Failure of high doses of propranolol to reduce experimental myocardial ischemic damage

Effect of Pre-Procedural Beta-Blocker on Clinical Outcome after Percutaneous Coronary Intervention in Acute Coronary Syndrome

The efficacy of pre-procedural beta-blocker use in patients with acute coronary syndrome (ACS) is not well established in the current percutaneous coronary intervention (PCI) era. We investigate the effect of pre-procedural beta-blocker use on clinical outcomes in patients with ACS undergoing PCI. Among 44,967 consecutive cases of PCI enrolled in the nationwide, retrospective, multicenter registry (K-PCI registry), 31,040 patients with ACS were selected and analyzed. We classified patients into pre-procedural beta-blocker group (n = 8,678) and pre-procedural no-beta-blocker group (n = 22,362) according to the use of beta-blockers at least for two weeks before index PCI. Propensity score-matching analysis was performed and resulted in 7,445 pairs. The primary outcome was in-hospital cardiac death. In propensity score-matched populations, the pre-procedural beta-blocker group had a lower incidence of in-hospital cardiac death compared with the pre-procedural no-beta-blocker group (1.1% versus 2.0%, unadjusted odds ratio [OR]: 0.56, 95% confidence interval [CI]: 0.42-0.73, P < 0.01). In subgroup analysis, the pre-procedural beta-blocker group had a lower incidence of in-hospital cardiac death, compared with the pre-procedural no-beta-blocker group in ST-segment elevation myocardial infarction subpopulation (3.1% versus 6.1%, unadjusted OR: 0.49, 95% CI: 0.34-0.71, P < 0.01) and non-ST-segment elevation myocardial infarction subpopulation (1.5% versus 2.9%, unadjusted OR: 0.51, 95% CI: 0.33-0.79, P < 0.01). However, in unstable angina subpopulation, the in-hospital cardiac death rate was comparable between both groups. In conclusion, the use of pre-procedural beta-blocker was associated with a lower risk of in-hospital cardiac death in patients with ACS undergoing PCI. This result adds to the body of evidence that use of pre-procedural beta-blocker in patients with ACS might be reasonable.

Comparison of Pyrroloquinoline Quinone and/or Metoprolol on Myocardial Infarct Size and Mitochondrial Damage in a Rat Model of Ischemia/Reperfusion Injury

The cardioprotective effectiveness of low-dose pyrroloquinoline quinone (PQQ, 3 mg/kg) was compared with metoprolol, a β1-selective adrenoceptor antagonist. Rats underwent 30 minutes of left anterior descending coronary artery occlusion and 2 hours of reperfusion. Metoprolol and/or PQQ were given at the onset of reperfusion to mimic clinical treatment. Metoprolol and/or PQQ reduced infarct size and protected against ischemia-induced left ventricular dysfunction after 2 hours of reper-fusion. Combined therapy augmented left ventricular developed pressure at the end of reperfusion. Metoprolol or PQQ alone enhanced mitochondrial respiratory ratios in ischemic and nonischemic myocardium. Although the PQQ/metoprolol combination therapy increased respiratory ratio values, the effects were small when compared with PQQ alone. Only PQQ decreased lipid peroxidation. Metoprolol and/or PQQ given at the onset of reperfusion reduce infarct size and improve cardiac function. Combination therapy further reduces infarct size. PQQ is superior to metoprolol in protecting mitochondria from ischemia/reperfusion oxidative damage

Early Intravenous Beta-Blockers in Patients With ST-Segment Elevation Myocardial Infarction Before Primary Percutaneous Coronary Intervention

BACKGROUND

The impact of intravenous (IV) beta-blockers before primary percutaneous coronary intervention (PPCI) on infarct size and clinical outcomes is not well established.

OBJECTIVES

This study sought to conduct the first double-blind, placebo-controlled international multicenter study testing the effect of early IV beta-blockers before PPCI in a general ST-segment elevation myocardial infarction (STEMI) population.

METHODS

STEMI patients presenting <12 h from symptom onset in Killip class I to II without atrioventricular block were randomized 1:1 to IV metoprolol (2 × 5-mg bolus) or matched placebo before PPCI. Primary endpoint was myocardial infarct size as assessed by cardiac magnetic resonance imaging (CMR) at 30 days. Secondary endpoints were enzymatic infarct size and incidence of ventricular arrhythmias. Safety endpoints included symptomatic bradycardia, symptomatic hypotension, and cardiogenic shock.

