Objective To investigate the effects of circumferential pulmonary vein isolation (CPVI) on atrial effective refractory period (ERP) in patients with paroxysmal atrial fibrillation.Methods 30 patients who underwent radiofrequency catheter ablation for paroxysmal AF were enrolled in this study.Using FAM mode,the RA and LA anatomical models were achieved in the CARTO 3 system.SVC,MRA,RAA,LA-A,LA-R,LA-P,LAA,LSPV,LIPV,RSPV,RIPV,CSp,CSd,were respectively located in the RA or LA anatomical model.Before and after CPVI,ERPs were measured in different locations of the atrium using programmed stimulation.The ERPs of the RA (SVC,MRA,RAA,CSp),LA (LA-A,LA-R,LA-P,LAA,CSd),PVs (LSPV,RSPV,LIPV,RIPV) were compared.Bilateral CPVIs were completed in all patients,and PV-LA bidirectional conduction block was achieved.The changes of electrophysiological characteristics of atrium before and after CPVI were observed.Results (1) ERP at different locations in the atrium before CPVI:Comparisons of ERPs at different locations of atrium:RAA had the minimal ERPs[(197.4 ± 28.6) ms (P ＜ 0.01);followed by PVs measuring,respectively,LSPV (213.0 ± 47.5) ms,LIPV (208.9 ± 45.9) ms,RSPV (209.3 ± 43.6) ms,RIPV (213.5 ± 48.1) ms and LAA (218.1 ± 27.7) ms.Comparisons of ERPs in RA,LA,and PVs showed:PVs had the lowest ERPs (211.2 ± 35.2) ms versus RA ERP (227.0 ± 23.7) ms versus LA ERP (241.0 ± 21.5) ms (P ＜ 0.05).(2) Comparisons of ERPs before and after CPVI:Comparisons of ERPs at different locations of atrium showed:RAA [(197.4 ± 28.6) ms vs.(208.6 ± 32.2) ms,P=0.003],CSp [(234.7 ± 29.1) ms vs.(246.9 ± 29.7) ms,P=0.007],LA-R [(242.9 ± 28.9) ms vs.(258.3 ± 26.9) ms,P=0.003],LA-P [(252.2 ± 28.5) ms vs.(261.1 ± 30.2) ms,P=0.039]and CSd [(238.6 ± 28.3) ms vs.(250.3 ± 23.6) ms,P =0.009].ERPs were found statistically prolonged at all different locations after CPVI.Comparisons of ERPs at RAand LA after CPVI showed:RA [(227.0 ± 23.7) ms vs.(235.9 ± 21.7)ms,P=0.002]and LA [(241.0 ± 21.5) ms vs.(249.7 ± 19.9) ms,P =0.001],which were statistically increased after CPVI.(3) A total of 90 episodes of atrial arrhythmias were induced before CPVI which were found at RAA (n =17),LAA (n =12),and PVs (n =36).After CPVI,8 episodes of atrial arrhythmias were induced which were found at,RAA (n =4),LAA (n =3),and SVC (n =1).Conclusions (1) Compared with other parts of atrium,ERPs at PVs,LAA and RAA are significantly shorter in patients with paroxysmal AF.At PVs,LAA and RAA,atrial arrhythmias are easily to be induce by programmed stimulation.(2) In patients with paroxysmal Af:PVs has the shortest ERPsfollowed by RAs whereas LA ERPs is the longest.There is a large ERP gradient change between PVs and LA.(3) The ERPs at RAs,LAs,As,and LA-PV are prolonged after CPVI.(4) Atrial arrhythmia is less likely to be induced after CPVI.