Assessment of pulmonary artery pulse wave velocity in children: An MRI pilot study

Purpose

To assess the feasibility of measuring pulmonary artery (PA) pulse wave velocity (PWV) in children breathing ambient air and 12% oxygen.

Methods

Velocity-encoded phase-contrast MR images of the PA were acquired in 15 children, aged 9–12 years, without evidence of cardiac or pulmonary diseases. PWV was derived as the ratio of flow to area changes during early systole. Each child was scanned twice, in air and after at least 20 minutes into inspiratory hypoxic challenge. Intra-observer and inter-observer variability and repeatability were also compared.

Results

PA PWV, which was successfully measured in all subjects, increased from 1.31 ± 0.32 m/s in air to 1.61 ± 0.58 m/s under hypoxic challenge (p = 0.03). Intra- and inter-observer coefficients of variations were 9.0% and 15.6% respectively. Good correlation within and between observers of r = 0.92 and r = 0.72 respectively was noted for PA PWV measurements. Mean (95% limit of agreement) intra- and inter-observer agreement on Bland–Altman analysis were − 0.02 m/s (− 0.41–0.38 m/s) and -0.28 m/s (− 1.06–0.49 m/s).

Conclusion

PA PWV measurement in children using velocity-encoded MRI is feasible, reproducible and sufficiently sensitive to detect differences in PA compliance between normoxia and hypoxia. This technique can be used to detect early changes of PA compliance and monitor PAH in children.     

The relationship between aortic stiffness and E/A filling ratio and myocardial strain in the context of left ventricular diastolic dysfunction in heart failure with normal ejection fraction: insights from magnetic resonance imaging

The purpose of this study is to investigate the relationship between aortic stiffness and diastolic dysfunction in heart failure with normal ejection fraction (HFNEF) and compare the results to normal subjects using magnetic resonance imaging (MRI). Sixteen human subjects (eight HFNEF and eight volunteers) were scanned on a 3.0-T MRI system. Aortic stiffness was assessed using pulse wave velocity (PWV). Left ventricle (LV) diastolic function was assessed by the early/atrial (E/A) filling ratio and different myocardial strain components. The results showed that, in HFNEF, a major part of LV filling occurred later during the atrial filling phase. The E/A ratio was less than 1 in HFNEF and greater than 1 in volunteers. Left ventricular myocardial dynamic strain range (difference between end-diastolic and end-systolic strains) was reduced in HFNEF, with less relaxation (strain rate) during the diastolic phase. Aortic PWV was higher in HFNEF than in volunteers due to less vessel compliance. The E/A ratio and myocardial strain measurements showed inverse correlations with aortic stiffness in HFNEF. The resulting inter- and intraobserver variabilities showed no bias between repeated cardiovascular measurements. In conclusion, a comprehensive MRI exam was developed for assessing patients with HFNEF. Heart failure with normal EF is associated with impaired LV diastolic function and significant ventricular and aortic stiffening. The degree of aortic stiffness involvement suggests reduced aortic compliance as a major factor in HFNEF.