Treatment of acute myocardial infarction with propranolol. Further studies on enzyme appearance and subsequent left ventricular function in treated and control patients with developing infarcts

Beta-blockers for suspected or diagnosed acute myocardial infarction

BACKGROUND

Cardiovascular disease is the number one cause of death globally. According to the World Health Organization, 7.4 million people died from ischaemic heart diseases in 2012, constituting 15% of all deaths. Acute myocardial infarction is caused by blockage of the blood supplied to the heart muscle. Beta-blockers are often used in patients with acute myocardial infarction. Previous meta-analyses on the topic have shown conflicting results ranging from harms, neutral effects, to benefits. No previous systematic review using Cochrane methodology has assessed the effects of beta-blockers for acute myocardial infarction.

OBJECTIVES

To assess the benefits and harms of beta-blockers compared with placebo or no intervention in people with suspected or diagnosed acute myocardial infarction.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, LILACS, Science Citation Index Expanded and BIOSIS Citation Index in June 2019. We also searched the WHO International Clinical Trials Registry Platform, ClinicalTrials.gov, Turning Research into Practice, Google Scholar, SciSearch, and the reference lists of included trials and previous reviews in August 2019.

SELECTION CRITERIA

We included all randomised clinical trials assessing the effects of beta-blockers versus placebo or no intervention in people with suspected or diagnosed acute myocardial infarction. Trials were included irrespective of trial design, setting, blinding, publication status, publication year, language, and reporting of our outcomes.

DATA COLLECTION AND ANALYSIS

We followed the Cochrane methodological recommendations. Four review authors independently extracted data. Our primary outcomes were all-cause mortality, serious adverse events according to the International Conference on Harmonization - Good Clinical Practice (ICH-GCP), and major adverse cardiovascular events (composite of cardiovascular mortality and non-fatal myocardial infarction during follow-up). Our secondary outcomes were quality of life, angina, cardiovascular mortality, and myocardial infarction during follow-up. Our primary time point of interest was less than three months after randomisation. We also assessed the outcomes at maximum follow-up beyond three months. Due to risk of multiplicity, we calculated a 97.5% confidence interval (CI) for the primary outcomes and a 98% CI for the secondary outcomes. We assessed the risks of systematic errors through seven bias domains in accordance to the instructions given in the Cochrane Handbook. The quality of the body of evidence was assessed by GRADE.

MAIN RESULTS

We included 63 trials randomising a total of 85,550 participants (mean age 57.4 years). Only one trial was at low risk of bias. The remaining trials were at high risk of bias. The quality of the evidence according to GRADE ranged from very low to high. Fifty-six trials commenced beta-blockers during the acute phase of acute myocardial infarction and seven trials during the subacute phase. At our primary time point 'less than three months follow-up', meta-analysis showed that beta-blockers versus placebo or no intervention probably reduce the risk of a reinfarction during follow-up (risk ratio (RR) 0.82, 98% confidence interval (CI) 0.73 to 0.91; 67,562 participants; 18 trials; moderate-quality evidence) with an absolute risk reduction of 0.5% and a number needed to treat for an additional beneficial outcome (NNTB) of 196 participants. However, we found little or no effect of beta-blockers when assessing all-cause mortality (RR 0.94, 97.5% CI 0.90 to 1.00; 80,452 participants; 46 trials/47 comparisons; high-quality evidence) with an absolute risk reduction of 0.4% and cardiovascular mortality (RR 0.99, 95% CI 0.91 to 1.08; 45,852 participants; 1 trial; moderate-quality evidence) with an absolute risk reduction of 0.4%. Regarding angina, it is uncertain whether beta-blockers have a beneficial or harmful effect (RR 0.70, 98% CI 0.25 to 1.84; 98 participants; 3 trials; very low-quality evidence) with an absolute risk reduction of 7.1%. None of the trials specifically assessed nor reported serious adverse events according to ICH-GCP. Only two trials specifically assessed major adverse cardiovascular events, however, no major adverse cardiovascular events occurred in either trial. At maximum follow-up beyond three months, meta-analyses showed that beta-blockers versus placebo or no intervention probably reduce the risk of all-cause mortality (RR 0.93, 97.5% CI 0.86 to 0.99; 25,210 participants; 21 trials/22 comparisons; moderate-quality evidence) with an absolute risk reduction of 1.1% and a NNTB of 91 participants, and cardiovascular mortality (RR 0.90, 98% CI 0.83 to 0.98; 22,457 participants; 14 trials/15 comparisons; moderate-quality evidence) with an absolute risk reduction of 1.2% and a NNTB of 83 participants. However, it is uncertain whether beta-blockers have a beneficial or harmful effect when assessing major adverse cardiovascular events (RR 0.81, 97.5% CI 0.40 to 1.66; 475 participants; 4 trials; very low-quality evidence) with an absolute risk reduction of 1.7%; reinfarction (RR 0.89, 98% CI 0.75 to 1.08; 6825 participants; 14 trials; low-quality evidence) with an absolute risk reduction of 0.9%; and angina (RR 0.64, 98% CI 0.18 to 2.0; 844 participants; 2 trials; very low-quality evidence). None of the trials specifically assessed nor reported serious adverse events according to ICH-GCP. None of the trials assessed quality of life. We identified two ongoing randomised clinical trials investigating the effect of early administration of beta-blockers after percutaneous coronary intervention or thrombolysis to patients with an acute myocardial infarction and one ongoing trial investigating the effect of long-term beta-blocker therapy.

