A double-blind trial of metoprolol in acute myocardial infarction. Effects on ventricular tachyarrhythmias

Effect of metoprolol on the submaximal stress test performed early after acute myocardial infarction

To determine the effect of beta-adrenergic blockade on the submaximal stress test after acute myocardial infarction (AMI), 36 post-AMI patients performed their treadmill test on 2 separate days, with and without metoprolol, in a double-blind, placebo-controlled, crossover design study. Rest and peak submaximal exercise heart rate was diminished by 100 mg of metoprolol administered twice daily (from 84 +/- 3 to 68 +/- 2 beats/min, p less than 0.001, and from 126 +/- 3 to 97 +/- 2 beats/min, p less than 0.001, respectively) compared with placebo. Rest and peak submaximal systolic blood pressure was also decreased (from 121 +/- 3 to 108 +/- 2 mm Hg, p less than 0.001, and from 151 +/- 4 to 124 +/- 3 mm Hg, p less than 0.001). Exercise-induced ST-segment depression of 1 mm or more from baseline occurred in 12 patients taking placebo. However, only 4 of these patients had ST depression when they exercised while taking metoprolol (p less than 0.05). Angina pectoris occurred in 4 patients taking placebo but in only 1 of these taking a beta-blocking drug. It is concluded that beta-blocking therapy renders the post-AMI submaximal stress test less sensitive for markers of exercise-induced ischemia than if the test is performed without the drug. Therefore, when using the prognostic information of published studies, it is important to define the conditions surrounding the exercise test.

The pharmacokinetics of lignocaine and beta-adrenoceptor antagonists in patients with acute myocardial infarction

Lignocaine (lidocaine) and beta-adrenoceptor antagonists are widely used after acute myocardial infarction. The therapeutic value of these agents depends on the achievement and maintenance of safe and effective plasma concentrations. Lignocaine pharmacokinetics after acute myocardial infarction (MI) are controlled by a number of variables. The single most important is left ventricular function, which affects both volume of distribution and plasma clearance. Other major factors include bodyweight, age, hepatic function, the presence of obesity, and concomitant drug therapy. Lignocaine is extensively bound to alpha 1-acid glycoprotein, a plasma protein which is also an acute phase reactant. Increases in alpha 1-acid glycoprotein concentration occur after an acute MI, decreasing the free fraction of lignocaine in the plasma and consequently decreasing total plasma lignocaine clearance without altering the clearance of non-protein-bound lignocaine. Complex changes in lignocaine disposition occur with long term infusions, and therefore early discontinuation of lignocaine infusions (within 24 hours) should be undertaken whenever possible. Because the risk of ventricular tachyarrhythmia declines rapidly after the onset of an acute MI, lignocaine therapy can be rationally discontinued within 24 hours in most patients. Lignocaine has a narrow toxic/therapeutic index, so that pharmacokinetic factors are critical in dose selection. In contrast, beta-adrenoceptor antagonists' adverse effects are more related to the presence of predisposing conditions (such as asthma, heart failure, bradyarrhythmias, etc.) than to plasma concentration. The pharmacokinetics of beta-adrenoceptor antagonists are important to help assure therapeutic efficacy, to provide information about the anticipated time course of drug action, and to predict the possible role of ancillary drug effects (such as direct membrane action) and loss of cardioselectivity. Lipid solubility is the main determinant of the pharmacokinetic properties of a beta-adrenoceptor antagonist. Lipid-soluble agents like propranolol and metoprolol are well absorbed orally, and undergo rapid hepatic metabolism, with important presystemic clearance and a short plasma half-life. Water-soluble drugs like sotalol, atenolol, and nadolol are less well absorbed, and are eliminated more slowly by renal excretion. Clinical assessment of beta-adrenoceptor antagonism is more valuable than plasma concentration determinations in evaluating the adequacy of the dose of a particular beta-adrenoceptor antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

Thrombolytic therapy for patients with acute myocardial infarction

Thrombolytic therapy is becoming an important addition to the care of patients with transmural (Q-wave) myocardial infarction. In this review, the authors analyze the mechanisms of effect and thrombolytic capabilities of several currently used thrombolytic interventions and review the influence of reperfusion in reducing mortality and protecting segmental ventricular function in animal models and patients. The problems related to thrombolytic therapy also are discussed and patient subgroups most likely to benefit from thrombolytic therapy identified. Finally, the authors speculate concerning future alterations in thrombolytic agents and additions to thrombolytic therapy as they might be usefully applied in the care of patients with acute transmural myocardial infarcts.

