Yes, hold both amiodarone and metoprolol when the heart rate is in the 50s
Both amiodarone and metoprolol list bradycardia as a known side effect, and continuing these medications with a heart rate in the 50s significantly increases the risk of symptomatic bradycardia, heart block, and cardiac arrest. 1, 2
Clinical Decision Framework
Immediate Assessment Required
When encountering a heart rate in the 50s in a patient on both medications, evaluate:
- Symptoms: Is the patient experiencing dizziness, lightheadedness, syncope, chest pain, or signs of poor perfusion?
- Hemodynamic stability: Check blood pressure and signs of end-organ perfusion
- Rhythm: Obtain ECG to assess for heart block (first-degree, second-degree, or third-degree AV block) or sinus node dysfunction
- Clinical context: Recent medication changes, electrolyte abnormalities (especially potassium and magnesium), or concurrent use of other rate-lowering agents
Holding Parameters
Hold both medications if:
- Heart rate <50 bpm with any symptoms
- Heart rate <45 bpm regardless of symptoms (this aligns with the metoprolol FDA contraindication for heart rate <45 bpm in MI patients) 2
- Any degree of symptomatic bradycardia
- Second- or third-degree heart block
- Significant first-degree heart block (PR interval ≥0.24 seconds)
The Pharmacologic Rationale
The 2025 AHA guidelines explicitly list bradycardia as a major side effect for both beta-blockers (including metoprolol) and amiodarone 3. The 2010 AHA ACLS guidelines similarly warn that both drug classes can cause problematic bradycardia 1.
Critical drug interaction: Amiodarone is a weak CYP2D6 inhibitor, which increases metoprolol plasma concentrations 4. This pharmacokinetic interaction means the combination produces more profound bradycardia than either agent alone. A 2023 study demonstrated that amiodarone use was associated with significantly higher metoprolol concentrations and lower heart rates 4.
Common Pitfall to Avoid
Do not continue these medications assuming "the 50s are acceptable" without assessing the patient. The 2018 ACC/AHA/HRS bradycardia guidelines shifted the definition of clinically significant bradycardia from <60 bpm to <50 bpm 3, but this does not mean heart rates in the 50s are always safe—particularly in patients on dual rate-controlling therapy.
After Holding: Next Steps
- Monitor continuously: Check heart rate every 1-2 hours initially
- Correct reversible causes: Check and correct electrolytes (potassium, magnesium), assess for other contributing medications
- Reassess need for both agents: Many patients do not require both amiodarone and metoprolol simultaneously
- Consider restarting cautiously: If heart rate improves to >60 bpm and patient remains asymptomatic, consider restarting ONE agent at a reduced dose—not both simultaneously
- Pacemaker consideration: If bradycardia persists and both medications are clinically necessary (e.g., for rhythm control in atrial fibrillation with heart failure), permanent pacemaker placement may be required 5, 6
Special Consideration for Atrial Fibrillation
If these medications were being used for rate control in atrial fibrillation, the 2006 ACC/AHA/ESC guidelines recommend that doses should be modulated to avoid bradycardia when combining AV nodal blocking agents 5, 7. The 2014 AATS guidelines for perioperative AF explicitly state that combination therapy doses should be "modified to avoid bradycardia" 8.
In patients with heart failure and reduced ejection fraction with atrial fibrillation, amiodarone may be preferred as monotherapy over metoprolol. A 2022 study showed amiodarone alone had lower cardiovascular mortality compared to metoprolol in this population 9.