Can amiodarone (antiarrhythmic medication) cause bradycardia (abnormally slow heart rate) in patients, particularly those with pre-existing cardiac conditions or taking other medications that slow the heart rate?

Can Amiodarone Cause Bradycardia?

Yes, amiodarone definitively causes bradycardia—this occurs in 4.9% of patients receiving IV amiodarone and is a well-established adverse effect of both intravenous and oral formulations. 1

Mechanism and Incidence

Amiodarone causes bradycardia through multiple electrophysiologic mechanisms:

• Depression of AV nodal conduction via calcium channel and beta-receptor blockade 2
• Suppression of sinus node automaticity through sympatholytic effects, resulting in consistent heart rate reduction both at rest and during exercise 2
• The bradycardia risk exists regardless of the dose administered 2

Risk Stratification by Patient Population

High-Risk Patients (24% incidence of symptomatic bradycardia)

Patients with pre-existing conduction disorders face substantially elevated risk 3:

• First-degree AV block
• Right or left bundle branch block
• Pre-existing sinus node dysfunction (sinus arrest or sinoatrial block)

In these patients, amiodarone can precipitate second- or third-degree AV block or intermittent sinus arrest requiring pacemaker placement 3

Standard-Risk Patients

Patients without baseline conduction abnormalities developed no symptomatic bradycardia in comparative studies, though asymptomatic heart rate slowing remains common 3

Clinical Presentation Patterns

IV Amiodarone

• Drug-related bradycardia occurs in 4.9% of patients 1
• Bradycardia requiring alterations in therapy occurs in approximately 3% of patients 1
• Progressive and terminal bradycardia has been reported despite interventions 1

Oral Amiodarone

• Sinus bradycardia occurs in 32% of patients during loading/saturation phase 4
• 11.2% experience bradycardia during maintenance therapy 4
• Heart rate slowing is usually not severe enough to require drug cessation or pacing 4

Gender-Specific Considerations

Amiodarone-associated bradycardia requiring permanent pacemaker implantation is more common in women than in men 5

Management Algorithm

Before Initiating Amiodarone

1. Assess for absolute contraindications 2, 1:

   • Bradycardia without pacemaker in place
   • Second- or third-degree heart block without pacemaker
   • Significant conduction system disease 6

2. Evaluate baseline heart rate and conduction 2:

   • If heart rate is 57 bpm or lower, use extreme caution—amiodarone is relatively contraindicated unless a pacemaker is present or the situation is immediately life-threatening with no safer alternatives 2

During IV Administration

1. Continuous ECG monitoring is mandatory for heart rate, AV conduction abnormalities, and QT prolongation 2

2. If bradycardia develops 1:

   • Slow the infusion rate immediately
   • If inadequate response, discontinue the infusion
   • Consider temporary pacing in refractory cases
   • In some patients, permanent pacemaker insertion is required 1

During Oral Therapy

1. Monitor heart rate weekly initially by pulse check, event recorder, or office ECG 5

2. Reduce doses of concomitant rate-control agents (beta-blockers, calcium channel blockers, digoxin) approximately 6 weeks after starting amiodarone 2

3. Discontinue rate-control medications entirely if excessive bradycardia develops 2

Critical Drug Interactions Potentiating Bradycardia

Concomitant medications that slow AV conduction create additive effects 2:

• Beta-blockers (e.g., propranolol)
• Calcium channel blockers (e.g., verapamil, diltiazem)
• Digoxin (reduce dose by 50% when starting amiodarone) 2, 1

Amiodarone should be used with extreme caution when combined with these agents due to possible potentiation of bradycardia, sinus arrest, and AV block; if necessary, amiodarone can continue after pacemaker insertion 1

Special Clinical Scenarios

Sofosbuvir Co-Administration

Severe bradycardia and syncope have been reported when amiodarone is combined with sofosbuvir (direct-acting antiviral for hepatitis C), requiring discontinuation of both drugs 7

Overdose Presentation

Amiodarone overdose manifests with hypotension, cardiogenic shock, bradycardia, and AV block—bradycardia may require temporary pacing 1

Common Pitfalls to Avoid

• Do not overlook pre-existing conduction abnormalities on baseline ECG—these patients have 24% risk of symptomatic bradycardia versus 0% in those without conduction disease 3
• Do not assume bradycardia only occurs with high doses—the risk is present regardless of dose 2
• Do not continue full doses of other rate-control agents after starting amiodarone—reduce or discontinue them to prevent excessive bradycardia 2
• Do not use amiodarone purely for rate control if possible, especially in elderly patients 6
• Ensure temporary pacing capability is available when administering amiodarone to patients with known predisposition to bradycardia or AV block 1