Therapeutic-Dose Flecainide-Induced Bradycardia and Syncope in a Structurally Normal Heart: A Contemporary Case Report

Background: Flecainide is a class Ic antiarrhythmic and is commonly used in rhythm control in patients with AF without structural heart disease. It is usually well tolerated when used properly, but may cause major conduction anomalies, including rare incidences of bradyarrhythmia. Case Presentation: The case of a 37-year-old man without a history of previous cardiac events was reported, who presented with dyspnoea and palpitations. Primary assessment indicated narrow- complex tachycardia with a PR interval longer than the RP interval. After the trial of intravenous metoprolol without success in managing the rate, AF was diagnosed, and flecainide 200mg/day was started. In two weeks, the patient experienced frequent syncope without premonitory symptoms. Even the primary follow-up ECG showed a prolonged QT interval and a slowed ventricular rate. Echocardiography revealed normal LV function and LA enlargement; coronary angiography did not reveal any obstructive disease. Flecainide was discontinued, and the rhythm changed to persistent AF with no additional syncope during 6 months of follow-up. Conclusion: The current case involves a rare case of therapeutic-dose flecainide-induced bradycardia and syncope in a normal heart structure. It highlights the need to monitor early postinitiation ECGs and be attentive to changes in conduct, even in low-risk patients, before they become life-threatening complications.