In February 2016, the first patient was enrolled in a physician-sponsored investigational device exemption study of the Valiant Thoracoabdominal Aortic Aneurysm Stent Graft System (Medtronic). Patrick Kelly, MD, performed the first procedure. Dr. Kelly developed the concept for the system and performed the study’s first procedure. Vascular Disease Management spoke with Dr. Kelly about the first procedure and the potential benefits of using this new device.
VDM: What are the current limitations that clinicians face today in treatment of thoracoabdominal aortic aneurysm?
Kelly: Open repair for thoracoabdominal aneurysm is a major undertaking. Four years ago, we treated the first patient with this stent graft system with compassionate use. Six months prior to that, I treated 2 patients with open repair, and both patients experienced serious complications, including paraplegia, bowel ischemia from material embolizing into the colon, and renal failure. I’ve heard lectures that quote a 25% in-hospital mortality rate with open thoracoabdominal aneurysm repair in most medical centers. There will be a few medical centers that will claim less than 5% in-hospital mortality, but that is not a reproducible number in the vast majority of centers. And most of our patients are found around the vast majority of centers, not the 3 or 4 major medical centers that can achieve less than 10% in-hospital mortality for open repair.
Over the last 4 years, we’ve treated 29 patients, and we are currently investigating the safety of this device. We know there are significantly more morbidities and mortalities with open repair. For endovascular repairs, there are currently no FDA-approved devices to treat thoracoabdominal aneurysms that involve visceral vessels. Everything in the United States is still investigational, that being Zenith t-Branch (Cook Medical), the Excluder (W. L. Gore), and the multifenestrated device by Cook Medical. And those devices have some promising utility in certain patient populations, in patients with the right anatomy. So far, we’ve not run into anatomical challenges that we have not been able to treat. That being said, we are currently in an investigational device exemption (IDE) setting to look at that more closely.
VDM: What are the plans for the investigational study?
Kelly: We have an early feasibility IDE through the FDA on a 2-piece system. The system is intended to create what I call “compartmentalized aortic flow.” We divide the aortic flow up the thoracic aorta into the visceral component for the celiac artery, superior mesenteric artery (SMA), and both renal arteries and the infrarenal component for the legs. The benefit of this is that because we divide that flow proximal to the celiac and SMA, we’re not constrained by the patient’s anatomy.
VDM: What makes this device unique?
Kelly: There are 2 very unique characteristics of this device. One is that by compartmentalizing flow in a non-anatomical way, we cannot be constrained by anatomical variations. The other is because we deploy our graft proximally to the visceral segment, there’s continuous uninterrupted flow to the vital organs and into the legs throughout the entire procedure. Other devices currently in use deploy across those vessels. In other devices, the proximal inlet and the distal outlet of the device used to debranch or to fenestrate the aorta, the proximal inlet is above the vessels, and the distal outlet is below the renal arteries. In our design, the proximal inlet and the distal outlet for the debranching component are above the celiac artery, so there’s continuous flow. All 4 vessels are debranched through that manifold. Now, we extend that infrarenal bypass, that infrarenal limb to the iliac arteries and we exclude the entire aneurysm, so we don’t shut the door to all those branches until we’re done securing all those branches. Those are the two biggest differences, and because our design is not anatomically based, it’s built the same every time so it becomes an off-the-shelf device.
VDM: So you can modify it per patient?
Kelly: You do it in situ. You can customize it inside the patient.
VDM: Did you notice anything surprising? An unintended benefit or something that you didn’t expect after you started using the stent graft system?
Kelly: No. It probably doesn’t happen very often, but it worked the way I intended it to work. There’s a thoracic bifurcated graft and then a 4-limb manifold. The 4-limb manifold hasn’t changed in design. The thoracic bifurcation was modified because we had type 3 endoleaks in the first 2 patients, so we quickly changed the design so that we had 2 separate legs in the thoracic bifurcation. Since the third patient, nothing has changed.
VDM: How many patients do you plan to treat in the IDE study?
Kelly: Our IDE is granted for 15 patients before we have to request additional numbers to treat.
VDM: Going forward, how might this system fit into the treatment paradigm for vascular clinicians when they’re treating this type of aneurysm?
Kelly: We found during compassionate use that this device could be particularly useful for thoracoabdominal aneurysms after chronic type B dissections. In a dissection, you can have some of the visceral branches come off of a true lumen and some come off a false lumen. Because they are two different types, or two different lumens, it is very difficult to secure flow to all four of those branches in a chronic dissection. Our design has allowed us to be able to cross into both lumens and keep flow to both kidney arteries. It’s opened the door to that patient population. We still need to run a clinical trial to examine the safety and efficacy, but when we’ve used it in compassionate use for that patient population, it has looked very promising.
VDM: Do you have a favorite patient story?
Kelly: One patient was a 58-year-old female who had both an aortic and mitral valve replaced and severe COPD with forced expiratory volume of 1.01. She was seen at a major medical center and was told there was nothing to offer her because of her underlying comorbidities. We treated her and she’s really done remarkably well.
VDM: What else do vascular clinicians need to know about the device?
Kelly: Often, physicians will say the branches to the renal arteries look too long in this device. If you look at the designs in use today, they have relatively short bridging stents. Our bridging stents are long. However, our design doesn’t break the rules that we’ve learned over the last 70 years in open bypass surgery. We have good inflow, we use good conduit, and we have good outflow. Our branches are a little bit longer (a branch with a length of 50 mm to 70 mm as opposed to 30 mm to 40 mm), but still very short. Because they are longer, the flow that we divert becomes laminar again by the time it gets to the native artery. If you have a very short bridging stent and you seal that blood flow off to go to the kidney or the SMA, it doesn’t have enough time in that bridging stent to get reorganized, so the flow is more turbulent when it finally meets the native vessel. Because our limbs are a little bit longer, we find when we do finite element analysis and other work-ups that by the time our flow gets to the native blood vessel, that flow is laminar again.
I attended LINC this year and heard a talk about the iliac branch device. The presenter said, “I was surprised to find that when the internal iliac branch was longer, it had better patency rates.” The reason for this, we feel, is it allows that flow to redevelop or become laminar again by the time it reaches the native blood vessel.
VDM: Do you think that might translate to other devices for other types of aneurysms?
Kelly: We hope so, because we’re working on other devices. We’ll be submitting a paper looking at our first 29 patients. Of the 108 branches that we’ve placed so far in these patients, 107 remained open. We had one silent occlusion; it occluded and we didn’t know it because kidney function was normal and we found it on an incidental CAT scan. So we have a better than 99% patency rate. Again, I’m not quoting safety and efficacy. In the patients we’ve treated so far, we’ve seen promising results on our patency rates in branches. I think it’s because that flow is allowed to redevelop before it gets to the native vessel.
Editor’s note: Patrick Kelly, MD, is a vascular surgeon with Sanford Health in Sioux Falls, South Dakota. Dr. Kelly reports royalties and patents with Medtronic.