Influence of Propranolol on the Ventricular Depolarization Gradient

Abstract

Sensing of the ventricular depolarization gradient (VDG) has recently been used as the basis of a closed-loop rate responsive pacemaker. Factors influencing this aspect of the evoked response have not been fully evaluated although previous reports have suggested that sympathetic stimulation and circulating catecholamines are primarily responsible for the observed changes during stress and exercise. In five patients (Table I), four males and one female (mean age 60.4 +/- 10.1 years) implanted with the Prism pacemaker, the pacing response to exercise and tilting was assessed before and after the infusion of propranolol. There was an increase in the pacing rate in all patients during the infusion of the drug (mean 27 +/- 12.9 beats/min) suggestive of a direct drug effect on the VDG. The rate control parameter (RCP) of the pacemaker, the numerical equivalent of the VDG, was significantly different after the administration of propranolol (P less than 0.01). However, exercise performance and pacing rate behavior were not different after beta blockade. The pacing rate increase observed when tilting patients to the supine position was not altered by propranolol. Out date suggest that factors other than adrenergic stimulation may be of importance in affecting the ventricular evoked response and accordingly the rate adaptation of the Prism pacemaker.