Aortic Arch Surgery: Indications, Decision Analysis, and Surgical Technique
Pearls
An aberrant right subclavian artery can be associated with a nonrecurrent recurrent vagus nerve and Ortner’s syndrome, a right-sided thoracic duct, and an anomalous right vertebral origin.
The treatment of Takayasu’s arteritis, in the acute, inflammatory phase, is nonoperative. These patients should be managed initially, and for as long as clinically possible, with steroids.
Patients with single trunk disease with a suitable ipsilateral donor vessel are well managed with cervical reconstruction of the diseased vessel via transposition or bypass, regardless of comorbid risk. Otherwise healthy patients with multi-trunk disease or no suitable ipsilateral donor vessel should be considered for aortic arch–based reconstruction via sternotomy. Poor-risk patients with significant comorbid conditions or with a history of sternotomy may best be treated endoluminally or with crossneck bypasses.
Atherosclerotic occlusive disease involving the branches of the aortic arch is common in patients over the age of 65. The Joint Study of Arterial Occlusions reported that one third of patients undergoing arteriography are found to have significant lesions involving one or more of the vessels supplying blood to the head and arms.1 Occlusive diseases affecting the brachiocephalic trunk vessels make up a relatively small fraction of them however. Furthermore, repair of occlusive lesions of the proximal brachycephalic vessels accounts for less than 10% of the operations performed on the extracranial cerebrovasculature. Despite this, and despite the fact that these vessels are relatively difficult to image using noninvasive technology, substantive data has accumulated regarding the natural history of the disease, and significant experience with surgical reconstruction has accrued over the past four decades. After two decades of experience with endoluminal therapy for treatment of arch branch disease, some useful data regarding angioplasty and stenting has now become available as well.
♦ Anatomy
The arch branches normally develop as three separate trunks taking origin from the proximal aorta within the superior mediastinum. The conventional definition includes the innominate artery, the subclavian arteries up to the origins of the vertebral arteries, and the common carotid arteries proximal to their bifurcations. The innominate artery and the left common carotid originate in close proximity to one another and ascend in the neck on either side of the trachea. The left subclavian artery is the third of three trunks and it originates posterior and to the left of the left common carotid. The vagus and right recurrent laryngeal nerves cross the anterior aspect of the right subclavian artery adjacent to the innominate bifurcation. On the left, the vagus and phrenic nerves cross one another between the left common carotid and the left subclavian under the cover of the pleura.
Anatomic variations are common, seen in over 20% of patients. The most common variation is the bovine-type aortic arch, where the first and second branches (innominate and left carotid) arise from a common ostium (16%) or as a single trunk (8%). The left vertebral artery originates as a separate branch arising from the aortic arch between the left common carotid and the left subclavian in 6% of the population. Developmental anomalies of the trunk vessels are less common. The arch configuration with an aberrant right subclavian artery that arises as the fourth of four vessels occurs in approximately 0.5% of individuals. A so-called truncus bi-carotidus, where the two carotids take origin together and the two subclavian vessels arise as one in a two-trunk configuration, occurs even less frequently. Retroesophageal subclavian arteries (RSAs), which are always found in association with these two configurations, occur with the same incidence of approximately 0.5%. In rare cases, certain symptom complexes including dysphagia (dysphagia lusoria) and chronic cough (from tracheal compression) can develop in patients with developmental errors and aberrant anatomy. Adjacent to the origin of an aberrant right subclavian artery there may be congenital dilatation of the wall called a diverticulum of Kommerell. This aortic wall outpouching is a remnant of the developmental right fourth aortic arch. The right inferior laryngeal nerve is not “recurrent” in patients with an aberrant right subclavian; instead, the nerve exits the vagus higher in the neck and takes a more direct route to the larynx resting on the wall of the right common carotid artery. A thoracic duct that empties into the right jugulosubclavian confluence should also be expected.
Developmental anomalies can also be found in conjunction with a right-sided or a double aortic arch. A mirror image of the left arch configuration occurs in most individuals with a right-sided arch. Right-sided arch anomalies are often associated with congenital cardiac abnormalities but they can occur in isolation as well.
