Po-05-220 creation of the atrial flutter substrate by remodelling of sinoatrial conduction pathways and the sinoatrial node as revealed by ultra-high density electroanatomic mapping

It is not known how remodelling of the sinoatrial node (SAN) and conduction pathways (SACP) may contribute to the typical atrial flutter (AFL) substrate. We used ultra-high density mapping to characterise the SAN and SACPs and investigated whether sinus node disease (SND) associated remodelling contributed towards the substrate for AFL. Maps from patients with typical AFL (n=15) and SVT (n=12) were analysed. Paced and sinus maps were annotated for earliest SAN activation, SACPs, sinus breakout, and conduction block. Remodelling of the SAN region was present in AFL patients, and superiorly extended or completed an intercaval line of block at the medial border of the SAN. Incomplete block in SVT patients was exclusively in the inferior portion of the RA. The minimum degree of block required for AFL was 50% of the intercaval distance (all AFL patients), whilst SVT patients all had <50% block. SAN conduction velocity (CV) was slower in AFL patients (0.60m/s [0.56-0.78m/s] vs 1.13m/s [1.00-1.21m/s], p=0.0021). Paced maps displayed a posterior line of block in AFL patients that was absent in SVT (figure 1A), with preferentially reduced intercaval region CV (0.26 ±0.11 vs 0.79 ±0.15m/s, p=<0.0001) and no differences in other regions. Corrected SAN recovery time (cSNRT) was longer in AFL vs SVT (552.3±182.9ms vs 325.4±138.3ms, p<0.0060) and correlated with degree of intercaval block (r=0.7236, p=0.0003; (figure 1B). SAN and SACP EGMs were identified in 17 patients. Multifocal sinus breakout sites were common (23 SACPs in 17 patients). SAN activation, SACPs and breakout can be accurately identified in most patients. The posterior line of conduction block required for typical AFL was more extensive in patients with documented AFL. Partial block, when present (either group), was always located inferiorly. Reduced CV and associated block in the SAN/SACP region (not present in other regions) contribute the superior part to complete this line of block and provide the substrate for reentry for typical AFL. This was present in AFL patients, but absent in reference. The line of block was always medial to the SAN, meaning it was present in the intercaval region, not the crista terminalis as has been previously postulated. AFL patients had prolonged cSNRT, and this was positively correlated with the degree of posterior block, suggesting that SND associated remodelling may contribute towards forming the substrate for typical AFL.