… VASCULAR SURGERY
Fenestrated endovascular aortic repair grafts
The development of fenestrated endovascular aortic repair (f-EVAR) grafting may make feasible the elective repair of abdominal aortic aneurysms (AAAs) that previously were unsuitable for endovascular repair. Use of the endovascular aortic repair (EVAR) approach has been hampered by the inability to place standard endovascular grafts without compromising flow to the renal and other visceral arterial systems. Endovascular grafts are composed of a nitinol, elgiloy, or stainless steel frame covered by a fabric, such as Dacron. Fenestrated grafts have the same configuration as traditional endovascular grafts, but openings in the material allow the graft to be placed over the orifice of the visceral vessel. Stents are then deployed into the visceral vessel, thereby connecting the visceral artery to the graft. Currently, fenestrated grafts have to be custom made. However, continued research is expected to produce fenestrated grafts that will accommodate a large portion of the population and can be “on the shelf” and ready to use.
>THE f-EVAR PROCEDURE
EVAR grafts have revolutionized the treatment of AAAs by reducing mortality and morbidity compared with the standard open approach.1,2 However, according to estimates, more than 50% of patients with an AAA cannot undergo endovascular repair using the currently commercially available devices because of unfavorable anatomy.3 The most common problem is lack of a suitable length of aorta just below the renal arteries (the aortic neck), where the proximal end of a conventional endovascular graft can land. Fenestrated aortic grafts were designed to extend the proximal sealing portion from this infrarenal segment to the juxtarenal and suprarenal aortic areas without compromise of renal or other visceral arterial system blood flow. CT scans provide measurements for the diameter and length of the aneurysm and determine the position of visceral arteries. Based on these measurements, a custom-made graft can be produced that includes fenestrations in the graft material that match the openings to these visceral vessels from the aorta.
Most commonly, with the patient undergoing general anesthesia in a surgical-radiologic hybrid room, one or both femoral arteries are exposed and the percutaneous access for insertion of the deployment device is created. The fenestrated main body is then completely deployed in the proximal abdominal aorta via the percutaneous route utilizing the femoral artery access. Deployment of visceral vessel stents through the fenestrations follows. The combination of the f-EVAR and subsequent stents achieves sealing of the aneurysm at the level of the visceral-aortic origin while preserving blood flow through the visceral arterial branches. In most cases, the entire aneurysm is excluded by the additional placement of graft components extending the graft inferiorly into the iliac arteries. The deployment devices are removed, and closure of the arteriotomy and/or repair of the femoral artery is accomplished along with closure of the incision.
In one retrospective cohort comparison study, 107 patients not eligible for EVAR were identified. Of this group, 54 underwent open repair and 53 underwent f-EVAR. The mortality outcomes reflected an observed crude risk reduction in the f-EVAR group of 5.5% when compared with open repair (9.2% vs 3.7%). The study then went on to calculate a hypothetical scenario in which the f-EVAR cohort underwent open repair utilizing the Vascular-Physiological and Operative Severity Score for the enUmeration of Mortality and Morbidity (V-POSSUM), a risk-adjusted scoring system for predicting 30-day mortality in patients undergoing vascular surgery. According to V-POSSUM, seven deaths (13.2%) would have occurred, resulting in an estimated risk-adjusted absolute risk reduction for f-EVAR of 9.5%.4 Only prospective randomized trials will prove this calculation correct.
>POSTOPERATIVE COURSE AND MONITORING
Successful deployment of the graft, along with an incidentfree intraoperative and postoperative course, can allow the patient to be discharged home on the following day. Patients typically return to normal activity within 1 to 2 weeks, depending on their overall preoperative health and pain tolerance for the groin incisions. The incisions are inspected 1 to 2 weeks postoperatively, and patients undergo lifelong monitoring of the graft repair.
Despite a significantly lower intraoperative and postoperative morbidity and mortality when compared with open repair, EVAR does carry a higher incidence of potential long-term problems. Some complications of EVAR and f-EVAR include stent graft migration, kinking, infection, thrombosis, and renal dysfunction. The most important complication to detect is continued aneurysm expansion leading to eventual rupture, which can occur even after successful f-EVAR or EVAR. In addition, f-EVAR carries concern for end-organ ischemia if the stents into the visceral arteries thrombose or the graft migrates up or down or twists from its intended position, causing disassociation of the stented visceral vessels and the potential for endograft leak and visceral vessel compromise.
