The V_3R/V₇ Index:A Novel Electrocardiographic Criterion For Differentiating Left From Right Ventricular Outflow Tract Arrhythmias Origins

Background:Several algorithms have been proposed to predict the origin of outflow tract ventricular arrhythmias(OT-VAs)using standard 12-lead ECG.However,the additive value of right precordial and posterior leads is unknown.Aims:To evaluate the utility of right precordial and posterior leads and develop a novel,more accurate ECG algorithm for distinguishing between LVOT and RVOT origins of OT-VAs.Methods:Standard 12-lead,right precordial(V3R,V4R,V5R)and posterior leads(V7,V8,V9)ECG were recorded and analyzed in a development cohort of consecutive patients undergoing OT-VAs ablation at a single center.These findings informed the development of a novel algorithm incorporating right precordial and posterior leads to discriminate between LVOT and RVOT foci.The performance of this novel algorithm which includes the V3R/V7 index was prospectively tested in a validation cohort of consecutive patients undergoing OT-VA ablation at 4 centers and compared to published algorithms.The location of the foci was determined by the site of successful ablation.Results:203 patients were recruited,of which 101 formed the validation cohort.(mean age of 45.8 ± 15.0,30%male,76%RVOT foci)During OT-VAs,a QS pattern in lead V3R and a S-wave in lead V7 was exclusively recorded in RVOT and LVOT foci respectively.The V3R/V7 index of LVOT origin was significantly greater than that of RVOT(1.48 ± 0.91 vs 0.28 ± 0.23,P<0.001).The V3R/V7 index(?)0.85 predicted an LVOT origin with 90%sensitivity and 96%specificity.In the prospective evaluation,the V3R/V7 index correctly predicted the site of successful ablation(LVOT vs.RVOT)in 95%(96 of 101)of cases.When the V3R/V7 index?0.85,an RVOT origin could be excluded with 98.7%accuracy.The AUC of V3R/V7 index(0.932)was larger than that of previously reported ECG criteria,including V2S/V3R(0.897),V2 transition ratio(0.819)and the TZ index(0.725).This novel index was also accurate in subgroups with cardiac rotation or lead V3 R/S transition.Conclusions:The V3R/V7 index is a novel and accurate ECG criterion that predicts OT-VAs origin.