Autonomic control of ventricular tachycardia: direct effects of beta-adrenergic blockade in 24 hour old canine myocardial infarction

The purpose of this study was to determine whether alpha- or beta-adrenergic influences directly modulate the rate of spontaneous ventricular tachycardia occurring 24 hours after left anterior descending coronary artery occlusion. Chloralose-anesthetized, open chest dogs (n = 41) with ventricular tachycardia were studied. The left anterior descending artery was cannulated distally. Neither intracoronary saline solution nor phenylephrine (0.3 to 12 micrograms) changed the rate of ventricular tachycardia; however, isoproterenol (0.01 to 10 micrograms) produced dose-dependent increases in the rate. In six dogs, metoprolol, 5 mg given intravenously, slowed ventricular tachycardia from 174 +/- 10 (mean +/- SE) to 140 +/- 17 beats/min (p less than 0.05). This was accompanied by decreases in mean arterial pressure from 106 +/- 7 to 95 +/- 8 mm Hg, cardiac output from 2.6 +/- 0.3 to 1.6 +/- 0.3 liters/min and prolongation of atrioventricular conduction from 134 +/- 10 to 189 +/- 29 ms (all p less than 0.05) during atrial pacing at a cycle length of 300 ms. In 10 dogs, metoprolol (0.5 mg) given intracoronary, a dose that shifted the isoproterenol dose-response curve to the right, slowed ventricular tachycardia from 174 +/- 7.2 to 140 +/- 9.7 beats/min (p less than 0.05) without hemodynamic changes. Additional metoprolol (4.5 mg) given intravenously produced hemodynamic alterations, but ventricular tachycardia did not slow further. Therefore, beta- but not alpha-adrenergic influences control the rate of ventricular tachycardia occurring 24 hours after left anterior descending coronary artery occlusion. Furthermore, beta-adrenergic blockade slows ventricular tachycardia solely by a direct electrophysiologic effect on the tachycardia foci and not indirectly as a result of hemodynamic effects.

Noninvasive evaluation of the effect of timolol on left ventricular performance after myocardial infarction and the consequence for prognosis

Left ventricular performance was evaluated noninvasively in 111 patients participating at one study center in the Norwegian Multicenter Study on Timolol After Myocardial Infarction. Systolic time intervals were measured in 55 patients treated with timolol and in 56 patients receiving placebo. Measurements were made before randomization, and after 1, 3 and 12 months of treatment. During the treatment period, the pre-ejection period/left ventricular ejection time ratio was significantly lower in the timolol-treated group, indicating better left ventricular function than in the placebo-treated patients. In the 27 patients who died during the follow-up period of 50 to 72 months, there was a significant increase in the pre-ejection period/left ventricular ejection time ratio from baseline to the last performed recording, indicating a deterioration in left ventricular performance in these patients. No such change occurred in the group that survived the entire follow-up period. Deterioration of left ventricular function is related to a high long-term mortality rate after myocardial infarction, and left ventricular function is better preserved in patients treated with timolol than in patients receiving placebo.

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.

