Effects of dobutamine on electrophysiological properties of the specialized conduction system in man

The electrophysiological effects of Dobutamine, a new beta adrenergic drug, were investigated using intracardiac electrograms and the extrastimulus method, in 19 patients with 1:1 AV conduction and in 10 other patients, five with second and five with third degree AV block. The electrophysiological effects were studied at three concentrations of the drug: 5, 10 and 15 micrograms/Kg/m'. Dobutamine induces: 1) an enhancement of SA node automaticity, showed by a decrease of the sinus cycle length (P less than 0.001 at the first concentration) and by a decrease in the corrected sinus node recovery time (P less than 0.001 at the second concentration); 2) a decrease in the effective atrial refractory period (P less than 0.001 at the first concentration); 3) an improvement of AV conduction, showed by a decrease in AH interval (P less than 0.001 at the first concentration) and by a shortening of functional and effective refractory periods (P less than 0.001 at the first concentration); 4) no change in the HV interval; 5) an improvement of conduction in patients with second degree AV block proximal to the His bundle; and 6) a minimal increase in the heart rate in patients with complete AV block distal to His bundle.