Abstract
Objective
To compare the clinical characteristics, electrocardiographic characteristics, and outcomes of radiofrequency catheter ablation in patients with idiopathic right ventricular outflow tract ventricular arrhythmias originating near the Hisian bundle region versus other right ventricular outflow tract regions.
Methods
A single-center study analyzed 126 patients undergoing radiofrequency catheter ablation for right ventricular outflow tract ventricular arrhythmias from May 2020 to October 2022. Patients were classified into the near-Hisian group (n = 10) and the right ventricular outflow tract group (n = 116) based on the arrhythmia origin. Clinical, electrocardiographic, and procedural characteristics as well as ablation outcomes were compared.
Results
The near-Hisian group had narrower QRS duration (132.3 ± 24.1 vs. 146.1 ± 28.3 ms), 100% positive QRS in lead I, smaller R-wave ratio in leads III/II (0.65 ± 0.20 vs. 0.97 ± 0.31), smaller Q-wave ratio in leads aVL/aVR (0.31 ± 0.29 vs. 1.03 ± 0.37), and larger R/S ratio in lead V2 (18.8 ± 10.9 vs. 12.0 ± 6.7) (all p < 0.05). Procedural metrics, acute success (90%), and long-term success (80%) were comparable between the two groups, with no major complications reported.
Conclusions
Right ventricular outflow tract ventricular arrhythmias near the Hisian bundle region have distinct electrocardiographic features. Radiofrequency catheter ablation is safe and effective, emphasizing the need for precise electrocardiogram interpretation and meticulous procedural planning.
Keywords
Introduction
Idiopathic ventricular arrhythmias (VAs) account for approximately 10% of all patients evaluated for ventricular tachycardia (VT).1,2 Among these patients, VAs most commonly originate from the outflow tract, with 70%–80% arising from the right ventricular outflow tract (RVOT).1,2 RVOT VAs near the Hisian (His) bundle are defined as those within 10 mm of the largest His bundle electrogram signal.3,4 Although these VAs share some common electrocardiographic (ECG) characteristics of RVOT VAs (narrow QRS complex, left bundle branch block (LBBB), and inferior axis), they also possess some unique features. 4
Radiofrequency catheter ablation (RFCA) is the preferred treatment modality for symptomatic RVOT VAs, including those near the His bundle. However, ablation in this region poses significant challenges due to the increased risk of atrioventricular block. In this study, we aimed to compare the clinical and ECG characteristics as well as the outcomes of RFCA in patients with idiopathic RVOT VAs originating near the His bundle region versus those originating from other RVOT regions.
Methods
Study design and population
This was an observational, single-center retrospective study involving 126 patients who underwent RFCA for VAs originating from the RVOT at E Hospital, Hanoi, Vietnam, between May 2020 and October 2022. The reporting of this study conforms to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines. 5 The cases included in this analysis were limited to those successfully ablated within the RVOT and right ventricle. Patients who required crossover to left ventricular outflow tract (LVOT) ablation or right coronary cusp (RCC) ablation were not included in the study cohort and were excluded from the analysis. This exclusion criterion was implemented to maintain a homogeneous study population focused on RVOT VAs. Patients were divided into two groups based on the origin of the VAs identified during catheter ablation. The near-His group included patients with VA origins located within 10 mm of the largest His bundle electrogram signal. The RVOT group consisted of patients with VAs originating from other regions of the RVOT.
The primary objective of this study was to compare the ECG characteristics and procedural outcomes, including efficacy and safety, of patients between the two groups. Procedural efficacy was defined as the proportion of patients free from VA recurrence at the end of follow-up. The primary safety endpoint was major complications, including death, cardiac tamponade, and permanent atrioventricular block. Secondary safety endpoints included minor complications such as vascular access issues and right bundle branch block (RBBB).
