FUNCTIONAL, ANGIOGRAPHIC AND INTRACORONARY DOPPLER FLOW CHARACTERISTICS IN SYMPTOMATIC PATIENTS WITH MYOCARDIAL BRIDGING - EFFECT OF SHORT-TERM INTRAVENOUS BETA-BLOCKER MEDICATION

Objectives. We sought to define the effects of short term beta-adrener gic blocking medication on intracoronary flow characteristics, clinica l symptoms and angiographic diameter changes in patients with severe m yocardial bridging of the left anterior descending coronary artery. Ba ckground. Controversy exists regarding the pathophysiology, clinical r elevance and optimal therapy in symptomatic patients with myocardial b ridges because antianginal drugs have not been systematically tested. Methods. In 15 symptomatic patients with myocardial bridging of the le ft anterior descending coronary artery, maximal lumen diameter reducti ons were evaluated by quantitative coronary angiography. There were no angiographic signs of coronary artery disease. Coronary blood flow ve locities (using a 0.014-in. [0.035 cm] Doppler guide wire) were measur ed at rest, during atrial pacing and during intravenous administration of a short-acting beta-blocker (esmolol, 50 to 500 mu g/kg body weigh t per min) with continuous atrial pacing. Results. The maximal angiogr aphic systolic lumen diameter reduction within the myocardial bridges was 83 +/- 9% at rest, with a persistent diastolic diameter reduction of 41 +/- 11% (mean +/- SD), Short-term intravenous beta-blocker thera py decreased the diameter reduction during both systole (from 83 +/- 9 % to 62 +/- 11%) and diastole (from 41 +/- 11% to 30 +/- 9%, both p < 0.001). The average diastolic peak how velocity was higher within the myocardial bridges (33 +/- 13 cm/s) than the proximal (26 +/- 13 cm/s) and distal bridges (17 +/- 4 cm/s, both p < 0.001). During tachypacin g, average diastolic peak flow velocity increased within the bridged s egments to 63 +/- 21 cm/s versus 29 +/- 12 cm/s in the proximal and 20 +/- 4 cm/s in the distal bridges (both p < 0.001). Beta-receptor bloc kade produced a return to baseline values (average diastolic peak flow velocity within bridge 35 +/- 16 cm/s, p < 0.001). ST segment changes and symptoms were abolished with beta-blocker administration. Conclus ions. In patients with myocardial bridges, administration of short-act ing beta-blockers during atrial pacing alleviates anginal symptoms and signs of ischemia. This effect was mediated by a reduction of vascula r compression and maximal flow velocities within the bridged coronary artery segment.