An anatomical approach to determine the location of the sinoatrial node during catheter ablation

Introduction: The sinoatrial node (SAN) should be identified before superior vena cava (SVC) isolation to avoid SAN injury. However, its location cannot be identified without restoring sinus rhythm. This study evaluated the usefulness of the anatomically defined SAN by comparing it with the electrically confirmed SAN (e-SAN) to predict the top-most position of e-SAN and thus establish a safe and more efficient anatomical reference for SVC isolation than the previously reported reference of the right superior pulmonary vein (RSPV) roof.

Methods and results: The e-SAN was identified as the earliest activation site in the electroanatomical map obtained during sinus rhythm. The anatomically defined SAN, the cranial edge of the crista terminalis (CT) visualized with intracardiac echocardiography (CT top), and the RSPV roof, which was obtained from the overlaid electroanatomical image of SVC and RSPV, were tagged on one map. The distance from the e-SAN to each reference was measured. Among 77 patients, the height of the e-SAN from the CT top was a median (interquartile range) of -2.0 (-8.0 to 4.0) mm. The e-SAN existed from 10 mm above the CT top or lower in 74 (96%) patients and from the RSPV roof or below in 73 (95%) patients. The reference of 10 mm above the CT top is more proximal to the right atrium than the RSPV roof and can provide longer isolatable SVC sleeves (30.0 [20.0-35.0] vs. 24.0 [18.0-30.0] mm, p < .001). The e-SAN tended to be found above the CT top when the heart rate during mapping was faster (adjusted odds ratio [95% confidence interval] per 10-bpm increase: 1.71 [1.20-2.43], p < .01).

Conclusion: The CT top is useful for predicting the upper limit of the e-SAN and can provide a better reference for SVC isolation than the RSPV roof.