Simultaneous epicardial-endocardial mapping of the sinus node in humans with structural heart disease: Impact of overdrive suppression on sino-atrial exits

Abstract Background The 3-dimensional nature of sino-atrial node (SAN) function has not previously been characterised in the intact human heart. Objective To characterize the 3-dimensional nature of SAN function in patients with structural heart disease (SHD) using simultaneous endocardial-epicardial phase mapping. Methodology Simultaneous intra-op endo-epicardial SAN mapping was performed during sinus rhythm at baseline (SRbaseline) and post-overdrive suppression at 600ms (SRpost-pace 600) and 400ms (SRpost-pace 400) using two HD Grid catheters. Uni and bipolar EGM's were exported for phase analysis to determine (a) activation exits, (b) wave front propagation sequence (c) endo-epicardial dissociation (EED) and (d) fractionation. Comparison of these variables was made between the three rhythms from an endo-epi perspective. Results Sixteen patients with SHD were included. SRbaseline activations were unicentric and predominantly exited cranially (87.5%) with endo-epi synchrony. However, with overdrive suppression, a tendency for caudal exit shift and endo-epi asynchrony was observed (SRpost-pace 600 vs SRbaseline: Cranial Endo 75 vs 87.5%, p=0.046; Cranial Epi 68.8 vs 87.5%, p=0.002; Caudal Endo 12.5 vs 6.2%, p=0.215; Caudal Epi 25 vs 6.2%, p=0.0003 and SRpost-pace 400 vs SRbaseline: Cranial Endo 81.3 vs 87.5%, p=0.335; Cranial Epi 68.7 vs 87.5%, p=0.0034; Caudal Endo 12.5 vs 6.2%, p=0.148; Caudal Epi 31.2 vs 6.2%, p=0.0017) consistent with multi-centricity. EGM fractionation was more prevalent with overdrive suppression. Conclusion During mapping in the intact human heart, the SAN demonstrated redundancy of sinoatrial exits with post overdrive shift in sites of earliest activation and epicardial-endocardial dissociation of sino-atrial exits.