Abstract
Objective
This study aimed to investigate the association between Epicardial adipose tissue (EAT) and premature ventricular contractions (PVCs) originating from different regions within the right ventricular outflow tract (RVOT).
Methods
Patients with PVCs originating from RVOT undergoing catheter ablation from January 2022 to June 2024 were retrospectively enrolled in this study. Based on actual mapping results, patients were categorized into two groups: RVOT septum and RVOT free wall. The volume and density of EAT were quantified using routine chest CT images. Furthermore, patients were stratified into subgroups by sex, age, and body mass index (BMI) to further compare the relationship between EAT and PVC in different populations.
Results
A total of 127 PVC patients were enrolled: 77 with septal RVOT origin and 50 with free-wall origin. Patients in the RVOT free wall group exhibited significantly higher volumes of total EAT and RV EAT compared to the RVOT septum group (P = 0.021; P = 0.040). No significant differences in EAT density were observed between the two groups. Subgroup analyses revealed that female patients and those with BMI < 23 in the free wall PVC group had larger RV EAT volume and total EAT volume than their counterparts with septum PVCs. However, this difference was not observed in male patients or higher BMI subgroups.
Conclusions
EAT may exhibit greater pathogenicity in PVCs originating from the RVOT free wall, particularly in female and low BMI patients.
Keywords
Introduction
Premature ventricular contractions (PVCs) represent a prevalent cardiac condition. Frequent occurrences of PVCs may result in tachycardia-induced cardiomyopathy, heart failure, and potentially mortality. Currently, effective interventions for PVCs include catheter ablation and pharmacological therapies, such as β-blockers and mexiletine. Nevertheless, the precise pathogenesis of PVCs remains incompletely elucidated.
Epicardial adipose tissue (EAT) is a fat deposit situated between the myocardium and the visceral pericardium. Recent studies have demonstrated that EAT is associated with various cardiovascular diseases, including arrhythmias. The underlying mechanism may involve EAT influencing cardiomyocytes through paracrine secretion of inflammatory factors such as IL-6 and TNF-α. 1 In the context of PVCs, patients with frequent PVCs exhibit larger EAT volumes compared to those without PVCs. 2 Additionally, EAT thickness has been independently associated with recurrence following catheter ablation for PVCs. 3 However, anatomically, EAT is predominantly distributed on the free wall of the heart. It remains uncertain whether EAT exerts differential effects on PVCs originating from various locations, particularly those arising from the interventricular septum.
This study aims to compare the differences in volume and density of EAT between patients with PVCs originating from the septum and free wall regions of the right ventricular outflow tract (RVOT). Additionally, it seeks to analyze these differences among various patient subgroups.
Materials and methods
Study cohorts
This retrospective study consecutively enrolled all patients who underwent catheter ablation for PVCs at our center from January 2022 to June 2024, with RVOT origin confirmed by mapping. Clinical data, including gender, age, height, and history of hypertension, diabetes, coronary artery disease, and statin use, were recorded. Patients with incomplete clinical or chest computed tomography (CT) data were excluded. Based on actual mapping results, patients were categorized into two groups: RVOT septum and RVOT free wall. Hypertension was defined as a reported diagnosis and/or use of antihypertensive medication, or newly diagnosed if systolic blood pressure ≥140mmHg and/or diastolic blood pressure ≥90 mmHg upon three measurements on different days. DM was defined as pre-diagnosed and/or on antidiabetic treatment. Heart failure encompassed HFrEF, HFmrEF, and HFpEF. A history of statin use was defined as continuous statin intake for more than three months. This retrospective study used fully anonymized patient data with all identifiers removed. The reporting of this study conforms to STROBE guidelines. 4 This study was conducted in full compliance with the ethical principles of the Declaration of Helsinki (1975) and its subsequent amendments through 2024. The Ethics Committee of the People's Hospital of Zhejiang Province, China, approved this study.
Mapping and ablation protocol
The RVOT geometry was established using a three-dimensional CARTO mapping system (Biosense Webster Inc., Diamond Bar, CA, USA). All antiarrhythmic drugs (AADs) were discontinued for at least five days prior to the procedure. The optimal ablation site was determined through activation mapping or pace mapping, with a 90% correlation identified as the ablation site. Radiofrequency energy was delivered using an ablation catheter (Thermocool SmartTouch, Biosense Webster, Inc.) with power set to 30–35 W. Acute success was defined as the absence of clinical PVCs 30 min after the last ablation, both with and without isoproterenol. 24-h Holter monitoring was performed during the in-hospital stay and three months after the procedure in all patients. Success was defined as a reduction of at least 90% in the PVC burden compared to the pre-procedural assessment.
EAT measurement
EAT quantification was performed using routine chest CT images. The EAT volume was measured utilizing 3D Slicer 5.6 software. Total-EAT was defined as all three-dimensional voxels ranging from −150 to −50 Hounsfield Units (HU) within the area extending from the left pulmonary artery to the apex of the left ventricle. Right ventricle EAT (RV-EAT) was identified as any adipose tissue surrounding the expected contours of the RV, delineated by manual tracing of the pericardium border. The software directly calculated the volume and density of EAT in the selected regions. To account for the influence of body mass index (BMI) and body surface area (BSA) on EAT, we adjusted the EAT volume and density using the BMI correction index (CI) or BSA CI.
