Cardiovascular magnetic resonance in pulmonary hypertension

Abstract

Pulmonary hypertension represents a group of conditions characterized by higher than normal pulmonary artery pressures. Despite improved treatments, outcomes in many instances remain poor. In recent years, there has been growing interest in the use of cardiovascular magnetic resonance (CMR) in patients with pulmonary hypertension. This technique offers certain advantages over other imaging modalities since it is well suited to the assessment of the right ventricle and the proximal pulmonary arteries. Reflecting the relatively sparse evidence supporting its use, CMR is not routinely recommended for patients with pulmonary hypertension. However, it is particularly useful in patient with pulmonary arterial hypertension associated with congenital heart disease. Furthermore, it has proven informative in a number of ways; illustrating how right ventricular remodeling is favorably reversed by drug therapies and providing explicit confirmation of the importance of the right ventricle to clinical outcome. This review will discuss these aspects and practical considerations before speculating on future applications.

Figure 1

Cardiovascular Magnetic Resonance in Group 1 PAH due to Congenital Heart Disease. Top left, In plane flow mapping demonstrating flow between left and right atrium (arrow) through an atrial septal defect; Top right, a steady state free procession cine showing flow (asterisk) from descending aorta to pulmonary artery via a persistent ductus arteriosus; Bottom left, Magnetic Resonance Angiography of an aberrant pulmonary vein (arrow) draining into the right atrium (RA); Bottom right, flow mapping in this patient in the main pulmonary artery and aorta allowed a Qp:Qs of 2.7 to be derived.

Figure 2

Abnormalities of Pulmonary Vasculature in Pulmonary Hypertension.; (A) White blood anatomy showing right upper pulmonary vein stenosis at the site of a prior ablation for atrial fibrillation (arrow). (B) Congestion and infarction in the right upper lobe on Half-Fourier Acquisition Single-Shot Turbo Spin-Echo images in the same patient (asterisk). (C) Magnetic Resonance Angiography from a separate patient with PH due to fibrosing mediastinitis; a varix is seen bypassing a stenosed left upper pulmonary vein (not shown) alongside stenoses of both right sided pulmonary veins (arrows). (D) Magnetic Resonance Angiography in patient with Chronic Thromboembolic Pulmonary Hypertension. The most striking feature is loss of the left descending pulmonary artery (arrow head).

Figure 3

Basal Slice Analysis. In the normal right ventricle (A) the angle between the left ventricular long axis (black dashed line) and basal slice (dashed white box) is approximately 90°. In PH patients (B), assuming the basal slice is prescribed as per recommendations [16] the angle becomes more obtuse as the right ventricle dilates. The basal slice will now include right atrium (seen centrally) with a shoulder of right ventricle seen laterally (C, arrow heads). The impact this interpretation has on delineation is shown in D. Also in B note how the most basal part of the right ventricle 'hoods' beyond the TV plane (arrows) and is effectively ignored by the acquisition.

Figure 4

The characteristic late gadolinium enhancement pattern of PH. (A-C) insertion region enhancement (arrows) is triangular in shape with the base at the epicardial surface where both ventricles meet and its apex directed into the interventricular septum. Corresponding short axis cine slices (D-F). The septomarginal trabeculation is arrowed (E) - enhancement is often seen within this structure.

Figure 5

Chasing Tricuspid Regurgitation. Accurate jet velocity analysis depends on two factors; positioning of the imaging slice through the jet core and jet core characteristics. The latter is where measurement of tricuspid regurgitation with CMR falls down; compare the discrete stenotic lesion as might be seen in aortic stenosis (left) to the dispersed jets of tricuspid regurgitation (right) and how they relate to the imaging plane (represented by boxed line with direction of velocity measurement arrowed, modified with permission [32]). In functional tricuspid regurgitation, the jets arise at a number of points of failed coaptation and so are numerous and narrow - meaning their core is rarely large enough to be measured.

Figure 6

Measuring Transit-Time PWV in the Pulmonary Arteries. Data is acquired in main pulmonary artery, left and right pulmonary artery (A) and the path length between them measured accurately. Using CMR phase-contrast velocity maps (B), the flow pulse is tracked (C) and differences (T) in arrival time (D, in this healthy case defined as halfway between the foot and maximum values) are determined. PWV is then calculated as T/Pathlength. MPA; main pulmonary artery, RPA; right pulmonary artery, LPA; left pulmonary artery, BPA; branch pulmonary artery, PWV; Pulse wave velocity.

Figure 7

The RV-PA unit and Survival in PAH. Work from the VU University Medical Center (Amsterdam) group demonstrating the importance of right ventricular dilatation [59] (A), ejection fraction[60] (B), and pulmonary artery stiffness [61](C) to prognosis. RVEDVI; indexed right ventricular end-diastolic volume, RVEF; right ventricular ejection fraction, RAC; relative area change.