Abstract
Background
Short proximal neck of an abdominal aortic aneurysm is associated with risk of treatment failure during abdominal aortic repair. Important side branches, such as renal arteries, cannot be covered without serious consequences.
Purpose
To test the feasibility of preoperative fenestration of abdominal aortic stent grafts with a re-entry catheter and steerable sheath to preserve the patency of renal arteries in an animal model.
Material and Methods
Three domestic pigs were anesthetised and a stent graft placed in the abdominal aorta, covering the renal arteries. An attempt was made to fenestrate the renal arteries through the prosthesis using the Outback re-entry catheter supported by the Channel Steerable sheath. The hole that was created was dilated and stented. The specimens were visually analyzed after sacrifice.
Results
In one pig, the graft material was successfully traversed and a guide wire advanced in the renal arteries. Due to insufficient guide wire support and a poor balloon profile, dilatation of the fenestration failed. In another pig, the procedure was technically successful, but a long warm ischemia time for the left kidney caused infarction. In the third experiment, the procedure had to be discontinued due to a technical failure of the Outback device.
Conclusion
Fenestration of a stent graft with a re-entry device through a steerable sheath is technically feasible in vivo. However, without further refinement of the instrumentation, the technique cannot be recommended in elective cases of abdominal aortic repair, but if the renal arteries are covered accidentally during endovascular treatment, the technique may be a valuable salvage option if surgical revascularization is not considered as an option.
Endovascular treatment of aorta has some limitations: the superior mesenteric artery and renal arteries should be left uncovered, and the celiac trunk should be covered only after serious consideration (1, 2). On the other hand, a short proximal and distal neck (i.e. ≤1.5 cm between the proximal end of the fabric and aneurysm) is associated with a higher risk of complications and eventual failure of the therapy (3, 4). If endovascular therapy is still desired, surgical revascularization of the branch vessels is necessary before deployment of the main prosthesis.
Pre-fabricated, custom-made fenestrated abdominal aortic stent grafts may overcome some of the previously mentioned problems, and they have shown encouraging short- and mid-term results in selected patients (5–10). However, customized stent grafts depend on excellent preoperative imaging, graft planning, and manufacturing. Successful device utilization requires fenestrations to be carefully aligned with the vessel ostia before the device is deployed. With tortuous anatomy, it can be extremely challenging and proper fenestration sealing may not be achieved. Customized stent-grafts are also very expensive and not available for acute syndromes. The durability of these prostheses is still unknown (11).
Intraoperative percutaneous puncture and fenestration of the stent graft fabric could ensure the patency of important side branches when the neck is too short or the side branch is inadvertently covered during the operation. Intraoperative fenestration of the renal arteries has been tested on animal models in two studies (12, 13), but a robust method to create the fenestrations is not yet available for clinical use.
Our purpose was to test the feasibility of fenestration of an aortic stent graft on the renal arteries in a pig model using a re-entry catheter and steerable sheath.
Material and Methods
Project approval was obtained from the National Animal Experiment Board for proposed experiments. Pigs were managed in compliance with The Finnish Act on Animal Experimentation.
