Why we use it
Adenosine is an endogenous nucleoside that hyperpolarizes AV-nodal tissue via A1 receptors, producing a brief, profound block at the AV node and slowing of the sinus node. The block is dramatic and short. That short window is exactly what makes adenosine so useful — we can stop a re-entrant SVT, expose an underlying atrial rhythm, or watch for dormant conduction without committing to a long pharmacologic effect.
Indication in the lab
- Terminating AV-nodal-dependent SVT (AVNRT, AVRT) — both diagnostic and therapeutic
- Unmasking atrial flutter or atrial tachycardia hiding behind 2:1 conduction
- PV reconnection testing after isolation — adenosine can transiently restore conduction across an incomplete line
- Accessory pathway testing — pre-excitation behavior under AV block can localize and characterize pathways
- Differential for wide-complex tachycardia in selected stable patients (use with care)
Dose and route
- Standard peripheral push: 6 mg rapid IV, immediately followed by a 10–20 mL saline flush.
- Repeat dose: 12 mg if the first dose doesn’t work; can give a second 12 mg.
- Central line dose: halve it (start at 3 mg) — closer delivery means a bigger hit.
- Pediatric dose: 0.1 mg/kg, then 0.2 mg/kg if needed.
Technique matters: use a stopcock with adenosine and the saline flush set up so the flush goes in within a second of the push. A slow push = no effect.
Onset and duration
- Onset: 10–20 seconds (one circulation time).
- Peak effect: a few seconds.
- Total duration: under 30 seconds.
Monitoring
- Continuous ECG with a printed strip or saved recording — review what happened during the pause
- Continuous BP and SpO2
- Pacing capability available (transcutaneous pads on, or temp wire in)
- A second team member at the patient’s head to coach them through the symptoms
What the patient feels
Warn before the push:
- “You’ll feel a wave of heat, maybe chest pressure or shortness of breath, and a strong sense that something is wrong. It lasts about 10 seconds and then it’s gone.”
- Many patients say this is the worst part of the case. Brief but intense.
Side effects to watch for
- Bronchospasm — caution or avoid in active asthma; theophylline and caffeine blunt the effect
- Profound bradycardia or asystole — usually self-limited, but be ready to pace
- Atrial fibrillation triggered by the push — short-lived in most, but a known complication
- Hypotension — brief, almost always resolves with the half-life
- Pre-excited AF — adenosine in WPW with AF can accelerate ventricular response via the accessory pathway. Avoid in this setting.
Cautions and interactions
- Heart transplant recipients — denervated supersensitive hearts; reduce dose by ~75%
- Dipyridamole — blocks reuptake, dramatically prolongs and intensifies effect
- Carbamazepine — potentiates AV block
- Methylxanthines (caffeine, theophylline) — antagonize; may need higher dose
Reversal
No specific reversal needed in practice — half-life is too short. If a prolonged pause occurs, transcutaneous or transvenous pacing bridges the gap. Aminophylline can theoretically antagonize but is rarely needed.
Common pitfalls
- Pushing slowly — the drug is metabolized before it reaches the heart.
- Not having the saline flush ready in the same syringe pathway.
- Forgetting to save the strip — the diagnostic value lives in that 10-second window.
- Giving full peripheral dose down a central line.