Endovascular repair of thoracoabdominal aortic aneurysms requires long segment stent graft coverage with concomitant revascularization of the renovisceral and potentially supraaortic arch segments. Such procedures represent the highest extent of complex endovascular therapy and are associated with increased technical demand, as well as the potential for iatrogenic injury to the target vessels and endoleak formation. Risk factors for intraprocedural loss of branch vessel patency include unstented vessels, high aortic angulation, dense intramural thrombus, multiple planned branch vessel involvement, and stenotic and/or small caliber (<4 mm) branch vessels. This chapter focuses on various intraprocedural complications associated with endovascular thoracoabdominal aortic aneurysm repair, including those related to target vessel events, retrograde type A aortic dissection, and bird-beak configuration.
Target Vessel Dissection and Occlusion
Lack of contrast opacification in renal or mesenteric branch vessels often indicates primary thrombotic occlusions or secondary occlusions caused by arterial dissection. Loss of branch vessel patency may be associated with sheath cannulation of a target vessel containing significant native ostial occlusive disease or prolonged sheath cannulation time.
Frequent flushing of in-dwelling sheaths with heparinized saline will aid in minimizing thrombus formation around or within long sheaths. In cases of challenging target vessel catheterization owing to small vessel diameter, ostial occlusive disease, or target vessel angulation, careful attention is advised in order to engage the target vessel origin and safely cannulate the vessel. Predilation of the target vessel origin, utilization of the sheath dilator during advancement into the branch vessel, and working over an intermediate to heavy stiff wire platform (e.g., Rosen [Cook Medical Inc., Bloomington, Indiana] or Amplatz wire [Boston Scientific Corp, Maple Grove, Minnesota]) will facilitate a smooth and atraumatic branch vessel cannulation. Excess wire manipulation within target vessels or advancement of the sheath without aid of a dilator increases the risk of intimal disruption and may lead to associated thrombus formation and/or flow-limiting dissection within the target vessel.
If target vessel occlusion or dissection is identified, the first step is to ensure maintenance of wire access to the distal target vessel. If wire access has been lost, it will be necessary to reestablish access using a combination of a soft hydrophilic wire and low-profile directional catheter. Once wire access into a distal branch is restored and exchanged for a stiffer wire platform, a flexible 6- or 7-French sheath can be advanced distal to the occlusion. Verification of patent outflow of the target vessel is performed using contrast angiography via the sheath side port. In cases of branch vessel thrombosis, balloon-expandable covered stent grafts may be used to exclude the thrombus and restore intraluminal patency of the vessel ( Fig. 18.1 ). If arterial dissection is present, confirmation of true lumen wire access can be obtained with use of intravascular ultrasound and/or contrast angiography. Self-expanding bare-metal stents are the preferred treatment modality in cases of dissection to minimize the risk of distal progression of the intimal flap.
Occlusion of target vessels after they have already been stented can also occur. In these cases, it is important not only to restore vessel patency but also to determine the cause of the occlusion. Anatomic and mechanical variables to assess include presence of untreated or unrecognized arterial dissection, a kink at the transition of the distal branch vessel stent as it transitions to the native vessel, or improper sizing of the stent graft relative to the native branch vessel diameter. Placement of an additional self-expanding bare-metal stent, frequently overlapping with the initial branch vessel stent that was originally placed, may be required to treat any residual arterial dissection or to reduce significant branch vessel angulation at the distal end of the stent.
