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Address reprint requests to Dr. David Spielvogel, Department of Surgery, Division of Cardiothoracic Surgery, New York Medical College, Westchester Medical Center, Valhalla, NY 10595
To reduce the morbidity and mortality associated with aortic arch repair, the reconstruction technique must be an integral part of the neurological protection scheme. The neurological risk can be divided between protection of neuronal viability during interruption of cerebral circulation and the prevention of cerebral emboli before, during, and after arch repair. From extensive clinical and laboratory experience with hypothermic cerebral protection, the safe limit of circulatory arrest is about 30 minutes at 15°C. Longer periods risk a higher incidence of overt stroke and subtle brain injury manifest as temporary neurologic dysfunction.
Therefore, if a longer interval of cerebral protection is expected, then restoration of blood flow is mandatory.
Early experience with retrograde cerebral perfusion to extend the ischemic interval seemed promising, but critical assessment of our clinical and laboratory data questioned the nutritive value of retrograde perfusion, and left only the maintenance of cerebral hypothermia as a possible beneficial effect.
Several surgeons began to accumulate experience with selective hypothermic antegrade cerebral perfusion using a catheter-based system and separate pumps to restore cerebral blood flow after a brief period of circulatory arrest. Reported results improved dramatically from early attempts, but antegrade cerebral perfusion still appeared complex and left the operative field cluttered with perfusion catheters.
Certain questions arose: Does instrumentation of the brachiocephalic vessels lead to cerebral embolization? Can the catheters become displaced—for example, into the right subclavian artery during innominate artery perfusion—with potentially catastrophic results?
How could the benefits of both techniques be combined? Initially, to reduce the hypothermic circulatory arrest time, a separate graft was sewn to the brachiocephalic vessels as a single patch of aortic tissue. This graft could be perfused separately while the rest of the arch replacement was completed. A further refinement incorporated axillary artery perfusion. The brain and upper body could be supported and the brachiocephalic graft attached to the full arch graft without interrupting cerebral circulation. Despite the significant reduction in circulatory arrest times, the risk of atherosclerotic emboli remained.
In many patients, conspicuously in the elderly, the aortic arch is sufficiently diseased with soft atheromata to make reconstruction hazardous. Looking beyond the lumen of the aortic arch, a careful observation confirmed the dissipation of the atherosclerotic disease a centimeter beyond the vessel origins. This observation—combined with the growing experience of our Japanese colleagues with the four-branched graft for aortic arch reconstruction—began the evolution to our current technique.
Figure 1A classic example of extensive thoracic aortic aneurysmal disease that required not only a two-stage repair but also a Bentall aortic root reconstruction or valve-sparing procedure. The need for concomitant coronary artery bypass grafting is determined by preoperative cardiac catheterization. In patients with extensive thoracic aortic aneurysm disease, a two-stage approach is clearly our preference. The interval between operations allows the patient to recover physically and mentally to prepare for another major surgical intervention. A small series of more extensive resections through a transverse thoracosternotomy proved overwhelming for some patients, requiring a prolonged period of convalescence. Several lesser procedures are well tolerated even in a very elderly patient. The stage I “elephant trunk” aortic arch replacement is performed through a median sternotomy extended a small distance cephalad and to the left, allowing exposure of the arch and the individual brachiocephalic vessels. The innominate vein is mobilized but not divided. In patients with extensive atherosclerotic disease, the patient is dissected away from the aneurysm, lest embolization occur even before cardiopulmonary bypass (CPB).
Figure 2(A) Arterial perfusion is exclusively performed via the right or occasionally the left axillary artery. A preoperative CT angiogram helps to choose the appropriate side, particularly if one or more of the brachiocephalic vessels are dissected. Our preferred method for both perfusion and safety is direct axillary artery cannulation with a right angle cannula (Edwards Lifesciences, Irvine, CA). Sizes 22 and 24 Fr are available. A transverse arteriotomy allows easy access and the cannula is secured with silastic snare. The artery is repaired at the conclusion of the operative procedure with running 6-0 polypropylene. (B) An alternative technique allows axillary artery perfusion using standard femoral artery cannulas. A Dacron graft, 8 mm or 10 mm is sewn end to side to a longitudinal arteriotomy with 5-0 polypropylene. The graft is carefully de-aired and cannulated with the arterial cannula and the perfusion line secured with a snare or heavy ties. At the conclusion of the operative procedure, the graft is transected and the stump oversewn. On several occasions, the same axillary artery is again utilized for perfusion with the graft stump used for a graft or direct cannulation. (C) For patients with small axillary arteries precluding direct cannulation or making an end-to-side anastomosis difficult, a simple technique is used. The axillary artery is transected and a 6 mm or 8 mm Dacron graft is anastomosed end-to-end with 5-0 polypropylene. This graft is used for perfusion and at the end of the procedure, the graft is trimmed and anastomosed to the distal axillary artery, restoring continuity.
