Question 6

Which of the following is a favorable feature for thoracic endovascular aortic stent graft access?

A.  Tortuous iliac arteries B.  Iliac diameter < 7 mm

C.  Suitable anatomy for conduit formation D.  Patent femoral arteries

E.  Calcified iliac arteries

Question 7

Which of the following is a favorable feature for thoracic endovascular aortic stent deployment?

A.  Bovine aortic arch

B.  Aortic diameter < 18 mm

C.  Transection is proximal to left subclavian artery D.  Patent vertebral arteries

E.  Acute angulated aortic arch

Answer = Q7: A&D

It was felt that her thoracic aorta was anatomically suitable for endovascular stent repair. Therewasanappropriatestentavailableinthehospitaltousefortheprocedure.Hercondition was much better and her hemodynamics had returned to within normal limits with the use of inotropic support. The vascular surgeons requested that her systolic blood pressure be kept at approximately 100 mmHg.

She underwent successful endovascular stent repair of her transected thoracic aorta (Figs. 15.6 and 15.7) and was transferred to the intensive care unit. After a prolonged hospitalstayshereturnedhomeandfinallyachievedindependentliving.Ondischargeshewas entered onto a thoracic endovascular aortic stent surveillance program.

Question 8

Which of the following are potential complications of thoracic aortic endovascular stent repair?

A.  Stroke

B.  Aortic rupture C.  Paraplegia

D.  Aortic thrombosis E.  Graft infolding F.  Graft collapse

Question 9

What imaging modality is usually employed for thoracic aortic stent surveillance?

A.  Thoracic computerized tomography B.  Chest radiography only

C.  Diagnostic subtraction angiography D.  Intravascular ultrasound

E.  Echocardiography

15.1  Commentary

Road traffic accidents are a common cause of trauma and resultant death for young persons. The injuries sustained are termed polytraumatic, as they occur to a number of anatomical and physiological systems. Deceleration injuries cause blunt trauma and the collision itself can result in penetrating injuries depending what impact is made with. In the case of the young female that we have presented, she collided with a stationary object. She was subjected to a sudden deceleration causing shear forces to her body and on impact she did not suffer from penetrating injuries, however did suffer crush injuries due to the vehicle’s compressive forces against the tree.

Shesufferedhead,neck,thoracic(lungandgreatvessel),abdominal(hepaticandsplenic) and long bone (femoral shaft) injuries. All of these in separation are life threatening, however the mortality is significantly greater if they occur simultaneously, as with this case.

When presented with such a patient suffering from polytraumatic injuries pre-hospital or in an emergency department, a clear and systematic approach to treating injuries in order of most life-threatening first should be adopted. A commonly used approach is the Advanced Trauma Life Support taught by the American College of Surgeons.1 Initially a primary survey is conducted where the common “ABCDE” approach is adopted after cervical spine immobilization, as airway injuries (A) have a higher mortality than breathing (B), than circulatory (C), than disability/neurologically (D) and then environmental/everything (E) else is treated last.

The correct answer to Question 1 is C (Q1 = C). Administration of high flow oxygen is beneficial to airway and breathing injuries and thus survival compared to the other options available. Answers A and B, address the circulatory system so would follow from airway control. Administration of analgesia is humane, however should not take priority over lifethreatening injuries and interventions.

Once the primary survey has been conducted and problems encountered addressed as best as possible for the circumstance, transfer to an appropriate facility is necessary for definitive care. Continuous reassessment of the primary survey is compulsory to detect any evolving injuries and deterioration, especially on arrival at the appropriate facility. Our lady’s arrival to an emergency department at a trauma hospital in our case revealed a number of possible injuries which included airway compromise, abdominal and long bone

trauma with an evolving head injury. These problems should be addressed immediately to saveherlife,thisapproachistermed“damagecontrol.”Itisadvisedthatamultidisciplinary team approach to trauma should be adopted as there may be a number of synchronous pathologies of which many expert opinions would be beneficial to the patient’s survival.

Next, primary radiology is performed. This consists of plain chest and pelvic radiographs with or without cervical spine lateral view, if indicated. The appropriate answer to Question 2 is D (Q2 = D). Computerized tomography and long bone radiographs can be performed after the primary radiology.

The patient began to deteriorate and hemodynamically started to display signs of hypovolaemic shock. Her heart rate rose and inversely her blood pressure dropped. She also showed signs of cerebral malperfusion by becoming more confused, combative and drowsy. A reduction of consciousness (Glasgow coma scale of < 8) should be treated by intubating the patient because the airway may be at risk of obstruction, thus our patient was eventually sedated and intubated.

