What is the first-line medication for a patient with supraventricular tachycardia (SVT)?

First-Line Medication for Supraventricular Tachycardia (SVT)

Adenosine is the recommended first-line medication for acute treatment of patients with regular SVT, including this 35-year-old woman with palpitations, lightheadedness, and stable tachycardia showing regular narrow QRS complex at a rate of 180 beats per minute. 1

Initial Management Algorithm

1. Vagal Maneuvers

   • First attempt should be vagal maneuvers (Class I, Level B-R recommendation) 1
   • Perform with patient in supine position
   • Valsalva maneuver: patient bears down against closed glottis for 10-30 seconds
   • Carotid sinus massage: after confirming absence of bruits, apply steady pressure for 5-10 seconds

2. Adenosine Administration (if vagal maneuvers fail)

   • Initial dose: 6 mg IV rapid bolus followed by saline flush 1, 2
   • If ineffective after 1-2 minutes, administer 12 mg IV rapid bolus
   • May repeat 12 mg dose once more if needed
   • Success rate approximately 95% for AVNRT 1

3. Alternative Medications (if adenosine fails or is contraindicated)

   • IV calcium channel blockers (Class IIa, Level B-R recommendation) 1
     • Diltiazem: 15-20 mg IV over 2 minutes
     • Verapamil: 2.5-5 mg IV over 2 minutes
   • IV beta blockers (Class IIa, Level C-LD recommendation) 1
     • Metoprolol: 5 mg IV over 1-2 minutes
     • Esmolol: 500 mcg/kg over 1 minute 3

4. Synchronized Cardioversion (if medications fail)

   • For hemodynamically unstable patients or when pharmacological therapy is ineffective/contraindicated (Class I, Level B-NR) 1
   • Initial energy: 50-100 J (biphasic)

Clinical Considerations

Advantages of Adenosine

• Rapid onset of action
• Very short half-life (few seconds) 4
• High efficacy rate (93% in over 600 reported episodes) 4
• Diagnostic value - can unmask underlying rhythm if not AVNRT 1

Cautions with Adenosine

• Common transient side effects: chest discomfort, dyspnea, flushing 4
• Contraindicated in patients with:
  • Second or third-degree AV block without pacemaker
  • Sick sinus syndrome without pacemaker
  • Severe asthma (relative contraindication) 2
• Reduce dose in patients taking dipyridamole or carbamazepine 2

Important Considerations for Calcium Channel Blockers

• Avoid in patients with suspected Wolff-Parkinson-White syndrome as they can accelerate conduction through accessory pathways 2
• Avoid in patients with heart failure or hypotension
• Slow infusion of calcium channel blockers has shown comparable efficacy to adenosine (98% vs 86.5%) with minimal risk of hypotension 5

Beta Blockers Considerations

• Safe alternative when calcium channel blockers are contraindicated
• Esmolol has rapid onset and short half-life, making it suitable for acute management 3
• Effective maintenance dose for esmolol: 50-200 mcg/kg/min 3

Long-term Management

• Refer to cardiology for consideration of catheter ablation (definitive treatment)
• Oral medications for ongoing management until definitive treatment:
  • Beta blockers, diltiazem, or verapamil (Class I, Level B-R) 1
  • Flecainide or propafenone for patients without structural heart disease (Class IIa, Level B-R) 1

This patient's presentation with regular narrow QRS tachycardia at 180 bpm is classic for SVT, and adenosine is the most appropriate first-line medication after attempting vagal maneuvers.