Eligible patients were those who underwent catheter ablation for frequent RVOT VAs during the study period. All patients underwent laboratory evaluations, including echocardiography, 12-lead ECG, and 24-hour Holter monitoring, to exclude structural heart disease, determine the VA burden, and assess VA morphology. Anti-arrhythmic medications were discontinued for at least five half-lives before the procedure.
This study was conducted in accordance with the ethical principles of the Helsinki Declaration of 1975, as revised in 2024.
ECG analysis
Sinus rhythm and VA ECG morphology were measured on the EP-Workmate Recording System (Abbott Medical, Chicago, IL USA), with the recordings displayed at a sweep speed of 100 mm/s. The measured ECG data were based on a typical VA QRS complex and included the following parameters: (a) QRS duration (ms); (b) coupling interval (ms); (c) positive QRS pattern in lead I; (d) R-wave ratio of leads III/II; (e) Q-wave ratio of leads aVL/aVR (calculated as the ratio of Q-wave amplitudes in aVL to aVR; in cases where no Q wave was present in lead aVL, the ratio was assigned a value of 0); (f) V2 R-wave duration (ms); (g) R-wave duration index (%); (h) R/S ratio in V2 (%); (i) V2S/V3R index; and (j) V2 transition ratio. Definitions of ECG criteria for the QRS complex in premature ventricular complexes (PVCs) are illustrated in Figure 1.
Definition of electrocardiographic (ECG) criteria for premature ventricular complex (PVC) QRS complex.
Electrophysiological mapping and ablation protocol
Ensite Velocity 3D EAM system and Workmate electrophysiological system (Abbott Medical, Chicago, IL USA) were used for visualization of catheters for localizing arrhythmogenic foci in RVOT. Two nonsteerable quadripolar catheters with 4-mm distal electrode were placed at the His bundle region and right ventricle apex via the right femoral vein. The radiofrequency (RF) ablation catheter used was 4.5 mm long, bidirectional deflectable, and nonirrigated (Safire Bi-directional Ablation Catheters, Abbott Medical, Chicago, IL, USA). As RF was applied at an ablation target near the His bundle, the ablation catheters were placed via an 8.5F long sheath (SL1; Abbott Medical) via the inferior cava vein through the right femoral vein under fluoroscopic guidance. Three-dimensional (3D) anatomic mapping was performed with both activation mapping and pace mapping. A nonsteerable quadripolar catheter (Supreme electrophysiology catheter, 6F, 2-5-2 mm spacing; Abbott Medical) was placed at the His bundle region with the largest His bundle electrogram signal at the distal electrode. The identified origin and ablation target were defined as the site at which VAs were eliminated with RF application. The distance between the largest His bundle electrogram signal and the ablation target was measured using calipers on 3D electroanatomic map. Ablation was only performed if this distance exceeded 5 mm to minimize the risk of atrioventricular block.
After identifying the ablation target based on activation mapping, pace mapping was performed at current outputs of 10 and 5 mA, pulse widths of 1.0 and 0.5 ms, and a pacing cycle length of 450 ms. The morphology of the paced QRS complex was compared with that of the spontaneous VA on the 12-lead ECG. RF energy was only delivered if the paced QRS morphology matched the spontaneous VA in ≥11 of the 12 leads.
RF energy was applied at a power of 20 W, which was then increased to a maximum power of 40 W. The goal of each ablation lesion was a reduction in the impedance of 10 Ohms. The maximum temperature was 60°C in the RVOT or 55°C in sites near the His bundle region. If VAs were eliminated during the first 30 s, RF application was continued. Otherwise, mapping was continued if VAs persisted. If the earliest activation time noted was at the site of the largest His bundle potential, RF energy was not delivered.
In this study, none of the near-His VAs required ablation at the maximum power of 40 W. The majority of cases were successfully ablated at power settings of 25–30 W, with an average achieved at a power of 28 W. The target temperature was set at >50°C. If the target temperature was not achieved at these power levels, the ablation catheter was repositioned to optimize tissue contact before considering further power escalation. Due to the relatively low power settings (25–30 W), no steam pops were observed during the procedures. However, junctional rhythm was noted in some cases during ablation. In our protocol, if the junctional rhythm was sporadic, slow, and interspersed with sinus rhythm, ablation was continued. However, if the junctional rhythm became rapid and sustained, RF delivery was immediately discontinued to avoid the risk of atrioventricular block.
