Amiodarone-Associated Bradycardia

Mechanism and Incidence

Amiodarone causes bradycardia through multiple electrophysiologic mechanisms, including depression of AV nodal conduction via calcium channel and beta-receptor blockade, and suppression of sinus node automaticity through sympatholytic effects, resulting in consistent heart rate reduction both at rest and during exercise 1
The bradycardia risk exists regardless of the dose administered 1

Patients with pre-existing conduction disorders, such as first-degree AV block, right or left bundle branch block, and pre-existing sinus node dysfunction, face substantially elevated risk of symptomatic bradycardia 1

Amiodarone-associated bradycardia requiring permanent pacemaker implantation is more common in women than in men 2

Before initiating amiodarone, assess for absolute contraindications, including bradycardia without pacemaker in place, second- or third-degree heart block without pacemaker, and significant conduction system disease 1
Evaluate baseline heart rate and conduction, and use extreme caution if heart rate is 57 bpm or lower, as amiodarone is relatively contraindicated unless a pacemaker is present or the situation is immediately life-threatening with no safer alternatives 1
During IV administration, continuous ECG monitoring is mandatory for heart rate, AV conduction abnormalities, and QT prolongation 1
During oral therapy, monitor heart rate weekly initially, and reduce doses of concomitant rate-control agents approximately 6 weeks after starting amiodarone 1, 2

Concomitant medications that slow AV conduction, such as beta-blockers, calcium channel blockers, and digoxin, create additive effects and increase the risk of bradycardia 1