It is important to note that this patient is young. Young victims and children often initially present with normal hemodynamics as they can compensate for blood loss due to an abundance of physiological reserve, compared to the elderly who usually also possess more comorbidities. However, they may show subtle signs of deterioration and then unexpectedly “crash” their hemodynamics. We know that she suffered from hypovolaemic shock as she was a transient responder to fluid administration, so she was volume depleted. The cause for this patient’s hypovolaemic shock could be due to poor oxygen delivery from her lung injuries and tension pneumothorax, her evolving peritoneal bleeding, hemorrhage from her long bone fracture, which can be profuse, or head injury. Bleeding was further confirmed byclinical and investigative reassessment whichshowed a falling hemoglobin level and profound metabolic acidosis.

The most appropriate injury to address first was her tension pneumothorax with needle decompression then the insertion of a chest drain, so the answer to Question 3 is A (Q3 = A). Addressing the circulatory injuries to the abdomen and long bones causing bleeding should follow.

Question 4 deals with appropriate diagnostic investigations in a stable patient in hypovolaemic shock responsive to fluid administration when the cause of bleeding is uncertain. Computerized tomography is often readily available in larger centers, but not to all. It offers a rapid cross-sectional multi-cavity imaging which can positively guide definitive management. It must be stressed that unstable patients should receive immediate treatment and not be investigated. Many patients have died due to inappropriate diagnostic imaging when “damage control” operative surgery is indicated. In this lady’s case, she was stable and there was a diagnostic uncertainty of the source of her bleeding. She had chest pathology displayed by her tension pneumothorax and widened mediastinum and hemothorax, as well as a tender, distending abdomen. She was also suffering from a head injury and neck injury, so answer B is correct (Q4 = B).

The computerized tomographical imaging demonstrated a number of her injuries in the thorax, abdomen, and head as well as a several bone fractures. She then went for operative treatment of her abdominal (liver and spleen) injuries and femoral shaft fracture.

Whilst “damage control” surgery was undertaken, the duty vascular surgeon and interventional radiologist evaluated the thoracic aortic transection image reconstructions with

particular interests to the vessels measurements and anatomical parameters. Some advocate that computerized tomographical angiography with contrast is best, however, if there is a true vascular traumatic transection, then contrast in a hematoma will obscure images.

An aortic transection is a laceration of all three layers of the vessel wall, not to be confused with aortic dissections, which are rarely, associated with trauma and usually longitudinal vessel wall tears. It is usually associated with rapid deceleration and crush injuries from blunt trauma caused from high speed road traffic collisions or falls from heights. Less frequently penetrating trauma such as stab wounds or gunshot injuries can cause transections. The majority of victims die immediately at the scene (80–90%) from exsanguination. Due to the rarity of sufferers actually reaching hospital, most centers have little experience in treating these injuries. These factors in conjunction with subtle and vague clinical signs,2–5 thus reliant on imaging for diagnosis make the prognosis poor with a consequently high mortality. The concomitant non-aortic injuries can be numerous as with the case presented. Involvement with multiple rib fractures (78%), liver lacerations (61%), head injuries (42%), first rib fracture (42%), splenic lacerations (36%), heart lacerations (34%), sternal fractures (28%) and cervical spinal fractures (26%) are not uncommon.3,6

Traditionally, conventional surgical repair of the traumatic transected thoracic aorta has been the gold standard,3,7 but carries a significant mortality and paraplegia rate ranging from 15% to 30% in contemporary studies.3,8,9 Endovascular treatment of the thoracic aortic was first described in 199110 and has become favorable over conventional open surgical techniquesfortreatingtraumatictransectionsinthepolytraumatisedpatientsduetoamuch lesser mortality and morbidity rate.3,11 Physiologically these patients are particularly vulnerable and a quick non-invasive procedure would be preferential. There are no randomized control trials of open vs. endovascular repair for traumatic aortic transections. There is an overwhelming abundance of mostly small case series3,12–30 and meta-analysis31–34 of these series all generally concluding that endovascular techniques have a reduced mortality and morbidity compared to the alternatives. Endovascular aortic transection repair can be conducted more quickly under local anesthesia in a supine position unlike open surgery which always requires general anesthetic, specific dual cuff intubating and lateral positioning in these polytraumatized subjects often with synchronous lung and cervical spine injuries. Conventional surgery often requires aortic cross-clamping, significant blood loss and use of cardiopulmonary bypass which increase spinal ischemia and thus paraplegia rates3,16 as well as renal ischemia times and ischemic reperfusion syndromes. Open surgical series have higher stroke and paraplegia rates and consequently have greater mortality and morbidity association. The post-operative pain, recovery,15 intensive care13 and monitoring required is significantly greater for open surgical repair.

