Twenty-five years in the making: flecainide is safe and effective for the management of atrial fibrillation

Authors, Journal, Affiliations, Type, DOI

• Etienne Aliot; Alessandro Capucci; Harry J. Crijns; Andreas Goette; Juan Tamargo
• Europace. 2011;13:161-173
• CHU Nancy; Universita Politecnica delle Marche Ancona; Maastricht University Medical Center; St. Vincenz Hospital Paderborn; Universidad Complutense Madrid
• Review article
• DOI: https://doi.org/10.1093/europace/euq382
• COI: Funded by Meda Pharmaceuticals (flecainide manufacturer) educational grant. Aliot: consultant fees from Meda, Sanofi-Aventis, Pfizer, BMS. Crijns: research funding and speaker fees from Meda. Goette: speaker fees from 3M Pharmaceuticals. Advocacy framing throughout; conclusions should be weighted accordingly.

Overview

This 2011 Europace review synthesises 25+ years of flecainide evidence in the context of AF management, arguing that CAST-related fears have inappropriately deterred its use in patients without structural heart disease. The review covers class 1C pharmacology including the critical post-repolarization refractoriness mechanism, comparative cardioversion efficacy data, pill-in-the-pocket strategy, long-term SR maintenance, and a re-evaluation of CAST attributing the excess mortality to proarrhythmia in post-MI structural disease rather than a class-wide effect. A notable preclinical finding connects flecainide's RyR2 open-state blockade to prevention of diastolic Ca2+ waves -- the mechanistic basis for its use in CPVT. Industry funding and substantial author COI limit objectivity; data are generally accurate but framing is promotional.

Keywords

Atrial fibrillation; class 1C antiarrhythmic; flecainide; proarrhythmia; sinus rhythm maintenance

Key Takeaways

Pharmacology -- Class 1C Mechanism

• Primary mechanism: Flecainide blocks the fast inward Na+ current (INa) and IKr at IC50 1-2 µmol/L. At higher concentrations (IC50 19 µmol/L), it also inhibits the late Na+ current (INaL) -- notably, INaL is more sensitive than peak INa, meaning flecainide can selectively suppress pathological late Na+ entry at concentrations that have minimal effect on peak INa. This is relevant to its off-label use in LQT3.
• Post-repolarization refractoriness (PRR): The defining pharmacodynamic feature of class 1C drugs. Flecainide has a very slow unbinding time constant from Na+ channels during diastole (t½ >10 s). This means it prolongs refractoriness to a greater extent than APD -- the drug extends the period during which cells cannot be re-excited even after the action potential has terminated. At the atrial level this markedly increases effective refractory period without requiring APD prolongation, which accounts for its efficacy in AF with minimal TdP risk.
• Use- and rate-dependence: Effects are most pronounced at high heart rates (use-dependent blockade), making flecainide especially effective during AF when atrial rate is 300-600 bpm. During sinus rhythm the same doses produce relatively minor atrial effects, which limits preventive efficacy between episodes. The use-dependent property also means the drug is most dangerous at high ventricular rates in structural heart disease (ischaemia/LV dysfunction).
• Atrial APD and refractoriness: In human atria, flecainide only prolongs APD in cells with a long plateau; it consistently produces tachycardia-dependent prolongation of atrial refractoriness across species. In canine AF models, flecainide terminates AF by causing a tachycardia-dependent increase in atrial effective refractory period and wavelength, reducing the number of sustainable re-entrant circuits. An alternative mechanism (goat model): widening of the temporal excitable gap until AF cannot sustain itself.
• Ventricular effects: Flecainide prolongs APD in ventricular muscle fibres but shortens APD in Purkinje fibres (consistent with Na+ channel blockade). Prolongs PR interval 17-29%, QRS complex 11-27%, and QTc only 3-8% (most QT change is from QRS widening, not ventricular repolarization prolongation). The JT interval and ventricular repolarization are relatively unaffected -- accounting for the low TdP risk.

