Inferior Sino-Atrial Node Exit Sites Are Associated With Electrical Remodeling

Electrical activity from the sino-atrial node (SAN) spreads via specific pathways into surrounding atrial tissue. Inferior sino-atrial node exit sites (SAN_i) have been observed in patients with structural heart disease and atrial fibrillation. However, determinants of preferential sino-atrial conduction pathways and the associated electrical properties of the SAN_i region remain poorly understood.

This study sought to examine differences in unipolar potential morphology and the degree of remodeling at the right atrium (RA) between patients with superior sino-atrial node exit sites (SAN_s) and SAN_i.

High-resolution epicardial mapping was performed in 27 patients with structural heart disease undergoing elective open-heart surgery. Electrodes within an 8-mm radius of the SAN exit site were classified as the SAN area. Electrophysiological properties, including potential voltage, conduction block, and R/S ratios, were computed.

SAN_i, identified in 7 patients, exhibited lower potential voltages (median: 1.3 [Q1-Q3: 1.2-1.7] vs 2.6 [Q1-Q3: 2.2-3.6] mV; P = 0.014) and unipolar rS-wave morphologies, whereas SAN_s had full S-wave morphologies. The total activation times of RA were prolonged in SAN_i patients (median: 89 [Q1-Q3: 79-98] vs 78 [Q1-Q3: 66-85] milliseconds; P = 0.046). Heart rates were comparable between groups and remained consistent during both the preoperative and intraoperative periods.

SAN_i identified by high-resolution epicardial mapping were associated with extensive RA remodeling and are most likely due to altered sino-atrial conduction pathways.