A novel pace mapping parameter to predict procedural success of left bundle branch area pacing: Lead II/III Discordance Index
B Hunuk, F Besiroglu, O Cagac, H Altay, O KozanAbstract
Background
Left-bundle-branch-area-pacing (LBBAP) has developed as a physiological pacing alternative, however optimal techniques still need to be elucidated. Pace-mapping the interventricular septum for the optimal septal penetration site, targeting DII/DIII discordance and a notch at the nadir of V1-QRS has been suggested in consensus papers.
Purpose
To test if pace-mapping derived Lead II/III Discordance Index (L2–3 DI) predicts electrical/procedural success of LBBAP, and to evaluate whether a V1-QRS-notch adds incremental value.
Methods
In a single-centre prospective observational cohort, we enrolled 72 consecutive patients (age: 70±11 years, male n:46) undergoing LBBAP over the last 2-years for Class-I CRT/pacing indications (advanced-atrioventricular-block n: 38/72) with lumenless lead. Patients with LVEF <20% and advanced-right-heart-failure were excluded. Before septal-penetration, unipolar pace-mapping was performed. According to paced-QRS-polarity in leads II and III, patients were classified as "discordant II+/III−" (n=42), "concordant −/−" with lead-II less-negative (n=16), and "concordant +/+" with lead-II more-positive (n=14). "L2–3 DI" was defined as (AII−AIII)/(|AII|+|AIII|)[range:+1 to -1], where A: net QRS-amplitudes including polarity. V1-QRS-notch was also recorded. Baseline QRS, LVEF, paced QRS, ΔQRS (baseline–paced), V6 R-wave peak time (RWPT), V6–V1-inter-peak-interval, procedure and fluoroscopy times, penetration attempts, dislodgements and V1-QRS-notch were compared between groups and in logistic models.
Results
Baseline QRS was similarly prolonged with slightly lower LVEF in the −/− group (Table-1). Discordant patients showed significantly narrower paced-QRS (110±10 vs 124±12 and 120±11 ms), greater QRS-narrowing (ΔQRS 38±20 vs 34±18 and 30±17 ms), shorter V6-RWPT (56±8 vs 68±10 and 64±9 ms) and longer V6–V1-inter-peak-interval (53±9 vs 47±5 and 38±9 ms; all p≤0.01). Procedure and fluoroscopy times were also significantly lower in the discordant group, with fewer penetration attempts and no micro-dislodgement. Visible V1-QRS-notch during pace mapping was more frequent at discordant II+/III− sites (76% vs 50% and 43%, p=0.02), but was not associated with QRS narrowing, V6-RWPT or LBB capture. "L2–3 DI" was highest in the discordant II+/III− group (0.78±0.12 vs 0.38±0.10 and 0.24±0.11; p<0.001) and, in logistic regression, each 0.1 increase towards "+1" in "L2–3 DI" independently predicted electrical success (adjusted odds ratio 1.30, 95% CI 1.05–1.60; p=0.01), whereas the presence of a V1 notch did not (Table-2).
Conclusions
Pace-mapping derived "L2–3 DI" identifies an optimal septal engagement site for LBBAP. Higher score (near= 1) reflects strong positive-discordance in leads II/III and is associated with more physiological activation and a more efficient implantation. V1-QRS-notch does not seem to predict procedural success beyond L2–3 DI. This index may help to standardise LBBAP lead deployment techniques.Table-1