Since its inception in 1992, thoracic endovascular aortic repair (TEVAR) was introduced as an alternative treatment option to conventional open surgery for patients with complicated Type B aortic dissection (TBAD), i.e., end-organ malperfusion, refractory hypertension or hypotension, and unrelenting pain. TEVAR is also now considered for treatment of dissections with aneurysmal degeneration with aortic diameter >55 mm or increased aortic diameter of >4 mm/year.
Tevar Versus Open Surgery
TEVAR has been shown to have significantly improved 30-day survival for TAA (84%–95% versus 70%) in contrast to open repair. When studying TBAD specifically, the registry of acute aortic dissection (IRAD) recommended TEVAR be the first line of treatment for patients with complicated TBAD. This report also indicated significant remodeling in favor of TEVAR (expansion of true lumen and regression of false lumen) especially when the stented segment continues to the visceral vessels, directly related to a decrease in the incidence of aortic wall degeneration, with subsequent decrease in likelihood of developing of aneurysms. Likewise, the findings of the VIRTUE study reinforced that aortic remodeling after TEVAR is a continuous process. Accordingly, many respected authorities suggest early endovascular intervention. Also, the recently published Acute Dissection: Stent Graft or Best Medical Therapy (ADSORB) trial found that TEVAR markedly facilitates aortic remodeling compared with medical therapy alone , potentially conferring a survival advantage as shown by the INSTEAD trial in 2009 and INSTEAD XL in 2013.
All procedures should be performed in a hybrid suite. Depending on the patient’s comorbidities, the surgeon’s experience with TEVARs, and the institutional ancillary staff, such procedures can be performed under local anesthesia with MAC sedation or sometimes under general anesthesia. Spinal cord drainage is not typically performed for emergency patients, while selective use in elective cases may be warranted, depending on the planned length of coverage. CTA evaluation is critical to aid in access site determination, with preference to the nondissected vessel if present for direct access to the true lumen. Access can be either surgical or percutaneous, as is standard for large access procedures. Initial access to the true lumen can be obtained with glide wire, Rosen wire, or glide catheter supported by the wire, with the catheter leading, to decrease the chance of dissection with a wire in the false lumen ( Fig. 26.1 ). The wire/catheter is assessed to be in the true lumen by using intravascular ultrasound (IVUS), transesophageal echocardiography (TEE), or a combination of the two, to characterize the extent and the size of the dissection entry point. Then a marked 5-French pigtail is advanced to the aortic arch with image intensifier at 30–40 LAO (left anterior oblique) angle, while an arch angiogram with 20–30 mL Visipaque (GE Health care) is performed. Arch vessels are identified and confirmed with IVUS/TEE (note: marking the monitor or using overlay or road mapping will help proper placement of the stent). Our practice is to keep mean blood pressure around 65–75 mmHg to prevent the windsock effect and to facilitate appropriate placement of the stent. The wire is exchanged for a double curve Landerquist (Cook Medical, Bloomington, Indiana) super stiff wire. The double curve wire enables the stent graft to conform to the outer aortic curvature. An appropriate sized stent graft (i.e., 10% oversized) can be advanced through the true lumen and provide adequate coverage of the dissection entry point (see Fig. 26.2A,B ). Further oversizing can be problematic with dissections, especially chronic dissections. The 2-cm landing zone required for aneurysmal dissections is less important, as migration after TEVAR for TBAD is not seen; however, it is critical to cover the entry tear completely. If there is a need to cover arch vessels, assessment of the vertebral flow should be done to minimize stroke risk further (SVS TEVAR guidelines). In order to preserve the cervical vessels, open debranching via carotid–subclavian bypass or parallel graft technique may be considered. In this instance, cannulation of subclavian or left carotid is performed retrograde fashion, and a covered stent (maximum 10% oversizing) is deployed, with the proximal end 4–5 mm proximal to the TEVAR into the aortic arch. Deployment of the thoracic stent graft is first, with sheaths already in place and snorkels/chimneys performed simultaneously. Ballooning of the stent graft, especially in the proximal sealing zone, should be avoided to decrease the risk of retrograde dissection.
If parallel grafts are used, it is important to measure correctly for graft size, using the equation area=πr 2 to calculate the surface area of chimney stent, stent graft, and native aortic lumen surface area.
Although the TEVAR procedure may sound simple, the timing of the procedure, peri-operative management, planning, and managing the potential complications all require a multidisciplinary team of vascular surgeon, cardiac surgeon, intensivist, neurologist, cardiovascular anesthesiologist, and well-trained ancillary staff to recognize and to manage complications. This can be accomplished by creating an Aortic Center of Excellence that manages referrals, facilitates admissions, and places protocols for such pathology.
Complications that may be Encountered Intraoperatively
Retrograde dissection: This is the most dreaded intraoperative complication and is directly related to graft oversizing >20 mm. The incidence in TBAD is 3% compared with 1% in degenerative aortic pathology. The proximal landing zone does not impact this issue and currently used stent configurations do not appear to increase risk, as did some older devices. Some experts suggest using grafts with no proximal hooks or grafts with large aggressive bare-metal stents in the proximal sealing zone to decrease the chance of retrograde dissection. Newer stent generations have no bare-metal parts or short parallel ones and no hooks. Use of TEE can be critical in identifying any proximal dissection after TEVAR completion.
Stent maldeployment: Proximal or distal migration resulting from missing the appropriate landing zone can happen. Using a device that the surgeon has experience with decreases that chance. Some devices need more rapid deployment, and others need slow controlled deployment. Some devices offer controlled staged deployment but care must be taken with distal migration. Rigorous control of hypertension and conforming the stent graft to the aortic-outer wall by maintaining forward pressure on Landerquest wire also decrease the risk of maldeployment.
Overlooking a large distal fenestration could lead to perfusion of the false lumen, with more chance of distal aortic degeneration, aneurysmal growth, and possible rupture; therefore, meticulous examination of all fenestration between true and false lumina is recommended.
Aortic rupture is extremely rare but may occur, especially with patients with connective tissue disease (CTD). In this scenario, emergency aortic occluding balloon and open surgical repair will likely be needed. All patients with known CTD with TBAD should be considered for open repair if judged medically fit.
Technical Recommendations for TEVAR
The clinician needs to have clear characterization of true and false lumina.
It is imperative to achieve coverage of the proximal entry tear that is usually located at or distal to the left subclavian artery ( Fig. 26.3 ). Strive to have a healthy looking proximal landing zone, even if coverage of the origin of left subclavian is necessary.