Can flecainide cause bradycardia?

Flecainide and Bradycardia

Yes, flecainide can cause bradycardia as a known adverse effect, particularly sinus bradycardia and various degrees of atrioventricular block. 1, 2

Mechanism and Cardiac Conduction Effects

• Flecainide is a class IC antiarrhythmic drug that primarily blocks sodium channels, affecting cardiac conduction by prolonging PR, QRS, and QT intervals 2
• It slows cardiac conduction in most patients, with PR interval increases averaging about 25% (0.04 seconds) and up to 118% in some patients 2
• Approximately one-third of patients may develop new first-degree AV heart block (PR interval ≥ 0.2 seconds) 2
• QRS complex duration typically increases about 25% (0.02 seconds) and up to 150% in some patients 2

Specific Bradyarrhythmias Associated with Flecainide

• Clinically significant conduction changes observed with flecainide include:
  • Sinus node dysfunction such as sinus pause, sinus arrest, and symptomatic bradycardia (1.2% of patients) 2
  • Second-degree AV block (0.5% of patients) 2
  • Third-degree AV block (0.4% of patients) 2
• Flecainide can also suppress ventricular escape rhythms, potentially worsening bradycardia 2

Risk Factors for Flecainide-Induced Bradycardia

• Pre-existing sinus node dysfunction or sick sinus syndrome significantly increases risk 1, 2
• Underlying AV conduction disturbances increase susceptibility to bradyarrhythmias 1, 2
• Concomitant use of other medications that affect cardiac conduction (beta-blockers, calcium channel blockers) 1
• Electrolyte disturbances, particularly hypokalemia or hyperkalemia, may enhance bradycardic effects 2
• Higher flecainide doses correlate with increased risk of bradyarrhythmias 3

Clinical Implications and Management

• Flecainide should be used with extreme caution in patients with sick sinus syndrome as it may cause sinus bradycardia, sinus pause, or sinus arrest 2
• Patients with permanent pacemakers require careful monitoring as flecainide increases endocardial pacing thresholds 2
• ECG monitoring is essential when initiating flecainide, with particular attention to PR and QRS intervals 4
• If second- or third-degree AV block or right bundle branch block with left hemiblock occurs, flecainide therapy should be discontinued unless a temporary or implanted ventricular pacemaker is in place 2
• Attempt to manage patients on the lowest effective dose to minimize conduction abnormalities 2

Special Considerations

• Bradyarrhythmias may be more pronounced immediately after conversion from atrial fibrillation to sinus rhythm 5
• In overdose situations, severe bradycardia and various degrees of AV block can occur and may be life-threatening 6, 7
• Patients with structural heart disease are at higher risk for bradyarrhythmias and other adverse effects 1, 2
• Flecainide is contraindicated in patients with sinus node dysfunction unless a pacemaker is present 1, 2

Monitoring Recommendations

• Baseline ECG should be obtained prior to initiating flecainide 4
• Regular ECG monitoring during treatment is recommended, with particular attention to PR and QRS intervals 4
• When feasible, monitor plasma flecainide levels, attempting to keep trough levels below 0.7 to 1.0 mcg/mL 2
• Electrolyte levels should be monitored and maintained within normal ranges 2

In conclusion, bradycardia is a well-documented adverse effect of flecainide that requires careful patient selection, appropriate monitoring, and dose adjustment to minimize risk.