Regional effects of propranolol on intraventricular conduction in coronary artery disease

In canines, propranolol slows conduction in acutely ischemic, but not in normal tissues. To determine propranolol effects on conduction in patients with coronary artery disease, we studied 7 patients after left anterior descending coronary artery bypass graft surgery. Bipolar electrodes were placed in the atrium, left ventricle (in the left anterior descending distribution), and right ventricle. On postoperative day 7, 3 mg propranolol were given intravenously. At a constant atrially paced rate, conduction intervals were measured from the earliest onset of the QRS in 3 simultaneously recorded surface electrocardiogram (ECG) leads to the major deflection of the electrogram recorded from each ventricle. Ten minutes after injection, conduction in the left ventricle was slowed by 4 ± 0.3 msec (10 ± 0.9%) and in the right ventricle by 0.4 ± 0.3 msec (1 ± 0.9%). QRS duration changed -1 msec (-0.8%). Stimulus to Q, a measure of propranol effect on A-V conduction, changed 16 ± 2%. The difference in propranolol effects on left and right ventricles was significant (p < 0.001). We suggest that in patients with coronary artery disease (1) propranolol has local anesthetic effects in slowing conduction; (2) the effects of propranolol vary with the region of ventricular myocardium; and (3) propranolol slows conduction more in the left than right ventricle. This difference may be due to potentiation of drug effects in left ventricular tissue that is abnormal due to chronic coronary artery disease.