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

Initial Treatment for Supraventricular Tachycardia (SVT)

Vagal maneuvers should be performed first in hemodynamically stable patients with SVT, with the modified Valsalva maneuver being the most effective technique, followed by adenosine if vagal maneuvers fail, and immediate synchronized cardioversion for hemodynamically unstable patients. 1, 2

Immediate Assessment and Stabilization

First, determine hemodynamic stability—look for hypotension, altered mental status, chest pain, or acute heart failure. 1

For Hemodynamically Unstable Patients

Perform immediate synchronized cardioversion without delay. 1, 2 This is the Class I recommendation when patients show signs of hemodynamic compromise, as pharmacological therapy takes too long and may be ineffective in unstable patients. 1

For Hemodynamically Stable Patients

Step 1: Vagal Maneuvers (First-Line)

Vagal maneuvers are the recommended initial intervention and should be performed with the patient in the supine position. 1, 2

The modified Valsalva maneuver is the most effective vagal technique, with significantly higher success rates than standard techniques:

• Modified Valsalva maneuver achieves 43-55% conversion rate and is 5.47 times more effective than carotid sinus massage 3, 4
• Perform by having the patient bear down against a closed glottis for 10-30 seconds, generating at least 30-40 mm Hg of intrathoracic pressure 1, 2

Alternative vagal maneuvers if modified Valsalva fails:

• Carotid sinus massage: Apply steady pressure over the carotid sinus for 5-10 seconds, but only after confirming absence of carotid bruits by auscultation 1, 2
• Cold stimulus (diving reflex): Apply an ice-cold, wet towel to the face 1, 2

Switching between different vagal maneuver techniques increases overall success to approximately 27.7%. 2

Critical Pitfall to Avoid

Never apply pressure to the eyeball—this practice is dangerous and has been abandoned. 1, 2

Step 2: Adenosine (First-Line Pharmacotherapy)

If vagal maneuvers fail, adenosine is the recommended first-line drug with 91-95% effectiveness. 1, 2, 4 Adenosine serves both therapeutic and diagnostic purposes, terminating AVNRT in approximately 95% of patients while unmasking atrial activity in other arrhythmias like atrial flutter. 1

Step 3: Alternative Pharmacological Agents

If adenosine fails or is contraindicated in hemodynamically stable patients:

Intravenous calcium channel blockers (diltiazem or verapamil) are highly effective for converting AVNRT to sinus rhythm (Class IIa recommendation). 1, 2 These agents have 80-98% success rates but should only be used after confirming the rhythm is not ventricular tachycardia or pre-excited atrial fibrillation. 1

Intravenous beta-blockers are reasonable alternatives (Class IIa recommendation), though they are less effective than calcium channel blockers. 1, 2

Critical Warnings About AV Nodal Blocking Agents

Avoid verapamil, diltiazem, and beta-blockers in patients with suspected pre-excitation (Wolff-Parkinson-White syndrome), as these agents may accelerate ventricular rate and precipitate ventricular fibrillation. 2, 5 In patients with pre-excited atrial fibrillation who are hemodynamically stable, use intravenous procainamide or ibutilide instead (Class I recommendation). 2

Step 4: Synchronized Cardioversion for Refractory Cases

If pharmacological therapy fails in hemodynamically stable patients, proceed to synchronized cardioversion (Class I recommendation). 1 Most stable patients respond to initial drug therapy, but in rare resistant cases where a second drug bolus or higher dose fails, cardioversion becomes necessary. 1

Key Clinical Pearls

• Proper ECG diagnosis before treatment is essential to distinguish SVT from ventricular tachycardia, as treatment approaches differ dramatically 2
• AVNRT is the most common form of SVT, typically occurring in young adults without structural heart disease, with ventricular rates of 180-200 bpm 1
• The condition is rarely life-threatening but patients present with sudden onset palpitations, possible shortness of breath, dizziness, and neck pulsations 1