What is the appropriate management of supraventricular tachycardia, including acute treatment for stable versus unstable patients and long‑term prevention?

Management of Supraventricular Tachycardia

For hemodynamically unstable SVT (hypotension, altered mental status, shock, chest pain, acute heart failure), proceed immediately to synchronized cardioversion at 50–100 J without attempting vagal maneuvers or medications—this achieves near-100% termination. 1, 2

Acute Management of Hemodynamically Stable SVT

Step 1: Vagal Maneuvers (First-Line)

• Attempt vagal maneuvers before any pharmacologic therapy—the modified Valsalva maneuver is most effective, achieving 43% conversion when performed correctly. 2, 3, 4
• Modified Valsalva technique: Position the patient supine, have them bear down against a closed glottis for 10–30 seconds generating ≥30–40 mmHg intrathoracic pressure, then immediately lay them flat with legs elevated. 2, 3
• Alternative vagal maneuvers include carotid sinus massage (5–10 seconds after confirming no bruit) or ice-water facial immersion, though these are less effective than modified Valsalva. 2, 3
• Critical safety warning: Never apply pressure to the eyeball during any vagal maneuver. 2

Step 2: Adenosine (First-Line Pharmacologic Agent)

• Adenosine is the drug of choice when vagal maneuvers fail, achieving 90–95% conversion in AVNRT and 78–96% in AVRT. 1, 2, 4
• Dosing protocol:
  • Initial dose: 6 mg rapid IV push (over 1–2 seconds) via large proximal vein (antecubital preferred), followed immediately by 20 mL saline flush 1, 2
  • If no conversion in 1–2 minutes: 12 mg rapid IV push with flush 1, 2
  • If still no conversion: repeat 12 mg once more (maximum cumulative dose 30 mg) 2
• Dose adjustments:
  • Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when giving via central line 1, 2
  • Increase dose in patients with high caffeine, theophylline, or theobromine levels 1, 2
• Absolute contraindications: Asthma or bronchospastic lung disease (risk of severe bronchospasm), second- or third-degree AV block without pacemaker, sick sinus syndrome. 1, 2
• Common transient side effects (<60 seconds): Flushing, dyspnea, chest discomfort. 2

Step 3: Alternative Pharmacologic Agents (When Adenosine Fails or Is Contraindicated)

• Intravenous diltiazem is the preferred alternative, especially for patients with asthma/COPD, achieving 64–98% conversion. 1, 2, 3
  • Dose: 15–20 mg (0.25 mg/kg) IV over 2 minutes 1, 2
• Intravenous verapamil is an acceptable alternative: 2.5–5 mg IV over 2 minutes. 1, 2
• Intravenous beta-blockers (metoprolol or esmolol) may be used with caution in severe COPD:
  • Metoprolol: 2.5–5 mg every 2–5 minutes (maximum 15 mg over 10–15 minutes) 2
  • Esmolol: useful for short-term control, especially with concurrent hypertension 1

Critical safety contraindications for calcium-channel blockers and beta-blockers: Do NOT use if (1) ventricular tachycardia cannot be excluded, (2) pre-excited atrial fibrillation (WPW syndrome) is present, (3) systolic heart failure is suspected, or (4) patient is hemodynamically unstable. 1, 2

Step 4: Synchronized Cardioversion (Drug-Refractory Cases)

• When pharmacologic therapy is ineffective or contraindicated in stable patients, perform elective synchronized cardioversion, which achieves near-100% termination of AVRT and AVNRT. 1, 2, 3

Post-Conversion Management

• Monitor continuously for immediate recurrence—premature atrial or ventricular complexes commonly trigger repeat SVT episodes within seconds to minutes. 2
• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker (oral diltiazem, verapamil, or beta-blocker) to prevent reinitiation. 1, 2
• If adenosine reveals underlying atrial flutter or atrial tachycardia (by transient AV block without conversion), shift to rate control with a longer-acting AV-nodal blocker rather than attempting rhythm conversion. 2

Long-Term Prevention and Definitive Management

Catheter Ablation (First-Line Definitive Therapy)

• Catheter ablation is the most effective, safe, and cost-effective first-line therapy for preventing recurrent SVT and should be offered to all patients with symptomatic, recurrent episodes. 3, 4, 5, 6
• Single-procedure success rates are 94.3–98.5% for AVNRT and AVRT, making it superior to chronic pharmacotherapy. 4, 5
• Electrophysiologic study with ablation option is useful for both diagnosis and definitive treatment. 3

Chronic Pharmacologic Therapy (For Patients Who Decline or Are Not Candidates for Ablation)

First-line oral agents:

• Oral beta-blockers, diltiazem, or verapamil are the preferred chronic medications for patients without ventricular pre-excitation or structural heart disease. 3, 6

Second-line oral agents:

• Flecainide or propafenone are reasonable alternatives for patients without structural heart disease or coronary artery disease—these agents must never be used in patients with structural heart disease or ischemic heart disease. 3

Third-line oral agents:

• Sotalol or dofetilide may be considered for patients who fail other therapies. 3

Patient Education and Self-Management

• Teach all patients the modified Valsalva maneuver for self-termination of future episodes—this empowers patients to manage recurrences independently. 2, 3
• Consider "pill-in-the-pocket" therapy (single-dose oral diltiazem or beta-blocker) as a personalized self-directed intervention for infrequent episodes. 2

Special Populations

Pregnancy

• Vagal maneuvers remain first-line therapy in pregnant patients. 1, 3
• Adenosine is safe and effective during pregnancy and is the first-line pharmacologic agent. 1, 2, 3
• If hemodynamically unstable, proceed to electrical cardioversion, which is safe at all stages of pregnancy—apply electrode pads away from the uterus. 3
• Avoid antiarrhythmic medications, especially in the first trimester, when risk of congenital malformations is greatest. 1

Adult Congenital Heart Disease (ACHD)

• Acute antithrombotic therapy is recommended for atrial tachycardia or atrial flutter, following atrial fibrillation anticoagulation guidelines. 1
• Intravenous adenosine is appropriate for SVT termination in ACHD patients. 1
• Intravenous diltiazem or esmolol may be used cautiously, monitoring closely for hypotension. 1
• Flecainide should not be administered in ACHD patients with significant ventricular dysfunction. 1
• Catheter ablation success rates are lower (70–85%) with higher recurrence rates (20–60% within 2 years) due to complex anatomy, hypertrophied atrial tissue, and multiple reentrant circuits. 1

Diagnostic Considerations

• Obtain a 12-lead ECG during tachycardia whenever possible to confirm the mechanism, differentiate from ventricular tachycardia, and exclude pre-excited atrial fibrillation. 2, 3
• Adenosine serves a dual therapeutic-diagnostic role—it terminates SVT but can unmask underlying atrial flutter or atrial tachycardia by producing transient AV block. 2
• All patients treated for SVT should be referred to a heart rhythm specialist for long-term management planning. 6

Common Pitfalls to Avoid

• Never give calcium-channel blockers or beta-blockers if ventricular tachycardia cannot be excluded or if pre-excited atrial fibrillation (WPW) is present—this can precipitate ventricular fibrillation or hemodynamic collapse. 1, 2
• Never administer adenosine to patients with asthma—use diltiazem or verapamil instead. 1, 2
• Never apply pressure to the eyeball during vagal maneuvers. 2
• Do not delay cardioversion in unstable patients to attempt vagal maneuvers or medications. 1, 2, 3