Volume 14, Issue 2 , Pages 136-149, Summer 2009
Operative Repair of Type B Aortic Dissection
Article Outline
Although endovascular repair of acute type B aortic dissections offers many advantages, no long-term data are available to analyze late outcomes, and endovascular capabilities are a relatively recent development and may not be universally available. Accordingly, conventional open repair remains a viable and valuable option. The operative repair of type B aortic dissections can be considered in the 3 following circumstances:
Acute Dissections
As outlined in previous publications, our preference for distal perfusion has remained femoral-femoral total bypass with an oxygenator and heat exchanger.2 Although many teams prefer left heart bypass techniques (left atrial-femoral bypass) with more modest heparin dosing, we prefer the flexibility afforded by total bypass, particularly the capability for hypothermic circulatory arrest, which is frequently necessary to allow construction of a hemostatic open proximal anastomosis.
Venous access is via a femoral cut-down. Although a right femoral cut-down may allow more direct access to the superior vena cava, exposure of the down groin can be difficult in the obese patient.
Initially, circumferential control of the distal descending thoracic aorta is obtained at approximately the T-5 level, well distal to the known entry tear. The distal extent of the repair may be extended to include all aneurysmal segments of the aorta.
Figure 1.
Operative details: exposure is gained via a left-sided posterolateral thoracotomy through the fourth interspace. Right radial arterial monitoring, central venous access, dual lumen endotracheal intubation, and transesophageal echocardiography (TEE) monitoring are standard. (A) Anterior view. (B) Posterior view.
Figure 2.
(A) Anterior view of both thoracotomy and left groin incisions. In the modern era with hydrophilic guide wires, catheter exchange techniques, and very stiff guide wires, we have been almost uniformly successful in passing a large (29-Fr.) venous catheter through the left femoral vein into the superior vena cava.
(B) Detail of both left femoral artery and vein exposure. Multiple options exist for arterial access. Most commonly, we use left femoral access, introducing a 22-Fr. catheter over a guide wire after arterial dilation (Seldinger technique). v. = vein.
Figure 3.
We have also draped the left arm free and placed an 8-mm chimney graft on the left common carotid artery through a separate neck incision. a. = artery; n. = nerve.
Figure 4.
Similarly, a chimney graft may be placed on the left subclavian artery through the thoracotomy incision. a. = artery; n. = nerve.
Figure 5.
Occasionally, when only a partial circumference of the descending thoracic aorta is dissected, we identify an undissected portion of the aortic wall and insert a 22-Fr. arterial catheter over a guide wire inserted through a pledgeted mattress suture and positioned carefully in the true lumen guided by TEE.
Figure 6.
Proximally, the mediastinal pleura is incised over the distal arch, exposing and carefully identifying and preserving the phrenic nerve, and vagus and recurrent laryngeal nerves. Circumferential control of the aortic arch between the left carotid and the left subclavian arteries is obtained, as well as control of the left subclavian artery. If this is at all difficult, we administer heparin, and commence cooling on CPB, so as to avoid any hemodynamic instability. After commencing bypass and using TEE, we assure true lumen flow. a. = artery; n. = nerve.
Figure 7.
During cooling, integrity of the aortic valve is ascertained by TEE, and if the valve is incompetent, or the left ventricle begins to distend after the onset of ventricular fibrillation (A), we vent the left ventricle either via the left inferior pulmonary vein and through the mitral valve (B), or via the left ventricular apex (C). LIPV = left inferior pulmonary vein.
Figure 8.
After achieving a core temperature of 18°C, with the operative field suffused with CO2, left ventricular venting is discontinued, followed by discontinuation of CPB. The distal thoracic aorta is clamped, and the proximal descending thoracic aorta is opened longitudinally. Then the proximal extent of the dissection is identified. The aorta is transected proximal to the proximal-most extent of the dissection, and an appropriately sized woven graft is sewn end to end with running 4-0 or 5-0 monofilament suture. a. = artery; n. = nerve.
Figure 9.
After completion of this anastomosis, the graft is re-cannulated, and reperfusion retrograde through the arch is commenced after meticulously de-airing the graft. Then the proximal graft is clamped. If the anastomotic site is proximal to the left subclavian artery orifice, the left subclavian artery can be reattached to the aortic graft with an interposed 8-mm woven Dacron limb.
Figure 10.
