The Potential for Unexpected Hazard of Intravenous Beta-Blockade for Acute Myocardial Infarction: Results from the GUSTO Trial

To evaluate the role of immediate intravenous (IV) β blockade in patients treated with thrombolytic agents and aspirin for acute myocardial infarction, we compared the outcome in the group of patients enrolled in the GUSTO trial who received atenolol IV followed by oral dose (gr.A, N = 16406) with the group receiving it only orally within the first 24 hours (gr.B, N = 6732). GUSTO tested four regimens of thrombolysis: accelerated t-P with IV heparin, streptokinase (SK) with IV/subcutaneous heparin and combination of t-P and SK with IV heparin, in 41,021 patients. Atenolol was administered, if not contraindicated, as two doses of 5 mg. IV, every 15 minutes followed by 50-100 mg. orally every day. In 9987 patients, there were contraindications to its use, as perceived by the enrolling physician. The baseline characteristics of the patients receiving IV atenolol were not unfavorable in terms of previous infarction, Killip class, assignment to t-PA, age, systolic pressure, heart rate or time to treatment, when compared with the whole cohort receiving atenolol within the first 24 hours. The main events are listed below: (CHF -- congestive heart failure, v.fib -- ventricular fibrillation): There was similar incidence of reinfarction and angiographic reocclusion in the 2 groups. Although not randomized comparison, the utilization of IV atenolol in the first 24 hours after myocardial infarction, was paradoxically associated with increased morbidity, when compared to the more gradual oral β blockade.