RESULTS

A total of 683 patients (mean age 62 ± 12 years; 75% male) were randomized to metoprolol (n = 336) or placebo (n = 346). CMR was performed in 342 patients (54.8%). Infarct size (percent of left ventricle [LV]) by CMR did not differ between the metoprolol (15.3 ± 11.0%) and placebo groups (14.9 ± 11.5%; p = 0.616). Peak and area under the creatine kinase curve did not differ between both groups. LV ejection fraction by CMR was 51.0 ± 10.9% in the metoprolol group and 51.6 ± 10.8% in the placebo group (p = 0.68). The incidence of malignant arrhythmias was 3.6% in the metoprolol group versus 6.9% in placebo (p = 0.050). The incidence of adverse events was not different between groups.

CONCLUSIONS

In a nonrestricted STEMI population, early intravenous metoprolol before PPCI was not associated with a reduction in infarct size. Metoprolol reduced the incidence of malignant arrhythmias in the acute phase and was not associated with an increase in adverse events. (Early-Beta blocker Administration before reperfusion primary PCI in patients with ST-elevation Myocardial Infarction [EARLY-BAMI]; EudraCT no: 2010-023394-19).

Rationale and design of a double-blind, multicenter, randomized, placebo-controlled clinical trial of early administration of intravenous β-blockers in patients with ST-elevation myocardial infarction before primary percutaneous coronary intervention: EARLY β-blocker administration before primary PCI in patients with ST-elevation myocardial infarction trial

BACKGROUND

β-Blockers have a class 1a recommendation in the treatment of patients with ST-elevation myocardial infarctions (STEMIs), as they are associated with a reduced mortality, recurrent myocardial infarction, life-threatening arrhythmias, and with prevention of unfavorable left ventricular remodeling. Whether early administration before primary percutaneous coronary intervention (PCI) of intravenous β-blockers reduces the infarct size in the current era is unknown.

HYPOTHESIS

We postulate that the early administration of β-blockers will reduce the myocardial infarcted area as assessed by magnetic resonance imaging (MRI) at 30 days.

DESIGN

In a multinational, multicenter, double-blind, placebo-controlled, randomized trial, patients with symptoms and signs of STEMI and transferred to a hospital for primary PCI will be randomized in a 1:1 fashion to intravenous metoprolol (5 mg twice daily) administration or placebo. Before admission, study treatment will be started as soon as possible after the diagnosis of STEMI. After admission, primary PCI will be performed as per standard of care. After primary PCI, medical treatment will occur as per current guidelines in all patients, including the use of oral β-blockers. The primary end point is the myocardial infarct size as assessed by MRI at 30 days. Based on a superiority design and assuming an 18% relative infarct size reduction (from 28% to 23.5%), 408 patients are required to be enrolled, accounting for 20% drop-out (α = .05 and power = 80%).

SUMMARY

The EARLY-BAMI trial is a multinational, multicenter, double-blind, placebo-controlled, randomized clinical trial that will investigate the impact of intravenous metoprolol administration before primary PCI for STEMI on myocardial infarct size as measured with MRI at 30 days.

Glucose-insulin-potassium-albumin infusion in the early phase of acute myocardial infarction--a controlled study

Fifty consecutive patients with acute myocardial infarction admitted to a coronary care unit within 6 hours from onset of symptoms were randomly assigned either to a treatment group (n=27) receiving glucose-insulin-potassium-albumin (GIKA) or to a control group (n=23), comparable regarding clinical data, receiving 5.5% glucose. Both infusions were given intravenously at a rate of 1.2 ml/kg b.wt./hour during 48 hours. The GIKA solution contained 40 mEq K+, 10 ml 20% albumin and 16 IU regular crystalline insulin per 1000 ml 10% glucose. Before the infusion, the treatment group received an i.v. loading dose of 50 ml 50% glucose. Serum time activity curves for creatine kinase (CK) and myoglobin (MG) were established from frequent blood level determinations. A 15-minute single-lead ECG was recorded every fourth hour and subsequently analysed for ventricular arrhythmias. The two patient groups did not differ regarding cumulative MG and CK release. The GIKA group had significantly more patients with high MG/CK ratios (p less than 0.02). No clinically significant difference was found between the two patient groups regarding ventricular arrhythmias, even if ventricular extrasystoles tended to occur less frequently in the GIKA group.

