Keywords
aortic arch aneurysm
Step 1
Surgical Anatomy
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Academic anatomists refer to the aortic arch as that part of the aorta that begins and ends with a line drawn in cross section across the aorta at a level corresponding to the lesser curve of the aortic arch. This therefore implies that the arch of the aorta starts at approximately the level of the superior reflection of the pericardial sac. However, surgical anatomists and surgeons tend to consider the aortic arch as that portion of the aorta that begins with a line drawn in cross section across the aorta at the level of the proximal origin of the ostium of the innominate artery and ending at the distal margin of the ostium of the left subclavian artery.
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The aortic arch tapers somewhat from anterior to posterior owing to the takeoff of the three large arterial branches—innominate artery, left common carotid artery, and left subclavian artery. In approximately 5% of patients, this anatomic configuration consists of a double ostium or so-called bovine aortic arch, where the innominate artery and left common carotid artery arise from a somewhat larger, but single, aortic ostium ( Fig. 25.1 ).
Figure 25.1
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Other anatomic structures of importance during aortic arch surgery include the left recurrent laryngeal nerve, left phrenic nerve, and right recurrent laryngeal nerve. These become important when considering separate replacement of the branch vessels in conjunction with aortic arch surgery.
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Aortic arch aneurysms seldom occur as isolated structures, but rather occur in conjunction with aneurysmal dilation of the proximal ascending aorta or distal aorta. Aneurysmal dilation often causes the aortic arch aneurysm to shift anteriorly and laterally to the right. Because most cases of aortic arch aneurysm surgery are performed through a median sternotomy, this anatomic change brings critical structures more anteriorly and may facilitate the repair ( Fig. 25.2 ).
Figure 25.2
Step 2
Preoperative Considerations
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Assessment of the patient’s fitness for aortic arch replacement has multiple facets. Most importantly, the patient needs to be of an age and physical condition that would withstand a major operation such as this. A careful consideration of noncardiovascular comorbidities such as respiratory and renal disease should be undertaken because these are significant independent predictors of poor outcome.
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From a cardiovascular point of view, left ventricular function and the presence or absence of significant valvular disease are important variables to consider. The presence of coronary disease does not preclude operation, but it would mandate additional coronary artery bypass procedures that would add to the length of the surgical procedure.
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The presence of significant peripheral vascular disease in the carotid arteries, subclavian arteries, or femoral arteries is an important consideration in terms of determining cannulation and perfusion strategies during circulatory arrest. Similar anatomic considerations apply to the configuration of the aortic arch anatomy as far as the great vessels are concerned. A history of previous stroke or transient ischemic attacks may indicate the presence of significant cerebrovascular disease, and this must be investigated thoroughly with thin-slice computed tomography (CT) scans, magnetic resonance imaging (MRI), or cerebral angiography. A recommended standard preoperative workup for patients undergoing aortic arch replacement is shown in Box 25.1 .
Box 25.1
Preoperative Assessment for Aortic Arch Replacement
History and Physical Examination
Family history of aneurysm disease or connective tissue disorders
Cardiovascular risk factors
History of cerebrovascular events
History of renal or pulmonary disease
Previous operations on the vascular system
Previous cardiac surgery through sternotomy
Cardiac murmurs on auscultation
Palpable peripheral pulses
Investigations
Peripheral vascular studies: carotid arteries, lower extremity arteries
Pulmonary function testing
Transthoracic echocardiography
Coronary arteriography
Thin-slice computed tomography angiogram of chest, abdomen, pelvis
Step 3
Operative Steps
1
Pharmacologic Adjuncts
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An important consideration with aortic arch replacement is cerebral preservation. Circulatory arrest in some form is required for aortic arch replacement, so a strategy should be undertaken to minimize the period and extent of cerebral hypoperfusion.
2
Cannulation Site and Adjunct Perfusion Strategy
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Selection of cannulation site is important. In general, for circulatory arrest times anticipated to be less than 30 minutes, current literature suggests that direct cannulation of the aneurysm distally, cooling the patient down to 18° to 20°C (64.4°–68°F), and discontinuation of the pump with no perfusion adjuncts for 10 to 15 minutes is safe.
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If it is anticipated that a longer time on circulatory arrest will be required, such as for full arch replacement, a strategy should be used to maintain some form of cerebral perfusion at this temperature. This strategy should provide the best cerebral perfusion while minimizing the clutter in the operative field. Among the currently available techniques of retrograde cerebral perfusion, direct perfusion of the great vessels with separate cannulae, and selective perfusion through the right axillary or innominate artery, we recommend selective antegrade cerebral perfusion, especially if the patient has a bovine aortic arch. We believe that this is the best strategy because of the following:
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The vast majority of patients have an intact circle of Willis, and therefore selective antegrade cerebral perfusion is usually appropriate for most cases of arch replacement;
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Retrograde cerebral perfusion has been associated with the development of brain edema and perhaps some neurologic dysfunction, and detailed studies have indicated that very little blood flow given this way actually reaches the cerebral cortex;
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Insertion of antegrade catheters into the ostia of the arch vessels is cumbersome, complicates the operative field, and may dislodge plaques if the arch is involved with atherosclerosis, possibly contributing to postoperative neurologic sequelae.
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The arterial side of the pump should be split to provide perfusion for this cannula and to enable a separate cannula to be inserted into the aortic arch graft.
3
Arterial Cannulation
Right Axillary Artery
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The right axillary artery is accessed through a right infraclavicular incision approximately 2 to 3 cm below the clavicle, inferiorly along the lateral aspect of the clavicle, just before the deltopectoral groove ( Fig. 25.3 ). This incision is approximately 5 to 7 cm long, depending on the patient’s habitus, through which a portion of the pectoralis major and usually most, if not all, of the pectoralis minor is divided. The axillary artery sits in the brachial plexus and is easily palpable. Electrocautery is not advised during this portion of the dissection to expose the axillary artery because of the risk of thermal injury to the brachial plexus. It is usually straightforward to identify and encircles the axillary artery over a distance of 3 to 4 cm.