♦ Epidemiology and Natural History
Atherosclerosis is, by far, the most common disease affecting the brachiocephalic vessels. Occlusive lesions less commonly result from inflammatory diseases such as Takayasu’s arteritis or can be the result of exposure to therapeutic radiation. The vessels also can dissect or become aneurysmal. More distally, the subclavian arteries can be damaged from the long-term effects of thoracic outlet syndrome. Symptoms from nonatherosclerotic diseases such as Takayasu’s or radiation-induced arteritis, dissections, aneurysms, and congenital lesions account for less than 20% of the disease that requires intervention.2 – 6 Atherosclerotic lesions tend to cause occlusive and embolic symptoms equally, whereas vessel obliteration from arteritis tends only to cause symptoms related to hemodynamic insufficiency.
Occlusive lesions involving the brachiocephalic trunks tend to develop in a younger age group than atherosclerotic occlusive lesions elsewhere in the extracranial cerebrovascular circulation. Mean and median ages are commonly reported to range from 50 to 61 years. Single-vessel atherosclerotic occlusive disease involving the brachiocephalic trunks is often seen in younger adults (fifth decade), whereas patients with extensive or multiple trunk involvement tend to be older. The usual male preponderance noted with other atherosclerotic vascular conditions may not be found with disease of the brachiocephalic trunks. Females were treated in 53% of cases in one large series.2 , 3 Cigarette smoking is certainly a significant risk factor for the development of atherosclerotic occlusive disease involving these vessels. Smoking is identified as a risk factor in 82% of all patients who require intervention.2 Concomitant coronary artery disease (CAD) is present in one quarter to two thirds of patients who present for supraaortic trunk reconstruction. In one report, 63% of patients had significant CAD and 15% had undergone a previous myocardial revascularization.2 In the same report, 47% of patients undergoing transthoracic reconstruction were hypertensive, and a smaller percentage (15%) were diabetic.
Atherosclerotic occlusive disease involving the brachiocephalic trunks can be either uni- or multifocal involving just one or more than one trunk vessel. In addition, the distribution of atherosclerosis within a single vessel can often be segmental in nature. Severe disease is defined as a >75% diameter stenosis. In addition, in symptomatic patients, a deep ulcerated plaque or a thrombus within the arterial lumen is also considered a severe lesion even though the defect may be <75% diameter. Severe lesions can be seen developing within and isolated to a single vessel. Alternatively, when the disease is seen in multiple trunks, the occlusive process is likely an extension of disease originating within the aortic arch that has “spilled over” into the vessel ostia. In one series of 283 transthoracic and cervical revascularizations of the brachiocephalic vessels, significant disease was present in more than a single vessel in 40% of cases.3 All three of the trunks were critically diseased in 13%. Revascularization of unifocal disease was necessary in 60% of cases. When disease was limited to one trunk, the left subclavian artery was the vessel most commonly found to be involved with disease.
When multiple trunks are involved, patients usually develop symptoms of vertebrobasilar ischemia from low flow. Single-trunk disease manifests more commonly as hemispheric or upper extremity emboli. Isolated proximal disease within the subclavian artery can lead to symptomatic subclavian–vertebral steal, whereas innominate occlusion can result in steal from the anterior cerebral circulation (carotidsubclavian steal). Obliteration of the common carotid lumen can occur in a retrograde fashion following occlusion of the carotid bifurcation and internal carotid artery. Alternatively, an occlusion originating in a lesion in the proximal common carotid may eventually propagate distally into the bifurcation. The internal carotid not uncommonly remains patent in this situation. Duplex or delayed arteriographic images may show that the internal carotid is perfused anterograde via retrograde external carotid flow.
The traditional description of aneurysms of the brachiocephalic trunks refers to those of syphilitic etiology. Nowadays aneurysms of syphilitic origin have virtually disappeared. Most of the aneurysms of the innominate artery (IA) encountered today are associated with concomitant dilatation of the proximal ascending aorta or of the thoracoabdominal aorta. Posttraumatic false aneurysms of the brachiocephalic vessels are uncommon, and they are usually the result of rupture of the intima-media complex during deceleration in motor vehicle accidents. These pseudoaneurysms usually involve the origin of the IA. An occasional aneurysm is seen in association with Takayasu’s disease. The most serious problems in patients with congenitally anomalous anatomy such as RSA are related to development of aneurysmal disease. These lesions usually involve the diverticulum at the origin of this artery (Kommerell).
