Symptomatic Bradycardia, Syncope, and Prolonged QTc Interval Associated with Dronedarone Therapy

Abstract

Objective To report a case of symptomatic bradycardia, prolonged QT interval, and syncope associated with dronedarone in a patient with atrial fibrillation who was maintained in sinus rhythm. Case Summary A 58-year-old man presented to the emergency department with a chief complaint of chest pain and “passing out.” Three months prior, dronedarone had been initiated for maintenance of sinus rhythm. An initial electrocardiogram (ECG) revealed normal sinus rhythm with a prolonged corrected QT (QTc) interval of 645 ms. Upon hospital admission, dronedarone was discontinued. Approximately 17 hours after hospitalization and 35 hours after the last ingested dronedarone dose, a repeat ECG revealed a QTc interval of 457 ms, and the patient reported symptomatic improvement. The patient was discharged home after a 3-day hospital stay without further event. The Naranjo Adverse Drug Reaction Probability Scale indicated a probable relationship between the patient's symptoms and dronedarone. Discussion Dronedarone is an antiarrhythmic drug that exhibits multiple mechanisms of action, including potassium, sodium, and calcium channel blockade, in addition to antiadrenegic activity. In clinical evaluations of dronedarone therapy, dronedarone was associated with a mean decrease in resting heart rate and potential to prolong the QT interval by 10 ms. These effects may result in clinically significant outcomes, as was observed in this patient. Conclusions This case of symptomatic bradycardia and prolonged QTc interval emphasizes the importance of monitoring the heart rate and ECG in patients prescribed dronedarone, particularly in those on concomitant drug therapy that may precipitate these events.