Discussion

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Dr Frank Arko (Dallas, Tex). Dr Deaton and coauthors discuss the early results of the phase I multicenter trial of the Aptus Endovascular Repair System. I congratulate the authors and the manufacturers for completing this initial phase. I have several questions for the authors.

Dr. Deaton, how many EndoStaples are actually necessary for each case to get a satisfactory outcome? What is the pull-out force for a staple in tissue as compared to a silicone model?

What is the learning curve on using these EndoStaples? I am the US principal investigator for a competitive endostapling device that's able to be used with any Dacron stent graft and I believe there is a learning curve to using these devices and I'd like to get your thoughts on what it is with this device.

Next, please comment on neck calcification, thrombus, angulation, and short neck length on the ability to accurately implant your EndoStaple and are any of these factors contraindications to using this endograft?

And then finally, with five currently approved devices within the United States, all of which have excellent 5-year results, can you elaborate on what you believe this repair system adds to the current treatment options?

Dr Deaton. The number of staples required in the phase I study was 2 but 4 was the number generally recommended and was the median number in the study. Only 1 patient received 2 staples and 1 patient had as many as 10. When more than 4 staples were applied, it was usually to address sealing issues. Fundamentally, the intention is to give the operator control over how many staples are needed in their clinical judgment.

While there is undoubtedly a learning curve, the controlled nature of this helical staple deployment provided for early success and no misdeployed staples throughout this initial experience. The positioning of the EndoGuide against the aortic wall followed by an electronically controlled and staged staple deployment made the initial learning curve for users fairly shallow.

With respect to the ability of the staple to penetrate aortic pathology, we don't have any evidence of staples that did not penetrate the tissue they were intended to penetrate. That being said, excessive calcification in the aortic neck is excluded in the trial. While there is ex vivo evidence of staple penetration through calcified aortic plaque, we will probably not understand the limitations of this helical staple until we have a much broader experience in less restricted clinical applications.

With respect to the pullout force, there is early work being done in a tissue model that I think will back up the numbers attained in an artificial silastic model. What is fundamentally different from most other endograft technologies is that the degree of fixation achieved by these staples appears to be related to the tissue into which they are implanted rather than the mechanical integrity of the staple itself. That is to say that what gives way is the tissue rather than the structure of the staple. So if it is weak tissue it will not achieve those high levels of pull-out force just as sutures in open surgery will tear through tissues with poor integrity. Another essential aspect of this type of fixation is that it is easily visualized on postoperative plain x-ray so we will be able to follow any compromise to the staple or any evidence of change in position of a particular staple.

Now, what did I miss?

Dr Arko. I think you got most of them. The last one is – and I'm going to add a little more to it since you made me stand up here – what do you think the advantages of this endograft is over other endografts?

And I'd like to ask you if you could describe the actual stent graft in some more detail including the distance from the top of the graft to the flow divider. I have found that with the shorter bodied stent grafts that it's actually a bit more difficult to implant the staples because I lose some ability to guide the catheter and in the shorter bodied stent grafts I have found it easier to go up both sides to implant the endostaples. Whereas with a longer bodied stent graft, I can really get the staples in from either side. Can you comment on that?

Dr Deaton. With respect to the staple implantation, on rare occasions we have used both limbs to implant staples, but in over 90% of the cases it is easy to implant staples circumferentially from one side. The main body in this study was 4 cm long. In the phase II study, there were 4, 5, and 6 cm body lengths to give the operator better sizing capabilities and to add flexibility to planning for unusual anatomic configurations. As for the body length inhibiting stapling, we have not seen that. The EndoGuide was specifically designed to work in the 4 cm length body and the unsupported nature of the main body also allows more flexibility in staple positioning and deployment.

One of the primary advantages of this endograft system is the possibility of achieving a degree of proximal fixation on a par with a hand-sewn anastomosis. If that proves to be the case, we may well be able to document a treatment paradigm that does not involve the lengthy and potentially dangerous necessity of annual CT scans. Another key advantage of a helical staple is the possibility of preventing future neck dilatation as the “bidirectional” nature of helical staple fixation should hold the aorta to the graft rather than just holding the graft up against the aortic wall. The separation of the fixation delivery from the graft delivery allows an entirely new approach to endograft design that maintains a very high degree of graft structural integrity while bringing the graft delivery catheter caliber down to 16F. There are a variety of other more nuanced features made possible by the design of the endograft that we are still learning about, the most prominent being the non-stented main body and the ability to treat angulated necks, facilitate contralateral cannulation, etc. Beyond the scope of this particular technology, I think any independent fixation technology will allow an entirely new approach to endograft design that will give the operator the ability to treat a broader group of patients more effectively with better long-term results.

