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Penetrating Injuries to the Aortic Arch and Intrathoracic Great Vessels
This chapter provides an overview of penetrating injures to the aortic arch and intrathoracic great vessels. Because these short-segment vascular structures are clustered in the confined space of the mediastium, the first portion of this chapter reviews the overall epidemiology, presentation, diagnosis, and management of all arterial injuries in this location. The second part of this chapter addresses penetrating injury to each of the innominate, subclavian, and common carotid arteries individually.
Arterial Injuries in the Mediastinum
Epidemiology
Penetrating trauma to the aortic arch and its major branch vessels is rare and associated with high mortality. Penetrating aortic arch injuries constitute 1% of all thoracic vascular injuries and 13% of all penetrating thoracic aortic injuries in the civilian setting. In an epidemiologic study by White and Rasmussen, brachiocephalic and subclavian injuries accounted for only 3% of all vascular injuries during a decade of war in Afghanistan and Iraq. In a separate comparison of arterial injury between military and civilian trauma registries, including blunt and penetrating mechanisms, these authors found the rate of innominate and subclavian injury to be higher in the civilian (6.4%) than in the military (3.7%) cohort. We speculate that this difference is likely a result of the higher incidence of motor vehicle crashes in the civilian population and the use of protective body armor in the military cohort.
In military and civilian studies, 95% of persons with penetrating injuries to the arch and great vessels are male, and single-projectile firearms are the leading cause of injury (69%) followed by stab (18%) and shotgun (12%) wounds. Despite developments in the diagnosis and management of vascular trauma leading to improved survival for persons sustaining blunt descending thoracic aortic injury, the lethality of penetrating aortic arch injury remains unchanged. Similar to that for blunt aortic injury, survival following penetrating arch and great vessel trauma depends upon the propensity for the vascular disruption to be contained by the adventitia of the vessel and surrounding soft tissue. In most instances of arch and great vessel trauma this favorable interval of vascular disruption does not occur and patients do not survive to be transferred to a medical treatment facility. Even if patients do survive to a treatment facility, only 12% survive to be discharged from the hospital.
As described, pseudoaneurysm formation following arch and great vessel injury is the only chance for survival, which emphasizes the importance of avoiding overresuscitation and hypertension in the immediate postinjury period because either could precipitate rupture of an otherwise contained injury. The mortality for patients with this injury pattern and an unrecordable blood pressure on admission or for patients who require a resuscitative thoracotomy with aortic clamping is nearly 100%.
Clinical Presentation
The majority of patients with penetrating aortic arch and great vessel injuries present in shock (82%), requiring immediate surgical intervention in the form of tube thoracostomy, resuscitative thoracotomy, or median sternotomy. Demetriades and colleagues reported that only 8% of patients with this injury pattern arrived at their facility with a systolic blood pressure of greater than 90 mm Hg, and nearly half (41%) were in extremis without a recordable pressure. Most patients with this injury pattern come to the hospital with hypovolemic shock, and a smaller percentage come to the hospital with cardiac tamponade, neurologic deficits, hemothorax, and/or a precordial bruit. Aortic arch injuries are often associated with multiple other vascular injuries, including vena cava, innominate vein, and pulmonary artery injuries. Injury to the innominate vein with an arteriovenous fistula has been reported in some cases of this injury pattern. Pulmonary injuries constitute 54% of concomitant noncardiovascular injuries with aortic arch trauma.
Diagnosis
Given the propensity of this injury pattern for hemorrhage, many arch injuries are first diagnosed during resuscitative anterolateral thoracotomy because patients are too unstable to undergo radiographic or angiographic evaluation. For patients who are able to undergo imaging, the most common appearance is a widened mediastinum on chest x-ray. Previously, angiography was the gold standard for the diagnosis and preoperative evaluation of this injury pattern, but contrast-enhanced computed tomography (CT) scanning is now the favored modality. To a large degree, contrast arteriography is now only performed in selected cases following a CT scan that diagnoses the injury. In these instances, subsequent arteriography may be used as a necessary step in consideration of endovascular treatment of the injury (e.g., placement of a covered stent) and not for diagnosis. Although either CT scan or arteriography is preferable before surgery, less than half of patients are stable enough to undergo such preoperative imaging.
