# Thoracic Endovascular Aortic Repair (TEVAR)

## Overview and Indications

Thoracic endovascular aortic repair (TEVAR) is the endovascular treatment of thoracic aortic pathology using stent-grafts deployed via femoral or iliac access. Primary indications include descending thoracic aortic aneurysm (DTAA) of 5.5-6.0 cm or greater or rapidly expanding (greater than 0.5 cm per year), complicated acute Type B dissection (malperfusion, rupture, rapid expansion), penetrating aortic ulcer with intramural hematoma, traumatic aortic transection (now first-line over open repair), and selected cases of mycotic or infected aneurysms with antibiotic coverage. Contraindications include inadequate landing zones, severe iliofemoral disease precluding access, and connective tissue disorders (relative).

## Anatomic Planning and Landing Zones

### Aortic Landing Zone Classification (Ishimaru Zones)

The Ishimaru classification guides proximal landing zone selection. **Zone 0** is the ascending aorta, requiring arch debranching or total arch replacement. **Zone 1** lies between the innominate and left common carotid arteries, requiring carotid-carotid bypass. **Zone 2** lies between the left common carotid and left subclavian artery, and may require left subclavian artery (LSA) revascularization. **Zone 3** is the proximal descending aorta distal to the LSA and serves as the standard landing zone. **Zone 4** is the mid-descending thoracic aorta. A minimum proximal and distal seal zone length of 2 cm of healthy, non-aneurysmal aorta is required. Oversizing is typically 10-20% relative to the reference vessel diameter.

### Left Subclavian Artery Management

Coverage of the LSA may be necessary for adequate proximal seal. Revascularization is recommended when there is a patent LIMA-LAD graft, dominant left vertebral artery, functioning left arm arteriovenous fistula for dialysis, or prior infrarenal aortic repair (with reliance on subclavian collaterals for spinal cord perfusion). Standard revascularization options include carotid-subclavian bypass or transposition. SVS guidelines recommend routine revascularization when elective LSA coverage is planned.

<image>Ishimaru landing zone classification diagram showing zones 0-4 of the thoracic aorta with branch vessel landmarks</image>

## Device Selection and Technical Considerations

Currently available devices include the conformable TAG (Gore), Valiant/Navion (Medtronic), Relay (Bolton), and Zenith Alpha (Cook). Key device characteristics include conformability (ability to adapt to aortic curvature, especially in the arch), radial force (maintaining seal against the aortic wall), delivery profile (sheath diameter typically 18-24 Fr), and the configuration of the proximal stent (bare spring versus covered). Access vessel assessment is critical, requiring CT angiography to evaluate iliofemoral diameter, calcification, and tortuosity. An iliac conduit may be needed if femoral or iliac vessels are too small or diseased. Intraoperative imaging uses fluoroscopy and intravascular ultrasound (IVUS). Controlled hypotension or rapid ventricular pacing during deployment prevents windsocking.

<image>TEVAR deployment sequence showing catheter advancement, stent-graft positioning at the landing zone, and controlled deployment under fluoroscopic guidance</image>

## Endoleak Classification and Management

### Types of Endoleak

**Type I** endoleaks occur at the attachment site — Type Ia at the proximal seal zone and Type Ib at the distal seal zone — and require immediate treatment with ballooning, extension cuffs, or conversion to open repair. **Type II** endoleaks result from branch vessel backbleeding (intercostal or bronchial arteries) and are the most common type after TEVAR; they are usually benign and treated only if sac expansion occurs. **Type III** endoleaks arise from graft defects or component separation and require intervention with relining by additional stent-graft. **Type IV** endoleaks are due to graft porosity and are self-limiting, rare with modern devices. **Type V (endotension)** describes sac expansion without an identifiable leak on imaging.

