Objective: To investigate the optimal range of quantitative ablation index (AI) value during superior vena cava (SVC) electrical isolation by radiofrequency catheter ablation (RFCA). Methods: First, in a development cohort of patients with atrial fibrillation (AF), the RFCA with 40W was performed to complete SVC isolation guided by the conduction breakthrough point from the right atrium to SVC. Then, the range of AI value was calculated by offline analysis on different segments of SVC. Lastly, for the validation of AF patients, the safety and effectiveness of SVC isolation with the optimized target range of AI value were evaluated with an additional adenosine test. Results: A total of 101 patients with AF were included in the study (44 patients in the development cohort / 57 in the validation cohort). The segmental ablation strategy was applied in 70% of the patients. According to the offline analysis of the AI values in the development cohort, the target AI value range was set as 350-400. The success rate of SVC isolation in the validation cohort was significantly higher than that in the exploration cohort (100% vs 90.9%, P = 0.02), and no complications occurred in the exploration cohort. During the adenosine test, the recovery rate of electrical conduction in SVC was significantly lower than that in the pulmonary vein (3.5% vs 17.5%). Conclusion: The target AI value with a range from 350 to 400 is safe and effective for high-power RFCA to complete SVC isolation.

Background: Low voltage Zones (LVZ) were usually targeted for ablation in atrial fibrillation (AF). But its relationship with AF initiation, maintenance, and termination remains to be studied. We tried to explore the relationships. Methods and Results: Consecutive AF patients were enrolled for assessment AF inducibility, AF duration or AF termination before ablation. Inducible AF was defined if induced AF last over 30 seconds. Sustainable AF was defined if it last over 300 seconds. Terminable AF was defined if it could be cardioverted into sinus rhythm within 1-hour after ibutilide administration. Voltage mapping was performed in sinus rhythm for all patients before stimulation or after cardioversion. LVZ was quantified as the percentage of LVZ area（LVZ%）to left atrium (LA) body surface. A total of 86 patients enrolled for AF induction and 36 for AF termination. 32 (37.2%) patients had inducible AF, 24 (27.9%) were sustainable, and 12 (33.3%) were terminable. Inducible AF patients had higher LVZ% in anterior wall (18.6±24.6 vs. 7.0±12.1, P=0.014). Global LVZ% was not different between inducible and uninducible AF patients. Global LVZ% was higher in patients with sustainable AF or interminable AF (LVZ%: sustainable vs unsustainable AF: 10.6±12.1 vs. 0.8±0.8, p=0.001; terminable vs. interminable: 17.1±13.5vs.40.6±24.5, p<0.001). Sustainable AF had larger LVZ% in roof, anterior wall, septum, floor. Interminable AF patients had higher LVZ% in anterior wall, septum, posterior wall and floor. Higher LVZ% was independent risk factor of recurrence (OR=1.015, P=0.042). Conclusion: The association between LVZ with AF initiation, perpetuation and termination were different.