Usefulness of the synthesized 18‐lead ECG in premature ventricular contractions from near the HIS bundle

Isolated premature ventricular complexes (PVCs) are the most common arrhythmias observed in patients even if without structural heart disease.1 Although most PVCs originate from the right ventricular outflow tract (RVOT), there are some PVCs that originate near the HIS bundle.2 The synthesized 18lead ECG consists of rightsided thoracic (V3R, V4R, V5R) and dorsal (V7, V8, V9) ECG leads derived from a mathematical calculation of the 12lead ECG, and the detailed mathematical formula is shown in Figure 1. The synthesized 18lead ECG has been reported to be effective for PVCs of an RVOT origin, but the rest remains to be elucidated.3 The aim of this study was to investigate the characteristics of the synthesized 18lead ECG in patients with PVCs originating from near the HIS bundle. The synthesized 18lead ECGs of 13 consecutive patients who underwent radiofrequency catheter ablation (RFCA) of idiopathic PVCs from near the HIS bundle at the Japan Community Healthcare Organization Osaka Hospital, Osaka General Medical Center, and Nara Prefectural Seiwa Medical Center from January 2018 to December 2020 were included in this retrospective analysis. The origin of the PVCs was identified by a cardiologist using a 3D mapping system (CARTO 3: Biosense Webster Inc or EnSite: Abbott Medical Inc). We analyzed the QRS morphology pattern of the synthesized 18lead ECG analyzed in those patients. This study was approved by the Ethics Committee of each hospital in accordance with the Declaration of Helsinki. The synthesized 18lead ECG and ECG characteristics in 13 patients with PVCs from near the HIS bundle are shown in Figure 2 and Table 1. The mean QRS duration of the ECG was 142.5 ± 26.9 ms. In 12 of 13 patients, a left bundle branch block pattern (92.3%) was present, and 11 of 13 patients had inferior axis deviation (84.6%). Regarding the rightsided chest leads of the synthesized 18lead ECG, in all patients, a QS pattern in lead V5R (100%) was observed, and in 12 of 13 patients, a QS pattern in leads V3R, V4R, and V5R (92.3%) was present. A comparison showed that the synthesized ECGs recorded during sinus rhythm and during PVCs were not consistent, as shown in Table 2. Several studies have shown that identifying PVCs originating from the vicinity of the ventricular septum remains complicated,4 and it is difficult to identify the origin of PVCs originating from near the HIS bundle based on the characteristics of the 12lead ECG. Noteworthy among our results was that there was a QS pattern in lead V5R in 100.0%. Igarashi et al reported that in the synthesized 18lead ECG recorded by pace mapping in the outflow tract, a QS pattern in lead V5R was observed in about 80% at the right coronary cusp (RCC), about 20% in the posterior RVOT, and nothing at the other sites.3 Combining the above study3 with our results, a QS pattern in lead V5R might have been specific to PVCs originating from near the HIS bundle and RCC. QRS morphology changes after RFCA are often observed in patients with idiopathic PVCs.5 In such cases, the use of the synthesized 18lead ECG's rightsided chest leads may assist in the remapping process. Regarding the mechanism of the QS pattern in lead V5R, in general the HIS bundle is anatomically closer to the RCC, and electrical conduction may propagate with a vector

