What is the initial treatment for Supraventricular Tachycardia (SVT)?

Initial Treatment for Supraventricular Tachycardia (SVT)

The initial treatment for supraventricular tachycardia (SVT) should be vagal maneuvers, with the modified Valsalva maneuver being the most effective technique, followed by adenosine if vagal maneuvers fail. 1

Assessment of Hemodynamic Stability

First, determine if the patient is hemodynamically stable:

• Hemodynamically unstable (hypotension, altered mental status, signs of shock, chest pain, acute heart failure)

  • Immediate synchronized cardioversion 1

• Hemodynamically stable

  • Proceed with stepwise approach below

Step 1: Vagal Maneuvers (First-Line)

Perform vagal maneuvers with the patient in the supine position:

• Modified Valsalva maneuver (preferred) - Most effective with conversion rates up to 43.7% 2, 3

  • Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mmHg)
  • Immediately after strain, position patient supine with legs elevated

• Standard Valsalva maneuver - Less effective with conversion rates of 24.2% 3

  • Patient bears down against closed glottis for 10-30 seconds

• Carotid sinus massage - Least effective with conversion rates of only 9.1% 3

  • Confirm absence of carotid bruit first
  • Apply steady pressure over right or left carotid sinus for 5-10 seconds

Step 2: Adenosine (Second-Line)

If vagal maneuvers fail:

• Initial dose: 6 mg IV rapid push through a large vein (e.g., antecubital) followed by 20 mL saline flush 1
• If ineffective after 1-2 minutes: Give 12 mg IV rapid push with saline flush 1
• If still ineffective: May repeat 12 mg dose once more

Adenosine is highly effective with conversion rates of approximately 95% for AVNRT 1

Adenosine Precautions:

• Have defibrillator available (risk of atrial fibrillation with rapid ventricular rates in WPW)
• Reduce initial dose to 3 mg in patients:
  • Taking dipyridamole or carbamazepine
  • With transplanted hearts
  • When given via central venous access
• Contraindicated in patients with asthma
• Larger doses may be needed with significant blood levels of theophylline, caffeine, or theobromine

Step 3: Calcium Channel Blockers or Beta-Blockers (Third-Line)

If adenosine fails or SVT recurs:

• IV diltiazem or verapamil 1

  • Effective in 64-98% of patients
  • Use only in hemodynamically stable patients
  • Consider slow infusion (up to 20 minutes) to minimize hypotension
  • Contraindicated if suspected VT, pre-excited AF, systolic heart failure

• IV beta-blockers (e.g., metoprolol, esmolol) 1

  • Less effective than calcium channel blockers but excellent safety profile
  • Good option for patients who cannot tolerate calcium channel blockers

Step 4: Synchronized Cardioversion

If pharmacological therapy fails or is contraindicated:

• Perform synchronized cardioversion after adequate sedation or anesthesia 1
• Highly effective in terminating SVT

Common Pitfalls to Avoid

1. Misdiagnosis of rhythm: Ensure SVT is correctly identified before treatment
2. Administering verapamil or diltiazem for ventricular tachycardia or pre-excited AF (can cause hemodynamic collapse)
3. Failure to have defibrillator available when giving adenosine (risk of atrial fibrillation with rapid ventricular rates in WPW)
4. Improper technique for vagal maneuvers, particularly the modified Valsalva which has superior efficacy
5. Delaying cardioversion in hemodynamically unstable patients

After successful conversion, monitor for recurrence and consider referral to a cardiologist or electrophysiologist for long-term management options, including catheter ablation for recurrent, symptomatic SVT.