Intravenous therapy with propranolol in acute myocardial infarction: effects on changes in the S-T segment and hemodynamics

Reduction in infarct size and enhanced recovery of systolic function after coronary thrombolysis with tissue-type plasminogen activator combined with beta-adrenergic blockade with metoprolol

The effect of beta-adrenergic blockade on the salvage and functional recovery of reperfused myocardium was investigated in anesthetized dogs. Immediately after thrombotic occlusion of the left anterior descending coronary artery, the cardioselective beta-blocking agent metoprolol was given intravenously at a dose of 0.5 mg/kg infused over 10 min. One hour after the onset of occlusion, recanalization was initiated by intravenous infusion of recombinant human tissue-type plasminogen activator (rt-PA, 10 micrograms/kg/min for 30 min). Anatomic infarct size expressed as percent of the left ventricular mass (I/LV), global ejection fraction, and mean systolic shortening of the segmental radii (SS) of the infarcted area were measured either after 24 hr or 1 week in six groups of six dogs each: group I (rt-PA + metoprolol, evaluated at 24 hr), group II (rt-PA + metoprolol, evaluated at 1 week, group III (rt-PA alone, evaluated at 24 hr), group IV (rt-PA alone, evaluated at 1 week), group V (persistent occlusion, evaluated at 24 hr), and group VI (persistent occlusion, evaluated at 1 week). The smallest infarcts were found in reperfused dogs given metoprolol, but the differences from dogs receiving rt-PA alone were not statistically significant (I/LV, expressed as mean +/- SEM: 5.5 +/- 0.9% in group I, 6.7 +/- 1.9% in group II, 15.4 +/- 5.0% in group III, 11.4 +/- 3.5% in group IV, 23.6 +/- 2.5% in group V, and 26.9 +/- 2.3% in group VI).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of metoprolol in acute myocardial infarction. A randomized, placebo-controlled multicenter study

The central hemodynamic effects of metoprolol in acute myocardial infarction have been studied in a multicenter, double-blind, randomized trial. One hundred and ninety patients with acute myocardial infarction not previously on beta blockers with heart rate greater than 65 beats/min and blood pressure greater than 105 mm Hg and without clinical signs of serious heart failure were included. After insertion of a pulmonary artery catheter, patients were randomized to metoprolol, 15 mg intravenously, and 50 mg 4 times a day orally (n = 95) or placebo (n = 95) with a mean delay of 7.2 hours. Hemodynamic measurements were made at baseline and repeatedly during 24 hours. Heart rate, systolic blood pressure and cardiac index were all immediately reduced by 10 to 20% in the metoprolol group and the difference compared with placebo was maintained throughout the 24 hours (p less than 0.001). Pulmonary capillary wedge pressure (PCWP) in the metoprolol group increased from 13.7 +/- 6.7 to a peak of 15.5 +/- 5.5 mm Hg 30 minutes after injection. The difference compared with placebo was maintained for 8 hours (p less than 0.01). This increase was seen only in the patient group with initial PCWP below the median of 13 mm Hg. In patients with initial PCWP above the median a continuous decrease was observed in both the placebo and metoprolol groups. Thus high initial PCWP was not associated with intolerance to metoprolol. Based on hemodynamic measurements tolerance to metoprolol was good.

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.

Effect of metoprolol on chest pain in acute myocardial infarction

A total of 1395 patients aged 40 to 74 years were included in a double blind trial with the beta 1 selective blocker metoprolol in suspected acute myocardial infarction. Metoprolol was given intravenously (15 mg) as soon as possible after admission to hospital followed by 200 mg daily for three months. A placebo was given in the same manner. The severity of chest pain in the acute phase was calculated by recording the number of injections of analgesics given and the time from the start of blind treatment to the time when the last analgesic was given (duration of pain). The patients receiving metoprolol were given a lower mean number of injections of analgesics during the first four days and after randomisation than those receiving a placebo. The estimated duration of pain was shorter in the metoprolol group than in the placebo group. These effects were related to the initial heart rate, the initial systolic blood pressure, and the final site of the infarct as determined electrocardiographically. Thus metoprolol given in the acute phase of suspected or definite myocardial infarction appears to reduce the severity of chest pain.

Persistent reduction in left ventricular asynergy in patients with acute myocardial infarction by intravenous infusion of nitroglycerin

Intravenous nitroglycerin (NG) infusion in patients with acute myocardial infarction (AMI) has been shown to improve left ventricular function and myocardial perfusion and to decrease ischemic injury and creatine kinase (CK) indexes of infarct size. To determine whether early NG infusions in patients with AMI decreases the extent of left ventricular asynergy, we used two-dimensional echocardiography to measure asynergic segments (akinesis and/or dyskinesis) at four serial short-axis levels from base to apex (mitral, M; chordal, C; midpapillary, MP; low papillary, LP) in 22 patients with a first anterior AMI. Patients were randomized between infusions of NG (n = 11) or 5% dextrose in water (controls, n = 11) within 5.6 hr after the onset of pain. NG infusion rates were titrated to lower mean arterial pressure to an average level of 7% below control (but not below 80 mm Hg) and were maintained at this level for the duration of the infusions (39 hr). After NG, left ventricular function improved as left ventricular filling pressure decreased (p less than .005), and sigma ST on precordial ST segment mapping decreased (p less than .001). These parameters did not change in control subjects. Computed CK infarct size was smaller in the NG group than in the control group (p less than .05). Before the infusions, the mean extent of left ventricular asynergy (% left ventricular circumference) were similar in both groups: M, 18% vs 21%; C, 22% vs 23%; MP, 26% vs 24%; LP, 32% vs 29%. In addition, the computed total left ventricular asynergy (% surface area) was also similar for these two groups before therapy (25% vs 25%). There was no change in left ventricular asynergy from pretreatment values by 1 hr and 10 days among control subjects: M, 18% vs 18% vs 17%; C, 22% vs 22%; MP, 26% vs 26% vs 22%; LP, 32% vs 33% vs 33%; total 25% vs 25% vs 24% (multiple measures analysis of variance). In contrast, there was a significant decrease (p less than .001) in left ventricular asynergy from pretreatment values by 1 hr and 10 days with NG: M, 21% vs 10% vs 8%; C, 23% vs 12% vs 10%; MP, 24% vs 13% vs 9%; LP, 29% vs 14% vs 10%; total, 25% vs 12% vs 9%.(ABSTRACT TRUNCATED AT 400 WORDS)