Differential right apical and left basal pacing: a new maneuver that rules out the presence of a left accessory pathway with retrograde conduction
Authors: Castrejon Castrejon S , Martinez Cossiani M M C , Guido Lopez L G L , Jauregui Abularach M J A , Sanchez Somonte P , Merino Fuentes D M F , Sanz Verdejo B S V , Handayani A H , Porro Fernandez J C P F , Contreras Lorenzo C C L , Martinez Maldonado M E M M , Moreno Gomez J R M G , Merino J L M L 
Published: May 2024

Abstract

Background
Differential apex-base pacing or entrainment is a very useful maneuver in patients with concealed septal accessory pathways. This study evaluates for the first time the diagnostic value of differential right apical pacing (aRV) and basal left ventricular pacing (bLV) in patients with left accessory pathways before and after ablation.

Purpose
To determine the value of differential aRV and bLV pacing as a simple maneuver to assess the successful ablation of left accessory pathways.

Methods
Successive patients with preexcitation or concealed left accessory pathways were prospectively included. Baseline pre-ablation (PRE) 1:1 retrograde conduction was evaluated by the S-A interval during pacing at the aRV (PREaRV) and at the bLV (PREbLV) measured to the earliest atrial electrogram detected by a decapolar catheter placed in the coronary sinus. The S-A interval resulting from direct atrial capture during high outputpacing at the bLV at (PREdir) was also measured. The same S-A intervals, pacing at the same locations and measured to the same dipole in the coronary sinus were reassessed after ablation (POSaRV, POSbLV, POSdir) in order to compare the total values and their differences.

Results
47 patients were included (age 31 yo [range 4 – 76 yo], 70% male sex, transeptal approach used in 62%). Ablation of the accessory pathway was successful in all patients. 5 patients could not be analyzed due to absence of 1:1 retrograde conduction before ablation, 27/43 (63%) patients had 1:1 retrograde nodal conduction after ablation. A significant prolongation of the S-A intervals were observed after ablation during pacing at the aRV (POSaRV – PREaRV = 43±38 ms, IC95% 27-59 ms, p&lt;0,001) and from the bLV (POSbVI – PREbVI = 126±53 ms, IC95% 105-147 ms, p&lt;0,001). As expected, the S-A interval during direct atrial capture from the bLV did not prolong (POSdir – PREdir = 2±10 ms, IC95% -2 – 6 ms, p=0,41).
The difference PREaRV – PREbLV before ablation (difPRE) was 80±26 ms (IC95% 72-88 ms) and never overlapped with the difference POSaRV – POSbLV after ablation (-6 ±33 ms, IC95% -19 – 8 ms) (difPOS) except in one case of left posteroseptal accessory pathway. The δ value (difPRE – difPOS) was 83±40 ms (IC95% 67-100 ms, p&lt;0,001). A difPOS value &lt;20 ms discriminated all successful ablations of non posteroseptal accesory pathways.

Conclusion
The S-A values obtained during differential RV apical and LV basal pacing before and after ablation are valid to discriminate the efficacy of the procedure. The POSaVD – POSbVI value is always &lt;20 ms after successful ablation and excludes retrograde conduction over any left non-posteroseptal accesory pathway. This same value is ≤0 ms in 72% of cases of successful ablation.Figure.