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

Initial Treatment for Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers immediately as first-line therapy, followed by intravenous adenosine if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients or those who fail pharmacological therapy. 1

Hemodynamic Assessment First

Immediately determine if the patient is hemodynamically stable or unstable, as this dictates the treatment pathway. 1

• Hemodynamically unstable patients (hypotension, altered consciousness, chest pain, severe dyspnea, syncope) require immediate synchronized cardioversion without delay for vagal maneuvers or medications. 1, 2
• Hemodynamically stable patients should proceed through the stepwise algorithm below. 1

Stepwise Treatment Algorithm for Stable Patients

Step 1: Vagal Maneuvers (Class I Recommendation)

Vagal maneuvers are the recommended first-line intervention and should be performed immediately. 1

Specific techniques include:

• Valsalva maneuver: Patient bears down against a closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure) while in the supine position. 1
• Modified Valsalva: The standard Valsalva has a 43% success rate and is more effective than carotid massage. 1, 3
• Carotid sinus massage: After confirming absence of carotid bruit by auscultation, apply steady pressure over the right or left carotid sinus for 5-10 seconds. 1
• Diving reflex: Apply an ice-cold, wet towel to the face, which can terminate SVT episodes. 1, 2
• Switching techniques: If one vagal maneuver fails, try another—this approach achieves an overall success rate of 27.7%. 1

Critical pitfall: Never apply pressure to the eyeball—this practice is dangerous and has been abandoned. 1

Step 2: Intravenous Adenosine (Class I Recommendation)

If vagal maneuvers fail, adenosine is the next recommended therapy with 90-95% effectiveness. 1, 3

• Adenosine terminates AVNRT in approximately 95% of patients and orthodromic AVRT in 90-95% of cases. 1
• Minor, brief side effects (<1 minute duration) occur in approximately 30% of patients. 1
• Adenosine serves both therapeutic and diagnostic purposes by unmasking atrial activity in other arrhythmias like atrial flutter. 1

Critical warning: Adenosine may precipitate atrial fibrillation that can conduct rapidly down an accessory pathway (in WPW syndrome) and potentially cause ventricular fibrillation, so electrical cardioversion equipment must be immediately available. 1

Step 3: Alternative Intravenous Medications (Class IIa Recommendation)

If adenosine fails or is contraindicated in hemodynamically stable patients:

• Intravenous diltiazem or verapamil: Particularly effective for converting AVNRT to sinus rhythm with 80-98% success rates. 1
• Intravenous beta blockers: Reasonable option with excellent safety profile, though less effective than calcium channel blockers. 1

Critical contraindications:

• Never use verapamil or diltiazem in wide-complex tachycardia of uncertain etiology, as this can cause hemodynamic collapse if the rhythm is ventricular tachycardia or pre-excited atrial fibrillation. 2
• Avoid AV nodal blockers (calcium channel blockers, beta blockers, adenosine) in patients with manifest accessory pathways (WPW syndrome) who develop atrial fibrillation—use procainamide or ibutilide instead, or perform immediate cardioversion. 2
• Avoid calcium channel blockers and beta blockers in patients with systolic heart failure. 1, 2

Step 4: Synchronized Cardioversion (Class I Recommendation)

Synchronized cardioversion is highly effective and recommended when:

• The patient is hemodynamically unstable at any point. 1
• Pharmacological therapy is ineffective or contraindicated in stable patients. 1
• Vagal maneuvers and adenosine fail to terminate the tachycardia. 1

Cardioversion should be performed after adequate sedation or anesthesia in stable patients. 1

Special Considerations

Pre-excited Atrial Fibrillation (WPW Syndrome)

• Immediate synchronized cardioversion for hemodynamically unstable patients. 1
• Ibutilide or intravenous procainamide for hemodynamically stable patients—never use AV nodal blocking agents. 1, 2

Post-Conversion Management

Patients often develop atrial or ventricular premature complexes immediately after conversion (whether from adenosine or cardioversion) that may reinitiate AVRT or AVNRT. 1 In this situation, an antiarrhythmic drug may be required to prevent acute reinitiation. 1

When to Escalate Care

Patients should seek emergency care if vagal maneuvers fail to terminate the episode within 15-20 minutes, if hemodynamic instability develops, or if syncope occurs during an episode. 2