Background of the Medtronic Endurant Stent Graft Device
The Endurant stent graft system is an evolution of previous abdominal stent graft systems to meet the challenges of hostile abdominal aortic aneurysm anatomy. After gaining CE marking in Europe in 2008 and FDA approval in 2010, it has become one of the preeminent endograft systems in the world. It consists of a high-density multifilament polyester graft with low porosity, externally supported by a nitinol stent structure ( Fig. 6.1 ).
Proximally, there is a suprarenal fixation system consisting of a nitinol stent with anchoring pins. Next is a series of nitinol stents constructed into a low amplitude sinusoidal M-shape, which allows more flexibility, conformability, and improved seal in short and angulated proximal aneurysm necks. The reduction of columnar strength also contributes to the flexibility of the stent graft. The Endurant II improved upon the previous iteration by extending the hydrophilic coating, loading the 28 mm graft into the smaller 18 French delivery system, introducing more contralateral limb lengths, and increasing the radiopacity of the markers for better visualization. Recently, the Endurant IIs (EIIs) was added to the armamentarium. The EIIs is a 3-piece system with standardized limbs, which allows more options with a smaller range of components and streamlines sizing and inventory.
The Endurant II and EIIs stent graft systems are indicated in treatment of aneurysms with a proximal neck ranging from 19 mm to 32 mm in diameter, length greater than or equal to 10 mm, and infrarenal neck angulation less than or equal to 60 degrees. The Endurant delivery system provides a stepwise, gradual deployment for utmost precision. The tip capture mechanism allows for fine adjustments until the very last moment before release of the suprarenal fixation pins. Combined with its low profile, hydrophilic delivery sheath, the Endurant system has been developed to become an industry standard.
The evolution of the Endurant endograft has not been without its growing pains. Minor, early design flaws and physician inexperience have occasionally resulted in suboptimal deployment, inadvertent occlusion of inflow or outflow vessels, additional procedures, and occasional conversion to an open repair. Some of these difficulties have been eliminated or reduced by improvements in design. For example, the graft fabric was changed to reduce the incidence of Type IV endoleaks ( Fig. 6.2 ), and a minor geometry change to the spindle component of the tip capture mechanism was made right after commercial launch in the United States. However, occasional complications still arise. These issues will be addressed in the following sections, along with some tips in managing these challenging situations.
Endurant Specific Complications
Deployment and Tip Capture
There are very few known issues with the Endurant device that do not apply to all endografts used to treat abdominal aortic aneurysms. One potential area that was identified early after its full clinical release is with the deployment mechanism of the endograft. Once position of the graft is satisfactory, deployment consists of rotating the backend thumb wheel, which advances the constraining tip to release the suprarenal stent and anchor pins ( Figs. 6.3 and 6.4 ). The potential malfunction of this mechanism is addressed within the Medtronic (Minneapolis, Minnesota) Endurant II/IIs Instructions for Use (IFU). In the section labeled ‘‘Bail-Out Techniques’’ the company outlines its recommendations in cases of delivery system failure.
The first situation is if there is partial deployment as a result of graft cover severance. In this incidence, the screw gear handle can be disassembled. This allows for manual retraction of the graft cover, salvaging a potentially devastating complication of a retained, partially deployed endograft. Hemostats can be inserted into the screw gear handle disassembly ports to disengage the front grip from the screw gear. After the front grip is removed, the screw gear can be separated in half to reveal the graft cover, which can then be manually retracted with a clamp.
Another rare situation that may be encountered is if the captured proximal tip of the suprarenal stent cannot be deployed. If the back-end wheel still works, a ballooning technique is described that may allow continued deployment of the endoprosthesis. To accomplish this, a compliant balloon is placed within the main body and inflated to profile. The balloon catheter is used to stabilize the stent graft position, while the tip capture deployment can be carried out per the IFU, followed by delivery system removal. However, if the deployment of the suprarenal stent fails because of a failure of the back-end wheel, the back-end handle can be disassembled to attempt manual disengagement. This involves inserting a hemostat into the rear handle disassembly port, allowing retraction of the handle from the delivery system. The spindle and tapered tip can then be manually advanced/withdrawn by pushing and pulling the exposed tabs of the back-end T-tube. In this situation, backward tension must be maintained on the tabs during system removal to keep the tapered tip recaptured over the spindle. The entire delivery system can then be removed from the patient as usual.
Lastly, the manufacturer discusses a snare technique if the deployment of the suprarenal stent is unable to be completed even after disassembling the back-end handle. A snare is introduced from a brachial or axillary access. Under fluoroscopy, the delivery tip is snared. The snare is then pulled back while stabilizing the distal delivery system from the femoral access. This should facilitate separation of the tip and sleeve from the suprarenal stent, allowing for full deployment. The remainder of the steps for removing the system follows those outlined earlier.
Another step that can be an issue with the Endurant stent graft is with retrieving the tapered tip, sleeve, and spindle after graft deployment ( Fig. 6.5 ). This is relevant particularly in situations of highly tortuous vessels and severely angulated necks. After deployment, the delivery tip must be withdrawn from the aorta, through the stent graft, and out of the femoral access site. There are multiple areas where this can catch during its extraction. Excessive force can lead to migration of the endoprosthesis or injury to the vessels. After identifying this issue with earlier iterations of the device, Medtronic adjusted the design to include a reverse taper on the spindle to streamline the profile. This has greatly reduced the occurrence of this complication with the Endurant II and EIIs endografts.