The consensus is that it will be very unlikely that a randomized control trial will be performed to definitively prove this superior benefit because from overwhelming current endovascular practice and preference, with such good results, a trial would be unethical.35 In a number of these abundant case series, endovascular repair has been performed on sickerpatientswithhigherseverityscorecomparedtoconventionalsurgeryseries,because these patients were deemed unfit for open repair. A suitable study would also require large numbers of patients to provide adequate statistical power which would be difficult with a prolonged study period due to the rare and acute nature of this traumatic disease.

The third management option which is discussed less by endovascular surgeons is the conservative medical treatment favored by physicians and intensivists. Accurate blood pressure control with short-acting beta-blockade such as esmolol or labetalol, to achieve a systolic blood pressure of approximately 100 mmHg and a relative bradycardia, has been shown to be beneficial to polytraumatised patients with aortic transections, mediastinal hematoma and thus pseudoaneurysm formation (aortic rupture contained by adventitia or peri-aortic tissue). Similarly to patients with thoracic aneurysm rupture or acute dissections, medical management can be used as a stop gap whilst other injuries are addressed and definitive management is planned. The rationale is that aortic wall stress and tension are decreased thus markedly reducing the risk of aortic rupture because wall tension is directly proportional to increases in pressure and inversely proportional to pulse rate.5 Treatment can be delayed for days, weeks, infrequently months and on a few occasions in the literature years.3,5,17,23,27,36–38

Question 5 is concerned with sites of thoracic traumatic transection and the correct answer is C (Q5 = C). The commonest site of injury is the aortic isthmus (93%) which is the portion of the proximal descending aorta between the left subclavian artery origin and ligamentum arteriosum.3,31,39 Fixation and tethering by the ligamentum arteriosum is believed to be accountable for the high frequency of injury in this position. The remaining 7% of injuries exist in the ascending aorta and arch. The order injury frequency is first the ascending aorta, then avulsion of the innominate artery followed by the lower descending aorta.40 These frequencies are correct for patients presenting to hospital, as mentioned earlier, the majority of patients with the injuries die instantly on scene and post-mortem investigations have showed a higher proportion who die suffer ascending aortic injuries. The percentages listed above have been defined by the American Association for the Surgery of Trauma (AAST), who performed the first prospective multicenter observational study of traumatic transections in 274 patients.41

There are a number of factors that determine suitability for thoracic endovascular aortic stent repair (TEVAR). These factors are highlighted in Question 6, where the correct answers for access are D (Q6 = C&D).

Access for stent device delivery is very important. Current devices require delivery access of at least 20–26 Fr, and thus a minimal iliac diameter of 7.6–9.1 mm. Patent, straight, non-tortuous and non-calcified iliac and femoral arteries are favorable for endovascular delivery of the large stent devices. Despite endovascular techniques being considerably less invasive than conventional open techniques, the older, first generation devices large and cumbersome, so always required femoral artery dissection and arterotomy. Thoracic stent devices are bigger than those used for abdominal aortic repair because the thoracic aorta is bigger and further away from the groin. As time progresses and investment in technology continues delivery systems have become more slim-line and percutaneous stent insertion is more frequently available. Imaging should include views of the iliac arteries to assess size, tortosity and composition, particularly for aneurysms, plaques and calcification. These features make access very difficult and can be a contraindication to this type of treatment due to poorer compliance. An alternative, which is underused in our opinion is endoconduit formation, however this makes the overall procedure more invasive. The common iliacs, upper limb and great vessels can be used as a suitable conduit, if the anatomy is suitable and disease is minimum, to deliver the stent device.

Factors that are favorable for accurate and successful thoracic endovascular aortic stent repair (TEVAR) and deployment are highlighted in Question 7, where the correct answers for access are A and D (Q6 = A&D).

Aortic size is very important. These groups of trauma patients are young and consequently have a tighter aortic curvature with smaller aortic and iliac diameters than patients suffering from other thoracic pathologies such as aneurysms, acute and chronic dissections.3,15,37,42 Device sizes are getting smaller with much innovative research but there is still a minimal size that can be treated, so this treatment cannot be offered to all. The smallest currently available aortic stent is 21 mm in diameter, however, smaller stents with diameters of 16–18 mm are in production. Additionally of relevance to our patient is that the thoracic aorta of females is significantly smaller than males, so size and stent availability is particularly relevant to our young female patient in this case.

Stent availability has also been touched-upon. To offer an emergency thoracic endovascular service, one needs to have a wide range of stents and variety of different sizes on consignment. For optimal fixation, stent grafts are commonly oversized by 10–15% compared with the landing zone aortic diameter3 to enhance conformability and adherence within a vessel. However in trauma, there is the potential for stent undersizing due to the patient’s hypovolemia causing a relatively smaller aortic caliber and sympathetic overdrive causing vasoconstriction.3,43 There are a number of different manufacturers who have devices with particular advantages and disadvantages. To possess an inventory of equipment to suit all is costly, requires storage and needs regular cataloging and replacing.

