Adenosine Use for SVT Post-Cardiac Arrest
Adenosine can be used for SVT post-cardiac arrest if the patient is hemodynamically stable with a regular, narrow QRS complex tachycardia, but synchronized cardioversion should be immediately available and is preferred if the patient remains unstable. 1
Hemodynamic Status Determines Treatment Approach
Hemodynamically Unstable Patients
- Synchronized cardioversion is the primary recommendation for any SVT causing hypotension, acutely altered mental status, signs of shock, chest pain, or acute heart failure 1
- Adenosine may be considered first only if the tachycardia is regular with a narrow QRS complex, but cardioversion equipment must be immediately available 1
- The ACC/AHA/HRS guidelines explicitly state that cardioversion should be performed when adenosine and vagal maneuvers are "ineffective or not feasible" in unstable patients 1
Hemodynamically Stable Patients
- Adenosine is the recommended first-line pharmacologic agent after vagal maneuvers, with 90-95% success rates for terminating AVNRT and AVRT 1, 2
- Initial dose: 6 mg rapid IV push via large proximal vein, followed immediately by 20 mL saline flush 2
- If no conversion within 1-2 minutes: 12 mg IV push, may repeat once 2
Critical Safety Considerations in Post-Arrest Context
Why Caution is Warranted Post-Arrest
- Post-cardiac arrest patients often have ongoing hemodynamic instability, myocardial stunning, and altered pharmacokinetics that make them higher risk 1
- Adenosine can precipitate atrial fibrillation (1-15% incidence), which may conduct rapidly in patients with accessory pathways and potentially trigger ventricular fibrillation 1
- A defibrillator must be immediately available when administering adenosine, particularly if Wolff-Parkinson-White syndrome is a consideration 2
Contraindications and Precautions
- Do not use adenosine in patients with severe asthma (risk of bronchospasm) 2
- Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, or those with transplanted hearts 2
- Larger doses may be required in patients with significant theophylline or caffeine levels 2
Practical Algorithm for Post-Arrest SVT
Assess hemodynamic stability immediately: Check blood pressure, mental status, signs of shock, chest pain, heart failure symptoms 1
If unstable: Proceed directly to synchronized cardioversion after appropriate sedation 1
- Exception: May attempt adenosine first if rhythm is regular, narrow QRS, and cardioversion is immediately available 1
If stable with regular narrow-complex tachycardia:
If wide-complex tachycardia: Treat as ventricular tachycardia unless proven otherwise; adenosine should be used with extreme caution 1
Evidence Supporting Use Post-Arrest
A case report documented successful adenosine conversion of SVT occurring after resuscitation from ventricular fibrillation with high-dose epinephrine, demonstrating feasibility in the post-arrest setting 3. A recent 2025 multicentre study found adenosine safe in unstable prehospital SVT patients, though electrical cardioversion had higher success rates (weighted OR 2.41) 4. Importantly, no complications occurred in either treatment group 4.
Common Pitfalls to Avoid
- Do not delay cardioversion in truly unstable patients to attempt adenosine 1
- Do not use calcium channel blockers or beta blockers if there is any possibility of ventricular tachycardia or pre-excited atrial fibrillation, as these can cause hemodynamic collapse 1
- Do not assume narrow-complex tachycardia is always SVT in post-arrest patients; continuous ECG monitoring is essential 2
- Be prepared for immediate recurrence after conversion; atrial or ventricular premature complexes may reinitiate tachycardia 1