4D magnetic resonance flow imaging for estimating pulmonary vascular resistance in pulmonary hypertension

Influence of Polymer Stiffness and Geometric Design on Fluid Mechanics in Tissue-Engineered Pulmonary Valve Scaffolds

There is still much unknown about the fluid mechanical response to cardiac valve scaffolds, even as their implementation in the clinic is on the horizon. Specifically, while degradable polymer valve scaffolds are currently being tested in the pulmonary valve position, their material and mechanical properties have not been fully elucidated. Optimizing these properties are important determinants not only of acute function, but long-term remodeling prospects. This study aimed to characterize fluid profiles downstream of electrospun valve scaffolds under dynamic pulmonary conditions. Valve scaffold design was changed by either blending poly(carbonate urethane) urea (PCUU) with poly(ε-caprolactone) (PCL) to modulate material stiffness or by changing the geometric design of the valve scaffolds. Specifically, two designs were utilized: one modeled after a clinically used bioprosthetic valve design (termed Mk1 design), and another using a geometrically "optimized" design (termed Mk2) based on anatomical data. Particle image velocimetry results showed that material stiffness only had a mild impact on fluid mechanics, measured by velocity magnitude, vorticity, viscous shear stress, Reynolds shear stress, and turbulent kinetic energy. However, comparing the two geometric designs yielded a much greater impact, with the Mk2 valve groups containing the highest PCUU/PCL ratio demonstrating the overall best performance. This report highlights the easily manipulable design features of polymeric valve scaffolds and demonstrates their relative significance for valve function.

4D flow cardiac MRI to assess pulmonary blood flow in patients with pulmonary arterial hypertension associated with congenital heart disease

PURPOSE

The purpose of this study was to evaluate the accuracy of four-dimensional flow cardiac magnetic resonance imaging (4D flow MRI) compared to right heart catheterization in measuring pulmonary flow (Qp), systemic flow (Qs) and pulmonary-to-systemic flow ratio (Qp/Qs) in patients with pulmonary arterial hypertension associated with congenital heart disease (PAH-CHD).

MATERIALS AND METHODS

The study was registered on Clinical-trial.gov (NCT03928002). Sixty-four patients with PAH-CHD who underwent 4D flow MRI were included. There were 16 men and 48 women with a mean age of 45.3 ± 13.7 (standard deviation [SD]) years (age range: 21-77 years). Fifty patients (50/64; 78%) presented with pre-tricuspid shunt. Qp (L/min), Qs (L/min) and Qp/Qs were measured invasively using direct Fick method during right heart catheterization and compared with measurements assessed by 4D flow MRI within a 24-48-hour window.

RESULTS

The average mean pulmonary artery pressure was 51 ± 17 (SD) mm Hg with median pulmonary vascular resistance of 8.8 Wood units (Q1, Q3: 5.3, 11.7). A strong linear correlation was found between Qp measurements obtained with 4D flow MRI and those obtained with the Fick method (r = 0.96; P < 0.001). Bland Altman analysis indicated a mean difference of 0.15 ± 0.48 (SD) L/min between Qp estimated by 4D flow MRI and by right heart catheterization. A strong correlation was found between Qs and Qp/Qs measured by 4D flow MRI and those obtained with the direct Fick method (r = 0.85 and r = 0.92; P < 0.001 for both).

CONCLUSION

Qp as measured by 4D flow MRI shows a strong correlation with measurements derived from the direct Fick method. Further investigation is needed to develop less complex and standardized methods for measuring essential PAH parameters, such as pulmonary arterial pressures and pulmonary vascular resistance.

Characterization of pulmonary arterial stiffness using cardiac MRI

Pulmonary arterial stiffness (PAS) is a pathologic hallmark of all types of pulmonary hypertension (PH). Cardiac MRI (CMR), a gold-standard imaging modality for the evaluation of pulmonary flow, biventricular morphology and function has been historically reserved for the longitudinal clinical follow-up, PH phenotyping purposes, right ventricular evaluation, and research purposes. Over the last two decades, numerous indices combining invasive catheterization and non-invasive CMR have been utilized to phenotype the character and severity of PAS in different types of PH and to assess its clinically prognostic potential with encouraging results. Many recent studies have demonstrated a strong role of CMR derived PAS markers in predicting long-term clinical outcomes and improving currently gold standard risk assessment provided by the REVEAL calculator. With the utilization of a machine learning strategies, strong diagnostic and prognostic performance of CMR reported in multicenter studies, and ability to detect PH at early stages, the non-invasive assessment of PAS is on verge of routine clinical utilization. In this review, we focus on appraising important CMR studies interrogating PAS over the last 20 years, describing the benefits and limitations of different PAS indices, and their pathophysiologic relevance to pulmonary vascular remodeling. We also discuss the role of CMR and PAS in clinical surveillance and phenotyping of PH, and the long-term future goal to utilize PAS as a biomarker to aid with more targeted therapeutic management.