AUTHORS' CONCLUSIONS

Our present review indicates that beta-blockers for suspected or diagnosed acute myocardial infarction probably reduce the short-term risk of a reinfarction and the long-term risk of all-cause mortality and cardiovascular mortality. Nevertheless, it is most likely that beta-blockers have little or no effect on the short-term risk of all-cause mortality and cardiovascular mortality. Regarding all remaining outcomes (serious adverse events according to ICH-GCP, major adverse cardiovascular events (composite of cardiovascular mortality and non-fatal myocardial infarction during follow-up), the long-term risk of a reinfarction during follow-up, quality of life, and angina), further information is needed to confirm or reject the clinical effects of beta-blockers on these outcomes for people with or suspected of acute myocardial infarction.

Early intravenous beta-blockers in patients with acute coronary syndrome--a meta-analysis of randomized trials

BACKGROUND

Intravenous (IV) beta-blockade is currently a Class IIa recommendation in early management of patients with acute coronary syndromes (ACS) without obvious contraindications.

METHODS

We searched the PubMed, EMBASE and the Cochrane Register for Controlled Clinical Trials for randomized clinical trials from 1965 through December, 2011, comparing intravenous beta-blockers administered within 12 hours of presentation of ACS with standard medical therapy and/or placebo. The primary outcome assessed was the risk of short-term (in-hospital mortality-with maximum follow up duration of 90 days) all-cause mortality in the intervention group versus the comparator group. The secondary outcomes assessed were ventricular tachyarrhythmias, myocardial reinfarction, cardiogenic shock, and stroke. Pooled treatment effects were estimated using relative risk with Mantel-Haenszel risk ratio, using a random-effects model.

RESULTS

Sixteen studies enrolling 73,396 participants met the inclusion ⁄ exclusion criteria. In- hospital mortality was reduced 8% with intravenous beta-blockers, RR=0.92 (95% CI, 0.86-1.00; p=0.04) when compared with controls. Moreover, intravenous beta-blockade reduced the risk of ventricular tachyarrhythmias (RR=0.61; 95 % CI 0.47-0.79; p=0.0003) and myocardial reinfarction (RR=0.73, 95 % CI 0.59-0.91; p=0.004) without increase in the risk of cardiogenic shock, (RR=1.02; 95% CI 0.77-1.35; p=0.91) or stroke (RR=0.58; 95 % CI 0.17-1.98; p=0.38).

CONCLUSIONS

Intravenous beta-blockers early in the course of appropriate patients with ACS appears to be associated with significant reduction in the risk of short-term cardiovascular outcomes, including a reduction in the risk of all-cause mortality.

Does the early administration of beta-blockers improve the in-hospital mortality rate of patients admitted with acute coronary syndrome?

OBJECTIVES

Beta-blockade is currently recommended in the early management of patients with acute coronary syndromes (ACS). This was a systematic review of the medical literature to determine if early beta-blockade improves the outcome of patients with ACS.