Pharmacology -- Anti-Remodelling Mechanism

• AF-induced rapid Na+ entry → cytosolic Na+ overload → increased Ca2+ entry via Na+/Ca2+ exchanger (NCX) → mitochondrial dysfunction and oxidative stress → structural remodelling (myolysis, glycogen accumulation, fibrosis). Flecainide's INa blockade attenuates Na+ entry during rapid atrial activation, thereby reducing Ca2+ loading and oxidative stress -- a rationale for early treatment to interrupt the 'AF begets AF' cycle.
• Preliminary human organotypic atrial tissue data: flecainide attenuated pacing-induced oxidative stress markers and abolished expression of hypertrophic kinases and inflammatory adhesion molecules.

Pharmacology -- RyR2 Open-State Blockade (CPVT Mechanism)

• Flecainide inhibits cardiac RyR2 Ca2+ release channels by open-state blockade, significantly reducing spark Ca2+ mass without causing compensatory increases in SR Ca2+ content. This prevents diastolic Ca2+ waves that cause triggered arrhythmias (afterdepolarizations). In ventricular myocytes from a CPVT mouse model, flecainide suppressed Ca2+ spark-driven VT. This mechanism is entirely distinct from Na+ channel blockade and explains flecainide's efficacy in CPVT -- a clinically important off-label application.

Pharmacokinetics

• Oral bioavailability 90-95%; no significant first-pass metabolism; dose 200-500 mg/day PO (max 300 mg/day). Half-life 12-27h. Hepatic metabolism via CYP2D6; 85% urinary excretion (inactive metabolites). Sustained-release capsule formulation available (lower peak QRS widening, potentially safer).
• IV dosing: slow injection 1-2 mg/kg over 10 min (max 150 mg); infusion 1.2-1.5 mg/kg/h x 1h then 0.12-0.25 mg/kg/h; maximum cumulative dose 600 mg over 24h.
• Oral loading (pill-in-the-pocket): initiate at 50 mg BID, increase by 50 mg BID every 4 days; first dose in monitored hospital setting; subsequent self-administration after confirmed safety.

Electrophysiological Effects

• Prolongs PA (right atrial), AH (AV nodal), and HV (His-Purkinje) intervals -- slows conduction throughout the heart.
• In dual AV nodal pathways: selectively prolongs retrograde fast-pathway refractoriness.
• In WPW/accessory pathways: slows conduction and increases both anterograde and retrograde refractoriness, with more pronounced effect on retrograde pathway (often causes complete retrograde block when basal refractoriness >270 ms).
• Increases endocardial pacing threshold -- pacemaker-dependent patients may require reprogramming.
• Increases corrected sinus node recovery time in patients with sinus node dysfunction.

Proarrhythmic Effects

• Class 1C flutter (supraventricular proarrhythmia): Flecainide slows AF to atrial flutter at ~200 bpm but does not slow AV conduction -- 1:1 AV conduction can occur, producing a bizarre wide-QRS tachycardia (resembling VT) at high ventricular rates. AV nodal blocking drug must always be co-prescribed. Patients should stop exercise when AF recurs. This proarrhythmia can be useful: catheter ablation of the 1C flutter isthmus (right atrial isthmus) while continuing flecainide reliably controls AF; effective isthmus ablation also eliminates this proarrhythmic risk.
• Ventricular proarrhythmia: Monomorphic sinusoidal wide-QRS VT or polymorphic VT/VF. Risk factors: reduced LV function, ventricular scar tissue, excessive dose, and rapid dose escalation. QRS widening on ECG is the premonitory sign; QRS should be monitored regularly during treatment.
• CAST and late proarrhythmia: CAST (1991) demonstrated increased mortality in post-MI patients with flecainide (encainide and moricizine also affected) -- attributed to proarrhythmia through the interaction of use-dependent Na+ channel blockade with ischaemia, late-onset CHF, and drug accumulation. Late proarrhythmia can occur at any time during therapy -- not only on initiation. Key implication: patients initially well-selected for flecainide who subsequently develop CAD or LV dysfunction are at risk.

