EFFECTS OF BETA-BLOCKADE AND ATROPINE ON ISCHEMIC RESPONSES IN LEFT-VENTRICULAR REGIONS SUBTENDING CORONARY STENOSIS DURING DOBUTAMINE STRESS ECHOCARDIOGRAPHY

Objectives. This study was designed to examine the effects of a beta-a drenergic blocking agent on the ischemic response to dobutamine stress and to determine the degree to which these effects can be abolished b y the addition of atropine, Background. Whether beta-blockade affects the sensitivity of dobutamine stress echocardiography for the diagnosi s of coronary artery disease has been controversial. Methods. In nine pigs, a left anterior descending coronary artery stenosis was created to reduce flow reserve (maximal/rest howl to 1.1 to 1.9 without baseli ne regional wall motion abnormalities, This corresponded to a 50% to 9 0% diameter stenosis. Wall thickening was measured using epicardial ec hocardiography. Regional lactate production and coronary venous pH wer e monitored from an adjacent cardiac vein. A standard protocol of dobu tamine stress echocardiography was first performed. After normalizatio n of the ischemic abnormalities elicited with this infusion, esmolol w as infused at 50 mu g/kg body weight per min and the dobutamine test H as repeated, with 1.0 mg of atropine added at the maximal dobutamine d ose. Results. Without esmolol, dobutamine stress induced myocardial is chemia with a reduction in regional wall thickening and lactate produc tion in all nine pigs, Multiple regression analysis revealed that coro nary how per heartbeat (p < 0.01) and lactate production (p < 0.05) in dependently correlated with regional wall thickening during dobutamine stress, The beta-blocker significantly reduced heart rate and regiona l oxygen consumption and altered the relation between coronary flow pe r heartbeat and regional wall thickening (p < 0.05) during dobutamine stress. Esmolol prevented dobutamine-induced ischemia (lactate product ion and wall motion abnormalities) in seven of nine pigs, The addition of atropine induced lactate production and a reduction in wall thicke ning in five of seven pigs in which ischemia had been prevented by bet a-blockade. However, lactate production Has higher and regional venous pH was lower with the baseline dobutamine infusion than with that per formed after esmolol with atropine added at the maximal dobutamine dos e (p < 0.05). Conclusions. A correlation between regional wall thicken ing and coronary how per heartbeat Has demonstrated during baseline do butamine stress, Beta-blockade shifted this relation so that dobutamin e stress-induced myocardial ischemia was attenuated The mechanisms by which beta-blockade prevents dobutamine-induced ischemia appeared to b e mainly through decreases in heart rate and rate of rise in left vent ricular pressure, improvement of regional coronary flow per heartbeat and attenuation of regional ischemic lactate production. Adding atropi ne in conventional doses enhanced the ability of dobutamine stress to induce myocardial ischemia but did not completely abolish the effects of beta-blockade on either the severity of dobutamine induced wall thi ckening abnormalities or regional metabolic disturbances. (C) 1996 by the American College of Cardiology