METHODS

The authors searched the PubMed and EMBASE databases for randomized controlled trials from 1965 through May 2009 using a search strategy derived from the following PICO formulation of our clinical question: Patients included adults (18+ years) with an acute or suspected myocardial infarction (MI) within 24 hours of onset of chest pain. Intervention included intravenous or oral beta-blockers administered within 8 hours of presentation. The comparator included standard medical therapy with or without placebo versus early beta-blocker administration. The outcome was the risk of in-hospital death in the intervention groups versus the comparator groups. The methodologic quality of the studies was assessed. Qualitative methods were used to summarize the study results. In-hospital mortality rates were compared using a forest plot of relative risk (RR; 95% confidence interval [CI]) between beta-blockers and controls. Statistical analysis was done with Review Manager V5.0.

RESULTS

Eighteen articles (total N = 72,249) met the inclusion/exclusion criteria. For in-hospital mortality, RR = 0.95 (95% CI, 0.90-1.01). In the largest of these studies (n = 45,852), a significantly higher rate (p < 0.0001) of cardiogenic shock was observed in the beta-blocker (5.0%) versus control group (3.9%).

CONCLUSIONS

This systematic review failed to demonstrate a convincing in-hospital mortality benefit for using beta-blockers early in the course of patients with an acute or suspected MI.

Effect of early treatment with anti-hypertensive drugs on short and long-term mortality in patients with an acute cardiovascular event

BACKGROUND

Acute cardiovascular events represent a therapeutic challenge. Blood pressure lowering drugs are commonly used and recommended in the early phase of these settings. This review analyses randomized controlled trial (RCT) evidence for this approach.

OBJECTIVES

To determine the effect of immediate and short-term administration of anti-hypertensive drugs on all-cause mortality, total non-fatal serious adverse events (SAE) and blood pressure, in patients with an acute cardiovascular event, regardless of blood pressure at the time of enrollment.

SEARCH STRATEGY

MEDLINE, EMBASE, and Cochrane clinical trial register from Jan 1966 to February 2009 were searched. Reference lists of articles were also browsed. In case of missing information from retrieved articles, authors were contacted.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing anti-hypertensive drug with placebo or no treatment administered to patients within 24 hours of the onset of an acute cardiovascular event.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed risk of bias. Fixed effects model with 95% confidence intervals (CI) were used. Sensitivity analyses were also conducted.

MAIN RESULTS

Sixty-five RCTs (N=166,206) were included, evaluating four classes of anti-hypertensive drugs: ACE inhibitors (12 trials), beta-blockers (20), calcium channel blockers (18) and nitrates (18). Acute stroke was studied in 6 trials (all involving CCBs). Acute myocardial infarction was studied in 59 trials. In the latter setting immediate nitrate treatment (within 24 hours) reduced all-cause mortality during the first 2 days (RR 0.81, 95%CI [0.74,0.89], p<0.0001). No further benefit was observed with nitrate therapy beyond this point. ACE inhibitors did not reduce mortality at 2 days (RR 0.91,95%CI [0.82, 1.00]), but did after 10 days (RR 0.93, 95%CI [0.87,0.98] p=0.01). No other blood pressure lowering drug administered as an immediate treatment or short-term treatment produced a statistical significant mortality reduction at 2, 10 or >/=30 days. There was not enough data studying acute stroke, and there were no RCTs evaluating other acute cardiovascular events.

AUTHORS' CONCLUSIONS

Nitrates reduce mortality (4-8 deaths prevented per 1000) at 2 days when administered within 24 hours of symptom onset of an acute myocardial infarction. No mortality benefit was seen when treatment continued beyond 48 hours. Mortality benefit of immediate treatment with ACE inhibitors post MI at 2 days did not reach statistical significance but the effect was significant at 10 days (2-4 deaths prevented per 1000). There is good evidence for lack of a mortality benefit with immediate or short-term treatment with beta-blockers and calcium channel blockers for acute myocardial infarction.

