Sinoatrial and atrioventricular dysfunction associated with the use of guanabenz acetate

Guanabenz acetate is an antihypertensive drug that is closely related to clonidine hydrochloride. Clonidine is well known to potentiate atrioventricular (AV) node conduction disturbances, but to date that effect has not been attributed to guanabenz. A case of electrocardiographic and electrophysiologic studies in a patient with both sinus and AV node conduction disturbances associated with the use of guanabenz acetate is reported. The sinus cycle length was increased by 50% after guanabenz and the sinus node recovery time was prolonged by 42%. AV block occurred proximal to the His bundle and His-ventricular prolongation of 42% also occurred. This drug should be used cautiously in patients with evidence of sinus or AV node dysfunction.