Figure 3Once secure axillary cannulation is established and appropriate connections are made to the heart-lung machine, CPB is begun. To assure adequate perfusion and rule out dissection, special attention is paid to the innominate artery, perfusion line pressures, and if available, transesophageal echocardiography.
With appropriate connections made to the heart-lung machine, CPB and cooling are instituted. Liberal use of epi-aortic scanning assists in choosing the ideal site for aortic cross-clamping. The myocardium is protected with both antegrade and retrograde blood cardioplegia. If a Bentall procedure or valve-sparing root reconstruction is necessary, the body temperature is slowly lowered to 20°C. Coronary artery bypass grafts are left long for trimming and proximal implantation later in the repair.
Figure 4In patients with significant aortic valve insufficiency or with the necessity of aortic root reconstruction, the ascending aorta is cross-clamped. The myocardium is protected with blood cardioplegia. In the case of severe atherosclerotic disease, epiaortic ultrasound is useful in selecting the best site for cross-clamping. When the proximal reconstruction is almost complete (i.e., when fashioning the left coronary button to the valve conduit), the patient is hard-cooled, lowering the esophageal temperatures to 12 to 15°C and bladder temperatures to 14 to 17°C. Jugular bulb saturations are measured at >95% to assure maximum cerebral metabolic suppression, and the head is packed in ice in preparation for circulatory arrest.
Figure 5Depending on the size of the brachiocephalic vessels, a trifurcated graft is constructed with a main graft of 12 to 14 mm woven Dacron with two side arm grafts of either 8 or 10 mm woven Dacron. The limbs are beveled and attached at a 45° angle closely spaced together. A 3-0 polypropylene suture assures a durable anastomosis, as no graft-to-graft healing will occur. Any combination of grafts is possible, including a fourth limb for direct re-implantation of a large left vertebral artery arising from the aortic arch proper. Premanufactured trifurcated grafts are available (Hemashield Vascular Grafts, Boston Scientific, Natick, MA).
Figure 6During deep hypothermic circulatory arrest, the brachiocephalic vessels are transected just distal to their origins sharply with a knife and mobilized distally. A superficial suture helps to suspend the vessels, and prevent retraction. The lumen of each brachiocephalic vessel is inspected. If significant atherosclerotic disease extends cephalad, additional segments are resected. The trifurcated graft is brought onto the field. The first 8 or 10 mm side arm graft is trimmed keeping the limbs as short as possible and anastomosed to the left subclavian artery with a running 5-0 polypropylene suture. The second limb is trimmed and sutured to the left common carotid artery. Finally, the main graft is cut short and attached to the innominate artery. Each limb is gently aspirated. The patient is placed in slight Trendelenburg position and perfusion is resumed via the right or left axillary artery, flushing out air and micro-debris. An alternative strategy of grafting the innominate and left common carotid arteries first allows shorter circulatory arrest times. The left subclavian anastomosis is completed during selective cerebral perfusion with a single clamp distally.
Figure 7Selective cerebral perfusion is begun by flushing and clamping the main portion of the trifurcated graft. The graft is reflected off the field, allowing easy access to complete the aortic arch reconstruction. Perfusion pressures are maintained between 50 to 60 mm Hg, with flows of 700 to 1000 mL/min. The temperature of the perfusate is allowed to drift upward and alpha-stat pH management is used throughout CPB.
Figure 8With the patient on selective cerebral perfusion, the elephant trunk is fashioned. When choosing the best site for the suture line, an attempt is made to avoid manipulation and injury to the recurrent laryngeal nerve. This has enormous impact on the patient’s subsequent ability to clear secretions and avoid respiratory infections. This often requires placement of the elephant trunk anastomosis proximally and involves oversewing one or more of the brachiocephalic origins. One or more of the head vessels can be oversewn with 3-0 polypropylene. The location of the suture line has no bearing on the remaining second-stage reconstruction. The lower body remains ischemic but sufficiently protected by residual hypothermia. Traditionally, a 10-cm elephant trunk is constructed but a longer trunk will facilitate the remaining repair. If the two-stage approach is chosen for an aneurysmal dissected aorta, then the length of the elephant trunk is limited by the size of the distal aortic fenestration. This assures flow in both true and false lumens.
Figure 9This illustration shows the double bevel used to complete the ascending to arch repair. When the elephant trunk is completed, the graft is everted back into the mediastinum, trimmed, beveled, and anastomosed to the previous ascending aortic graft or to the sino-tubular junction.