Differential risk patterns associated with 3 month as compared with 3 to 12 month mortality and reinfarction after non-Q wave myocardial infarction. The Diltiazem Reinfarction Study Group

Follow-up data for 515 survivors of acute non-Q wave myocardial infarction were categorized according to mortality: 1) between hospital discharge and 3 months after infarction (early), and 2) between 3 and 12 months after infarction (late). The mortality rate decreased steadily for the first 3 months and was constant thereafter. There were 25 early and 32 late deaths. After adjustment for the longer time associated with the 3 to 12 month period, the relative risk per unit time of early as compared with late mortality was 2.64. Risk factors for early mortality were different from those that predicted late mortality. Independent predictors of mortality between hospital discharge to 3 months after infarction were ST segment depression that persisted during hospitalization (p less than 0.0001), in-hospital reinfarction (p = 0.0006) and a history of congestive heart failure (p = 0.0255). Persistent ST depression and in-hospital reinfarction had neither a univariate nor an independent association with 3 to 12 month mortality. Age (p less than 0.0001), reinfarction between discharge and 3 months (p = 0.0147) and diabetes (p = 0.0404) were independently associated with late mortality. Early mortality was only 0.5% (1 of 199) in patients with no ST depression at either baseline or discharge (group 1); 4.8% (8 of 168) in those with ST depression at exactly one time point (group 2) and 13.7% (16 of 117) in those who had ST depression present at both time points (group 3). All pairwise differences were significant (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced risk of death at 28 days in patients taking a beta blocker before admission to hospital with myocardial infarction

OBJECTIVE

To see whether patients taking an oral beta blocker at the time of admission to hospital with myocardial infarction have a reduced risk of death at 28 days.

DESIGN

Retrospective analysis of data collected on patients admitted over four years.

SETTING

Community based study.

PATIENTS

2430 Consecutive patients living in the Perth statistical division admitted to hospital with myocardial infarction during 1984-7.

MAIN OUTCOME MEASURE

Survival at 28 days among patients taking a beta blocker at onset of myocardial infarction.

RESULTS

Patients were grouped into those who were and were not taking a beta blocker at the time of admission. Though patients taking a beta blocker were older and more likely to have a history of myocardial infarction, angina, or hypertension, the overall mortality at 28 days was similar in the two groups. A logistic regression model used to adjust for factors predictive of cardiac death at 28 days confirmed that patients taking a beta blocker at the time of admission had a significantly reduced risk of death (relative risk 0.50; 95% confidence interval 0.34 to 0.76). Though the incidence of fatal ventricular fibrillation was similar in the two groups, mean peak creatine kinase activity was significantly lower in the beta blocker group.

CONCLUSIONS

These data support the value of long term use of beta blockers in patients at risk of myocardial infarction. They suggest that patients taking these agents before admission to hospital with myocardial infarction have a significant survival advantage at 28 days, which may be due to a reduction in infarct size.

Does acute-phase beta-blockade reduce mortality in acute myocardial infarction by limiting infarct size?

The mechanism by which early intervention with beta-blockers reduces mortality in acute myocardial infarction is unclear. Therefore the effects of intravenous, followed by oral, metoprolol on indices of infarct size were studied in a double-blind fashion with a median delay of 6.75 hours from onset of symptoms. In 129 patients peak enzyme release and QRS score on the electrocardiogram were assessed, while myocardial perfusion score on thallium-201 scintigraphy was studied in 45 patients. There was a close correlation between all the indices of infarct size. While the correlation coefficients did not appear to be influenced by metoprolol treatment, the slope of the regression was affected. Peak aspartate aminotransferase and lactic dehydrogenase were lower by 11 and 7%, respectively, in the metoprolol-treated group, but no reduction was noted in QRS score or in thallium-201 perfusion defect size in the actively treated group. Thus, it seems likely that early intervention with metoprolol in acute myocardial infarction reduces mortality, not by limiting infarct size, but by some other mechanism.

According to MIAMI and ISIS-I trials, can a general recommendation be given for beta blockers in acute myocardial infarction?