### Endoleak Classification Summary

| Type | Source | Frequency | Clinical Significance | Management |
|------|--------|-----------|----------------------|------------|
| Ia | Proximal attachment site | Common | High — requires treatment | Ballooning, extension cuff, or open conversion |
| Ib | Distal attachment site | Less common | High — requires treatment | Distal extension cuff |
| II | Branch vessel backbleed (intercostal, bronchial) | Most common after TEVAR | Usually benign | Observe; treat only if sac expansion |
| III | Graft defect or component separation | Uncommon | High — requires intervention | Relining with additional stent-graft |
| IV | Graft porosity | Rare (modern devices) | Self-limiting | Observation |
| V (endotension) | Sac expansion without identifiable leak | Rare | Uncertain | Close surveillance; consider intervention |

### Surveillance Protocol

CT angiography is obtained at 1 month, 6 months, 12 months, and then annually. Sac diameter stability or shrinkage indicates successful exclusion, while any sac expansion requires investigation for endoleak.

## Complications

### Device-Related

**Retrograde Type A aortic dissection (RTAD)** occurs in 1-4% of cases and is a catastrophic complication. Risk factors include oversizing greater than 20%, a bare metal proximal stent, and ascending aortic disease; it requires emergent open ascending repair. Other device-related complications include stent-graft migration, stent-graft collapse (especially in tight arches), and bird-beaking — incomplete apposition of the proximal edge to the lesser curvature.

### Access-Related

Access complications include iliofemoral dissection, rupture, thrombosis, and embolization.

### Neurologic

**Spinal cord ischemia** occurs in 3-8%, with higher rates when coverage length exceeds 20 cm, there has been prior abdominal aortic repair, the LSA is covered without revascularization, or hypotension occurs. Prevention strategies include CSF drainage, staged procedures, maintaining MAP above 80 mmHg, and LSA revascularization. **Stroke** occurs in 3-6%, especially with Zone 0-2 landing.

<image>Endoleak classification diagram showing Types I through V with arrows indicating flow patterns around the stent-graft</image>

## Hybrid Approaches for Complex Aortic Pathology

Several hybrid approaches extend the applicability of TEVAR to more complex anatomy. **Arch debranching plus TEVAR** involves staged or simultaneous great vessel bypass followed by Zone 0-2 TEVAR. The **frozen elephant trunk (FET)** combines open total arch replacement with antegrade stent-graft deployment into the descending aorta. **Branched and fenestrated endografts** are custom devices with branches for arch vessels that are either investigational or physician-modified. **Chimney or snorkel grafts** are parallel stent-grafts used to maintain branch patency as an off-label approach.

## Outcomes and Long-Term Durability

Thirty-day mortality is 2-5% for elective cases and 10-20% for emergencies. The reintervention rate is 10-15% at 5 years. Long-term durability concerns include disease progression beyond the treated segment, material fatigue and component separation, and late endoleak development. For young patients (under 60 years) and those with connective tissue disorders, open repair is generally preferred for durability.

<image>CT angiography three-dimensional reconstruction showing successful TEVAR with complete aneurysm sac exclusion and patent branch vessels</image>

## Clinical Pearls

The entire aorta from root to bifurcation should always be assessed because thoracic pathology rarely exists in isolation. Spinal cord protection with CSF drainage should be proactively placed for extensive coverage, prior AAA repair, or LSA coverage. Retrograde Type A dissection is the most feared complication, and risk is minimized by avoiding excessive oversizing and not treating diseased ascending aortas. Post-deployment hypertension management is crucial, with systolic blood pressure kept below 120 mmHg in the first 24 hours to reduce endoleak and migration risk. Lifelong surveillance imaging is mandatory — TEVAR is not a "one and done" procedure. Access planning is as important as the aortic repair itself, and iliac conduit should be part of the surgical plan when needed.

## References

- Makaroun MS et al. "Five-year results of endovascular treatment with the Gore TAG device." *J Vasc Surg*. 2011.
- Fairman RM et al. "Pivotal results for the Medtronic Valiant thoracic stent graft system." *J Vasc Surg*. 2012.
- Matsumura JS et al. "SVS Practice Guidelines for thoracic endovascular aortic repair." *J Vasc Surg*. 2021.
- Riambau V et al. "ESVS 2017 Clinical Practice Guidelines on the Management of Descending Thoracic Aorta Diseases." *Eur J Vasc Endovasc Surg*. 2017.
- Williams JB et al. "Retrograde Type A dissection after TEVAR: a systematic review." *Ann Thorac Surg*. 2017.