Management of Supraventricular Tachycardia After Failed Vagal Maneuvers
Adenosine is the next step in treating supraventricular tachycardia when vagal maneuvers fail, administered as a 6 mg IV rapid bolus via proximal IV access. 1
Adenosine Administration Protocol
- Initial dose: 6 mg IV rapid bolus via proximal IV access
- If ineffective: Increase to 12 mg IV rapid bolus
- If still ineffective: May administer another 12 mg dose
- Success rate: 90-95% for terminating SVT 1
Administration Technique
- Administer as a rapid bolus
- Follow immediately with a saline flush
- Use proximal IV access to ensure rapid delivery to the heart
- Have patient raise arms during administration to enhance delivery
Alternative Pharmacological Options (If Adenosine Fails)
Calcium Channel Blockers
- Diltiazem or Verapamil IV (Class IIa, LOE B-R)
- Effectiveness: 64-98% termination rate 1
- Contraindications:
- Suspected systolic heart failure
- Hypotension
- Pre-excited atrial fibrillation
- Ventricular tachycardia
Beta Blockers
- Esmolol, Metoprolol, or Propranolol IV (Class IIa, LOE C-LD) 1
- Esmolol dosing: 500 mcg/kg as bolus over 1 minute, followed by maintenance infusion of 50 mcg/kg/min 2
- Contraindications:
- Severe conduction abnormalities
- Sinus node dysfunction
- Bronchospastic disease
Amiodarone
- Consider if other options fail
- Initial dose: approximately 1000 mg during first 24 hours
- Followed by maintenance infusion of 0.5 mg/min 1
- Requires close monitoring due to risk of hypotension
Special Considerations
Hemodynamic Instability
- If patient shows signs of hypotension, altered mental status, shock, or severe chest pain, proceed directly to synchronized cardioversion 1
Pre-excited Atrial Fibrillation
- Avoid adenosine in patients with known WPW syndrome and pre-excited atrial fibrillation
- Have a defibrillator available when administering adenosine due to risk of initiating atrial fibrillation with rapid ventricular rates 1
Potential Complications of Adenosine
- Transient AV block (occurs in approximately 6% of patients) 3
- Rare but serious: ventricular fibrillation (even in structurally normal hearts) 4
- Bronchospasm in patients with reactive airway disease 3
- Flushing, dyspnea, and chest discomfort (occur in about 20% of patients) 5
Long-term Management
- All patients should be referred for heart rhythm specialist evaluation after acute management 6
- Catheter ablation is recommended as first-line method for long-term management of recurrent, symptomatic SVT 7
- For chronic management, oral beta-blockers or calcium channel blockers may be used until definitive treatment 1
Prognostic Considerations
A prognostic index can help identify patients less likely to respond to adenosine:
- Formula: (age/heart rate at admission) + number of past SVT episodes
- High values suggest lower likelihood of response to adenosine 8
Remember that adenosine remains the drug of choice for acute therapy of SVT when vagal maneuvers fail, as recommended by the 2019 ESC guidelines 9. However, always be prepared for potential adverse reactions by having resuscitation equipment readily available.