Highlights
Fenestrated and branched endovascular aortic repair (F/BEVAR) represents one of the most technically demanding procedures in vascular surgery. A new retrospective cohort study analyzing 100% Medicare fee-for-service claims from 2016 to 2023 reveals that both hospital and surgeon annual volume significantly impact patient survival outcomes following these complex repairs. The research identifies clear inflection points—9 cases per year for hospitals and 7 cases per year for surgeons—below which patients face substantially elevated mortality risk within 30 days of surgery. Low hospital volume was associated with a 43% increase in adjusted odds of death (aOR 1.43, 95% CI 1.02-1.99), while low surgeon volume correlated with a 51% increase in mortality risk (aOR 1.51, 95% CI 1.04-2.18). These findings hold critical implications for the future dissemination of F/BEVAR technology as commercial devices become more widely available.
Background
Aortic aneurysms, particularly thoracoabdominal aneurysms, remain a formidable clinical challenge in vascular medicine. When these aneurysms involve critical branch vessels supplying the kidneys, intestines, and other vital organs, traditional open surgical repair carries prohibitively high morbidity and mortality rates. Fenestrated and branched endovascular aortic repair emerged as a transformative alternative, allowing surgeons to seal complex aneurysms while preserving perfusion to essential branch vessels through custom-designed stent grafts.
Over the past decade, F/BEVAR has evolved from an experimental procedure performed only at select academic centers to an increasingly mainstream treatment option. This shift has been accelerated by advances in imaging technology, manufacturing innovations enabling fenestrated and branched configurations, and growing operator experience. However, the complexity of these procedures—which often involve multiple simultaneous branch vessel reconstructions—raises important questions about the relationship between procedural volume and patient outcomes.
The volume-outcome relationship is well-established in many high-risk surgical procedures. For standard open and endovascular aortic repair, numerous studies have demonstrated that patients treated at higher-volume centers and by more experienced surgeons experience superior outcomes. Despite this knowledge, the specific volume thresholds that optimize safety for F/BEVAR have remained undefined. This gap in evidence creates challenges for healthcare systems seeking to establish quality standards, for insurers developing coverage policies, and for patients hoping to make informed decisions about their care.
Study Design
The research team, led by investigators from multiple academic medical centers, conducted a retrospective cohort study using 100% Medicare fee-for-service claims data spanning January 2016 through December 2023. This large administrative dataset provided access to essentially all F/BEVAR procedures performed on Medicare beneficiaries in the United States during this period, offering unprecedented statistical power to detect volume-outcome relationships that smaller single-center or registry studies could not identify.
The study population included adults aged 65 years and older who underwent fenestrated or branched repair of thoracoabdominal or pararenal aortic aneurysms. Patients were identified using procedural codes specific to fenestrated and branched endovascular grafts, ensuring accurate classification of the exposure of interest.
To identify optimal volume thresholds, the investigators employed sophisticated statistical methodology. Locally estimated scatterplot smoothing (LOESS) was used to visualize the relationship between annual volume and 30-day mortality, allowing the data to reveal natural inflection points rather than imposing arbitrary cutoffs. Derivative-based methods provided additional confirmation of these thresholds. Once thresholds were established, multivariable logistic regression analysis was performed to quantify the association between volume category and mortality, adjusting for numerous patient-level risk factors including age, sex, comorbidities, and frailty indicators.
The primary endpoint was 30-day all-cause mortality, a standard and robust outcome measure in surgical quality research that captures early procedural safety. Secondary analyses examined the independent contributions of hospital volume and surgeon volume to outcomes.
Key Findings
The study identified 8,015 patients who underwent F/BEVAR during the study period, representing the largest cohort of Medicare beneficiaries undergoing these procedures examined to date. The patient population reflected the typical epidemiology of aortic aneurysms: mean age was 76.1 ± 6.8 years, only 27.7% were female, and 90.9% were White. These demographic characteristics align with known patterns of aortic aneurysm disease, which predominantly affects older white males.
The volume distribution across hospitals and surgeons revealed a striking finding: both annual hospital and surgeon caseloads were remarkably low. The median annual hospital volume was just 2 cases per year, with a range extending from 1 to 70 cases. Similarly, the median surgeon performed only 1 F/BEVAR annually, with a range from 1 to 51 cases. This distribution stands in stark contrast to other high-risk cardiac and vascular procedures, where minimum volume standards often require dozens or even hundreds of annual cases.
Overall, 350 patients (4.4%) experienced mortality within 30 days following their procedure. While this mortality rate may appear modest, it must be interpreted in context—these are elective procedures performed on patients who, by selection, were deemed appropriate surgical candidates. Each death represents a potentially preventable adverse outcome.
