PhD Student, University of Colorado - Children's Hospital Colorado
Develop non-invasive MRI characterization and diagnostic tools for pediatric pulmonary hypertension
Background: Hemodynamic evaluation via catheterization is essential for diagnostic and therapeutic investigation of children with pulmonary hypertension (PH). Measurement of pulmonary flow is required to calculate pulmonary vascular resistance index (PVRi), an important component of investigation and a predictor of outcome. Calculation of cardiac (CI) index using the Fick principle in most catheter laboratories relies on an estimate of oxygen consumption which may limit its reliability. In this study, we compared CI assessed by the Fick principle and thermodilution (TD) with gold-standard flow waveform evaluation technique -- phase-contrast MRI (PC-MRI).
Materials and Methods: Twenty-four patients with pre-diagnosed idiopathic PH (n=19) or PH associated with congenital heart disease (n=5) (age: 14.2 ± 4.6 (range: [4, 20]), M:F = 10:14) underwent same-day right-heart catheterization and PC-MRI for hemodynamic evaluation. CI computed from the catheterization (Fick and TD) were compared with PC-MRI (indexed integrated flow waveform multiplied by heart rate) using linear regression models (beta ± standard error) and Bland-Altman analysis.
Results: PC-MRI and Fick’s derived CI was obtained in all patients and in 12 patients with TD. CI measured by the Fick principle and PC-MRI failed to show significant correlation (0.06 ± 0.24, p = 0.8030. Furthermore, no significant correlation existed between TD and PC-MRI (0.78 ± 0.44, p = 0.1080). Respective Bland-Altman analysis revealed a bias in CI of -2.8 and -2.4 L/min/m2 between Fick vs. PC-MRI and TD vs. PC-MRI, respectively. The limits of agreement for the Fick method vs. PC-MRI were -2.6 to 2.4 L/min/m2 and -2.1 to 2.1 L/min/m2 for TD vs. PC-MRI.
Conclusions: CI calculations from catheterization dramatically differ from PC-MRI. Stronger agreement existed between TD vs. PC-MRI than between Fick vs. PC-MRI. Uncertainty, in flow catheterization measurements may create significant error in calculation of PH diagnostic determinants. Future studies are required to evaluate differences between prognostic potentials of PVRi and CI calculated using different modalities.
Abstract: Aortic 3-dimensional blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy.Four-dimensional flow MRI measured in vivo 3-dimensional blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4 mm; n=15 RN-BAV, 39.6±7.2 mm); aorta size controls with tricuspid aortic valves (n=30, 41.0±4.4 mm); healthy volunteers (n=15, 24.9±3.0 mm). Aortopathy type (0-3), systolic flow angle, flow displacement, and regional wall shear stress were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional wall shear stress (P<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV in comparison with aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV patients (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV patients were associated with altered flow displacement in the proximal and mid AAo for type 1 (42%-81% decrease versus type 2) and distal AAo for type 3 (33%-39% increase versus type 2).The presence and type of BAV fusion was associated with changes in regional wall shear stress distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiological mechanism by which the valve morphology phenotype can influence phenotypes of BAV aortopathy.