Three domestic pigs, weighing 50–60 kg each, were anesthetized. Both femoral arteries were punctured and an 8F sheath introduced. Both renal arteries were catheterized under fluoroscopic control (GE Innova IQ 3100 Excellence, GE Healthcare, Waukesha, WI, USA) from the left groin, and 5 mm/20 mm PTCA (percutaneous transluminal coronary angioplasty) Balloon Catheters (Maverick, Boston Scientific, Natrick, MA, USA) were advanced into both renal arteries (Fig. 1). A 16-mm iliac extension stent graft (Endurant, Medtronic, Minneapolis, MN, USA) was deployed in the abdominal aorta covering the renal arteries in the first pig, and a Talent (Medtronic) stent graft in the second and the third pig. Thereafter, a Channel steerable sheath (CR Bard, Murray Hill, NJ, USA) was advanced into the aorta from the right groin. This device with an 8F or 9F inner diameter is intended to access the left atrium for purposes of diagnosing and treating left-sided atrial arrhythmias. The device has a flexible tip that can be bent at a 0–180° angle, and the sheath remains in the precise position once set (Fig. 2). The steerable sheath is necessary to point the needle in an exact manner towards the renal artery ostium and to give support to the re-entry catheter during needle penetration of the resilient stent graft fabric. Balloons in the renal arteries were inflated and served as markers when the stent graft was punctured with an Outback re-entry catheter under the guidance of fluoroscopy (Cordis, Miami Lakes, FL, USA) (Fig. 3). The Outback catheter is a 6F system that uses orthogonally oriented radiopaque markers and the main indication of the device is to aid the re-entry of the dissecting wire into the true lumen distal to an occlusion in the peripheral arteries (14–16). In our experiment, we directed the 22-gauge re-entry needle towards the arterial orifice.
(a) Pre-procedural angiography. PTCA balloons were placed in the renal arteries to serve as markers. (b) The needle of the Outback device pointing in the direction of the right renal artery. (c) A 0.014-inch guide wire was passed through the fenestration, and the hole was sequentially dilated to 5 mm. (d) A 6-mm bare stent was positioned in the fenestration. (e) Completion of the angiograph of the right renal artery. (f) The Outback device pointing in the direction of the left renal artery, and the guide wire was passed through the fenestration
Channel Steerable sheath. The flexible tip can be bent at a 0–180° angle with the lever in the handle. Image published with the courtesy of CR Bard Inc
The Outback LTD re-entry catheter is a single-lumen, over-the-wire, 6F sheath-compatible catheter with a curved nitinol cannula within the outer shaft that runs the full length of the catheter to serve as the guide wire lumen. The nose cone at the catheter tip possesses an L-shaped radiopaque marker that indicates needle direction. When the image intensifier is orthogonally moved, a “T” shape appears to check whether the catheter is overlying the artery to confirm the alignment of the catheter with the artery. Image published with the courtesy of Cordis, a Johnson & Johnson company
As the deflation of the balloon in the renal artery indicated successful puncture, a 0.014-inch guide wire was advanced through the fabric into the renal artery. The Outback device was changed to a PTCA balloon and the fenestration sequentially dilated to 5 mm. A 6-mm balloon expandable renal stent (Racer, Medtronic) or a 6-mm covered stent (Jostent, Abbot Vascular Instruments, Rangendingen, Germany) was placed in the fenestration to keep it patent. After the procedure was completed, the pigs were euthanized and autopsied.
Results
In all three cases, the steerable sheath gave enough support that it was easy to maneuver to point towards the ostium of the renal arteries.
In the first pig, successful needle puncture and the introduction of a 0.014-inch guide wire through an Endurant stent graft was achieved in both renal arteries. Unfortunately, the available guide wire (ATW, Cordis) did not give enough support for the 3-mm PTCA balloon (Maveric, Boston Scientific), and we could not advance the balloon through the fenestration. In the second pig, using a Talent stent graft and a heavy duty guide wire (Mailman, Boston Scientific), a low profile 1.5-mm PTCA balloon (Maveric, Boston Scientific) was advanced into the fenestration, which was then sequentially dilated to 5 mm. A 6-mm/18-mm (Racer, Medtronic) renal stent was delivered into the right renal artery and a 6-mm/28-mm (Jostent, Abbot Vascular Instruments) balloon expandable stent graft was delivered into the left kidney. During the experiment with the third pig, the needle of the Outback device fractured and the procedure had to be discontinued. In the case of completed intervention, the ischemia time was 24 min and 55 min for the right and left kidneys, respectively. The left kidney showed clear signs of ischemic injury when autopsied (Fig. 4). No hematoma was found around the aorta in any of the three pigs, indicating that there was no retroperitoneal bleeding, despite several punctures through the stent graft with the Outback needle.
