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Comparison of Long-term Outcomes following Endovascular Repair of Abdominal Aortic Aneurysms Based on Size Threshold
Charles J Keith, Jr., Marc A Passman, Michael J Gaffud, Zdenek Novak, Marjan U Mujib, Thomas C Matthews, Mark A Patterson, William D Jordan, Jr.
University of Alabama at Birmingham, Birmingham, AL

BACKGROUND - Size threshold for operative repair of abdominal aortic aneurysms (AAA) has been determined based on risks and outcomes of open repair versus surveillance. The influence of endovascular repair (EVAR) on this threshold is less established. The purpose of this study is to determine whether long-term outcomes of EVAR are affected by maximum diameter at time of treatment.
METHODS - All patients whom underwent EVAR with modular stent grafts between January 2000 and December 2011 at a single academic institution were identified from a prospectively maintained database. Patients were stratified based on maximum aortic diameter at time of repair: small (4.0-4.9 cm), medium (5.0-5.9 cm), and large (6.0 cm). Comparisons of demographics, indications for repair, and peri-operative complications were made between the groups. Long-term follow-up was reviewed for expansion of the native aneurysm sac 5 mm, secondary intervention involving the native aneurysm or stent graft, and all-cause mortality. Statistical analyses were made using ANOVA, chi square, and Kaplan-Meier plots.
RESULTS - Seven hundred forty patients underwent EVAR with modular stent grafts during the study period: 157 (21.2%) small, 374 (50.5%) medium, and 209 (28.2%) large. Preoperative patient characteristics were similar among the groups with exception to mean age (69.3±8.09, 71.7±8.55, and 73.6±8.77 years for small, medium, and large, respectively; P<0.001), history of coronary artery disease (42% small, 57% medium, 51.2% large; P=0.01), prior coronary angioplasty (14.6% small, 18.2% medium, 9.6% large; P=0.02), congestive heart failure (5.7% small, 15.2% medium, 19.6% large; P=0.01), prior vascular surgery (7% small, 15.8% medium, 10% large; P=0.016), and COPD (21% small, 27% medium, 33% large; P=0.038). Clinical classification differed significantly as a larger percentage of small AAAs were symptomatic (19.7% small, 7.5% medium, 8.1% large; P<0.001). No difference in peri-operative complication rates (P=0.399) or all-type endoleak at any surveillance visit (40.8% small, 41.7% medium, 44.5% large; P=0.73) was observed between the groups. However, the small AAA group developed fewer type I endoleaks (5.1% versus 6.95% medium and 14.8% large; P=0.001). Aneurysm sac expansion 5 mm was observed in 2.6% of small, 5.6% of medium, and 7.2% of large AAAs during the follow-up period but did not achieve a significant difference (P=0.148). Secondary intervention rates differed significantly as 5.1% of small, 7.5% of medium, and 12.9% large AAAs required secondary intervention (P=0.018). In direct comparison with small AAAs, both medium (P=0.39) and large (P<0.001) groups required secondary intervention more frequently with hazard ratios of 2.32 (95% CI: 1.045-5.156) and 4.74 (95% CI: 2.115-10.637), respectively. Overall 10-year survival was 72% in the small, 63.1% in the medium, and 49.8% in the large group (P<0.001) with no known AAA-related deaths. Age-adjusted all-cause mortality differed significantly among the 75-84 year-old group (30.4% small, 51.6% medium, 55.7% large; P=0.017).
CONCLUSIONS - EVAR for small AAAs demonstrates improved long-term outcomes when compared to EVAR for medium and large AAAs. This data suggests that EVAR for AAAs ranging 4-5 cm may have better outcomes than EVAR for age-matched patients with larger aneurysms.


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