Flecainide Safety, Contraindications, and Monitoring Guidelines

Tolerability and Common Non‑Cardiac Side Effects

In patients without structural heart disease, flecainide is generally well‑tolerated; dizziness occurs in ~15‑20% and visual disturbances in ~15% of such patients, while most adverse effects are mild, transient, and appear during dose up‑titration. 1
Most patients who develop these non‑cardiac symptoms can remain on therapy after dose adjustment. [1][2]

The CAST randomized trial demonstrated that flecainide increased total mortality and the risk of non‑fatal cardiac arrest and arrhythmic death in post‑myocardial‑infarction patients. [1][2]3
Proarrhythmia associated with flecainide most often presents as monomorphic ventricular tachycardia (not torsades de pointes). [1][2]3
When therapy is started at 200 mg/day with slow upward titration, 13 % of patients develop new or worsened ventricular arrhythmias. 4
Flecainide possesses potent negative inotropic activity and can exacerbate heart failure in patients with coronary artery disease or pre‑existing heart failure (NYHA class II‑IV or LVEF < 30 %). [1][2]3
Intravenous administration may cause hypotension due to vasodilation, and the same risks of ventricular proarrhythmia and heart‑failure worsening persist. [1][2]3

Flecainide can convert atrial fibrillation to atrial flutter; concomitant AV‑nodal blockade (beta‑blocker or non‑dihydropyridine calcium‑channel blocker) is recommended to prevent rapid 1:1 AV conduction. [4][5]
An increase in QRS duration >25 % from baseline signals heightened proarrhythmic risk and warrants dose reduction or drug discontinuation. [4][5]
Regular ECG monitoring is mandatory at initiation and with each dose increase to detect QRS widening. [4][5]

History of coronary artery disease or prior myocardial infarction. [4][1][2][5]
Reduced left‑ventricular ejection fraction (< 40 %). [4][1][2][5]
Established heart failure (NYHA class II‑IV). [1][2]3
Any structural heart disease (including ventricular scar tissue or left‑ventricular dysfunction). [4][1][2][5]
Baseline ventricular conduction delay (QRS > 120 ms) or left bundle‑branch block. [1][2]3 and [4][5] respectively.
Severe renal impairment (creatinine clearance < 35 mL/min) without appropriate dose adjustment. 6

Obtain a baseline 12‑lead ECG before starting flecainide. [4][5]6
Perform ECG after initiation and after each dose increase; discontinue or reduce dose if QRS widens >25 % from baseline. [4][5]6
In patients > 50 years or with atherosclerotic risk factors, consider formal ischemia assessment (e.g., stress testing) before therapy. 6
Monitor renal function regularly to guide dose adjustments in patients with impaired clearance. 6
Co‑prescribe an AV‑nodal blocking agent to mitigate rapid ventricular response if atrial flutter emerges. [4][5]6

Presence of structural heart disease markedly raises the likelihood of life‑threatening flecainide toxicity. [1][2]3
Underlying ventricular scar tissue further increases risk. [1][2]3
Left‑ventricular dysfunction (reduced ejection fraction) is an additional major risk factor. [1][2]3