Of all the potential complications of either EVAR or f-EVAR, endoleaks are the most common and require the most significant intervention. An endoleak is persistent blood flow outside the lumen of the graft but within an aneurysm sac or adjacent vascular segment being treated by the device. Endoleaks result from incomplete sealing or exclusion of the aneurysm sac and thus cause reflux of blood flow into the sac. Four types of endoleaks are currently known:
- Type I: blood flow into the aneurysm sac due to incomplete seal or ineffective seal at the end of the graft. This type of endoleak usually occurs early in the treatment course, especially at the time of graft deployment, but it may also occur later. A type I endoleak requires urgent intervention, usually with further endovascular procedures.
- Type II: blood flow into the aneurysm sac due to opposing blood flow from collateral vessels. In the case of abdominal aneurysms, the paravertebral vessels are usually involved. This is the most common endoleak and may or may not require intervention. More frequent surveillance and monitoring of progression is required for decision making.
- Type III: blood flow into the aneurysm sac due to inadequate or ineffective sealing of overlapping graft joints or rupture of the graft fabric. Like type I, this endoleak usually occurs early after treatment, due to technical problems, or later, due to device breakdown. It requires urgent intervention.
- Type IV: blood flow into the aneurysm sac due to the porosity of the graft fabric, causing blood to pass through from the graft and into the aneurysm sac. Conservative management, similar to that of a type II endoleak, is appropriate.
As with EVAR, f-EVAR will come at a cost of lifelong imaging surveillance. This is due to the complications described, which can occur any time after the procedure, necessitating reintervention. While not necessary in the early postoperative period, CT imaging is recommended within 5 years of open AAA repair to detect aneurysmal degeneration involving the pararenal aorta, iliac arteries, graft, or anastomotic sites. Following EVAR, the most widely used surveillance regimen includes multiphasic contrast-enhanced CT scans at 1, 6, and 12 months and yearly thereafter.5
- Fenestrated endovascular aortic repair (f-EVAR) has the potential to allow a greater number of patients to undergo endovascular repair of abdominal aortic aneurysms.
- The current fenestrated grafts must be customized to the individual patient's vascular anatomy.
- Endoleaks are the most common complication post f-EVAR procedure and may require additional surgical interventions.
>OTHER POTENTIAL f-EVAR INDICATIONS
EVAR can be utilized in repairing ruptured AAAs and has been shown to have significantly lower 30-day mortality and a greater 5-year survival rate than open repair.6 Presently, the use of f-EVAR for emergent repair is difficult because each graft must be constructed to patient specifications. However, some authors have reported that modifications made to nonfenestrated grafts in the operative suite have allowed their use as a fenestrated graft in the emergency situation.7,8
Endovascular repair of AAAs has been embraced by the vascular surgery community. Fenestrated endovascular repair of AAAs is the logical next step to repairing those aneurysms whose anatomy does not provide a secure landing area for the graft below the renal and other visceral vessels. While the early morbidity and mortality reported with endovascular repair is less than with open procedures, additional monitoring and endovascular interventions are necessary with EVAR. Those same issues are presumed to persist with interventions utilizing f-EVAR, along with the additional concern for endorgan ischemia. In addition to fenestrated grafts, grafts with scallop, “chimney,” and side branch configurations are being developed. PAs need to keep abreast of developments and understand the benefits and concerns associated with these applications in order to guide and monitor patients whose conditions are suitable for these emerging interventions.
1. Ren S, Fan X, Ye Z, Liu P. Long-term outcomes of endovascular repair versus open repair of abdominal aortic aneurysm. Ann Thorac Cardiovasc Surg.
2. Nedeau AE, Pomposelli FB, Hamdan AD, et al. Endovascular vs open repair for ruptured abdominal aortic aneurysm. J Vasc Surg.
3. Ricotta JJ 2nd, Oderich GS. Fenestrated and branched stent grafts. Perspect Vasc Surg Endovasc Ther.
2008;20(2):174-187; discussion 188-189.
4. Canavati R, Millen A, Brennan J, et al. Comparison of fenestrated endovascular and open repair of abdominal aortic aneurysms not suitable for standard endovascular repair. J Vasc Surg.
6. Mehta M, Byrne J, Darling RC 3rd, et al. Endovascular repair of ruptured infrarenal abdominal aortic aneurysm is associated with lower 30-day mortality and better 5-year survival rates than open surgical repair. J Vasc Surg.
7. Oderich GS, Ricotta JJ 2nd. Modified fenestrated stent grafts: device design, modifications, implantation, and current applications. Perspect Vasc Surg Endovasc Ther.
8. Ricotta JJ 2nd, Tsilimparis N. Surgeon-modified fenestrated-branched stent grafts to treat emergently ruptured and symptomatic complex aortic aneurysms in high-risk patients. J Vasc Surg.