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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.
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.
Neurologic outcome after ascending aorta-aortic arch operations.