Failure of intravenous metoprolol to limit acute myocardial infarct size in a nonreperfused porcine model

The usefulness of intravenous beta-adrenergic receptor blockade in limiting infarct size when neither reperfusion nor collateral flow occurs is unknown. The effect of intravenous metoprolol on limiting myocardial infarct size was therefore examined in a nonreperfused porcine model. Closed-chest techniques were used to occlude the left anterior descending coronary artery, after which animals were randomized at 20 minutes to receive intravenous metoprolol, 0.75 mg/kg, or placebo. Infarct size examined at 5 hours with Evans blue and triphenyltetrazolium staining techniques was expressed as a percentage of total ventricular myocardium at ischemic risk. This percentage was not significantly different between the groups (84% +/- 5% with metoprolol vs 90% +/- 4% with placebo; p = 0.4). Myocardial infarct size was not significantly decreased at 5 hours by early administration of intravenous metoprolol when the infarct artery remained occluded and collateral flow was minimal.

Effects of metoprolol on early infarct expansion after acute myocardial infarction

The effects of metoprolol on early infarct expansion after acute myocardial infarction were studied in rats (n = 54) that underwent either left coronary artery ligation (MI) or sham operation. Immediately after surgery, the rats received either metoprolol (M) by mouth, which had been dissolved in drinking water, for 72 hours supplemented with three intraperitoneal doses over the first 24 hours or no treatment (H2O). Three days after the initial surgery, hemodynamic measurements were made before and after volume loading. The rats were killed, the hearts were removed, and passive pressure-volume curves were obtained. The hearts were then fixed at a constant pressure and analyzed morphometrically. Infarct size was nonsignificantly lower in the metoprolol-treated group compared with the untreated group (38% +/- 5% MI-M vs 48% +/- 3% MI-H2O, p = 0.10) Compared with infarcted untreated rats, infarcted metoprolol-treated rats had a lower heart rate (322 +/- 13 beats/min MI-M vs 452 +/- 19 beats/min MI-H2O, p < 0.001), lower left ventricular systolic pressure (63 +/- 4 mm Hg MI-M vs 90 +/- 6 mm Hg MI-H2O, p = 0.004), and lower +dp/dt (1340 +/- 169 mm Hg/sec MI-M vs 2872 +/- 273 mm Hg/sec MI-H2O, p < 0.001), but left ventricular end-diastolic pressure and cardiac index did not differ between the two groups. Left ventricular weight corrected for body weight was higher in infarcted rats treated with metoprolol compared with infarcted untreated rats (2.76 +/- 0.07 gm/kg MI-M vs 2.41 +/- 0.09 gm/kg MI-H2O, p < 0.05). The initial slope of the pressure-volume relationship Ki, an index of operative volume stiffness, was lower in infarcted rats treated with metoprolol compared with infarcted untreated rats (p = 0.03). There were, however, no significant differences in the expansion index, thinning ratio, or left ventricular volume between the two infarcted groups. Thus metoprolol therapy begun in the immediate postinfarction period promotes an increase in left ventricular weight and reduces operative volume stiffness but has no significant effect on indexes of early infarct expansion.

Effect of atenolol on myocardial infarct expansion in a nonreperfused rat model

Acute myocardial infarct expansion is associated with a poor prognosis. This study was performed to assess potential beneficial effects of beta-blockers on inhibiting expansion. A pilot study showed that atenolol (10 mg/kg) achieved sustained beta-blockade in rats. In the main study, following left coronary ligation, 36 rats received atenolol and 18 rats received placebo daily for 7 days. Infarct size was similar in treated and control rats (25 +/- 13% versus 28 +/- 11%). Expansion grades and a quantitative index of expansion were similar for both groups. Infarct size and expansion index were significantly related, but linear regression lines were similar for treated and control rats. We conclude that atenolol has no significant effect on infarct expansion in this nonreperfused rat model.

