Surgical decision making for patients with thoracic aortic aneurysm revolves around the estimation of natural risk of rupture and dissection. Risk is currently predicted on the basis of symptoms and the size of the aneurysm [1Davies R.R. Goldstein L.J. Coady M.A. et al.Yearly rupture or dissection rates for thoracic aortic aneurysms: simple prediction based on size.Ann Thorac Surg. 2002; 73: 17-27Abstract Full Text Full Text PDF PubMed Scopus (665) Google Scholar]. The size criterion can be adjusted for patient body size to achieve higher patient specificity [2Davies R.R. Gallo A. Coady M.A. et al.Novel measurement of relative aortic size predicts rupture of thoracic aortic aneurysms.Ann Thorac Surg. 2006; 81: 169-177Abstract Full Text Full Text PDF PubMed Scopus (359) Google Scholar]. Although size is a valuable and effective predictor, and size algorithms lead to safe patient triage [3Elefteriades JA, Farkas EA. Thoracic aortic aneurysm: clinically pertinent controversies and uncertainties. J Am Coll Cardiol 201;55:841–57.Google Scholar], progress is needed toward even better prediction by the use of other parameters not based on size [3Elefteriades JA, Farkas EA. Thoracic aortic aneurysm: clinically pertinent controversies and uncertainties. J Am Coll Cardiol 201;55:841–57.Google Scholar], such as radiographic inflammation [4Reeps C. Essler M. Pelisek J. Seidl S. Eckstein H.H. Krause B.J. Increased 18F-fluorodeoxyglucose uptake in abdominal aortic aneurysms in positron emission/computed tomography is associated with inflammation, aortic wall instability, and acute symptoms.J Vasc Surg. 2008; 48: 417-423Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar], circulating biomarkers [5Trimarchi S. Sangiorgi G. Sang X. et al.In search of blood tests for thoracic aortic diseases.Ann Thorac Surg. 2010; 90: 1735-1742Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar], and engineering characteristics [6Koullias G. Modak R. Tranquilli M. et al.Mechanical deterioration underlies malignant behavior of aneurismal human ascending aorta.J Thorac Cardiovasc Surg. 2005; 130: 677-683Abstract Full Text Full Text PDF PubMed Scopus (119) Google Scholar]. This article [7Shang E.K. Nathan D.P. Sprinkle S.R. et al.Peak wall stress predicts expansion rate in descending thoracic aortic aneurysms.Ann Thoraci Surg. 2013; 95: 593-598Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar] extends biomechanical analysis, previously applied to the abdominal aorta, to the descending thoracic aorta and is subject to similar limitations [8Humphrey J.D. Holzapfel G.A. Mechanics, mechanobiology, and modeling of human abdominal aorta and aneurysms.J Biomech. 2012; 45: 805-814Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar]. The key findings of this article are as follows: (1) peak wall stress occurred at the neck, not the belly, of the aneurysm; (2) patients with higher growth rate had higher wall stress; and (3) patients requiring surgical correction had higher wall stress. The follow-up period is short (mean, 17 months). The aortic growth rates reported here are higher than in prior studies (40% of patients grew at more than 4 mm per year). The vagaries of measurement of aortic growth are well known, especially over short intervals, and that may have influenced this apparent rapid growth. Although the calculated p value was significant, the actual differences in wall stress between the high and low growth rate groups are small (245 vs 213 kPa), and the standard deviations are large (64 and 32 kPa). One fundamental engineering shortcoming needs emphasis. Strain represents stretching of a material, and stress represents the force needed to produce that stretch. There are two means to get at stress. Either one must know the geometry (strain) and measure the applied loads (pressures) to compute the stresses, or one can measure the strain and know the stress/strain relation. The authors did not measure pressures; to permit stress calculations, they assumed that the stress/strain properties of thoracic aneurysms were equal to those reported for abdominal aneurysms. This assumption may not be valid, inasmuch as the aorta is disparate in these two locations (75 vs 28 lamellae). The authors are to be congratulated for their important work and intriguing findings. Owing to the low patient numbers and short duration of follow-up, the findings must be viewed as preliminary. The thrust of this work may improve patient triage among therapies in the future. Peak Wall Stress Predicts Expansion Rate in Descending Thoracic Aortic AneurysmsThe Annals of Thoracic SurgeryVol. 95Issue 2PreviewAortic diseases, including aortic aneurysms, are the 12th leading cause of death in the United States. The incidence of descending thoracic aortic aneurysms is estimated at 10.4 per 100,000 patient-years. Growing evidence suggests that stress measurements derived from structural analysis of aortic geometries predict clinical outcomes better than diameter alone. Full-Text PDF