What's the next step for a 62-year-old patient with a history of infective endocarditis, native mitral valve rupture, and cardiogenic shock, who is 2 months post-operative from bioprosthetic mitral valve replacement (MVR) with left ventricular ejection fraction (LVEF) of 45%, currently experiencing hypovolemia-induced atrial fibrillation (AF) with tachycardia, unresponsive to fluid bolus and bisoprolol, and already on warfarin for full anticoagulation?

Management of Atrial Fibrillation Post Bioprosthetic Mitral Valve Replacement

For this patient with hypovolemia-induced atrial fibrillation not responding to fluid bolus and beta-blocker therapy, amiodarone should be restarted at 400mg daily for 4-6 weeks, then reduced to a maintenance dose of 200mg daily. 1

Patient Assessment

This 62-year-old patient presents with:

• History of infective endocarditis leading to native mitral valve rupture and cardiogenic shock
• Post-operative bioprosthetic mitral valve replacement with LVEF 45%
• Previous treatment with IV amiodarone 150mg once (2 weeks pre-surgery) for atrial flutter with RVR
• Previous oral amiodarone 200mg TDS tapered over a week
• Current episode (2 months post-op) of hypovolemia-induced fast AF with stable vitals (HR 110 bpm)
• Not responding to fluid bolus and bisoprolol up to 5mg daily
• Already on full anticoagulation with warfarin

Treatment Algorithm

1. Rate Control Strategy

• Current rate control with bisoprolol 5mg daily is inadequate (HR 110 bpm)
• Options for intensifying rate control:

For patients with LVEF >40% (applicable to this patient with LVEF 45%):

• Add digoxin to the beta-blocker (bisoprolol) regimen 1
  • Start with 0.125-0.375mg daily orally
  • Monitor for digitalis toxicity, heart block, and bradycardia
  • Note: The combination of beta-blocker with digoxin can improve rate control while avoiding excessive bradycardia 1

2. Rhythm Control Strategy (Preferred for this patient)

• Restart amiodarone therapy since:
  • Patient previously responded to amiodarone for atrial flutter
  • Current AF is not responding adequately to rate control strategy
  • Patient has moderately reduced LVEF (45%)

Amiodarone Loading and Maintenance Protocol:

• Start with 400mg daily for 4-6 weeks 1
• Then reduce to maintenance dose of 200mg daily 1
• Monitor for:
  • QT interval prolongation
  • Thyroid function
  • Pulmonary toxicity
  • Warfarin interaction (reduce warfarin dose as amiodarone increases INR) 1

3. Anticoagulation Management

• Continue warfarin therapy as the patient already has an indication for full anticoagulation
• Target INR 2.0-3.0 for bioprosthetic mitral valve replacement 2
• Monitor INR more frequently after restarting amiodarone due to known interaction that increases INR 1
• Reduce warfarin dose in anticipation of this interaction 1

Rationale for Recommendation

1. Why amiodarone is preferred:

   • Patient has previously responded to amiodarone for atrial flutter
   • Amiodarone is effective for both rate and rhythm control
   • Amiodarone is safe in patients with structural heart disease and reduced LVEF 1, 3
   • The ACC/AHA/HRS guidelines state that amiodarone can be useful when other measures are unsuccessful 1

2. Why not just intensify rate control:

   • Current rate control strategy with beta-blocker has failed
   • Adding digoxin alone may not be sufficient for exercise-induced tachycardia 1
   • Rhythm control may provide better symptom relief in this post-operative setting

3. Why not other antiarrhythmics:

   • Many other antiarrhythmics have negative inotropic effects that could worsen cardiac function
   • Patient has moderately reduced LVEF (45%), limiting options
   • Amiodarone has minimal negative inotropic effects 1

Monitoring and Follow-up

• ECG monitoring for QT interval and heart rate response
• Check thyroid function tests and liver enzymes at baseline and periodically
• Monitor INR more frequently (initially weekly) after restarting amiodarone
• Assess for adequate rate control both at rest and with activity
• Target heart rate <110 bpm at rest (lenient control), with stricter control if symptoms persist 1

Potential Pitfalls and Caveats

• Amiodarone-warfarin interaction: Amiodarone increases warfarin effect, requiring warfarin dose reduction (typically 25-50%)
• Long half-life: Amiodarone has a very long half-life, so effects persist for weeks to months after discontinuation
• Loading period: Full antiarrhythmic effect may take 1-3 weeks to develop 1
• Monitoring burden: Regular monitoring of thyroid, liver, and pulmonary function is required for long-term amiodarone use

If the patient remains symptomatic despite optimal medical therapy, consider AV node ablation with pacemaker implantation as a last resort for rate control 1.