Cardiac sympathetic activity in myocardial ischemia: release and effects of noradrenaline

Sympathetic overactivity in myocardial ischemia is closely associated with the progression of myocyte injury and the incidence of malignant arrhythmias. Adrenergic stimulation of the ischemic myocardium is predominantly due to increased local noradrenaline concentrations in the heart, whereas plasma catecholamine levels are of minor relevance. During the first few minutes of ischemia, efferent sympathetic nerves are activated. Excessive accumulation of noradrenaline, however, is prevented since adenosine, formed in the ischemic myocardium, suppresses exocytotic noradrenaline release, and released noradrenaline is rapidly removed as long as catecholamine reuptake is functional. With progression of ischemia to more than 10 min, the myocardium is no longer protected against excess catecholamine accumulation in the interstitial space, since local metabolic release mechanisms become increasingly important. This release, which is independent of central sympathetic activity and from extracellular calcium, occurs in two steps: First, noradrenaline escapes from its intracellular storage vesicles and accumulates in the cytoplasm of the neuron. In a second, rate-limiting step, noradrenaline is transported across the plasma membrane into the interstitial space, using the neuronal uptake carrier in reverse of its normal transport direction. As a consequence of local metabolic catecholamine release, extracellular noradrenaline reaches 1000 times the normal plasma concentration within 20 min of ischemia. Studies using acute and chronic sympathetic denervation and antiadrenergic agents demonstrate that local metabolic, rather than centrally induced noradrenaline release is critically involved in the progression of ischemic cell damage within the occurrence of ventricular fibrillation in early ischemia. Myocardial ischemia results in a temporary supersensitivity of the myocytes to catecholamines. This is due to a twofold increase of alpha 1- and a 30% increase of beta-adrenergic receptor number at the cell surface. The sensitization of adenylate cyclase during the first 20 min of total ischemia is followed by a rapid inactivation of the enzyme. The beta-adrenergic hyperresponsiveness to catecholamines is therefore limited to the first few minutes of ischemia. The deleterious combination of extremely high noradrenaline concentrations with a temporarily enhanced responsiveness to catecholamines of the tissue is thought to accelerate the propagation of the wavefront of irreversible cell damage within the ischemic myocardium. Moreover, the inhomogenous distribution of catecholamine excess within the heart is considered to promote malignant arrhythmias by unmasking and enhancing electrophysiological disturbances in early ischemia.

Drug treatment of hypertension

There are several first choices for the treatment of mild and moderate hypertension. The selection of a drug may be influenced by concomitant pathology, with positive indications for particular drugs, e.g. coexistent angina, indicating use of a beta-receptor blocking drug or calcium antagonist; fluid retention indicating a diuretic; or contraindication e.g. asthma, and beta-adrenoceptor blocking drugs. beta-Adrenoceptor blocking drugs have the advantage of a long history and of possibly being cardioprotective following myocardial infarction, but they have not yet been established as primary preventive agents in hypertensive patients. The alpha-receptor blocking drugs have the advantage of favourably affecting lipid profile and blood pressure. Therefore, there may be advantages in the use of combined alpha- and beta-blockade. The diuretics, which have the advantage of being inexpensive, are widely used but long term metabolic effects, particularly hypokalaemia, cause concern. This is correctable by co-administration of a potassium sparing diuretic and often preventable by using low doses of the diuretic. Diet may be important as hypokalaemia appears to be less of a problem where potassium intake is high. Experience with calcium antagonists is widening but the use of converting enzyme inhibitors is more limited, and some physicians are less ready to use them as first choice in mild hypertension at present. Drugs like methyldopa, clonidine, the adrenergic neurone inhibitory drugs are now used more as reserve agents. More severe cases of hypertension may require drugs from 2 of the 3 major groups: beta-blocking drugs, vasodilators and diuretics. In some cases, drugs from each of these 3 groups will be required.

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).

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.

Effects of pindolol therapy on the size of experimentally induced myocardial infarction in the pig

The effect of pindolol on experimental myocardial infarction was studied in a pig model. Intravenous application of 0.05 mg pindolol per kg body weight was initiated one hour after coronary ligation and repeated at 12-hour intervals for five days. No significant difference in infarct size could be found between pindolol-treated animals (20.4 +/- 0.6% SEM of whole ventricular mass, n = 6) and untreated controls (20.5 +/- 1.2% SEM, n = 9). Hemodynamic data did not change significantly throughout the experiment. These results differ in part from those reported by other investigators: The disagreement may be due to the specific pharmacological properties of the applied drug, to variations in the dosages of beta blockers, as well as to differences in the study design.

