How to manage a 67-year-old female with A-fib, CAD, and SSS on metoprolol tartrate and digoxin with concerns for bradycardia and pacemaker malfunction?

Management of Atrial Fibrillation with Bradycardia in a Patient with Pacemaker

The patient should discontinue digoxin and have metoprolol tartrate dose reduced or switched to a longer-acting beta blocker for rate control of atrial fibrillation, with close monitoring of heart rate and pacemaker function. 1, 2

Current Clinical Situation

This 67-year-old female has:

• Complex cardiovascular history: CAD s/p CABG and PCI, atrial fibrillation on Xarelto, sick sinus syndrome with Medtronic pacemaker
• Recent hospitalization for chest pain and palpitations with A-fib with RVR
• Current rate control medications: metoprolol tartrate and digoxin
• Episodes of bradycardia (HR 30s-50s) and asystole despite pacemaker
• Pacemaker interrogation showed proper functioning

Rate Control Medication Assessment

Issues with Current Regimen

1. Combination therapy problems:

   • Metoprolol tartrate + digoxin is causing excessive bradycardia despite functioning pacemaker
   • This combination increases risk of severe bradycardia, especially in elderly patients with sick sinus syndrome 3

2. Digoxin concerns:

   • Limited efficacy as monotherapy for rate control during activity 1
   • Associated with increased mortality in AF patients without heart failure 4
   • Significant drug interactions with other medications

3. Metoprolol tartrate issues:

   • Short-acting formulation requiring multiple daily doses
   • May cause more pronounced fluctuations in heart rate 2
   • FDA labeling warns about increased risk of bradycardia in patients with first-degree AV block, sinus node dysfunction, or conduction disorders 2

Management Recommendations

Immediate Actions

1. Modify rate control strategy:

   • Discontinue digoxin due to its association with bradycardia and limited efficacy in AF rate control 1, 4
   • Reduce metoprolol tartrate dose or consider switching to metoprolol succinate (extended-release) for more stable rate control 1, 2

2. Optimize beta-blocker therapy:

   • Initial dose reduction: Decrease current metoprolol tartrate dose by 50%
   • If switching to metoprolol succinate: Start at 25-50 mg daily (lower than equivalent tartrate dose) 1
   • Titrate slowly based on heart rate response with weekly monitoring initially 1

3. Pacemaker optimization:

   • Request cardiology consultation for pacemaker programming assessment
   • Consider adjusting lower rate limit settings to prevent symptomatic bradycardia

Follow-up Plan

1. Short-term monitoring (1-2 weeks):

   • Heart rate and rhythm assessment with home monitoring or event recorder
   • Symptom diary to correlate bradycardia episodes with symptoms
   • ECG to assess PR interval, QRS duration, and overall conduction 1

2. Medium-term follow-up (1 month):

   • 24-hour Holter monitoring to assess rate control throughout daily activities
   • Pacemaker interrogation to evaluate percentage of pacing and any episodes of bradycardia
   • Target heart rate: 60-80 bpm at rest, not exceeding 110 bpm with moderate activity 1

Special Considerations

1. Beta-blocker selection rationale:

   • Beta-blockers are first-line for AF rate control in patients with CAD 1, 5
   • Metoprolol is appropriate for this patient with CAD history but requires careful dosing 2
   • Extended-release formulations provide more stable rate control with less risk of bradycardia 1

2. Pacemaker-specific issues:

   • Despite proper pacemaker function, rate-controlling medications can still cause bradycardia if:
     • Pacemaker lower rate limit is set too low
     • Medications suppress intrinsic rhythm and create pacemaker dependence
     • Rate response features are inadequately programmed

3. Common pitfalls to avoid:

   • Abrupt discontinuation of beta-blockers in CAD patients (can precipitate angina or MI) 2
   • Failure to recognize drug interactions (especially between rate-controlling agents)
   • Inadequate monitoring during medication changes

By carefully adjusting the rate control strategy and optimizing pacemaker settings, this patient's episodes of bradycardia can be minimized while maintaining adequate control of her atrial fibrillation.