The goal of early intervention of acute coronary occlusion by beta blockers is to reduce ultimate infarct size and to consequently reduce morbidity and mortality. Until 1986 small early intervention trials suggested that infarct size may be reduced by 25% if treatment was started within 6 to 10 hours after the onset of symptoms. At this time, an average of 80% of the infarct is fully developed. On the basis of previous trials, the reduction of infarct size has been associated with improvement of symptoms, prevention of infarct development, reduced occurrence of arrhythmias and reinfarctions, and earlier discharge from the hospital. Although the trials suggested some benefit in mortality, this issue has not been solved. The MIAMI trial randomized 5778 patients to blind treatment with metoprolol or placebo. ISIS-I randomized 16,027 patients to atenolol with an open label. No titration of the effect on lowering myocardial oxygen requirement was attempted. Both studies included less than 25% of all eligible patients. Exclusions were chiefly due to current beta blocker or calcium blocker treatment. Thus, the results obtained concern only a selected group of patients. In MIAMI only 15% received treatment within 6 hours, while in ISIS 38% were treated within 4 hours. It is therefore likely that in most patients the infarcts were completed before intervention was started. Thus, the two trials did not differentiate between primary and secondary effects on the acute myocardial infarct. Mortality was reduced by 13% (NS) and 15% (p less than 0.04), respectively, in MIAMI and ISIS.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of different pharmacological interventions on enzymatic parameters during acute myocardial infarction

The concept that acute myocardial infarction is a dynamic event and that different interventions can modify the extent of the necrosis, has led to renewed interest in early pharmacological and surgical treatments designed to reduce the ischemic injury. To evaluate the effects of different pharmacological interventions aimed to reduce the extent of necrosis, we studied 166 patients (138 male and 28 female, mean age of 59.4 +/- 11.3 years) admitted within 6 h after chest pain and treated with a single therapy during the first 72 h. Enzymatic infarct size (IS) was calculated by serial creatine kinase isoenzyme MB determinations using a compartmental model. Six groups of patients were evaluated: 33 patients were treated only with antiplatelet drugs, 38 with anticoagulants, 34 with intravenous thrombolytic therapy, 20 with calcium channel blockers, 25 with nitrates, and 16 with beta-blockers. Estimated IS (gEq/m2) and elimination constant (Kd, U/L/h) did not differ in the six groups, but patients treated with streptokinase had higher release constant (Ka, U/L/h) and shorter time to peak CK-MB value. Early treatment (less than or equal to 2 h after chest pain) had a favourable effect on the enzymatic IS only in patients treated with calcium channel blockers (p less than 0.005).

Meta-analysis of clinical trials as a scientific discipline. I: Control of bias and comparison with large co-operative trials

Meta-analysis is an important method of bridging the gap between undersized randomized control trials and the treatment of patients. However, as in any retrospective study, the opportunities for bias to distort the results are widespread. Attempts must be made to introduce the controls found in prospective studies by blinding the selection of papers and extraction of data and making blinded duplicate determinations. Informal and personalized methods of obtaining data are probably more liable to error and bias than employing only published data. Publication bias is a serious problem requiring further research. There also need to be more comparisons of meta-analysed small studies with large co-operative trials.

Infarct size reduction: a review of the clinical trials

The most important finding to emerge from this review of experimental and clinical studies is that the earlier therapy is begun after the onset of symptoms of acute MI, the greater the potential for reduction of infarct size and possibly mortality. It is difficult to define a precise time after which therapy would not have an effect, since the clinical trials for each drug group vary significantly in respect to time of therapy initiation. In experimental studies, major salvage of ischemic myocardium occurs when the drug is given within two hours of coronary artery occlusion. If drug therapy is begun four to six hours postocclusion, then only minor or no reductions in infarct size will occur. The ability of any drug or intervention to reduce infarct size in humans would be optimized if therapy were begun less than four hours of onset of symptoms. With the realization of the wavefront phenomenon and the potential salvage of myocardium at risk with reperfusion, the introduction of reperfusion in the clinical setting with thrombolytic agents or other procedures becomes highly desirable. Clot-selective thrombolytic agents, such as tissue plasminogen activator, diminish the adverse effects and high costs of intracoronary thrombolytic therapy or PTCA. Consequently, it is probable that the initial procedure of choice would be the use of clot-selective thrombolytic therapy. Thrombolytic therapy only lyses thrombi and does not affect the underlying causes of the coronary artery occlusion. Therefore, therapy to reduce the chances of reinfarction and death must also be initiated. Percutaneous transluminal coronary angioplasty, in selected patients, should reduce the reocclusion rate. Beta-adrenoceptor blocking agents appear to be an excellent therapy for reducing mortality when administered chronically; these agents reduce myocardial oxygen consumption and reverse the imbalance between oxygen supply and oxygen demand caused by activation of the sympathetic nervous system and actions of catecholamines. Since thrombus formation has occurred at least once in patients who survive an MI, it is probable that the conditions for thrombus formation still exist. Therefore, institution of antiplatelet aggregating drugs, such as aspirin, would seem to be an appropriate prophylactic regimen. Beta blockers and possibly nitroglycerin have desirable effects when thrombolysis is unavailable. The efficacy of calcium-channel blocking agents on reduction of infarct size appears to be limited, although in the setting of stable and unstable angina postinfarction, these agents can play an important role.(ABSTRACT TRUNCATED AT 400 WORDS)

