What is the recommended surveillance for patients on flecainide (antiarrhythmic medication)?

Surveillance of Flecainide Therapy

Patients on flecainide require baseline ECG assessment followed by regular ECG monitoring focused on QRS duration changes, with dose reduction or discontinuation mandated if QRS widens ≥25% from baseline, along with periodic plasma level monitoring targeting trough levels of 0.2-1.0 mcg/mL. 1, 2

Baseline Assessment Before Initiation

Before starting flecainide, obtain the following:

• 12-lead ECG to measure baseline PR interval, QRS duration, and QT interval—this baseline is critical for calculating the 25% QRS increase threshold 1
• Echocardiogram to exclude structural heart disease and assess left ventricular ejection fraction (flecainide is contraindicated with LVEF <30%) 1
• Serum electrolytes (potassium and magnesium) to ensure normal levels 1
• Baseline liver function tests including SGPT/ALT 1
• Renal function assessment as severe renal impairment requires dose adjustment and more frequent monitoring 2

ECG Monitoring During Therapy

Initial Titration Phase

• Obtain ECG after each dose change and calculate percentage change in QRS duration from baseline 1
• Weekly ECG monitoring is recommended during dose titration or after any dose increase 1
• Monitor PR interval, QRS duration, and QT/QTc interval on each ECG 3, 1

Critical Thresholds Requiring Action

QRS widening ≥25% from baseline is the critical threshold that signals proarrhythmia risk and mandates either dose reduction or drug discontinuation. 1 Additionally:

• QRS duration should not exceed 150% of pretreatment duration 1
• Development of new bundle branch block requires close monitoring and precautions 1
• Stop flecainide immediately if sustained monomorphic ventricular tachycardia develops 1

Expected vs. Dangerous Changes

PR interval prolongation is an expected therapeutic effect of flecainide's sodium channel blockade and does not mandate discontinuation in patients with normal cardiac conduction. 1 Focus monitoring on QRS duration changes, not PR interval changes, as PR prolongation without excessive QRS widening is expected and therapeutic. 1

However, stop flecainide immediately if:

• High-grade AV block develops 1
• Symptomatic bradycardia occurs 1
• New structural heart disease or reduction in LVEF develops 1

Plasma Level Monitoring

• Monitor trough plasma levels periodically (measured less than one hour pre-dose), targeting therapeutic range of 0.2-1.0 mcg/mL 2
• The probability of adverse cardiac events increases with trough levels exceeding 1.0 mcg/mL 2
• Plasma level monitoring is required (not optional) in patients with severe renal failure, severe hepatic disease, or on concurrent amiodarone therapy 2
• Plasma level monitoring is also strongly recommended in patients with CHF and moderate renal disease 2

Ongoing Maintenance Monitoring

• Regular ECG monitoring to assess QRS duration, PR interval, and QT/QTc interval during ongoing maintenance therapy 1
• Heart rate monitoring at approximately weekly intervals, either by pulse check, event recorder, or office ECG tracings 3
• Monitor for atrial flutter with rapid ventricular conduction, particularly ensuring concomitant AV nodal blockade is in place 1

Special Monitoring Situations

Patients with Renal Impairment

• Frequent plasma level monitoring is required in severe renal impairment (creatinine clearance ≤35 mL/min/1.73 m²) 2
• Dosage increases should be made very cautiously when plasma levels have plateaued (after more than four days) 2

Patients on Concurrent Medications

• Monitor digoxin levels when initiating flecainide, as levels typically rise; reduce digoxin dose by 30-50% 3
• Monitor INR closely and reduce warfarin dose by 50% in anticipation of INR increases 3
• When flecainide is given with amiodarone, reduce flecainide dose by 50% and use plasma level monitoring to guide therapy 2

Patients with Pacemakers

• Determine pacing threshold prior to instituting flecainide therapy 2
• Recheck pacing threshold after one week of administration and at regular intervals thereafter, as flecainide increases endocardial pacing thresholds 2

Critical Pitfalls to Avoid

• Failing to obtain baseline ECG makes it impossible to calculate the critical 25% QRS increase threshold and increases proarrhythmic risk 1
• Do not confuse expected PR prolongation with dangerous conduction changes—focus on QRS widening 1
• Avoid outpatient initiation in patients with symptomatic sick sinus syndrome, AV conduction disturbances, or bundle branch block; initial conversion should be undertaken in hospital 3
• For sustained ventricular tachycardia, flecainide should always be initiated in-hospital with rhythm monitoring 2
• Do not increase doses more frequently than every four days, as steady-state plasma levels may not be achieved until 3-5 days of therapy at a given dose 2