Experimental and clinical observations on the efficacy of esmolol in myocardial ischemia

Beta blockers reduce myocardial oxygen demand and are therefore useful in ischemic states. They reduce angina pectoris and reduce the risk of death when administered long-term after acute myocardial infarction. Some studies suggest that when administered early after coronary occlusion they can reduce myocardial infarct size. Relative contraindications to beta blockers, such as a history of congestive heart failure, chronic obstructive lung disease, atrioventricular conduction defects and low blood pressure, limit their use. Conventional beta blockers have a relatively long duration of action and are either contraindicated or must be used with particular caution in patients with these contraindications. Esmolol is an ultrashort-acting beta blocker with a biologic half-life of 9 minutes. Therefore, such an agent may be useful in patients with ischemic heart disease in whom reducing heart rate would be beneficial but in whom there is concern that beta blockers might not be tolerated. Esmolol reduced myocardial infarct size in 2 experimental studies of coronary occlusion followed by reperfusion, and improved the recovery of the stunned myocardium when administered during experimental myocardial ischemia. Esmolol's brief duration of action may make it safer than conventional beta blockers for the management of patients with unstable angina or myocardial infarction.

Effects of beta-adrenergic blockade on the natural progression of myocardial infarct size and compensatory hypertrophy

Using contrast-enhanced computed tomography, the effects of beta-adrenergic blockade were assessed on experimentally produced myocardial infarcts in dogs evaluated serially over the course of approximately 1 month. Infarct size, initial perfusion defect (jeopardized segment) and noninfarcted muscle mass were studied in two groups of conditioned mongrel dogs. Group 1 (n = 11) served as the control group and Group 2 (n = 10) was pretreated with propranolol (2 mg/kg). Each animal in the propranolol-treated group was given identical amounts of the agent twice daily for 7 days after coronary occlusion. Both groups developed increases in the noninfarcted muscle mass of the left ventricle (compensatory hypertrophy). The mean increase averaged 19.8% over 30 days when the two groups were included together. Infarct size was smaller in the propranolol-treated group, and averaged 28% less (p less than 0.05) than that of the control group 30 days after initial myocardial infarction. Thus, pharmacologic interventions were shown by computed tomography to alter the size of an acute experimental myocardial infarct, particularly when examined over the time course of infarct healing. Moreover, compensatory hypertrophy occurred in both the control and propranolol-treated groups.

The effect of beta-adrenoceptor blocking agents on evolving myocardial necrosis in coronary ligated rats with and without reperfusion

The left coronary artery of rats was ligated either permanently, or for a period of 40 or 60 min, with subsequent reperfusion. In experiments with permanent occlusion, the hearts were removed and investigated 5 h after the coronary ligation, or immediately after death in animals which died earlier. The hearts from the reperfusion experiments were investigated 60 min after reopening the occluded artery. The extent of the ischaemic and necrotic areas of the hearts was determined. A quantitative photometric method was developed for this purpose, using "negative staining" with Evans blue for the ischaemic area, and "negative staining" with triphenyltetrazolium chloride for the necrotic area. In experiments in which ligation was permanent, the percentage of the ischaemic area which underwent necrosis increased with the time after coronary occlusion. In reperfusion experiments, myocardial necrosis was detected earlier than in experiments with permanent coronary ligation. The beta-adrenoceptor blocking agents pindolol, propranolol, and metoprolol significantly decreased the percentage of necrosis in experiments with permanent ligation of the coronary artery. The most selective of the beta-adrenoceptor blockers, i.e. metoprolol was tested in the reperfusion experiments. In these experiments, the amount of necrosis was also significantly decreased.

Comparative effects of propranolol, timolol and metoprolol on myocardial infarct size after experimental coronary artery occlusion

