title: Descending aortic diameter of 5.5 cm or greater is not an accurate predictor of acute type B aortic dissection.
abstract: OBJECTIVE
  The risk of acute type B aortic dissection is thought to increase with descending thoracic aortic diameter. Currently, elective repair of the descending thoracic aorta is indicated for an aortic diameter of 5.5 cm or greater. We sought to investigate the relationship between aortic diameter and acute type B aortic dissection, and the utility of aortic diameter as a predictor of acute type B aortic dissection.
  
  
  METHODS
  We examined the descending aortic diameter at presentation of 613 patients with acute type B aortic dissection who were enrolled in the International Registry of Acute Aortic Dissection between 1996 and 2009, and analyzed the subset of patients with acute type B aortic dissection with an aortic diameter less than 5.5 cm.
  
  
  RESULTS
  The median aortic diameter at the level of acute type B aortic dissection was 4.1 cm (range 2.1-13.0 cm). Only 18.4% of patients with acute type B aortic dissection in the International Registry of Acute Aortic Dissection had an aortic diameter of 5.5 cm or greater. Patients with Marfan syndrome represented 4.3% and had a slightly larger aortic diameter than patients without Marfan syndrome (4.68 vs 4.32 cm, P = .121). Complicated acute type B aortic dissection was more common among patients with an aortic diameter of 5.5 cm or greater (52.2% vs 35.6%, P < .001), and the in-hospital mortality for patients with an aortic diameter less than 5.5 cm and 5.5 cm or greater was 6.6% and 23.0% (P < .001), respectively.
  
  
  CONCLUSIONS
  The majority of patients with acute type B aortic dissection present with a descending aortic diameter less than 5.5 cm before dissection and are not within the guidelines for elective descending thoracic aortic repair. Aortic diameter measurements do not seem to be a useful parameter to prevent aortic dissection, and other methods are needed to identify patients at risk for acute type B aortic dissection.
authors: Policlinico San Donato IRCCS, Cardiovascular Center E. Malan, University of Milano, Milan, Italy. santi.trimarchi@unimi.it
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