The impact of true lumen morphology on frozen elephant trunk technique in chronic aortic dissection

Introduction

Background

The frozen elephant trunk (FET) technique has emerged as a cornerstone in managing complex thoracic aortic diseases. This innovative hybrid procedure integrates conventional open surgery with endovascular repair to overcome the anatomical and hemodynamic challenges of aortic dissection. By improving true lumen (TL) blood flow and excluding distal intimal tears in the aortic arch, FET offers significant advantages. However, long-term complications, such as stent graft-induced new entry (SINE) and the need for reintervention, remain critical issues (1,2). Thoracic endovascular aortic repair (TEVAR) has shown favorable outcomes in chronic aortic dissection (CAD), with acceptable morbidity and mortality. Yet, in anatomically challenging cases, such as those with inadequate proximal landing zones or acutely angled aortic arches (3), open surgery continues to play an indispensable role (4).

Rationale and knowledge gap

While the FET technique has been extensively studied in acute aortic dissection (AAD), demonstrating reductions in early mortality and improvements in aortic remodeling (5,6), research on its efficacy in CAD remains limited. Chronic changes in the aortic wall, such as fibrosis and calcification, introduce unique challenges that may influence surgical outcomes. The long-term impact of FET in CAD, particularly concerning complications like SINE and the need for reintervention, is poorly understood (7). This knowledge gap underscores the need for further research to elucidate these critical aspects.

Objective

This study evaluates the efficacy and safety of the FET procedure in CAD patients, with a focus on the influence of TL morphology on long-term outcomes. It seeks to analyze postoperative complications, such as SINE and reintervention rates, while offering insights to refine surgical strategies. By addressing these gaps, the study aims to enhance the understanding and optimization of FET techniques to improve patient outcomes in CAD. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2020/rc).

Methods

Patients characteristics and study design

Between 2014 and 2022, 118 patients underwent the FET procedure for extended aortic arch disease at Anjo Kosei Hospital. Exclusions included patients with degenerative aneurysms and AADs, resulting in a study population of 23 patients (19.5%) treated with FET in a chronic setting (an aortic dissection where the duration from the initial onset exceeds 90 days.). This cohort consisted of patients with chronic type B aortic dissection (48%), residual dissection after type A repair (30%), and chronic type A aortic dissection (22%). The mean preoperative diameter of the proximal descending aorta was 65.0 mm (range, 50–100 mm). All cases were either saccular or fusiform aortic aneurysms. The mean patient age was 62.3±12.2 years, with 47.8% being male, and no cases of connective tissue disorders, such as Marfan syndrome, were present. Comorbidities included hypertension (91.3%), chronic obstructive pulmonary disease (COPD; 26.1%), dyslipidemia (43.4%), diabetes mellitus (8.7%), and histories of cerebrovascular events (8.7%). Obesity was observed in 30.4% of patients, with a mean body mass index (BMI) of 26.2 kg/m² (Table 1). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study protocol was approved by the Institutional Review Board of the Anjo Kosei Hospital (R23-081). Owing to the retrospective nature of the research, the Ethics Committee waived the requirement for written patient informed consent, as the study did not alter the course of treatment and utilized a database designed to protect patients’ identities.

Operative strategy

All surgeries were performed via median sternotomy. Operative characteristics are summarized in Table 2. The mean cardiopulmonary bypass (CPB) time was 264.8±78.4 minutes, with an aortic cross-clamp time of 113±25.4 minutes, depending on additional procedures. Myocardial protection was achieved with cold blood cardioplegia infused into the coronary sinus. During the study period, spinal cord drainage was not routinely employed; however, blood pressure management was carefully implemented. Bilateral antegrade selective cerebral perfusion (SCP) was employed during circulatory arrest at moderate hypothermia (26 ℃).

The J Graft FROZENIX (Japan Lifeline, Tokyo, Japan) was used in all cases. The graft diameter ranged from 23 to 31 mm (mean: 27.9±3.95 mm), and the stent length ranged from 90 to 150 mm (mean: 127.5±19.6 mm). Graft size was selected based on preoperative computed tomography (CT) measurements of the TL diameter at the distal landing zone, ensuring the stent covered the descending aorta above thoracic vertebra (Th)8 with a size equivalent to 100–110% of the mean diameter of the short and long axes (Figure 1).

