What are the sizing criteria for Thoracic Endovascular Aortic Repair (TEVAR)?

TEVAR Sizing Criteria

For thoracic aortic aneurysms, select a stent-graft diameter that exceeds the reference aortic diameter at the landing zones by 10-15%, with a minimum landing zone length of 20 mm proximally and distally. 1

Stent-Graft Diameter Oversizing

For Thoracic Aortic Aneurysms (TAA)

• Oversize the stent-graft by 10-15% relative to the reference aortic diameter measured at the proximal and distal landing zones. 1
• This oversizing range provides optimal seal while minimizing complications such as endoleak and stent-graft induced new entry (SINE). 1
• Oversizing beyond 20% increases risk of complications, particularly annular rupture in abdominal repairs and SINE in dissections. 2

For Type B Aortic Dissection

• Apply minimal to no oversizing (0-10%) when treating acute type B dissection. 1
• The goal is to cover the proximal entry tear and induce false lumen thrombosis without excessive radial force. 1
• Excessive oversizing (>10%) is an independent predictor of distal SINE development (odds ratio 1.858), which occurred in 27.8% of patients in one series. 2
• Oversizing ≤10% in complicated type B dissection showed a trend toward 50% reduction in aortic-related events (hazard ratio 0.455). 3

Special Consideration: Hemodynamic Instability

• In patients with systolic blood pressure ≤90 mmHg or mean arterial pressure ≤70 mmHg despite resuscitation, the aortic diameter may be reduced by >15% compared to normal state. 4
• In hemodynamically unstable patients (particularly blunt thoracic aortic injury), oversizing up to 130% based on intraoperative aortography measurements may be appropriate, as this translates to approximately 122% oversizing once hemodynamics normalize. 4

Landing Zone Requirements

Length Specifications

• A minimum landing zone length of 20 mm (2 cm) is required both proximally and distally for safe deployment and durable fixation. 1
• This length ensures adequate seal and prevents migration or endoleak. 1

Diameter Limitations

• The proximal landing zone should not exceed 40 mm in diameter for standard TEVAR devices. 1
• Evaluate the entire iliofemoral access route, as delivery systems range from 14-24 French. 1

Pre-Procedural Measurement Technique

Imaging Requirements

• Obtain contrast-enhanced CT with ≤3 mm slice thickness (ideally ≤0.25 mm) of the entire aorta from supra-aortic branches to femoral arteries. 1, 5
• Use ECG-gated CT for the ascending aorta to account for cardiac motion, which can cause 5-10% variation in diameter between systole and diastole. 1

Measurement Methodology

• Perform diameter measurements perpendicular to a centerline reconstruction using three-dimensional software. 3, 5
• Measure at the intended proximal landing zone (typically zone 2 of the aortic arch for descending thoracic repairs). 3
• For dissections, measure the total aortic diameter (true lumen + false lumen) to estimate the pre-dissection diameter. 2, 3

Critical Pitfall: Different measurement techniques for estimating pre-dissection diameter in acute dissection can vary by 1.7-4.0 mm on average, with variability up to 8.4 mm, potentially leading to selection of different stent-graft sizes. 3 Use consistent methodology and consider intraoperative imaging (IVUS or TOE) for real-time verification. 1

Anatomic Assessment Beyond Sizing

Evaluate for High-Risk Features

• Assess aortic tortuosity at the proximal landing zone, as increased tortuosity index significantly predicts type III endoleak, stroke, and all-cause mortality after TEVAR. 1
• Identify relationship to critical branch vessels (left subclavian artery, intercostal arteries supplying spinal cord). 1
• Measure distances between arch vessels and alignment if arch coverage is planned. 1

Access Route Evaluation

• Assess iliofemoral artery diameter, calcification burden, and tortuosity to ensure compatibility with large delivery devices (up to 24 French). 1

Intraoperative Considerations

• Reduce systolic blood pressure to <80 mmHg (using nitroprusside, adenosine, or rapid ventricular pacing) during stent-graft deployment to prevent downstream displacement. 1
• Consider intraoperative IVUS or TOE for real-time diameter verification, particularly in hemodynamically unstable patients or when navigating the true lumen in dissections. 1
• Perform completion angiography immediately to detect type I endoleak requiring immediate correction. 1