Twelve cohort studies were included in the review (n=11,933 patients; 2,469 in the statin groups and 9,464 in the control groups). There were 11 retrospective cohort studies and one prospective cohort study. Quality scores for the studies ranged from 3 to 8 (seven studies were considered to be of high quality). Maximum follow-up ranged from two years to over five years.
Expansion rate (seven studies, n=4,197 patients): A reduction in abdominal aortic aneurysm expansion rate was found in patients taking a statin compared with those who did not (SMD -0.37mm/year, 95% CI -0.65 to -0.08; I2= 89%). When the analysis was restricted to studies with over 200 patients, or to high quality studies, no significant treatment effects were found between the two groups and heterogeneity was substantially reduced.
30-day mortality rate after aneurysm repair (two studies, n=6,293 patients): No significant between-group difference was found in 30-day mortality following abdominal aortic aneurysm repair (OR 0.22, 95% CI 0.02 to 2.90; I2=71%). Sensitivity analysis was not possible.
Short-term and long-term mortality rates after aneurysm repair (four studies, n=7,335 patients): A significantly lower mortality rate was found at one year (OR 0.44, 95% CI 0.25 to 0.76; I2 =59%), two years (OR 0.43, 95% CI 0.25 to 0.72; I2=72%) and five years (OR 0.57, 95% CI 0.42 to 0.79; I2=67%) after abdominal aortic aneurysm repair in patients taking statins compared with those who were not. When the analysis was restricted to studies with over 200 participants, or to high quality studies, the estimates remained significantly unchanged from the overall analysis. Significant statistical heterogeneity was found for all sensitivity analyses, except at one year follow-up.
Funnel plots for abdominal aortic aneurysm expansion, as well as two-year and five-year mortality lacked symmetry, which suggested the possibility of publication bias. The funnel plot for one-year mortality demonstrated adequate symmetry.