Electrocardiographic abnormalities in patients with cluster headache on verapamil therapy

Background: High dose verapamil is an increasingly common preventive treatment in cluster headache (CH). Side effects include atrioventricular block and bradycardia, although their incidence in this population is not clear. Method: This audit study assessed the incidence of arrhythmias on high dose verapamil in patients with cluster headache. Results: Of three hundred sixty-nine patients with cluster headache, 217 outpatients (175 men) received verapamil, starting at 240 mg daily and increasing by 80 mg every 2 weeks with a check electrocardiogram (EKG), until the CH was suppressed, side effects intervened, or to a maximum daily dose of 960 mg. One patient had 1,200 mg/day. Eighty-nine patients (41%) had no EKGs. One hundred eight had EKGs in the hospital notes, and a further 20 had EKGs done elsewhere. Twenty-one of 108 patients (19%) had arrhythmias. Thirteen (12%) had first-degree heart block (PR > 0.2 s), at 240 to 960 mg/day, with one requiring a permanent pacemaker. Four patients had junctional rhythm, and one had second-degree heart block. Four patients had right bundle branch block. There was bradycardia (HR < 60 bpm) in 39 patients (36%), but verapamil was stopped in only 4 patients. In eight patients the PR interval was lengthened, but not to > 0.2 s. The incidence of arrhythmias on verapamil in this patient group is 19%, and bradycardia 36%. Conclusion: We therefore strongly recommend EKG monitoring in all patients with cluster headache on verapamil, to observe for the potential development of atrioventricular block and symptomatic bradycardia.