Aim: To evaluate the effect of current treatment with non-selective or cardioselective beta-blockers on the outcome of a first acute myocardial infarction in hypertensive patients.
Outcome measures: Peak aspartate aminotransferase was measured as an indirect estimate of infarct size, the occurrence of circulatory arrest from ventricular tachyarrhythmias and in-hospital mortality.
Design: A retrospective analysis was performed on data collected in a continuously operating register of all hospitalized acute myocardial infarctions in Malmö, Sweden.
Patients: A total of 2114 hypertensive patients were admitted to hospital with a first acute myocardial infarction. Of these patients, 323 were treated with a non-selective beta-blocker on admission and 338 with a cardioselective beta-blocker.
Results: In patients given a non-selective beta-blocker the mean peak aspartate aminotransferase was 3.02 +/- 0.15 mukat/l, which was significantly lower than the peak (3.78 +/- 0.35 mukat/l) recorded in the patients given a cardioselective beta-blocker. In a multiple regression analysis, treatment with a non-selective beta-blocker was significantly and inversely related to peak aspartate aminotransferase after adjustment for several clinical characteristics. Age, anterior myocardial infarction, peak aspartate aminotransferase, serum potassium and treatment with a cardioselective beta-blocker were significantly and independently associated with the occurrence of circulatory arrest due to ventricular tachyarrhythmias. The relative risk of circulatory arrest in patients taking cardioselective beta-blockers was 1.73 (95% confidence interval 1.16-2.58) and in patients taking non-selective beta-blockers 1.02 (95% confidence interval 0.64-1.66). Advanced age, a history of diabetes mellitus, a history of stroke, anterior myocardial infarction, a high serum potassium level and a high peak aspartate aminotransferase level significantly predicted in-hospital mortality. The relative risk of in-hospital mortality in patients taking non-selective beta-blockers was 0.92 (95% confidence interval 0.64-1.30), and in patients taking cardioselective beta-blockers 0.84 (95% confidence interval 0.59-1.19).
Conclusions: The study suggests that current treatment with non-selective beta-blockers may have reduced the enzymatically estimated infarct size and the occurrence of circulatory arrest due to ventricular tachyarrhythmias. Both non-selective and cardioselective beta-blockers may also have reduced the in-hospital mortality in this population of hypertensive patients suffering a first acute myocardial infarction. In a clinical study using with adrenaline infusions in healthy volunteers, we found that beta 2-receptor blockade improved potentially arrhythmogenic variables, such as hypokalemia and hypomagnesemia, but the adrenaline-induced reduction in diastolic blood pressure was reversed. Pretreatment with the new beta-blocker carvedilol preserved the beneficial electrolyte effects without increasing blood pressure during the adrenaline infusion.