The left kidney was pale and looking non-viable, indicating a definitive ischemic injury. No signs of hematoma or bleeding were seen around the aorta
Visual inspection of the stent grafts showed no damage to the graft material despite several punctures.
Discussion
In situ fenestration with a re-entry catheter and steerable sheath seems technically feasible, though some refinements have to be made. The warm ischemia time was too long in our experiments and definite renal infarction was found at autopsy. Because the animals were euthanized immediately after the procedure, possible renal failure could not be monitored. Results from clinical human studies indicate that kidney damage occurs when warm ischemia is longer than 30 min, and that the damage is only partially reversible (17). In a test conducted by Riga et al. (12) in which the investigators performed antegrade fenestration into the renal arteries of a pig model with the help of a robot arm (the Sensei system), the total operation time was 45 min, which is also too long for warm ischemia of the kidneys. Tse et al. (13) tested both the Pioneer catheter and Brockenbrough needle in the same setting in a canine model. The Brockenbrough needle performed better, but the ischemia time reached 60 min. Notably, these experiments were conducted with healthy, young animals, in which the anatomy is very straightforward. In humans and real life patients, the anatomy is usually more challenging, leading to catheterization difficulties.
The technical failure of the Outback device that we encountered in one of our experiments is worrisome and could lead to unnecessary delays, prolonging the already long ischemia time. Notably, that Outback device is not indicated for traversing graft fabrics.
The fabric of the Endurant stent graft was also very resilient and made it difficult to advance the relatively low profile 3-mm PTCA balloon through the hole created with the needle. In-vitro testing has also indicated that enlarging the hole in the Endurant graft requires high pressure, up to 24–26 atm (18). The cutting balloon facilitates more effective dilatation of the fabric than the conventional balloon but traversing the prosthesis with this large profile device necessitates previous dilatation with a low profile PTCA balloon (18).
In the first pig, our guidewire was too slack and did not give enough support for the initial balloon to traverse the fabric. Unfortunately, we did not have stiffer guidewires available in the stock of our animal laboratory. Based on this experience, we were better equipped for the second experiment and by a stiffer guidewire in combination with a very low profile balloon, we were able to dilate the fenestration and to stent it.
We used both bare metal stents and stent grafts in our experiments. In pre-fabricated fenestrated stent grafts, bare metal stents were used at the beginning to secure the fenestrations. We advocated to achieve better sealing of the fenestration, which is usually necessary when fenestration is done to achieve adequate proximal neck for the aortic stent graft. Stent graft systems are often quite stiff and their crossing profile is considerably higher than that in bare metal stents. Therefore, it may not be possible to place a stent graft in the fenestration in the situations, when for example renal arteries are accidentally covered by an aortic stent graft. In those situations, the distance between the fenestration and the aneurysm is usually sufficient and there should no bee risk for type III endoleak even if bare stents are used.
As far as we know, the different fabrics respond differently to puncture and balloon dilatation (18), it would be worthwhile to test different kind of stent grafts also in-vivo conditions.
Based on our experiments, we cannot recommend this technique in elective interventions. However, in bailout situations when the renal artery is inadvertently covered during an operation, the end organ could be salvaged by fenestration of the graft with the Outback device. Surgical revascularization can be an option on some patients. However, most of the patients, who are considered as candidates for endovascular aortic repair have several co-morbidities and tend to be older and cannot tolerate major surgery.
In conclusion, as the risk of complications of this method, such as retroperitoneal hematoma, seems to be scarce, we do not hesitate to try fenestration as a bail out procedure if there is risk of losing the functioning kidney. A steerable sheath facilitates the catheterization and appears to be mandatory to achieve enough support for the re-entry catheter. A stiff guide wire and very low profile balloon are obligatory when traversing the fabric and enlarging the fenestration for the side branch stent.