Operations to replace the distal aortic arch are usually carried out from a left lateral thoracotomy in the fourth intercostal space. These procedures are usually conducted using a heart–lung machine or a left heart bypass. Clamping of the aortic arch is usually done between the left common carotid artery and the left subclavian artery. Extreme care is needed here to protect the recurrent nerve and vagus nerve. In many cases, there is marked arteriosclerosis in these aneurysms, so that there is a relatively high risk of cerebral embolization. The surgical sequence does not differ from that in other aneurysm operations, with appropriate dissection of the proximal and distal aortic stump, suturing of the intercostal arteries, and replacement with a presealed Dacron tube prosthesis.
Endoluminal stent implantation into the aortic arch with prior revascularization of the supra-aortic vessels (hybrid operation)
Another form of treatment for aortic arch aneurysms involves a combination of endovascular stent graft implantation and open surgical revascularization of the supra-aortic branches. This hybrid operation is carried out via a median sternotomy. In the first step, an inverted Y Dacron prosthesis is used to revascularize the brachiocephalic trunk and left common carotid artery. The left subclavian artery is then revascularized with another separate prosthesis limb. Once revascularization of the supra-aortic branches has been ensured, a stent graft is advanced under radiographic guidance from the groin up to the distal ascending aorta. This not only eliminates the aortic arch aneurysm but also occludes the supra-aortic branches (the debranching operation).
Initial experience with this hybrid procedure has been positive, but the surgical effort and costs involved should not be underestimated.
Surgical techniques for replacing the descending aorta
Surgical replacement of the descending aorta
In recent years, surgical replacement of the descending aorta has clearly been overshadowed by endoluminal stent implantation. As discussed in the Results section below, the published results with endoluminal stent implantation are clearly superior to those with the surgical method (in terms of neurological complications, bleeding complications, and the overall postoperative course). The topic is therefore only mentioned here for the sake of completeness. A clear indication for surgical replacement of the descending aorta is present in chronic type B dissections with aneurysm formation, in which the intestinal arteries originate in the false lumen. The dissection flap has to be generously resected here to ensure blood flow both into the true lumen and into the false lumen. In these cases, stent implantation is almost impossible and conventional surgery is the treatment of choice.
The patient is intubated with a dual-lumen tube and positioned for a left thoracotomy—i.e., at an angle of 80–90° on the table. Draping must be carried out in such a way that the left inguinal region remains free in order to connect the heart–lung machine or for an atriofemoral bypass (left heart bypass). The thoracotomy is carried out posterolaterally in the fourth intercostal space. The intercostal space selected depends on whether the operation is on the proximal or distal descending aorta. For the proximal descending aorta, the thoracotomy should be as high as possible, while the sixth intercostal space is usually used for the distal descending aorta. Following appropriate dissection of the descending aorta, the aorta is clamped with pressure control either distal to the subclavian artery or between the carotid and subclavian arteries. To prevent reverse bleeding from the intercostal arteries as much as possible, the descending aorta is clamped in the proximal third or in the middle, and the diseased aortic segment is dissected. All bleeding intercostal arteries are immediately sutured with 4–0 Prolene. The actual anastomosis is then carried out with 3–0 Prolene over felt strips (Fig. 2.1-14). Once the anastomosis has been created, the prosthesis is clamped and the sealing of the anastomosis is tested. The descending aorta is now clamped in a relatively healthy section and the rest of the descending aorta is opened. Arteries of Adamkiewicz or other large intercostal arteries are initially blocked with a red Fogarty catheter and then reimplanted into the prosthesis. All other intercostal arteries are also quickly sutured with 4–0 Prolene. The distal anastomosis is then carried out with 3–0 Prolene over felt strips.
With this anastomosis, special caution needs to be exercised relative to the esophagus, bronchus, and recurrent nerve, which must not be injured during this phase.
Endoluminal stent implantation into the descending aorta
Endovascular treatment is nowadays the treatment of choice for aneurysms in the descending aorta (including acute type B dissection). It requires precise measurement of the size of the aneurysm and of the proximal and distal landing zones for the endovascular stent. There are common sizes of up to 46 mm, but in individual cases larger stents can also be produced individually.
Fig. 2.1–13a-r The modified elephant trunk technique (Svensson and Crawford 1997). (a) Median sternotomy, connection to heart-lung machine via separate cannulation of the superior and inferior venae cavae, and cannulation of the right subclavian artery. Hypothermia and isolated antegrade cerebral perfusion. (b) Before the start of isolated cerebral perfusion, a 10-mm graft corresponding to the size of the distal aortic arch is anastomosed end-to-side to the larger Dacron prosthesis. In the next step, the proximal prosthesis is inverted into the distal prosthesis using the anastomosed side arm. (c) After exposure of the aorta, the proximal aorta is completely transected. (d) The distal aorta is also transected. (e) The inverted prosthesis is then placed in the descending aorta. (f) The prosthesis is anastomosed using a continuous Prolene suture in the region of the proximal descending aorta. (g) This anastomosis is usually sutured in an anticlockwise direction. (h) The two sutures are finally tied. (i, j) If there are any bleeding points, they are managed using felt-supported retention sutures. (k) The inverted prosthesis is now pulled out of the descending aorta prosthesis. (l) An opening for the arch vessels is cut into the prosthesis, and the posterior row of sutures is initially created. (m) The anterior row of sutures is then created. (n) 1. The sutures are tied. 2. Antegrade whole-body perfusion is then carried out via the side arm of the prosthesis. Alternatively, perfusion via the subclavian artery can be continued. (o) Completion of the proximal anastomosis after clamping of the distal ascending aorta prosthesis. (p) Several weeks or months after the operation, the patient is readmitted for replacement of the descending aorta (1) or thoracoabdominal aorta (2). (q) After exposure of the descending aorta, the elephant trunk prosthesis is grasped and clamped. (r) The descending aorta or thoracoabdominal aorta is replaced with the usual technique.
Preoperative clarification includes the issue of whether the stent can be securely anchored distal to the origin of the subclavian artery or whether the proximal landing zone will lie between the left common carotid artery and subclavian artery. If it is necessary to cover the subclavian artery, it needs to be clarified preoperatively whether subclavian transposition should be carried out before the procedure in order to prevent later neurological complications (e.g., posterior cerebral infarction and left upper extremity ischemia). For this purpose, an exhaustive neurological examination needs to be carried out preoperatively to determine:
These data allow one to decide either for or against subclavian transposition (Weigang et al. 2007a).
The actual surgical procedure is preferably conducted in a hybrid operating