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

Initial Treatment for Supraventricular Tachycardia (SVT)

Vagal maneuvers are the recommended first-line treatment for hemodynamically stable patients with SVT, followed by intravenous adenosine if vagal maneuvers fail. 1

Treatment Algorithm for SVT

For Hemodynamically Stable Patients:

1. First-line: Vagal Maneuvers (Class I, LOE B-R)

   • Modified Valsalva Maneuver (MVM) is the most effective vagal maneuver 2
   • Technique: Patient raises intrathoracic pressure by bearing down against a closed glottis for 10-30 seconds (equivalent to 30-40 mmHg) in supine position 1
   • Carotid sinus massage can be attempted if Valsalva fails (after confirming absence of carotid bruit) 1
   • Success rate of vagal maneuvers alone: up to 25% of PSVTs 1

2. Second-line: Adenosine IV (Class I, LOE B-R)

   • Initial dose: 6 mg rapid IV push through a large vein (e.g., antecubital) followed by 20 mL saline flush 1
   • If no response within 1-2 minutes: 12 mg rapid IV push with saline flush 1
   • Success rate: approximately 95% for AVNRT 1
   • Important: Have a defibrillator available when administering adenosine if WPW is suspected 1

3. Third-line: IV Calcium Channel Blockers or Beta Blockers (Class IIa, LOE B-R/C)

   • Diltiazem or verapamil IV (Class IIa, LOE B-R) 1
     • Success rate: 64-98% of patients 1
     • Contraindicated in suspected VT, pre-excited AF, systolic heart failure 1
   • Beta blockers IV (Class IIa, LOE C-LD) 1
     • Less effective than calcium channel blockers but excellent safety profile 1

4. Fourth-line: Synchronized Cardioversion (Class I, LOE B-NR)

   • For stable patients when pharmacological therapy is ineffective or contraindicated 1
   • Perform after adequate sedation or anesthesia 1

For Hemodynamically Unstable Patients:

1. Immediate Synchronized Cardioversion (Class I) 1
   • Indicated for SVT resulting in hypotension, altered mental status, signs of shock, chest pain, or acute heart failure 1
   • Consider adenosine first if the tachycardia is regular with narrow QRS complex 1

Special Considerations

Medication Adjustments:

• Adenosine dose modifications:
  • Reduce to 3 mg initial dose in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 1
  • Larger doses may be required for patients with significant blood levels of theophylline, caffeine, or theobromine 1
  • Contraindicated in patients with asthma 1

Common Pitfalls:

• Failure to distinguish SVT from VT or pre-excited AF before administering calcium channel blockers, which can cause hemodynamic compromise or accelerated ventricular rate leading to ventricular fibrillation 1
• Inappropriate use of synchronized cardioversion for rhythms that break or recur spontaneously 1
• Underestimating the effectiveness of modified Valsalva maneuver, which has shown superior results compared to standard Valsalva or carotid sinus massage 2, 3

Monitoring After Conversion:

• Monitor for recurrence after conversion 1
• For recurrent episodes, treat with adenosine or a longer-acting AV nodal blocking agent (e.g., diltiazem or beta-blocker) 1
• If adenosine or vagal maneuvers reveal another form of SVT (such as atrial fibrillation or flutter), consider treatment with a longer-acting AV nodal blocking agent for more sustained rate control 1

Following this evidence-based approach to SVT management will maximize the chances of successful conversion while minimizing risks to the patient.