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

Abstract

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 (ClinicalTrials.gov 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 (α) defined as α = v _E/[(v _S + v _D)/2]. Correlation, regression and Bland-Altman analysis were employed to investigate the relationship between α and PAWP, α-based diagnosis of elevated PAWP (>15 mmHg) was analyzed by receiver operating characteristic curve analysis.

Results: α correlated very strongly with PAWP (r = 0.94). Standard deviation of differences between RHC-derived PAWP and PAWP estimated from linear regression model (α = 0.61 + 0.10·PAWP) was 2.0 mmHg. Employing the linear-regression-derived cut-off α = 2.10, the α-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 α and RHC-derived PAWP suggests α as potential non-invasive parameter for the estimation of PAWP and the distinction between pre- and post-capillary PH.

Keywords: 4D flow; cardiac magnetic resonance (CMR) imaging; pulmonary artery wedge pressure; pulmonary hypertension; right heart catheterization (RHC).

Figure 1

Illustration of the determination of LA peak in- and outflow velocities. Measurement cut planes are indicated on an early diastolic magnitude image with color-encoded vector plot of the three-dimensional velocity field. PV pulmonary vein; v_S, systolic LA peak inflow velocity; v_D, diastolic LA peak inflow velocity; v_E, early diastolic LA peak outflow velocity; v_A, late diastolic LA peak outflow velocity; v_{S, vein}, systolic peak velocity determined in the pulmonary vein; v_{D, vein}, diastolic peak velocity determined in the pulmonary vein; v_{E, tip}, early diastolic peak velocity determined at the level of the mitral valve tips; v_{A, tip}, late diastolic peak velocity determined at the level of the mitral valve tips.

Figure 2

Scatter plots and linear regressions of early diastolic LA peak outflow v_E (A), late diastolic LA peak outflow v_D (B), systolic LA peak inflow v_S (C), and early diastolic LA peak inflow v_D (D) velocity on PAWP. PAWP, mean pulmonary artery wedge pressure; r, correlation coefficient; RMSE, root-mean-square error.

Figure 3

Scatter plot and linear regression of LA acceleration factor α on PAWP (A), and Bland-Altman plot comparing RHC-derived PAWP and PAWP_calc calculated from inverted linear regression equation (B). PAWP, mean pulmonary artery wedge pressure; RMSE, root-mean-square error; LoA, limits of agreement; SD, standard deviation of differences.

Figure 4

ROC curve for the diagnosis of PAWP > 15 mmHg employing the LA acceleration factor α. AUC, area under the ROC curve.

Figure 5

Scatter plots and linear regressions of the LA acceleration factors on PAWP, with LA acceleration factors calculated from peak velocity measurements at the level of mitral valve tips α_tip (A), within the pulmonary vein α_vein (B), and both α_tip/vein (C). PAWP, mean pulmonary artery wedge pressure; r, correlation coefficient; RMSE, root-mean-square error.