Takayasu’s arteritis frequently involves all three vessels proximally. The true etiology of this inflammatory disease has not been elucidated but it is known predominantly to affect females in their second and third decades of life. The hypertrophic occlusive lesions of Takayasu’s disease have a smooth surface with a low embolic potential, and most symptoms relate to low flow as the disease progresses to multivessel occlusion. The histologic appearance of the lesions depends on the phase of the disease. They appear intensely inflammatory during the acute phase and more sclerotic when the disease is “burned out.” The inflammatory process is usually most noticeable in the adventitial and medial layers of the involved vessels.
Giant cell arteritis rarely affects the proximal brachiocephalic trunks. Occasionally it does involve the more distal subclavian arteries and can be differentiated from Takayasu’s by its location and by the fact that it affects a much older patient population.
Irradiated arteries develop an accelerated form of atherosclerosis as a result of radiation injury to the vessels. The rate at which the process develops depends on the radiation dose range. The brachiocephalic trunks may be involved after radiotherapy for, among other diseases, breast cancer, intrathoracic tumors, and Hodgkin’s lymphoma.
Isolated brachiocephalic trunks dissection is rare, but type A aortic arch dissections may disrupt or extend into the trunk vessels impinging on cerebrovascular or upper extremity flow or prompting local thrombus, which can embolize. Like dissections elsewhere, chronic aneurysmal changes can develop over time, but this is rare.
♦ Indications for Reconstruction
Indications for revascularization of the brachiocephalic trunks are multiple. Symptomatic atherosclerotic occlusive disease may manifest as ocular, hemispheric, or vertebrobasilar transient ischemic attack (TIA) or stroke. Commonly patients present with a combination of both anterior and posterior cerebrovascular ischemic symptoms. In addition, some patients present with symptoms of upper extremity ischemia. Patients may develop varying degrees of arm ischemia, ranging from the claudication observed in patients with subclavian steal to limb-threatening ischemia resulting from extensive arterial occlusion or emboli. A third, less common problem is that of myocardial ischemia from the phenomena of coronary steal, which can develop in patients with innominate or subclavian disease proximal to an internal mammary revascularization of the coronary arteries. Rarely, patients with developmental anomalies involving the arch vessels require surgery to treat symptoms arising from esophageal or tracheal compression or for the treatment of symptomatic aneurysmal changes in or near the trunk vessels. True, asymptomatic, degenerative aneurysms involving the normally configured trunks are very rare, but when found they should be repaired in good-risk patients to prevent emboli to the brain or, less likely, vessel rupture.
Asymptomatic severe (>75%) atherosclerotic lesions of the innominate or common carotid arteries should be repaired in patients who present a reasonable risk (including patients with common carotid occlusion and a patent bifurcation), for the same reasons we repair asymptomatic severe carotid bifurcation stenoses. Asymptomatic lesions in the proximal subclavian artery should also be repaired in patients contemplating myocardial revascularization via an internal mammary artery and in patients with bilateral subclavian artery disease to permit and facilitate blood pressure management.
In general, no operation should be undertaken on patients with Takayasu’s arteritis while in an active phase. An active state is usually signaled by the presence of the constitutional symptoms associated with acute inflammation and an elevated erythrocyte sedimentation rate. Steroid therapy usually treats the acute inflammatory process and makes attempts at surgical reconstruction much safer.
Of particular note, in our institution over the last 5 years, the most common indication for surgical manipulation of the brachiocephalic trunks has been to prepare patients with thoracic and thoracoabdominal aortic aneurysms, dissections, or traumatic tears for an endovascular stent-graft repair. Subclavian artery and even left common carotid artery transpositions as well as complete arch debranching procedures are not infrequently performed in order to preserve vertebral and left upper extremity flow while extending the proximal neck “landing zone” prior to endograft deployment.
♦ Disease Treatment
Four broad-based approaches have been developed for the treatment of brachiocephalic trunk lesions, each with distinct advantages and disadvantages: medical management, direct transthoracic reconstruction, remote cervical reconstruction, and endovascular recanalization ( Table 19.1 ). Medical management includes the use of antiplatelet medications as with carotid bifurcation disease. The addition of statin medications along with smoking cessation may even lead to some plaque regression. The treatment for acute exacerbations of inflammatory diseases like Takayasu’s includes the use of high-dose steroids tapered over time.
