed a tendency to decrease with E, to increase with E + Iso, and significantly decreased with E + betaB. Ventricular tachyarrhythmias were induced in a half of dogs with E + Iso, but were not induced with E + betaB. In the presence of adrenergic activation, I(Kr) blockers may exhibit a decreased antiarrhythmic effect. Beneficial synergism can be expected when an I(Kr) blocker is combined with a beta-blocker in the subacute phase of myocardial infarction.

Prevention of suboptimal beta-blocker treatment in patients with myocardial infarction

OBJECTIVE

To review the published data and clinical guidelines on the use of beta-blockers in myocardial infarctions (MIs) and contrast that with actual clinical practice.

DATA SOURCES

A MEDLINE search (January 1970-June 1999) was performed to identify all relevant articles. References from these articles were also evaluated for review if deemed important.

DATA SYNTHESIS

Intravenous and oral beta-blockers have been proven to improve outcomes in patients with MIs in numerous clinical trials. In current clinical practice, only 15% of MI patients receive intravenous beta-blockers and long-term beta-blocker therapy is used in <40% of patients without contraindications. However, they could be safely administered to 40% and 70% of these patients, respectively. Furthermore, most of these patients are receiving doses far below those found beneficial in clinical trials. Many of the real and perceived contraindications to beta-blockers are reviewed to allow the practitioner to identify patients who are incorrectly excluded from beta-blocker therapy. Also discussed are special clinical situations in which the benefits observed during clinical trials may not apply.

CONCLUSIONS

Beta-blockers are valuable drugs in the treatment of peri- and post-MI. In clinical practice, most patients are not treated or are inadequately treated with beta-blockers. Pharmacists should ensure that such patients actually have an absolute contraindication or unusual situation where therapy is not firmly indicated. Patients without absolute contraindications warrant titration to specific target doses or a target heart rate of 55-60 beats/min.