Introduction Flecainide is a class 1C antiarrhythmic primarily usedfor the management of supraventricular arrhythmias. Adverse effects in patientswith pacemakers are poorly described in the current literature. We report acase of worsening intracardiac conduction in a patient with baseline atriallatency. Case A patient with paroxysmalatrial fibrillation and recently implanted dual chamber pacemaker withresultant atrial latency underwent flecainide treatment resulting in worseningatrial latency, progressive dyspnea, and pacemaker syndrome physiology. The patientexperienced symptomatic improvement with pacemaker reprogramming to AAI andreduced flecainide dosages. Conclusion Prudence should be exercised when initiating flecainide therapy, particularly in pacemaker‐dependentpatients, who may be at risk for increasedthresholds, inconsistent capture, and latency. In the setting of apparentcapture latency, changing to AAI mode may both confirm the diagnosis andprovide a symptomatic benefit.

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