The aortic size index (ASI) was not found to be superior to the normal aortic diameter (AD) in predicting the development of abdominal aortic aneurysms (AAAs) and aortic growth >5 mm in men and women, according to study results published in the Scandinavian Cardiovascular Journal.

In this study, data from 2 phases of the Tromsø population-based prospective multiphase study were examined.

A total of 6679 patients (ages, 55-74) from the Tromsø 4 phase of the study (conducted between 1994 and 1995), who had an ultrasound of the infrarenal aorta performed, during which the AD was measured and the presence of AAA examined, were included. Of those participants, 5003 patients were re-examined in the Tromsø 5 phase conducted in 2001. A total of 4435 participants were included in both phases, of whom, the data of 4161 patients (53% women; ages, 25-82) were examined, after excluding patients with missing data or those with a reduction in AD >5 mm or with an AAA observed during the Tromsø 4 phase.

The study’s primary outcome was the occurrence of an AAA (ie, AD ≥30 mm at the Tromsø 5 phase). The secondary outcome was a growth of the aorta >5 mm between Tromsø 4 and 5. Patient demographics, lifestyle questionnaires, basic clinical evaluations, and routine blood work were collected at both visits.

Of the 4161 patients included in this study, 53.2% were women, the mean baseline age was 59.3 years, the mean ASI was 1.1 cm/m², the mean baseline AD was 19.9 mm, and the mean follow-up AD was 20.3 mm. The men in this cohort had a higher body surface area compared with women (1.95 vs 1.71 m², respectively; P <.001), and a comparable body mass index (26.0 vs 25.8 kg/m², respectively; P =.19). There were a total of 124 AAAs, 79.8% of which occurred in men. Patients who experienced an AAA tended to be older and to have higher body surface areas, body mass indexes, blood pressure, and cholesterol levels.

The mean ASIs at Tromsø 4 were 1.09±0.13 cm/m2 and 1.28±0.19 cm/m2 and the mean ADs were 19.8±2.6 and 24.7±2.7 in patients who did not vs did experience an AAA, respectively (P <.001 for both). In adjusted univariate models, an increase in ASI (odds ratio [OR], 2.58; 95% CI, 2.2-3.0) and in AD (OR 1.83; 95% CI, 1.7-2.0) were found to be significant predictors of AAA development. The use of multivariable models indicated that ASI and AD were independent predictors of aortic growth (OR, 1.13; 95% CI, 1.02–1.24; P =.016 and OR, 1.09; 95% CI, 1.03–1.15; P =.002, respectively).

Sensitivity analyses in which the 2 predictive models were compared indicated that AD was a better predictor of AAAs than ASI (area under the curve, 0.92 vs 0.90, respectively; P =.009).

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Study limitations include the relatively small incidence of AAAs, the possibility of inaccuracies in the ultrasound measurements, and the potential for bias due to the use of self-reported questionnaires.

“ASI was a highly significant and independent predictor of incident AAA for both men and women. In addition, ASI was a significant predictor of aortic growth >5mm over 7 years,” concluded the study authors. 

Reference

Nyrønning LÅ, Skoog P, Videm V, Mattsson E. Is the aortic size index relevant as a predictor of abdominal aortic aneurysm? A population-based prospective study: the Tromsø study [published online January 7, 2020]. Scand Cardiovasc J. doi: 10.1080/14017431.2019.1707864