Three cases of sinoatrial block induced by anticonvulsants

Diphenylhydantoin (DPH) and Carbamazepine have been widely used as anticonvulsants and known to have antiarrhythmic properties. Previous reports have shown that arrhythmias such as sinus bradycardia and atrioventricular block can be induced by these agents. In this paper, sinoatrial block (SA block) induced by these agents which were used as anticonvulsants in 3 aged patients is reported. Thre patients, 2 women and 1 man, were over 60 years old. In 2 cases, administration of DPH for recurrent epileptic seizures was followed by SA block. After withdrawal of DPH, SA block disappeared, but resumption of DPH resulted in SA block again. In 1 of these 2 patients, overdrive suppression test revealed normal sinus node recovery time. In the third patient, in addition to DPH which was administered for epileptic seizures, Carbamazepine was given for shoulder pain, then SA block occurred. Withdrawal of these agents restored normal sinus rhythm and combined administration of these 2 agents again induced SA block. Autopsy revealed decreased conduction cells in the sinus node.