What is the initial treatment approach for a patient presenting with supraventricular tachycardia (SVT)?

Initial Treatment of Supraventricular Tachycardia

Vagal maneuvers should be performed immediately as first-line treatment, followed by adenosine if unsuccessful, with synchronized cardioversion reserved for hemodynamically unstable patients or pharmacological failure. 1, 2

Immediate Assessment and Stabilization

• Determine hemodynamic stability first – unstable patients (hypotension, altered mental status, chest pain with ischemia, acute heart failure) require immediate synchronized cardioversion without attempting vagal maneuvers or medications 1
• Obtain a 12-lead ECG to confirm narrow-complex tachycardia and exclude ventricular tachycardia, which can masquerade as SVT 3
• Critical pitfall: Look for evidence of pre-excitation (delta waves, short PR interval) – if present, avoid all AV nodal blocking agents (adenosine, calcium channel blockers, beta-blockers) as they may precipitate ventricular fibrillation 1, 2

Step-by-Step Treatment Algorithm for Hemodynamically Stable Patients

First-Line: Vagal Maneuvers (Class I Recommendation)

• Modified Valsalva maneuver is superior to all other vagal techniques with a 43.7% success rate for initial conversion and 28.1% sustained rhythm at 5 minutes 4, 5
• Perform with patient supine (critical for success): have patient bear down against closed glottis for 10-30 seconds generating at least 30-40 mm Hg pressure, then immediately lay patient flat with legs elevated 1
• If modified Valsalva fails, attempt carotid sinus massage: first confirm absence of carotid bruit by auscultation, then apply steady pressure over right or left carotid sinus for 5-10 seconds 1
• Alternative technique: apply ice-cold wet towel to face (diving reflex) 1, 2
• Never apply pressure to eyeballs – this dangerous practice has been abandoned 1, 2
• Switching between vagal techniques increases overall success to 27.7% 1, 2

Second-Line: Adenosine (Class I Recommendation)

• Adenosine is the first-line pharmacological agent with 90-95% effectiveness for terminating SVT 1, 2
• Administer as rapid IV push: 6 mg initial dose, followed by 12 mg if needed 1
• Have defibrillator immediately available – adenosine may precipitate atrial fibrillation that conducts rapidly down an accessory pathway, potentially causing ventricular fibrillation 1
• Common transient side effects occur in 30% of patients but last <1 minute 1
• Contraindication: Do not use if pre-excitation (WPW pattern) is present on ECG 2

Third-Line: IV Calcium Channel Blockers or Beta-Blockers (Class IIa Recommendation)

• IV diltiazem or verapamil are highly effective for AVNRT conversion with 80-98% success rates 1
• These are more effective than beta-blockers for acute termination 1
• Critical contraindications:
  • Pre-excited atrial fibrillation (may cause ventricular fibrillation) 1, 2
  • Suspected ventricular tachycardia 2
  • Systolic heart failure 1
  • Wide-complex tachycardia of uncertain etiology 2
• IV beta-blockers (esmolol, metoprolol) are reasonable alternatives with excellent safety profile but lower efficacy 1

Fourth-Line: Synchronized Cardioversion (Class I Recommendation)

• Perform synchronized cardioversion if pharmacological therapy fails in stable patients 1
• This is the definitive treatment when medications are ineffective or contraindicated 1

Special Scenario: Pre-Excited Atrial Fibrillation

• If wide, irregular QRS complexes suggest pre-excited AF:
  • Hemodynamically unstable: immediate synchronized cardioversion 1, 2
  • Hemodynamically stable: IV ibutilide or procainamide (Class I recommendation) 1, 2
  • Absolutely avoid: adenosine, calcium channel blockers, beta-blockers, digoxin – all may accelerate ventricular rate and cause death 1, 2

Post-Conversion Management

• All patients require referral to cardiac electrophysiology for risk stratification and consideration of catheter ablation 2, 6
• Educate patients on proper vagal maneuver techniques for self-management of future episodes 2
• Consider ongoing pharmacological therapy (oral beta-blockers, diltiazem, or verapamil) for recurrent symptomatic episodes 1, 2