Can flecainide (Flecainide) cause bradycardia (abnormally slow heart rate)?

From the Guidelines

Flecainide can cause bradycardia, and patients taking this medication should be closely monitored for signs of decreased heart rate, especially those with pre-existing conduction abnormalities or sinus node dysfunction. Flecainide is a Class IC antiarrhythmic medication primarily used to treat certain types of abnormal heart rhythms, but it can slow heart rate as a side effect due to its sodium channel blocking properties, which affect the heart's electrical system 1. This sodium channel blockade can lead to decreased heart rate, especially in patients with underlying conduction disorders or when used at higher doses. The risk of bradycardia is higher in patients with underlying sinus node dysfunction, conduction disorders, or those taking other medications that slow heart rate, such as beta blockers or nondihydropyridine calcium channel antagonists 1.

Some key points to consider when prescribing flecainide include:

• Starting with lower doses and adjusting based on patient response and monitoring
• Measuring the PR interval, QRS duration, and QT interval as necessary when initiating flecainide therapy
• Monitoring patients for signs of bradycardia, which may include dizziness, fatigue, weakness, or syncope
• Being aware of the potential for flecainide to cause bradycardia requiring permanent pacemaker implantation, although this is more frequent with amiodarone 1
• Considering the use of transtelephonic monitoring or other methods of ECG surveillance to monitor cardiac rhythm and conduction as pharmacological antiarrhythmic therapy is initiated in patients with AF.

Overall, while flecainide can be an effective medication for treating certain types of abnormal heart rhythms, its potential to cause bradycardia must be carefully considered and monitored to minimize the risk of adverse effects.

From the FDA Drug Label

Clinically significant conduction changes have been observed at these rates: sinus node dysfunction such as sinus pause, sinus arrest and symptomatic bradycardia (1.2%), second-degree AV block (0.5%) and third-degree AV block (0. 4%). Flecainide acetate should be used only with extreme caution in patients with sick sinus syndrome because it may cause sinus bradycardia, sinus pause, or sinus arrest. Flecainide does not usually alter heart rate, although bradycardia and tachycardia have been reported occasionally.

Flecainide can cause bradycardia, as evidenced by the occurrence of symptomatic bradycardia, sinus bradycardia, and sinus pause or arrest in some patients. The incidence of symptomatic bradycardia is reported to be 1.2% 2. Therefore, caution should be exercised when using flecainide, especially in patients with preexisting conduction abnormalities or sick sinus syndrome.

From the Research

Flecainide and Bradycardia

• Flecainide has been associated with bradycardia in several studies, including a case report of a patient who experienced recurrent syncope due to bradycardia-dependent torsade de pointes (TdP) associated with flecainide-related bradycardia and QT prolongation 3.
• Another study reported a case of flecainide toxicity resulting in pacemaker latency and intermittent failure to capture, with the patient presenting with bradycardia and a heart rate between 30 to 40 beats per minute 4.
• Flecainide may depress sinus node activity in patients with pre-existing sinus node disease, which can lead to bradycardia 5.
• The use of flecainide has been curtailed due to concerns about ventricular proarrhythmia, but it has been shown to be safe and well-tolerated in patients without structural heart disease, with bradycardia being a potential side effect 6, 7.

Mechanism of Flecainide-Induced Bradycardia

• Flecainide can cause bradycardia-dependent TdP with QT prolongation, which can be considered one of the mechanisms of flecainide-induced proarrhythmia 3.
• The drug can also increase the ventricular capture threshold for pacemakers, leading to pacemaker ventricular capture latency or failure to capture, which can result in bradycardia 4.
• Flecainide's effects on the sinus node and the specialized conduction system can also contribute to the development of bradycardia 5.