Factors influencing enlargement rate of small abdominal aortic aneurysms

The purpose of this study was to determine the factors influencing enlargement rate of small abdominal aortic aneurysms. Fifty-seven high-risk patients with asymptomatic abdominal aortic aneurysms initially measuring 3.5 to 5.9 cm in the largest transverse diameter were followed with serial echographic measurements for 6 to 78 months (mean 24). The mean enlargement rate (MER) and the occurrence of sudden change in size (SCS) for each aneurysm were correlated to 23 variables. MER ranged from 0 to 1.8 cm/year (mean 0.48). During the study period 17 aneurysms showed SCS. The results of univariate analysis indicated that 8 variables were statistically correlated to the degree of MER and 5 to the occurrence of SCS. A multiple regression model was generated by stepwise regression analysis and demonstrated that 2 variables were independent predictors of the degree of MER: (1) the absence of distal arterial occlusive disease and (2) the ratio of the diameter of the aneurysm to that of the aorta (RD). The overall model P value was less than 0.001. A statistically valid multiple regression model to predict the occurrence of SCS was not feasible (P = 1.0). We conclude that the occurrence of SCS of small abdominal aortic aneurysms is often unpredictable and that the RD rather than the value of the aneurysmal diameter per se must be considered in selecting high-risk patients for echographic follow-up.