Treatment of Supraventricular Tachycardia (SVT)

Step 1 — First: Hemodynamic Assessment

• Unstable → immediate synchronized electrical cardioversion (see below)
• Stable → proceed stepwise with vagal maneuvers, then pharmacotherapy

Step 2 — Stable SVT: Vagal Maneuvers

Contraindication: Carotid sinus massage is avoided in patients with prior stroke within 3 months, significant carotid stenosis, or any history of ventricular arrhythmia. — Harriet Lane Handbook, 23rd ed.

Step 3 — Stable SVT: Pharmacotherapy

Adenosine (first-line)

• Dose: 6 mg rapid IV bolus via large-bore IV, followed immediately by a saline flush; if no response, repeat at 12 mg
• Success rate 85–90% for AVNRT
• Mechanism: transient AV block interrupts AV-node-dependent reentry
• If adenosine terminates the tachycardia → confirms AV-node-dependent SVT (AVNRT or AVRT)
• If adenosine does NOT terminate it but slows ventricular rate → suggests atrial flutter, ectopic AT, or junctional tachycardia; treat the underlying cause

"Administration of 6 or 12 mg of adenosine to cause transient AV block is usually successful in terminating an AV nodal-dependent SVT or diagnosing a non-AV nodal-dependent SVT such as atrial tachycardia or atrial flutter." — Harrison's Principles of Internal Medicine, 22E

• Avoid if heart transplant recipient (exaggerated response)
• Use with caution if irregular wide-complex tachycardia (may be AF with WPW — can precipitate VF)
• Pediatric dosing: 0.1 mg/kg IV/IO

Refractory cases (after failed adenosine)

"In refractory cases, diltiazem, esmolol, or metoprolol are options." — Rosen's Emergency Medicine

Step 4 — Unstable SVT: Synchronized Cardioversion

• Deliver synchronized DC cardioversion
• Adults: 100–200 J (biphasic preferred)
• Children: 0.5–1 J/kg
• Sedate if patient is conscious prior to cardioversion
• For atrial flutter: often responds to as little as 20–50 J

Special Situations

SVT with Accessory Pathway (WPW syndrome)

• Acute management of orthodromic AVRT (narrow QRS): vagal maneuvers → adenosine (as for routine SVT)
• ⚠️ AVOID: verapamil, diltiazem, and digoxin in WPW with AF/flutter — they may enhance conduction through the accessory pathway and precipitate ventricular fibrillation
• ⚠️ Avoid flecainide in patients with WPW
• Unstable → immediate synchronized cardioversion
• Refer all patients with symptomatic accessory pathway for catheter ablation

"Verapamil and digoxin should not be used in this setting because they may precipitate lethal dysrhythmias." — Tintinalli's Emergency Medicine

SVT if rhythm does NOT convert with adenosine

• Consider: atrial flutter, ectopic atrial tachycardia, or junctional tachycardia
• Rate control: calcium channel blockers or β-blockers (use β-blockers cautiously in pulmonary disease or CHF)
• Treat underlying cause; seek expert consultation

Long-Term Management (Recurrent SVT)

"Pill in the Pocket" (self-treatment for infrequent, well-tolerated SVT)

• Diltiazem or β-blocker taken at onset of palpitations
• Class I recommendation for infrequent AVNRT in patients who do not want ongoing medication or ablation

Summary Algorithm

SVT identified on ECG
        │
        ├── UNSTABLE ──────────────► Synchronized cardioversion
        │                            (adults: 100–200 J biphasic; child: 0.5–1 J/kg)
        │
        └── STABLE ─────────────────►
                │
                ▼
        Vagal maneuvers (modified Valsalva preferred)
                │
          Converts?── Yes ──► Observe; treat recurrence with adenosine or CCB/β-blocker
                │
                No
                ▼
        Adenosine 6 mg IV rapid bolus + flush
        (repeat 12 mg if no effect)
                │
          Converts?── Yes ──► Probable AVNRT/AVRT; observe, discharge with follow-up
                │
                No
                ▼
        Diltiazem / Esmolol / Metoprolol IV
        Consider cardiology consultation
                │
        Still refractory or instability develops?
                │
                ▼
        Synchronized cardioversion