Decapolar catheters, DecaNav (DecaNav, Biosense Webster, Inc.) were placed epicardially and endocardially and aligned to record across a geometrically opposed transmural area, traversing healthy tissue, scar-borderzone, dense scar, or all three (Figure 1 ). S1–S2 restitution curves were then performed at twice the diastolic capture threshold before clinical ablation, from the endocardium and epicardium in these catheter positions, as previously described.9 (link) In each region, steady state was achieved by pacing at basic cycle length of 600 ms for 3 min. Following this an S1–S2 protocol was performed beginning with an extra stimulus (S2) at 1000 ms. The S1–S2 coupling interval was then decremented in 50 ms steps until an S2 of 400 ms, then by 20 ms intervals between 400 and 300 ms, and thereafter, in 5 ms steps until effective refractory period (ERP) of the tissue. At ERP an S2 stimulus at 10 ms + ERP was applied followed by further decrementing S2 in steps of 2 ms to confirm ERP. All patients gave informed consent, the study was approved by our regional ethics board (LO10/H0715/19) and complied with the declaration of Helsinki.
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