Integrated Diagnostics Characterization of Right Ventricular Diastolic Flow Dynamics in Pulmonary Arterial Hypertension

The adaptive changes that result from chronic pressure overload in pulmonary arterial hypertension (PAH) lead to myocardial hypertrophy, stiffening, and right ventricular diastolic dysfunction (RVDD). A growing body of evidence has identified RVDD as an important prognostic indicator for PAH.1 Diagnosis of RVDD relies upon 1) elevated brain natriuretic peptide (BNP), which correctly identifies RVDD in the PAH population but remains a nonspecific marker, and 2) echocardiography, as defined by reduced early (E') tricuspid annular velocity, elevated ratio of early filling tricuspid inflow peak velocity to E' (E/E'), and prolonged relaxation time (RT). 2 However, the right ventricle's unusual anatomy and susceptibility to altered loading conditions have raised questions about the ability of echo indices to accurately reflect complex diastolic mechanics. The development of a robust non-invasive application for RV diastolic assessment may improve the understanding, diagnosis, and management of RVDD and therefore PAH.

Similar to the left ventricle, rheological analysis of right ventricular inflow in canine models has identified the formation of diastolic vortex rings.3 Vortex rings develop from high velocity diastolic jet emanating from the valvular annulus interacting with stationary blood in the ventricle. Vortex ring formation time has successfully identified left ventricular diastolic dysfunction.4 Numerous additional vortex properties exist, including depth, transverse position, length, width, and sphericity index, that offer novel and robust diastolic flow characterization with the potential incremental diagnostic value to existing echo parameters. Vortex formation and analysis in RVDD has yet to be studied.

Vortex measurement can be performed using dimensional (4D) (time-resolved three-dimensional) cardiac MRI (CMR). 4D CMR captures the complex multidirectional nature of flow through volumetric rendering of fluid vectors and velocity using blood flow streamlines and particle traces. In contrast to echocardiography, 4D CMR is not limited by poor acoustic windows commonly seen in patients with respiratory disease and PAH, making it an ideal noninvasive modality for vortex characterization.

The biological adaptations resulting from chronic pressure overload in PAH might be correlated to the blood levels of different categories of biomarkers. They might play a role in the screening, diagnosis, monitoring or prognosis of patients with PAH and RVDD. Special mention can be made to the natriuretic peptides (BNP, NT-proBNP) based on their clinical value as hemodynamic markers in congestive heart failure. Cardiac markers of necrosis (asTroponin-I, and particularly the high sensitivity assays) might identify even minimal areas with such myocardial cell damage. The biological evaluation of cardiac fibrosis, might be assessed by markers of fibrosis, as Hyaluronic acid (HA), Procollagen III amino terminal peptide (PIIINP) and Tissue inhibitor of metalloproteinase 1 (TIMP-1). The potential role of the inflammatory component, can be evaluated with MPO (myeloperoxidase, pro-inflammatory enzyme), IL-6 (pro-inflammatory cytokine), C-RP (C-reactive protein)

The present study aims to:

1. Characterize and quantify RV vortex flow in normal subjects and PAH subjects with RVDD
2. Assess the feasibility of 4D CMR right ventricular diastolic vortex analysis for diagnosis of RVDD Hypothesis: 4D CMR vortex analysis accurately identifies RVDD, and the information provided by biomarkers helps by adding diagnostic information.