Effect of propranolol after acute myocardial infarction in patients with congestive heart failure

The incidence of congestive heart failure was studied in the Beta Blocker Heart Attack Trial in which postmyocardial infarction patients between the ages of 30 and 69 years, with no contraindication to propranolol, were randomly assigned to receive placebo (n = 1921) or propranolol 180 or 240 mg daily (n = 1916) 5 to 21 days after admission to the hospital for the event. Survivors of acute myocardial infarction with compensated or mild congestive heart failure, including those on digitalis and diuretics, were included in the study. A history of congestive heart failure before randomization characterized 710 (18.5%) patients: 345 (18.0%) in the propranolol group and 365 (19.0%) in the placebo group. The incidence of definite congestive heart failure after randomization and during the study was 6.7% in both groups. In patients with a history of congestive heart failure before randomization, 51 of 345 (14.8%) in the propranolol group and 46 of 365 (12.6%) in the placebo group developed congestive heart failure during an average 25 month follow-up. In the patients with no history of congestive heart failure, 5% in the propranolol group developed congestive heart failure and 5.3% in the placebo group developed congestive heart failure. Baseline characteristics predictive of the occurrence of congestive heart failure by multivariate analyses included an increased cardiothoracic ratio, diabetes, increased heart rate, low baseline weight, prior myocardial infarction, age, and more than 10 ventricular premature beats per hour.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial therapy for mild hypertension

The treatment of mild hypertension has been a subject of controversy because its benefits versus risks are not as well established as they are for moderate to severe hypertension. Results of several studies, however, now show that treatment reduces the frequency of stroke in those with milder blood pressure elevations. New guidelines published by the Joint National Committee recommend that treatment of mild hypertension begin with either a diuretic or a beta blocker. The effect on the most common complication of mild hypertension, that is, coronary heart disease (myocardial infarction and sudden cardiac death), has, however, not been encouraging in studies in which diuretics have been used as first-line treatment. Two large-scale primary preventive studies compared the efficacy of diuretics and beta blockers in reducing coronary heart disease in hypertensive patients; results were in favor of beta blocker regimens in men. So far there is some evidence, but no hard scientific proof, that certain beta blockers offer advantages over diuretics in preventing myocardial infarction and sudden cardiac death in hypertensive patients. A major concern with the use of diuretics is the risk of hypokalemia; this can be reduced when they are combined with beta blockers.

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.

Effect of propranolol in patients with myocardial infarction and ventricular arrhythmia

The Beta-Blocker Heart Attack Trial was a placebo-controlled, randomized, double-blind clinical trial of the long-term administration of propranolol hydrochloride to patients who had had at least one myocardial infarction. Among 3,837 patients followed up for an average of 25 months, 3,290 (85.7%) had 24 hour ambulatory electrocardiograms performed at the baseline examination. Four classifications of arrhythmia were examined. One of these, the presence of complex ventricular arrhythmias (at least 10 ventricular premature beats/h, or at least one pair or run of ventricular premature beats or multiform ventricular premature beats) was the subgroup of major interest. Regardless of the classification, the presence of arrhythmia identifies a group of patients with a higher risk of total mortality, coronary heart disease mortality, sudden cardiac death and instantaneous cardiac death. The a priori subgroup hypothesis that sudden death would be preferentially reduced by propranolol in patients with complex ventricular arrhythmias was not supported. The relative benefit of propranolol in reducing sudden death for this subgroup was 28 versus 16% for the subgroup without ventricular arrhythmia (relative risk of 0.72 versus 0.84, a nonsignificant relative difference of 14%). There were similar findings for two of the three other classifications of arrhythmia and for the other response variables. Although propranolol does not appear to be of special relative benefit in patients with ventricular arrhythmia, the presence of the arrhythmia does identify a high-risk group. The mechanism by which propranolol reduces mortality is still unclear, but is probably not solely an antiarrhythmic one.