Statistical analysis
Baseline characteristics and comorbidities were analyzed using descriptive statistics. Continuous variables were presented as mean ± standard deviation (SD), while categorical variables were reported as frequency (percentage). Group differences were assessed using an unpaired Student's t-test or the MannnWhitney U test, depending on the results of Levene's test. Categorical variables were compared using the chi-square test or Fisher's exact test. A two-tailed P-value of <0.05 was considered statistically significant. Statistical analyses were conducted using SPSS version 26.0 (IBM, Armonk, NY, USA).
Results
Clinical characteristics of the study population
The study enrolled 127 patients undergoing RVOT PVC ablation. Table 1 presents the participant characteristics. Of the total, 77 (60.63%) patients had PVCs originating from the RVOT septum, while 50 (39.37%) had PVCs originating from the free wall area. The study population had a mean age of 52.94 ± 14.76 years, with 73.23% (93/127) being female. The mean BMI was 23.99 ± 3.09 kg/m2, and the mean BSA was 1.68 ± 0.15 m2. No significant differences in clinical characteristics or disease history were observed between the two groups.
Clinical characteristics of the study population.
Values are presented as mean ± standard deviation or numbers (percentage). BMI: body mass index; BSA: body surface area.
Association between epicardial adipose tissue and RVOT PVC origin
A significant difference in EAT volume was observed between the PVC groups. Patients in the RVOT free wall group exhibited a higher volume of total-EAT and RV-EAT compared to the RVOT septum group (74.96 ± 44.99 vs. 94.76 ± 49.20 cm3, P = 0.021; 31.87 ± 18.06 vs. 38.43 ± 16.42 cm3, P = 0.040; Table 2). This significant difference persisted even after adjusting for BMI and BSA. No differences in EAT density were reported across the two groups, neither for total-EAT density nor RV-EAT density (−81.63 ± 3.44 vs. −82.51 ± 3.67 HU, P = 0.170; −81.06 ± 4.48 vs. −82.06 ± 4.48 HU, P = 0.219). Additionally, the ratio of volume and density of RV-EAT and total-EAT among different PVC origin groups did not demonstrate a statistically significant difference (0.44 ± 0.10 vs. 0.43 ± 0.10, P = 0.170; 0.99 ± 0.03 vs. 0.99 ± 0.03, P = 0.760).
Comparison of EAT of patients with PVCs originating from RVOT septum and free wall.
EAT: epicardial adipose tissue; PVCs: premature ventricular contractions; ROVT: right ventricular outflow tract; RV: right ventricle; EATv: EAT volume; EATd: EAT density; BMI: body mass index; BSA: body surface area; CI: correction index.
*P <0.05, ** P <0.01.
A subgroup analysis was conducted to evaluate potential factors associated with EAT differences and RVOT PVC origin. The study population was stratified into two or three subgroups based on gender, age, or BMI. Among female patients, those with PVCs originating from the RVOT free wall demonstrated significantly greater RV-EAT and total-EAT volumes compared to those with RVOT septum origin (29.83 ± 17.40 vs. 40.18 ± 16.35 cm3, P = 0.006; 66.75 ± 38.72 vs. 93.69 ± 45.63 cm3, P = 0.003; Table 3). However, EAT volume did not show statistical differences in male cohorts. Age did not demonstrate a significant association with EAT volume and RVOT PVC origin (Table 4). According to the WHO Asia-Pacific guidelines, a BMI of 23–27.5 is classified as overweight. Based on this, we divided the patients into two groups: BMI < 23 and BMI ≥ 23. In the BMI < 23 subgroup, both RV-EAT and Total-EAT volumes were higher in the RVOT free wall group compared to the RVOT septum group (22.69 ± 15.65 vs. 33.75 ± 17.32 cm3, P = 0.030; 47.77 ± 28.35 vs. 71.51 ± 42.47 cm3, P = 0.028; Table 5). Although the BMI ≥ 23 subgroup exhibited a trend towards higher EAT volume in RVOT free wall PVC patients, this trend did not achieve statistical significance.
Subgroup analysis of EAT volume according to gender.
EAT: epicardial adipose tissue; RV: right ventricle; EATv: EAT volume; BMI: body mass index; BSA: body surface area; CI: correction index. **Statistically significant.
Subgroup analysis of EAT volume according to age.
EAT: epicardial adipose tissue; RV: right ventricle; EATv: EAT volume; BMI: body mass index; BSA: body surface area; CI: correction index.
Subgroup analysis of the EAT volume according to BMI.
EAT: epicardial adipose tissue; BMI: body mass index; RV: right ventricle; EATv: EAT volume; BSA: body surface area; CI: correction index.
*Statistically significant.
Discussion
This study examined the variations in EAT thickness and density between PVCs originating from the septal and free wall regions of the RVOT. The findings indicate that patients with PVCs from the free wall region exhibited larger total EAT volume and EAT volume near the RV compared to those with PVCs originating from the septal region. These differences remained significant after adjusting for BMI and BSA. However, no significant differences were observed in total-EAT density and RV-EAT density between the two groups. Furthermore, stratified analysis revealed that the differences in EAT volume were only present in the female population and existed in patients with a lower BMI.
