Comparison by magnetic resonance phase contrast imaging of pulse-wave velocity in patients with single ventricle who have reconstructed aortas versus those without

Cross-Sectional Study of Arterial Stiffness in Adolescents with Down Syndrome

OBJECTIVES

To test whether youth with Down syndrome have aortic stiffness indices, as measured by pulse wave velocity (PWV), that differ from youth without Down syndrome and to compare reference-based age-adjusted (age-PWV-Z) and height-adjusted (Ht-PWV-Z) in youth with and without Down syndrome.

STUDY DESIGN

Cross-sectional study of PWV in 129 adolescents with Down syndrome and 97 youth of comparable age, sex, race/ethnicity, and body mass index (BMI). PWV, age-PWV-Z, and Ht-PWV-Z were compared. Regression models were developed to test for associations with PWV.

RESULTS

Youth with Down syndrome and controls were comparable in BMI-Z (1.4 [-1.5 to 2.8] vs 1.2 [-2.0 to 2.8], P = .57) but not Ht-Z (-2.3 [-4.7 to 0.8] vs 0.4 [-2.0 to 2.6], P < .0001). PWV (m/s, 5.0 [3.1-7.9] vs 5.0 [3.6-8.0], P = .5) and mean arterial pressure (MAP, mm Hg) (78 [61-102] vs 74 [64-97], P = .09) were not different between groups. In adjusted analyses confined to Down syndrome, PWV was associated only with BMI, but not age, black race, or MAP (R2 = 0.11). In contrast, BMI, age, black race, and MAP were all positively associated with and better explained PWV in controls (R2 = 0.50). PWV was not associated with height in youth with or without Down syndrome. Although age-PWV-Z was not different in Down syndrome (-0.36 [-2.93 to 3.49]) vs -0.15 [-2.32 to 3.22]), Ht-PWV-Z was greater in Down syndrome (0.32 [-2.28 to 4.07] vs -0.08 [-2.64 to 2.64], P = .002), and Ht-PWV-Z was greater than age-PWV-Z in Down syndrome (P < .0001).

CONCLUSIONS

The lack of relationship of PWV, an independent predictor of adult cardiovascular events, with its traditional determinants including MAP suggests Down syndrome-specific phenomena may alter such relationships in this population. In youth with Down syndrome, Ht-adjusted PWV may overestimate aortic stiffness.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT01821300.

Relationship of Aortic Stiffness to Exercise and Ventricular Volumes in Single Ventricles

BACKGROUND

Patients with single ventricle (SV) may often undergo aortic reconstruction that creates a stiff large vessel, increasing afterload and affecting exercise performance. The objective of this study was to determine the relationship of pulse wave velocity (PWV) and distensibility in reconstructed and normal aortic arches after Fontan with exercise variables.

METHODS

PWV and distensibility of the descending aorta at the level of the diaphragm (DAo) were calculated with real-time exercise cardiac magnetic resonance in 48 patients with SV after Fontan (18 after aortic reconstruction; 30 without aortic reconstruction) and compared with metabolic exercise stress test variables.

RESULTS

PWV was greater in the reconstructed group than in the non-reconstructed group (median 4.4 m/s [range: 2.3 to 9.8 m/s] versus 3.6 [range: 2.6 to 6.3 m/s], respectively, p = 0.003). Statistically significant inverse correlations were found between PWV and end-diastolic, end-systolic, and stroke volumes at rest and at exercise in the reconstructed group. In addition, inverse correlations also existed in the reconstructed group between distensibility of the DAo and the exercise variables such as peak oxygen pulse (R = 0.56, p = 0.02), peak oxygen consumption (R = 0.63, p = 0.008), oxygen consumption at ventilatory anaerobic threshold (R = 0.48, p = 0.04), and peak work (R = 0.54, p = 0.02). Similar correlations were not seen in patients with non-reconstructed aortas.

