Trazodone and imipramine: comparative effects on canine cardiac conduction.

Lead II EKG and His bundle electrograms were recorded in closed-chest pentobarbital-anesthetized dogs. Trazodone, a structurally distinct, new antidepressant agent, had no effect on His--Purkinje (HV interval) or intraventricular (HS interval) conduction following intravenous injection at graded doses between 1 and 30 mg/kg. In contrast, the tricyclic psychotropic agent imipramine (0.5--5 mg/kg) significantly slowed impulse conduction as indicated by increases in both the HV and HS intervals. Imipramine (5 mg/kg) also slowed impulse transmission across the atrium (PA interval). These responses to imipramine were associated with a concurrent prolongation of both the PR interval and QRS duration. In the anesthetized dog, trazodone administration promoted no evidence of heart block or sign of rhythm disturbances other than slowing in normal sinus rhythm.