Functional Conduction Block During Extrastimulus Mapping Masks Deceleration Zones and Reveals Additional VT Substrate

Area of Science:

• Electrophysiology
• Cardiac Arrhythmia Research
• Medical Device Technology

Background:

• Extrastimulus pacing may expose decremental conduction, a proarrhythmic property, during ventricular tachycardia (VT) substrate identification.
• The role of functional conduction block during extrastimulus pacing as a marker of arrhythmogenicity remains unclear.

Purpose of the Study:

• To compare ventricular tachycardia substrate identification using steady-state (S1) and single extrastimulus (S2) pacing.
• To analyze deceleration zones (DZs) and annotation delta (ΔS1S2) to understand substrate behavior changes.

Main Methods:

• Isochronal late activation mapping with S1 and S2 pacing (ventricular effective refractory period +20 ms) during right ventricular pacing.
• Identification of DZs and calculation of ΔS1S2 to assess decremental conduction and functional block.
• Analysis of DZ location and ΔS1S2 changes to characterize altered substrate behavior.

Main Results:

• DZ locations differed significantly between S1 and S2 maps.
• Extrastimulus pacing identified 5 new DZs, but functional block masked 4 DZs on S2 maps.
• Significant ΔS1S2 regions colocalized with primary DZs in most cases.

Conclusions:

• Extrastimulus pacing alters DZ location and can reveal additional VT substrate.
• Functional block during S2 pacing may mask critical substrate areas.
• Combined analysis of S1 and S2 maps enhances substrate characterization and identifies potential ablation targets.