Appropriate Management of Thoracic Aortic Aneurysms
By Michael H. Crawford, MD
Professor of Medicine, Lucy Stern Chair in Cardiology, University of California, San Francisco
SYNOPSIS: Among patients with arch and descending thoracic aorta aneurysms followed over a mean of 20 months, aneurysm-related mortality was predicted by the size and growth rate of the aneurysms, along with age and sex.
SOURCE: Sharples L, Sastry P, Freeman C, et al. Aneurysm growth, survival, and quality of life in untreated thoracic aortic aneurysms: The effective treatments for thoracic aortic aneurysms study. Eur Hear J 2022;43:2356-2369.
Although once thought to be rare, the expanding use of CT scans and an aging population have raised the reported incidence rates of arch and descending thoracic aortic aneurysms. The authors of the Effective Treatments of Thoracic Aortic Aneurysms (ETTAA) study examined the natural history of TAA before any intervention to identify any features that predict a poor outcome.
ETTAA was an observational cohort of 886 National Health Service (NHS) patients in England identified between 2014 and 2018 at 30 cardiothoracic or vascular units. Patients had arch or descending TAAs, defined as a diameter ≥ 4 cm on CT or MRI (36% women, mean age = 71 years). The authors excluded patients with acute dissection and previous surgical intervention. Also, patients with isolated ascending AAs were not included (unless such episodes involved the arch). Outcomes were aneurysm growth, survival, quality of life (QOL), and hospital admissions. A core lab reviewed the aortic diameter measurements. QOL was measured at each follow-up visit using a standard NHS instrument.
Patients were divided by their intended management into four groups: conservative management by patient choice, comorbidities, or high procedural risk; watchful waiting if the aneurysms were small and at low risk of rupture; endovascular stent grafting (ESG); or open surgical replacement (OSR). The latter three cohorts were labeled the intention-to-treat group. If ESG or OSR were performed, patients were censored at that time. Conservative management patients were 13% of the population. Median follow-up was 20 months. Mortality occurred at a rate of 6.6% deaths per patient-year in the intention-to-treat group and 20% per patient-year in the conservative management group. One- and three-year survival rates were 92% and 78%, respectively; aneurysm-related survival was 97% and 88%, respectively. Aneurysms of 4 cm to 6 cm, 7 cm, and 8 cm led to one-year mortality rates of < 10%, 12%, and 22%, respectively, and three-year mortality rates of 21%, 37%, and 58%, respectively. After adjusting for age, sex, and New York Heart Association class, the authors noted the risk of death increased with aneurysm size at baseline: hazard ratio (HR), 1.88; 95% confidence interval (CI), 1.64-2.16 per cm; P < 0.001. If aneurysm growth was detected on imaging, the mortality HR was 2.02 (95% CI, 1.70-2.41 per cm; P < 0.001). Also, mortality was higher in women (HR, 2.60; 95% CI, 1.58-4.29; P < 0.001).
In addition, aneurysm mortality was related to age at entry (HR, 1.50/decade; 95% CI, 1.09-2.05; P = 0.012). Hospital admissions increased with aneurysm size, but size was not related to QOL. Finally, descending TAAs grew at a faster rate than ascending or arch aneurysms. The authors concluded surveillance imaging of aneurysms of the arch or descending aorta should happen at a minimum of 12-month intervals for aneurysms of 4 cm to 6 cm in diameter, with shorter intervals for larger aneurysms, descending TAAs, older patients, and women.
Patients with TAAs are difficult to study as many are not diagnosed until symptoms occur (unless they undergo a chest X-ray for other reasons). Hence, the ETTAA investigators should be commended for assembling this relatively large group of patients. The risk of an aneurysm-related death began to accelerate at 5 cm and increased faster when > 6 cm.
Beyond this, there were some other interesting observations. Descending AAs grew faster than arch aneurysms. Initial size and growth were the major aneurysm-related factors determining outcomes, but female sex carried the highest overall risk. No clinical factors for accelerated growth and bad outcomes were discovered. Also, there were few non-fatal dissections or ruptures, so intervening before these events occur is important. In addition, only half of all deaths in this population were aneurysm-related, yet the observed mortality rate in ETTAA was considerably higher than the general English population. Thus, TAA patients have other comorbidities that need to be addressed.
Since this was an observational study of routine practice, no causal relationships can be inferred. Although the cohort was relatively large, there were several weaknesses. The authors excluded patients with ascending TAAs, which initially seems odd, but it is because they did not exclude patients with prior dissections or surgical correction of the ascending aorta. However, ascending aneurysms are more frequent and carry a bad prognosis. Also, only 7% of the aneurysms studied were in the arch, so this was largely a study of descending TAAs.
In addition, not all imaging studies were analyzed in the core lab, and the measurements were not indexed to body size. Finally, the follow-up period was rather short. Regardless, the study does point out convincingly that future guideline committees should consider aneurysm growth, patient sex, and age in addition to aneurysm size for determining the frequency of follow-up imaging.
Among patients with arch and descending thoracic aorta aneurysms followed over a mean of 20 months, aneurysm-related mortality was predicted by the size and growth rate of the aneurysms, along with age and sex.
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