| Objective:Wolff-Parkinson-White (WPW) syndrome is the abnormality of the atrioventricular conduction, and the conduction accessory pathway (AP) is its anatomic basis. The abnormal accessory pathway can take part in composing the reentrant circuit, and lead to tachycardia which causes symptoms. Nowadays radiofrequency catheter ablation has become the preferred treatment for patients with symptomatic WPW syndrome. If detailed and accurate localization of the AP is available before the procedure, it can be helpful for choosing the catheters and methods during the procedure, finally reducing fluoroscopy time and improving success rates. A plenty of reports have documented the excellent sensitivity and specificity of the surface 12-lead electrocardiograph (ECG), and many sets of criteria for the localization were published. However, these criteria were different for the assignment of the APs, and that of the left APs was too crude to be localized much accurately. In the meantime, it was controversial whether the APs could be differentiated with the frontal Delta wave axes and the frontal plane QRS axes. The aim of the present study was to retrospectively analyze the surface ECG recorded from those patients with left overt APs which were successfully ablated, and derive a new ECG criterion according to the assignment of the left APs in our country. Finally, this criterion, together with those proposed by Arruda et al and D'Avila et al, was used to blinded determine the APs location then the accuracy by each algorithm was compared. What is more, both the frontal Delta wave axes and the frontal plane QRS axes were compared among the different locations of left accessory pathways.Methods:152 consecutive patients with WPW syndrome underwent successful radiofrequency catheter ablation between January 1999 and December 2003. Excluding seven patients with multiple accessory pathways, Bundle-Branch block, Ebstein's anomaly or other structure heart disease, 145 patients were present, including 67 males and 78 females, with mean age of 37.33±16.35 years. Analyzing 71 surface ECGs of left overt APs before procedure, both the frontal Delta wave axes and the frontal plane QRS axes were measured. Furthermore, surveying the algebraic sum of QRS amplitude in Ⅱ and aVL, the accessory pathway axes were calculated in the new hexaxial system in which aVL lead was reversed. The cut-off values on the AP axes of the different left APs were defined to derive a new criterion. The criterion, together with Arruda methods and D'Avila methods was respectively used to determine the locations of the APs by analyzing the pre-procedural ECGs of the patients with successfully abated WPW syndrome, followed by compared with the ablated sites which was defined as the distance from the orifice of coronary sinus to the target site. Continuous variables were expressed as the mean value ± standard deviation (±s), groups were compared using Kruskal-Walls Test for several independent nonparametric samples. Relations between two variables were evaluated with Spearman correlation or Pearson correlation and linear regression. Receiver Operating Characteristics (ROC) analysis was performed to define the cut-off value on the AP axes of the different left APs. The above statistical analyses were performed using SPSS 11.5 statistical software. At the same time, the sensitivity,specificity and accuracy among the different criteria were compared by SAS 6.12 statistical software with chi-square test. A p value <0.05 was considered statistically significant. Results:Among the 145 patients with successfully ablated WPW syndrome, there were 71 accessory pathways located in the left side, including 11 in left posteroseptal (LPS), 12 in left posterolateral (LPL), 41 in left lateral (LL) and 7 in left anterolateral (LAL). Both the degree of frontal Delta wave axes and the degree of frontal plane QRS axes were significantly different among the different left APs, but they showed a large overlap. The frontal Delta wave axes correlated fairly with t...
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