Metoprolol. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy, in hypertension, ischaemic heart disease and related cardiovascular disorders

During the intervening years since metoprolol was first reviewed in the Journal (1977), it has become widely used in the treatment of mild to moderate hypertension and angina pectoris. Although much data have accumulated, its precise mechanisms of action in these diseases remain largely uncertain. Optimum treatment of hypertension and angina pectoris with metoprolol is achieved through dose titration within the therapeutic range. It has been clearly demonstrated that metoprolol is at least as effective as other beta-blockers, diuretics and certain calcium antagonists in the majority of patients. Although a twice daily dosage regimen is normally used, satisfactory control can be maintained in many patients with single daily doses of conventional or, more frequently, slow release formulations. Addition of a diuretic may improve the overall response rate in hypertension. Several controlled trials have studied the effects of metoprolol administered during the acute phase and after myocardial infarction. In early intervention trials a reduction in total mortality was achieved in one moderately large trial of prolonged treatment, but in another, which excluded patients already being treated with beta-blockers or certain calcium antagonists and where treatment was only short term, mortality was significantly reduced only in 'high risk' patients. Overall results with metoprolol have not demonstrated that early intervention treatment in all patients produces clinically important improvement in short term mortality. Thus, the use of metoprolol during the early stages of myocardial infarction is controversial, largely because of the requirement to treat all patients to save a small number at 'high risk'. This blanket coverage approach to treatment may be more justified during the post-infarction follow-up phase since it has been shown that metoprolol slightly, but significantly, reduces the mortality rate for periods of up to 3 years. Metoprolol is generally well tolerated and its beta 1-selectivity may facilitate its administration to certain patients (e.g. asthmatics and diabetics) in whom non-selective beta-blockers are contraindicated. Temporary fatigue, dizziness and headache are among the most frequently reported side effects. After a decade of use, metoprolol is well established as a first choice drug in mild to moderate hypertension and stable angina, and is beneficial in post-infarction patients. Further study is needed in less well established areas of treatment such as cardiac arrhythmias, idiopathic dilated cardiomyopathy and hypertensive cardiomegaly.

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

Heart rate after an acute myocardial infarction (AMI) is an index of late mortality. The hypothesis--that the potential beneficial effect of beta-blocking drugs after an AMI is quantitatively dependent on the reduction of heart rate obtained by such treatment--was examined by reviewing available data from acute and long-term intervention trials. Only properly randomized and double-blind trials were considered. In acute intervention trials only patients who received treatment within 12 hours after onset of pain were included. In early intervention trials there was a close relation between the reduction in heart rate and infarct size as determined by accumulated creatine kinase release (r = 0.97, p less than 0.001). A reduction in heart rate of at least 15 beats/min during infarct evolution was associated with a reduction of infarct size between 25 and 30%. The data suggest that a reduction in heart rate less than 8 beats/min has no effect or may actually increase infarct size. Comparison of post-AMI trials indicated a relation between the actual reduction of resting heart rate and percentage of reduction in mortality obtained in each trial (r = 0.60, p less than 0.05). An almost similar relation was demonstrated between the reduction in resting heart rate and nonfatal reinfarctions (r = 0.59, p less than 0.05). Confounding properties of a beta blocker, such as intrinsic sympathomimetic activity or prolongation of the QT interval, may reduce its efficacy. These results strongly suggest that the beneficial effect of beta blockers is related to a quantitative reduction in heart rate, probably indicating an antiischemic effect. However, the data do not exclude the possibility that other protective mechanisms may be operative.

