Descending Thoracic Aneurysm Risk of Rupture or Dissection
What is the natural history of descending thoracic aortic aneurysm?
A single-institution Thoracic Aortic Center Database included 3,247 patients ≥17 years of age with thoracic aortic aneurysm registered between July 1992 and August 2013. From those, 257 patients (ages 72.4 ± 10.5 years, 143 women) were identified with descending thoracic or thoracoabdominal aortic aneurysm (DTA/TAAA), without a history of connective tissue disorder (Marfan, Loeys-Dietz, Ehlers-Danlos syndromes) or inflammatory/neoplastic aortic disease, and without history of past aortic dissection or surgical intervention. Medical records were retrospectively assessed. The primary endpoint was a composite of aortic dissection, aortic rupture, or sudden death.
Baseline mean maximal aortic diameter was 52.4 ± 10.8 mm with 103 patients having diameters ≥55 mm. During a median follow-up of 25.1 months (interquartile range, 8.3-56.4 months), definite and possible aortic events occurred in 19 (7.4%) and 31 patients (12.1%), respectively. On multivariable analyses, maximal aortic diameter at baseline emerged as the only significant predictor of aortic events (hazard ratio [HR], 1.12; 95% confidence interval [CI], 1.08-1.15). Estimated rates of definite aortic events within 1 year were 5.5%, 7.2%, and 9.3% at aortic diameters of 50 mm, 55 mm, and 60 mm, respectively. Receiver operating characteristics for discriminating aortic events were higher for indexed aortic sizes referenced by body size (areas under curve [AUC] = 0.832-0.889), but not significantly different from absolute maximal aortic diameter (AUC = 0.805).
Aortic size was the principle factor related to aortic events in unrepaired DTA/TAAA. Although the risk of aortic events started to increase with a diameter above 5.0-5.5 cm, the authors concluded that it is uncertain if repair of TAAs in this range leads to overall benefit, and that the threshold size for repair requires further evaluation.
Much of what is known about the relationship between aorta size and aortic dissection comes from the aortic size among patients who present with dissection. This natural history study provides additional data that patients with a larger descending thoracic aorta diameter are at progressively greater risk of dissection. As the authors note, balancing the morbidity and mortality associated with ‘prophylactic’ aortic repair leaves open the ideal aortic size threshold at which intervention is associated with a net reduction in risk.
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