Abstract 9133: Abnormal Response of Superior Sinoatrial Node to Sympathetic Stimulation is a Characteristic Finding in Patients with Atrial Fibrillation and Symptomatic Bradycardia

Abstract

Introduction: We hypothesize that unresponsiveness of superior sinoatrial node (SAN) to sympathetic stimulation is strongly associated with the development of symptomatic bradycardia in patients with atrial fibrillation (AF). Methods and Results: We performed 3-dimensional endocardial mapping in healthy control (Group 1, n=10) and in patients with AF without (Group 2, n=57) or with (Group 3, n=15) symptomatic bradycardia at baseline and during isoproterenol infusion. Sympatomatic bradycardia includes cardiac syncope, presyncope or dizziness associated with either sinus bradycardia (<40 bpm; n=7) or prolonged sinus pauses (>3.0 seconds; n=8) Corrected SAN recovery time (CSNRT) was abnormal (> 550ms) in 0%, 11% and 36% of groups 1, 2 and 3, respectively (p=0.02). At baseline, 90%, 36% and 7% (p<0.001) of the patients had multicentric SAN activation patterns. For groups 1, 2 and 3, respectively, the median distance from the superior vena cava-right atrial junction to the most cranial earliest activation site (EAS) was 5.0 (25-75 percentile range, 3.5-21.3) mm, 10.0 (4-20) mm and 17.5 (12-34) mm at baseline (p=0.01), and was 4.0 (0-5) mm, 5.0 (1-10) mm and 15.0 (5.4-33.3) mm during isoproterenol infusion (p=0.01), suggesting upward shift of EAS during isoproterenol infusion. However, while the EAS during isoproterenol infusion was at the upper 1/3 of crista terminalis in 100% of Group 1 and 78% of Group 2 patients, only 20% of the groups 3 patients moved EAS to that region (p < 0.001). We analyzed the comparative efficacy of CSNRT and 3D mapping in differentiating Group 2 and Group 3 patients. The sensitivity and specificity of CSNRT test are 35% and 89%, respectively, and of the 3D mapping test are 78% and 78%, respectively. Conclusions: Superior SAN serves as the EAS during sympathetic stimulation in normal patients and in most patients with AF without symptomatic bradycardia. In contrast, unresponsiveness of superior SAN to sympathetic stimulation is a characteristic finding in patients with AF and symptomatic bradycardia.