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Fate of the Unoperated Ascending Aortic Thoracic Aneurysm
Quick Takes
- Using observational data from an institutional database and studying only patients with ascending thoracic aortic aneurysm (ATAA) who did not undergo subsequent intervention, the risk of adverse aortic events (AAE) (dissection, rupture, or aortic death) increased rapidly at an aortic diameter ≥5 cm.
- ATAA on average grew slowly (mean annual growth rate 0.10 ± 0.01 cm/yr), and aortic growth ≥0.2 cm/yr was rare.
- The exclusion of operated patients could have unintentionally excluded patients at higher risk for rapid growth or subsequent AAE.
Study Questions:
What is the natural history of ascending thoracic aortic aneurysm (ATAA) without surgical intervention?
Methods:
The Aortic Institute of Yale University utilizes an institutional, observational database with anthropomorphic, radiologic, and clinical data retrospectively accrued from electronic medical records cross-referenced with state death certificates. The current study included patients ≥18 years of age with imaging documentation of maximal ascending aortic diameter ≥3.5 cm; and excluded patients with penetrating aortic ulcer or intramural hematoma at the time of first encounter, patients with congenital aortic malformation, and patients with surgical intervention for ATAA. There were 964 unoperated ATAA patients included in the final analysis; follow-up was complete in 905 patients (93.8%), with a median follow-up of 7.9 years (interquartile range [IQR] 4.4–12.7 years, range 0.1–34 years; total follow-up 8,163.7 person-years). The primary study endpoint was a composite of adverse aortic events (AAE), defined as dissection, rupture, or aortic death.
Results:
At aortic sizes of 3.5-3.9, 4.0-4.4, 4.5-4.9, 5.0-5.4, 5.5–5.9, and ≥6.0 cm, the average yearly risk of AAE was 0.2%, 0.2%, 0.3%, 1.4%, 2.0%, and 3.5%, respectively (p < 0.001), and the 10-year survival free from AAE was 97.8%, 98.2%, 97.3%, 84.6%, 80.4%, and 70.9%, respectively (p < 0.001). The risk of AAE was relatively flat until an aortic diameter of 5 cm, at which size it began to increase rapidly (p for nonlinearity < 0.001). The mean annual growth rate was estimated to be 0.10 ± 0.01 cm/yr. ATAAs grew very slowly, and aortic growth over 0.2 cm/yr was rare. Multivariable Cox regression identified aortic size (hazard ratio [HR], 1.78; 95% confidence interval [CI], 1.50-2.11; p < 0.001) and age (HR, 1.02; 95% CI, 1.00-1.05; p = 0.015) as significant independent risk factors for AAE. Hyperlipidemia (HR, 0.46; 95% CI, 0.23-0.91; p = 0.025) was found to be a significant protective factor for AAE in univariable Cox regression.
Conclusions:
ATAA on average grew very slowly (mean annual growth rate 0.10 ± 0.01 cm/yr), and aortic growth over 0.2 cm/yr was rare. The risk of AAE increased rapidly at an aortic diameter ≥5 cm. The authors conclude that an aortic size of 5 cm, rather than 5.5 cm, may be a more appropriate criterion for intervention for prophylactic ATAA repair, and that aortic growth may not be an applicable indicator for intervention.
Perspective:
ATAA size and growth rate are understood to be predictors of risk for future AAE; current guideline thresholds for prophylactic intervention among patients with ATAA include aortic diameter ≥5.5 cm (or ≥5.0 cm with an experienced surgeon in a Multidisciplinary Aortic Team) or growth rate ≥0.5 cm in 1 year or ≥0.3 cm/yr in 2 consecutive years. This observational study excluded patients who underwent prophylactic surgery with the goal to help define the ‘real’ natural history of ATAA, with the hypothesis that censoring outcomes data at the time of surgery obscures the true natural history of disease.
The study finding that the risk of AAE (dissection, rupture, or aortic death) was relatively flat until an aortic diameter ≥5 cm adds data to support a lower threshold for prophylactic intervention. The findings that the average aortic growth rate was seemingly very slow (mean annual growth rate 0.10 ± 0.01 cm/yr) and that more rapid growth was rare (growth ≥0.2 cm/yr was observed in no patient) deserve additional consideration. First, serial radiological imaging was available for only 507 of 964 patients and at a median follow-up of only 3.7 years. Second, the exclusion of patients who underwent intervention after the initial imaging study might have had unintended consequences in this observational study, including the exclusion of patients who underwent intervention due to documentation of past rapid growth (potentially including imaging at another institution prior to referral) or due to clinical assessment of high risk (potentially including patients with known or suspected heritable thoracic aortic disease). Assessment of the ‘really real’ natural history of ATAA would involve impossibly never intervening on any patient.
Clinical Topics: Cardiac Surgery, Dyslipidemia, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Prevention, Vascular Medicine, Aortic Surgery, Cardiac Surgery and Arrhythmias, Interventions and Imaging, Interventions and Vascular Medicine
Keywords: Aortic Aneurysm, Thoracic, Aortic Rupture, Cardiac Surgical Procedures, Diagnostic Imaging, Dissection, Hematoma, Hyperlipidemias, Pre-Exposure Prophylaxis, Risk Factors, Rupture, Secondary Prevention, Vascular Diseases
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