Figure 10A 2-0 polypropylene suture is used to secure long-term durability of graft-to-graft suture lines. Selective cerebral perfusion is continued throughout.
Figure 11With the graft-to-graft anastomosis completed between the Bentall graft and the elephant trunk, the ascending aortic graft is distended and the site for implantation of the trifurcated graft marked. The main limb of the trifurcated graft is trimmed and beveled, and then sewn with 2-0 or 3-0 polypropylene to an elliptical opening made with an ophthalmic electrocautery in the right lateral aspect of the ascending aortic graft. Before securing the anterior aspect of the anastomosis, the heart and aortic grafts are carefully de-aired. The suture line is pulled up and tied. The clamp on the trifurcated graft is removed and flows increased to distend the entire reconstruction. For Bentall root repair, the location of the right coronary button is marked along with sites for proximal coronary artery bypass grafts. This reconstruction is undertaken without interruption of selective cerebral perfusion.
Figure 12For patients requiring coronary artery bypass, the grafts are left long. Locations for proximal reimplantation are marked after full reconstruction and grafts are then trimmed to the appropriate length. The patient is again placed on SCP (selective cerebral perfusion) by reducing flows and clamping the main portion of the trifurcated graft. Small openings are fashioned with ophthalmic electrocautery in the appropriate graft locations. The coronary button is attached with 4-0 or 5-0 polypropylene and proximal coronary grafts are sewn with 5-0 polypropylene. Once again, the grafts are de-aired and suture lines pulled up and tied; full perfusion is restored and the patient rewarmed. No attempt is made to rewarm the patient before restoring full perfusion, as the lower body remains hypothermic and ischemic.
Figure 13In some patients, the size of the aortic arch displaces the left subclavian artery to the left, posterior and cephalad making access from a median sternotomy difficult. This is determined by preoperative CT angiography. A preprocedural left subclavian to left common carotid bypass will shorten the circulatory arrest time and make the reconstruction possible with a bifurcated graft. A small amount of back-bleeding into the aortic arch despite proximal ligation requires oversewing the origin of the left subclavian artery before elephant trunk reconstruction.
Figure 14Total aortic arch replacement for acute type A aortic dissection. If the ascending aorta can be cross clamped then aortic valve re-suspension is performed first. This procedure can be completed without aortic cross clamping, during SCP, albeit with a longer lower body ischemic time. The next step is HCA and reconstruction of the arch with the trifurcated graft. The limbs of the graft should be kept as short as possible to allow placement of the main limb on the ascending or arch grafts.
Figure 15During selective cerebral perfusion, the layers of the aorta are brought together with a broad strip of Teflon felt and the “elephant trunk “constructed with 3-0 polypropylene. The two grafts are beveled and anastomosed with 2-0 polypropylene. Finally an elliptical opening is created in the ascending aortic graft with ophthalmic electrocautery and the trifurcated graft trimmed, beveled and sewn in place (see Figure 11).
Figure 16(A) Type I: This illustrates the elephant trunk anastomosis just distal to the origin of the left subclavian artery. This location may jeopardize the recurrent laryngeal nerve.
Figure 16(A) Type I: This illustrates the elephant trunk anastomosis just distal to the origin of the left subclavian artery. This location may jeopardize the recurrent laryngeal nerve.
Figure 17Type 3: Oversewing the stumps on the left subclavian artery and left common carotid arteries allows a more proximal location when the aorta is calcified distally or an anatomic neck is present.
Figure 18In cases of re-operative aortic arch replacements with marked dilation throughout, the aorta and the site of the distal anastomosis of the Bentall or ascending aortic graft are often the best surgical neck with closure of all brachiocephalic vessels. This illustrates the flexibility of this technique regardless of the pathologic condition encountered.
Figure 19In a minority of patients, the left vertebral artery exits the aortic arch directly. This anomaly can be detected on pre-operative CT angiogram and the status of the contralateral vertebral artery assessed by duplex ultrasound. Several options exist for the left vertebral artery’s preservation and re-implantation: The vertebral artery can be anastomosed directly to the adjacent left common carotid artery or extended with a portion of reverse saphenous vein and implanted on a Dacron graft. If the right vertebral artery is patent then the left vertebral artery can be temporarily occluded during selective cerebral perfusion (SCP) and reconstructed during re-warming and implanted on the main portion of the arch graft. If the right vertebral is occluded, the left vertebral artery should be reconstructed during HCA and implanted on the trifurcated graft for perfusion during SCP. Occasionally a diminutive left vertebral artery can be ligated.
Contemporary series of total aortic arch replacements show increasingly improved results, with substantially lower perioperative mortality rates and a low incidence of permanent neurological injury.
