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Background Due to improved surgical strategies a growing number of patients survive acute aortic dissection. Patent false lumen (FL) is common in chronic dissection and it has been associated with poor prognosis, which is mainly driven by FL expansion. Several variables indirectly related to flow characteristics have been associated with progressive aortic dilation. We aimed to evaluate whether the maximum systolic flow deceleration rate (MSDR) in the FL, quantified by 4D-flow MR, is related to FL dilation in chronic type B aortic dissection. Methods Twenty-nine patients with a patent FL after aortic dissection and a prior follow-up of at least 3 years underwent contrast-enhanced 4D-flow MR. Marfan patients were excluded. Time-resolved FL flow acceleration was calculated in a 5 cm-long volume of the descending aorta around the level of the pulmonary bifurcation. MSDR was determined as the maximum minus the minimum acceleration in systole over the corresponding time interval (Figure 1a). Aortic growth rate (GR) was measured as the difference between final and initial maximum FL diameters obtained by angio-CT divided by follow-up duration. Population was divided into tertiles based on GR. Results Demographic and clinical variables were similar among GR tertiles (Table). MSDR was lower in patients with a GR <1mm/year (group 1) compared to both the other two patient groups (p = 0.009 and 0.003 for groups 2 and 3, respectively) (Figure 1c). MSDR showed a marked positive linear correlation with GR (R = 0.481, p = 0.008) (Figure 1b). Conclusions The MSDR in the FL of chronic type B aortic dissection is linearly related to FL growth rate and discriminated between tertiles of aortic dilation. Prospective longitudinal studies are need to unveil possible prognostic value of this parameter. Table Group 1 (n = 9) Group 2 (n = 10) Group 3 (n = 10) p-value Age (years) 63.44 ±13.54 62.50 ± 13.60 64.56 ± 6.67 0.902 BSA (m2) 2.00 ± 0.18 1.77 ± 0.20 1.94 ± 0.12 0.213 Men 6 (86%) 4 (57%) 4 (100%) 0.210 Hypertension 4 (66%) 5 (71%) 4 (100%) 0.438 Atheroclerosis 1 (17%) 1 (14%) 0 (0%) 0.699 Initial Diameter (mm) 45.00 ± 7.69 36.00 ± 4.20 37.00 ± 6.48 0.078 Final Diameter (mm) 49.50 ± 6.74 44.86 ± 5.70 59.25 ± 9.84 0.049 Follow-up (year) 11.83 ± 8.79 7.82 ± 3.34 8.08 ± 4.05 0.921 GR (mm/year) 0.27 ± 0.29 1.18 ± 0.26 2.64 ± 0.97 <0.001 MSDR (cm/s3) 1212.18 ± 467.61 2410.54 ± 1034.30 2558.16 ± 1098.06 0.005 Abstract P1600 Figure 1

Aims To assess aortic flow and stiffness in patients with Loeys–Dietz syndrome (LDS) by 4D flow and cine cardiovascular magnetic resonance (CMR) and compare the results with those of healthy volunteers (HV) and Marfan syndrome (MFS) patients. Methods and results Twenty-one LDS and 44 MFS patients with no previous aortic dissection or surgery and 35 HV underwent non-contrast-enhanced 4D flow CMR. In-plane rotational flow (IRF), systolic flow reversal ratio (SFRR), and aortic diameters were obtained at 20 planes from the ascending (AAo) to the proximal descending aorta (DAo). IRF and SFRR were also quantified for aortic regions (proximal and distal AAo, arch and proximal DAo). Peak-systolic wall shear stress (WSS) maps were also estimated. Aortic stiffness was quantified using pulse wave velocity (PWV) and proximal AAo longitudinal strain. Compared to HV, LDS patients had lower rotational flow at the distal AAo (P = 0.002), arch (P = 0.002), and proximal DAo (P < 0.001) even after adjustment for age, stroke volume, and local diameter. LDS patients had higher SFRR in the proximal DAo compared to both HV (P = 0.024) and MFS patients (P = 0.015), even after adjustment for age and local diameter. Axial and circumferential WSS in LDS patients were lower than in HV. AAo circumferential WSS was lower in LDS compared to MFS patients. AAo and DAo PWV and proximal AAo longitudinal strain revealed stiffer aortas in LDS patients compared to HV (P = 0.007, 0.005, and 0.029, respectively) but no differences vs. MFS patients. Conclusion Greater aortic stiffness as well as impaired IRF and WSS were present in LDS patients compared to HV. Conversely, similar aortic stiffness and overlapping aortic flow features were found in Loeys–Dietz and Marfan patients.

