What is the next treatment regimen for a 48-year-old male patient with cardiomyopathy and tachycardia on metoprolol succinate (metoprolol) 150 mg twice a day, suspected of having SVT (Supraventricular Tachycardia)?

Management of Tachycardia in a Patient with Cardiomyopathy on High-Dose Metoprolol

For a 48-year-old male with cardiomyopathy on metoprolol succinate 150 mg twice daily with elevated heart rate and suspected SVT, the most appropriate next step is to add ivabradine (7.5 mg twice daily) to the current metoprolol regimen. 1

Current Medication Assessment

• The patient is currently on metoprolol succinate 150 mg twice daily (300 mg total daily dose)
• This is below the maximum recommended daily dose of 400 mg 1
• The high dose of metoprolol already being used suggests:
  • Beta-blocker resistance
  • Inadequate rate control despite substantial beta-blockade
  • Possible need for alternative or additional therapy

Therapeutic Options

Option 1: Optimize Beta-Blocker Therapy

• Metoprolol succinate could be increased to the maximum dose of 400 mg daily 1, 2
• However, the patient is already on a substantial dose (300 mg daily)
• Further dose increases may increase risk of hypotension, bradycardia, and worsening heart failure symptoms

Option 2: Add Ivabradine (Recommended)

• Ivabradine specifically targets the sinoatrial node to reduce heart rate without affecting blood pressure or cardiac contractility 1, 3
• Evidence supports the combination of ivabradine with metoprolol succinate:
  • In a small observational study, adding ivabradine (7.5 mg twice daily) to metoprolol succinate (95 mg daily) reduced heart rate more effectively than metoprolol alone 1
  • The combination resolved symptoms in all patients and was well tolerated 1
• The ACC/AHA/HRS guidelines give a Class IIb recommendation for this combination in patients with inappropriate sinus tachycardia 1

Option 3: Consider Alternative Antiarrhythmics

• Amiodarone could be considered but carries significant long-term risks including thyroid disorders 3
• Calcium channel blockers are generally contraindicated in cardiomyopathy due to negative inotropic effects

Implementation Plan

1. Add ivabradine 7.5 mg twice daily to the current metoprolol regimen

2. Monitor for:

   • Heart rate response
   • Potential bradycardia (combination therapy risk)
   • Visual side effects (phosphenes occur in approximately 3% of patients) 1
   • Improvement in symptoms

3. If inadequate response after 2 weeks, consider:

   • Electrophysiology study to confirm the exact mechanism of tachycardia
   • Catheter ablation if a focal SVT is identified 3

Special Considerations for Cardiomyopathy

• Beta-blockers are first-line therapy for rate control in cardiomyopathy patients
• Ivabradine has shown benefit in heart failure patients with reduced ejection fraction
• The combination has been well-tolerated in heart failure trials 1
• Avoid calcium channel blockers due to negative inotropic effects in cardiomyopathy

Diagnostic Considerations

• A 12-lead ECG during tachycardia is essential to differentiate between:

  • Sinus tachycardia
  • SVT
  • Atrial fibrillation/flutter
  • Ventricular tachycardia

• If the diagnosis remains uncertain after adding ivabradine, consider:

  • 24-hour Holter monitoring
  • Event recorder
  • Electrophysiology study

Monitoring Parameters

• Heart rate (target <100 bpm at rest)
• Blood pressure (watch for hypotension)
• Symptoms of heart failure
• ECG for QT interval and conduction abnormalities
• Renal and hepatic function

The combination of metoprolol succinate and ivabradine offers the best balance of efficacy and safety for this patient with cardiomyopathy and suspected SVT who is already on a substantial dose of beta-blocker therapy.