Prevention of ventricular fibrillation during acute myocardial infarction by intravenous propranolol

Effect of intravenous streptokinase on left ventricular function and early survival after acute myocardial infarction

In a double-blind trial of streptokinase for acute myocardial infarction, 219 consecutive patients presenting with infarction within four hours (mean, 3.0 +/- 0.8) of the onset of chest pain were randomly assigned to treatment with streptokinase (1.5 million units) or placebo, given intravenously over 30 minutes. The primary end point of the study was left ventricular function in patients with first infarctions. Patients who could undergo beta-blockade also received intravenous propranolol. Heparin (for 48 hours) and a combination of low-dose aspirin and dipyridamole were administered to both groups until cineangiography was performed at three weeks. In the patients with first infarctions treated with streptokinase, the left ventricular ejection fraction was 6 percentage points higher (streptokinase vs. placebo, 59 +/- 10.5 vs. 53 +/- 13.5 percent; P less than 0.005), with benefit to patients with either anterior infarction (57 +/- 11.9 vs. 49 +/- 15.9 percent; P less than 0.05) or inferior infarction (60 +/- 9.1 vs. 55 +/- 11.3 percent; P less than 0.05). Left ventricular function was improved regardless of whether concomitant propranolol was given. Survival (at 30 days) was improved with streptokinase: 2 deaths occurred among 79 patients who received this drug, as compared with 12 deaths among 93 patients who received placebo (2.5 vs. 12.9 percent, P = 0.012). Rates of reinfarction (streptokinase vs. placebo, 3 vs. 1 percent) and requirements for surgery or angioplasty (7 vs. 5 percent) were similar in the two groups. We conclude that administration of intravenous streptokinase (1.5 million units) to patients with a first myocardial infarction results in improved left ventricular function and short-term survival.

In-hospital prognosis of patients with acute myocardial infarction complicated by primary ventricular fibrillation

The in-hospital prognosis of patients with acute myocardial infarction complicated by primary ventricular fibrillation has not been satisfactorily defined. We addressed this question by studying patients with primary ventricular fibrillation derived from a large study (11,712 patients) of intravenous streptokinase in the treatment of acute myocardial infarction. Ventricular fibrillation was considered to be primary when it complicated a first myocardial infarction not associated with heart failure or shock and occurred within 48 hours of hospital admission. The 332 patients with primary ventricular fibrillation represented an overall incidence of 2.8 percent. A significant excess of in-hospital deaths was found in the patients with primary ventricular fibrillation as compared with those in the reference group (10.8 percent vs. 5.9 percent; relative risk, 1.94; 95 percent confidence interval, 1.35 to 2.78). Thrombolytic treatment with intravenous streptokinase did not afford protection against primary ventricular fibrillation. We observed that being over 65 years old had a protective effect against primary ventricular fibrillation (relative risk, 0.6; 95 percent confidence interval, 0.45 to 0.80). Our data do not indicate whether primary ventricular fibrillation is simply a marker for patients at increased risk of death or a direct cause of the increase in mortality. Our results do show, however, that primary ventricular fibrillation occurring in a coronary care unit is a negative predictor of short-term survival in patients with acute myocardial infarction.

Interventions that potentially limit myocardial infarct size: overview of clinical trials

Theoretically, interventions that restore the balance between oxygen supply and demand when given during the early hours of a heart attack may reduce infarct size and prevent fatal arrhythmias and thereby prolong survival. Data on mortality from the available randomized trials of thrombolytic therapy, intravenous beta blockers, hyaluronidase, intravenous nitrates and calcium channel blockers in acute myocardial infarction, are systematically reviewed. Analyses confirm that intravenous streptokinase reduces mortality by about 25% but suggests that measures to prevent reinfarction may be required after thrombolytic therapy. beta blockers reduced mortality by approximately 15%. The pooled data from the existing trials of hyaluronidase and intravenous nitrates are consistent with a 15% to 20% decrease in mortality; ideally this should be confirmed in future large randomized trials. Currently, there is no evidence either from individual studies or the aggregate of all the trials that calcium channel blockers reduce mortality. The collective experience from the trials carried out over the last 2 decades suggests that most interventions in acute myocardial infarction have, at best, only moderate effects with a 10% to 20% reduction in mortality. Current and future trials that assess the effects of cardiovascular treatments on mortality should therefore aim to randomize 10,000 to 20,000 average risk patients or a few thousand high risk patients.

