Do beta-adrenergic blocking agents increase coronary flow reserve?

Background Beta-adrenergic blocking agents are the cornerstone in the treat ment of coronary artery disease (CAD). The exact pathophysiologic mechanism is not clear but depends largely on the oxygen-sparing effect of the drug, thus, the effect of metoprolol on coronary flow reserve and coronary flow velocity reserve (CFVR) was determined in patients with CAD. Methods Corona blood flow velocity was measured with the Doppler Row wire i n 23 patients (age: 56 +/- 10) undergoing percutaneous transluminal coronar y, angioplasty for therapeutic reasons. Measurements were carried out at re st, after 1-min vessel occlusion (postischemic CFVR) as well as after intra coronary adenosine (pharmacologic CFVR) before and after 5 mg intravenous m etoprolol. In a subgroup (n=15), absolute flow was measured from coronary f low velocity multiplied by coronary cross-sectional area. Results Rate-pressure product decreased after metoprolol from 9.1 to 8.0 x 10(3) mm Hg/min (p<0.001). Pharmacologic CFVR was 2.1 at rest and increased after metoprolol to 2.7 (p=0.002). Likewise, postischemic CFVR increased f rom 2.6 to 3.3 (p<0.001). Postischemic CFVR was significantly higher than p harmacologic CFVR before as well as after metoprolol. Coronary vascular res istance decreased after metoprolol from 3.4 +/-2.0 to 2.3 +/-0.7 mm Hg x s/ cm (p<0.02). Conclusions The following conclusions were drawn from this study. Metoprolo l is associated with a significant increase in postischemic and pharmacolog ic MIR. However, postischemic CFVR is significantly higher than pharmacolog ic CFVR. The increase in CFVR by metoprolol can be explained by a reduction in vascular resistance. The increase in CFVR (=increased supply) and the r eduction in oxygen consumption (= decreased demand) after metoprolol explai n the beneficial effect of this beta-blocker in patients with CAD. (J Am Co ll Cardiol 2001;38:1866-71) (C) 2001 by the American College of Cardiology.