Beneficial effects of intravenous and oral carvedilol treatment in acute myocardial infarction. A placebo-controlled, randomized trial

BACKGROUND

Evidence of efficacy and safety of beta-blockers after thrombolysis for acute myocardial infarction (AMI) is equivocal. Newer beta-blockers such as carvedilol have not been tested in this setting.

METHODS AND RESULTS

This study investigated the effects of acute (intravenous) and long-term (6 months, oral) treatment with carvedilol versus placebo in 151 consecutive patients with AMI. Exercise ECG, ambulatory monitoring, and two-dimensional echocardiography were performed before hospital discharge and at 3 and 6 months. All patients were followed up and cardiovascular events recorded. The Cox proportional hazards model was used to compare time from randomization with the occurrence of a cardiovascular event, and Kaplan-Meier survival curves were calculated. Carvedilol was found to be safe, and it significantly reduced cardiac events compared with placebo (18 on carvedilol and 31 on placebo, P < .02). Fifty-four patients had heart failure at study entry; 34 received carvedilol. There were no adverse effects of carvedilol therapy and no excess events in this subgroup. Carvedilol produced significant reductions in heart rate (P < .0001), blood pressure (P < .005) at rest, and rate-pressure product at peak exercise (P < .003), but exercise capacity was unchanged. Left ventricular ejection fraction was not altered significantly by carvedilol, but stroke volume was higher at pre-hospital discharge examination (63 versus 53 mL; P < .01). Diastolic filling of the left ventricle (E/A ratio) was also improved (1.2 versus 0.9; P < .001). In a subgroup with left ventricular ejection fraction < 45% (n = 49 patients; 24 on carvedilol and 25 on placebo), carvedilol showed attenuation of remodeling.

CONCLUSIONS

Carvedilol was well tolerated and safe to use in patients immediately after AMI, including those with heart failure, and significantly improved outcome.

Magnesium sulfate reduces myocardial infarct size when administered before but not after coronary reperfusion in a canine model

BACKGROUND

The role of magnesium in treating acute myocardial infarction (AMI) has been controversial. Several small clinical trials indicate that magnesium may have a role in treating AMI early, whereas the other results suggest that magnesium is of questionable benefit.

METHODS AND RESULTS

We looked at the effect of magnesium on infarct size (IS) when given during a coronary occlusion and after reperfusion. Magnesium sulfate (6-mEq bolus plus 2 mEq/h for 5 hours) was given at 15 or 45 minutes of coronary occlusion or 15 minutes of reperfusion. The left anterior descending coronary artery was occluded for 90 minutes, followed by 300 minutes of reperfusion. IS to area at risk (IS/AR) was measured by planimetry after triphenyltetrazolium chloride staining. Collateral myocardial blood flow was measured with radioactive microspheres. The IS/AR ratio in the control group was 52.3 +/- 19.6% compared with 20.5 +/- 11.7% and 21.3 +/- 6.5% at 15 and 45 minutes of occlusion, respectively (P < .05). There were no significant differences in the reduction in IS at 15 and 45 minutes of occlusion. Although there was a reduction in the IS when magnesium was administered during reperfusion (38.2 +/- 13.4%), it was not statistically significant. There was no significant difference in the AR relative to the total left ventricular weight between the four groups.

CONCLUSIONS

The data suggest that magnesium infusion during a coronary occlusion has a significant benefit in reducing the IS in this model. Magnesium may have a beneficial clinical role in AMI, especially if administered before reperfusion as a bolus followed by a constant infusion.

Exercise testing after myocardial infarction: relative values of the low level predischarge and the postdischarge exercise test

This study was undertaken to compare the relative values of the low level predischarge exercise test and the postdischarge (6 weeks) symptom-limited test in 518 consecutive patients admitted with an acute myocardial infarction. Of the patients who did not develop significant ST segment depression or angina during the predischarge test, the symptom-limited test also remained negative in 91.5 and 91.9% of the patients, respectively. Similar results were obtained with ST segment elevation and the systolic blood pressure response during the two exercise tests with only 2.1 and 11.4% changing from normal to abnormal, respectively. Discriminant function analysis was done to predict the occurrence of coronary events (unstable angina, reinfarction, cardiac failure, cardiac death) with use of the data from the exercise tests together with other clinical and investigational data. The jackknife method correctly classified 71.9 and 71.4% of the patients with the data from the predischarge exercise test and symptom-limited test, respectively. Combining the data from the two tests improved the overall predictive accuracy to only 75.0%. It is concluded that the routine performance of a symptom-limited test 6 to 8 weeks after infarction does not reveal any significant additional information in those patients who have undergone a predischarge low level exercise test. Thus the 6 to 8 week test should be restricted to selected patients after myocardial infarction.

Prediction of coronary events following myocardial infarction using a discriminant function analysis

This study was undertaken to derive an index for predicting coronary events in the first year after a myocardial infarction in "low-risk" patients enrolling in a Cardiac Rehabilitation Program. Data from 145 consecutive patients were analysed. The events were classified as follows: angina requiring further therapy, re-infarction and coronary death. Seventy patients had events: Angina--52, Re-infarction--8, Coronary Death--10. A discriminant function analysis was performed to predict such events using data available at the time of discharge from hospital. The following were significant predictors: (1) previous infarction/angina, (2) radiological evidence of cardiomegaly or lung congestion in the Coronary Care Unit, (3) Non-Q wave infarction and (4, 5 and 6) angina, atrial arrhythmias and a decrease in R wave amplitude in V5 during a pre-discharge exercise test. The jack-knife method classified correctly 71.2% of those with events and 72.6% of those without events. In patients with discriminant scores greater than +0.2, 82% developed events.