What is the purpose of using adenosine (adenosine) after electrophysiology (EP) ablation?

Adenosine Use After Electrophysiology Ablation

Adenosine is administered after EP ablation to unmask "dormant conduction" - the phenomenon where ablated pathways appear electrically silent but can resume conduction under specific conditions, identifying patients at high risk for arrhythmia recurrence who need additional ablation. 1, 2

Primary Mechanism and Rationale

Adenosine testing reveals incomplete ablation lesions by inducing transient AV nodal block, which unmasks residual conduction through ablated pathways that would otherwise remain hidden during standard post-ablation assessment. 3

• Adenosine causes membrane hyperpolarization and temporary recovery of excitability in stunned but viable tissue at ablation sites 1
• During the bradycardia phase induced by adenosine, dormant pathways can conduct when AV nodal conduction is blocked, revealing incomplete lesion sets 1
• This mechanism differs from adenosine's primary therapeutic use (terminating SVT via AV nodal blockade) - here it serves as a provocative diagnostic test 4, 3

Clinical Applications by Ablation Type

Accessory Pathway Ablation

Dormant accessory pathway conduction occurs in approximately 12% of patients after apparently successful ablation and predicts an 8.5-fold increased risk of requiring repeat ablation. 1

• Adenosine unmasks both anterograde and retrograde accessory pathway conduction that appears eliminated by standard testing 1, 3
• In patients with pre-excitation, adenosine (12-24 mg IV) produces high-grade AV block with maximal pre-excitation if the pathway remains viable 3
• Complete pathway ablation is confirmed when adenosine produces both AV block during atrial pacing AND VA block during ventricular pacing 3
• Transient adenosine-induced pathway conduction predicts late clinical recurrence requiring repeat intervention 5

Atrial Flutter Ablation (Cavotricuspid Isthmus)

Adenosine reveals dormant CTI conduction in approximately 9% of patients after achieving bidirectional block, identifying a subgroup with 43% recurrence risk versus 1.3% in adenosine-negative patients (32-fold increased risk). 2

• Standard pacing maneuvers confirm bidirectional CTI block, but adenosine can still unmask transient or persistent conduction resumption 2
• Patients with positive adenosine challenge have dramatically higher flutter recurrence rates (relative risk 31.7) 2
• Additional ablation should be performed for persistent (but not necessarily transient) resumption of conduction 2

Pulmonary Vein Isolation for Atrial Fibrillation

Dormant PV conduction occurs in 28% of patients (16.5% of individual veins) after apparent isolation, but only when adenosine produces AV block - making adequate dosing critical. 6

• All cases of dormant PV conduction occur during AV block (100% sensitivity), making AV block achievement essential for valid testing 6
• Optimal dosing requires 18-24 mg IV to reliably produce AV block in most patients 6
• Critical caveat: Patients >110 kg have significantly reduced AV block rates (65% vs 91%), requiring higher doses or alternative assessment 6

Practical Administration Protocol

Administer adenosine as rapid IV bolus (12-24 mg) through large peripheral vein followed immediately by 20 mL saline flush, with continuous ECG monitoring to document both AV block and any pathway reconnection. 4, 6

• Initial dose: 12 mg for most patients, but reduce to 3 mg if patient takes dipyridamole/carbamazepine or has transplanted heart 4
• Escalate to 18-24 mg if initial dose fails to produce AV block, as dormant conduction cannot be assessed without AV block 6
• Monitor for transient side effects (flushing, dyspnea, chest discomfort) which resolve within seconds due to adenosine's 10-second half-life 4
• Document timing of any pathway conduction relative to AV block onset - conduction during bradycardia phase confirms dormant pathway 1

Clinical Decision-Making Algorithm

1. Confirm apparent procedural success by standard criteria (bidirectional block, loss of pre-excitation, PV isolation) 7, 3

2. Administer adenosine challenge with continuous ECG recording to capture transient events 4, 6

3. Verify adequate AV block occurred - without AV block, test is invalid and cannot exclude dormant conduction 6

4. If dormant conduction appears:

   • Persistent conduction → Perform additional ablation immediately 2
   • Transient conduction → Consider additional ablation given high recurrence risk, though some operators ablate only persistent conduction 1, 2

5. If no dormant conduction with adequate AV block → Proceed with standard post-ablation monitoring 3

Important Caveats and Pitfalls

• Weight-based dosing failure: Standard 12 mg doses produce inadequate AV block in patients >110 kg, creating false-negative results 6
• Timing is critical: Dormant conduction appears specifically during the bradycardia phase; missing this window yields false reassurance 1
• Contraindications must be respected: Avoid in asthma patients (bronchospasm risk) and use extreme caution in WPW with atrial fibrillation history 4
• Hemodynamic effects: Mean blood pressure drops 22-27 mmHg across dose ranges, requiring monitored setting 6
• Not universally adopted: Despite evidence of prognostic value, adenosine testing remains controversial and is not mandated by current guidelines, representing an area of evolving practice 7, 6