Major findings
In clinical settings, to determine the origin of OTVAs, we might get confused by different diagnostic criteria. This is the first systemic and comprehensive study that included 10 parameters to identify OTVA origin between 2002 and 2020. The main findings of our study are summarized as follows. (1) Among the seven parameters without restrictions in the transition lead, the larger ISA in leads V1 and V2 exhibited the best predictive value in differentiating the VAs in the LVOT, with a cutoff value of 57 ms × mv, which was different from a previous study (cutoff value of 15 ms × mv)[10], and the V2S/V3R index exhibited the best predictive value in differentiating the VAs in the RVOT, with a cutoff value of 1.5. (2) The algorithm combining the larger ISA in V1 and V2 and the V2S/V3R index has the best predictive value in determining the origin of OTVAs without restrictions in the transition lead. (3) Among the 10 parameters with the transition lead in V3, the V3 R-wave deflection interval exhibited a greater power to predict the origin of VAs than the other parameters. It has an accuracy similar to the algorithm proposed by us. (4) In the validation study, the algorithm exhibited optimal accuracy (95%). Taken together, the findings suggest that the algorithm can reliably determine the origin of the OTVA without restrictions in the transition lead.
Need forreviewing and comparing the accuracy of different diagnostic criteria for determining OTVA origin
The criteria proposed to differentiate OTVA origin spanned nearly two decades, with considerable discrepancies among the studies. (1) Different cases were included in the studies. The outflow tract was classified into six subdivisions: RV septum, RV free wall, RV near the His-bundle region, LV endocardium, ASC, and LV epicardium remote from the LSV[15]. Ouyang et al.[3] and Yoshida et al.[5] just enrolled patients with VAs originating from the RVOT and ASC. Di et al.[9] and Cheng et al.[6] did not enroll patients with the OTVAs originating from the LV epicardium. However, patients with OTVAs originating from all six subdivisions were enrolled in other studies. These discrepancies in the included cases might inevitably lead to different diagnostic accuracies. (2) A considerable discrepancy was present in the number of participants among the different studies. Ouyang et al.[3] only enrolled 15 cases, whereas Xia et al.[11] enrolled 382 cases. (3) Considerable differences in sample capacity might lead to different diagnostic accuracies, whether or not accounting for sinus rhythm. Betensky et al.[4], Yoshida et al.[5], and Di et al.[9] performed QRS measurement during sinus rhythm. This measure takes into account variations in body habitus, cardiac rotation, respiration, and ECG lead position. (4) Precordial transition lead. The criteria established by Betensky et al.[4], Cheng et al.[6], and Di et al.[9] just included OTVAs with the transition lead in V3. However, other studies included OTVAs without restrictions in the precordial transition lead. Given the discrepancy among the studies mentioned above, we need to comprehensively review and compare these criteria. In our retrospective and validation study, 200 patients with OTVAs originating from all six subdivisions were enrolled. The precordial transition lead varied from V1 to V6. Given the anatomic complexity of the ventricular outflow tract, it may be difficult to differentiate the origin of PVCs using a single parameter. Therefore, it is better to combine several simple and credible parameters to predict OTVA origin.
Thelarger ISA in leads V1 and V2 and theV2S/V3R index have great power in predicting VA origin without restrictions in the transition lead
The precordial V1–V3 leads are adjacent to the LVOT and RVOT and are the best parameters to distinguish OTVA. As the focus moves far away from the lead, R-wave amplitude increases, and S-wave amplitude decreases. This results in a higher R-wave amplitude and lower S-wave amplitude in the V1–V3 leads during OTVAs originating from the LVOT than those originating from the RVOT. Therefore, VAs originating from the LVOT would have a larger ISA and a smaller V2S/V3R index than those originating from the RVOT.
The ablation targets of five patients who were misdiagnosed by the algorithm were analyzed. In three patients, the VA was located in the septum of the RVOT (misdiagnosed as in the LVOT), and in two, the VA was located in the LCC (misdiagnosed as in the RVOT). Anatomically, the location of the RVOT is more anterior and leftward of the LVOT, whereas that of the LVOT is more posterior and rightward of the RVOT. The intimate nature of these two structures explains why OTVAs from these two distinct locations can be morphologically similar on surface ECG and result in successful ablation in the RVOT with the origin in the LVOT, or vice versa[16, 17].