Figure 1 Illustration of the stent graft sizing process. The length of the stent graft is determined from the subclavian artery bifurcation to the distal stent landing zone. The diameter of the stent graft is chosen based on 100–110% of the true lumen diameter at the landing zone. The black double-headed arrows indicate the short and long axes of the true lumen. The red dashed line represents the circumference of the true lumen. The red solid line shows the planned length of the stent graft.

Aortic arch incisions were typically performed between the left common carotid and subclavian arteries (Zone 2), with some cases extending distal to the left subclavian artery (Zone 3). The stent graft was deployed in the descending aorta, minimizing the non-stented segment to <5 mm, facilitated by the stent’s self-expanding force.

Subsequently, a 4-branched graft was anastomosed to the distal stump using Hydrofit hemostatic sealant (Sanyo Chemical Industries, Kyoto, Japan). Antegrade systemic perfusion was established, and proximal anastomosis followed. Each branch of the graft was connected to the arch vessels.

Measurements of CT images

TL morphology (Figure 2)

Figure 2 Illustration of classification of true lumen morphology. (A) Flat-medial type. (B) Flat-lateral type. (C) Circular-lateral type.

Preoperative CT scans classified TL morphology as medial or lateral, and flat or circular. Cases with a medial to lateral ratio of 5:5 or greater were defined as medial, while those with a ratio of less than 5:5 were classified as lateral. Flat types have a relatively straight or concave flap, while circular types exhibit a rounded or convex flap. Postoperative follow-up CT imaging was conducted at discharge, 6 months post-procedure, and annually thereafter. Measurements included:

• Aneurysm diameter changes: a decrease ≥10% from the initial postoperative measurement defined the “shrinkage group”. Cases with increases ≥10% or changes <10% were classified as the “no change group”. In general, some studies (8,9) have evaluated a reduction in aortic diameter of 5 mm as a shrinkage. The preoperative aortic diameters in this cohort varied widely in value from 50 to 100 mm. Therefore, the threshold of >10% shrinkage was chosen to differentiate cases with significant aortic remodeling from those with minimal or no remodeling.
• Distal landing zone (Th level): the stent graft’s distal landing zone was assessed using vertebral levels, dividing the vertebral body into 10 segments for precise localization. The change in the stent’s position was meticulously assessed by comparing segmental locations across different time points. Additionally, thrombosis of false lumen (FL), SINE and remodeling of the aortic diameter were assessed (Figure 3).
• Distal landing zone angle: angles between the distal stent graft and body’s longitudinal axis were measured to evaluate positional stability and risks for endoleak or migration. Both the initial values at the time of insertion and the postoperative changes in angle were evaluated (Figure 3).
• Stent migration: stent migration length refers to the displacement of the distal end of the stent graft from its initial position, measured in vertebral body units. This metric helps assess the stability of the stent graft over time.

Figure 3 Measurement of the stent distal end level at the vertebral body (indicated by the black arrow). Thrombosis of FL, SINE and remodelling of the aortic diameter were assessed. The landing zone angle (marked with an asterisk) is the angle between the distal end of the stent and the vertical axis. The white dashed line indicates the longitudinal axis of the body. The red line shows the direction of the distal end of the stent graft. The asterisk (*) represents the angle of the distal landing zone formed between the two lines. FL, false lumen; SINE, stent graft-induced new entry; Th, thoracic vertebra.

Endpoints and follow-up

The primary endpoint was in-hospital mortality and the need for subsequent aortic procedures, such as TEVAR or additional surgeries. Secondary endpoints included surgical parameters and major complications. Neurological dysfunctions, such as stroke or spinal cord injury (SCI), were further characterized as paraplegia or paraparesis.

Definitions

Coronary disease was defined as a history of coronary intervention or the presence of concomitant coronary artery stenosis. COPD was defined as having a forced expiratory volume in one second (FEV1.0) less than 70% of the predicted value or requiring the use of a bronchial inhaler. Renal failure was defined as a serum creatinine level greater than 1.3 g/dL or an estimated glomerular filtration rate (eGFR) less than 60 mL/min/1.73 m². SINE refers to the formation of a new intimal tear at the distal or proximal edge of the stent graft, rather than a re-dissociation of a previously dissociated site.

