What are antegrade (current) and retrograde (contracurrent) pacing maneuvers to reveal an accessory pathway?

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Antegrade and Retrograde Pacing Maneuvers to Reveal Accessory Pathways

Antegrade (current) pacing involves atrial pacing to assess anterograde accessory pathway conduction, while retrograde (contracurrent) pacing involves ventricular pacing to assess retrograde accessory pathway conduction—both are fundamental electrophysiologic techniques used during EP studies to identify, localize, and characterize accessory pathways in patients with suspected Wolff-Parkinson-White syndrome or concealed pathways.

Understanding the Terminology

The terms "current" and "contracurrent" refer to the direction of electrical impulse propagation relative to normal cardiac conduction:

  • Antegrade (current) pacing: Stimulating from the atrium to assess forward conduction through an accessory pathway toward the ventricle—following the normal direction of cardiac activation
  • Retrograde (contracurrent) pacing: Stimulating from the ventricle to assess backward conduction through an accessory pathway toward the atrium—opposite to normal cardiac activation

Antegrade Pacing Maneuvers

Purpose

To identify and validate manifest accessory pathways that conduct in the anterograde direction, demonstrating pre-excitation 1.

Key Techniques

Atrial extrastimulus pacing is performed to:

  1. Induce complete block between the atrial electrogram and the accessory pathway potential (APP): This is the only specific validation criterion for confirming a true anterograde APP, as it cannot be achieved with split atrial electrograms 2

  2. Induce complete block between the APP and ventricular electrogram: While this can be achieved, it is not specific for accessory pathways since it can also occur with split atrial electrograms 2

  3. Assess anterograde concealed conduction: Simultaneous AV pacing can demonstrate anterograde concealment into concealed pathways by shortening their effective refractory period, particularly when pacing near the pathway location 3

Critical Pitfall

Three of the four commonly used validation maneuvers for anterograde APPs are not specific—they can produce false-positive results with split atrial electrograms. Only the ability to induce complete block between the atrial electrogram and the suspected APP reliably confirms a true accessory pathway 2.

Retrograde Pacing Maneuvers

Purpose

To identify concealed accessory pathways (conducting only retrogradely) and localize all types of accessory pathways based on atrial activation patterns 1.

Key Techniques

Ventricular pacing at multiple cycle lengths to:

  1. Map retrograde atrial activation patterns: The site of earliest atrial activation and the interval from this site to the His bundle atrial electrogram (delta A) characterizes pathway location:

    • Left lateral: 66 ± 17 ms
    • Left posterior: 50 ± 8 ms
    • Posteroseptal: 33 ± 7 ms
    • Right free wall: 22 ± 15 ms
    • Anteroseptal: 0 ± 0 ms 4

  2. Perform ventricular extrastimulus testing: Assess the effective refractory period of the accessory pathway and distinguish it from AV nodal conduction

  3. Execute parahisian pacing: Vary pacing output at the His bundle region without changing catheter position or cycle length to differentiate septal accessory pathways from AV nodal conduction, and identify free-wall pathways, intermittent conduction, and multiple pathways 5

  4. Apply dual-chamber sequential extrastimulation: Use an atrial extrastimulus at AV nodal effective refractory period followed by ventricular pacing to unmask slowly conducting concealed pathways that remain hidden with standard maneuvers. This technique exploits anterograde concealed conduction to prolong AV nodal refractoriness (mean 138 ± 46 ms) much more than accessory pathway refractoriness (mean 12 ± 8 ms), allowing the pathway to become manifest 6

Critical Consideration

When performing ventricular pacing, retrograde fusion with concomitant AV nodal conduction can obscure the true accessory pathway location. The delta A interval must be comparable during both ventricular pacing and orthodromic tachycardia to ensure accurate localization 4.

Clinical Context

These pacing maneuvers are essential components of EP studies performed during catheter ablation procedures, which have high success rates for accessory pathway elimination 1. The ACC/AHA/HRS guidelines emphasize that EP study is necessary to establish the diagnosis of rare accessory pathway variants including atriofascicular (Mahaim), nodofascicular, nodoventricular, and fasciculoventricular pathways 1.

Manifest pathways conducting anterogradely pose a risk of sudden cardiac death (10-year risk 0.15-0.24%) when rapid conduction occurs during atrial fibrillation, particularly with shortest pre-excited R-R intervals <250 ms 1. This underscores the importance of accurate pathway characterization through comprehensive pacing protocols.

References

5
Research

Parahisian pacing: technique, utility, and pitfalls.

Journal of interventional cardiac electrophysiology : an international journal of arrhythmias and pacing, 2014

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