Abstract 15242: The Flipside of Flecainide: A Case of Flecainide Induced Loss of Capture

Abstract

Introduction: Flecainide is a class 1c anti-arrhythmic agent that slows phase 0 of the fast inward sodium (Na) channels in a rate-dependent fashion leading to decreased conduction velocity in the His-Purkinje and ventricular myocardium. Its high affinity and slow unbinding prolong QRS duration on electrocardiogram (EKG). Partial renal excretion and a narrow therapeutic index of 0.2-1mcg/mL can cause drug toxicity. Case: A 72-year-old woman presented with palpitations and weakness. She had a history of non-ischemic cardiomyopathy, biventricular (BiV) implantable cardioverter defibrillator, frequent premature ventricular contractions on flecainide 100 mg twice a day, and chronic kidney disease. She was hypotensive and with acute kidney injury. EKG showed wide complex ventricular rhythm, QRS duration of 305 ms and intermittent ventricular pacing (Fig.1A), changed since EKG 6 months ago (Fig.1B). Device interrogation revealed normal sensing and impedances but failure to capture from all 3 leads. She had stable lead parameters and appropriate BiV pacing 6 months ago. Chest X ray showed stable lead positions. Flecainide toxicity was suspected, and Na bicarbonate infusion was started. Flecainide level was 2.4mcg/mL (normal <1mcg/mL). She went into an idioventricular rhythm which terminated spontaneously (Fig.1C). After 48 hours of Na bicarbonate infusion, lead capture was noted with narrower QRS (198 ms) (Fig.1D) and on day 6, EKG was back to effective BiV pacing with QRS duration 127 ms (Fig.1E). Discussion: This case highlights the EKG manifestations of flecainide toxicity including QRS widening, sine-wave pattern and loss of pacing capture due to prolonged ventricular refractoriness. It also underscores the reversibility of this condition with prompt treatment using Na bicarbonate. Conclusion: Early recognition and rapid treatment of the cardiac effects of flecainide toxicity is critical in managing a life threatening but reversible medical condition.