Notable Pacemaker Shift in the Sinoatrial Node After Administration of Isoproterenol

A 63-year-old woman underwent a redo catheter ablation for recurrent atrial fibrillation (AF) after an initial cryoballoon ablation. After confirming the electrical isolation of 4 pulmonary veins, empiric superior vena cava (SVC) isolation was performed without documenting AF triggers. A 20-pole PentaRay NAV catheter (Biosense Webster, Diamond Bar, CA) was used to create an activation map during sinus rhythm to identify the anatomic location of the sinoatrial node (SAN). The earliest atrial activation site (EAS) at baseline was the basal lateral wall of the right atrial appendage (Fig. 1A). Notably, the EAS shifted to a more anterior-superior location from baseline after administration of isoproterenol (0.02 μg/kg/minute) (Fig. 1B). The distance between the 2 EASs was 21.2 mm (Fig. 1C), and the SVC was successfully isolated 10 mm above the superior EAS without any complications. SVC isolation is an important adjunctive ablation strategy but can potentially injure the SAN.1Chen G. Dong J.Z. Liu X.P. et al.Sinus node injury as a result of superior vena cava isolation during catheter ablation for atrial fibrillation and atrial flutter.Pacing Clin Electrophysiol. 2011; 34: 163-170Crossref PubMed Scopus (37) Google Scholar The physiology of SAN is quite complex and is still under investigation. A diverse population of pacemaking cells operating in synchrony with their neighbors is one hypothesis.2Michaels D.C. Matyas E.P. Jalife J. Mechanisms of sinoatrial pacemaker synchronization: a new hypothesis.Circ Res. 1987; 61: 704-714Crossref PubMed Scopus (207) Google Scholar The presence of 2 distinct leading pacemaker cells—the superior SAN (sSAN) and inferior SAN (iSAN)—controlling the surrounding tissues is the other hypothesis.3Brennan J.A. Chen Q. Gams A. et al.Evidence of superior and inferior sinoatrial nodes in the mammalian heart.JACC Clin Electrophysiol. 2020; 6: 1827-1840Crossref PubMed Scopus (37) Google Scholar In the current case, we identified the 2 distinct EASs at baseline and after administration of isoproterenol, which might correspond to the pacemaker shift from the iSAN to sSAN. Identification of the sSAN is crucial for avoiding any unexpected injury to the SAN.4Hayashi T. Mizukami A. Kuroda S. et al.Sinus node dysfunction characterized by reduction only in maximum heart rate during exercise after superior vena cava isolation in atrial fibrillation catheter ablation-A potential complication.HeartRhythm Case Rep. 2020; 6: 206-209Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar No funding was received for this article.