Thoracic stents exist for treating aortic aneurysms and also for treating dissections.15,39 These two pathologies are distinctly different and thus require different devices to treat endovascularly. Traumatic thoracic transections are rare and thus there are few dedicated stents developed for these situations, such as the newly released conformable GORE TAGTM stent. One has to, by using best judgment and in-depth knowledge of available stent technology, rapidly assess what is best for the patient. For this reason a vascular specialist with endovascular training should plan these cases.

Despite the significantly smaller mortality and morbidity of endovascular stent repair over conventional surgery, TEVAR still is not without complications and should not be underestimated. Poor preparation and planning of measurements and sizings could lead to inadequate stent positioning. An inappropriately positioned stent can lead to stroke, paraplegia, graft infolding, graft collapse, aortic thrombosis and aortic rupture to name a few. Thus the answer to Question 8 is all of the available options (Q8 = A&B&C&D&E&F).

The use of imaging for aortic vessel measurements and to locate the precise anatomical position of the transection is vital. For successful stent deployment and fixation, one requires an appropriate proximal and distal stent landing zone. With the most common site of transection being adjacent to the ligamentum arteriosum, as previously mentioned, the distal landing zone is usually sufficient and not a problem. However, proximal landing zones require particular attention due to the left subclavian artery and other great vessels. A proximal landing zone distance of approximately 20 mm minimum is recommended, however with increased experience, boundaries are expanding and smaller distances are being attempted with correspondingly good results. In some cases when the site of injury is close to the left subclavian artery, partial or total vessel coverage may be required. Conveniently, the arterial tree of this young group of effected patients contains little

disease so normally the vertebral circulation to the posterior Circle of Willis is suitable for cerebral collateralization and thus perfusion. However, this may not be the case for an older patient suffering transection. If left subclavian coverage is required then simultaneous carotid-left subclavian vessel bypass may be indicated to prevent posterior circulatory stroke, spinal cord ischemia or subclavian steal syndrome.44 Peri-operatively, the physiological consequences of left subclavian artery coverage and thus occlusion can be tested by temporary balloon insufflation within the arterial osteum. Some centers routinely bypass all patients for elective thoracic aneurysm and dissection procedures prophylactically during the same operation simultaneously or in a staged alternative sitting.3,12,17,25,37 Their evidence for this hybrid technique is mostly extrapolated from the EUROSTAR (European Collaborators on Stent Graft Techniques for Thoracic Aortic Aneurysm and Dissection Repair) database and the UK Thoracic Aortic Data Registry,35,45 which suggests a small complication rate (paraplegia and stroke rate in particular) for bypassing patients. Not all believe and practice this technique. Transections proximal to the left subclavian artery pose a challenge to primary endovascular treatments in the polytraumatised patient who requires a short operation and rapid vigorous re-warming and intensive resuscitation, but hybrid techniques can be conducted such as carotidcarotid arterial bypass.3

The “Bovine Aorta” which is present in 20% of the population, may cause particular difficulty. In this variant of aortic structure, the left subclavian artery originates from the innominate artery, thus there is usually an increased stent proximal landing zone length, but any coverage of the innominate origin requires a bypass.

Thelastanatomicalconsiderationistotheaorticcurvature.Thelesserandgreateraortic curves are exerted to different hemodynamic forces as are the proximal, middle and distal stent fabrics. Also consideration should be paid to the size discrepancy between ascending and descending aorta. The more curved aortic arch may not be ideal for the available devices in stock for these trauma patients and may compromise the final outcome. The high pressures of blood jetted to a stent during deployment can make accurate millimeter positioning more difficult, so a systolic blood pressure of 100 mmHg is recommended and during actual stent deployment, some administer adenosine to temporarily cease cardiac activity and others use rapid cardiac pacing. With such delirious consequences to malpositioning, such as stent collapse, proximal of distal migration, great vessel coverage and stroke, proximal dissection formation, incomplete stent opening, poor seals and endoleaks, these procedures require adequate intraoperative imaging, kit availability and staff with endovascular familiarity and thus expertise. To achieve all of this many vascular surgeons now advocate centralization of such endovascular services.46–49

All patients with an abdominal aortic endovascular stent enter a local hospital surveillance program. Similar for all thoracic stented patients, they should undergo lifelong surveillance. The intention of long-term surveillance imaging is to detect endoleaks, occlusions, stent migration, fracture and collapse early and thus evoke early surgical repair.50 In answer to the final Question 9, the most usual imaging technique employed for thoracic stent surveillance is A (Q9 = A). Thoracic Computerized tomography, is the most common modality, however post-stent surveillance is a popular research area and rapid advancesincludeintravascularultrasound,contrastultrasound,virtualangiographyaswell as magnetic resonance imaging will possibly become common place in the future.