Aortic reflection coefficients and their association with global indexes of wave reflection in healthy controls and patients with Marfan's syndrome

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Abstract
Early return of reflected pressure waves increases the load on central arteries and may increase the risk of aortic rupture in patients with Marfan's syndrome (MFS). To assess whether wave reflection is elevated in MFS, we used ultrasound and MRI to measure central pressure and flow waveforms in 26 patients (13–54 yr of age) and 26 age- and gender-matched controls. Aortic systolic and diastolic cross-sectional areas were measured at the ascending and descending aorta (AA and DA), diaphragm (DIA), and lower abdominal aorta (AB). From these measurements, local characteristic impedance (Z0-xx) and local reflection coefficients (Γxx-yy) were calculated. Calculated global wave reflection indexes were the augmentation index (AIx) and the ratio of backward to forward pressure wave (Pb/Pf). The aorta was wider in MFS patients at AA (P < 0.01) and DA (P < 0.01). Aortic pulse wave velocity was 42 cm/s higher in MFS patients (P < 0.05). Z0-xx was not different between groups, except at DA, where it was lower in MFS patients. In controls, ΓAA-DA was 0.31 ± 0.08, ΓDA-DIA was 0.00 ± 0.11, and ΓDIA-AB was 0.31 ± 0.16. Mean values of Γxx-yy were not different between MFS patients and controls. In controls, aging diminished ΓAA-DA but increased ΓDIA-AB. Clear age-related patterns were absent in MFS patients. AIx or Pb/Pf was not higher in MFS patients than in controls. There were indications for enhanced wave reflection in young MFS patients. Our data demonstrated that the major determinants of AIx were pulse wave velocity and the effective length of the arterial system and, to a lesser degree, HR and Pb/Pf.