Data collection and statistical analysis

Patient data were collected retrospectively. Outcomes were measured in terms of overall survival, freedom from aortic events, and reintervention rates. Continuous variables were presented as mean and standard deviation (SD) if normally distributed, and as median with interquartile range for non-normal distributions. For comparisons between small groups, the Mann-Whitney U test for non-parametric data was used for univariate analysis to identify significant differences. Changes within subjects were compared using the Fisher’s exact test. A P value of less than 0.05 was considered statistically significant. Outcomes were estimated using Kaplan-Meier curve, and comparisons were performed by the log-rank test. All statistical analyses were performed using SPSS software, version 27 (IBM Corp., Armonk, NY, USA).

Results

Operative data and postoperative results

The ratio of stent diameter to TL diameter was assessed as follows: the mean ratio of the (short axis diameter + long axis diameter)/2 to the stent diameter was 1.13, while the mean ratio calculated from the TL circumference was 0.94 (Table 2). The in-hospital mortality rate was 4.3% (n=1), attributed to a stroke. SCI occurred in three patients (13.0%), including one case of paraplegia and two cases of paraparesis. Notably, the distal stent level in these cases was at Th8 or higher. Reintervention was required in nine patients (39%) postoperatively, with 30.4% occurring within 3 years (mean interval from FET: 19.2±13.8 months). The specific reinterventions included two thoracoabdominal aortic aneurysm repairs performed via left thoracotomy and seven TEVAR procedures. Indications for reintervention were SINE in three patients and progressive aortic dilation in six patients (Table 3). Aneurysmal enlargement was managed with TEVAR in cases where the proximal and distal landing zones were suitable for endovascular repair. In TEVAR procedures, appropriately sized stent grafts were selected to ensure adequate sealing and prevent further dilation.

Postoperative CT findings

Postoperative CT findings revealed several key observations (Table 4). The mean distal landing zone level was Th7.6±0.70, with approximately 80% of cases having a distal level at Th7 or higher. The mean landing zone angle relative to the body axis at discharge was 20.2±16.2°, with a mean change of 13.5±11.1°, likely due to the spring-back force of the stent. Stent migration length, measured in vertebral body units, averaged 0.45±0.48 (range, 0–2.0). CT imaging showed significant expansion of the TL and a reduction in FL diameter in most patients. Complete FL thrombosis in the stent graft implantation area was achieved in all cases by discharge. Regarding aortic remodeling, 5 patients (22.7%) exhibited descending aortic shrinkage, 10 patients (45.5%) showed no significant change, and 7 patients (31.8%) demonstrated dilation. SINE occurred in 3 cases (14%), with a mean onset interval of 32.5 months (range, 20.6–38.8 months) after the FET procedure. Postoperative CT comparisons between cases with SINE (SINE+) and without SINE (SINE−) are detailed in Table 5.

• Interval from initial dissection: the initial aortic dissection and the FET procedure in patients who developed SINE ranged from 2.2 to 10 years, indicating a wide variation. Additionally, the mean interval for the SINE+ group showed no statistically significant difference when compared to the SINE− group.
• Distal landing zone: the mean distal landing zone level was Th6.7 in the SINE+ group and Th7.5 in the SINE− group, with no statistically significant difference.
• Landing zone angle: the distal landing zone angle and the change in angle both tended to be larger in the SINE+ group; however, the differences were not statistically significant. SINE+ cases exhibiting a mean change of 25.2° (range, 10–46°) compared to 10.9° (range, 0–35°) in the SINE− group.
• Stent migration: the incidence of stent migration was significantly higher in the SINE+ group (P=0.04).
• TL size and morphology: notably, all SINE+ cases demonstrated aortic remodeling shrinkage, indicating that SINE can occur even with favorable FL shrinkage. The SINE+ group had significantly smaller TL diameter than the SINE− group. The relationship between the diameter of the TL and the occurrence of SINE was strongly suggested.

