How to Administer Adenosine in SVT
Adenosine should be administered as a rapid 6 mg intravenous bolus through a proximal (large-bore) IV line, immediately followed by a 20 mL saline flush, with the patient supine and continuous ECG monitoring. 1, 2
Administration Technique
Standard Dosing Protocol
- Initial dose: 6 mg IV rapid bolus
- If unsuccessful: 12 mg IV rapid bolus (may repeat once)
- Maximum cumulative dose: Up to 12 mg per attempt 1, 3
Critical Technical Points
IV Access and Injection Site:
- Use a proximal/large-bore peripheral IV (antecubital or higher) 2
- Avoid distal hand or wrist IVs—adenosine's ultra-short half-life (seconds) means it may be metabolized before reaching the heart if given distally
- If using a central line, reduce initial dose to 3 mg (77% success rate vs 37% peripherally) 4
Injection Technique:
- Administer as a rapid bolus push (not slow infusion)
- Immediately follow with 20 mL normal saline flush using the double-syringe technique
- Push the saline flush rapidly to propel adenosine into central circulation 1, 2
Patient Positioning:
Essential Monitoring and Safety
Before Administration:
- Confirm continuous ECG monitoring is in place 2
- Have electrical cardioversion equipment immediately available (adenosine can precipitate atrial fibrillation with rapid ventricular response or ventricular fibrillation in pre-excited patients) 2
- Ensure resuscitation equipment is at bedside 1
During/After Administration:
- Record continuous ECG strip during and after injection to capture:
- Successful termination vs. failure
- Immediate reinitiation of tachycardia
- Unmasking of underlying atrial flutter or atrial tachycardia 2
Expected Outcomes and Timing
Efficacy:
- 90-95% success rate for AVNRT and orthodromic AVRT 1, 2
- Average time to conversion: 30 seconds 3
- First 6 mg dose succeeds in 57-80% of cases 5, 6, 3
- Cumulative success with 6 mg then 12 mg: 93-94% 3
Common Side Effects (occur in ~30-36% but last <1 minute):
- Chest discomfort, dyspnea, flushing, throat tightness 2, 3
- These are expected and brief—warn the patient beforehand
Clinical Algorithm
First-line: Attempt vagal maneuvers (Valsalva, carotid massage) 1, 2
If vagal maneuvers fail:
- Adenosine 6 mg rapid IV bolus + immediate 20 mL saline flush
- Wait 1-2 minutes
If no conversion:
- Adenosine 12 mg rapid IV bolus + immediate 20 mL saline flush
- May repeat 12 mg dose once if needed
If adenosine fails or contraindicated:
Critical Contraindications and Pitfalls
Absolute Contraindications:
- Second- or third-degree AV block (without pacemaker)
- Sick sinus syndrome (without pacemaker)
- Asthma or bronchospastic lung disease
- Known hypersensitivity to adenosine 7
Major Pitfall—Pre-excited Atrial Fibrillation:
- DO NOT give adenosine if you suspect pre-excited AF (irregular wide-complex tachycardia in WPW)
- Adenosine can precipitate ventricular fibrillation in this setting 2
- Use synchronized cardioversion or procainamide/ibutilide instead 2
Drug Interactions:
- Methylxanthines (caffeine, theophylline, aminophylline) antagonize adenosine—may need higher doses 7
- Dipyridamole and carbamazepine potentiate adenosine—consider lower initial dose (3 mg) 7
Weight-Based Dosing Consideration
Recent evidence suggests weight-based dosing (≥0.1 mg/kg) may improve first-dose success rates without increasing adverse effects 8. However, the 2015 ACC/AHA/HRS guidelines remain the standard with fixed 6 mg and 12 mg doses 1. For patients >120 kg, consider starting with 12 mg if the 6 mg dose fails, rather than repeating 6 mg.
Hemodynamically Unstable Patients
If the patient is hemodynamically unstable (hypotension, altered mental status, shock, acute heart failure):
- Synchronized cardioversion is first-line 1, 2
- However, adenosine may be attempted first if immediately available and the patient has not yet deteriorated to cardiovascular collapse 2, 9
- Recent data suggests adenosine can be safely attempted in unstable SVT before cardioversion, potentially avoiding sedation risks 9