Conduction behaviour of deceleration zones identified during substrate mapping for ventricular tachycardia using S1-S2-S3 protocol
J Reventos-Presmanes, N Pierucci, J B Guichard, T Rosseel, M Regany, J M Tolosana, E Guasch, L Mont, J Brugada, E Arbelo, I Roca, A Porta-SanchezAbstract
Background
Programmed stimulation reveals dynamic conduction behaviour in ventricular tachycardia (VT) substrates. As coupling intervals shorten, regions near scar may show decrement or unidirectional block, reflecting local excitability and refractoriness. These responses define functional boundaries of reentry, yet their characterization during mapping remains largely qualitative.
Objective
To systematically characterize regional conduction behaviour during S1–S2–S3 ventricular stimulation, identifying and quantifying areas with decremental conduction or unidirectional block.
Methods
We included patients who underwent ablation for VT in whom the complete S3 stimulation protocol was attempted. Ventricular latest deflection activation maps were sequentially generated for S1(drive train), S2(ERP+30 ms), and S3(ERP+50 ms) beats, with the activation window divided into 8 equally timed isochrones. Deceleration zones (DZs) were identified in each map. Each DZ was classified based on its presence across the three maps, yielding 7 possible combinations: S1, S2, S3, S1 & S2, S2 & S3, S1 & S3, or S1& S2 & S3. For each DZ, the latest activation time was extracted, and dynamic conduction behaviour was assessed through local decrement evoked potential (DeEP) mapping by computing temporal differences between S2–S1, S3–S2, and S3–S1 maps (Δt). Positive Δt values indicated DeEP, whereas negative Δt values suggested unidirectional block.
Results
Twenty-six patients were included (92% male, 68% ischemic). A total of 116 DZs were identified. The mean number of DZs per map increased from S1 (1.85±0.9) to S2 (2.11±1.0) and S3 (3.20±1.1), with significant differences between S2 vs S3 and S1 vs S3 (p<0.01). Most DZs were found in S3 (38, 32.8%) and S1&S2&S3 (23, 19.8%), yet a portion appeared exclusively in S1 (9, 7.8%) or S2 (14, 12.1%), indicating that functionally relevant areas may be missed if only S3 is assessed. The dynamic conduction behavior of DZs across the DeEP maps (ΔtS2–S1, ΔtS3–S2, and ΔtS3–S1) is shown in Figure 1. DZs present only in S1 were not seen using extrastimuli due to conduction block of the late potentials, whereas DZs only seen in S3 unmask functional conduction slowing. DZs present only in S2 showed decremental conduction in ΔtS2–S1 but block in ΔtS3–S2 (Figure 2A). Among DZs present in two maps, those on S2 & S3 showed decremental behaviour (Figure 2B). In contrast, DZs on S1 & S2 (Figure 2C) and on S3 & S1exhibited negative Δt values in the S3 and S2 maps, respectively, indicating functional block . DZs persisting across all three maps maintained conduction decrement throughout all DeEP maps (Figure 2C).
Conclusion
DeEP mapping during S3 protocol revealed distinct conduction dynamics across premature beats. DZs present in multiple maps showed progressive delay, whereas those disappearing with extrastimulation show unidirectional block. The quantitative comparison of S1-S2-S3 maps is key to define highly arrhythmogenic areas.