flecainide toxicity acmt ecg

What agent would most likely be responsible for these ECG findings?

  1. Cyclobenzaprine
  2. Digoxin
  3. Flecainide
  4. Sotalol

3. Flecainide

Background [1-3]

Flecainide is a class IC antiarrhythmic that binds to the voltage-gated sodium channel of the myocardium, slowing depolarization and prolonging phase 0 of the action potential.  In toxicity, bradydysrhythmias, AV nodal blockade, ventricular tachycardia, and rate-dependent QRS widening occur.  This EKG shows a wide complex (QRS 240 msec), irregular rhythm with left bundle branch block morphology at a rate slower than expected (90 bpm) for a ventricular arrhythmia such as ventricular tachycardia.

How do you treat flecainide toxicity? [4-8]

  • The treatment of choice for toxicity from cardiac sodium channel blocking agents such as flecainide is sodium bicarbonate which competes for the cardiac sodium channel and leads to dissociation of the xenobiotic from the binding site.
  • Hypertonic saline has also been used for sodium channel-blocking agent toxicity.
  • Other therapies to consider in severe toxicity are lipid emulsion and extracorporeal membrane oxygenation (ECMO)
  • Flecainide is not effectively cleared by hemodialysis.

Here is the patient’s EKG after administration of a 300 mEq sodium bicarbonate showing significant improvement of the cardiac sodium channel blockade as evidenced by a narrower QRS complex.

Response to bicarb

What are other agents that block cardiac socium channels? [1]

  • Tricyclic antidepressants
  • Other Class 1 antiarrhythmics such as Lidocaine, Quinidine, Procainamide, Propafenone
  • Cocaine
  • Diphenhydramine
  • Venlafaxine
  • Propranolol
  • Chloroquine/hydroxychloroquine

Clinical Pearls

  • Flecainide causes cardiac sodium channel blockade and prolongs the QRS interval and toxicity can lead to ventricular arrhythmia.
  • The treatment of choice for toxicity due to cardiac sodium channel-blocking agents is sodium bicarbonate.
  • Other therapies to consider in severe toxicity include lipid emulsion and ECMO.


  1. Kolecki PF, Curry SC. Poisoning by sodium channel blocking agents. Crit Care Clin. 1997 Oct;13(4):829-48. PMID: 9330843.
  2. Valentino MA, Panakos A, Ragupathi L, Williams J, Pavri BB. Flecainide Toxicity: A Case Report and Systematic Review of its Electrocardiographic Patterns and Management. Cardiovasc Toxicol. 2017 Jul;17(3):260-266. PMID: 27435408.
  3. Wilgenhof A, Michiels V, Cosyns B. An irregular, extremely broad QRS complex rhythm. Am J Emerg Med. 2019 Oct;37(10):1989.e1-1989.e3. doi: 10.1016/j.ajem.2019.158356. Epub 2019 Jul 21. PMID: 31362853.
  4. McCabe DJ, Walsh RD, Georgakakos PK, Radke JB, Wilson BZ. Flecainide poisoning and prolongation of elimination due to alkalinization. Am J Emerg Med. 2022 Jun;56:394.e1-394.e4. doi: 10.1016/j.ajem.2022.03.006. Epub 2022 Mar 9. PMID: 35287973.
  5. Devin R, Devin R, Garrett P, Anstey C. Managing cardiovascular collapse in severe flecainide overdose without recourse to extracorporeal therapy. Emerg Med Australas. 2007 Apr;19(2):155-9. doi: 10.1111/j.1742-6723.2006.00909.x. PMID: 17448102.
  6. Sivalingam SK, Gadiraju VT, Hariharan MV, Atreya AR, Flack JE, Aziz H. Flecainide toxicity–treatment with intravenous fat emulsion and extra corporeal life support. Acute Card Care. 2013 Dec;15(4):90-2. doi: 10.3109/17482941.2013.841949. Epub 2013 Nov 7. PMID: 24200150.
  7. Bruccoleri RE, Burns MM. A Literature Review of the Use of Sodium Bicarbonate for the Treatment of QRS Widening. J Med Toxicol. 2016 Mar;12(1):121-9. doi: 10.1007/s13181-015-0483-y. PMID: 26159649; PMCID: PMC4781799.
  8. Reynolds JC, Judge BS. Successful treatment of flecainide-induced cardiac arrest with extracorporeal membrane oxygenation in the ED. Am J Emerg Med. 2015 Oct;33(10):1542.e1-2. PMID: 26299692.
Timothy Harmon, MD

Timothy Harmon, MD

Emergency Medicine Resident
Inova Fairfax Medical Campus, George Washington University
Timothy Harmon, MD

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Alexander Sidlak, MD

Alexander Sidlak, MD

Clinical Assistant Professor of Emergency Medicine
Emergency Medicine and Medical Toxicology Faculty
Inova Fairfax Medical Campus, George Washington University
Alexander Sidlak, MD

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Meagan Singletary, PharmD

Meagan Singletary, PharmD

Clinical Pharmacist
Inova Fairfax Medical Campus
Meagan Singletary, PharmD

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