Comparison of the efficacy and safety of esmolol, a short-acting beta blocker, with placebo in the treatment of supraventricular tachyarrhythmias. The Esmolol vs Placebo Multicenter Study Group

The efficacy and safety of esmolol, a short-acting intravenous beta-adrenergic-blocking agent, and placebo were compared in patients with supraventricular tachyarrhythmias (heart rate greater than 120 bpm) in a multicenter, double-blind, partial-crossover study. Seventy-one patients were randomized to receive either esmolol (n = 36) or placebo (n = 35) as initial treatment. Therapeutic failures were crossed over to the other study medication. Therapeutic response was defined as greater than or equal to 20% reduction in heart rate, heart rate less than 100 bpm, or conversion to normal sinus rhythm. The therapeutic response to esmolol during the initial treatment period (72%) was similar to that obtained when esmolol was given as a second agent. The average esmolol dosage producing a therapeutic response was 97.5 micrograms/kg/min. Four patients (6%) converted to normal sinus rhythm during esmolol infusion. In the majority of patients (80%), therapeutic response was lost within 30 minutes following discontinuation of esmolol infusion, a finding indicative of rapid reversal of beta-adrenoceptor blockade. The most prevalent adverse effect during esmolol infusion was hypotension which occurred in eight patients (12%). Hypotension and associated symptoms resolved within 30 minutes after discontinuation of esmolol infusion, which is consistent with the short duration of action of esmolol (elimination half-life of 9.2 minutes).

Effect of oxprenolol on ventricular arrhythmias: the European Infarction Study experience

In 736 patients, 24 hour electrocardiographic recordings were performed 14 to 36 days after acute myocardial infarction before the start of randomized treatment with 320 mg of slow release oxprenolol (n = 358) or placebo (n = 378). Follow-up 24 hour electrocardiographic recordings were obtained 5 to 12 days (median 10) and 3, 6 and 12 months after the first administration of the study medication. Oxprenolol-treated patients had a significantly lower daytime heart rate as compared with the placebo group, whereas no difference was found at night. At baseline, 22.1% of the patients allocated to oxprenolol treatment and 29.6% of the placebo group had more than 30 ventricular extrasystoles in 1 hour at least once during 24 hour monitoring; multiform ventricular extrasystoles were present in 58.4 and 62.7%, ventricular couplets in 29.6 and 33.9% and ventricular tachycardia (3 or more consecutive ventricular extrasystoles) in 21.5 and 20.9% of the oxprenolol-treated and placebo-treated patients, respectively. During the 1 year follow-up period, the prevalence of these arrhythmias did not change significantly in either treatment group. There was a trend toward a reduction in the daytime frequency of ventricular couplets in the oxprenolol group. After 3 and 6 months, only multiform ventricular extrasystoles were significantly less frequent in the oxprenolol group than in the placebo group (47.4 and 42.7% versus 59.7 and 57.9%, respectively). Twelve months after the acute event, however, multiform ventricular extrasystole frequency was the same in both groups of patients (52.1 versus 51.0%, respectively). Thus, oxprenolol had a weak suppressant effect on ventricular tachyarrhythmias in survivors of myocardial infarction.

Long-term treatment with metoprolol after myocardial infarction: effect on 3 year mortality and morbidity

The effects of metoprolol treatment in patients surviving acute myocardial infarction have been investigated in a double-blind randomized study. The patients were stratified according to age, infarct size and type of ventricular arrhythmias before administration of metoprolol, 100 mg twice daily (n = 154), or placebo (n = 147). All patients were followed up for 36 months. There were 31 (29 cardiac) and 25 (20 cardiac) deaths in the placebo and metoprolol groups, respectively. Subgroup analyses showed a significant reduction of cardiac death in patients with a large infarct (32.1% with placebo versus 12.5% with metoprolol, p less than 0.05) as a result of active treatment. Sudden death rates were 14.7% in the placebo versus 5.8% in the metoprolol group (p less than 0.05). The incidence of nonfatal reinfarction was 21.1% in the placebo versus 11.7% in the metoprolol group (p less than 0.05). The reduction in nonfatal reinfarction was similar in all pretreatment risk strata. The difference between the two groups in cumulative number of cardiac deaths and patients experiencing nonfatal reinfarction increased throughout the study. Furthermore, cerebrovascular events (p less than 0.05) and coronary bypass surgery (p = 0.058) were more frequent in the placebo group. In conclusion, after 36 months of metoprolol treatment after myocardial infarction, there was a significant reduction of nonfatal reinfarction and sudden death in all patients and a reduction of cardiac death in those with a large infarct.

