Introduction and Background
The introduction of thoracic stent grafts into clinical practice over the past two decades and the ability to image the thoracic aorta in high definition have offered a paradigm shift in the way we have been able to diagnose and to treat thoracic aortic pathologies. Looking at national registry data from 2002–2012, Wang et al. described a majority shift toward endovascular treatment of thoracic aortic aneurysms and dissections. Given the number of products available to date to treat thoracic pathology, it is increasingly important that the vascular surgeon understands the capabilities and limitations for each device used. In 2009, Medtronic introduced the Valiant thoracic stent graft with Captivia delivery system to the US market. In 2018, Medtronic received CE mark approval for the Valiant Navion thoracic stent graft system. The Navion device had acceptable safe profiles with a low 30-day perioperative mortality of 2.3% and secondary procedures at 2.3%. Type Ia endoleaks at 1.2% at 1-month imaging follow-up. The Valiant thoracic stent graft is essentially a tube graft composed of polyester graft fabric that is scaffolded by nitinol wires sewn on the outside of the graft, together with nonabsorbable sutures. There is no longitudinal backbone metal support, allowing the advantage of the graft to conform to tortuous patient anatomy. There are several configurations of the graft available, giving a physician the ability to choose between proximal and distal bare-spring extension fixation as well as tapered grafts to accommodate size discrepancies. In the case of large flow lumen, large aneurysms in the descending thoracic distal fixation should be considered. The Valiant offers distal strut configuration for fixation and can be augmented with APTUS fixation systems to prevent device migration in the dynamic thoracic aorta.
Radiopaque markers are embedded into the graft to allow precision deployment at the proximal and distal fabric lines. There are four markers shaped as a figure 8, which delineate the proximal fabric edge. In the midgraft there is a single figure 8 marker showing the minimum amount of overlap needed to treat the longer aortic segments.
The Captiva delivery system is designed for the proximal bare-metal stent thoracic pieces. It allows recapturing and repositioning the stent graft in the event of malpositioned deployment. The deployment system for the closed web stent graft components does not allow recapturing because of the lack of front end bare-metal stent pieces. This ability to recapture the proximal seal zone can be advantageous for precise deployment in zone 0–1 settings.
The indications for use for the Valiant thoracic stent graft with the Captiva delivery system is to repair fusiform aneurysms, saccular aneurysms, and penetrating ulcers of the descending thoracic aorta in patients with appropriate anatomy, including: iliac–femoral vessels compatible with vascular access techniques, devices and accessories, nonaneurysmal aortic diameter ranging from 18 to 42 mm (44 mm for traumatic dissections), and nonaneurysmal aortic proximal and distal neck lengths >20 mm.
Unique to this graft, it does not require a separate sheath and can be barebacked into the patient for lower profile access arteries. The outer diameter of the device (24 French) is on a par with being the lowest available on the market up to 2017. When barebacked, the device has its own hydrophilic lining, allowing ease of delivery and less tissue trauma.
In terms of the safety profile of the device, Conrad et al. demonstrated the 5-year safety data showing a 94.8% freedom from aneurysm-related death, 89% sac showing no growth or shrinking aneurysm, no loss of stent graft integrity, no migration and loss of patency. In terms of endoleaks, Type I endoleaks as an aggregate of the data showed a rate of 7.2% and Type II endoleaks with a rate of 10.7%.
Device Insertion and Deployment
The delivery and deployment of the Valiant Captiva system can be tailored to the operator’s preferences. Based on operator experience, the case will start with obtaining bilateral common femoral artery access. This can be done percutaneously with US guided access and preclosure technique, with the deployment of two Proglide sutures or by an open cutdown. On the contralateral side, a 5-French sheath is placed for a marking flush catheter placed in the proximal aorta and used for an angiogram. On the ipsilateral side, a double curve Lunderquist wire is placed near the aortic root. The wire is delivered through a catheter after systemic heparinization. The device is then mounted on the wire and barebacked into the aorta. A thoracic aortic angiogram is then performed to map the anatomy.
Once the origins of the vessels are marked, the device is positioned. A technical point of note is that during deployment, the Lunderquist wire should have some inward pressure applied to allow the wire to create good outer aortic wall opposition. This allows the device to deploy primarily along the outer curve precisely with relation to the arch vessels and effective seal zone.
To ensure precise deployment at the proximal landing zone, there is benefit to dampening the cardiac impulse. This can be achieved in a variety of mechanisms including pharmacological manipulation, temporary rapid cardiac pacing, or with preload reduction via IVC transient balloon occlusion.
An uncommon event occurs when the thoracic aneurysm is so large that the outer curve of the aneurysm affects the wire bias and deployment of the graft. The physician should then deploy a maximum of two stent pieces so that the Captiva constraining mechanism can allow repositioning of the graft if it becomes displaced by the vacuum of the aneurysm’s size.
A point of consideration: if multiple pieces are to be used, the device should be placed in a separate sheath to allow bloodless exchanges.
The clinician at this point has a choice between rapid and slow deployment. Slow deployment is accomplished by turning the large blue handle on the device while keeping the gray (graft) portion secure to prevent any graft migration. If using the Captiva product with bare-metal fixation, the proximal portion of the graft is still partially constrained. A rapid deployment is accomplished by pressing the trigger on the blue handle and dragging the blue away from the fixed gray portion of the deployment system. If Captiva fixation is used, a secondary constraining mechanism is in place that needs to be turned and pulled off to release the bare-metal proximal fixation. Once deployed, the delivery system can be pulled into the abdominal aorta and, depending on the aortic pathology being treated, the final angiogram can be performed with or without the pigtail being repositioned in the proximal aorta. If repositioning is done, the catheter should be straightened with a wire before repositioning so as not to drag on the graft. It is a relatively rare occurrence that the graft will require balloon angioplasty, but if a Type I endoleak occurs, gentle angioplasty should be the first maneuver. If the graft is placed for dissection, oversizing should be minimized and angioplasty is not recommended. During removal of the large sheath, the anesthesiologist should be made aware and communication about blood pressure drop should be noted in case the iliac artery has an iatrogenic pathology. Closure is then completed as per routine.
In the event of graft cover severance, which leads to the graft not deploying, the physician will need to disassemble the delivery system manually. The first step is to retract the blue slider all the way back. Take a hemostat and locate the manual disassemble ports on the gray portion of the graft. Push in the ports until a loud pop is heard; this will need to be done on both sides. Step three is to stabilize the delivery system and to advance the front grip forward. Doing so allows the screw gear to be separated in halves. This exposes the graft cover severance from the main delivery system. Then using hemostat, the graft cover can be pulled back while fixating the graft. This is depicted in Figs. 23.1–23.5 .