Initial Treatment for Supraventricular Tachycardia (SVT)
Vagal maneuvers should be performed immediately as first-line treatment, followed by intravenous adenosine if vagal maneuvers fail, and synchronized cardioversion if the patient is hemodynamically unstable or pharmacologic therapy is ineffective. 1
Immediate First-Line: Vagal Maneuvers
Vagal maneuvers are the recommended initial intervention and should be attempted before any pharmacologic therapy in hemodynamically stable patients. 1
Technique Specifics:
Valsalva maneuver: Patient bears down against a closed glottis for 10-30 seconds while supine, generating intrathoracic pressure of at least 30-40 mmHg 1
Carotid sinus massage: After confirming absence of carotid bruit by auscultation, apply steady pressure over the right or left carotid sinus for 5-10 seconds 1
Diving reflex: Apply an ice-cold, wet towel to the face, or facial immersion in water at 10°C (50°F) 1
Never apply pressure to the eyeball - this practice is dangerous and has been abandoned 1
Second-Line: Adenosine
If vagal maneuvers fail, adenosine is the recommended pharmacologic agent with 78-96% success rates for AVNRT and AVRT. 1
Dosing Protocol:
- Initial dose: 6 mg rapid IV bolus through a proximal/large vein, followed immediately by saline flush 1, 2
- If ineffective, administer 12 mg rapid IV bolus (up to 2 doses) 1
- Recent evidence suggests starting with 12 mg may be more effective (54.2% vs 40.6% conversion rate with 6 mg initial dose) 3
Critical Considerations:
- Administer via proximal IV with rapid bolus followed by saline flush 1
- Continuous ECG recording during administration helps distinguish failure to terminate versus successful termination with immediate reinitiation 1
- Have cardioversion equipment immediately available - adenosine may precipitate atrial fibrillation that could conduct rapidly in patients with accessory pathways 1, 4
- Side effects (chest discomfort, shortness of breath, flushing) are common but brief due to very short half-life 1
Alternative Pharmacologic Agents (If Adenosine Fails)
Intravenous beta blockers (metoprolol, propranolol), diltiazem, or verapamil are reasonable alternatives in hemodynamically stable patients. 1
Important Caveats:
- Never use verapamil or diltiazem in pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White with AF) - they can accelerate ventricular rate and cause hemodynamic collapse 1, 4
- For pre-excited AF, use ibutilide or IV procainamide if hemodynamically stable 1
- Use extreme caution with rate-controlling agents in patients with low baseline heart rates 4
Synchronized Cardioversion
Synchronized cardioversion is the treatment of choice for hemodynamically unstable patients and should be performed immediately without delay for pharmacologic therapy. 1
Indications:
- Immediate cardioversion: Hemodynamically unstable patients (hypotension, altered mental status, chest pain, acute heart failure) 1
- Elective cardioversion: Hemodynamically stable patients when pharmacologic therapy fails or is contraindicated 1
- Consider earlier in patients with low baseline heart rates who may not tolerate pharmacologic interventions 4
Energy Dosing:
- Initial energy: 50-100 joules for SVT 4
- Perform after adequate sedation/anesthesia in stable patients 1
Critical Pitfalls to Avoid
- Do not skip vagal maneuvers - they are safe, effective, and avoid medication side effects 1
- Do not use AV nodal blockers (beta blockers, calcium channel blockers) in pre-excited AF - use procainamide or ibutilide instead, or proceed directly to cardioversion 1, 4
- Do not delay cardioversion in unstable patients - synchronized cardioversion should be performed immediately 1
- Prepare for post-conversion arrhythmias - atrial or ventricular premature complexes may trigger recurrent SVT after successful conversion 1
- Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia) may not respond to cardioversion and require different approaches 4