Beta-Blocker Heart Attack Trial: impact of propranolol therapy on ventricular arrhythmias

The natural history of and the effect of propranolol on ventricular arrhythmias post-myocardial infarction were analyzed using data from the Beta-Blocker Heart Attack Trial (BHAT). The Beta-Blocker Heart Attack Trial was a multicenter, randomized, double-blind, placebo-controlled trial among 3,837 patients entered from 5 to 21 days after hospitalization for acute myocardial infarction. At baseline, prior to randomization, 3,290 (85.7%) patients underwent 24-hr ambulatory ECG monitoring which was repeated in approximately 25% of a randomly selected subset of the study population at 6 weeks. Ventricular arrhythmias were divided into eight different categories which defined the prevalence of ventricular arrhythmias in terms of frequency and/or complexity. Ventricular arrhythmias at baseline were associated with age, past history of myocardial infarction, and use of diuretics and digitalis. Paired data (baseline and 6-week) were available for 428 patients on propranolol and 412 on placebo. Propranolol markedly blunted the two- to threefold increase in ventricular arrhythmias that occurred from baseline to 6 weeks in the placebo group. Propranolol decreased the proportion of patients having ventricular arrhythmias during waking hours compared with sleep. These data show that propranolol has an antiarrhythmic effect and suggest that an antiarrhythmic mechanism may in part be responsible for the observed reduction in sudden cardiac death mortality in BHAT.

The long-term increase of baseline and reflexly augmented levels of human vagal-cardiac nervous activity induced by scopolamine

We tested the hypothesis that transdermal scopolamine increases vagal-cardiac nervous outflow over the long term in 16 healthy young men. Twenty-four hours after application of one scopolamine patch, the average RR interval was increased by 13% and the average standard deviation of the RR interval (taken as an index of the level of vagal-cardiac nervous activity) was increased by 31%. Baroreceptor-cardiac reflex responsiveness (as reflected by prolongation of RR interval provoked by graded neck suction) also was increased substantially. These findings suggest that vagal-cardiac nervous activity can be augmented pharmacologically in man on a long-term basis. Since vagal outflow influences cardiac electrical properties in an important way, these findings may have therapeutic implications.

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.

A randomized trial of low-dose beta-blockade therapy for idiopathic dilated cardiomyopathy

Beta-blockade therapy to improve survival in idiopathic dilated cardiomyopathy (IDC) has been both advocated and criticized. However, randomized studies have not been performed. Thus, 50 patients with IDC were randomized in pairs to standard therapy (C) alone or with beta blockade (BB). Beta-blockade therapy with metoprolol was titrated from 12.5 to 50 mg twice daily as tolerated (final average dose, 61 mg/day). Groups were comparable in age (C, 50 +/- 15 years; BB, 51 +/- 13 years), gender (C, 76% male; BB, 56% male), entry functional class (C, 2.8 +/- 0.8; BB, 2.7 +/- 0.7), and left ventricular ejection fraction (C, 27 +/- 12%; BB, 29 +/- 10%). Follow-up averaged 19 months (range 1 to 38). One subject in each group was lost to follow-up. There were 3 early BB dropouts (within 2 days) due to low-output syndrome (2 patients) or fatigue (1 patient). Eleven patients died. By intention to treat, 5 BB and 6 C patients died (difference not significant). By actual treatment, 3 BB patients died, including 2 late dropouts (at 0.2, 10 and 17 months), and 8 C patients died (at 2, 9, 9, 15, 18, 24, 29 and 32 months, p = 0.12). In additional, functional evaluation on follow-up (functional class, San Diego questionnaire and exercise time) all tended to favor those receiving BB. Low-dose BB is tolerated in 80% of IDC patients on a long-term basis. Those continuing to take BB have a good prognosis. Mortality in C patients, however, is less than in some retrospective studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Short- and long-term influence of beta-adrenergic antagonists after acute myocardial infarction

