Aortic Blood Flow Characteristics in Turner Syndrome

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 596-630-Pediatric Endocrinology
Clinical
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-617
Iris Gutmark-Little*1, Lisa Prahl Wittberg2, Stevin van Wyk2 and Philippe Ferdinand Backeljauw3
1Cincinnati Children's Hospital M, Cincinnati, OH, 2KTH, Stockholm, Sweden, 3Cincinnati Chldrn's Hosp Med C, Cincinnati, OH
Background

Cardiovascular morbidity is estimated to affect ~50% of Turner Syndrome (TS) patients (1). Cardiovascular risk assessment and pathophysiology of dissection and vasculopathy in TS patients is not well developed. Increased risk of dissection occurs in those with hypertension and the presence of coarctation, BAV, aortic root dilatation (ARD), or elongation of the transverse aorta (ETA) (2). The consequence of anatomic malformations and the resulting anomalous flow patterns are endothelial changes and vessel remodeling. This may be due to abnormal pressure, low wall shear stress (WSS), or high oscillatory shear index (OSI) (wide fluctuations in WSS) (3). Areas prone to these types of changes are arterial branching or curvature, where blood flow patterns are complex and multi-directional due to recirculation (4).

Computational fluid dynamics (CFD) enables calculation and localization of complex flow in the cardiovascular system relevant to clinical disease.

Objective

To determine blood flow characteristics in three aortae with anatomic anomalies common in TS.

Subjects/Methods

CFD was applied to virtually reconstructed aortic models using cardiac MR (CMR) of three TS patients with ARD (with a normal arch), ETA, and coarctation, and compared to normal. A time-dependent velocity waveform was imposed to mimic a cardiac cycle, and hemodynamic features were calculated. Clinical data was obtained from our TS database.

Results

The volume of blood leaving each branch on the aortic arch and the descending aorta differs between the three geometries (ARD 88% leaves through the descending aorta; coarctation 63%; ETA 50%).

ETA and coarctation have larger and more recirculation zones along the aorta, and persist throughout the cardiac cycle compared to ARD. Areas of low WSS coincide with recirculation zones in all three, and display a high OSI (highly fluctuating WSS). ETA is subjected to more regions of low WSS and elevated OSI.

The volume fraction of RBC’s exiting the three branches and descending aorta is influenced by recirculation zones. The volume fraction of ETA and coarctation was changed by >5% compared with ARD, resulting in 40% blood viscosity change.

Conclusion

Increased recirculation zones in ETA and coarctation lead to redistribution of RBC’s and consequent changes in viscosity, thus altering resistance to flow. This leads to changes in the routing of blood flow and impacts WSS/OSI in a way that may cause vessel wall pathology. The rapid cyclic mechanical forces result in breakdown of reinforcing vessel wall fibers and may lead to dissection (3).

CMR has been recommended for the management of TS patients (1). This type of high-resolution imaging is ideal for accurate CFD virtual reconstruction and flow study used to predict pathologic flow patterns. Clinical correlation could identify patients at risk for disease. Early diagnosis and treatment are critical for preserving lifespan in TS.

(1) Ho VB, Bakalov VK, Cooley M, Van PL, Hood MN, Burklow TR, Bondy CA.  Major vascular anomalies in Turner syndrome: prevalence and magnetic resonance angiographic features. Circulation 2004;110:1694-1700.(2) Matura LA, Ho VB, Rosing DR, Bondy CA.  Aortic dilatation and dissection in Turner syndrome.  Circulation 2007;116:1663-1670.(3) Ku DN.  Blood flow in arteries.  Annu Rev Fluid Mech 1997;29:399-434.(4) Shahcheraghi N, Dwyer HA, Cheer AY, Barakat AI, Rutaganira T.  Unsteady and three-dimensional simulation of blood flow in the human aortic arch.  J Biomech Eng 2002;124:378-387.

Disclosure: PFB: Investigator, Ipsen, Member of advisory committees or review panels, Ipsen. Nothing to Disclose: IG, LP, SV

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Departmental support