These improvements are multifactorial in etiology, involving factors such as increasing experience, better perioperative patient care, improved myocardial protection, and specific advances in cerebral protection. Antegrade cerebral perfusion, intuitively the most physiological option, has established neurological and metabolic benefits. Its use in total arch replacement, where the systemic circulatory arrest period is anticipated to exceed 30 minutes, is well established. Its resurgence followed the recognition that hypothermia in conjunction with SCP enables use of lower flow rates and produces superior results compared with cerebral perfusion at normothermia.
Nevertheless, there remain important variations in the way SCP is delivered. Many surgeons place flexible balloon-tipped catheters into the arch vessels under direct vision during a brief period of HCA and achieve excellent results with this technique. Clearly, the optimal strategy for global cerebral protection and the ideal conditions for minimizing stroke may not be entirely compatible, and one must strike a balance between them to achieve the best results. Inserting catheters into the vessels for SCP minimizes HCA, and therefore, reduces the incidence of global injury but risks embolization. As an alternative, one can maintain continual perfusion through the right axillary artery and clamp the innominate vessel proximally: acceptable neurological results with total arch replacement have also been obtained with this methodology.
It avoids HCA entirely, but risks injury and embolization at the clamp site, as well as providing variable perfusion to the left cerebral hemisphere dependent on an intact circle of Willis.
In light of the severe consequences of an embolic event, our philosophy has been to avoid all cerebral vessel manipulation and clamping. We have adopted the strategy of transecting the brachiocephalic vessels cephalad to their origins, inspecting the lumen, resecting additional vessel if necessary, and anastomosing them separately to a trifurcated graft. This technique avoids manipulation of the often-diseased vessel ostia, which may prevent embolic stroke, but it does require HCA for longer periods than the balloon catheter and other SCP techniques. The cephalad portions of the brachiocephalic vessels can reproducibly be attached to the trifurcated during a relatively short interval of HCA considered well within safe limits at deeply hypothermic temperatures.
The branch graft operation does not require cluttering the operative field with multiple cannulae or monitoring multiple pumps, and is therefore suitable for use by surgeons who only occasionally are required to replace the aortic arch. The small diameter vessels can be anastomosed to the branches of the graft securely without reinforcement, as attested to by the very low incidence of reoperation for hemorrhage. In patients with Marfan’s syndrome, the current procedure has the advantage over our previous technique in which a patch of aorta including all the cerebral vessels was left in situ: the branch graft technique removes all of the aneurysmal tissue in the arch, making recurrence unlikely. Also unique to this technique is the ability to site an “elephant trunk” graft proximally, in the mid-arch or even in the ascending aorta. This is especially important to patients with dilation of the arch and descending aorta, leaving no area of near normal diameter in which to anchor an elephant trunk more distally. The graft is placed through the arch into the proximal descending aorta, the aorta is closed proximally incorporating the graft, and the brachiocephalic vessel origins are oversewn. Thus, the aortic arch remains pressurized until the descending aortic resection or stent insertion takes place.
Results with the Trifurcated Graft Techniques
In the first 109 consecutive nonemergent total aortic arch replacements using the trifurcated graft technique, there were five hospital deaths (4.6%) and five permanent strokes (4.6%), one of which was fatal. Mean duration of HCA was 31.2 ± 6.6 minutes at a mean esophageal temperature of 12.8 ± 2.2°C. Mean duration of SCP was 65.3 ± 60.9 minutes. The most frequent complication was respiratory: Prolonged intubation (>48 hrs) was necessary in 15 (13.8%) patients. Transient neurological dysfunction (TND) was noted in 6 patients (5.5%). Re-operation for bleeding was required in 3 patients (2.8%). Renal support with hemofiltration was needed in 4 patients (3.7%), but none had permanent renal failure. Median intensive care unit stay was 3 days and hospital stay was 9 days. With careful suturing, few additional stitches are necessary, and adequate hemostasis achieved with little clotting factors or platelets. Aprotinin is used routinely with minimal untoward effects. All patients receive aspirin 325 mg postoperatively, if tolerated, to avoid platelet thrombi.
Some uncertainty remains as to the optimal hemodynamic and perfusion parameters for SCP. Our current strategy includes an alpha-stat pH management, mean perfusion pressure between 50 to 60 mm Hg with flows of approximately 10 mL/kg/min. After the period of circulatory arrest, the perfusate temperature is allowed to drift upward reaching 18 to 20°C on completion of the entire arch reconstruction.
We believe this technique illustrates the essential components of an enduring surgical procedure.
References
Hagl C.
Ergin M.A.
Galla J.D.
et al.
Neurologic outcome after ascending aorta-aortic arch operations.
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