Acute success was defined as complete elimination of spontaneous VAs after the procedure. Long-term success was defined as the number of PVCs <1000 beats recorded on the 24-hour Holter, as well as no evidence of any VAs during the follow-up period of at least 1 month.
Follow-up and outcome assessment
Patients were followed up after discharge at the outpatient clinic with 24-hour Holter monitoring. The recurrence status was identified as the presence of sustained VT, nonsustained VT, or greater than 1000 PVCs on 24-hour Holter ECG.
Statistical analysis
Continuous variables were represented as the mean and standard deviation (SD), whereas categorical variables were described as percentages and frequencies. All statistical analyses were conducted using the Statistical Package for the Social Sciences (SPSS) software, version 13.0 (IBM Corp., Armonk, NY, USA). A two-sided p-value <0.05 was considered statistically significant. There were no missing data in the primary variables.
All patient data were carefully de-identified prior to analysis to ensure complete anonymity. No personal identifiers were accessible during data collection or manuscript preparation.
Results
A total of 126 patients underwent RFCA for RVOT VAs during the study period. Of these, 10 patients were categorized into the near-His group, while the remaining 116 patients had VAs originating from other regions of the RVOT (RVOT group). However, in the near-His group, one patient did not undergo ablation as the earliest activation time of the ventricular signal was located at the site with the largest His bundle electrogram signal, making ablation unsafe. Consequently, procedural outcomes were analyzed for 9 patients in the near-His group and 116 patients in the RVOT group.
Clinical characteristics
Table 1 summarizes the clinical characteristics of the study population. The overall mean age was 50.8 ± 13.4 years, with no significant difference observed between the two groups (54.3 ± 18.6 years in the near-His group vs. 50.5 ± 12.9 years in the RVOT group; p = 0.38). Female patients constituted the majority of the patients in the total cohort (77.8%) as well as within each subgroup (70.0% in the near-His group and 78.4% in the RVOT group). The primary clinical symptoms reported were palpitations (73.0%), chest pain (58.7%), dyspnea (39.7%), and dizziness/syncope (15.9%). There were no statistically significant differences in the prevalence of these symptoms between the two groups (p > 0.05). Arrhythmias documented on 24-hour Holter monitoring were predominantly premature ventricular contractions, which were observed in 77% of the total population, 80.0% of the near-His group, and 76.7% of the RVOT group. VT accounted for 23% of all cases. The distribution of arrhythmia types was similar between the two groups (p > 0.05).
Clinical characteristics of the study patients.
PVC: premature ventricular complex; RVOT: right ventricular outflow tract; VT: ventricular tachycardia; SD: standard deviation.
ECG characteristics
The near-His group demonstrated a QRS duration of 132.3 ± 24.1 ms and a coupling interval of 448.5 ± 76.7 ms. All patients in this group exhibited a prominent positive R wave in lead I. Specific characteristics of the R wave included an R-wave ratio in leads III/II of 0.65 ± 0.20, an R/S ratio in lead V2 of 18.8 ± 10.9, and an R-wave duration in lead V2 of 32.9 ± 16.6 ms. Additional electrocardiographic features observed in the near-His group were a Q-wave ratio of leads aVL/aVR of 0.31 ± 0.29, a peak deflection index of 0.53 ± 0.10, and a V2S/V3R index of 3.56 ± 1.23 (Table 2). As shown in Figure 2, although VAs originating near the His bundle typically display a positive QRS complex in lead aVL, two cases in the near-His group exhibited a QS pattern in lead aVL. This finding may reflect the inherent variability in ECG morphology despite the anatomical proximity to the His bundle. In our study, the classification of near-His VAs was based on the measured distance (<10 mm) from the ablation target to the largest His bundle signal on the 3D electroanatomic map, rather than relying solely on QRS morphology.
