Evidence for Endovascular Repair
Two randomized European trials comparing EVAR to open surgery (OS) and 1 randomized trial comparing EVAR to no intervention were published in 2005.The first was the Dutch Randomized Endovascular Aneurysm Management (DREAM) trial, randomizing 351 patients with asymptomatic AAAs >5 cm in diameter with suitable stent graft anatomy to OS or EVAR. This study suggested a 30-day benefit in mortality favoring EVAR (1.2% EVAR versus 4.6% OS; P=0.10).The trend toward an early mortality advantage was lost, however, 12 months into the 2-year study follow-up.
The second trial, from the United Kingdom, labeled EVAR trial 1 (EVAR 1) was similar to DREAM in comparing EVAR to OS in patients with suitable stent graft anatomy and aneurysm size 5.5 cm.28 This study randomized a large group of patients (1082), with 94% receiving their allocated treatment. EVAR 1 more clearly demonstrated an early perioperative mortality benefit for EVAR (1.7% EVAR versus 4.7% OS; P=0.009).31 Blood product use and length of hospital stay also favored EVAR. In contrast, the primary end point of all-cause mortality did not show a lasting benefit for EVAR at the 4-year study conclusion, although aneurysm-related death was decreased (3.5% EVAR versus 6.3% OS; P=0.02). Complication rates (17.6 per 100 person-years EVAR versus 3.3 per 100 person-years OS; P<0.0001) and reintervention rates (6.9 per 100 person-years EVAR versus 2.4 per 100 person-years OS; P<0.0001) were much higher for stent graft repair than for open repair.
EVAR trial 2 (EVAR 2) randomized 338 patients >60 years of age with aneurysms 5.5 cm who were deemed unfit for open surgical repair to EVAR or no intervention. Between the 2 arms of the study, 142 patients died during follow-up, which correlated to a 64% overall mortality by Kaplan–Meier estimates at 4 years. This study was complicated by long delays in EVAR after randomization and a 27% patient crossover rate from the no intervention group. In the final analysis, no benefit to EVAR over medical management was detected in either overall mortality or aneurysm-related mortality for patients unfit for open surgery.
Ongoing in the United States is the Open Versus Endovascular Repair (OVER) trial, a 9-year study that began in 2002 comparing endovascular aneurysm repair with standard open surgery using a multicenter randomized trial through the Department of Veteran Affairs (VA) Cooperative Study Group.
Clinical Use
The FDA approved the transluminal stent graft treatment of abdominal aortic aneurysms in 1999. Whereas 2 devices were initially approved, AneuRx by Medtronic (Minneapolis, Minn) and Ancure by Endovascular Technologies Inc (EVT; Menlo Park, Calif), the Ancure device was removed from the market in 2001 after the company failed to submit >2500 medical device reports to the FDA. Three additional devices now also hold FDA approval, including the Zenith (Cook Inc, Bloomington, Ind), Excluder (W.L. Gore and Associates, Flagstaff, Ariz), and Powerlink (Endologix Inc, Irvine, Calif) systems. Multiple other stent grafts bearing the CE (Conformité Européenne) mark are employed in Europe after demonstrating safety for their intended use. Many stent grafts have undergone modification, with resulting technologies in the third generation and beyond. Despite the diversity among the devices, a generalized discussion of device implantation is indicated.
Preprocedural planning is the most critical component of a technically successful endovascular abdominal aortic aneurysm repair. CT provides the backbone for evaluating patient candidacy. In addition to the indications of either an asymptomatic aneurysm of appropriate maximal diameter, or a small aneurysm with features putting it at increased risk of rupture, patients being considered for EVAR must fulfill several anatomic criteria. These include -
- lliofemoral access vessels that will allow safe insertion and deployment of the device, adequate seal, and sufficient length to provide axial support for the graft
- An infrarenal aortic neck of adequate length, limited angulation, and appropriate diameter. These anatomic features, as well as the presence or absence of thrombus and calcium at each level, can be evaluated using CT.
