What is the best course of action for a patient with new onset palpitations and minimal ST elevation in inferior leads, whose symptoms worsen on metoprolol (metoprolol) XR 100 mg orally twice a day?

Management of New Palpitations with ST Elevation and Worsening on Metoprolol

For a patient with new palpitations and minimal ST elevation in inferior leads who experiences worsening symptoms on metoprolol XR 100 mg BID, the most appropriate action is to discontinue metoprolol and switch to a calcium channel blocker such as diltiazem for rate control.

Clinical Assessment and Rationale

Current Situation Analysis

• Patient presents with:
  • New onset palpitations
  • Minimal ST elevation in inferior leads
  • Worsening symptoms on metoprolol XR 100 mg BID
  • Possible underlying arrhythmia (likely atrial fibrillation based on presentation)

Why Metoprolol Should Be Discontinued

1. Worsening symptoms: The patient's palpitations are increasing on metoprolol, indicating treatment failure or possible adverse effect 1
2. Potential contraindication: The presence of ST elevation in inferior leads may indicate:
   • Possible inferior wall ischemia or injury
   • Risk of developing bradycardia or heart block with continued beta-blocker use 1
3. Excessive dosing: Current dose (100 mg BID) is at the higher end of the therapeutic range, which may be contributing to adverse effects 2

Recommended Management Algorithm

Step 1: Immediate Actions

• Discontinue metoprolol due to symptom exacerbation
• Obtain 12-lead ECG to evaluate the ST elevation and assess for arrhythmias
• Check vital signs with attention to heart rate, blood pressure, and signs of hemodynamic compromise

Step 2: Rate Control Alternative

• Initiate diltiazem for rate control if atrial fibrillation or other supraventricular tachycardia is confirmed 1, 3:
  • Initial IV dose: 0.25 mg/kg (typically 15-20 mg) over 2 minutes
  • May repeat with 0.35 mg/kg after 15 minutes if needed
  • Maintenance infusion: 5-15 mg/hour

Step 3: Diagnostic Workup

• Cardiac biomarkers to evaluate for myocardial injury
• Echocardiography to:
  • Assess wall motion abnormalities corresponding to ST changes
  • Evaluate for structural heart disease
  • Rule out other causes of palpitations (e.g., atrial myxoma) 4

Step 4: Definitive Management Based on Findings

• If confirmed atrial fibrillation/flutter with ST changes:

  • Continue calcium channel blocker therapy (preferably diltiazem or verapamil) 1
  • Consider anticoagulation based on CHA₂DS₂-VASc score
  • Plan for cardioversion if hemodynamically unstable

• If confirmed STEMI:

  • Activate cardiac catheterization laboratory
  • Initiate STEMI protocol per institutional guidelines
  • Avoid beta-blockers in patients with risk factors for cardiogenic shock 1

Important Considerations and Pitfalls

Contraindications to Calcium Channel Blockers

• Avoid in patients with:
  • Decompensated heart failure
  • Pre-excited atrial fibrillation
  • Severe hypotension 1, 3

Monitoring Requirements

• Continuous cardiac monitoring during medication transition
• Regular blood pressure checks
• Reassessment of symptoms

Special Situations

• If patient has underlying structural heart disease, amiodarone may be preferred for rhythm control 1
• In cases of suspected Lyme carditis (rare but possible cause of new arrhythmias with conduction abnormalities), consider empiric antibiotic therapy 5

By discontinuing metoprolol and transitioning to a calcium channel blocker, you address both the worsening symptoms and provide appropriate rate control while allowing for further diagnostic evaluation of the ST changes.