By Gustavo S Oderich
Inadequate proximal neck limits the use of standard endovascular approaches in up to 40% of patients because of short length, angulation or involvement of the visceral arteries. Fenestrated and branched stent grafts have been increasingly utilised to treat complex aneurysms with high rates of technical success, low morbidity and mortality. This article summarises the basic concepts of device design, techniques of implantation and some of the “bail-out” manoeuvres that may be required during endovascular repair using fenestrated stent grafts
The Zenith Fenestrated stent graft (Cook Medical) has been approved for treatment of patients with short-neck or juxtarenal abdominal aortic aneurysms who do not meet the proposed anatomical criteria for use of infrarenal stent grafts and have an infrarenal neck length >4mm and 18mm and <32mm, no calcium or thrombus.
Bilateral femoral access is established. The patient is systematically heparinised with a target activated clotting time >300 seconds. The right femoral access is used for catheterisation of the fenestrations and placement of side stents, while the left femoral access is used for introduction of the fenestrated device. Multi-sheath access via the right femoral artery is obtained using a 20F Check-Flo sheath (Cook Medical), which is accessed with two short 7F sheaths for placement of pre-selective catheters. Aortography is avoided during the implantation of the device. Instead, hand injections of 3ml of contrast in 7ml of saline are sufficient to demonstrate the anatomy for side stent placement. Once the target vessels are catheterised, the fenestrated component is oriented extra-corporeally, introduced via the left femoral approach, and deployed with perfect apposition between the fenestrations and the target catheters. Each selective catheter is sequentially removed from the target artery and used to regain access into the fenestrated component, fenestration and target vessel. After access into the renal arteries is established with hydrophilic sheaths, the diameter-reducing tie is removed, followed by deployment and retrieval of the top cap and balloon dilatation of the proximal neck using a compliable balloon. Each alignment stent is sequentially deployed; flared and selective angiography is performed with hand injection. The repair is extended distally using a universal bifurcated component and a contralateral limb. The procedure is completed by balloon dilatation of the attachment sites and final angiography to demonstrate patency of the visceral arteries, main body, iliac limbs and iliac arteries.
Difficult target vessel catheterisation
Although most target vessels are accessed without difficulty, several manoeuvres can be used to facilitate catheterisation. The 7F Ansel sheath may be positioned in the fenestration with support of a 0.018-inch guidewire allowing a 5F “buddy” catheter (eg. Van Schie 3) to be used to locate the renal artery. In cases of down-going, tortuous or diseased renal arteries, the catheter and guidewire may bounce up into the top cap, providing enough support to advance the catheter into the renal artery. Advancement of the sheath may be facilitated by using an undersized balloon instead of the dilator.
Avoiding damage to side stents during exchanges
The dilator of the bifurcated device often encroaches the contralateral renal stent. In these cases it is useful to leave a 10mm balloon ready to be inflated in the renal stent to protect from any damage.
Misalignment of fenestrations
Neck angulation, tortuosity and errors of design can lead to misalignment between fenestration and target vessel. The fenestrations may be pulled slightly more posterior because of the diameter-reducing tie, which runs posteriorly. Rotation of each fenestration to an anterior position often allows successful catheterisation. Other manoeuvres are rarely needed but include use of curved catheters (eg. VS1 or SOS); microcatheters and, less frequently, balloon displacement of the main stent graft.
Branch perforation or dissection
Branch vessel perforation and/or dissection can be prevented by meticulous technique, visualisation of the tip of the guidewire and avoiding manipulations. The guidewire should not be positioned in small terminal branches, which are prone to perforate or dissect. It should be stabilised during exchanges, avoiding forward or retrograde movement. If perforation occurs, it should be immediately recognised and treated by coil embolisation.
Endoleaks from attachment sites such as type I and III endoleaks are infrequent (<1% to 3%) with proper selection of a healthy landing zone. In the event of a type Ia endoleak, the proximal neck may be re-dilated, but all the alignment stents need to be protected by separate balloons.
Stent kinks or narrowing
Kinks can be anticipated from review of CT angiography and completion angiography. If a kink is evident by completion angiography, a self-expandable stent should be deployed distal to the balloon expandable stent. Kinks remain a cause of re-intervention or branch vessel loss if not recognised.
Endovascular repair of complex aneurysms involving the visceral arteries has become a reality. Fenestrated stent grafts have been increasingly utilised to treat pararenal and thoracoabdominal aneurysms. The technique is safe, effective and can be performed with high technical success and low risk of complications by experienced physicians. Over 6,500 patients have been treated by Zenith fenestrated endografts. Single-centre reports and a US prospective trial have shown high technical success, exceptionally low rates of type I and III endoleak and excellent branch.
Gustavo S Oderich is professor of Surgery, director of Endovascular Therapy, Division of Vascular and Endovascular Therapy, Mayo Clinic, Rochester, USA