The LOESS analysis identified clear inflection points in the volume-mortality relationship. For hospitals, the critical threshold emerged at 9 cases per year. Below this volume, mortality rates showed a steep negative trajectory; above it, the relationship flattened considerably. For surgeons, the corresponding inflection point was 7 cases per year. These thresholds remained robust across multiple sensitivity analyses.
In adjusted analyses, both low hospital volume and low surgeon volume emerged as independent predictors of 30-day mortality. Patients treated at hospitals performing 9 or fewer F/BEVAR procedures annually faced a 43% increase in the odds of death (adjusted odds ratio 1.43, 95% confidence interval 1.02-1.99) compared with those treated at higher-volume centers. Similarly, patients operated on by surgeons performing 7 or fewer procedures per year experienced a 51% increase in odds of mortality (aOR 1.51, 95% CI 1.04-2.18) compared with those treated by higher-volume operators.
Notably, these two volume metrics appeared to operate somewhat independently, suggesting that both institutional experience and individual operator skill contribute to patient outcomes. A hospital might have adequate overall volume but distribute cases among multiple surgeons, each below the individual threshold. Alternatively, a high-volume surgeon might practice at a relatively low-volume institution where perioperative support systems may be less refined.
Expert Commentary
The findings from this study arrive at a pivotal moment in the evolution of complex endovascular aortic repair. As commercial fenestrated and branched devices gain regulatory approval and broader market availability, these procedures will inevitably diffuse to more centers and practitioners. The current data provide a evidence-based framework for thinking about how to manage this dissemination responsibly.
The volume thresholds identified—9 cases annually for hospitals and 7 for surgeons—should not be interpreted as aspirational benchmarks. Rather, they represent minimum thresholds below which outcomes appear to suffer. In an ideal healthcare system, optimal outcomes would likely require substantially higher volumes than these minimums. Higher-volume centers would benefit from refined perioperative protocols, more experienced multidisciplinary teams, and greater familiarity with managing rare but life-threatening complications.
Several limitations merit consideration when interpreting these results. First, the study relied on administrative claims data, which cannot capture procedural technical success, anatomical complexity, or intraoperative complications with the same granularity as clinical registries. Second, the Medicare population studied represents primarily older, non-disabled beneficiaries, and findings may not generalize to younger patients or those with different insurance structures. Third, the observational design cannot definitively establish causation—while volume is associated with outcomes, centers that perform more procedures may also differ in other important ways such as nursing expertise, institutional culture, or access to ancillary services.
The survival advantage observed at higher-volume centers likely reflects multiple factors operating simultaneously. Technical proficiency in branch vessel cannulation and gate selection improves with practice. Institutional familiarity with rare complications—such as spinal cord ischemia, mesenteric ischemia, or massive hemorrhage—enables faster recognition and more effective management. Anesthesia teams, perfusion specialists, and postoperative care units develop protocols optimized for this specific patient population.
From a policy perspective, these findings support the development of volume-based referral recommendations or center-of-excellence designations for F/BEVAR. Such policies exist for other complex procedures, including pancreatic cancer surgery, esophagectomy, and transcatheter aortic valve replacement. While minimum volume requirements can be controversial and may limit patient access in some regions, they represent one of the few evidence-based tools available to health systems seeking to optimize outcomes for complex surgical care.
Conclusion
This landmark study provides the first robust evidence defining volume-outcome thresholds for fenestrated and branched endovascular aortic repair. The identification of critical inflection points at 9 annual hospital cases and 7 annual surgeon cases offers concrete targets for quality improvement and policy development.
As F/BEVAR technology continues to mature and commercial availability expands, the medical community faces a critical decision point. The findings presented here argue strongly for thoughtful dissemination strategies that maintain adequate patient volumes at treating centers. Regionalization of care to high-volume centers, investment in training programs that produce adequately experienced operators, and development of referral networks that guide patients to experienced centers all represent potential implementation pathways.
For patients facing complex thoracoabdominal aortic aneurysms, these findings reinforce the importance of seeking care at experienced centers with demonstrated high-volume experience. For clinicians and health systems, the data provide a quantitative foundation for establishing appropriate quality standards. The ultimate goal remains ensuring that advances in endovascular technology translate into real-world improvements in patient survival and quality of life—and this study suggests that volume-based quality standards may be essential to achieving that objective.
The full implications of this research will unfold as professional societies, payers, and health policy makers consider how best to integrate these findings into practice guidelines and coverage decisions. What is clear is that the relationship between experience and excellence in complex aortic surgery is not merely theoretical—it is quantifiable, clinically significant, and amenable to policy intervention.
Funding and Clinical Trial Information
Study data were derived from Medicare claims files. Full funding disclosures and author conflicts of interest are detailed in the original publication in Annals of Surgery.