The effects of equiblocking doses of three beta-adrenergic blocking agents, propranolol, timolol and metoprolol, on myocardial infarct size were evaluated in 28 dogs after acute experimental coronary artery occlusion. Heart rate, arterial pressure and arterial free fatty acid concentration were measured in an attempt to evaluate their effects on the extent of myocardial injury. The zone at risk of infarction in each dog 1 minute after left anterior coronary artery occlusion was assessed by injecting highly radioactive albumin microspheres into the left atrium, and the hypoperfused zone was determined by autoradiography. After 15 minutes, the dogs were randomized into four groups: control dogs (n = 7), propranolol-treated dogs (1.2 mg/kg intravenously, n = 7), timolol-treated dogs (0.2 mg/kg intravenously, n = 7) and metoprolol-treated dogs (1.2 mg/kg intravenously, n = 7). After 6 hours, the dogs were killed. The left ventricle was sliced and stained with triphenyl-tetrazolium chloride for measurement on infarct size. The same slices were then autoradiographed for measurement of the hypoperfused zone. The percent of hypoperfused zone that evolved to infarction (the ratio of infarct size to hypoperfused zone) was 90.4 +/- 1.9% in the control group, 72.4 +/- 2.4% in the propranolol-treated dogs (p less than 0.05 versus control group); 57.9 +/- 4.4% in the timolol-treated dogs (p less than 0.01 versus control group; p less than 0.05 versus propranolol) and 54.4 +/- 3.7% in the metoprolol-treated dogs (p less than 0.01 versus control group; p less than 0.05 versus propranolol). Thus, propranolol, timolol and metoprolol reduced myocardial infarct size in dogs by 20, 36 and 40%, respectively, after experimental coronary artery occlusion. Metoprolol and timolol protected the ischemic myocardium more effectively than did propranolol.

Usefulness of intravenous propranolol in predicting left anterior descending blood flow during anterior myocardial infarction

The effect of propranolol on precordial ST-segment elevation was studied in 24 patients with acute anterior myocardial infarction. The electrocardiographic response to the drug was correlated with the early angiographic appearance of the left anterior descending coronary artery (LAD). After a 30-minute observation period, intravenous propranolol (average dose 3.5 +/- 2.2 mg) was given a mean of 2.8 +/- 1.9 hours after the onset of persistent chest pain. Coronary angiography was performed 3.6 +/- 2.0 hours after the onset of symptoms. Patients were classified into 2 groups according to the angiographic findings. Group A consisted of 7 patients with a stenotic but patent LAD and 1 patient with excellent collateral blood flow to that area. Group B consisted of 16 patients with a completely occluded LAD and poor or absent collateral blood flow. Patients in group A showed a mean reduction in precordial ST-segment elevation of 77 +/- 18% and patients in group B showed a mean reduction of 13 +/- 14% (p less than 0.005). Left ventricular ejection fraction at discharge was 0.6 +/- 0.07 in group A and 0.37 +/- 0.08 in group B (p less than 0.001). Thus, the electrocardiographic response to intravenous propranolol given early in the course of acute anterior myocardial infarction predicts the presence of blood flow to the infarcting zone. The combination of residual blood flow and reduction of ST-segment elevation secondary to propranolol is associated with preservation of ventricular function.

Enhancement of salvage of reperfused myocardium by early beta-adrenergic blockade (timolol)

Although reperfusion of severely ischemic myocardium with thrombolytic agents or surgery has shown reduction in infarct size, the time after coronary occlusion during which reperfusion can salvage ischemic myocardium is limited. To determine whether beta-adrenergic blockade could enhance the salvage of ischemic myocardium by reperfusion, the left anterior descending coronary artery was occluded in 18 anesthetized dogs. An in vivo area at risk was determined by injecting technetium-99m-labeled albumin microspheres into the left atrium 5 minutes after occlusion and carrying out radioautography to define the poorly perfused tissue. Fifteen minutes after coronary occlusion, the dogs were randomized either to a control (saline-treated) group (n = 8) or to a timolol-treated group (n = 10). Timolol was administered until a decrease of 20% in heart rate or blood pressure occurred (mean total dose = 0.85 +/- 0.22 mg/kg +/- standard error of the mean). Coronary occlusion was maintained for 3 hours and was followed by 3 hours of reperfusion in both groups. At the end of 6 hours, infarct size was defined by triphenyltetrazolium chloride staining and masses of infarct and risk were calculated. Percent left ventricular mass at risk was similar for both groups (control = 20.9 +/- 2.4%, timolol-treated = 23.7 +/- 2.1%, p = not significant). Mass of necrosis/mass at risk was significantly smaller in the timolol-treated reperfusion group (27.3 +/- 2.7%) versus saline reperfusion alone (46.5 +/- 5.6%) (p less than 0.005). Thus, beta-adrenergic blockade administered early after coronary occlusion results in substantial enhancement of the salvage achieved by reperfusion alone.

