Left atrial acceleration factor as a magnetic resonance 4D flow measure of mean pulmonary artery wedge pressure in pulmonary hypertension

Background: Mean pulmonary artery wedge pressure (PAWP) represents a right heart catheter (RHC) surrogate measure for mean left atrial (LA) pressure and is crucial for the clinical classification of pulmonary hypertension (PH). Hypothesizing that PAWP is related to acceleration of blood throughout the LA, we investigated whether an adequately introduced LA acceleration factor derived from magnetic resonance (MR) four-dimensional (4D) flow imaging could provide an estimate of PAWP in patients with known or suspected PH. Methods: LA 4D flow data of 62 patients with known or suspected PH who underwent RHC and near-term 1.5 T cardiac MR ( identifier: NCT00575692) were retrospectively analyzed. Early diastolic LA peak outflow velocity (v(E)) as well as systolic (v(S)) and early diastolic (v(D)) LA peak inflow velocities were determined with prototype software to calculate the LA acceleration factor (alpha) defined as alpha = v(E)/[(v(S) + v(D))/2]. Correlation, regression and Bland-Altman analysis were employed to investigate the relationship between alpha and PAWP, alpha-based diagnosis of elevated PAWP (> 15 mmHg) was analyzed by receiver operating characteristic curve analysis. Results: alpha correlated very strongly with PAWP (r = 0.94). Standard deviation of differences between RHC-derived PAWP and PAWP estimated from linear regression model (alpha = 0.61 + 0.10.PAWP) was 2.0 mmHg. Employing the linear-regression-derived cut-off alpha = 2.10, the alpha-based diagnosis of elevated PAWP revealed the area under the curve 0.97 with sensitivity/specificity 93%/92%. Conclusions: The very close relationship between the LA acceleration factor alpha and RHC-derived PAWP suggests alpha as potential non-invasive parameter for the estimation of PAWP and the distinction between pre- and post-capillary PH.