Use of beta blockers in postinfarct prophylaxis: aspects on quality of life

The value of beta blockade after myocardial infarction is extremely well documented. Close to 50 randomized trials have been performed, involving about 40,000 patients with short- or long-term follow-up. Over 20,000 patients have been included in more than 20 placebo-controlled trials with a follow-up period of 3 months or more. In long-term follow-up studies, about 1 to 2 weeks to 1 year after myocardial infarction, mortality was reduced by 21% and reinfarction by 24% (about 20,000 patients in 24 trials). The trial medication was withdrawn in about 20% in both placebo and beta-blocker groups in the major trials. In addition to reduction of mortality and reinfarction rate, benefits have clearly been demonstrated on severity of chest pain, arrhythmias, and other thromboatherosclerotic complications, as well as on readmissions. Significantly more patients experienced congestive heart failure, hypotension, bradycardia, and cold hands with beta-blocker treatment, whereas no clear-cut difference was found for atrioventricular block, bronchial constriction, and intermittent claudication. Some studies have reported more tiredness, depression, and gastrointestinal disturbances. In the Stockholm metoprolol trial, analyses on quality of life have been performed. In this trial, 3 years of metoprolol treatment after myocardial infarction resulted in a prolongation of both survival and time spent completely asymptomatic, as well as in an optimal functional state. Furthermore, less time was spent disabled after serious atherosclerotic complications. Long-term beta blockade after myocardial infarction reduces mortality and morbidity but causes adverse reactions in some patients. With proper selection of patients and type and dosage of beta blocker, survival without atherosclerotic complications and side effects can be prolonged.

Metoprolol in acute myocardial infarction reduces ventricular arrhythmias both in the early stage and after the acute event

Fifty three of the 5778 patients included in the MIAMI (Metoprolol in Acute Myocardial Infarction) trial were investigated with long-term ECG recordings in order to evaluate the effect of acute beta-blockade on premature ventricular complexes in and after acute myocardial infarction. Twenty five patients were given placebo and 28 metoprolol in a double-blind randomized fashion for 15 days. After this period the patients were put on open beta-blockade without breaking individual study codes. The mean number of premature ventricular complexes during the inclusion day (day 0) was the same in the two groups. The median numbers were also similar in the two groups: 190 and 154 in the placebo and metoprolol groups, respectively. Metoprolol significantly reduced the median number of premature ventricular complexes in the randomized period. The median numbers on days 1, 2 and 15 were 146, 101, 84 in the placebo group and 73, 59 and 10 in the metoprolol group, respectively (P less than 0.05). Also during the further follow-up, when investigated 1, 3 and 6 months after the infarction, the median number of premature ventricular complexes was lower in the metoprolol group (74, 257, 142 in the placebo group and 7, 5 and 11 in the metoprolol group, P less than 0.05). This indicates that metoprolol treatment in the acute phase of myocardial infarction reduces ventricular arrhythmias both in the early stage and also after the acute event.

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.

Obtaining medically meaningful answers from an overview of randomized clinical trials

Answers that have medical value can often be obtained from overviews of randomized clinical trials if care is taken in formulating a biologically sensible question and unbiased and careful methods are used in collecting, extracting and analysis the results. This article discusses some of the pitfalls that are encountered during this process, outlines some solutions and emphasizes the need for a conservative interpretation of the results.

Immediate and long-term pathophysiologic mechanisms underlying the genesis of sudden cardiac death in patients with congestive heart failure

Congestive heart failure is the most important predisposing factor to the occurrence of sudden death in patients with cardiovascular disease. As left ventricular dysfunction deteriorates and symptoms of heart failure become evident, ambulatory ventricular arrhythmias become increasingly frequent and complex, and sudden cardiac death becomes an increasingly common occurrence. When the left ventricular ejection fraction has declined to less than 30 percent and symptoms of heart failure become refractory to treatment with digitalis and diuretics, 35 to 50 percent of patients will die of a lethal cardiac arrhythmia within three years. A number of factors interact to determine the occurrence of malignant ventricular arrhythmias in patients with congestive heart failure. Myocardial fibrosis and enhanced left ventricular wall stress may alter the electrophysiologic properties of the myocardium, but these factors may not be sufficient to explain the development of lethal rhythm disturbances. Neurohormonal activation may exacerbate the frequency and complexity of ambulatory arrhythmias in these patients, but such activation can persist for long periods without fatal electrophysiologic sequelae. Recent investigations suggest that electrolyte depletion may provide an important immediate precipitating cause for the occurrence of fatal ventricular tachyarrhythmias in the patient with severe left ventricular dysfunction whose susceptibility is markedly heightened by preexisting structural, hemodynamic, or neurohormonal factors. Further work is needed to determine if prophylactic therapy directed at preventing electrolyte depletion can favorably modify the long-term outcome of these severely ill patients.

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.

Hormone-electrolyte interactions in the pathogenesis of lethal cardiac arrhythmias in patients with congestive heart failure. Basis of a new physiologic approach to control of arrhythmia

Congestive heart failure is the most arrhythmogenic disorder in cardiovascular medicine. As left ventricular performance deteriorates and symptoms of dyspnea and fatigue become progressively more severe, nearly all patients with heart failure experience frequent and complex ventricular tachyarrhythmias and nearly half die suddenly during long-term follow-up. This imminent risk of sudden death appears to be present for all patients with congestive heart failure; ambulatory electrocardiographic monitoring and programmed electrical stimulation are not useful in distinguishing patient subsets that are particularly predisposed to fatal arrhythmic events. Although conventional antiarrhythmic agents are widely prescribed as a nonspecific approach to prevent sudden death in these patients, there is little evidence to indicate that these drugs possess clinically important antiarrhythmic activity in patients with congestive heart failure, and these agents frequently serve to exacerbate the heart failure state and the underlying ventricular tachyarrhythmia. A useful approach to the prevention of sudden death in patients with congestive heart failure addresses the reversible causes of lethal ventricular arrhythmias in these individuals. Both experimental and clinical evidence indicates that circulating neurohormones and electrolyte deficits (particularly of potassium and magnesium) interact to provoke malignant ventricular ectopic rhythms and that the prevention of electrolyte depletion and the use of neurohormonal antagonists may exert clinically important antiarrhythmic actions. This physiologic approach may prove to be a more effective means of ameliorating the problem of sudden death than the empiric administration of conventional antiarrhythmic drugs.

