Discussion
EVAR was first developed in 1990 and revolutionized the treatment of aortic aneurysms and rapidly became standard practice internationally. The technology and outcomes of EVAR have improved dramatically with each new generation of stent graft; however, the procedure is still associated with complications. Endoleaks, persistent flow of blood into the aneurysm sac, were first classified in 1997 and remain the most frequent technical complication of endovascular repair. Of the five endoleak subcategories, T3ELs remain one of the least well understood due to their relative scarcity.
This study is the single largest retrospective study to evaluate T3ELs. The first series of EVAR in the 1990s had a T3EL rate of 17%.14 Second-generation and third-generation grafts in the early 2000s improved those rates to 1.9%.15 In 2014, the Veterans Affairs prospective multicenter Open Versus Endovascular Aneurysm Repair (OVER) trial examined their predictors and outcomes of endoleaks; they described a 3% rate of T3EL, with the majority being detected more than 2 years after the initial procedure.16 Similarly, in 2017, a retrospective single-center study described a T3EL rate of 2.6% with an average time until diagnosis of 5.6 years.17 In our study, the overall rate of any T3EL in patients with standard EVAR derived over a time period of obligatory reporting up to 21 months and optional reintervention reporting following was 1.1%. These rates are lower than what has previously been described in the literature, likely due to differences in device generations captured by previous studies.18 This current study does not capture data from before 2003, and thus does not account for the early devices that had high rates of endoleak, and additionally captures more recent data and newer grafts that are thought to have a lower rate of endoleaks. We place our T3EL rates in context to existing literature in online supplemental table 2.
Unlike previous studies, this study subdivides the overall rate of T3EL in standard EVAR into leaks identified during index hospitalization (T3EL rate 0.4%) and leaks identified at long-term follow-up (T3EL rate 0.7%). This demonstrates that the majority of T3ELs were identified at follow-up and were not present during the initial hospitalization. Although previous studies do not denote different rates for different time periods, all previous studies highlight the fact that the majority of T3ELs were found at follow-up, making the results of this study consistent with previous research. Overall, this research indicates that the registry-identified rate of T3EL is lower than previously demonstrated in smaller series, and trials and that appropriate imaging surveillance must be maintained, as the majority of these endoleaks occur at follow-up.
T3ELs occur through two modalities, modular disconnections (3a) or graft fabric disruptions (3b). The exact cause of these disconnections and disruptions has been evaluated by several institutions and occur through multiple mechanisms. In cases of type 3a endoleaks, studies have demonstrated modular disconnections at every level of graft overlap.19 Several studies hypothesize that fabric disruptions are related to excessive endovascular graft manipulation, excessive ballooning, or fabric degradation over time.20 21 The results of this study are consistent with previous series that describe the majority T3EL occurring secondary to modular disconnections.17 In this study, for both endoleaks discovered during index hospitalization and at long-term follow-up, 85% were attributed to mid-graft separation and 15% were attributed to mid-graft fabric holes.
Endoleaks are a feared complication due to their potential to increase the risk of rupture by exposing the aneurysm sac to systemic blood pressure. Previous studies, including case studies and large-scale studies such as the OVER trial11 and EUROSTAR registry,6 have found a relationship between T3EL and aneurysm sac growth and rupture. Studies comparing the total mortality benefit of EVAR compared with open repair have shown that the overall mortality benefit of EVAR is lost over long-term follow-up after 1–2 years in the OVER trial,16 2 years in the EVAR1 trial,7 and 5 years in the DREAM trial.22 In 2015, Schermerhorn et al23 published the long-term results of EVAR in Medicare patients and found that after 3 years, the mortality was equal between EVAR and open repairs due to higher late rupture rates in EVAR. In 2016, 15-year follow-up of the EVAR1 data was published, which demonstrated an association between endoleaks (type 1, type 2, and type 3) and secondary aortic sac rupture leading to an increased risk for mortality.7 The data presented in our study align with the results of these large trials. Within this study, T3EL found during follow-up in standard EVAR cases were associated with decreased 5-year survival (74% vs 80%, p=0.041). Our dataset has capture of rupture events, but we are unable to characterize within the database reporting which patients with rupture may have also had T3EL. Given this association, it is imperative to understand how to best prevent, detect, and treat these endoleaks.
Limitations
Although every effort was made to ensure accuracy and reproducibility of this study, several limitations must be addressed. While the 2019 Annual VQI report indicates strong sustained enrollment of centers across the USA with the addition of 110 new reporting centers, the VQI is not yet entirely comprehensive in its representation of EVAR implantations in the country.24 Additionally, early procedural volumes in the VQI are less robust, given given the national expansion that occurred after 2011 and subsequent extension of the registry to Canadian centers; however, annual EVAR procedural volumes in VQI remain significantly higher than those available in other US national surgical quality databases.12 25 An additional limitation is inherent to analysis of the VQI, in that the data are derived on a voluntary basis from individual surgeons, and assumptions must be made regarding the veracity of the data. Thus, although the VQI compares entries against hospital claims data, it is possible that discrepancies, intentional or unintentional, exist within the data due to its self-reported nature. Despite these factors, specificity in endoleak reporting for this EVAR-specific complications is unavailable in other surgical quality databases or claims-based administrative data, currently making VQI our most representative sample of clinical practice in North America.
With regard to diagnosis of T3EL, there is no absolute certainly of when a T3EL occurred, unless it occurred during the index procedure where completion angiographic runs are standard of care. Postprocedural imaging studies prior to discharge are not mandatory or advised in the absence of patient clinical indications. Therefore, a T3EL could develop during index hospitalization but not be diagnosed until follow-up imaging; modalities and duration of long-term follow-up imaging in the window of 9–21 months are recorded but pose potential for lack of documentation in the registry of findings from commonly employed 1-month procedural scans. Ultimately, the nature of the endoleak type (fabric hole or device modular disconnection) makes it unlikely that a T3EL would spontaneously resolve or be missed at the long-term follow-up interval if a reintervention had not been recorded. In the future, if needed to better understand the exact timing, a more explicit time to diagnosis variable in VQI could reduce uncertainty or creation of type-specific endoleak billing codes could facilitate linkage to claims data. A final significant limitation seen in this study is the lack of continuity within patients’ follow-up. Of the initial patients who had an EVAR device implanted, 37% were lost to follow-up. This presents several analytical difficulties, and whether this represents poor documentation of the behalf of physicians or if patients are truly not returning for surveillance after surgical intervention is unknown. Further, the lack of follow-up makes drawing conclusions regarding survival, both positive and negative, difficult. Initial attempts to address the limitations presented earlier include the MDEpiNet Vascular Implant Surveillance & Interventional Outcomes Network coordinated research network initiative expanding administrative claims and other data source linkages to VQI data which can aid in extension of long-term capture of patient care.26
Despite the aforementioned shortcomings, the VQI database represents the single largest well-regulated data available for analysis with the granular detail to study T3ELs. While these limitations should be taken into consideration when evaluating the conclusions presented in this paper, all studies that interpret the VQI data face the aforementioned difficulties and the limitations do not invalidate the findings or conclusions.
Finally, the presence of a T3EL at 9–21 months was associated with trends toward decreased survival; we suspect this trend would continue if data were available for follow-up in ensuing years; however, consistent reporting of 5 and 10 years is unavailable in this observational database at present. Future analyses using linkage of EVAR patients to Medicare claims data may allow for further longitudinal assessment of the mortality impact.