Endo-epicardial mapping of human sinus node in vivo: Novel electrophysiologic findings and anatomic correlations

Background: The human sinoatrial node (SAN) pacemaker is a complex structure located at the right atrium (RA)–superior vena cava (SVC) junction. Objective: This study aimed to perform in vivo endocardial and epicardial electroanatomic mapping of human SAN in inappropriate sinus node tachycardia (IST) and to correlate electrical findings with anatomic observations from thoracoscopy during hybrid SAN-sparing IST ablation. Methods: All consecutive patients with diagnosis of symptomatic IST, refractory to or intolerant of drugs, and endocardial and epicardial mapping of SAN during hybrid ablation were included. Local activation time was defined by steepest −dV/dT on unipolar electrogram (EGM). Exit zone (EZ) was defined as the earliest activation site on endocardial and epicardial maps. Endo-epicardial delay was the time difference between the first endo-epicardial activations. Bipolar EGM morphology and SVC sleeve extension were analyzed. Results: A total of 61 patients were included. The SAN-EZ area was 1.4 ± 0.6 cm²; it was located in the superior anterior region of the RA in 46 (75.4%) patients and in the mid RA in 15 (24.6%) patients. The earliest activation occurred on epicardial SAN-EZ in all patients. The local activation time of the epicardial vs endocardial SAN-EZ was −30.8 ms vs −12.4 ms (P < .001). Endo-epicardial delay was 19.7 ms. Bipolar EGM reversed polarity at SAN-EZs was observed in 43 (70.5%) patients. SVC sleeve extension was 31.2 mm and inversely correlated with age. Conclusion: The earliest SAN-EZ was found in the epicardium. Bipolar EGM reversed polarity is a novel electrophysiologic marker for SAN-EZs.