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

Initial Treatment for Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers as first-line therapy for hemodynamically stable SVT patients, specifically using the modified Valsalva maneuver (bearing down for 10-30 seconds generating 30-40 mmHg pressure in the supine position), which is 2.8-3.8 times more effective than standard Valsalva and achieves a 43% conversion rate. 1, 2

Immediate Assessment

Determine hemodynamic stability first:

• Unstable patients (hypotension, altered mental status, chest pain, acute heart failure) require immediate synchronized cardioversion at 50-100J initial energy 1
• Stable patients proceed with the algorithmic approach below 1

First-Line: Vagal Maneuvers (Stable Patients)

Modified Valsalva maneuver technique: 1, 2

• Position patient supine 2
• Patient bears down against closed glottis for 10-30 seconds, generating at least 30-40 mmHg intrathoracic pressure 1, 2
• Success rate: 27.7% when switching between techniques, up to 43% with modified technique 1, 2

Alternative vagal maneuvers if Valsalva fails: 1

• Carotid sinus massage (5-10 seconds after confirming no carotid bruit by auscultation) - less effective than Valsalva 1, 2
• Ice-cold wet towel to face (diving reflex) 1

Critical caveat: Vagal maneuvers work only for SVTs involving the AV node in a reentrant circuit (AVNRT, AVRT), not for automatic tachycardias like multifocal atrial tachycardia 1, 2

Second-Line: Adenosine (If Vagal Maneuvers Fail)

Adenosine achieves 90-95% success rate in AVNRT and orthodromic AVRT: 1, 2, 3

• Dosing: 6 mg rapid IV push through large (antecubital) vein, followed immediately by 20 mL saline flush 1
• If no conversion in 1-2 minutes: 12 mg rapid IV push with same technique 1
• Must have defibrillator immediately available due to risk of precipitating rapid ventricular rates in unrecognized Wolff-Parkinson-White syndrome 1

Dose modifications required: 1

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, transplanted hearts, or central venous administration 1
• Higher doses may be needed with theophylline, caffeine, or theobromine 1
• Contraindicated in asthma patients 1

Expected side effects (common but transient): flushing, dyspnea, chest discomfort 1, 3

Third-Line: IV Calcium Channel Blockers or Beta-Blockers

For hemodynamically stable patients when adenosine fails or is contraindicated: 1, 2

• IV diltiazem or verapamil achieve 80-98% success rates 1, 2
• IV beta-blockers (esmolol) are reasonable alternatives with excellent safety profile 1, 4

Critical safety warnings: 1, 2

• Never give calcium channel blockers or beta-blockers if:
  • Ventricular tachycardia is possible (wide-complex tachycardia of uncertain origin)
  • Pre-excited atrial fibrillation (WPW with AF) - can cause ventricular fibrillation
  • Suspected systolic heart failure
• These patients require immediate cardioversion instead 1, 2

Synchronized Cardioversion

Indications: 1

• Hemodynamically unstable patients (immediate) 1
• Stable patients when pharmacological therapy fails or is contraindicated 1
• Initial energy: 50-100J for SVT (lower than the 120-200J needed for atrial fibrillation) 1
• Increase energy stepwise if initial shock fails 1

Common Pitfalls to Avoid

• Do not use calcium channel blockers or beta-blockers in wide-complex tachycardia until VT is definitively ruled out - can cause cardiovascular collapse 1, 2
• Do not perform carotid massage without first auscultating for bruits - risk of stroke 1, 2
• Do not use adenosine in asthma patients - can precipitate bronchospasm 1
• Automatic tachycardias (ectopic atrial tachycardia, MAT, junctional tachycardia) will not respond to cardioversion and require rate control with AV nodal blocking agents instead 1
• Adenosine is safe in pregnancy, unlike some other agents 1

Post-Conversion Management

• Monitor for immediate recurrence - may require antiarrhythmic medication to prevent acute reinitiation 2
• Atrial or ventricular premature complexes commonly occur immediately after conversion 2
• All patients should be referred to a heart rhythm specialist for long-term management consideration, including potential catheter ablation (94-98% single-procedure success rate) 5