In the present study, we found that VOT PVCs/VT exhibiting qrS morphology or QS morphology with a notch on the descending limb in lead V1 could arise from RVOT, LCC, RCC, L-RCC, ILCC respectively, and be effectively treated with RFCA. Combining TZ index and QRS morphology in lead I to predict origin site of these kind VAs is a convenient, simple and reliable method and facilitates the RFCA procedure.
Several previous studies showed that VOT PVCs/VT exhibiting qrS morphology or QS morphology with a notch on the descending limb in lead V1 rose from L-RCC. Yamada et al.  performed successful ablation of 146 cases of PVCs with a ventricular outflow tract origin. Among these 146 cases, 5 cases had qrS pattern in lead V1 ~ V3, all of which were successfully ablated from L-RCC; the rest 141 cases arose from other sites of outflow and none of them have qrS pattern in V1 ~ V3. In addition, Yamada et al. paced multiple sites in the aortic root in the control subjects demonstrated that only pacing from the L-RCC could reproduce a qrS pattern in leads V1–V3. Thus, they concluded that the ventricular arrhythmias with qrS in the right chest leads had a high specificity in discriminating the L-RCC origin with RVOT and other LVOT origins. Bala et al.  investigate the electrocardiographic characteristics related to ventricular arrhythmias arising from the L-RCC. Among 35 consecutive patients with ventricular arrhythmias arising from the aortic cusp region, they found a QS morphology in lead V1 with a notch on the descending limb was exhibited in 15 of 19 ventricular arrhythmias arising from the L-RCC compared to 2 of 18 ventricular arrhythmias from other aortic cusp sites, thus they proposed that common features of ventricular arrhythmia originating from L-RCC was QS pattern with a notch on the descending limb in lead V1, and the precordial transitional zone was prior to lead V3. Both studies indicated VOT PVCs with V1 presenting qrS or QS pattern with notching on the descending limb mainly originating from the L-RCC.
In the past 8 years we had performed successfully RFCA in 49 PVCs/VT presenting qrS or QS pattern with notching on the descending limb in lead V1. We confirmed that 26 PVC cases had RVOT origin, and 23 had LVOT origin (16 from L-RCC, 4 from LCC, 2 from RCC and 1 from ILCC, respectively). According to the ECG diagnosis criteria proposed by Bala et al. , the majority cases in our study were supposed to have a L-RCC origin, however, only 16 cases actually arose from L-RCC origin. However, we found combining TZ index and QRS morphology in lead I, the origin of VOT PVCs with qrS or QS pattern with notching on the descending limb in lead V1 can be precisely predicted.
We used to think that PVCs/VT with a LVOT origin has an early TZ before lead V3, however, recent studies demonstrated that the predicting value of TZ ≤ V3 for LVOT was actually not so good owing to the complex anatomical structure of VOT and cardiac rotation. Ouyang et al.  reported that for VOT PVCs/VT, the morphology of QRS complexes in leads V1 ~ V2 may be used to identify RVOT or LVOT origin, they suggested that the PVCs were of LVOT origin when the R/S amplitude index >0.3 or R wave duration index >0.5, otherwise it was from RVOT. Yoshida et al.  once proposed that utilizing the V2S/V3R index to distinguish left VOT-VAs from right VOT-VA, when the V2S/V3R index ≤1.5, a LVOT origin was considered. Another study by Yoshida N et al.  found that precordial TZ index (refers to the PVCs/VT precordial transitional zone minus the sinus rhythm precordial transitional zone) < 0 had a higher sensitivity, specificity and accuracy in predicting LVOT-originated ventricular arrhythmias. Liu Z et al.  suggested that multiple intercostal recordings resulted in the interpretation of the depolarization vector of the outflow tract ventricular arrhythmia in a more comprehensive way, and proposed the combined TZ index ≤0.25 helped identify the ASC origin more accurately. In our study, we referred to the ECG criteria proposed by ouyang et al. and Yoshida et al. for they were simple and convenient, the predictive ability of precordial TZ < 3, precordial TZ index < 0, and R wave duration index > 50% and R/S amplitude index > 30% for LVOT origin was compared with each others, the TZ index < 0 was demonstrated to be the best ECG criterion among them. In the purpose of rapidly and accurately locating VOT PVCs with lead V1 presenting qrS pattern or QS pattern with a notch on the descending limb before RFCA, we suggested the precordial TZ index < 0 should be primarily adopted to differentiate the LVOT origin from the RVOT origin. In addition, in our study, we found that Ouyang et al.’ criterion R wave duration index >0.5 and R/S amplitude index > 0.3 did not show a good ability for identifying LVOT origin, thus we suggested that Ouyang criterion which mainly based on QRS morphology in lead V1-V2 was actually not suitable for this special kind PVCs/VT.
The QRS morphology in lead I was further adopted to differentiate PVCs origin within ASCs. Ouyang et al.  showed that ventricular arrhythmias with different origins within the aortic sinus cusps(ASCs) exhibited certain differences in lead I, PVCs from the LCC region typically have an rS in lead I, whereas, PVCs from the RCC typically are positive and notched in lead I. In our study, we found the ventricular arrhythmias with LCC origin in lead I had mainly negative waves, while the ventricular arrhythmias with RCC and L-RCC origin in lead I had primarily positive waves with r, R, m or Rs pattern. The distinctive morphology in lead I of these ASC ventricular arrhythmias was mainly caused by the their depolarization direction, depolarization of the ventricular arrhythmias with LCC origin was usually toward the opposed direction of lead I, thus resulted in a mainly negative wave, while the depolarization direction of the ventricular arrhythmias with L-RCC or RCC origin was usually toward the same direction of lead I, thus resulted a mainly positive waves. Therefore, the morphology of the QRS complex in lead I may help to further determine the origin of ventricular arrhythmias exhibiting qrS or QS pattern with notching in the descending limb in lead V1. When the r, m, R or Rs morphology in lead I was applied to predict L-RCC and RCC origin in our study, it was demonstrated with sensitivity of 94.44%, specificity of 60%, positive predictive value of 89.47% and negative predictive value of 75.00%.
Based on our observation, we concluded that VOT PVCs/VT with V1 presenting qrS patten or QS pattern with a notch in descending limb did not all originate from L-RCC, when predicting the exact origins of this kind PVCs/VT, both the TZ index and morphology in lead I should be taken into account.
Limitations of this study included, ① location of PVC/VT origins were mainly based on X-ray images (aortic sinus angiography) and three-dimensional mapping system, nonetheless, the advanced intracardiac ultrasound technique was not applied; ② our sample size was small, which could lead a certain level of sampling bias. Thus, a future study with a large cohort is warranted to corroborate our findings.