Dr Wayne Zhang (Loma Linda, Calif). You use staples for proximal fixation. Do you have any migration after deployment of the stent graft before you put staples?

The second question is are you worried about bleeding? Can the staples cause penetration and bleeding? Do you need to do a CT scan immediately after the procedure?

And another question is, when you deploy the staples, if you have an angled neck, how do you position?

Dr Deaton. We don't see any bleeding from implanting the staples. We haven't seen it in an animal model. And it really is the helical nature of it is much less than what you would do in open surgery.

We do make a point to angle the C-arm so that we're looking straight across that proximal stent, because that is where we like to implant the staples.

And your first question again was?

Dr Zhang. Do you have any migration after deployment of the stent graft before you put staples?

Dr Deaton. Can you move the graft? It can move, but that proximal sealing stent has a fairly high radial force so it's done with some difficulty. But before you do that, when you uncover the entire graft, it's easily mobile at that point.

Dr Wesley Moore (Los Angeles, Calif). Does the device go up bare or are you putting it in through a sheath?

How far beyond the outer wall of the aorta does the staple go? Do you have any concern about puncturing the left renal vein or the cava when you put the staple in place?

Dr Deaton. As far as the staple penetration, it's 4 mm and it's designed to basically just go through the aortic wall. We've not seen any complications related to it. And I've neglected to show you a slide, but it's very different, when you penetrate a vessel with a barb, you have a barb sticking through the aorta. This helical screw has a much lower profile. It doesn't have something sticking up like a nail, if you will.

Dr Moore. Does this go bare or through a sheath?

Dr Deaton. It's designed to go bareback and it can. If they have adequate iliac access vessels, we do place a sheath just to facilitate exchanges and intraoperative imaging but there is no reason you have to place a sheath. The delivery system, as you can see, is tapered and we generally re-jacket the entire delivery system on removing it to prevent any iliac trauma.

Dr Moore. Finally, in one of the patients you mentioned that you placed one or two cuffs proximally. Was that because the graft moved before you had a chance to staple it, or did you staple it and had to place cuffs in addition to that?

Dr Deaton. It wasn't because the graft moved, but I think it was because of some irregularity in the neck that the short stent didn't fulfill the sealing requirements and so we added support to the main body to lengthen the sealing zone. In the phase II study, which is underway now, an aortic cuff designed specifically for this unique endograft system has been added to the portfolio of the system. This allows operators the ability to provide for a longer sealing zone in the main body with the fully-stented aortic cuff positioned within the main body or to extend the length of the main body cephalad when a more distal area is deemed more appropriate for staple implantation.

Dr Jean Panneton (Norfolk, Va). As a co-investigator in the Aptus trial, I can tell you all that it's actually a very slick device. I think the delivery is very intuitive which, as surgeons, we like. I think the learning curve for the EndoStapler is actually pretty short. I think it's also very intuitive to use and very user friendly.

One potential improvement would be shortening the radius of the EndoStapler, especially when there is angulation of the aneurysm neck; I think it would help the stapling.

My concern is the limb occlusion rate. I'm sure you have that same concern. I think you might explain this as technical difficulties or maybe from the iliac anatomy, but do you think there is a need to change the graft to try to prevent this problem? Is it because it is so flexible and does not have columnar strength that it's going to be more likely to kink or occlude in tortuous iliacs?

Dr Deaton. We've had 2 patients with limb occlusions and 1 of those was diagnosed with a severe hypercoagulability condition postoperatively. The other patient with a limb occlusion was likely the result of deploying the limb too low in the docking zone resulting in an unsupported proximal limb that happened to be at an angulated portion of the aorta where the neck terminated into the aneurysm sac. Having said that, there have been several design changes in the endograft system being used in the phase II to provide for better adaptation to tortuosity such that even acute bends of 90° can be accommodated by the graft limbs without luminal compromise.