June 04, 2026
Physician-modified endografts (PMEGs) offer a tailored and timely solution for select people requiring complex endovascular aneurysm repair. Mayo Clinic in Florida is now approved by the Food and Drug Administration through an investigational device exemption to modify endografts for thoracoabdominal aortic aneurysm (TAAA) repair. Surgeons integrate engineering-based planning principles with advanced technical expertise during the modification process.
"When we do aortic repairs, specifically aneurysms, we have to think like engineers," says Young M. Erben, M.D., a vascular surgeon at Mayo Clinic in Jacksonville, Florida. "Each patient's anatomy presents unique nuances that must be carefully incorporated into the plan. Success is ultimately determined at the moment of device deployment within the vessel, leaving little margin for error in the planning process."
Applying engineering principles to PMEG planning
Modifying a standard endograft for TAAA endovascular aneurysm repair (EVAR) represents a dynamic intersection of engineering and vascular surgery. Problem-solving is central to the PMEG process, which broadly follows an engineering protocol:
- Problem identification. Advanced imaging and 3D reconstruction are used to define patient-specific anatomy and characterize the thoracoabdominal aneurysm.
- Meticulous planning. Device selection and modification strategies are evaluated from multiple perspectives, accounting for device constraints and patient-specific anatomic parameters.
- Expert execution. A multidisciplinary team with extensive endovascular experience performs modifications to the endograft and proceeds with its placement. Team members are capable of innovating and adapting to address interoperative challenges.
- Postoperative assessment. Procedural outcomes are systematically reviewed to refine planning and modification protocols for future cases.
Within this engineering-inspired protocol, Dr. Erben stresses that collaboration and adaptability are critical to achieving optimal outcomes.
"When we do aortic repairs, specifically aneurysms, we have to think like engineers. Each patient's anatomy presents unique nuances that must be carefully incorporated into the plan."
Collaboration to create a precise thoracoabdominal aortic aneurysm repair plan
The complexity of TAAA repair varies by patient but consistently demands rigorous preoperative planning. For the Mayo Clinic team, modifications may involve bridging up to five visceral vessels. Serial CT angiography (CTA) of the aorta and 3D reconstruction are critical to accurately characterize anatomical complexity and guide fenestration design.
The planning team typically comprises vascular surgeons, a radiologist and at least one design engineer support staff from the endograft manufacturer. Together, they evaluate all aspects of the anatomy and procedure, including:
- Graft oversizing. Oversizing, typically by 20%, ensures adequate radial force and alignment with the vessel. Careful consideration of how oversizing influences angulation and modification strategies is critical.
- Proximal graft coverage and positioning. Adequate proximal fixation is required to minimize endoleak risk while avoiding unnecessary coverage of critical segments, such as lumbar arteries.
- Fenestration placement and resheathing. Anticipated technical challenges related to fenestration placement and device reloading must be considered in advance.
- Vessel orientation and angulation. Spatial relationships among target vessels inform fenestration design and determine whether incorporation of branches is necessary.
"There is no room for error when it comes to measurement," Dr. Erben says. "That is why the analysis is never performed by a single individual. Four of us independently review the design, and we must reach a unanimous agreement before proceeding."
Device modification and adaptation in a high-stress environment
Endograft modification is performed in the hours immediately preceding surgery to maintain device sterility, although all design decisions are finalized well in advance. By the time the surgical team reconvenes on the day of the procedure, the strategy is clearly defined, and execution can proceed without delay.
Mayo Clinic surgeons employ manufacturer-equivalent techniques for graft modification, including the use of fine, tightly spaced suturing to create and reinforce fenestrations. Reloading the modified graft demands considerable precision and experience to preserve fenestration integrity and ensure accurate alignment. When resheathing proves technically challenging, the delivery system itself may require modification. However, this rarely occurs.
Effective execution depends on a coordinated operating room team. "Every member of the surgical team — including nursing staff, surgical technologists and anesthesiologists — must understand the workflow and be prepared to innovate in the operating room," Dr. Erben says. "As graft modification is completed, the patient is simultaneously being prepared for surgery. These processes occur in parallel and require seamless coordination."
The team also must be prepared to manage intraoperative challenges during device deployment. Manufacturer representatives are present to assist with real-time troubleshooting.
In scenarios when vessel cannulation is unsuccessful or when anatomy behaves differently than anticipated, surgeons must make rapid, high-stakes decisions regarding alternative strategies. Although Dr. Erben has not yet encountered this situation, she anticipates its likelihood as procedural volume increases.
"These are inherently high-intensity cases," Dr. Erben says. "Even with extensive experience, the stress level does not decrease, given the individualized nature of each repair."
PMEG as an evolving clinical process
Each PMEG case contributes to an expanding body of institutional knowledge. Dr. Erben and her colleagues continuously refine their approach based on their own procedural experience and insights gained from others using PMEG for TAAA repair.
While Mayo Clinic's current PMEG protocols provide reliable solutions, ongoing collaboration between clinicians and device manufacturers is essential to drive innovation in graft design and deployment.
"There are prototypes and platforms in the early stages of discussion and development," Dr. Erben says. "Although they are not yet commercially available, the potential for advancement is there — and very exciting."
For more information
Refer a patient to Mayo Clinic.