S1-S2 pacing protocols are often used in cardiac electrophysiology simulations to assess arrhythmic risk. However, as the S2 stimulus may originate anywhere in the myocardium, exhaustive spatial sampling is often computationally prohibitive. We therefore developed and evaluated a conduction block pre-test to stratify S2 sites prior to full monodomain simulation.
The pre-test estimates conduction block propensity by identifying regions where S2 activation precedes local S1 repolarisation, quantified by the resulting blocked myocardial volume. Performance was evaluated through comparison with 9,254 monodomain S1-S2 protocols across 24 benchmarks, with 179 episodes of induced ventricular tachycardia (VT).
Pre-test blocked myocardial volume was greater among S2 sites where VT was inducible in monodomain simulations (19±7 cm³) vs. non-inducible sites (4±5 cm³). Pre-test block volume was highly predictive of VT induction in monodomain simulations, with an area under the curve of 0.95 on ROC analysis. Even at 100% sensitivity, 72±22% of S2 sites could be excluded from full monodomain simulation, yielding substantial computational savings.
Altogether, this conduction block pre-test can effectively stratify S2 sites when analysing functional arrhythmic substrates, which may facilitate large-scale dense S2 sampling in cardiac digital twin arrhythmic risk assessments.