Morphological factors associated with progression of subaneurysmal aortas

Abstract

Background: The aim of this population-based cohort study was to assess the association between aortic morphological baseline factors in 65-year-old men with subaneurysmal aortic diameter (25-29 mm) and risk of later progression to abdominal aortic aneurysm (AAA) generally considered to be at a diameter for repair (at least 55 mm).

Methods: Men with a screening-detected subaneurysmal aorta between 2006 and 2015 in mid-Sweden were re-examined using ultrasonography after 5 and 10 years. Cut-off values for baseline subaneurysmal aortic diameter, aortic size index, aortic height index, and relative aortic diameter (with respect to proximal aorta) were analysed using receiver operating characteristic (ROC) curves, and their associations with progression to AAA diameter at least 55 mm evaluated by means of Kaplan-Meier curves and a multivariable Cox proportional hazard analysis adjusted for traditional risk factors.

Results: Some 941 men with a subaneurysmal aorta and median follow-up of 6.6 years were identified. The cumulative incidence of AAA diameter at least 55 mm at 10.5 years was 28.5 per cent for an aortic size index of 13.0 mm/m2 or more (representing 45.2 per cent of the population) versus 1.1 per cent for an aortic size index of less than 13.0 mm/m2 (HR 9.1, 95 per cent c.i. 3.62 to 22.85); 25.8 per cent for an aortic height index of at least 14.6 mm/m (58.0 per cent of the population) versus 2.0 per cent for an aortic height index of less than 14.6 mm/m (HR 5.2, 2.23 to 12.12); and 20.7 per cent for subaneurysmal aortic diameter 26 mm or greater (73.6 per cent of the population) versus 1.0 per cent for a diameter of less than 26 mm (HR 5.9, 1.84 to 18.95). Relative aortic diameter quotient (HR 1.2, 0.54 to 2.63) and difference (HR 1.3, 0.57 to 3.12) showed no association with development of AAA of 55 mm or greater.

Conclusion: Baseline subaneurysmal aortic diameter, aortic size index, and aortic height index were all independently associated with progression to AAA at least 55 mm, with aortic size index as the strongest predictor, whereas relative aortic diameter was not. These morphological factors may be considered for stratification of follow-up at initial screening.

Fig. 1

Flow chart of cohort of men with a subaneurysmal aorta measuring 25–29 mm at baseline ultrasound screening Causes of death of 176 men with a subaneurysmal aorta (SAA), regardless of follow-up time: malignancy 73; cardiac disease 40; pulmonary disease 15; stroke 10; trauma 6; sepsis 5; ruptured iliac aneurysm 1; other 13; unknown 13. AAA, abdominal aortic aneurysm; rAAA, ruptured AAA; EVAR, endovascular aortic repair; OR, open repair.

Fig. 2

Subaneurysmal aortic diameters at initial ultrasound screening Data are shown for 941 men. SAA, subaneurysmal aorta.

Fig. 3

Kaplan–Meier estimates of cumulative incidence of baseline subaneurysmal aortic diameter, height, and body surface area with abdominal aortic aneurysm at least 55 mm as outcome variable a Aortic size index (AHI) 13.0 mm/m² or more versus less than 13.0 mm/m²; b aortic height index (AHI) 14.6 mm/m or more versus less than 14.6 mm/m; c subaneurysmal aorta (SAA) (anteroposterior) diameter 26 mm or more versus less than 26 mm; and d SAA (anteroposterior) diameter stratified by size in millimetres.

Fig. 4

Kaplan–Meier estimates of cumulative incidence of relative subaneurysmal aortic diameter to proximal aorta at baseline with abdominal aortic aneurysm at least 55 mm as outcome variable a Relative aortic diameter quotient 12.0 or more versus less than 12.0; b relative aortic diameter quotient 50% or more versus less than 50%; and c relative aortic diameter difference 5.0 mm or more versus less 5.0 mm.