Electrocardiographic characteristics of idiopathic right ventricular arrhythmias originating near the His bundle region compared with those originating from other regions of the RVOT.
RVOT: right ventricular outflow tract; SD: standard deviation; *significance level at p < 0.05.
Twelve-lead electrocardiogram of idiopathic right ventricular arrhythmia originating from the near-Hisian (His) bundle region (Top: Case 1 to Case 10). Activation mapping of the premature ventricular complexes (PVCs) originating from the near-His region in the right ventricle (Bottom: Case 10), with local ventricular electrogram recorded from the distal bipole of the ablation catheter, preceding the onset of the QRS by 35 ms.
Analysis of ECG parameters revealed significant differences between the near-His group and RVOT group. Patients in the near-His group exhibited a narrower QRS duration (132.3 ± 24.1 vs. 146.1 ± 28.3 ms), 100% prevalence of positive QRS complexes in lead I, smaller R-wave ratio in leads III/II (0.65 ± 0.20 vs. 0.97 ± 0.31), and smaller Q-wave ratio in leads aVL/aVR (0.31 ± 0.29 vs. 1.03 ± 0.37). Conversely, the near-His group demonstrated a larger R/S ratio in lead V2 (18.8 ± 10.9 vs. 12.0 ± 6.7) than the RVOT group. All of these differences were statistically significant (p < 0.05) (Table 2).
Procedural parameters and outcomes of RF catheter ablation
The procedural outcomes of catheter ablation are summarized in Table 3. The procedure time (62.2 ± 13.5 vs. 63.6 ± 14.2 min), fluoroscopy time (422.7 ± 92.1 vs. 342.3 ± 78.5 s), ablation time (444.8 ± 98.5 vs. 392.0 ± 86.3 s), and average number of lesions (6.8 ± 1.5 vs. 7.5 ± 1.9) were comparable between the two groups (p > 0.05). The acute success rate was 90% in the near-His group, while the long-term success rate was 80%. These outcomes were comparable to those of the RVOT group, with no statistically significant differences observed between the two groups. Regarding procedural safety, minor complications were observed in both groups, including transient and reversible RBBB. No major complications, such as cardiac tamponade or permanent atrioventricular block, were reported in either group.
Procedural parameters and outcomes of radiofrequency catheter ablation in patients with idiopathic RVOT ventricular arrhythmias.
RF: radiofrequency; RVOT: right ventricular outflow tract; SD: standard deviation.
Discussion
Idiopathic RVOT VAs typically originate from single foci and are not associated with structural heart disease. Their sites of origin can often be predicted using 12-lead surface ECGs. The characteristic ECG pattern of RVOT VAs includes an LBBB morphology with an inferior axis, represented by positive R waves in leads II, III, and aVF, and negative deflections in leads aVR and aVL.6–8 Additionally, the QRS morphology of VAs provides further insights into their precise origin within the RVOT, including differentiation between free wall/septal regions, anterior/posterior locations, and proximal/distal positions.9,10
The decision to not proceed with ablation in one patient due to the proximity of the earliest activation site to the His bundle highlights the technical challenges and risks associated with near-His VAs. This case was considered a procedural failure in our analysis, resulting in an acute success rate of 90% and a long-term success rate of 80% for the near-His group. To minimize the risk of atrioventricular block, we carefully measured the distance between the ablation target and the site of the largest His bundle signal using calipers on the 3D electroanatomic map. Ablation was only performed if this distance exceeded 5 mm, ensuring a safe margin for effective lesion formation while avoiding damage to the His bundle.
