What is the best next step for a 40-year-old female with metastatic lung cancer and supraventricular tachycardia (sVT) currently on metoprolol (beta-blocker)?

Management of SVT in a Patient with Metastatic Lung Cancer

For a 40-year-old female with metastatic lung cancer presenting with supraventricular tachycardia (SVT) who is already taking metoprolol, the best next step in treatment is to administer intravenous adenosine for acute termination of the SVT episode.

Acute Management of SVT

First-line approach:

• Vagal maneuvers should be attempted first if the patient is hemodynamically stable 1
• Intravenous adenosine (6 mg rapid IV bolus, followed by 12 mg if needed) is the drug of choice for acute termination of SVT when vagal maneuvers fail 1
  • Adenosine has a very short half-life (seconds) and effectively terminates 90-95% of SVT episodes
  • It works by temporarily blocking AV nodal conduction

Special considerations in this cancer patient:

• The patient is already on metoprolol (beta-blocker), which has not prevented this SVT episode
• Cancer patients are at increased risk for arrhythmias due to:
  • Increased sympathetic drive from pain and emotional stress
  • Paraneoplastic conditions
  • Cancer therapy effects 1
• Metastatic lung cancer may cause direct or indirect cardiac effects that can precipitate arrhythmias

Treatment Algorithm

1. Assess hemodynamic stability:

   • If unstable (hypotension, altered mental status, chest pain, heart failure): proceed directly to synchronized cardioversion 1
   • If stable: proceed with medical management

2. For stable patients:

   • Try vagal maneuvers (Valsalva, carotid sinus massage)
   • If unsuccessful, administer adenosine 6 mg IV push, followed by 12 mg if needed 1
   • Have resuscitation equipment ready as adenosine can rarely cause bronchospasm or brief asystole

3. If adenosine fails:

   • Consider IV diltiazem or verapamil as next option 1
   • Avoid additional beta-blockers since patient is already on metoprolol
   • Consider synchronized cardioversion if medications fail 1

Long-term Management Options

After acute termination of SVT, consider:

1. Optimization of current beta-blocker therapy:

   • Adjust metoprolol dosage if inadequate rate control 1, 2
   • Consider switching to a different beta-blocker if metoprolol is ineffective

2. Addition of other antiarrhythmic medications:

   • Consider adding calcium channel blockers (diltiazem or verapamil) if beta-blocker alone is insufficient 1
   • For refractory cases, consider flecainide or propafenone (if no structural heart disease) 1

3. Electrophysiology consultation:

   • Consider EP study and catheter ablation if SVT is recurrent and significantly impacts quality of life 1
   • Ablation may be particularly beneficial in this younger patient with cancer to reduce medication burden

Cautions and Pitfalls

• Avoid verapamil or diltiazem if there's suspicion of ventricular tachycardia or pre-excited AF 1
• Monitor for drug interactions between cancer therapies and antiarrhythmic medications 1
• Be cautious with antiarrhythmic drugs in patients with electrolyte abnormalities, which are common in cancer patients
• Recognize that metastatic disease can directly involve the myocardium and conduction system, potentially causing refractory arrhythmias 3, 4

The management of SVT in cancer patients requires careful consideration of both the arrhythmia and the underlying malignancy. Acute termination with adenosine followed by optimization of rate control medications offers the best approach to improve symptoms and quality of life in this challenging clinical scenario.