Early use of beta-adrenergic-blocking agents in acute myocardial infarction

Of recent interest is the acute use of beta-adrenergic-blocking agents in patients who have suffered an acute myocardial infarction (AMI). Acute use of beta-blockers refers to initiation of therapy within hours following the onset of symptoms suggestive of AMI. The proposed goal of therapy is to alter the infarction process to improve mortality. Because of the hyperadrenergic activity present in patients during an infarction, beta-blockers are theoretically an attractive therapeutic intervention because of their sympatholytic properties. Acute use of beta-blockers has been shown to limit infarct size, as determined by cardiac enzyme activity, and reduce the incidence of major ventricular arrhythmias. Beta-blockers may also prevent infarction in patients with symptoms suggestive of infarction. However, the acute use of beta-adrenergic-blocking agents has not been shown to reduce short-term (less than or equal to 30 d) mortality. In view of this fact, the acute use of beta-adrenergic-blocking agents cannot be recommended.

Circulating catecholamine and potassium concentrations early in acute myocardial infarction: effect of intervention with timolol

In a prospective study, 20 patients with a first acute myocardial infarction and no current treatment with diuretics or cardioactive drugs were randomized to treatment with intravenous timolol (10 patients) or placebo (10 patients). Plasma adrenaline, noradrenaline, and serum potassium were estimated at baseline (mean +/- SD 3.6 +/- 0.8 hours after the onset of the infarction) and 4 hours after the start of treatment. The patient selection criteria embraced a low-risk study population. Before treatment, the serum potassium concentrations correlated inversely with plasma adrenaline but not with plasma noradrenaline concentrations. A rise of serum potassium (mean +/- SD mmol/L) from 4.1 +/- 0.3 to 4.4 +/- 0.4 (p less than 0.05) in the placebo group and from 4.0 +/- 0.4 to 4.5 +/- 0.5 (p less than 0.05) in the timolol group was in multivariate analysis associated with infarct size, estimated as cumulative creatine kinase release, in the placebo group, and with the mean individual plasma adrenaline concentrations in the timolol group. By reversing the effect of adrenaline from a decrease to an increase in the serum potassium concentrations, timolol changes the relationships between circulating adrenaline, potassium, and infarct size.

Basic pharmacology of esmolol

Preclinical studies show that esmolol is an ultrashortacting, cardioselective beta blocker that possesses minimal partial agonist action or membrane-depressant properties. The electrophysiologic and hemodynamic actions of esmolol are the result of beta blockade. No direct, beta receptor-independent cardiovascular actions have been identified with beta-blocking doses in laboratory experiments. Because esmolol slows atrioventricular conduction, increases atrioventricular refractoriness and decreases the determinants of myocardial oxygen demand, it should have use in the treatment of supraventricular tachycardias and acute myocardial ischemia. Esmolol, because of its ultrashort duration of action, should be safe for the induction of beta blockade in patients who are critically ill and is ideally suited for rapidly changing levels of beta blockade in this clinical situation.

Uncoupling between beta-adrenoceptors and adenylate cyclase in dog ischemic myocardium

We evaluated the effects of ischemic injury on the myocardial adenylate cyclase system, 5 h after ligation of the left anterior descending coronary in 5 anesthetized dogs. Crude cardiac membrane preparations were isolated from control and ischemic areas of ventricular myocardium and tested for: 1. L-(125I)iodocyanopindolol binding, in the absence and presence of +/- -isoprenaline and GTP, and 2. adenylate cyclase activity. The density of beta-adrenoceptors increased by 35% in membranes from ischemic areas while the proportion of receptors in a high affinity state for +/- -isoprenaline decreased from 43% to 20%. Adenylate cyclase activities in the basal state and under stimulation with NaF, forskolin, Gpp(NH)p, +/- -isoprenaline and VIP were all markedly and similarly reduced, being only about 30% of comparable activities in membranes from control areas. The +/- -isoprenaline subsensitivity of cardiac adenylate cyclase can, thus, be attributed to a defective enzymatic system and not to a reduction in the number of beta-adrenoceptors implying that the internal components of the system were more sensitive to acute ischemia than the outward oriented hormone receptors. It is tempting to ascribe this uncoupling to a functional depletion in the guanine nucleotide-binding regulatory protein Ns that might reflect a loss of high energy phosphate stores including GTP.

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.