Background Substrate modification guided bv CARTO system has been introduced to facilitate linear ablation of ventricular tachycardia(VT)after myocardial infarction(MI).However,there is no commonly accepted standard approach available for drawing these ablation Iines.Therefore,the aim of the present study was to practically refine this time consuming procedure.Methods Substrate modification was performed in 23 consecutive patients with frequent VTs after MI using the CARTO system.The initial target site(ITS)for ablation was identified by pace mapping(PM)during sinus rhythm and/or entrainment pacing(EM)during VT.According to the initial target site,two approaches were used.The initial target site in approach one has a similar QRS morphology as VT and an intervaI from the stimulus to the onset of QRS cmplex (S-QRS)of≥50 ms during PM in sinus rhIythm or a difference of the post pacing interval and VT cycle length≤30 ms during concealed entrainment pacing of VT;The initial target site in approach two has an similar QRS morphology as VT and an S-QRS of＜50 ms during PM in sinus rhythm.Results Overall,50 lines were performed with a length of(35±11)mm.Procedure time averaged (232±56)minutes,fluoroscopy time(10±8)minutes.Sixteen patients were initially involved into approach one.After completion of 3±1 ablation Iines,no further VT was inducible in 13 patients.The remaining 3 patients were switched to use the alternative approach.However,In none of them the alternative approaches were successful.Approach two was initially used in 7 patients.After completion of 3±1 ablation Iines,no further VT was inducible in only 2 patients.The remaining 5 patients were switched to approach one,which resulted in noninducibility of VT in 4 of them.The initial successfuI rate was significantly higher in the group of approach one compared to that in the group of approach two(13/16 patients vs 2/7patients,P=0.026).Conclusions The approach for substrate modification of VT after MI can be optimized by identifying the appropriate initiaI target site with specific characte ristics within the zone of slow conduction.The refined approach may facilitate linear ablation of VT and further reduce the procedure and fluoroscopy time.