Background Connective tissue disorders, such as Loeys-Dietz (LDS) and Marfan (MFS) syndromes, are rare genetic diseases associated with progressive aortic dilation. Aortic dissections have been observed at lower aortic root diameters in LDS than in MFS, and research on aortic flow dynamics and biomechanics in LDS is lacking. Purpose To evaluate rotational aortic flow and aortic stiffness in LDS compared to healthy volunteers (HV) and MFS patients, using 4Dflow CMR. Methods Twenty-one LDS and 44 MFS patients, without previous aortic dissection or surgery, and 44 HV underwent a non-contrast-enhanced 4D flow CMR. In-plane rotational flow (IRF), systolic flow reversal ratio (SFRR) and local aortic diameters were obtained at 20 equidistant planes from the ascending (AAo) to the proximal descending aorta (DAo). Aortic stiffness was quantified at the AAo and DAo using pulse wave velocity (PWV). Results LDS patients had lower IRF at the distal AAo and proximal DAo compared to HV (p=0.053 and 0.004, respectively), once adjusted for age, stroke volume and local aortic diameter; but no differences were found with respect to MFS (Figure). Although SFRR at the proximal DAo was increased in LDS patients compared to both HV (p=0.037) and MFS populations (p=0.015), once adjusted for age and aortic diameter, the difference in magnitude was small (Figure). On the other hand, AAo and DAo PWV revealed stiffer aortas in LDS patients compared to HV but no differences versus MFS patients (Table). Conclusions LDS patients showed decreased in-plane rotational flow and abnormally-high regional aortic stiffness compared to healthy controls, and similar hemodynamics and aortic stiffness with respect to MFS patients Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): Instituto de Salud Carlos III, La Maratό TV3

Funding Acknowledgements Spanish Ministry of Economy and Competitiveness RTC-2016-5152-1, ISCIII PI17/00381, La Marató de TV3 (20151330), Eur FP7/People 267128 and CIBERCV Background Histological findings of fibrillin-1 deficiency in bicuspid aortic valve (BAV) ascending aorta (AAo), as observed in Marfan (MFS), supported the existence of intrinsic aortic wall abnormalities, but recent studies reported the absence of an intrinsic impairment in stiffness. A recent study in MFS showed that AAo longitudinal strain was reduced in MFS and predicted dilation and aortic events. This parameter has not been studied in BAV. Purpose We investigated whether ascending aorta longitudinal strain is intrinsically altered in BAV with respect to tricuspid aortic valve (TAV) individuals. Methods 80 BAV, 31 healthy volunteers (HV) and 29 TAV with AAo aneurysm, all without moderate valvular disease, were consecutively included. AAo dilation was defined as a z-score > 2. The 1.5T CMR protocol included a set of 2D cine CMR stacks covering the proximal aorta in saggital, coronal and axial views. AAo longitudinal strain was computed by an in-house Matlab code performing a feature tracking of the aortic valve in each of the cine images. Results Twenty (25%) of BAV had AAo dilation. AAo longitudinal strain was lower in non-dilated BAV compared to HV, but the difference was not significant in multivariate analysis adjusted for AAo diameter and systolic blood pressure. Similarly, the difference between dilated BAV and dilated TAV found in univariate analysis was not confirmed by multivariate analysis. On the other hand, both dilated BAV and TAV showed decreased AAo longitudinal strain compared to HV, which were confirmed in multivariate analyses. Conclusions AAo longitudinal strain, a marker of aortic stiffness with predictive value in MFS, is not altered in BAV patients compared to TAV matched for dilation prevalence. Reduced AAo longitudinal strain was independently associated with dilation in both BAV and TAV. Table 1 HV vs. NON-DILATED BAV DILATED BAV vs DILATED TAV HV vs. DILATED BAV HV vs. DILATED TAV HV NON-DILATED BAV Univariate /multivariate p-value DILATED TAV DILATED BAV Univariate /multivariate p-value Univariate/ Multivariate p-value Univariate p-value N 31 20 29 60 Age [years 35 ± 8 49 ± 16 <0.001/ NS 66 ± 13 49 ± 14 <0.001 / <0.001 <0.001 / 0.052 <0.001 / NS Sex [% male] 42 35 0.629 24 42 0.097 / NS 0.969 0.149 BSA [m2] 1.83 ± 0.17 1.81 ± 0.14 0.702 1.95 ± 0.24 1.82 ± 0.22 0.015 / <0.001 0.881 0.030 / NS SBP [mmHg] 119 ± 11 132 ± 16 0.002 / 0.029 133 ± 17 138 ± 19 0.304 <0.001 / NS <0.001 / NS DBP [mmHg] 69 ± 11 73 ± 6 0.099 / NS 77 ± 9 79 ± 11 0.455 <0.001 / 0.016 0.004 / 0.023 Ascending aorta diameter [mm] 26 ± 4 33 ± 3 <0.001 / 0.006 46 ± 7 43 ± 6 0.032 / NS <0.001 / 0.001 <0.001 /0.007 AAo long strain [%] 10.5 ± 3.6 8.4 ± 4.1 0.067/ NS 5.9 ± 2.7 7.7 ± 3.6 0.023 / NS 0.001 / 0.002 <0.001 / 0.023 Demographics and uni- and multivariate analyses of AAo longitudinal strain