Flecainide Toxicity in a Patient with a Functioning Pacemaker

Flecainide is a class Ic anti-arrhythmic that demonstrates use dependence, meaning the medication has an increased effect on the myocardium at high heart rates. Flecainide toxicity can be identified by wide QRS complexes on an electrocardiogram (ECG). We discuss a case of a 75-year-old patient with a pacemaker who presented with concern for flecainide toxicity. The patient had several risk factors known to increase the likelihood for toxicity, including structural heart disease and acute kidney injury. The initial ECG showed tachycardia with wide QRS complexes. The patient had a pacemaker set in a tracking mode (DDD) that resulted in rapid ventricular pacing with failure to mode switch. However, with modification to the VVI mode, the patient experienced tachycardia resolution with an improvement in QRS complexes. This case emphasizes the use dependence of flecainide and illustrates the utility of pacing mode in the management of flecainide toxicity in patients with pacemakers.