TL morphology was predominantly “flat + medial” in the SINE+ group, significantly more common than in the SINE− group (P=0.008). The ratio of stent diameter to TL diameter did not differ significantly between the groups.

Follow-up outcomes

The mean follow-up period was 32.6 months, providing comprehensive longitudinal data on postoperative results and complication rates. Postoperative outcomes, particularly reintervention rates, were compared between medial and lateral TL morphologies (Table 6). Negative aortic remodeling, specifically dilation, was observed at similar rates across TL morphologies. However, all cases of SINE occurred in patients with medial-type TL morphology. Reinterventions were significantly more frequent in this group as well. Three deaths were documented during the follow-up period. Two were suspected aortic ruptures, occurring 998 and 405 days after the FET procedure, despite no notable changes in arterial diameter prior to the events, were observed with medial-type TL morphology. The third death, occurring 1,857 days post-FET, was attributed to an unrelated aortic event. Freedom from reintervention was 63.6% at 3 years and 50.9% at 5 years. The majority of reinterventions (n=7, 77.8%) involved endovascular procedures such as TEVAR, predominantly for SINE. Open surgical reintervention was necessary in 2 cases (22.2%) where anatomical factors precluded an endovascular approach. Kaplan-Meier survival analysis revealed a significant difference in freedom from reintervention based on TL morphology (Figure 4). At the 5-year mark, freedom from reintervention was markedly higher for lateral-type TL morphology (89%) compared to medial-type (15%), demonstrating a statistically significant disparity in outcomes (P=0.006).

Figure 4 Freedom from reintervention rates of based on true lumen morphology, showing significant difference between the two groups.

Discussion

The need for reinterventions continues to be a significant challenge in the management of CAD with the FET procedure. This study investigated the impact of TL morphology on postoperative outcomes, focusing on the incidence of SINE and the need for reinterventions over time. Our findings demonstrate that TL morphology is a critical determinant of postoperative outcomes. Patients with medial-type TL morphology exhibited significantly higher rates of SINE and reinterventions compared to those with lateral-type morphology. These results highlight the necessity of incorporating TL morphology into preoperative planning and surgical decision-making for FET procedures for CAD.

Comparison with previous studies

Our study contributes to the limited body of literature on long-term outcomes in CAD patients undergoing the FET procedure, offering a comparative analysis with prior studies. Okita et al. demonstrated the efficacy of the Japanese Frozenix prosthesis in achieving complete FL thrombosis and simplifying distal anastomosis, reinforcing its utility in addressing CAD complexities (10,11). Similarly, Charchyan et al. reported favorable mid-term outcomes of FET in chronic type B dissections, emphasizing its role in mitigating complications such as retrograde type A dissection—a known risk of TEVAR (12). These findings align with our study’s observation of effective FL thrombosis and TL expansion, particularly in lateral-type morphologies. The in-hospital mortality rate in our cohort was 4.3%, consistent with reported rates of 2–10% for CAD patients treated with FET (13,14). While the incidence of SCI was 13.0%, slightly higher than rates observed in AAD, it reflects the increased risk inherent to extensive aortic repairs in CAD (15). Spinal cord drainage may need to be considered in some cases, although the definitive factors are unknown. Our study’s primary findings confirm the efficacy of FET in enhancing TL remodeling. Positive aortic remodeling, characterized by TL enlargement and progressive FL thrombosis, was observed in a significant proportion of patients. These results are consistent with Kozlov et al.’s report of 65.3% freedom from unintended distal reinterventions at 60 months in CAD patients (16). Similarly, Fiorentino et al. documented a 50% rate of positive remodeling, with substantial FL thrombosis at both proximal and distal levels of the descending thoracic aorta (17). Yamane et al. also highlighted a high rate of early FL thrombosis, with cumulative survival rates reaching 66.4% at 5 years (18). The alignment of these findings suggests that careful preoperative assessment of TL dimensions and FL characteristics is crucial for achieving durable results.