Role of beta-adrenergic blockade in the therapy of patients with myocardial infarction

Beta-adrenergic blockade appears to have beneficial effects on ischemic myocardium, both in experimental animals and in patients. There is substantial evidence that beta blockade, when induced promptly after coronary occlusion, is capable of limiting the size of experimentally produced infarcts. Although many mechanisms of action have been proposed, the bulk of available evidence suggests that beta blockade reduces the severity of myocardial ischemia by reducing myocardial oxygen demands. Intravenous and oral therapy with beta-blockers is safe when patients are carefully selected and observed. Invasive hemodynamic monitoring is not usually necessary for safe use of these drugs. Preliminary reports based on studies with several beta-blockers indicate that early intervention might limit infarct size or even prevent its occurrence, particularly in patients with evidence of increased sympathetic activity. However, before early beta blockade can be recommended as standard therapy for uncomplicated myocardial infarction, these findings should be confirmed in rigorously controlled clinical trials utilizing several techniques for assessment of infarct size. The most significant finding with beta-blockers in patients with myocardial infarction has been that these drugs can improve survival when administered to patients on a long-term basis after infarction. Although the mechanism of this protective effect is not yet understood, the results are clear enough to warrant the routine administration of a beta-blocker to patients who have had infarction and who have no contraindications to such therapy.

Limitation of myocardial infarct size by atenolol, nadolol and propranolol in dogs

The importance of cardioselectivity and membrane depressant activity in the ability of beta-adrenergic antagonists to limit myocardial infarct size was assessed in the dog. Infarction was produced by a 60 min occlusion of the left circumflex coronary artery followed by reperfusion into a critical stenosis. Infarct size was significantly reduced by atenolol, nadolol and propranolol. Thus, limitations of infarct size by beta-adrenergic antagonists occur with agents which possess or lack cardiac selectivity or membrane depressant activity.

Beneficial effects of vagal stimulation on the ischaemic myocardium during beta-receptor blockade

The effect of vagal stimulation on the myocardial ischaemia produced by acute coronary occlusion during beta-receptor blockade has been examined. Epicardial ST-segment elevation, myocardial surface temperature and regional blood flow were determined 10 min after coronary occlusion in the dog. Coronary occlusion after beta-receptor blockade alone raised the average ST-segment from 0.5 +/- 0.3 to 3.1 +/- 0.5 mV (SEM) (p less than 0.001). Subsequent vagal stimulation with beta-receptor blockade, which reduced heart rate from 129 to 50 beats/min, mean arterial pressure from 123 to 78 mmHg, but increased cardiac output from 1164 to 1855 ml/min, resulted in marked reduction in ST-segment elevation to 0.3 +/- 0.2 mV which was not different from the control before occlusion. Epicardial temperature was markedly decreased in the ischaemic area following coronary occlusion. The temperature difference between central ischaemic and surrounding areas became smaller after beta-receptor blockade, and vanished during vagal stimulation. Vagal stimulation caused a 55% decrease of blood flow in all non-ischaemic regions. A smaller reduction took place in the border zone where flow values close to those of the non-ischaemic myocardium were obtained. In the central ischaemic area blood flow remained unchanged despite the reduction in arterial pressure. Thus, vagal stimulation resulted in decreased collateral resistance in the ischaemic area and a marked reduction of myocardial oxygen requirement of both non-ischaemic and border zone myocardium, additional to that obtained with beta receptor blockade. The provision of energy to the ischaemic myocardium is therefore very favourably balanced with its actual demand during vagal stimulation.

Myocardial infarction in the dog: effects of intravenous propranolol

The effects of propranolol on myocardial perfusion and metabolism during acute myocardial infarction were studied in 18 mongrel dogs. A reversible snare was placed on the left anterior descending coronary artery; regional myocardial perfusion was continuously measured using the short-lived isotope krypton-81m, and myocardial metabolism was assessed using the epicardial electrocardiogram and measurement of release of creatine kinase activity from the affected segment of myocardium. Six dogs with no arterial occlusion acted as "sham operated" dogs; six others in which the snare was occluded acted as a control group and a third group of six were given propranolol, 0.5 mg/kg, 30 minutes after coronary occlusion. All variables were recorded before and for 5 hours after coronary occlusion. Dogs treated with propranolol showed a significant improvement in regional myocardial perfusion to the affected segment, decreased loss of electrically active myocardium at the end of each experiment for any given degree of early S-T segment elevation and a delay in the local release of creatine kinase activity compared with that in the control dogs. These results suggest that propranolol exerts a beneficial effect on the progress of ischemic myocardial damage when given shortly after the onset of infarction.