Evaluating Growth Patterns of Abdominal Aortic Aneurysm Diameter With Serial Computed Tomography Surveillance

Abstract

IMPORTANCE Small abdominal aortic aneurysms (AAAs) are common in the elderly population. Their growth rates and patterns, which drive clinical surveillance, are widely disputed.OBJECTIVE To assess the growth patterns and rates of AAAs as documented on serial computed tomography (CT) scans. DESIGN, SETTING, AND PARTICIPANTSCohort study and secondary analysis of the Non-Invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (N-TA 3 CT), a randomized, double-blind placebo-controlled clinical trial conducted from 2013 to 2018, with CT imaging every 6 months for 2 years. The trial was a multicenter, observational secondary analysis, not related to treatment hypotheses of data collected in the N-TA 3 CT. Participants included 254 patients with baseline AAA diameter between 3.5 and 5.0 cm. EXPOSURES Patients received serial CT scan measurements, analyzed for maximum transverse diameter, at 6-month intervals. MAIN OUTCOMES AND MEASURESThe primary study outcome was AAA annual growth rate. Secondary analyses included characterizing AAA growth patterns, assessing likelihood of AAA diameter to exceed sex-specific intervention thresholds over 2 years.RESULTS A total of 254 patients, 35 women with baseline AAA diameter 3.5 to 4.5 cm and 219 men with baseline diameter 3.5 to 5.0 cm, were included. Yearly growth rates of AAA diameters were a median of 0.17 cm/y (interquartile range [IQR], 0.16) and a mean (SD), 0.19 (0.14) cm/y. Ten percent of AAAs displayed minimal to no growth (<0.05 cm/y), 62% displayed low growth (0.05-0.25 cm/y), and 28% displayed high growth (>0.25 cm/y). Baseline AAA diameter accounted for 5.4% of variance of growth rate (P < .001; R 2 , 0.054). Most AAAs displayed linear growth (70%); large variations in interval growth rates occurred infrequently (3% staccato growth and 4% exponential growth); and some patients' growth patterns were not clearly classifiable (23% indeterminate). No patients with a maximum transverse diameter less than 4.25 cm exceeded sex-specific repair thresholds at 2 years (men, 0 of 92; 95% CI, 0.00-0.055; women, 0 of 25 ; 95% CI, 0.00-0.247). Twenty-six percent of patients with a maximum transverse diameter of at least 4.25 cm exceeded sex-specific repair thresholds at 2 years (n = 12 of 83 men with diameter ranging from 4.25 to <4.75 cm; 95% CI, 0.091-0.264; n = 21 of 44 men with diameter ranging from 4.75-5.0 cm; 95% CI, 0.362-0.669; n = 3 of 10 women with diameter Ն4.25 cm; 95% CI, 0.093-0.726).CONCLUSIONS AND RELEVANCE Most small AAAs showed linear growth; large intrapatient variations in interval growth rates were infrequently observed over 2 years. Linear growth modeling of AAAs in individual patients suggests smaller AAAs (<4.25 cm) can be followed up with a CT scan in at least 2 years with little chance of exceeding interventional thresholds.

Longer follow-up intervals following endovascular aortic aneurysm repair are safe and appropriate after marked aneurysm sac regression

“…In our analysis, once the aneurysm sac regressed to at least 40 mm, aneurysm sacs remained stable over a long period of time. In a secondary analysis of the Non-Invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (N-TA3CT) trial, Olson et al 26 showed that even small untreated aneurysms (<4.25 cm) showed linear growth with no patients reaching repair thresholds at 2 years and suggested that increasing surveillance intervals in this patient population to every 2 years would be safe. It is thus very plausible that aneurysm sacs with significant regression after EVAR would be suitable for an even longer follow-up interval.…”

Vascular Deformation Mapping of Abdominal Aortic Aneurysm

“…Additionally, AAAs display a wide variety of growth ranging from completely stable to rapid growth (>1 cm/year). While small aneurysms typically display slow linear growth, up to 30% of such AAAs display non-linear, intermittent, and rapid growth behavior [13,36].…”

Smaller size is more suitable for pharmacotherapy among undersized abdominal aortic aneurysm: A systematic review and meta-analysis

“…Even though some papers describe smaller undersized AAAs (30–40 mm) or even ectatic aortas (25–30 mm) can grow in size, most small AAAs are stable without reaching 55 mm or experiencing rupture. 23,24 More importantly, their causes of fatal outcomes are not necessarily aneurysm-related, but rather cardiovascular events or cancer. 24,25 It is also noted that it takes 5 years or even longer to see the natural growth of ectatic or smaller, undersized AAAs, posing a question for the optimal follow-up term of future RCTs.…”