Clinical Efficacy -- Cardioversion

• IV flecainide: SR restoration in up to 95% of patients within 1h of infusion start (haemodynamically stable, acute-onset AF <48h, preserved LV function). AHRQ pooled analysis (8 RCTs): conversion rates 52-95%.
• Head-to-head comparison: Single-blind RCT -- IV flecainide 90% vs propafenone 72% vs amiodarone 64% SR achievement (P=0.008).
• Oral loading dose (pill-in-the-pocket): 50-60% conversion at 3h; 75-85% at 6-8h. Suitable only for: recent onset (<48h), normal QRS, preserved LV function, no SA/AV node dysfunction, no bundle branch block, no structural cardiomyopathy, no Brugada syndrome.
• Pre-cardioversion use: IV flecainide pretreatment improves first-shock success rate (65% vs 30% placebo) and reduces internal cardioversion threshold.
• WPW-AF: IV flecainide reduces accessory pathway conduction and ventricular rate, then converts to SR. Effective and safe.

Clinical Efficacy -- SR Maintenance

• Meta-analysis (60 studies): 65% of patients responsive short-term; 49% long-term -- sustained benefit over time.
• Flecainide significantly reduces AF symptoms: more patients in flecainide group reported suppression of palpitations (P<0.001), tachycardia, and chest pain vs placebo; 31% had 'complete freedom from symptoms' vs 9% placebo.

Clinical Safety

• Meta-analysis (122 studies, n=4811 SVA patients, mean exposure 241 days): Ventricular arrhythmias <3%; total mortality 0.166% (annualized: 0.397/100 patient-years). Proarrhythmic episodes lower than controls (2.7% vs 4.8%). Lower rates of angina, hypotension, diarrhoea, headache vs controls.
• Danish registry (n=151,500 first-time AF hospitalisations 1995-2004): No association between antiarrhythmic treatment and increased mortality in appropriately selected patients. Annualized mortality (per 100 person-years): flecainide 2.54, propafenone 4.25, sotalol 5.29, amiodarone 7.42.
• Bradycardia (13.2%) and ventricular extrasystoles (10.6%) most common proarrhythmic events in controlled-release formulation study. AV block 4.0%, SVT 2.2%, BBB 1.8%.

Contraindications and Patient Selection

• Absolute: CAD, prior MI, LVEF <35%, structural heart disease (cardiomyopathy), Brugada syndrome (can unmask Brugada phenotype), 2nd/3rd degree AV block, LBBB, RBBB with left hemiblock, cardiogenic shock, significant renal or hepatic impairment.
• Monitoring required: QRS interval (use-dependent widening); exercise test at initiation; regular ECG; ischaemia screening; pacemaker threshold reprogramming if pacemaker-dependent.
• Appropriate population: Normal heart, hypertension, minor heart disease with good LV function -- estimated 80% of PAF patients and 50% of persistent AF patients.

Limitations of the Document

• Industry-funded by Meda Pharmaceuticals (flecainide manufacturer); Aliot and Crijns receive direct financial relationships with Meda. Promotional framing; conclusions overstate safety relative to balanced evidence.
• 2011 publication -- predates widespread use of catheter ablation as first-line therapy for many AF patients; current guidelines position PVI as Class I/A for paroxysmal AF.
• Head-to-head comparative efficacy (vs propafenone, dronedarone) relies on single small RCTs or indirect comparison tables -- not robust head-to-head evidence.
• CAST reinterpretation (attributing excess mortality solely to proarrhythmia in structural disease) is plausible but not proven; the mechanism remains partly speculative.
• RyR2 open-state blockade data are preclinical (mouse model); human CPVT efficacy evidence not reviewed here.
• Long-term follow-up data largely absent; most efficacy studies short duration.

Key Concepts Mentioned

• concepts/Drug-Induced-Arrhythmia -- class 1C flutter, CAST, proarrhythmia mechanisms
• concepts/Cardiac-Action-Potential -- PRR mechanism, APD vs refractoriness distinction
• concepts/Antiarrhythmic-Drugs -- class 1C classification

Key Entities Mentioned

• entities/Flecainide -- primary subject
• entities/Atrial-Fibrillation -- primary indication; all clinical data
• entities/CPVT -- RyR2 open-state blockade mechanism
• entities/RYR2 -- preclinical open-state blockade data
• entities/Amiodarone -- comparator in head-to-head cardioversion RCT; DIONYSOS comparator context

Wiki Pages Updated

• Created: wiki/sources/flecainide-af-europace-2011
• Created: wiki/entities/Flecainide
• Updated: wiki/entities/Atrial-Fibrillation
• Updated: wiki/entities/CPVT
• Updated: wiki/entities/RYR2