Electrophysiological effects of intravenous clonidine on sinus node function and conduction in man.

We studied the electrophysiological effects of clonidine in 10 patients (mean age, 69 years) without sinus dysfunction or atrioventricular block. An endocavitary study was performed with two multipolar catheters, one to record and stimulate the right atrium, the other to record the His bundle potential. The stimulations were delivered by an orthorhythmic stimulator. Clonidine, 150 micrograms, was injected intravenously over 10 min. The usual electrophysiological parameters for studying atrioventricular conduction and sinus function were measured under basal conditions, between the 10th and 25th min, and between the 25th and 40th min following the onset of the injection of clonidine. Sinus cycle length, maximum corrected sinus node recovery time, estimated atrio-sinoatrial conduction time, and premature atrial stimulation-response curve were not influenced by clonidine. There were also no changes in conduction interval, anterograde conduction point, effective refractory period of the atrioventricular node, and intraventricular conduction time. We conclude that intravenous clonidine does not change the electrophysiological parameters in man.