Endo-Epicardial Mapping of InVivo Human Sinoatrial Node Activity.

Abstract

The aim of the current study was to examine electrophysiological characteristics of sinoatrial node (SAN) activity from an endo-epicardial perspective. Electrophysiological properties of the invivo human SAN and its exit pathways remain poorly understood. 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 2mm). Conduction times, endo-epicardial delays (EEDs), and R/S ratio were examined in the surrounding 10mm of SAN activation. Areas of conduction block were defined as conduction delays≥12ms and endo-epicardial asynchrony as EED≥15 m. 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 10ms (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 10mm from the SAN-FAP was 125cm/s (80 to 250 cm/s). All 6 SAN-FAPs at the mid RA were observed in patients with a history of atrial fibrillation. 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 exitpathways.