Right heart catheterization is an invasive exam that is currently the gold standard to assess pulmonary hemodynamics for diagnosis and follow-up of pulmonary arterial hypertension (PAH) associated with congenital heart diseases (CHD). Cardiac magnetic resonance 4D flow (4D CMR flow) emerges as a promising non-invasive imaging. We assess the accuracy of 4D CMR flow to measure pulmonary cardiac output (Qp).

We prospectively included 28 patients (median age was 42years old [35–52] with PAH and CHD (pre-tricuspid shunt n=23, 82.1%, median mean pulmonary artery pressure 46mmHg [40–58]; median pulmonary vascular resistance 15.0 WU.m² [7.5–25.6]). Qp was measured invasively using Fick principle (direct oxygen consumption measure) during a right heart catheterization (QpF) and compared to Qp measured by 2D (Qp2D) and 4D flow CMR (Qp4D) on the same day.

4D CMR flow analysis was feasible in all patients. Qp4D and QpF were strongly correlated (rho=0.87, P<0.0001; r²=0.68, P<0.0001). Using Bland Altman analysis, mean difference was 0.0±1.0L/min. Mean difference within two observers (interobserver variability) was 0.3±0.4L/min (Fig. 1). Mean difference within one observer (intra-observer variability) was 0.1±0.3L/min. Qp2D and QpF were moderately correlated (rho=0.54, P=0.008; r²=0.41, P=0.0007). Using Bland Altman analysis, mean difference was 0.6±2.3L/min (Fig. 1).

Qp measured by 4D CMR flow is well correlated to QpF. Further studies are needed to explore other potential interests of using 4D CMR flow to assess PAH, including the derivation of additional hemodynamic parameters such as pulmonary artery compliance, wall shear stress and pulse wave velocities, which could provide further insights into pulmonary artery remodelling and interactions between pulmonary arterial stiffening and right ventricular dysfunction.