What is the initial treatment for supraventricular tachycardia?

Initial Treatment for Supraventricular Tachycardia

Begin with vagal maneuvers immediately in all hemodynamically stable patients with SVT, followed by intravenous adenosine if vagal maneuvers fail, and proceed directly to synchronized cardioversion in any hemodynamically unstable patient. 1

Immediate Assessment and Treatment Algorithm

Step 1: Assess Hemodynamic Stability

• If hemodynamically unstable (hypotension, altered consciousness, chest pain, severe dyspnea, or syncope): proceed directly to synchronized cardioversion without attempting vagal maneuvers or medications 1, 2
• If hemodynamically stable: begin with vagal maneuvers 1

Step 2: Vagal Maneuvers (First-Line for Stable Patients)

The modified Valsalva maneuver is the most effective vagal technique, with significantly higher success rates than standard carotid sinus massage 3. The ACC/AHA/HRS guidelines recommend vagal maneuvers as Class I, Level B evidence for acute SVT treatment 1.

Technique specifics:

• Modified Valsalva maneuver: Patient bears down against a closed glottis for 10-30 seconds (generating at least 30-40 mm Hg intrathoracic pressure) while supine, then immediately lies flat with legs elevated 1, 3
• Standard Valsalva: Less effective than the modified version, with only 27.7% overall success rate when combined with carotid massage 1
• Carotid sinus massage: Apply steady pressure over right or left carotid sinus for 5-10 seconds after confirming absence of bruit by auscultation 1
• Ice-cold towel to face: Apply ice-cold wet towel to activate diving reflex; facial immersion in 10°C water is effective in laboratory settings 1, 2

Critical safety note: Never apply pressure to the eyeball—this practice is dangerous and abandoned 1

Step 3: Adenosine (Second-Line for Stable Patients)

If vagal maneuvers fail, adenosine is the next intervention, with 90-95% effectiveness for terminating SVT 1. This is a Class I, Level B recommendation from ACC/AHA/HRS 1.

Dosing and administration:

• Rapid IV bolus via peripheral line 4
• Have electrical cardioversion equipment immediately available, as adenosine may precipitate atrial fibrillation that conducts rapidly to ventricles and potentially causes ventricular fibrillation 1

Common adverse effects (occurring in ~30% of patients): flushing, chest discomfort, shortness of breath, headache, throat/neck/jaw discomfort, gastrointestinal discomfort, dizziness—all brief (<1 minute duration) 1, 4

Step 4: Alternative Pharmacologic Options (If Adenosine Fails or Contraindicated)

For hemodynamically stable patients when adenosine is ineffective:

• Intravenous diltiazem or verapamil: 80-98% success rates for SVT conversion 1
• Intravenous beta blockers: Reasonable alternative with excellent safety profile, though less effective than calcium channel blockers 1
• Oral beta blockers, diltiazem, or verapamil: May be reasonable when IV access unavailable, particularly combined with continued vagal maneuvers 1

Step 5: Synchronized Cardioversion

Indications for cardioversion:

• Immediate: Any hemodynamically unstable patient 1
• After failed pharmacotherapy: Stable patients who don't respond to medications or have contraindications 1
• Perform after adequate sedation/anesthesia in stable patients 1

Critical Safety Warnings

Pre-Excited Atrial Fibrillation (Wolff-Parkinson-White Syndrome)

Never use AV nodal blocking agents (adenosine, verapamil, diltiazem, beta blockers) in patients with wide-complex tachycardia or known accessory pathways, as these can precipitate ventricular fibrillation 2, 5. Instead:

• If unstable: immediate synchronized cardioversion 1
• If stable: use IV procainamide or ibutilide 1, 2

Contraindications to Calcium Channel Blockers

• Systolic heart failure: Avoid verapamil and diltiazem 1, 2
• Wide-complex tachycardia of uncertain etiology: Can cause hemodynamic collapse if rhythm is ventricular tachycardia 2
• Second- or third-degree AV block: Unless functioning pacemaker present 4

Drug Interactions

• Methylxanthines (caffeine, aminophylline, theophylline): Interfere with adenosine activity 4
• Dipyridamole: Increases adenosine activity 4

When to Escalate Care

Instruct patients to seek emergency care if: 2

• Vagal maneuvers fail to terminate episode within 15-20 minutes
• Hemodynamic instability develops (hypotension, altered consciousness, chest pain, severe dyspnea)
• Syncope occurs during episode