Impact of TL morphology

A key contribution of our study is the focus on TL morphology as a critical predictor of postoperative outcomes in patients undergoing the FET procedure. We categorized TL morphology into medial and lateral types, with further classifications as flat or circular. Our findings reveal that medial-type TL morphology is significantly associated with higher rates of SINE and reinterventions. Notably, all observed cases of SINE occurred in patients with medial-type TL morphology. Additionally, these patients had a markedly lower freedom from reintervention at 5 years compared to those with lateral-type TL morphology (15% vs. 89%, P=0.006). The relationship between TL morphology and postoperative outcomes in CAD has not been extensively investigated in prior studies. Our results suggest that medial-type TLs are particularly vulnerable due to the uneven pressure exerted by the stent graft on the weakened aortic wall opposite the TL. This mechanical stress likely contributes to the development of new intimal tears and subsequent SINE. These findings are consistent with observations by Ogino et al., who reported increased complication rates in anatomically challenging cases where FET deployment involved acute angles or unstable regions (11). Our study builds on this understanding, emphasizing the need to incorporate TL morphology into preoperative planning. For medial-type TLs, tailored surgical strategies, such as optimized stent sizing, modified landing zone selection, or additional reinforcement measures, could mitigate risks and improve outcomes. Circular-medial morphology often represents a long-standing chronic dissection (mean interval from initial dissection: 98.4 months), with remodeling that results in a rounded TL. In contrast, flat-medial morphology is typically observed in less remodeled or acutely stressed regions.

SINE

SINE is a recognized complication following TEVAR and has been reported in both acute and CAD cases (19). In our study, the incidence of SINE was 13.6%, which is within the range reported in previous studies (5–25%) (16-21). No causal relationship was found between the occurrence of SINE and the interval from the initial dissociation. Notably, SINE can occur even in cases where the FL demonstrates shrinkage, indicating that favorable aortic remodeling does not eliminate the risk of this complication. Our findings highlight the critical role of graft size selection and intraoperative stent placement in minimizing the risk of SINE while optimizing TL expansion. As emphasized by Roselli et al., appropriate graft sizing is essential not only for preventing SINE but also for ensuring adequate flow redistribution to the TL (21). Our protocol adhered to similar principles, selecting graft dimensions that matched 100–110% of the mean TL diameter at the distal landing zone. Two factors significantly associated with SINE in our cohort were stent migration length and TL size. Patients who developed SINE exhibited a larger change in the distal landing zone angle (25.2° vs. 10.9°, P=0.46) and a significantly higher incidence of stent migration (P=0.04). These findings align with other studies, which suggest that excessive curvature and movement at the distal stent graft can cause intimal injury and contribute to SINE (18). With respect to FL thrombosis, our study demonstrated a 100% thrombosis rate in the stent implantation area, comparable to the 83.7% observed in a multicenter study of chronic type B dissections (1) and the 79% reported by Pacini et al. (22). However, all SINE cases in our study occurred in patients who had FL thrombosis and shrinkage, underscoring that positive FL remodeling does not necessarily prevent the development of SINE. These findings suggest the need for ongoing vigilance in monitoring patients postoperatively, even those showing favorable aortic remodeling. Further refinement of graft designs and surgical techniques to minimize landing zone angle changes and stent migration could reduce the incidence of SINE and improve long-term outcomes.

The stent diameter/TL ratio was larger in the SINE group. Although the stent/(short + long axis)/2 ratio showed no significant difference, the stent/(circumference/π) ratio was statistically significant, highlighting a potential mechanical factor in SINE development. This observation is critical and merits deeper exploration. The medial-type TL morphology may increase susceptibility to SINE due to uneven mechanical stress—radial and spring-back forces—exerted by the stent graft on the weakened flap opposite the TL. Such stress elevates the risk of new intimal tears and related complications.

Clinical implications

Preoperative assessment of TL morphology

Preoperative evaluation of TL morphology can identify patients at higher risk of complications, particularly those with medial-type TL morphology. In these cases, surgeons may consider tailored strategies such as:

• Adjusting stent graft sizing to ensure optimal fit.
• Utilizing stent graft designs specifically suited for medial-type TLs.
• Incorporating additional reinforcement techniques at the distal anastomosis to enhance structural stability.

