Sinus arrest associated with clonidine therapy.

A 65-year-old male with diabetes, hypertension, and mild renal failure developed dizziness and syncope one week after starting clonidine 0.45 mg/day. A continuous ECG recording revealed sinus bradycardia, nodal rhythm, and multiple episodes of sinus arrest lasting up to 4.5 seconds. Upon discontinuation of clonidine, serial continuous ECG recordings revealed gradual decrease in the number and duration of the sinus arrest episodes, until their complete disappearance shortly after the third day off clonidine. This report shows that clonidine may cause a concentration-dependent sinus node dysfunction in addition to the atrioventricular (AV) node abnormalities previously ascribed to it.