Abstract: AIM: To study the surface electrocardiogram(ECG) characteristics of outflow tract ventricular arrhythmias as possible guidance for catheter ablation.METHODS: ECG characteristics in 207 consecutive patients who underwent radiofrequency catheter ablation of VT/PVCs originating from LVOT or RVOT were analyzed,respectively.The amplitudes of R wave and S wave of precordial leads were measured.The relationship between the origin site and the precordial lead at which R/S translated was analyzed and R/S amplitude ratios were calculated.RESULTS: The number of patients whose transition of R/S on precordial leads was before lead V2,in lead V3 and after lead V4 were 18 aged(44±17) years,76 aged(46±13) years and 113 aged(42±14) years,respectively.In the 18 cases of R/S wave transition before lead V2,LVOT origin was defined in 17 patients(specificity 99%,sensitivity 68%,positive predictive value 94% and negative predictive value 96%).In the 113 cases of R/S transition after lead V4,RVOT origin was defined in all the patients(specificity 100%,sensitivity 62%,positive predictive value 100% and negative predictive value 26%.In the 76 cases of R/S wave transition in lead V3,RVOT and LVOT origin were defined in 68 patients and eight patients,respectively.The lead V2 R/S amplitude ratios from RVOT and LVOT were 0.32±0.17 vs.0.64±0.21(P<0.05) respectively.CONCLUSIONS: The specificity of identifying the origin of ventricular arrhythmias from LVOT by R/S transition before lead V2 is high as well as the specificity and sensitivity of identifying origin from RVOT by R/S transition after lead V4.In the cases of R/S wave transition in lead V3,R/S amplitude ratios of the VAs originating from LVOT were higher than those from RVOT.