A new insight into the anatomical ablation approach at R-L ILT for VAs with a left ventricular summit origination: electrophysiological characteristics and catheter ablation

4.1 Major findings

The main findings of this study are as follows: (1) ECG characteristics of VAs successfully ablated in the R-L ILT region varied remarkably with different EAS locations. Most VAs’ ECG patterns met the criteria for a left ventricular outflow tract (LVOT) origin, while a certain portion of patients exhibited patterns indicating an RVOT origin. The ATV3 pattern, a simple and distinct electrocardiographic pattern indicative of an origin from the septal margin of the LV summit, was rarely observed in this study. (2) Different mapping results were observed in this study, with a different EAS either at the RVOT region, R-L ILT, or epicardial region. An anatomical ablation approach at the R-L ILT region was effective for VAs with an LV summit origin, even with poor pace and activation mapping results. An EAS observed at the GCV/AIV region with poor pace-mapping results in both the endocardial and epicardial regions may have predictive value for a failed ablation result.

4.2 ECG characteristic with different EAS location

Most VAs’ ECGs in this study presented a morphology indicative of LVOT origination (910). Other ECG patterns included a relatively narrow QRS duration, a Q-wave amplitude ratio of lead aVL/aVR < 1.5, and an MDI index < 0.55, which was inconsistent with epicardial VAs originating from the epicardial region of GCV/AIV8. An rS or QS pattern in lead I was observed in 63% of VAs, which contradicted the manifestation of RCC origination [11]. This result also partially differed from a previous study in which the ECG characteristic of VA ablated successfully in the R-L ILT had been described [7]. These ECG characteristics in this study may indicate VA originates from the base of the LV summit (inaccessible area).

The different ECG patterns for different EAS locations were first reported in this study. A higher percentage of rS/QS patterns in lead I and a narrower QRS duration were observed in VAs with EAS located in the RVOT region compared with the other two groups. This pattern may indicate that the VA originated from the intramural region of the ventricular septum in LVS. Liao [6] reported an ATV3 pattern as a simple and distinct electrocardiographic pattern indicative of an origin from the septal margin of the LV summit, which could be successfully ablated from the R-L ILT vantage point. However, only 1 patient in this study presented with an ATV3 pattern. This pattern was also rarely observed in Ma’s study [7]. The diversification of ECG patterns observed in this study was considered to be caused by the different VA’ origins in the LVS region and its preferential conduction.

4.3 Mapping and ablation

An inaccessible region of the LVS superior to the GCV was considered the real origin of VAs in this study, based on the ECG pattern and mapping results. Percutaneous epicardial ablation was often unlikely to be successful due to the proximity to coronary arteries and pericardial fat [12,13,14]. Ablation within the GCV was more often successful when VAs originated from the lateral portion of the LV summit. The approach to ablation in the distal GCV or AIV was always limited by branch diameter, high impedance, and the adjacent coronary artery. Therefore, ablation attempts at the EAS or the endocardial site closest to the VA origin were recommended in previous studies (67). However, a subvalvular endocardial approach was only utilized in 49% of LV summit VA according to a recent multicenter study [5]. In this study, the mapping and ablation results were further explored. Different mapping results were obtained with different EAS locations in this study, consistent with previous studies. However, a higher percentage of the location of EAS in the RVOT region was observed in our study. For this group, an ideal pace-mapping result at EAS was also observed in 38% of VAs, and ablation at EAS was transiently effective in 67% of VAs. Considering the unique ECG patterns compared with the other two groups, it was hypothesized that the VAs might originate from the intramural region of the septum at LVS adjacent to EAS and had preferential conduction to RVOT. Though poor activation and pace-mapping results were obtained in the R-L ILT, it had a close relationship with the RVOT septal. The real origin of VA was supposed to be just between these two locations. The mean distance of the R-L ILT target to RVOT EAS was 13.8 ± 3.0 mm. That’s why all VAs in this group could be eliminated at the R-L ILT finally. In group 2, a spike presystolic potential at the R-L ILT could be recorded in 6 VAs, while poor pace-mapping results at this region were observed in 7 patients. This result was consistent with a previous study, which indicated that the R-L ILT was not the VAs’ real origin but was adjacent to the region of VAs’ origin. Therefore, ablation at the R-L ILT was effective in all patients in this group.

In group 3, different ablation results were observed compared with the other 2 groups. While all the VAs were successfully ablated in groups 1 and 2, 57% (4/7) of patients ultimately failed in this group. Although an EAS was observed in the GCV/AIV, poor pace-mapping results in the epicardial region were noted in VAs. A rS morphology of unipolar potential was also observed in 1 VA. For the 4 failed VAs, 1 patient only received endocardial ablation attempts due to a high impedance of more than 300 in the AIV target, and the other 3 patients underwent both endocardial and epicardial ablation attempts. Ablation was transiently effective in the R-L ILT region in 3 VAs and reduced the PVC burden by 70% in 1 patient during the 1-year follow-up. EAS in the endocardial region were observed in the RVOT region in most VAs (6/7) in this group. It was considered that the VAs’ origin in this group was located more closely to the RVOT and epicardial region of the LVS. An earlier EAS may be observed in the region of the distal branch of the GCV/AIV where the mapping catheter couldn’t reach. Although ablation at the R-L ILT results in direct contact with the myocardium of the LV ostium according to a previous study, it was still possible that the ablation energy couldn’t penetrate deep enough to reach the location of the VA’s real origin in the LVS due to different anatomical structures of the LVS in every patient. On the other hand, a lower energy applied within the GCV was another reason why failures occurred in the epicardial region.

4.4 Study limitation

First, mapping of the summit-CV failed in certain patients due to anatomical or instrumental limitations. Even for other patients, it was difficult to obtain potential information at the region of the distal AIV or other distal branches of the GCV. The real activation pattern of the inaccessible epicardial region of the LVS was not illustrated in this study. Second, an intracardiac echo was not utilized in all patients due to high costs. Thus, the precise location of the catheter tip and its anatomical relationship with the aortic valve could not be shown during the procedures. Third, this study was not prospective, and the sample size was relatively small due to the low morbidity of this specific type of VAs.

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