Pub.: 19 Dec '13, Pinned: 08 Jun '17
Abstract: Four-dimensional (4D) flow magnetic resonance imaging (MRI) was employed for the simultaneous assessment of morphometry and flow parameters along the thoracic aorta to investigate associations between flow, age, aorta diameter, and aortic valve morphology.One hundred and sixty-five subjects, 65 controls, 50 patients with bicuspid aortic valve (BAV), and 50 patients with a dilated aorta, and a tricuspid aortic valve (TAV) underwent 4D flow MRI. Following 3D segmentation of the aorta, a vessel centreline was calculated and used to extract aorta diameter, peak systolic velocity, and normalized systolic flow displacement. Validation of 4D flow MRI-based morphometric measurements compared with manual diameter measurements from standard contrast-enhanced MR angiography in 20 controls showed good agreement (mean difference = 0.4 mm, limits of agreement = ±1.31 mm) except at the sinus of valsalva. BAV showed significant differences in average peak velocity (PV; P < 0.016) compared with TAV and controls between the left ventricle outflow tract to sino-tubular junction (BAV: 1.3 ± 0.3 m/s; TAV: 1.2 ± 0.2 m/s; controls: 1.0 ± 0.1 m/s) and the ascending aorta for average normalized flow displacement (BAV: 0.11 ± 0.02; TAV: 0.09 ± 0.02; controls: 0.06 ± 0.01, P < 0.016) despite similar average aortic dimensions for BAV (37 ± 1 mm) and TAV (39 ± 1 mm). Multivariate linear regression showed a significant correlation of maximal aortic diameter to age, PV, and normalized flow displacement (R(2) = 0.413, P < 0.001).A single acquisition of 4D flow MRI characterized local morphological and haemodynamic differences between groups along the aorta. BAV showed altered haemodynamics when compared with TAV in spite of having similar aorta dimensions. Maximal aorta diameter was associated with age, PV, and normalized flow displacement.
Pub.: 18 Sep '15, Pinned: 08 Jun '17
Abstract: There are very few validated prognostic markers in pediatric pulmonary hypertension. Cardiac MRI is a useful, noninvasive method for determining prognosis in adults. The present study is the first to assess its prognostic value in children.A total of 100 children with pulmonary hypertension (median, 10.4 years; range, 0.5-17.6 years) were evaluated (idiopathic, n=60; repaired congenital heart disease, n=22; miscellaneous, n=18). In all patients, ventricular volumes and great vessel flow were measured. Volumetric data were obtained using retrospectively gated cine imaging (n=37) or real-time imaging (n=63), depending on the patient's ability to hold his or her breath. During a median follow-up of 1.9 years, 11 patients died and 3 received lung transplantation. Of the cardiac MR parameters measured, right ventricular ejection fraction and left ventricular stroke volume index were most strongly predictive of survival on univariate analysis (2.6- and 2.5-fold increase in mortality for every 1-SD decrease, respectively; P<0.05). These results were reflected in good separation of tertile-based Kaplan-Meier survival curves for these variables.Cardiac MR measures correlate with clinical status and prognosis in children with pulmonary hypertension. Cardiac MR is feasible and may be useful in clinical decision making in pediatric pulmonary hypertension.
Pub.: 11 Apr '13, Pinned: 08 Jun '17
Abstract: To develop a new predictive equation for oxygen consumption (VO2) in children and adults with congenital and acquired heart disease.We retrospectively reviewed data from 502 consecutive patients (age 0-59 years) undergoing cardiac catheterisation with measured VO2 (M-VO2) and compared M-VO2 with VO2 from the LaFarge equations (LF-VO2) in patients <3 years (Group 1) and ≥3 years (Group 2). Factors associated with inaccurate LF-VO2 were used to develop a new predictive equation, which was prospectively validated in 100 consecutive patients (age 0-59 years).LF-VO2 was inaccurate in 42% of Group 1 (n=201) and 13% of Group 2 (n=301). Multivariable predictors of inaccurate LF-VO2 included age (OR 0.41, p=0.01) and single ventricle anatomy (OR 2.98, p=0.03) in Group 1 and anaemia (OR 0.84, p<0.001) in Group 2. Critical illness was borderline significant in both groups. The new predictive equation for VO2:[Formula: see text] Intraclass correlation between M-VO2 and the new predictive equation was good (r=0.53), whereas LF-VO2 was not (r=0.17). Bland-Altman analysis comparing M-VO2 with the new equation and with LF-VO2 demonstrated superiority of the new equation (mean bias 2.5 mL/min/m(2) vs -5.0 mL/min/m(2); limits of agreement -51.6, 56.5 vs -82.1, 72).VO2 derived from the LaFarge equations is frequently inaccurate, particularly in younger patients, and will lead to erroneous haemodynamic calculations. We developed and prospectively validated a new VO2 predictive equation for use in patients of all ages with congenital and acquired heart disease.
Pub.: 28 Nov '14, Pinned: 08 Jun '17
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