What are the indications, planning steps, and procedural details for using a physician-modified thoracic endograft to treat a thoracic aortic aneurysm?

Physician-Modified Endografts for Thoracic Aortic Aneurysm

Physician-modified thoracic endografts (PMEGs) are a viable endovascular option for treating thoracic aortic aneurysms when standard thoracic endovascular aortic repair (TEVAR) cannot achieve adequate proximal or distal landing zones without covering critical branch vessels, particularly in urgent/emergent settings or high-risk patients unsuitable for open repair.

Indications for Physician-Modified Thoracic Endografts

PMEGs should be considered when:

• Inadequate landing zones exist for standard TEVAR due to proximity of the left subclavian artery, left common carotid artery, or other arch vessels 1
• Urgent or emergent repair is needed (acute type B dissection, symptomatic aneurysm, rupture) and commercial custom devices are unavailable 2, 3
• High surgical risk precludes open repair (advanced age, significant comorbidities, conditions like cold agglutinin disease) 4
• Aortic arch involvement requires preservation of cervical arteries while achieving adequate seal 2

The most common indications in published series include acute type B aortic dissection (40.5%), degenerative aneurysm (33.3%), and chronic dissection with aneurysmal degeneration 2.

Critical Planning Steps

Pre-procedural Imaging and Measurements

CTA with contrast (chest, abdomen, pelvis) is mandatory for PMEG planning 1. The imaging protocol must include:

• Arterial and delayed phases to assess endoleak risk
• ECG gating for ascending aorta and arch measurements to account for 5-10% diameter variation during cardiac cycle 1
• Multidetector technique with isotropic resolution for software compatibility 1

Anatomic Assessment

Measure and document:

• Proximal and distal landing zone dimensions (diameter, length ≥2cm preferred)
• Distance between arch vessels and alignment
• Total length of pathologic aorta requiring coverage 1
• Iliofemoral artery diameters (mean 7.6±1.1mm in PMEG series) and degree of calcification/tortuosity for access planning 1, 2
• Aortic tortuosity index at fixation zones—high tortuosity predicts increased endoleak, stroke, and mortality risk 1
• Aortic arch angulation along centerline to predict bird-beak configuration risk (gap between stent and lesser curve leading to type Ia endoleak) 1

Device Modification Planning

Determine the specific modifications needed:

• Fenestrations for branch vessel preservation (most commonly for left subclavian artery—38 fenestrations reported in one series) 2
• Scallops for partial vessel coverage (4 scallops for common carotid artery reported) 2
• Branches for more complex anatomy (30 branches for left subclavian artery in one series) 2

Low-profile devices (e.g., Zenith Alpha Thoracic Endovascular Graft) are preferred when iliofemoral anatomy is small or tortuous 2.

Procedural Details

Device Modification Technique

The modification process involves:

1. Un-sheathing the commercial thoracic endograft in sterile environment
2. Creating fenestrations or branches using:
   • Manual cutting with reinforcement using nitinol wire 5
   • Automated laser cutting (ALMEG technique—faster, less human error) 6
   • Suturing covered stents to create outer branches when needed 7
3. Reinforcing all fenestrations to prevent tear propagation 5
4. Re-sheathing the modified device for deployment 6

Newer automated techniques reduce modification time from hours to minutes, critical in ruptured cases 6.

Deployment Strategy

• Precise alignment of fenestrations/branches with target vessels using fluoroscopic guidance
• Balloon-expandable covered stents (e.g., iCast) deployed through fenestrations into branch vessels 5
• Confirmation of branch patency and seal before completing procedure
• Assessment for endoleaks with completion angiography

Outcomes and Complications

Technical Success and Mortality

Published series demonstrate:

• 88-96.6% treatment success at mean 11-18 month follow-up 2, 5, 8
• 30-day mortality 4-3.4% 5, 8
• Perioperative stroke rate 2.4% with full neurological recovery 2
• No unintentional branch coverage when properly executed 2

Endoleak Rates

• Type Ia endoleak: 4.8% requiring reintervention 2
• Type IIIa endoleak: 7.1% requiring reintervention 2
• Type II endoleak: 24.1% (mostly observation) 8

High aortic tortuosity significantly increases endoleak risk—these patients require closer postoperative surveillance 1.

Spinal Cord Ischemia

• Severe SCI rate: 0-4% in PMEG series 2, 5
• Permanent SCI: 4% 5

Consider posterior fenestrations to preserve intercostal artery perfusion in extensive thoracoabdominal repairs 9.

Critical Pitfalls and How to Avoid Them

Bird-beak configuration develops when highly angulated arch prevents stent apposition to lesser curve:

• Measure arch angulation preoperatively on CTA centerline analysis 1
• Plan for oversizing and longer landing zones in high-angulation anatomy
• Schedule closer imaging follow-up (every 3-6 months initially) 1

Access complications (2.4% rate):

• Mandatory iliofemoral assessment on preoperative CTA 1
• Consider percutaneous vs. open access based on vessel diameter and calcification 10
• Have conduit placement capability available

Device durability concerns:

• Long-term data remain limited—median follow-up in most series <2 years 2, 3
• Continued surveillance is mandatory with CTA at 1,6,12 months, then annually 3

Patient Selection Criteria

Reserve PMEGs for patients who meet ALL of the following:

1. Unsuitable anatomy for standard TEVAR (inadequate landing zones)
2. High risk for open repair OR urgent/emergent indication
3. Adequate iliofemoral access (≥7mm diameter preferred) 2
4. Treatment at high-volume center with experienced operators 5, 3

PMEGs should NOT be first-line for elective cases when commercial custom devices are available and time permits 3. However, under FDA-approved Investigational Device Exemption protocols, some centers use PMEGs electively with promising results 5, 3.

The technique requires careful preoperative planning, meticulous execution, and commitment to long-term surveillance to ensure durability 5, 3.