Distally, the aortic cross-clamp is removed, and the aorta is transected. The normal anatomy of the aorta is reconstituted by approximating the intimal, medial, and adventitial layers circumferentially, frequently using Teflon felt as a neo-medial layer. The aortic graft is then sewn end to end to the reconstituted true lumen, as an open distal anastomosis, again using a running 4-0 monofilament suture. The graft and distal aorta is de-aired by flowing up from the femoral arterial cannula. Then antegrade perfusion of the body is reinstituted through the aortic graft, and rewarming is commenced. If angiography is available, as in a hybrid operating suite, aortography is performed to assure perfusion of visceral vessels. Interventional strategies can be utilized to assure distal perfusion. After sufficient rewarming, the left ventricular vent is removed, and the patient is weaned from CPB. After de-cannulation, the heparin is reversed, and hemostasis is obtained. Wounds are closed as per routine.
Chronic Dissections
Open surgical repair of complications of chronic aortic dissections is more frequently used because of the questionable utility of endovascular repair. Many reports are surfacing suggesting poor long-term durability of early interventional successes, emphasizing the necessity for conventional open techniques. In general, the same operative techniques are employed, with the exception of the distal aortic anastomosis.
Again, with the capability for total cardiopulmonary bypass (CPB) the aorta is exposed through a left thoacotomy, with the incision centered about the area of interest, usually the proximal descending thoracic aorta, which has become aneurysmal over time. Proximal control of the aortic arch is obtained between the left carotid and the left subclavian arteries and the left subclavian artery is also controlled. Distally, circumferential control is gained at a level where the aorta resumes a more normal diameter. Usually, access can be gained through a chest incision only to the distal thoracic aorta within 2 to 3 cm of the celiac axis by incising the diaphragmatic crura. If an extensive replacement of the distal descending thoracic aorta is contemplated, hypothermic circulatory arrest may be utilized for spinal cord protection.
Figure 11.
After commencing CPB and attaining the desired core temperature, clamps are placed at proximal and distal sites, and the aorta is incised. The dissection flap must then be resected to allow visualization of patent intercostal arteries, which are oversewn in the upper thorax. The proximal anastomosis is then constructed as previously noted. If we anticipate a distal anastomosis distal to the T-10 level, we will usually reattach 2 to 3 pairs of intercostal arteries as an onlay patch, de-air our graft, and re-establish flow to these intercostal arteries.
Figure 12.
We then construct our distal anastomosis using the open technique. Perfusion from the femoral artery is temporarily interrupted, and the distal clamp is removed. The aorta is transected circumferentially, taking care to include the adventitia posteromedially. We then excise a tongue-shaped portion of the dissection septum, usually as far distally as we can visualize, taking care not to buttonhole the aortic wall, creating a single lumen aorta for a distance of 5 to 8 cm. The distal anastomosis is then constructed again using 4-0 monofilament suture, sewing to the new widely fenestrated single lumen aorta. Air is flushed from the distal aorta and graft by retrograde flow up from the femoral artery cannula. The anastomosis is secured; the clamp on the aortic graft is removed, and antegrade flow is re-established. Rewarming is accomplished as necessary. CPB is discontinued; cannula are removed, and protamine is administered. After assuring hemostasis, wounds are closed as per routine.
Figure 13.
If we anticipate the necessity for further aortic surgery, we may incorporate an elephant trunk into our distal anastomosis, shorter in length than our septectomy, which allows proximal control in the future without the necessity for the tedious dissection necessary for control of the previously resected aorta. Patients are then followed longitudinally for the potential of aneurysmal dilation of their remaining chronically dissected aorta.
As stent graft technology advances, many more innovative approaches will be devised. Presently, we are limited by currently available devices. Future developments will almost surely include devices with lower radial strength, so as to avoid intimal tears, precurved devices to better adapt to arch anatomy, branched endografts, and uncovered (and possibly tapered) stents, which may be deployed throughout the entire length of the aorta, encouraging thrombosis of the false lumen, and allowing branch vessel perfusion through the uncovered graft interstices. Surely, further developments in this field will be both valuable and exciting.
References
PII: S1522-2942(09)00063-4
doi:10.1053/j.optechstcvs.2009.06.007
© 2009 Elsevier Inc. All rights reserved.
Volume 14, Issue 2 , Pages 136-149, Summer 2009