Effect of early treatment with propranolol on left ventricular function four weeks after myocardial infarction

Left ventricular function and exercise capacity were assessed in 79 patients randomised to receive intravenous and oral propranolol (n = 44) or conventional therapy (n = 35) within four hours of onset of their first myocardial infarction. Cineangiocardiography and exercise testing were performed four weeks after infarction to allow for maximum recovery of myocardial function. Left ventriculography showed no improvement in ejection fraction or preservation of regional contractile function in patients treated with propranolol compared with controls. A trend towards smaller end diastolic volumes was seen in the propranolol group (mean (SD) 151(42) ml) compared with controls (167(42) ml). Exercise duration and frequency of angina were not significantly different in the two groups. It is concluded that limitation of infarct size by propranolol does not lead to a significant improvement in ventricular systolic function, although left ventricular dilatation may be reduced. These findings are consistent with the known effect of early intravenous beta blockade which limits infarct size by preservation of subepicardial myocardium.

Beta blockade during and after myocardial infarction: an overview of the randomized trials

Long-term beta blockade for perhaps a year or so following discharge after an MI is now of proven value, and for many such patients mortality reductions of about 25% can be achieved. No important differences are clearly apparent among the benefits of different beta blockers, although some are more convenient than others (or have slightly fewer side effects), and it appears that those with appreciable intrinsic sympathomimetic activity may confer less benefit. If monitored, the side effects of long-term therapy are not a major problem, as when they occur they are easily reversible by changing the beta blocker or by discontinuation of treatment. By contrast, although very early IV short-term beta blockade can definitely limit infarct size, more reliable information about the effects of such treatment on mortality will not be available until a large trial (ISIS) reports later this year, with data on some thousands of patients entered within less than 4 hours of the onset of pain. Our aim has been not only to review the 65-odd randomized beta blocker trials but also to demonstrate that when many randomized trials have all applied one general approach to treatment, it is often not appropriate to base inference on individual trial results. Although there will usually be important differences from one trial to another (in eligibility, treatment, end-point assessment, and so on), physicians who wish to decide whether to adopt a particular treatment policy should try to make their decision in the light of an overview of all these related randomized trials and not just a few particular trial results. Although most trials are too small to be individually reliable, this defect of size may be rectified by an overview of many trials, as long as appropriate statistical methods are used. Fortunately, robust statistical methods exist--based on direct, unweighted summation of one O-E value from each trial--that are simple for physicians to use and understand yet provide full statistical sensitivity. These methods allow combination of information from different trials while avoiding the unjustified direct comparison of patients in one trial with patients in another. (Moreover, they can be extended of such data that there is no real need for the introduction of any more complex statistical methods that might be more difficult for physicians to trust.) Their robustness, sensitivity, and avoidance of unnecessary complexity make these particular methods an important tool in trial overviews.

Prevention of ventricular fibrillation during acute myocardial infarction by intravenous propranolol

A trial of intravenous followed by oral propranolol, started within 4 h of onset of suspected myocardial infarction and continued over 27 h, was carried out in 735 patients; 364 received propranolol, 371 were controls. Ventricular fibrillation during the first 48 h after entry to the trial occurred in 2 treated patients and in 14 controls (p = 0.006). Rates of hospital mortality, complications other than ventricular fibrillation, and progression from threatened to completed infarction did not differ between treated and control patients. Ventricular fibrillation was not apparently prevented by prior beta-blocker treatment, which was not a reason for exclusion from the trial. This intravenous/oral propranolol regimen seems to prevent ventricular fibrillation due to evolving myocardial infarction.

