A Non-Invasive Approach to Pulmonary Hypertension

Abstract

Pulmonary hypertension (PH) is a life-threatening cardiopulmonary disease associated with a poor prognosis, with progressive right ventricular (RV) failure being the main cause of death in this vulnerable population. Right heart catheterization remains the gold standard for assessing pulmonary hemodynamics. However, due to its invasive nature, non-invasive imaging methods are gaining increasing interest. Two-dimensional transthoracic echocardiography serves as the primary screening tool for PH and is widely used to estimate its likelihood. Nevertheless, this technique has several limitations, partially addressed through the assistance of a three-dimensional echocardiography. Cardiac magnetic resonance imaging (CMR) provides a comprehensive evaluation of both the morphology and hemodynamics of right ventricle-pulmonary artery unit, offering essential information for diagnosis, prognosis, and therapeutic monitoring. While two-dimensional cardiac CMR enables non-invasive characterization of pulmonary hemodynamics, advances in 4D-flow cardiac CMR allow for a more detailed analysis. These advancements enable the assessment of flow patterns, energetics, wall shear stress and severity, offering a more nuanced understanding of the disease. This review aims to provide an in-depth summary of the current data on advanced non-invasive imaging techniques for PH.

Keywords: cardiac magnetic resonance; non-invasive imaging; pulmonary hypertension; right ventricle-pulmonary artery unit.

Figure 1

Transthoracic Echocardiography 2D views: (A) apical 4-chamber view illustrating severe tricuspid regurgitation assessed through Doppler echocardiography. (B) Subcostal view utilized for the management of the inferior vena cava and evaluation of its respirophasic collapsibility, aiding in the assessment of right atrial and PA pressures. (C) Apical 4-chamber view at end-diastole in a patient with RV dilation, determined by measuring basal, medial, and longitudinal diameters. (D) Apical 4-chamber view with M-mode for estimating lateral tricuspid annulus excursion towards the apex during systole, used as a marker of RV systolic function. (E) Pulsed-wave Doppler echocardiography for measuring the RVMPI. (F) Speckle-tracking echocardiography at the level of the RV free wall for assessing global RV deformation in a patient with PH. Abbreviations: 2D, two-dimensional; PA, pulmonary artery; RV, right ventricle; RVMPI, right ventricle myocardial performance index; PH, pulmonary hypertension; RA, right atrium; LA, left atrium; LV, left ventricle.

Figure 2

Cardiac magnetic resonance parameters for the assessment of the right ventricle and pulmonary artery: (A) Cine-CMR 4-chamber view showing dilated right heart chambers. (B) T1-weighted double inversion-recovery black-blood turbo spin-echo images in patient with PH, demonstrating dilatation of the PA with pulmonary flow artifact in the distal right PA (arrow). (C) Short-axis CMR image illustrating RV planimetry, involving manual tracing of myocardial boundaries: the epicardial border is marked in green, and the endocardial border is marked in red, measured in end-diastole. Abbreviations: RV, right ventricle; CMR, cardiac magnetic resonance; PA, pulmonary artery; PH, pulmonary hypertension.

Figure 3

Cardiac magnetic resonance parameters for the assessment of the pulmonary artery: (A) axial cine SSFP images showing a cross-section of the MPA and its branches, with measurement planes for blood flow analysis demarcated by blue and red lines. (B) Two-dimensional-PC through-plane imaging using CMR, with the flow measurement region in the MPA highlighted by a blue overlay. (C) Two-dimensional-PC through-plane imaging using CMR, with the flow measurement region in the RPA, highlighted by a green overlay. Abbreviations: SSFP, steady-state free precession; 2D-PC CMR, two-dimensional phase-contrast cardiac magnetic resonance; MPA, main pulmonary artery; RPA, right pulmonary artery.

Figure 4

4D-Flow CMR (A) Streamlines depicting the instantaneous direction and velocity of blood flow within a vessel or cavity. The color map represents flow velocity, with red indicating higher speeds and blue indicating lower speeds. (B) Flow pattern visualization in a patient with PH. (C) 3D reconstruction of the PA tree, showing the anatomical vessel geometry and flow regions labeled as Flow 1, Flow 2, and Flow 3 for detailed analysis. Abbreviations: 4D-flow CMR, four-dimensional flow cardiac magnetic resonance; 3D, three-dimensional; PA, pulmonary artery.

Figure 5

Torsion Imaging. (A) Schematic representation of RV subendocardial myofibers arranged in a longitudinal orientation. (B) Model illustrating a ventricular torsion, defined as the rotational motion between the base (top) and apex (bottom) during the cardiac cycle. The apex rotates counterclockwise (green arrow), while the base rotates clockwise (red arrow). “Twist” refers to the angular difference in rotation between the apex and base of the heart. Torsion is the twist normalized by the length (L) between the base and apex, describing the rate of twist per unit length of the ventricle. (C) Velocity-time curves in the PAs. The vertical axis indicates the mean velocity in cm/s, and the horizontal axis shows time in milliseconds. The curves represent the MPA (red), RPA (green), and LPA (yellow). (D) WSS in the PAs. The vertical axis indicates the circumferential WSS in Pa, and the horizontal axis shows time in milliseconds. The color-coded curves correspond to different regions: MPA (red), RPA (green), and LPA (yellow). Abbreviations: RV, right ventricle; LV, left ventricle; WSS, wall shear stress; MPA, main pulmonary artery; RPA, right pulmonary artery; LPA, left pulmonary artery.

Figure 6

RV strain measurement using CMR FTI. (A) FTI map overlaid with longitudinal strain on a 4-chamber cine SSFP image. The green contour delineates the epicardium of the LV, while the red contour outlines the LV endocardium. Similarly, the blue contour represents the epicardium of the RV, and the yellow contour corresponds to the RV endocardium. (B) Graph illustrating RV global longitudinal strain, typically represented as negative values, plotted on the vertical axis (e.g., −13%). The horizontal axis represents time in ms. (C) FTI map overlaid with radial strain on short-axis cine SSFP image. (D) Graph illustrating RV radial strain, typically expressed as positive values, shown on the vertical axis (e.g., 4.3%). The horizontal axis represents time in ms. Abbreviations: FTI, feature tracking imaging; RV, right ventricle; LV, left ventricle; ms, milliseconds; CMR, cardiac magnetic resonance; SSFP, steady-state free precession.

Figure 7

Tissue characterization: (A,B) LGE CMR image of a short-axis view highlighting fibrosis at the RV insertion points on the IVS (arrows). (C) T1-mapping short-axis view. Abbreviations: LGE-CMR, late gadolinium enhancement cardiac magnetic resonance; RV, right ventricle; IVS, interventricular septum.