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Relative importance of aneurysm diameter and body size for predicting AAA rupture in men and women
Ruby C. Lo, MD1, Bing Lu, MD/PhD2, Mark F. Conrad, MD3, Mark F. Fillinger, MD4, Robina Matyal, MD1, Allen D. Hamdan, MD1, Marc L. Schermerhorn, MD1.
1Beth Israel Deaconess Medical Center, Boston, MA, USA, 2Brigham & Women's Hospital, Boston, MA, USA, 3Massachusetts General Hospital, Boston, MA, USA, 4Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA.

OBJECTIVES
Women have an increased risk of AAA rupture at any given aneurysm diameter compared to men. The accepted 5.5cm repair threshold was derived from natural history studies based primarily on men. We evaluated the relationship between rupture and aneurysm diameter relative to body size for men and women with the goal of testing a novel method of rupture risk stratification that is more appropriate for women.
METHODS
We reviewed all patients in the VSGNE database who underwent endovascular or open AAA repair. We evaluated height, weight, body mass index (BMI) and body surface area (BSA) as well as each of these values indexed to the aortic diameter [e.g. BSA index = aneurysm diameter (cm) / BSA (m2)]. Along with other relevant clinical variables, we constructed multivariable-adjusted logistic regression models using forward selection to determine predictors of rupture repair vs. elective repair. Models for men and women were developed separately and different models were compared using the area under the curve (AUC).
RESULTS
We identified 4045 patients who underwent AAA repair (11% ruptured, 53% EVAR, 78% male). Women had significantly smaller diameter aneurysms, lower BSA, and higher BSA indices than men (Table). For men, the primary determinant of rupture was aneurysm diameter (AUC = 0.82), (<55mm: referent); (55-64mm: OR 0.9, 95% CI 0.5-1.7, P=.771); (65-74mm: OR 3.9, 95% CI 1.9-1.0, P<.001); (≥75mm: OR 11.3, 95% CI 4.9-25.8, P<.001). In contrast, for women, BSA index was most predictive of rupture (AUC = 0.81), with higher odds of rupture at higher BSA indices (<25: OR 3.9, 95% CI 0.5-28.2, P=.175); (25-29: OR 3.3, 95% CI 0.8-14.5, P=.111);(30-34: referent);(35-39: OR 6.4, 95% CI 1.7-24.1, P=.006); (≥40: OR 9.5, 95% CI 2.3-39.4, P=.002). For women, aneurysm diameter alone was not a significant predictor of rupture after adjusting for BSA index.
CONCLUSION
Aneurysm diameter indexed to body size is the most important determinant of rupture for women whereas aneurysm diameter alone is most predictive of rupture for men. Women with the largest diameter aneurysms and the smallest body sizes are at the greatest risk of rupture.
TABLE. Demographics and multivariable predictors of ruptured repair.
MenWomen
Demographics(n=3138)(n=907)P
Age in yrs, mean (SD)71.9 (8.7)74.3 (7.7)<.001
Aneurysm Diameter, mm<.001
20-54mm, n (%)1032 (32.9)368 (40.6)
55-64mm, n (%)1170 (37.3)350 (38.6)
65-74mm, n (%)452 (14.4)111 (12.2)
75+ mm, n (%)483 (15.4)78 (8.6)
BSA, m2*<.001
<1.8m2, n (%)%405 (12.9)551 (60.7)
1.8-1.9m2, n (%)%1073 (34.2)258 (28.5)
2.0+ m2, n (%)%1660 (52.9)98 (10.8)
BSA Index**<.001
<25cm/m2, n (%)%668 (21.3)77 (8.5)
25-29cm/m2, n (%)%1136 (36.2)231 (25.5)
30-34cm/m2, n (%)%678 (21.6)297 (32.7)
35-39cm/m2, n (%)%342 (10.9)171 (18.8)
40+cm/m2, n (%)%314 (10.0)132 (14.5)
Predictors of Ruptured RepairOR (95% CI)¥POR (95% CI)£P
Aneurysm Diameter, mm
20-54mm, %1.01.0
55-64mm, %0.9 [0.5-1.7]0.81.1 [0.3-3.7]0.85
65-74mm, %3.9 [1.9-8.0]<.013.3 [0.8-12.7]0.09
75+mm, %11.3 [4.9-25.8]<.013.2 [0.7-14.5]0.13
BSA Index**
<25cm/m2, %0.6 [0.3-1.4]0.233.9 [0.5-28.2]0.18
25-29cm/m2, %0.8 [0.5-1.5]0.533.3 [0.8-14.5]0.11
30-34cm/m2, %1.01.0
35-39cm/m2, %0.8 [0.5-1.4]0.526.4 [1.7-24.1]<.01
40+cm/m2, %1.4 [0.8-2.6]0.29.5 [2.3-39.4]<.01
*BSA = BSA (m²) = 0.20247 x Height(m)0.725 x Weight(kg)0.425
**BSA Index = aneurysm diameter (cm) / BSA (m2)
¥AUC = 0.82
£AUC = 0.81


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