What is the recommended initial and subsequent management of supraventricular tachycardia?

Managing Supraventricular Tachycardia

Immediate Assessment: Hemodynamic Stability

For hemodynamically unstable patients (hypotension, altered mental status, shock, chest pain, or acute heart failure), proceed directly to synchronized cardioversion without attempting vagal maneuvers or pharmacologic therapy. 1

• Synchronized cardioversion restores sinus rhythm in virtually all hemodynamically unstable SVT cases and should not be delayed. 1
• If the patient is hypotensive but conscious, provide immediate sedation before cardioversion. 1

First-Line Therapy for Stable Patients: Vagal Maneuvers

Vagal maneuvers are the mandatory first intervention before any drug administration in hemodynamically stable patients. 1

Recommended Techniques (in order of effectiveness):

• Modified Valsalva maneuver (most effective): Patient performs forced exhalation against a closed airway for 10–30 seconds (≈30–40 mm Hg intrathoracic pressure) while supine, then immediately lie the patient flat with legs elevated. 1, 2

  • Success rate: 43.7% for initial conversion, with 28.1% maintaining sinus rhythm at 5 minutes. 2
  • This is superior to standard Valsalva (24.2% success) and carotid massage (9.1% success). 2

• Carotid sinus massage: Apply steady pressure over the carotid sinus for 5–10 seconds after confirming absence of a bruit. 1

• Ice-water facial immersion: Place an ice-cold wet towel on the face. 1

• Critical safety warning: Never apply pressure to the eyeball. 1

• Overall success rate of vagal maneuvers across all techniques is approximately 27% in adult populations. 1

Second-Line Therapy: Adenosine

When vagal maneuvers fail, adenosine is the first-line pharmacologic agent, achieving 90–95% conversion in AVNRT and 78–96% in AVRT. 1, 3

Administration Protocol:

• Initial dose: 6 mg rapid IV push via a large proximal vein, followed immediately by a 20 mL saline flush. 1
• Second dose: If rhythm does not convert within 1–2 minutes, administer 12 mg IV push. 1
• Third dose: May repeat 12 mg once more if needed. 1

Dose Modifications:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access. 1
• Increase dose for patients with significant blood levels of theophylline, caffeine, or theobromine. 1

Absolute Contraindication:

• Do not give adenosine to patients with asthma due to risk of severe bronchospasm. 1
• Adenosine is also contraindicated in second- or third-degree AV block, sick sinus syndrome, and bronchospastic lung disease. 1

Common Side Effects:

• Flushing, dyspnea, and chest discomfort are most common but transient (lasting <60 seconds). 1

Safety Requirement:

• A defibrillator must be available when administering adenosine to any patient in whom Wolff-Parkinson-White syndrome is a consideration, due to the possibility of initiating atrial fibrillation with rapid ventricular rates. 1

Third-Line Therapy: Alternative Pharmacologic Agents

If adenosine is contraindicated (e.g., asthma) or fails, use calcium-channel blockers or beta-blockers. 1

Calcium-Channel Blockers (Preferred Alternatives):

• Diltiazem: 15–20 mg IV over 2 minutes (64–98% conversion rate for AVNRT). 1
• Verapamil: 2.5–5 mg IV over 2 minutes. 1, 4
  • Verapamil converts approximately 60% of SVT cases to sinus rhythm within 10 minutes. 4

Beta-Blockers:

• Esmolol (IV): Useful for short-term SVT control, particularly when concurrent hypertension is present. 1
• Metoprolol (IV): Acceptable alternative. 1

Critical Safety Warnings for Calcium-Channel Blockers:

Do NOT administer verapamil or diltiazem if: 1

• Ventricular tachycardia cannot be excluded (risk of hemodynamic collapse)
• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White) is present (risk of ventricular fibrillation)
• Suspected systolic heart failure exists

Fourth-Line: Synchronized Cardioversion

For stable patients where pharmacologic therapy is ineffective or contraindicated, elective synchronized cardioversion achieves near-100% termination of SVT. 1

Post-Conversion Management

Immediate Monitoring:

• Continuous cardiac monitoring is essential immediately after conversion because patients commonly experience premature complexes that may trigger recurrent SVT within seconds to minutes. 1

Treatment of Recurrence:

• For immediate recurrence: Repeat adenosine or consider a longer-acting AV nodal blocking agent (diltiazem or beta-blocker). 1
• For frequent recurrences: An antiarrhythmic drug may be required to prevent acute reinitiation. 1

Long-Term Prevention Strategy:

Catheter ablation should be considered as first-line therapy for preventing recurrent SVT, as it is the most effective, safe, and cost-effective approach. 1

• Catheter ablation has a high success rate and low complication rate, especially for AVNRT and AVRT. 5
• Alternative: Oral beta-blockers, diltiazem, or verapamil for long-term prevention of AVNRT. 1

Patient Education:

• Teach vagal maneuvers (modified Valsalva, carotid massage, ice-water facial immersion) for self-termination of future episodes. 1
• Consider "pill-in-the-pocket" therapy as a personalized, self-directed intervention. 5, 1

Special Populations

Pregnancy:

• Vagal maneuvers remain the first-line approach. 1
• Adenosine is safe and effective during pregnancy. 1
• If the patient becomes hemodynamically unstable, electrical cardioversion is indicated. 1

Adult Congenital Heart Disease (ACHD):

• IV adenosine is appropriate for SVT termination. 1
• IV diltiazem or esmolol may be used cautiously, monitoring for hypotension. 1
• Flecainide should be avoided in the presence of significant ventricular dysfunction. 1
• Acute antithrombotic therapy is recommended for atrial tachycardia or atrial flutter, following atrial fibrillation guidelines. 1

Diagnostic Considerations

• A 12-lead ECG must be obtained while the tachycardia is ongoing to differentiate SVT mechanisms and exclude ventricular tachycardia or pre-excited atrial fibrillation. 1
• Adenosine administration can unmask underlying atrial flutter or atrial tachycardia, aiding diagnosis. 1
• Continuous ECG recording during adenosine administration helps distinguish between drug failure and successful termination with immediate reinitiation. 1

Common Pitfalls to Avoid

• Never assume a wide-complex tachycardia is supraventricular—when in doubt, treat as ventricular tachycardia. 1
• Do not use calcium-channel blockers for wide-complex tachycardias unless absolutely certain of the diagnosis. 1
• Vagal maneuvers are often ineffective when performed incorrectly; ensure proper technique, especially with the modified Valsalva maneuver. 5, 2
• Monitor for recurrence after successful conversion, as SVT commonly reinitiates within minutes. 1