Flecainide is a class IC antiarrhythmic agent used for prevention of paroxysmal supraventricular tachycardias (PSVT), paroxysmal atrial fibrillation, and life-threatening ventricular arrhythmias. The CAST trial demonstrated increased mortality in post-MI patients, so use is restricted to patients without structural heart disease.
Second- or third-degree AV block without pacemaker
The bottom line
Evidence rating moderate. Most-documented uses: effective for maintaining sinus rhythm in atrial fibrillation (without structural heart disease), useful for psvt prevention, effective for wpw-related arrhythmias. 10 sources indexed (1995–2024), with 1 interaction record on file.
The science
How it works, mechanistically.
Core mechanism
Potent sodium channel blocker (class IC) that markedly slows conduction velocity throughout the heart. Prolongs His-Purkinje and ventricular conduction (widens QRS). Has minimal effect on action potential duration and repolarization. Slows conduction in accessory pathways, making it useful for WPW-related arrhythmias. Also has minor potassium channel blocking effects.
Class
Class IC Antiarrhythmic
Dosing
Dosing & protocol.
Common range
PSVT/PAF: 50–150 mg twice daily; Sustained VT: 100–200 mg twice daily (as prescribed by your physician)
Recommended form
Oral tablet
Can be taken with or without food; well absorbed orally with ~95% bioavailability
Safety
Full safety detail.
Side effects
Dizziness and visual disturbances (blurred vision)
Pro-arrhythmia (ventricular tachycardia, including 1:1 atrial flutter)
Flecainide has a narrow cardiac safety margin and can cause serious proarrhythmia in susceptible patients. Low potassium is a recognized risk factor for torsades de pointes and can worsen arrhythmia vulnerability when antiarrhythmic drugs are involved. Potassium supplementation is only appropriate for documented or likely deficiency and should be monitored.
Recommendation: Keep potassium in the normal range while taking flecainide, especially if you use diuretics or have vomiting, diarrhea, or poor intake. Do not start high-dose potassium unless your clinician is checking potassium, kidney function, and ECG status. Seek urgent care for fainting, severe dizziness, wide-complex palpitations, or chest pain.
Valentino MA, Panakos A, Ragupathi L et al.. Flecainide Toxicity: A Case Report and Systematic Review of its Electrocardiographic Patterns and Management. Cardiovascular toxicology. 2017
Zarembski DG, Nolan PE Jr, Slack MK et al.. Treatment of resistant atrial fibrillation. A meta-analysis comparing amiodarone and flecainide. Archives of internal medicine. 1995
Hauguel-Moreau M, Guedeney P, Dauphin C et al.. Flecainide to Prevent Atrial Arrhythmia After Patent Foramen Ovale Closure: AFLOAT Study, A Randomized Clinical Trial. Circulation. 2024
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