EAT is situated between the visceral layer of the serous pericardium and the epicardial surface of the heart, in direct contact with the myocardium. 5 Beyond adipocytes, EAT comprises fibroblasts, pre-adipocytes, macrophages, and various other cell types. 6 Recent research has established a connection between EAT and ventricular arrhythmias. Studies demonstrate that individuals with frequent PVCs exhibit larger EAT volumes compared to control populations. 2 Furthermore, EAT thickness independently correlates with the failure of ablation procedures for ventricular premature beats. 3 These findings suggest EAT is involved in the pathogenesis of PVCs. Moreover, PVCs originating from different cardiac regions display distinct EAT characteristics. 7 Patients with RVOT originating PVCs show a greater disparity in EAT volume between left and right ventricles compared to control groups. Conversely, patients with left ventricular outflow tract (LVOT)-originating PVCs exhibit differences in EAT density between the ventricles. This evidence indicates that EAT may have varying roles in ventricular arrhythmias depending on their point of origin.
Our study revealed that PVCs originating from the free wall of the RVOT were associated with larger RV EAT and total EAT volumes compared to those originating from the RVOT septum. Anatomically, the RVOT free wall is in closer proximity to the EAT-infiltrated area. EAT serves as a primary source of inflammatory cytokines. For instance, IL-1β can extend the action potential duration in cardiomyocytes, while TNF-α and IL-6 can downregulate repolarizing potassium currents, thereby prolonging the action potential. 8 These cytokines affect cardiomyocytes in a paracrine manner, with cells adjacent to EAT being more susceptible to their influence. Additionally, EAT is associated with alterations in cardiomyocyte gap junctions. Research by Egan et al. 9 demonstrated that increased EAT volume following a high-sugar diet correlated with Cx43 downregulation and enhanced susceptibility to ventricular arrhythmias. Furthermore, direct EAT infiltration into the myocardium may separate myocardial fibers, resulting in slowed or blocked conduction, thus facilitating reentrant arrhythmias. 10 The focal pro-arrhythmic mechanisms of EAT, coupled with its uneven distribution in the ventricles, induce heterogeneous electrophysiological conditions and promote the occurrence of ventricular arrhythmias.
Research indicates that women tend to have a higher volume of EAT compared to men. 11 In our investigation, female patients with free wall PVCs exhibited larger RV EAT volume and total EAT volume, a distinction not observed in male patients with free wall PVCs. These gender-specific differences in EAT are not limited to arrhythmias. Kim et al. 12 demonstrated that EAT is associated with left ventricular function in elderly women, but not in men. The underlying mechanism may be attributed to age-related changes in the expression of serum adipokines and other derived mediators, which appear to have a more pronounced effect on females than on males.
Previous research has demonstrated that obesity correlates with an increase in EAT volume or alterations in EAT phenotype, 13 leading to electrical and structural remodeling that enhances arrhythmogenic potential. 2 In our research, significant differences in EAT volume between patients with free wall PVCs and those with septal PVCs were observed in the subgroup of BMI < 23, while no statistically significant variations were found in subgroups with higher BMI values. This seemingly paradoxical phenomenon has also been reported by others, 14 that EAT is independently associated with left ventricular mass only in nonobese individuals (BMI < 25). This phenomenon suggests that in nonobese populations, EAT may be a significant driver of cardiopathy compared to overall body fat. In contrast, in obese populations, systemic factors such as BMI may mask the local effects of EAT.
Limitations
This study has several limitations. Firstly, the observational cross-sectional nature of the results precludes direct inference of a causal relationship between EAT and the origin of PVCs. Secondly, the study's focus on patients with PVCs originating from the RVOT leaves the relationship between EAT and PVCs originating from different LVOT locations unclear. Finally, the relatively small sample size in certain subgroups, such as the lower proportion of male patients, leading to an unbalanced gender distribution, may introduce bias into the results. We did not perform the calculation of the sample size due to the relatively small sample size; instead, all consecutive patients undergoing catheter ablation for premature ventricular contractions during the predefined study period were enrolled. The potential for Type II error cannot be excluded.
Conclusion
In comparison to patients with RVOT septal PVCs, those with RVOT free wall PVCs exhibited greater volumes of total EAT and right ventricular (RV) EAT. These distinctions were more pronounced in certain subgroups of free-wall PVC patients, notably in female and low BMI populations. Additionally, no significant differences in EAT density were observed among the groups. These findings suggest a potential association between regional EAT distribution and the origin of PVCs.
Footnotes
Author contributions
HY designed the research, conducted analyses, and revised the paper; JC, LXL, and XZ performed data collection and data analysis and wrote the draft of the paper.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (Nos. 82200338 and 82100502) and the Traditional Chinese Medicine Scientific Research Foundation of Zhejiang Province (No. 2023ZL013).
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data availability statement
Deidentified data supporting findings are available from the corresponding author upon reasonable request, subject to institutional approvals.