The above techniques generally lead to effective treatment in the renal arteries because occlusions and dissections tend to be limited to a short segment and occur proximal to renal artery branches. While uncommon, iatrogenic dissection or occlusion of the superior mesenteric artery (SMA) warrants immediate revascularization. In cases of dissection, entry into the true lumen can similarly be facilitated with intravascular ultrasound, contrast angiography, or advancement of the wire through the tip of a balloon angioplasty catheter with the balloon inflated at the orifice of the target artery. Dissection flaps within the SMA are treated with bare-metal stents that are sized 1:1 relative to the native vessel diameter ( Fig. 18.2 ). In cases of thrombotic occlusion, it is important to assess the length and extent of occlusion relative to main branches of the SMA (e.g., middle colic, jejunal) prior to treatment. Extension of thrombus into the mid and distal SMA branches warrants consideration for adjunct procedures such as percutaneous pharmacomechanical thrombolysis or percutaneous mechanical thrombectomy. If there is difficulty obtaining antegrade access, some reports have described successful retrograde cannulation via celiac collaterals and using a snare to establish a through-and-through wire for sheath and stent advancement. If percutaneous options fail to restore visceral patency adequately, other reports have described laparotomy and exposure of the SMA at the root of the mesentery with open thrombectomy and possible patch angioplasty repair as indicated.
Distal embolization may occur in the setting of subtherapeutic intraprocedural systemic heparinization, aggressive wire or sheath manipulation, or as a result of dissection or occlusion in the more proximal target vessel. Less commonly, thrombus may form in distal side branches during stent deployment, particularly with balloon-expandable stents requiring prolonged inflation times.
In all cases of embolic events, the target vessel can often be salvaged with use of a variety of techniques. Catheter-directed thrombolysis can be successfully used for cases involving extensive thrombus burden or in those extending into smaller target vessel branches. Clot retrieval devices (e.g., Export Advance aspiration catheter [Medtronic AVE, Santa Rosa, California], Indigo [Penumbra, Inc, Alameda, California]) are used in cases involving thrombus in the larger caliber primary target vessel or in cases with residual thrombus following thrombolysis ( Fig. 18.3 ). These devices typically use an 0.014- or 0.018′′ system and can be easily advanced to distal branch vessels, if needed. Pharmacomechanical devices (e.g., AngioJet system [Boston Scientific Corp, Malborough, MA]) have also been described for salvage therapy of target vessels.
Excessive wire manipulation, unnecessary wire advancement, and use of stiff wires within renovisceral vessels increase the risk of perforation. Initial management includes identifying the exact site of injury with contrast angiography and, if possible, attempting to achieve initial hemostasis via tamponade from prolonged gentle balloon inflation. Continued extravasation following attempts at balloon tamponade warrants definitive treatment and varies depending on the location of the perforation within the target vessel. Proximal perforation prior to the take-off of named branch vessels may be treated by placement of either a balloon-expandable or self-expandable covered stent graft with proximal extension of the stent into the main body of the device. Distal perforations can often be treated with coil embolization if it will not sacrifice significant end-organ perfusion ( Fig. 18.4 ). A useful technique in such cases is to deliver coils through inflated balloon angioplasty catheters placed proximally to ensure hemostasis during coil delivery. Renal branch vessels may be sacrificed with the known consequence of ischemic injury to the supplied territory of renal parenchyma, whereas distal branches of the SMA may often be coil embolized without ischemic complications as a result of redundant collateral supply.
Although uncommon, distal migration may occur during deployment of stent grafts within target branch vessels. This often occurs in the setting of undersized stent grafts. For this reason, it is important to use balloon-expandable stents that are 15%–20% oversized relative to the native vessel diameter. This most commonly involves 6–7-mm stents in the renal arteries and 8–9-mm stents in the SMA. Distal migration may also occur during sheath manipulation, particularly if sheaths within target vessels are advanced without appropriate protection. If the surgeon discovers that this has occurred, recovery of migrated grafts can be achieved through a combination of a long flexible sheath placed immediately adjacent to the migrated stent graft. A 10-mm goose-neck snare (Medtronic AVE, Santa Rosa, CA) can then be advanced through the sheath and over the distal end of the stent graft ( Fig. 18.5 ). An angioplasty balloon may then be advanced through the stent graft and partially inflated. The entire apparatus is then pulled back until the stent graft is at an appropriate position, the adjacent snare and sheath removed, and the stent graft balloon inflated to profile, with use of additional bridging stents as required.