Management
Open Operative Management
Operative management of penetrating arch and great vessel injuries depends on the named vessel or vessels that are injured. The aortic arch can be divided into three segments: ascending, transverse aorta with the origins of the proximal great vessels (innominate, carotid, and subclavian arteries) and descending distal to the left subclavian artery and proximal to the main thoracic aorta. For instances of diagnosed or suspected injury to the first and second sections, a median sternotomy is the operative exposure of choice. ( Figure 1 ). Care must be taken in these cases to avoid injury to the innominate vein, which crosses superficial to the aorta and proximal great vessels in the superior aspect of this exposure.
Sternotomy followed by division of the innominate vein allows the pericardium to be opened for release of any associated cardiac tamponade. Once these maneuvers have been accomplished, a sternotomy provides visualization and control of the ascending aorta as well as the innominate and proximal right carotid and subclavian arteries (see Figure 1 ). Exposure of these vessels can be facilitated by extending the sternotomy incision proximally on the right as a longitudinal cervical or supraclavicular incision with division of the sternocleidomastoid muscle. The aortic arch traverses in an anteroposterior direction in the mediastinum, making exposure of the distal transverse arch and proximal left common carotid challenging through a median sternotomy. However, these vessels can be controlled using this approach alone or in conjunction with an extension to a left cervical or supraclavicular incision, including division of the sternocleidomastoid. Injuries of the arch distal to the left common carotid, including those to the left subclavian artery origin, typically require a high left anteromedial thoracotomy.
At the time of operative exposure, one often encounters a hematoma surrounding the vessel that must be entered to control and repair the injury. Blood loss notwithstanding, this task is necessary and often results in identification of an arterial disruption that can be controlled with a finger or a Kittner dissecting sponge. Before entering such a hematoma, the surgeon can take heart in knowing that patients with large or complete vessel disruptions with free hemorrhage would not have survived to undergo the operation.
Small lacerations of the transverse aortic arch or proximal great vessels can be primarily repaired often using full-thickness polypropylene sutures with pledgets. When possible, use of a strong partial-occlusion (side-biting) clamp such as a Wiley J-clamp allows isolation of the injured segment of the ascending aorta, innominate, or even proximal carotid artery. If it can be applied and secured proximal to the injury site, the partial-occlusion clamp greatly facilitates full-thickness primary repair with pledgets in some cases.
Injuries to the proximal innominate and origin of the common carotid arteries at or just distal to the aortic arch can be managed with a synthetic bypass graft (single or bifurcated). In these instances the proximal portion of the graft originates from an area of the ascending aorta proximal to the zone of injury. The distal anastamosis or bypass limbs are sewn distal to the subclavian and or the carotid artery as the intervening segment of injured vessel is oversewn.
More extensive injuries to the transverse arch and origins of the great vessels require a synthetic patch, vessel replacement, or interposition or graft. Although median sternotomy provides access for cardiopulmonary bypass, this maneuver is exceedingly rare in the setting of trauma. Even if the appropriate surgical and perfusion teams are readily available, the hypothermia and coagulopathy associated with bypass make the use of this adjunct very uncommon.
A technical note to be mindful of pertains to selection of the suture needle. In many instances the surgeon is more effective using a needle that is large enough (e.g., small half [SH] or CT needle) to be seen and steered in considerable amounts of blood. Although it seems intuitive to select a smaller, atraumatic needle, this often leads to frustration because the needle is difficult to see and manipulate to achieve full thickness purchase in arterial wall.
Endovascular Management
The difficult nature of exposure and repair of aortic arch and proximal great vessel injuries makes endovascular management appealing. The use of covered stent grafts to manage proximal common carotid and even innominate artery injuries has been reported. However, because of the complex anatomic relationships involving the origins of the carotid and vertebral arteries, endovascular repair is not as straightforward as it can be in the longer, more distal branch vessels or the descending thoracic aorta. Furthermore, motion from the beating heart and the need to image vessels in the thorax make placement of endovascular devices in this region less precise than in other locations. Unlike stent grafts in the management of descending thoracic aortic and selected side-branch injuries, use of this technique to repair transverse aortic arch injuries has not been established. Growing experience with staged debranching procedures originating from the ascending aorta to perfuse the great vessels beyond the zone of injury makes it possible that hybrid, open, and endovascular procedures may be used more in the future to treat selected cases of transverse arch injury.
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