Lung Magnetic Resonance Imaging: Technical Advancements and Clinical Applications

ABSTRACT

Since lung magnetic resonance imaging (MRI) became clinically available, limited clinical utility has been suggested for applying MRI to lung diseases. Moreover, clinical applications of MRI for patients with lung diseases or thoracic oncology may vary from country to country due to clinical indications, type of health insurance, or number of MR units available. Because of this situation, members of the Fleischner Society and of the Japanese Society for Magnetic Resonance in Medicine have published new reports to provide appropriate clinical indications for lung MRI. This review article presents a brief history of lung MRI in terms of its technical aspects and major clinical indications, such as (1) what is currently available, (2) what is promising but requires further validation or evaluation, and (3) which developments warrant research-based evaluations in preclinical or patient studies. We hope this article will provide Investigative Radiology readers with further knowledge of the current status of lung MRI and will assist them with the application of appropriate protocols in routine clinical practice.

Qualification of Ventricular Flow in Patients With Precapillary Pulmonary Hypertension With 4-dimensional Flow Magnetic Resonance Imaging

PURPOSE

Our goal was to study both right and left ventricular blood flow in patients with precapillary pulmonary hypertension (pre-PH) with 4-dimensional (4D) flow magnetic resonance imaging (MRI) and to analyze their correlation with cardiac functional metrics on cardiovascular magnetic resonance (CMR) and hemodynamics from right heart catheterization (RHC).

MATERIALS AND METHODS

129 patients (64 females, mean age 47 ± 13 y) including 105 patients with pre-PH (54 females, mean age 49 ± 13 y) and 24 patients without PH (10 females, mean age 40 ± 12 y) were retrospectively included. All patients underwent CMR and RHC within 48 hours. 4D flow MRI was acquired using a 3-dimensional retrospectively electrocardiograph-triggered, navigator-gated phase contrast sequence. Right and left ventricular flow components including the percentages of direct flow (PDF), retained inflow (PRI), delayed ejection flow (PDE), and residual volume (PRVo) were respectively quantified. The ventricular flow components between patients with pre-PH and non-PH were compared and correlations of flow components with CMR functional metrics and hemodynamics measured with RHC were analyzed. Biventricular flow components were compared between survivors and deceased patients during the perioperative period.

RESULTS

Right ventricular (RV) PDF and PDE significantly correlated with RVEDV and RV ejection fraction. RV PDF negatively correlated with pulmonary arterial pressure (PAP) and pulmonary vascular resistance. When the RV PDF was <11%, the sensitivity and specificity of RV PDF for predicting mean PAP ≥25 mm Hg were 88.6% and 98.7%, respectively, with an area under the curve value of 0.95 ± 0.02. When RV PRVo was more than 42%, the sensitivity and specificity of RV PRVo for predicting mean PAP ≥25 mm Hg were 85.7% and 98.5%, respectively, with an area under the curve value of 0.95 ± 0.01. Nine patients died during the perioperative period. Biventricular PDF, RV PDE, and PRI of survivors were higher than nonsurvivors whereas RV PRVo increased in deceased patients.

CONCLUSIONS

Biventricular flow analysis with 4D flow MRI provides comprehensive information about the severity and cardiac remodeling of PH and may be a predictor of perioperative death of patients with pre-PH.

Tensions in Taxonomies: Current Understanding and Future Directions in the Pathobiologic Basis and Treatment of Group 1 and Group 3 Pulmonary Hypertension

In the over 100 years since the recognition of pulmonary hypertension (PH), immense progress and significant achievements have been made with regard to understanding the pathophysiology of the disease and its treatment. These advances have been mostly in idiopathic pulmonary arterial hypertension (IPAH), which was classified as Group 1 Pulmonary Hypertension (PH) at the Second World Symposia on PH in 1998. However, the pathobiology of PH due to chronic lung disease, classified as Group 3 PH, remains poorly understood and its treatments thus remain limited. We review the history of the classification of the five groups of PH and aim to provide a state-of-the-art review of the understanding of the pathogenesis of Group 1 PH and Group 3 PH including insights gained from novel high-throughput omics technologies that have revealed heterogeneities within these categories as well as similarities between them. Leveraging the substantial gains made in understanding the genomics, epigenomics, proteomics, and metabolomics of PAH to understand the full spectrum of the complex, heterogeneous disease of PH is needed. Multimodal omics data as well as supervised and unbiased machine learning approaches after careful consideration of the powerful advantages as well as of the limitations and pitfalls of these technologies could lead to earlier diagnosis, more precise risk stratification, better predictions of disease response, new sub-phenotype groupings within types of PH, and identification of shared pathways between PAH and other types of PH that could lead to new treatment targets. © 2023 American Physiological Society. Compr Physiol 13:4295-4319, 2023.

