Longitudinal and circumferential strain of the proximal aorta

Background: Accurate assessment of mechanical properties of the proximal aorta is a requisite first step for elucidating the pathophysiology of isolated systolic hypertension. During systole, substantial proximal aortic axial displacement produces longitudinal strain, which we hypothesize causes variable underestimation of ascending aortic circumferential strain compared to values in the longitudinally constrained descending aorta. Methods and Results: To assess effects of longitudinal strain, we performed magnetic resonance imaging in 375 participants (72 to 94 years old, 204 women) in the Age, Gene/Environment Susceptibility-Reykjavik Study and measured aortic circumferential and longitudinal strain. Circumferential ascending aortic area strain uncorrected for longitudinal strain was comparable in women and men (mean [95% CI], 8.3 [7.8, 8.9] versus 7.9 [7.4, 8.5]%, respectively, P=0.3). However, longitudinal strain was greater in women (8.5 ± 2.5 versus 7.0 ± 2.5%, P < 0.001), resulting in greater longitudinally corrected circumferential ascending aortic strain (14.4 [13.6, 15.2] versus 13.0 [12.4, 13.7]%, P=0.010). Observed circumferential descending aortic strain, which did not require correction (women: 14.0 [13.2, 14.8], men: 12.4 [11.6, 13.2]%, P=0.005), was larger than uncorrected (P < 0.001), but comparable to longitudinally corrected (P=0.12) circumferential ascending aortic strain. Carotid-femoral pulse wave velocity did not correlate with uncorrected ascending aortic strain (R=-0.04, P=0.5), but was inversely related to longitudinally corrected ascending and observed descending aortic strain (R=-0.15, P=0.004; R=-0.36, P < 0.001, respectively). Longitudinal strain was also inversely related to carotid-femoral pulse wave velocity and other risk factors for higher aortic stiffness including treated hypertension. Conclusions: Longitudinal strain creates substantial and variable errors in circumferential ascending aortic area strain measurements, particularly in women, and should be considered to avoid misclassification of ascending aortic stiffness.