Complications of Endovascular Aneurysm Repair
The numbers of adverse events possible with EVAR are many, because it is a technically complex procedure typically performed on a high-risk patient population. One of the most common adverse events is the need for a secondary intervention of some type. Data from the EUROpean collaborators on Stent/graft Techniques for aortic Aneurysm Repair (EUROSTAR) registry of 2846 patients treated from December 1999 until December 2004 revealed that EVAR resulted in a cumulative incidence of secondary interventions of 6.0%, 8.7%, 12%, and 14% at 1, 2, 3, and 4 years, respectively. Secondary interventions are typically performed when the aneurysm sac has become repressurized because of incomplete exclusion of blood flow from the sac. The term “endoleak” was created to describe this complication in 1996, and a classification scheme has been adopted.Type I and type III endoleaks are treated with immediate intervention to halt perigraft flow or flow between modular components. Type II endoleaks are typically managed expectantly with intervention reserved for persistent endoleaks in the presence of aneurysm sac enlargement. The presence of a persistent type II endoleak for 6 months, however, has been associated with aneurysm enlargement, increased rate of secondary interventions, and even aneurysm rupture. Type IV endoleaks rarely occur with modern stent graft design, and type V endoleaks (endotension), although still reported, are much less frequent after modification of the Gore Excluder device in 2004 to a low-permeability expanded polytetrafluoroethylene layer. Secondary interventions occur in a spectrum ranging from diagnostic angiography to endograft removal with conversion to open repair, although the majority are percutaneous treatment of type II endoleaks with source embolization.
A related cause of endoleak and potential complication of EVAR is device failure. The integrity of stent graft materials and maintenance of proper positioning within the aneurysm are critical in preventing pressurization of the aneurysm sac and rupture. Material failure includes fracture of any of the metallic components of the stent graft, including stents, hooks, or barbs, or tears in the fabric component of the stent graft. Loss of proper stent graft position can occur for many reasons. Material failure, inadequate proximal or distal seal zone, aneurysm remodeling after EVAR, or features of the vessel, such as thrombus or calcium, that limit stent purchase, have all been implicated in the migration of stent grafts. Each of these modes of failure needs to be analyzed within the context of their clinical significance. A stent fracture that leaves the graft fabric intact and is not in a critical region for maintaining fixation would likely need only follow-up, whereas modular component separation resulting in a large type III endoleak will require urgent intervention to restore stent graft integrity.
Approach to the Small Abdominal Aortic Aneurysm
Whereas randomized clinical trials have focused on establishing the proper use of EVAR for larger aneurysms, its application for the treatment of small aneurysms is still an area of controversy. Early open aneurysm repair for aneurysms <5.5 cm in diameter does not confer a long-term survival advantage. However, retrospective analysis of the large EUROSTAR database revealed that EVAR for aneurysms with diameters between 4.0 cm and 5.4 cm had lower incidence of type I endoleak and improved cumulative freedom from aneurysm-related death relative to 2 comparison groups with aneurysm diameters of 5.5 to 6.4 cm and 6.5 cm. Level 1 evidence is lacking at this time, but the Positive Impact of EndoVascular Options for Treating Aneurysms EarLy (PIVOTAL) and Comparison of surveillance versus Aortic Endografting for Small Aneurysm Repair (CAESAR) trials were initiated in an attempt to provide such evidence. Both are device specific, randomize patients with smaller aneurysms to EVAR or surveillance, and use an FDA-approved Medtronic device or the Cook Zenith device, respectively. Until the results of these trials are published, the optimal management of small aneurysms remains ambiguous and a patient-specific approach that takes into account aneurysm morphology, biology, and patient comorbidities should be used.
Published Clinical Guidelines
The 2005 American College of Cardiology/American Heart Association practice guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic) states that it is reasonable to offer EVAR of infrarenal aortic and/or common iliac aneurysms in patients at high risk of complications from open operations because of cardiopulmonary or other associated diseases and that repair may be considered in patients at low or average surgical risk. Whereas this document proposes a treatment algorithm setting the threshold for surgical repair at 5.5 cm except in cases of rapid expansion, it also states, “Ultimately, once an infrarenal aortic aneurysm reaches an appropriate size for graft replacement, a choice must be made between a traditional open operation or endovascular repair. Like all other aspects of aneurysm management, this decision requires a balanced judgment of relative risks.” Other features, such as saccular aneurysm morphology, patient gender, heredity, uncontrolled hypertension, and chronic obstructive pulmonary disease may also be important considerations.
Conclusions
The patient described in the vignette meets all the recommended criteria for aneurysm repair. His age, ethnic background, and heavy smoking history are typical of patients with this disease process. The absolute aneurysm size and history of rapid expansion suggest that repair would offer a mortality benefit. Before offering EVAR, however, anatomic suitability must be confirmed by an experienced clinician using accurate imaging. Once it is established that the patient is an appropriate candidate for endovascular repair, the risks and benefits of both open and endovascular approaches should be discussed. Given the advanced age and pulmonary morbidity of this patient, endovascular repair would be appropriate therapy.
