Effect of intravenous metoprolol or intravenous metoprolol plus glucagon on dobutamine-induced myocardial ischemia

Study Objective. To determine the effect of metoprolol on dobutamine stress testing with technetium-99m sestamibi single-photon emission computed tomo graphy imaging and ST-segment monitoring, and to assess the impact of intra venous glucagon on metoprolol's effects. Design. Randomized, double-blind, placebo-controlled trial. Setting. Community hospital. Patients. Twenty-two patients with known reversible perfusion defects. Intervention. Patients underwent dobutamine stress tests per standard proto col. Before dobutamine was begun, no therapy was given during the first vis it, and patients were randomized on subsequent visits to receive metoprolol or metoprolol plus glucagon 1 mg. Metoprolol was dosed to achieve a restin g predobutamine heart rate below 65 beats/minute or a total intravenous dos e of 20 mg. Measurements and Main Results. Metoprolol reduced maximum heart rate 31%, s ummed stress scores 29%, and summed difference scores 43% versus control. M etoprolol plus glucagon also reduced the maximum heart rate 29% versus cont rol. Summed stress and summed difference scores were not significantly redu ced, although they were 18% and 30% lower, respectively, than control. No s ignificant differences were found in any parameter between metoprolol and m etoprolol-glucagon. Conclusion. During dobutamine stress testing, metoprolol attenuates or elim inates evidence of myocardial ischemia. Glucagon 1 mg, although somewhat ef fective, does not correct this effect to the extent that it can be administ ered clinically.