CONCLUSIONS

Patients with SV with reconstructed aortas have increased aortic stiffness, increasing afterload on the ventricle. Native DAo stiffness distal to the reconstruction is inversely correlated with exercise performance, presumably to decrease impedance mismatch to maintain homogeneity of the aortic wall. This information suggests a possible mechanism for decreased exercise performance in patients with SV with aortic reconstructions.

Aortic length measurements for pulse wave velocity calculation: manual 2D vs automated 3D centreline extraction

BACKGROUND

Pulse wave velocity (PWV) is a biomarker for the intrinsic stiffness of the aortic wall, and has been shown to be predictive for cardiovascular events. It can be assessed using cardiovascular magnetic resonance (CMR) from the delay between phase-contrast flow waveforms at two or more locations in the aorta, and the distance on CMR images between those locations. This study aimed to investigate the impact of different distance measurement methods on PWV. We present and evaluate an algorithm for automated centreline tracking in 3D images, and compare PWV calculations using distances derived from 3D images to those obtained from a conventional 2D oblique-sagittal image of the aorta.

METHODS

We included 35 patients from a twin cohort, and 20 post-coarctation repair patients. Phase-contrast flow was acquired in the ascending, descending and diaphragmatic aorta. A 3D centreline tracking algorithm is presented and evaluated on a subset of 30 subjects, on three CMR sequences: balanced steady-state free precession (SSFP), black-blood double inversion recovery turbo spin echo, and contrast-enhanced CMR angiography. Aortic lengths are subsequently compared between measurements from a 2D oblique-sagittal plane, and a 3D geometry.

RESULTS

The error in length of automated 3D centreline tracking compared with manual annotations ranged from 2.4 [1.8-4.3] mm (mean [IQR], black-blood) to 6.4 [4.7-8.9] mm (SSFP). The impact on PWV was below 0.5m/s (<5%). Differences between 2D and 3D centreline length were significant for the majority of our experiments (p < 0.05). Individual differences in PWV were larger than 0.5m/s in 15% of all cases (thoracic aorta) and 37% when studying the aortic arch only. Finally, the difference between end-diastolic and end-systolic 2D centreline lengths was statistically significant (p < 0.01), but resulted in small differences in PWV (0.08 [0.04 - 0.10]m/s).

CONCLUSIONS

Automatic aortic centreline tracking in three commonly used CMR sequences is possible with good accuracy. The 3D length obtained from such sequences can differ considerably from lengths obtained from a 2D oblique-sagittal plane, depending on aortic curvature, adequate planning of the oblique-sagittal plane, and patient motion between acquisitions. For accurate PWV measurements we recommend using 3D centrelines.

Variable Myocardial Response to Load Stresses in Infants with Single Left Ventricular Anatomy: Influence of Initial Physiology and Surgical Palliative Strategy

Initial surgical strategies in neonates with single left ventricular (LV) anatomy vary based on adequacy of pulmonary and systemic blood flow. Differing myocardial responses to these strategies, as reflected in indices of systolic function, ventricular size, and mass have not been well defined. We sought to evaluate single LV myocardial response to varied physiology and initial palliation and determine whether the response is consistent and predictable. Infants with single LV physiology were divided based on neonatal palliation: no palliation/PA band (NO); BT shunt only (BT); or Norwood procedure (NP). Echo measures were obtained at presentation, early post-bidirectional Glenn (BDG), late post-BDG follow-up, and post-Fontan procedure. Measures included ejection fraction, LV mass indexed to height^2.7 and end diastolic volume indexed to body surface area, and mass/volume ratio. The cohort included 38 children (13 NO, 13 BT, 12 NP). Ejection fraction was similar but depressed in all groups at all stages. LV mass was higher in the NP group than the BT group at early post-BDG (p = 0.03) and higher than both BT and NO groups (p < 0.01) at late post-BDG, but the difference was resolved by post-Fontan follow-up. The NP group had the most remarkable remodeling in LV size from BDG to Fontan, suggesting that volume unloading is most valuable in this subgroup. Ventricular remodeling can be identified by echocardiography in children with single LV physiology, despite variable initial surgical palliative strategies. Importantly, these initial surgical strategies do not result in significant differences after Fontan palliation during early childhood.