Isolated premature ventricular complexes (PVCs) are the most common arrhythmias observed in patients even if without structural heart disease. 1 Although most PVCs originate from the right ventricular outflow tract (RVOT), there are some PVCs that originate near the HIS bundle. 2 The synthesized 18-lead ECG consists of rightsided thoracic (V3R, V4R, V5R) and dorsal (V7, V8, V9) ECG leads derived from a mathematical calculation of the 12-lead ECG, and the detailed mathematical formula is shown in Figure 1. The synthesized 18-lead ECG has been reported to be effective for PVCs of an RVOT origin, but the rest remains to be elucidated. 3 The aim of this study was to investigate the characteristics of the synthesized 18-lead ECG in patients with PVCs originating from near the HIS bundle.
The synthesized 18-lead ECGs of 13 consecutive patients who underwent radiofrequency catheter ablation (RFCA) of idiopathic PVCs from near the HIS bundle at the Japan Community Healthcare Organization Osaka Hospital, Osaka General Medical Center, and Nara Prefectural Seiwa Medical Center from January 2018 to December 2020 were included in this retrospective analysis. The origin of the PVCs was identified by a cardiologist using a 3D mapping system (CARTO 3: Biosense Webster Inc or EnSite: Abbott Medical Inc). We analyzed the QRS morphology pattern of the synthesized 18-lead ECG analyzed in those patients. This study was approved by the Ethics Committee of each hospital in accordance with the Declaration of Helsinki.
The synthesized 18-lead ECG and ECG characteristics in 13 patients with PVCs from near the HIS bundle are shown in Figure 2 and Table 1. The mean QRS duration of the ECG was 142.5 ± 26.9 ms.
In 12 of 13 patients, a left bundle branch block pattern (92.3%) was present, and 11 of 13 patients had inferior axis deviation (84.6%).
Regarding the right-sided chest leads of the synthesized 18-lead ECG, in all patients, a QS pattern in lead V5R (100%) was observed, and in 12 of 13 patients, a QS pattern in leads V3R, V4R, and V5R (92.3%) was present. A comparison showed that the synthesized ECGs recorded during sinus rhythm and during PVCs were not consistent, as shown in Table 2.
Several studies have shown that identifying PVCs originating from the vicinity of the ventricular septum remains complicated, 4 and it is difficult to identify the origin of PVCs originating from near the HIS bundle based on the characteristics of the 12-lead ECG.
Noteworthy among our results was that there was a QS pattern in lead V5R in 100.0%. Igarashi et al reported that in the synthesized 18-lead ECG recorded by pace mapping in the outflow tract, a QS pattern in lead V5R was observed in about 80% at the right coronary cusp (RCC), about 20% in the posterior RVOT, and nothing at the other sites. 3 Combining the above study 3 with our results, a QS pattern in lead V5R might have been specific to PVCs originating from near the HIS bundle and RCC. QRS morphology changes after RFCA are often observed in patients with idiopathic PVCs. 5 In such cases, the use of the synthesized 18-lead ECG's right-sided chest leads may assist in the re-mapping process. Regarding the mechanism of the QS pattern in lead V5R, in general the HIS bundle is anatomically closer to the RCC, and electrical conduction may propagate with a vector This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. F I G U R E 1 Schematic of the synthesized 18-lead ECG. The 18-lead ECG is synthesized from the 12-lead ECG by a specific arithmetic process.
F I G U R E 2 Details of the ECGs of the 13 cases. Only the 7th case is considered to be a PVC caused by the HIS bundle based on the characteristics of the ECG. away from the right-sided chest leads such as lead V5R. Based on the characteristics of the ECG, only case 7 was considered to have a PVC from the HIS bundle. An identification of PVCs originating from near the HIS bundle or from the HIS bundle was attempted based on the characteristics of the synthesized ECG, but was not possible due to an insufficient number of cases. Although a 3D mapping system was used in this study, the distance between the HIS bundle and the ablation site was not measured, and it was considered necessary to include the distance in future studies.
A QS pattern recorded in lead V5R of the synthesized 18-lead ECG was characteristic of PVCs originating from near the HIS bundle. This observation might assist in identifying the origin of PVCs during RFCA.

AUTH O R CO NTR I B UTI O N S
H Kida, R Nakanishi, and N Ogasawara participated in the design of the study and coordination and helped draft the manuscript. All authors read and approved the final manuscript.

ACK N OWLED G M ENT
We would like to express our gratitude to Mr. John Martin for his linguistic revision of the manuscript.