A 2:1 atrioventricular block developed during treatment with the tricyclic antidepressant imipramine in a 74-year-old man with a three-year history of right bundle-branch block. Serial cardiographic studies and determinations of blood imipramine concentrations showed that the heart block was directly related to the plasma concentration of the drug and occurred below the atrioventricular node in the His-Purkinje system.
(JAMA 231:1364-1366, 1975)
Kantor SJ, Bigger JT, Glassman AH, Macken DL, Perel JM. Imipramine-Induced Heart Block A Longitudinal Case Study. JAMA. 1975;231(13):1364–1366. doi:10.1001/jama.1975.03240250034022