Among patients with PVCs or VT originating from the RVOT in our study, 10 of 126 cases (11.7%) were identified as having foci near the His bundle. Our findings indicated that the near-His group exhibited a shorter QRS duration, a prominent positive R-wave pattern in lead I, and reduced QRS amplitude in lead aVL. Notably, an R or rR pattern in lead aVL was frequently observed in VAs originating near the His bundle and could serve as a predictor for this specific arrhythmia focus. Furthermore, the positive R pattern in lead I was universally present in VAs near the His bundle, a feature not commonly associated with other RVOT VAs, except those originating from the posterior aspect of the RVOT.
Ban et al. previously demonstrated that the ECG characteristics of para-Hisian RVOT VAs could effectively distinguish them from posterior RVOT VAs prior to RF ablation. 4 Consistent with their findings, our study revealed significant differences in QRS duration, R-wave ratio in leads III/II, Q-wave ratio in leads aVL/aVR, R/S ratio in lead V2, and the presence of a positive QRS pattern between the near-His and RVOT groups (p < 0.05). These findings align with those of previous studies that highlighted that PVCs or VT originating near the His bundle exhibit specific ECG features beyond the general LBBB morphology with an inferior axis. These include a narrower QRS duration, a left inferior axis with a dominant R wave in lead I, positivity in lead aVL, and a QS pattern in lead V1. Additionally, the QRS transition in VAs from near the His bundle, typically occurring after lead V3, resembles that observed in other RVOT regions.2,4,11–13
In our study, arrhythmias monitored via 24-hour Holter were predominantly PVCs alone (77.0%), while the remaining cases (23.0%) involved PVCs accompanied with VT, consistent with the findings from previous studies. Specifically, Yamada et al. analyzed data from 264 patients who underwent RF ablation for RVOT VAs and reported that 178 patients (67.4%) presented solely with frequent PVCs, while 86 patients exhibited PVCs combined with VT (sustained and/or nonsustained VT). 1 Similarly, Liang et al. observed that 87% of patients had frequent PVCs, with the remainder presenting with VT. 14 Repetitive monomorphic VT is the most common clinical manifestation (60%–90%), characterized by frequent PVCs, couplets, and salvos of nonsustained VT. This type of arrhythmia is the most frequent presentation of idiopathic VAs originating from the RVOT and is adenosine-sensitive with an activation mechanism mediated by cAMP.7,15 However, we observed that the frequency of PVCs recorded via 24-hour Holter monitoring varied significantly across different monitoring periods. This variability is influenced by multiple factors, including exercise status, emotional stress, and menstruation. Consequently, the results obtained from short-term monitoring may not accurately reflect the overall burden of arrhythmias in the long term.
The ablation strategy for VAs originating near the His bundle in our study was consistent with that for other sites in the RVOT. We performed activation mapping using the Earliest Activation Time (EAT) criteria of 15–40 ms to identify the ablation target, which was then reconfirmed with pacing maps, ensuring a match in >11 of the 12 leads. The pacing cycle lengths were set to match the coupling interval of the PVCs, with pacing thresholds ranging from 0.5 to 1.5 V and a pulse width of 0.4 ms. In our study, 9 of the 10 cases underwent RF ablation, with an acute success rate of 100% and a long-term success rate of 88.9%, which are comparable to those of previous reports.3,4,15 Although the success rate was numerically higher in the near-His group than in the RVOT group, this difference did not reach statistical significance. We hypothesized that the difference in success rates between the two groups may be attributed to the specific ECG characteristics of the VA foci. The QRS patterns of VAs originating near the His bundle are distinct, which plays a key role in accurately localizing the VA origin. In contrast, the QRS patterns of RVOT VAs are more similar to those from other regions, such as the pulmonary valve, left ventricular summit, or the LVOT. Consequently, failure or the need for a repeat procedure may be due to the origins located in structures adjacent to the RVOT or related to arrhythmogenic right ventricular cardiomyopathy.1,12
There are several factors that influence the efficacy of RF ablation for near-His VAs, including the accuracy of the 3D electroanatomic mapping system and the quality of catheter-tissue contact. To ensure optimal catheter-tissue contact and stability, we used long sheaths to guide the ablation catheter. Achieving stable catheter-tissue contact during the procedure is more challenging in the near-His region, which contributed to longer procedural and fluoroscopy times in the near-His group than in the RVOT group.
