Noninvasive Investigation of Pulmonary Blood Flow in Children with Pulmonary Hypertension Using the TRV/RVOT VTI Ratio

Objectives: Determination of the right ventricular outflow tract velocity time integral (RVOT VTI) is a part of the non-invasive investigation of pulmonary flow in adults with pulmonary hypertension (PH). The normal range of RVOT VTI in adults is stable, and differences serve as indicators for changes in RV stroke volume. In children, non-invasive techniques to assess pulmonary blood flow are of interest. Recently, we provided normative age-related pediatric RVOT VTI values in order to introduce RVOT VTI assessment to echocardiographic protocols for pediatric PH evaluation. The tricuspid regurgitation velocity (TRV)/RVOT VTI ratio, as a reliable measure of pulmonary blood flow in adults with PH, approximates the ratio of pulmonary artery pressure to pulmonary blood flow, with pediatric data to date missing. The aim of our study was to investigate RVOT VTI and TRV/RVOT VTI ratio in children with PH with respect to healthy controls and growth-related differences.

Methods: The PH study group consisted of 59 children with PH (median age: 5.3; range: 3 month to 18.3 years; 22 females): 36 children had PH associated with congenital heart disease (PH-CHD), 11 had PH associated with bronchopulmonary dysplasia (PH-BPD), and 12 had idiopathic PH (iPH). All PH patients had measurable mild to moderate TR so that TR jets could be reliably interrogated. RV systolic pressure was estimated by CW-Doppler of TRV. The peak systolic RV pressure was divided by the systolic aortic pressure to express the RV pressure as a percentage of systemic pressure.

Results: RVOT VTI values significantly correlated with age (r = 0.602), BW (r = 0.404), BL (r = 0.434), and BSA (r = 0.422). The median RVOT VTI values of our PH patients were 10.1 cm (range: 5.0–20.1 cm). 33 out of 59 PH patients (56%) were identified as having impaired RVOT VTI values compared to age-related normative values (z-score < −2). The TRV/RVOT VTI ratio ranged between 0.16 and 0.98 (median: 0.36) in our PH patients. The TRV/RVOT VTI ratio was found to rise with increasing RV pressure (r = 0.849, p < 0.001).

Conclusion: The TRV/RVOT VTI ratio was found to increase with higher RV pressure in our PH cohort. For clinical practice, RVOT VTI values from now on can be judged as being normal or abnormally impaired in children with PH.