Abstract 4388: In-Vivo Pulmonary Vascular Stiffness Obtained from Color M-Mode Tissue Doppler Imaging and Pressure Measurements Predicts Clinical Outcomes Better than Indexed Pulmonary Vascular Resistance in Pediatric Patients with Pulmonary Arterial Hypertension

Abstract

Introduction: Pulmonary vascular stiffness (PVS) is increasingly recognized as an important component of right ventricular afterload in patients with pulmonary arterial hypertension (PAH). In adult and pediatric PAH populations, stiffness has also been shown to improve prediction of mortality and outcomes, respectively. Despite these promising findings, methods to determine PVS clinically remain limited. Here we examine the ability of a minimally-invasive method to quantify proximal PVS in a pediatric PAH population, and hypothesize this measurement will offer better disease outcomes prediction over indexed pulmonary vascular resistance (PVRI), the current gold standard. Methods: Color M-mode Tissue Doppler Images of the right pulmonary artery (RPA) were obtained using ultrasound during right-heart catheterization of 36 individuals undergoing reactivity testing (n=86) who ranged in age from 1 month to 19 yrs (mean = 6.5±5.2 yrs, 19 males). These measurements yielded RPA diameter and intravascular pressure, from which an estimate of the circumferential elastic (Young’s) modulus (E), the continuum component of stiffness, was derived. Echo imaging added only 5 minutes to the procedure. Follow up was obtained in 19 patients (mean = 4.9±4.7 yrs, range 1 month to 16 yrs, 9 males) at a median time of 15 months (range 1–26 months). Cumulative logistic regression was used to relate continuous values of E and PVRI to three outcomes categories: improvement; stable (no change); or worsening. These were determined from change in WHO score from initial assessment to follow up. Results: E had better correlation to pulse pressure (PP) (R2=0.61) compared to mean pressure (R2=0.43); this agrees with other findings of PP as a good proxy of stiffness. E displayed substantially better correlation (R2L=0.49) to outcomes compared to PVRI (R2L=0.33). In more practical terms, E wrongly predicted outcome only once (5%), compared to four errors by PVRI (21%), and offered clearer prognosis in an additional 3 individuals; thus 37% of the group would benefit from such improved prediction. Conclusion: We conclude that elastic modulus is a measure of proximal vascular stiffening and most importantly offers superior outcomes prediction compared to pulmonary vascular resistance.