Our findings also demonstrate that the complication rates for ablation were low in both groups. Minor complications, such as transient RBBB, were observed, but no major complications, such as cardiac tamponade or permanent atrioventricular block, occurred. Atrioventricular block is a known risk when performing ablation near the His bundle. To minimize this risk, we carefully marked the anatomical locations of His potential with different colors and measured the distance between them on the 3D map after correcting for nonlinear to linear 3D surface variations using the Field Scale algorithm (Figure 3). Additionally, we started ablation with low power (20 W) and gradually increased the power only if the target temperature of 50°C was not achieved during the procedure. One patient with a QRS interval of 35 ms at the site of the largest His signal required cessation of the procedure due to the risk of inducing atrioventricular block.
The locations of the para-Hisian region and ablation target on the activation mapping (Case 7). The locations were marked with different colors: the premature ventricular complex (PVC) focus (green dot) and the site of the largest His signal (yellow dot). RVOT: right ventricular outflow tract; RA: right atrium; RV: right ventricle.
This study has several limitations that should be acknowledged. First, the observational and single-center design may limit the generalizability of our findings to broader populations or different healthcare settings. Second, the relatively small sample size, particularly in the near-His group, may have reduced the statistical power to detect subtle differences in outcomes and procedural parameters between the two groups. Third, although 24-hour Holter monitoring was used to assess arrhythmic burden and long-term outcomes, it may not fully capture the variability of arrhythmias over an extended period, as arrhythmic events can be influenced by factors such as physical activity, emotional stress, or hormonal changes. Fourth, the reliance on fluoroscopy during ablation procedures, despite the use of 3D electroanatomic mapping systems, may have introduced procedural variability and contributed to operator-dependent outcomes. Fifth, the exclusion of patients who required crossover to LVOT ablation or RCC ablation may limit the generalizability of our findings to the broader population of outflow tract VAs. Finally, the absence of systematic assessment for potential subclinical structural heart disease, such as cardiac magnetic resonance imaging, may have limited our ability to exclude patients with underlying arrhythmogenic substrates entirely. Future studies with larger sample sizes, multicenter designs, and more comprehensive evaluation protocols are needed to validate and expand upon these findings.
Conclusions
Idiopathic RVOT VAs originating near the His bundle region exhibit distinct electrocardiographic features, reflecting potentially unique underlying mechanisms. Despite the procedural challenges associated with this anatomically sensitive region, catheter ablation has proven to be both effective and safe, offering high success rates with minimal complications. These findings highlight the critical role of precise ECG interpretation and meticulous procedural planning in achieving optimal outcomes.
Footnotes
Acknowledgements
We thank our colleagues from the Cardiovascular Center, E Hospital (Hanoi, Vietnam) who treated the study patients during hospitalization and thus laid the foundation for the study and made its completion possible.
Author contributions
Ba Van Vu designed the study and performed the ablation procedures. Kien Trung Hoang, Thinh Duc Do, and Hung Manh Nguyen collected and analyzed the electrocardiographic and ablation data. Linh Thi Hai Ngo and Long Hoang Vo contributed to data interpretation and international collaboration. Kien Trung Hoang, Thinh Duc Do, and Dung Tien Le assisted in patient enrollment and clinical assessments. Nguyen Thao Phan and Huu Cong Nguyen supervised the study, revised the manuscript critically, and approved the final version. All authors have read and approved the final manuscript.
Data availability statement
The data used to support the findings of this study are available from the corresponding authors upon request.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethical approval
This retrospective study was approved by the Ethics Board of Vietnam Military Medical University, Hanoi, Vietnam (Approval No. 2892/QĐ-HVQY; Date: 15/11/2022). All procedures complied with the Helsinki Declaration and its amendments.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