After coronary arterial occlusion, catecholamines are released from storage depots in the left ventricle and injured myocardial cells are exposed to relatively high concentrations of catecholamines during the evolutionary period in which cell injury is becoming progressively more severe. In addition, in experimental animal models, there is a substantial increase in beta-adrenergic receptor density without any alteration in affinity within 1 hour of permanent coronary arterial occlusion. Recent data suggest that alpha-adrenergic receptor density increases within 30 to 60 minutes after coronary arterial occlusion in experimental animal models. The administration of catecholamines during the early phases of evolving myocardial injury can result in heightened adrenergic biochemical responses in severely injured compared with normally perfused tissue in the hearts of experimental animals. Thus, there is adequate rationale for anticipating that beta-adrenergic antagonists would protect ischemic myocardium and potentially reduce the incidence of life-threatening arrhythmias in individuals with evolving acute myocardial infarction (AMI). Studies in animal models demonstrate that the administration of beta-adrenergic antagonists in the first few minutes after coronary artery occlusion may reduce the ultimate extent of myocardial necrosis. Clinical data from several different trials in which beta-adrenergic antagonists were administered to (1) protect ischemic myocardium and preserve ventricular function and (2) reduce the severity of serious ventricular arrhythmias in patients with AMI are reviewed. The effects of longer-term administration of beta-adrenergic antagonists in patients after AMI in prolonging life and reducing risk of reinfarction are presented.

Prophylactic antiarrhythmic therapy in acute myocardial infarction

Safe, effective prophylaxis of arrhythmias in acute myocardial infarction (AMI) is an important clinical goal. Despite rescue squads, out-of-hospital ventricular fibrillation (VF) has a poor prognosis. Even in-hospital VF has an important morbidity and mortality. Successful prophylactic therapy may also prevent infarct size enlargement associated with tachyarrhythmias. Several antiarrhythmic drugs have been investigated. In 3 studies, mortality was significantly reduced, but all of these have serious methodologic flaws and the validity of their conclusions is debatable. More reliance can be placed on 2 other studies which suggested that VF was significantly reduced by prophylactic therapy. However, in one of these studies, which used high-dose intravenous lidocaine, an unusually high incidence of VF was observed in the placebo-treated patients. The second study, reporting the use of metoprolol in AMI, was based on retrospective subset analysis. The reduction in VF was seen from the fourth day onwards and not during the acute phase of infarction. The favorable results with high-dose intravenous lidocaine are the basis for widespread use of prophylactic arrhythmia therapy in AMI. Uncontrolled observations provide some corroboration of the benefit. However, the claimed efficacy for lidocaine remains scientifically poorly substantiated and the safety of the high-dose regimen is controversial. Effective prophylaxis of arrhythmias in AMI could have important clinical benefit. However, the strategy would entail administration of a drug to many patients not at risk of arrhythmias (those without AMI) and to a number of patients in whom the complications of infarction are destined to develop.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blockade may prolong life in post-infarction patients in part by increasing vagal cardiac inhibition

Beta-adrenergic blocking drugs prolong lives of post-infarction patients primarily by preventing sudden cardiac death. The mechanisms responsible for this beneficial effect are not understood clearly, since beta-blockers, in doses used in most clinical trials, are only weakly effective against stable ventricular arrhythmias. Arrhythmias during myocardial ischemia may differ from arrhythmias in other clinical settings in that they depend importantly upon autonomic neural factors, including the balance between levels of sympathetic cardiac stimulation and parasympathetic cardiac inhibition. Beta-blockers reduce sympathetic cardiac stimulation, and they may influence this balance favorably in another important way: a well documented, but not generally appreciated property of beta-blocking drugs is that they also increase levels of vagal cardiac inhibition. I propose that beta-blockade prevents arrhythmic deaths in post-infarction patients in part by increasing levels of vagal cardiac inhibition.

