TEVAR: A valid alternative for traumatic injuries

Acute traumatic rupture of the thoracic aorta is a life-threatening injury that is often the result of a motor vehicle accident. This injury results in immediate death in the vast majority of cases (80-85%). The prevalence of the injury is such that approximately 10-15% of deaths due to serious car accidents are due to traumatic aortic rupture(1), and a mere 10-15% of victims arrive at the hospital alive.(2) The outcome for these patients is determined by the degree of damage to the aorta, as well as other injuries sustained. The seriousness of such events is evidenced by a mortality rate in non-operated patients of approximately 1% per hour for the first 48 hours.(3) Those who survive can develop a potentially unstable aortic rupture. In these patients, the outcome is an aortic pseudo-aneurysm, which can expand and rupture.

Identifying traumatic ruptures
While the diagnosis of an aortic rupture can be elusive, the results of a standard chest radiograph can give an indication that suggests the diagnosis. Theses include fractures of the sternum, clavicle or first two ribs, an abnormal aortic contour, rightward displacement of the trachea and oesophagus, a widened mediastinum, an apical pleural cap, and others.

Imaging options
In the patient is stable with a suggestion of aortic pathology on chest radiograph, it is recommended that the patient undergo a computed tomography (CT) scan. Today, the diagnosis of an aortic rupture can be confirmed with 100% sensitivity and 99.7% specificity(4)[Fig 1], following standard spiral contrast-enhanced CT trauma protocols. In particular, these images reveal the crucial elements that must be known if one is considering thoracic endovascular aortic repair (TEVAR). These measurements include the proximal and distal diameters of the aorta, aortic angulation, and distance of the tear from the left subclavian artery.

However, CT is not the only modality available. MRI, trans-esophageal echocardiogram and aortic angiography have all demonstrated success in diagnosing aortic ruptures, although not without their shortcomings.

Open repair
The standard treatment for such a condition has been open repair since the first case in 1959(5). Tube graft replacement of the injured segment via a left thoracotomy approach requires single-lung ventilation and aortic clamping for both proximal and distal aortic control. This clamp and sew procedure has the major associated morbidity of paraplegia in 7% of cases.(6)

In an effort to reduce this risk, other techniques have been added to the original procedure. They have brought with them added dangers, however. For example, shunting and cardiopulmonary bypass have been known to reduce spinal cord complications, but due to systemic heparinisation requirements, is not without additional dangers. Moreover, the open surgical procedure can be a long undertaking which is a particular drawback considering the patient may have additional life-threatening injuries that require surgical attention.

Endovascular repair
The era of endovascular surgery has brought a less invasive option for treating traumatic aortic ruptures. Thoracic endovascular aortic repair (TEVAR) has the advantage of reducing the time of the procedure to less than an hour allowing the physician to treat any other surgical injuries the patient may have sustained.

Before performing TEVAR for a thoracic aortic tear, other life-threatening injuries (eg, head trauma and abdominal haemorrhage) should be addressed. In addition, it is also important to note that during this period hypertension, excessive intravenous fluids and blood products should be avoided in order to maintain aortic stability prior to treatment.

Using contrast-enhanced CT images, the aortic diameter should be measured from adventitia to adventitia on the normal aorta proximal and distal to the tear using oblique or central-lumen line CT reconstructions. It is also recommended that when choosing an endograft one should oversize the aortic diameter by 10-20%. Due to the nature of these injuries, this group of patients are young (mean age 39.9)(8), compared to their aneurysm counterparts. Therefore the smallest commercially available endografts can be too large for these non-dilated aortas. It is recommended that the short grafts are used to guarantee exclusion of the focal injury. It is also important to assess the access vessels by CT scan, to ensure a minimum diameter of at 8mm.

There still remains some debate as to the use of pharmacologically induced-hypotension and/or cardiac arrest at the time of graft deployment. If a Type I endoleak is identified on completion angiography, ballooning of the proximal and/or distal ends of the graft maybe required.

Fate of the left subclavian artery
As traumatic rupture of the thoracic aorta is typically close to the left subclavian artery, it is often necessary to cover its origin when placing an endograft to obtain an adequate proximal sealing zone. However, this is contraindicated in patients with left internal mammary to coronary artery bypasses. Nevertheless, it has been demonstrated to be safe, (10) although if a dominant vertebral is identified some support a prophylactic transposition of the left subclavian artery to the left common carotid artery.(11)

Post-operative surveillance and outcomes
Following TEVAR, a contrast-enhanced CT angiogram (CTA) should be performed as early as possible. In order to detect graft migration or endoleaks, CTA and four-directional plain chest radiographs should be obtained after six and 12 months. Once complete aortic healing is noted on CTA (7), annual radiographs should provide sufficient imaging surveillance.

Thus far, the short-term results for TEVAR for an a traumatic rupture have been very promising. Not only does the technical success approach 84-100% (7,11,14,15,16), but stroke complicating TEVAR for aortic trauma is less commonly seen when compared to the treatment of aneurysmal disease. Although a single posterior stroke has been reported.(11) Device-related complications have been primarily due to oversizing, including Type I endoleaks and graft infolding. Access complications have been recorded in some series,(11,13,15). However, the frequency of such events should be reduced as smaller devices become available.