Incidence of small abdominal aortic aneurysms rupture, impact of comorbidities and our experience with rupture risk prediction based on wall stress assessment

Characteristics and One-year Outcomes of Patients with Rupture of Small Abdominal Aortic Aneurysms

OBJECTIVES

Rupture of abdominal aortic aneurysms (rAAA) is typically associated with large sac diameter, however some patients experience rupture before reaching operative thresholds for elective repair. We aim to investigate the characteristics and outcomes of patients who experience small rAAA.

METHODS

The Vascular Quality Initiative database for open AAA repair and endovascular aneurysm repair (EVAR) from 2003-2020 were reviewed for all rAAA cases. Based on the 2018 Society for Vascular Surgery guidelines on operative size thresholds for elective repair, patients with infrarenal aneurysms <5.0cm in women or <5.5cm in men were categorized as "small rAAA." Patients who met operative thresholds or had a concomitant iliac diameter ≥3.5cm were categorized as "large rAAA.". Patient characteristics and perioperative as well as long-term outcomes were compared via univariate regression. Inverse probability of treatment weighting (IPTW) using propensity scores was employed to examine the relationship between rAAA size and adverse outcomes.

RESULTS

There were 3,962 cases that met inclusion criteria, with 12.2% small rAAA. The mean aneurysm diameter was 42.3mm and 78.5mm in the small and large rAAA groups, respectively. Patients in the small rAAA group were significantly more likely to be younger, African American, have lower BMI, and had significantly higher rates of hypertension. Small rAAA were more likely to be repaired via EVAR (p=0.001). Hypotension was significantly less likely in patients with small rAAA (p<0.001). Rates of perioperative myocardial infarction (p<0.001), total morbidity (p<0.004) and mortality (p<0.001) were significantly higher for large rAAA cases. After propensity matching, there was no significant difference in mortality between the 2 groups, but smaller rAAA was associated with lower rates of MI (OR=0.50[0.31-0.82]). On long-term follow up, no difference in mortality was noted between the two groups.

CONCLUSIONS

Patients presenting with small rAAA represent 12.2% of all rAAA and are more likely to be African American. Small rAAA is associated with similar risk of perioperative and long-term mortality compared to rupture at larger size after risk adjustment.

Characteristics and outcomes of small abdominal aortic aneurysm rupture in the American College of Surgeons National Surgical Quality Improvement Program database

OBJECTIVE

The current guidelines recommend elective abdominal aortic aneurysm (AAA) repair at 5.5 cm for men and 5.0 cm for women. However, rupture can occur in patients with an aneurysm smaller than these size thresholds. In the present study, we investigated the proportion of AAAs that rupture at sizes less than elective operative thresholds and compared the outcomes of repair with those of aneurysms that had ruptured at a larger size. Our hypothesis was that the rupture of small AAAs carries mortality similar to that of rupture at larger sizes.

METHODS

The American College of Surgeons National Surgical Quality Improvement Program targeted vascular files for open AAA repair and endovascular aneurysm repair (EVAR) were reviewed for all cases of ruptured AAAs (rAAAs) from 2011 to 2018. The patients were divided into two groups: those with small AAAs that had ruptured at a size less than the current size guidelines for elective repair and those with large AAAs that had ruptured at a size that had met the criteria for elective repair. Univariate analyses were conducted to compare the comorbidities and perioperative outcomes of infrarenal rAAA repair between the groups. Multivariable logistic regression was performed to examine the differences in mortality between small and large rAAAs after controlling for confounding variables.

RESULTS

Of the 1612 rAAA repairs, 167 (10.4%) were small rAAAs. The proportion of small rAAAs did not significantly change during the study period (P = .15). The large rAAA group was more likely to have juxtarenal or suprarenal aneurysms compared with the small rAAA group (27% vs 16%; P = .001). A comparison of infrarenal rAAAs only demonstrated that the mean small rAAA (n = 141) diameter was 4.1 cm in the women and 4.5 cm in the men compared with the large rAAAs (n = 1051), with a mean diameter of 7.1 cm in women and 8.3 cm in men (P < .01 for the women; P < .01 for the men). The patients in the small rAAA group had had a significantly lower body mass index but were more likely to be African American and to have hypertension. The small rAAA group was more likely to present without hypotension and to have undergone EVAR. The repair of small rAAAs was associated with lower bleeding and mortality and a shorter mean operative time but with more readmissions. Multivariable regression analysis demonstrated that size was not associated with outcome after adjusting for other variables.

CONCLUSIONS

Of all AAA repairs classified as treating rupture, 10% were for patients with small AAAs. Patients with small rAAA were less likely to present with hypotension and were more likely to have undergone EVAR. Further research into sac morphology and more sensitive imaging modalities might help identify small rAAAs at high risk of rupture that would benefit from elective repair.