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.

Beta-adrenoceptor blockade: electrophysiology and antiarrhythmic mechanisms

Beta-adrenoceptor-blocking agents reduce beta-adrenergic activity and depress sinoatrial and atrioventricular nodal conduction. These agents are thus useful for controlling supraventricular tachyarrhythmias. For the treatment of ventricular arrhythmias, beta-adrenoceptor-blocking agents possess antifibrillatory properties, depress diastolic depolarization of ectopic pacemaker activity, reduce electrical instability associated with prolongation of the QT interval, and are specifically effective in suppressing ventricular arrhythmias that are rate (tachycardia) dependent and/or caused by catecholamine-sensitive automaticity. Furthermore, beneficial hemodynamic effects of beta-adrenoceptor blockade on ischemic myocardium may also contribute to the antiarrhythmic potency of these agents.

Symposium on the management of ventricular dysrhythmias. Antifibrillatory versus antiectopic therapy

The concept of antifibrillatory action distinct from antiarrhythmic effect has recently been recognized. An antiarrhythmic (antiectopic) action leads to a decrease in the frequency of ventricular ectopic beats. In contrast, an antifibrillatory drug action increases myocardial electric stability, decreasing the propensity for ventricular fibrillation. Agents with predominant antiarrhythmic action (designated class I) include lidocaine, quinidine, procainamide and disopyramide. Bretylium is an agent with predominant antifibrillatory action (class III). Amiodarone and sotalol are experimental class III drugs. The beta-blockers (class II) also possess antifibrillatory action, particularly in ischemic heart disease. The rationale for the use of agents with antiarrhythmic (antiectopic) effects is the reduction of triggering events for more complex ventricular tachyarrhythmias. These agents act by slowing conduction, decreasing abnormal automaticity and affecting phase IV depolarization. In contrast, agents with antifibrillatory action may exert little effect on cardiac conduction and automaticity. However, they raise the energy threshold required for premature electrical discharge to initiate ventricular fibrillation (ventricular fibrillation threshold). The inhomogeneity of electrophysiologic properties and adrenergic tone in different portions of the heart may be reduced or eliminated. Direct electrophysiologic effects of agents such as bretylium include a general lengthening of the refractory period and the action potential duration in the heart and a diminution in the disparity of their durations between normal and abnormal myocardium. Clinical studies are incomplete, but they support the concept of antifibrillatory therapy. In postmyocardial infarction patients at intermediate risk of sudden death, the broad use of oral antiarrhythmic agents has not decreased the incidence of sudden death, whereas high-dose beta-blocker therapy, which exerts experimental antifibrillatory effects, may reduce sudden death by 30 to 70%.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between infarct size and incidence of severe ventricular arrhythmias in a double-blind trial with metoprolol in acute myocardial infarction

In 585 patients having an acute myocardial infarction for the first time the relationship was investigated between estimated infarct size and the incidence of ventricular fibrillation and treated ventricular tachycardia during hospitalization. The size of the infarct was estimated from analyses of heat stable lactate dehydrogenase (LD) (EC 1.1.1.27.) in serum collected every 12 hr for 48-108 hr. All patients participated in a double-blind comparison of the beta 1-selective blocker metoprolol with placebo in suspected acute myocardial infarction. A correlation was observed between the enzymatically estimated infarct size and the incidence of ventricular fibrillation and treated ventricular tachycardia in patients on placebo (P less than 0.001), while this could not be demonstrated in patients on the beta-blocker (P greater than 0.2). In placebo treated patients there was a correlation between the maximum heat stable LD activity and early ventricular fibrillation (P = 0.034), late ventricular fibrillation (P less than 0.001), primary ventricular fibrillation (P = 0.002) as well as secondary ventricular fibrillation (P = 0.034). It is concluded that there seems to be a relatively strong correlation between the final size of the infarction and the occurrence of severe ventricular arrhythmias. Treatment with beta-blockade appeared to disturb this correlation.