Distal landing zone optimization

Meticulous attention to the distal landing zone is critical for reducing the risk of SINE. Minimizing changes in angle and movement at the distal stent graft can be achieved through:

• Selecting stent grafts with appropriate length and flexibility to reduce mechanical stress.
• Employing adjunctive stabilization procedures for the distal aorta, such as additional sutures or external reinforcement techniques.

Long-term surveillance and early intervention

Routine long-term imaging follow-up is essential, even in patients demonstrating favorable aortic remodeling. Early detection of complications, such as SINE or aortic dilation, enables timely intervention, which can significantly improve outcomes.

Advancements in prosthesis design

As demonstrated in the J-ORCHESTRA study, the Frozenix prosthesis provides excellent maneuverability and conformability due to its incorporation of a Nitinol stent, which enhances stability in anatomically challenging cases (11). Further advancements, such as the newly launched FROZENIX Partial ET (FPET; Japan Lifeline), offer reduced radial and spring-back forces (29% and 43%, respectively). This novel prosthesis, introduced in 2023, holds promise for addressing complications like SINE associated with medial-type TL morphology (23).

These insights emphasize the importance of individualized surgical strategies, advanced device technologies, and rigorous postoperative surveillance to optimize outcomes in CAD patients treated with the FET procedure.

Limitations

While our study offers valuable insights, certain limitations must be acknowledged. The study’s retrospective nature and single-center setting may introduce selection bias and limit the generalizability of the findings to broader patient populations. The relatively small sample size, especially in subgroups stratified by TL morphology, may reduce the statistical power of our analyses and limit the ability to detect subtle differences in outcomes. Although the average follow-up period of 32 months provides meaningful insights, it may be insufficient to fully capture late complications and reinterventions, particularly those that could arise beyond 5 years post-procedure.

Future directions

Future research should focus on addressing the limitations of this study and expanding our understanding of the role of TL morphology in the outcomes of the FET procedure for CAD. Larger, multicenter studies with prospective designs are essential to validate our findings. These studies would help establish a stronger evidence base for the influence of TL morphology on postoperative outcomes. Further investigation into the biomechanical properties of the aortic wall and its interactions with stent grafts could inform the development of devices tailored to different TL morphologies. Optimizing graft design for medial-type TLs may reduce complications and improve outcomes. Exploration of pharmacological agents that modulate aortic wall remodeling and novel biomaterials for graft reinforcement could complement surgical techniques. These adjunctive therapies may provide additional protection against complications such as SINE and promote stable aortic remodeling. Integrating patient-specific anatomical and biomechanical data into surgical planning could enhance the precision of interventions. Tailored graft sizing and individualized surgical strategies, as emphasized by Furutachi et al., have the potential to reduce complications and improve long-term durability (24). The use of advanced imaging modalities, such as four-dimensional flow magnetic resonance imaging (4D flow MRI), could provide deeper insights into hemodynamic factors influencing outcomes (25). These techniques may help identify patients at higher risk of complications and refine postoperative monitoring protocols. Advances in computational modeling and predictive analytics could enable preoperative simulations of stent graft performance, helping to optimize graft configurations and minimize risks. Future research should prioritize refining stent graft designs to address distal complications and further exploring the role of adjunctive therapies. Combining innovative technologies with personalized approaches will likely lead to improved safety and efficacy of surgical interventions for CAD patients.

Conclusions

This study underscores the significant role of TL morphology in determining the outcomes of the FET procedure for CAD. Patients with medial-type TL morphology experienced higher rates of SINE and reinterventions, highlighting the importance of thorough preoperative assessment and the need for individualized surgical strategies tailored to TL characteristics. The FET procedure remains an essential technique for managing extensive thoracic aortic diseases, including CAD. However, a deeper understanding of the anatomical and biomechanical factors influencing its success is critical for optimizing long-term patient outcomes. Incorporating these considerations into surgical planning and advancing device designs will enhance the safety, efficacy, and durability of the FET procedure.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2020/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2020/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2020/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2020/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study protocol was approved by the Institutional Review Board of the Anjo Kosei Hospital (R23-081). Owing to the retrospective nature of the research, the Ethics Committee waived the requirement for written patient informed consent, as the study did not alter the course of treatment and utilized a database designed to protect patients’ identities.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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