March 3, 2026Heart Rhythm0 citations

Line of block: A simple pacing maneuver to distinguish AV nodal from accessory pathway ventriculoatrial conduction

AMAhmed T. Mokhtar ASAllan C. Skanes PLPeter Leong-Sit

Key Points

The pacing maneuver effectively distinguishes between AV nodal and accessory pathway conduction types.
This method demonstrates a success rate of over 90% in identifying the conduction pathway.

Structured PICO

Does the 'line of block' pacing maneuver distinguish AV nodal from accessory pathway ventriculoatrial conduction in patients undergoing an EP study?

Population

24 patients undergoing an electrophysiology (EP) study between October 2023 and April 2025, including 10 with proven accessory pathways and 14 without.

Intervention

Line of block pacing maneuver (measuring stimulation-to-atrial time from basal RV [SA1] and 2-3cm deeper towards apex [SA2] to calculate Δ SA1-SA2)

Comparator

Patients without an accessory pathway (AV nodal conduction)

Outcome

Difference in stimulation-to-atrial time (Δ SA1-SA2) to distinguish AV nodal from accessory pathway conductionsurrogate

The 'line of block' pacing maneuver perfectly discriminated between accessory pathway and AV nodal conduction by comparing stimulation-to-atrial times from the basal and apical right ventricle.

Abstract

BACKGROUND Septal accessory pathways (AP), including concealed APs can be difficult to diagnose using standard EP maneuvers. We introduce a simple technique utilizing the "line of block" concept that can potentially added to the list of standard maneuvers in cases where the presence of a septal AP is suspected. OBJECTIVE To determine the efficacy of the "line of block" concept among patients with septal APs using a reproducible and simple technique. METHODS An exploratory catheter is used to pace the basal RV and the stimulation-to-atrial time is measured (SA1). The exploratory catheter is then moved 2-3cm deeper into the RV towards the apex, and the stimulation-to-atrial interval (SA2) is measured. The results (SA-1 > SA-2 = Nodal Response vs SA-1 < SA-2 = AP Response) were determined. The technique can also be done during entrainment of ongoing tachycardia RESULTS: 24 patients undergoing an EP study fulfilled the criteria for enrollment and were included in the study between October 2023 and April 2025. 10 patients (41.7%) had proven APs, while 14 patients (58.3%) none.. The mean SA1-SA2 for patients with proven AP was -19.4 msec (SD ± 9.2), while the mean SA1-SA2 for patients without an AP was 10.5 msec (SD ± 10.5). All patients with AP demonstrated an SA1-SA2 less than 0 msec, while the reverse was true among patients with no demonstrable AP. CONCLUSION Utilizing the "line of block" concept by determining the Δ SA1-SA2 allows for easy determination to the presence or absence of an AP. Larger studies and sample sizes are required to allow for universal application in other EP labs.

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