Ventricular arrhythmias during the first year after acute myocardial infarction: influence of long-term treatment with metoprolol

Three hundred and one patients who had been hospitalized for acute myocardial infarction, were less than 70 years old, were in sinus rhythm, and did not have complete bundle branch block were stratified before discharge according to age, size of infarction, and type of ventricular arrhythmias as determined on a 6 hr electrocardiogram (ECG). They were thereafter randomly assigned to double-blind treatment with 100 mg bid metoprolol or placebo. Repeat 6 hr ECGs were recorded 3 days and 1, 6, and 12 months after treatment had begun. In the placebo group there was a significant increase in the proportion of patients with complex premature ventricular complexes (PVCs) (i.e., multiform, paired and R-on-T PVCs, or ventricular tachycardia) as well as increased numbers of PVCs in the patients during the follow-up. In contrast, an initial decrease in the number of PVCs (p less than .001) was found in the metoprolol group, whereas the complexity of PVCs was constant in those patients who continued on metoprolol therapy throughout the follow-up period. We conclude that the increase in complexity and number of PVCs that is part of the natural clinical course after myocardial infarction is counteracted by long-term treatment with metoprolol.

Effect of propranolol in postinfarction patients with mechanical or electrical complications

In "post hoc" subgroup analyses, a simple classification system for patients, based on the presence or absence of findings indicative of electrical and/or mechanical complications early during short-term hospitalization, was applied to the data from the Beta-Blocker Heart Attack Trial (BHAT). In the largest subgroup of BHAT patients who had no reported complications, the 25 month mortality was low and the observed benefit of propranolol therapy small. Patients with electrical complications only had intermediate mortality and a pronounced effect of treatment was observed. Those with mechanical complications had the highest mortality and experienced an intermediate relative benefit of beta-blocker treatment. They also reported the most adverse effects. Post hoc analyses should always be interpreted cautiously. It is important to determine whether these findings are present in other completed beta-blocker trials. On the basis of these analyses alone it is suggested that the present practice of prescribing beta-blockers in postinfarction patients should not be altered.

Effects of beta-adrenoceptor antagonists on the pharmacokinetics of lignocaine

In theory, beta-adrenoceptor antagonists could lower the clearance of free lignocaine in three ways (a) by decreasing hepatic blood flow, (b) by competing for plasma binding sites or (c) by inhibiting the enzymes responsible for metabolising lignocaine. The first mechanism has been demonstrated for propranolol and is probably common to all agents lacking intrinsic sympathomimetic activity. The second mechanism is discounted by data showing that propranolol, one of the more highly bound beta-adrenoceptor antagonists, does not alter the free fraction of lignocaine in plasma. In vitro studies support the third mechanism for the more lipid-soluble beta-adrenoceptor antagonists, as does the fact that observed decreases in the clearance of lignocaine in vivo are generally greater than the anticipated maximum lowering of hepatic blood flow.

Modulation of the Q-T interval by the autonomic nervous system

Recent investigations have clarified some of the effects of the autonomic nervous system on duration and spatial distribution of the Q-T interval in humans. The use of atrial pacing to fix heart rate or 24-hour continuous electrocardiographic recording to develop a regression formula for individual patients has provided a means to interpret the effects of an intervention that alters both the heart rate and the Q-T interval. Drugs that affect the autonomic nervous system can influence Q-T interval directly or by changing rate. Bazett's formula to correct for rate may be misleading after certain drug interventions. For example, the Q-T interval during sinus rhythm or atrial pacing and the ventricular effective refractory period shorten after atropine plus propranolol, but corrected Q-T interval using Bazett's formula does not change. No change occurs in the Q-T interval during sinus rhythm or atrial pacing, or in ventricular effective refractory period after administration of propranolol although corrected Q-T interval using Bazett's formula markedly shortens. Q-T interval during sinus rhythm and atrial pacing and ventricular effective refractory period decrease after atropine but correct Q-T interval lengthens.(ABSTRACT TRUNCATED AT 250 WORDS)