Endo-Epicardial Mapping of In Vivo Human Sinoatrial Node Activity

OBJECTIVES The aim of the current study was to examine electrophysiological characteristics of sinoatrial node (SAN) activity from an endo-epicardial perspective. BACKGROUND Electrophysiological properties of the in vivo human SAN and its exit pathways remain poorly understood. METHODS Twenty patients (75% male; median age 66 years [59 to 73 years]) with structural heart disease underwent simultaneous endo-epicardial mapping (256 unipolar electrodes, interelectrode distance 2 mm). Conduction times, endo-epicardial delays (EEDs), and R/S ratio were examined in the surrounding 10 mm of SAN activation. Areas of conduction block were defined as conduction delays $12 ms and endo-epicardial asynchrony as EED $15 m. RESULTS Three distinct activation patterns were observed in a total of 28 SAN-focal activation patterns (SAN-FAPs) (4 patients exhibited >1 different exit site), including SAN activation patterns with: 1) solely an endocardial exit site (n = 10 [36%]); 2) solely an epicardial exit site (n = 13 [46%]); and 3) simultaneously activated endo-epicardial exit sites (n = 5 [18%]). Median (interquartile range) EED at the origin of the SAN-FAP was 10 ms (6 to 14 ms) and the prevalence of endo-epicardial asynchrony in the surroundings of the SAN-FAP was 5% (2% to 18%). Electrograms at the origin of the SAN-FAPs exhibited significantly larger R-peaks in the mid right atrium (RA) compared with the superior RA (mid R/S ratio 0.15 [0.067 to 0.34] vs. superior R/S ratio 0.045 [0.026 to 0.062]; p = 0.004). Conduction velocity within a distance of 10 mm from the SAN-FAP was 125 cm/s (80 to 250 cm/s). All 6 SAN-FAPs at the mid RA were observed in patients with a history of atrial fibrillation. CONCLUSIONS Variations in activation patterns of the SAN observed in this study highlight the complex 3-dimensional SAN geometry and indicate the presence of interindividual differences in SAN exit pathways. Solely in patients with a history of atrial fibrillation, SAN activity occurred more caudally, which indicates changes in preferential SAN exit pathways. (C) 2021 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation.

Automated summary

"The study found three distinct activation patterns of the SAN, indicating the complex geometry of the SAN and individual differences in SAN exit pathways. SAN activity occurred more caudally in patients with a history of atrial fibrillation, suggesting changes in preferential SAN exit pathways."