Is it reasonable to discontinue metoprolol tartrate in a patient with A-fib, SSS, and a functioning pacemaker, who has experienced episodes of bradycardia?

Management of Metoprolol in a Patient with Atrial Fibrillation, Sick Sinus Syndrome, and Bradycardia

It is reasonable and appropriate to discontinue metoprolol tartrate in this patient with atrial fibrillation, sick sinus syndrome, and documented episodes of bradycardia despite a functioning pacemaker. 1

Rationale for Discontinuing Metoprolol

Patient-Specific Factors

• 67-year-old female with multiple cardiovascular comorbidities:
  • Atrial fibrillation on Xarelto
  • Sick sinus syndrome with Medtronic pacemaker
  • Heart failure with preserved ejection fraction (HFpEF)
  • Coronary artery disease status post CABG and PCI
• Current episode featured:
  • A-fib with rapid ventricular response (RVR) requiring IV Cardizem
  • Episodes of bradycardia with heart rates in the 30s-50s
  • Episode of asystole despite confirmed proper pacemaker function

Evidence-Based Considerations

1. Beta-Blocker and Bradycardia Risk

   • The FDA label for metoprolol specifically warns that "bradycardia, including sinus pause, heart block, and cardiac arrest have occurred with the use of metoprolol" and that "patients with first-degree atrioventricular block, sinus node dysfunction, or conduction disorders may be at increased risk" 2
   • The immediate-release formulation of metoprolol (tartrate) is associated with nearly twice the risk of emergent bradycardia compared to the slow-release formulation 3

2. Rate Control Strategy

   • The patient is currently on both metoprolol tartrate and digoxin for rate control
   • Maintaining two rate-controlling medications may be excessive, especially given the documented bradycardia episodes

3. Pacemaker Considerations

   • Despite having a functioning pacemaker, the patient experienced bradycardia and asystole
   • According to the ACC/AHA/HRS guidelines, "the slowing of heart rate and cardiac conduction produced by beta-blockers is generally asymptomatic and thus generally requires no treatment; however, if the bradycardia is accompanied by dizziness or lightheadedness or if second- or third-degree heart block occurs, physicians should decrease the dose of the beta-blocker" 4

Management Algorithm

1. Discontinue metoprolol tartrate

   • Given the patient's episodes of bradycardia despite a functioning pacemaker, discontinuing metoprolol is appropriate
   • Maintain digoxin as the sole rate control agent initially

2. Monitor heart rate and symptoms

   • Observe for resolution of bradycardia episodes
   • Monitor for potential rebound tachycardia or worsening A-fib with RVR

3. If inadequate rate control occurs after metoprolol discontinuation:

   • Consider non-beta blocker alternatives for rate control
   • Options include:
     • Titration of digoxin dose (with careful monitoring of levels)
     • Low-dose calcium channel blocker (e.g., diltiazem)
     • Amiodarone for refractory cases

4. Pacemaker optimization

   • Ensure pacemaker settings are optimized for the patient's condition
   • Consider programming adjustments to prevent bradycardia episodes

Important Considerations and Caveats

1. Avoid abrupt discontinuation

   • Metoprolol should be tapered rather than stopped abruptly, especially in patients with coronary artery disease
   • The FDA label warns: "When discontinuing chronically administered metoprolol, particularly in patients with coronary artery disease, the dosage should be gradually reduced over a period of 1 to 2 weeks" 2

2. Monitor for worsening heart failure

   • Beta-blockers provide mortality benefit in heart failure patients
   • Watch for signs of worsening HFpEF after discontinuation

3. Sick sinus syndrome and atrial fibrillation interaction

   • Patients with sick sinus syndrome have a higher risk of developing atrial fibrillation 5
   • The coexistence of these conditions makes management more challenging and requires careful medication selection

4. Pacemaker dependency assessment

   • Evaluate if the patient has become pacemaker-dependent
   • According to Praxis Medical Insights, "assessing chronotropic incompetence with exercise stress testing in patients with pacemakers is particularly important for pacemaker-dependent patients" 1

By discontinuing metoprolol tartrate while maintaining digoxin for rate control, the risk of bradycardia should decrease while still providing adequate management of the patient's atrial fibrillation.