Combined receptor intervention and myocardial infarction

The aims of treatment in acute myocardial infarction are to limit evolving muscle necrosis, prevent heart failure, maintain electrical stability, and preserve the coronary circulation to avoid progressive or recurrent infarction. No single treatment achieves all these objectives. The rationale for the use of adrenoceptor blocking drugs is that they will oppose the effects of the increased sympathomimetic activity which follows acute infarction and which may adversely affect outcome. More is known of the clinical use of pure beta-blockade than of combined alpha- and beta-blockade with labetalol but in theory combined receptor blockade will produce additional beneficial effects over beta-blockade alone. beta-Adrenoceptor antagonists have a theoretical role in limiting infarct size. They may reduce the oxygen deficit of jeopardised though potentially viable tissue, limiting infarct size by their favourable effect on heart rate, systolic pressure, contractility, and metabolic pathways. That beta-blockade reduces myocardial damage has been confirmed in animal studies. Studies in man using enzyme release or R wave scoring as indicators of infarct size also suggest that oral or intravenous beta-blockers after infarction encourage myocardial salvage. Few studies have been reported in which the effects of combined alpha- and beta-blockade on infarct size have been determined. The actions of a dual blocking agent are more complex and the outcome less predictable than from beta-blockade alone: the advantages of the beta-blocking component will be retained while the alpha-blocking component may conceivably further diminish oxygen demand by reducing systolic pressure and heart size. Less favourably, coronary perfusion pressure may also fall. It is apparent that further clinical studies are needed. Adrenergic blockade may be used to prevent or treat ventricular arrhythmias which develop after infarction in the face of heightened sympathetic tone and continued ischaemia. Clinical and experimental evidence points to the efficacy of beta-blockade in ischaemia-related arrhythmias, but beta-blockade alone is probably ineffective against arrhythmias arising during reperfusion. In experimental studies, alpha-blockers are effective against both forms of arrhythmia although the doses required for reperfusion effects may produce unacceptable hypotension in clinical use. It is possible that combined alpha- and beta-blockade may have broader antiarrhythmic activity than beta-blockers alone but present clinical data on the value of labetalol in controlling postinfarction arrhythmias are sparse.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular pharmacology of ASL-8052, an ultra-short acting beta blocker

ASL-8052, a novel ultra-short acting beta receptor blocking agent, was infused i.v. and its cardiovascular effects were investigated in conscious, as well as anesthetized rabbits. On i.v. infusion, its effects reached a steady state within 6 min and on termination of infusion, complete recovery occurred within 20 min. In conscious rabbits it inhibited isoproterenol-induced tachycardia and hypotension. There was more pronounced inhibition of the cardioaccelerator effects of isoproterenol than its hypotensive effects. ASL-8052 produced dose dependent bradycardia in conscious rabbits which was more marked in rabbits pretreated with atropine methyl nitrate. When infused in larger doses, a significant decrease in mean arterial pressure was seen in conscious as well as anesthetized rabbits. This hypotensive effect was not blocked by prior beta receptor blockade with propranolol. ASL-8052-induced hypotension was found to be due to a significant decrease in total peripheral resistance. It also produced vasodilation in the mesenteric vascular bed. The role of the liver in the clearance of ASL-8052 was investigated. When infused into the portal vein, the response to ASL-8052 was markedly attenuated, while an equivalent dose infused into the femoral vein produced a significant level of beta receptor blockade. These results suggest that ASL-8052 is an ultra-short acting beta receptor blocking agent with vasodilator effects in rabbits. While the liver may play a significant role in the clearance of ASL-8052 from circulation, the role of extra-hepatic mechanisms in the rapid decay of its pharmacological effects remains to be investigated.

Effects of acebutolol on myocardial infarct extension: a randomized electrocardiographic, enzymatic and angiographic study

The effect of acebutolol (1 mg/kg i.v. during the first 2 days followed by a daily oral dose of 600 mg for 3 weeks) was studied in a randomized trial involving 26 patients seen within 24 hours after the onset of uncomplicated anterior transmural myocardial infarction (TMI). Myocardial ischemia and necrosis were evaluated by precordial maps recorded daily for 9 days. Left ventricular pump function and dyssynergy were quantitatively measured on 30 degrees right anterior oblique cineangiograms. Angiography was performed, using the postextrasystolic potentiation technique, within the first 24 hours after TMI and was repeated 1 month later. The basal and postextrasystolic beats from the initial angiography were computerized and compared with those from the final angiogram. MB-CK serum level was measured from blood samples drawn every 3 hours for the first 72 hours. Fourteen patients selected at random received acebutolol within the first 24 hours; 12 subjects were untreated and served as controls. During the 1-month study, no other drugs were administered. Treated patients showed a significant reduction in capillary wedge pressure, extent of hypokinesis and ST-segment elevation; no significant differences were observed in the control group. However, the predictability based on the angiographic data was the same in both groups, and beta blockade did not alter this predictability significantly. Furthermore, no significant difference was found during the final evaluation for treated compared with control patients for any single variable or set of variables. The incidence of infarct extension was not decreased, but only significantly delayed in treated patients. The high variability of the measurements, probably related to the high variability of the pathophysiologic factors, may account for the failure to demonstrate the efficacy of acebutolol.