Surgical transthoracic revascularization may be chosen in good-risk patients with isolated innominate artery stenosis or occlusion and in patients with disease that involves multiple trunks. Remote cervical and endovascular techniques are alternatives to direct reconstruction and should be considered in patients with single-vessel disease that involves the carotid or subclavian arteries and in patients who have previously undergone a median sternotomy or who have a prohibitive medical comorbidity. Endoluminal therapies have become more commonplace over the last decade and clearly represent a less invasive alternative.
Direct Reconstruction
Direct reconstruction of the brachiocephalic trunks is approached through a complete or partial median sternotomy ( Fig. 19.1 ). The cervical target vessels are easily exposed through this same full or partial sternotomy via an extension of the incision onto the neck as necessary.
Endarterectomy remains an option for reconstruction, particularly for isolated middle or distal innominate stenoses. Lesions that involve the more proximal vessel are more difficult to manage with endarterectomy. The majority of atherosclerotic lesions of the innominate do involve the proximal portion of the vessel; these lesions are contiguous with the atherosclerotic plaque that extends over the dome of the aortic arch and insinuates, as well, into the origin of the left common carotid and subclavian arteries. In this common situation, endarterectomy of the IA requires division, under direct view, of the plaque as it blends with the aortic arch atheroma. This divided intima media can easily separate and become the origin of a dissection if it is not properly tacked. Another disadvantage of innominate endarterectomy follows from the fact that in 24% of patients, the origin of the IA and left common carotid artery are shared in a bovine configuration. In this circumstance, clamping the origin of the IA will also impinge upon left common carotid artery flow and result in unacceptable brain ischemia. Furthermore, to perform an adequate endarterectomy of these often-calcified innominate lesions, the plane from which the plaque must be removed mandates leaving an extremely thin wall through which sutures often tear or cause leaks. There are very few indications for IA endarterectomy today except in the rare circumstance of a lesion involving just the middle or distal innominate artery where the surgeon does not wish to dissect the ascending aorta or open the pericardium.
Bypasses that take origin from the ascending aorta tend to be safer and less demanding technically than endarterectomy ( Fig. 19.2 ). With few exceptions, the aorta 4 to 6 cm above the aortic valve is usually spared disease, even if the rest of the aortic arch is involved. After the pericardium is open and a sufficient length of the ascending aortic arch is exposed, a partial occlusion Lemole-Strong clamp can be placed on the anterior wall of the ascending aorta, and a bypass conduit (usually a 9- or 10-mm prosthesis) is anastomosed to it. The proximal anastomosis is easier and less likely to leak if the systolic blood pressure can be maintained below 110 mm Hg. Also, heparin should be held until after the graft is sewn in place and the clamp has been removed. Much of the morbidity of the transthoracic approach is related to embolization from the clamp site in the ascending aorta. It is important that the proximal anastomotic site be well flushed to prevent particle embolization and that the patient be placed in the Trendelenburg position when the clamp is removed to prevent air embolization. Heparin is administered when the suture line is hemostatic.
The bypass conduit is then passed behind the brachiocephalic vein to reach the target vessel. When bypasses to more than one trunk vessel are planned, it is better to use sequential bypass grafting with hand-sewn limbs rather than utilize commonly manufactured bifurcated grafts. We use this approach because this type of limb arrangement ( Fig. 19.3 ) has a smaller diameter than does a commercially available bifurcated graft. The side arms of sequential bypasses can be oriented in such a fashion so as not to crowd the thoracic inlet. These side branches can then be routed to any of the proximal trunks or up to a carotid bifurcation.
The anterior approach to the proximal left subclavian artery, a posterior mediastinal structure, can be difficult. To dissect the proximal left subclavian artery through a median sternotomy usually requires ligation and division of the innominate vein to separate the sternal edges enough to permit dissection of the posterior mediastinum. Dividing the innominate vein should be avoided whenever possible, as significant arm swelling has been noted in some patients following this maneuver. Once the reconstruction is completed, the thymus, which has been divided through the midline or flipped laterally, is interposed between the sternum and the prosthetic graft. An alternative is to approach the proximal subclavian through a high posterolateral thoracotomy, although a cervical approach usually has as much utility. Our preference is to transpose the left subclavian into the bypassed left common carotid artery as a separate reconstruction as described below.
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