Low Guideline Compliance for AAA May Increase Rupture Risk After EVAR


The majority of patients receiving endovascular repair for an aortic abdominal aneurysm failed to meet criteria for intervention as opposed to surveillance, and more than 58% of these patients failed to meet conservative criteria for device use based on manufacturer instructions, according to a large retrospective database study.

In addition, at 5 years post EVAR, 41% of the patients showed aneurysm sac enlargement, an outcome considered a surrogate for potential aneurysm rupture, according to a report published online April 10 in Circulation.

This is an important issue because "in 2006, 21,725 EVAR procedures were performed in the United States, exceeding for the first time the number of open surgical AAA repairs," according to Dr. Andres Schanzer of the University of Massachusetts, Worcester, and his colleagues at the Harvard School of Public Health, Boston, and the Cleveland Clinic Foundation.

In addition, although studies have demonstrated substantially lower morbidity and mortality after EVAR than after open repair, "late survival of these cohorts has demonstrated that the early survival advantage of patients undergoing EVAR disappears with time and a significant proportion of late deaths after EVAR are due to aneurysm rupture."

Dr. Schanzer and his colleagues conducted a retrospective analysis of patients in M2S Inc.’s imaging database. M2S has served as the core imaging laboratory for several large aneurysm management trials and provides these services to both public and private academic hospitals globally. The study population consisted of 10,228 patients who underwent EVAR for AAA repair in 1999-2008, and who had a baseline CT scan before EVAR and at least one follow-up CT scan. The patients were primarily men (84.1%) with a mean age of 73.9 years, and represented all regions of the United States.

Key anatomical measurements included maximum AAA sac diameter, aortic diameter at the lowest renal artery, aortic neck length (distance between the lowest renal artery and the origin of the aneurysm, indicated by a 10% increase in diameter), aortic neck angulation (angle calculated between the lowest renal artery, the origin of the aneurysm, and the aortic bifurcation), conical neck (aortic diameter at 15 mm below the lowest renal artery greater than or equal to 10% larger than the aortic diameter at the lowest renal artery), AAA volume, maximum common iliac diameter, and length from the lowest renal artery to the aortic bifurcation. Data on the exact endovascular device used were not available, and there were no data available regarding secondary interventions (Circulation 2011 April 10 [doi:10.1161/CIRCULATIONAHA.110.014902]).

The instructions for use (IFU) for each approved endovascular device was reviewed, and these criteria were incorporated into three descriptive variables: conservative IFU (most restrictive), liberal IFU (least restrictive), and time-dependent IFU (reflecting the most liberal IFU at each time point during the study period).

The primary end point was AAA sac enlargement (defined as a growth of 5 mm or more in the AAA maximal diameter from before EVAR to any post-EVAR CT scan, based on Society for Vascular Surgery reporting standards). The secondary end point was endoleak (defined as the presence of contrast-opacified blood within the aneurysm sac and outside the endovascular stent graft).

The average preoperative AAA maximum diameter was 54.8 mm, with 6,075 patients (59%) having an AAA maximum diameter of less than 55 mm. The average neck diameter was 23.1 mm, with a mean length of 20.7 mm and a mean angle of 36.9 degrees. In addition, 11.9% were found to have at least one common iliac aneurysm greater than 20 mm in diameter.

When all patients were classified according to IFU criteria, 5,983 patients (58.5%) were outside compliance with the conservative IFU, 3,178 patients (31.1%) were outside the liberal IFU, and 4,507 patients (44.1%) were outside the time-dependent IFU.

Population characteristics changed over the 10-year study period. An increasing number of patients undergoing EVAR were 80 years of age or older; the maximum AAA diameter before EVAR did not significantly change over time, but the average diameter of the AAA neck did increase significantly; and significantly more patients undergoing EVAR had highly angulated aortic necks (7.0% in 1999-2003 vs. 9.5% in 2008) or conical aortic necks (30% vs. 35.7%). In addition, the external iliac diameter in patients decreased significantly over the study period, with 14.8% having both external iliac arteries measuring less than 6 mm in 1999-2003, compared with 17.5% in 2008.

Mean follow-up was 31 months, with an average of three postoperative CT scans per patient. At 1, 3, and 5 years after EVAR, AAA sac enlargement was seen in 3%, 17%, and 41% of patients, respectively.


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