4D flow cardiovascular magnetic resonance recovery profiles following pulmonary endarterectomy in chronic thromboembolic pulmonary hypertension

BACKGROUND

Four-dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR) allows comprehensive assessment of pulmonary artery (PA) flow dynamics. Few studies have characterized longitudinal changes in pulmonary flow dynamics and right ventricular (RV) recovery following a pulmonary endarterectomy (PEA) for patients with chronic thromboembolic pulmonary hypertension (CTEPH). This can provide novel insights of RV and PA dynamics during recovery. We investigated the longitudinal trajectory of 4D flow metrics following a PEA including velocity, vorticity, helicity, and PA vessel wall stiffness.

METHODS

Twenty patients with CTEPH underwent pre-PEA and > 6 months post-PEA CMR imaging including 4D flow CMR; right heart catheter measurements were performed in 18 of these patients. We developed a semi-automated pipeline to extract integrated 4D flow-derived main, left, and right PA (MPA, LPA, RPA) volumes, velocity flow profiles, and secondary flow profiles. We focused on secondary flow metrics of vorticity, volume fraction of positive helicity (clockwise rotation), and the helical flow index (HFI) that measures helicity intensity.

RESULTS

Mean PA pressures (mPAP), total pulmonary resistance (TPR), and normalized RV end-systolic volume (RVESV) decreased significantly post-PEA (P < 0.002). 4D flow-derived PA volumes decreased (P < 0.001) and stiffness, velocity, and vorticity increased (P < 0.01) post-PEA. Longitudinal improvements from pre- to post-PEA in mPAP were associated with longitudinal decreases in MPA area (r = 0.68, P = 0.002). Longitudinal improvements in TPR were associated with longitudinal increases in the maximum RPA HFI (r=-0.85, P < 0.001). Longitudinal improvements in RVESV were associated with longitudinal decreases in MPA fraction of positive helicity (r = 0.75, P = 0.003) and minimum MPA HFI (r=-0.72, P = 0.005).

CONCLUSION

We developed a semi-automated pipeline for analyzing 4D flow metrics of vessel stiffness and flow profiles. PEA was associated with changes in 4D flow metrics of PA flow profiles and vessel stiffness. Longitudinal analysis revealed that PA helicity was associated with pulmonary remodeling and RV reverse remodeling following a PEA.

Pulmonary Hypertension in Children is Associated With Abnormal Flow Patterns in the Main Pulmonary Artery as Demonstrated by Blood Speckle Tracking

Background

Paediatric pulmonary arterial hypertension (PAH) is characterized by increased pulmonary vascular resistance resulting in increased pulmonary artery (PA) and right ventricular pressure (RV). This is associated with disturbed flow dynamics in the PA and RV that are not well characterized. We aimed to compare flow dynamics in children with PAH compared with healthy controls using blood speckle tracking echocardiography.

Methods

Patients <10 years of age with PAH and healthy controls were included. We examined flow dynamics in the main PA (MPA) and right ventricle based on acquisition blood speckle tracking images obtained from the RV and PA. Qualitative and quantitative analyses were performed.

Results

Eighteen subjects were included in each group. A diastolic vortex in the MPA was identified in 16 of the patients with PAH, but not in controls. Significantly higher MPA systolic (4.84 vs 2.42 mW/m; P = 0.01) and diastolic (0.69 vs 0.14 mW/m; P = 0.01) energy loss, as well as increased vector complexity (systole: 0.21 vs 0.04, P = 0.003; diastole: 0.13 vs 0.05, P = 0.04) and diastolic vorticity (15.2 vs 4.4 Hz; P = 0.001), were noted in PAH compared with controls.

Conclusion

This study demonstrates the presence of abnormal flow patterns in the MPA with diastolic vortex formation in most patients with PAH. This diastolic vortex likely results from reflected waves from the distal pulmonary bed. Our data indicate that the diastolic vortex could potentially be used in the diagnosis of PAH. The clinical significance of the energy loss findings warrants further investigation in a larger cohort of patients with PAH.

Correlation between Pulmonary Artery Pressure and Vortex Duration Determined by 4D Flow MRI in Main Pulmonary Artery in Patients with Suspicion of Chronic Thromboembolic Pulmonary Hypertension (CTEPH)

Chronic thromboembolic pulmonary hypertension (CTEPH) is one of the causes of pulmonary hypertension (PH) and requires invasive measurement of the mean pulmonary artery pressure (mPAP) during right heart catheterisation (RHC) for the diagnosis. 4D flow MRI could provide non-invasive parameters to estimate the mPAP. Twenty-five patients with suspected CTEPH underwent cardiac MRI. Mean vortex duration (%), pulmonary distensibility, right ventricular volumes and function were measured using 4D flow MRI and cine sequences, and compared with the mPAP measured by RHC. The mPAP measured during RHC was 33 ± 16 mmHg (10−66 mmHg). PH (defined as mPAP > 20 mmHg) was present in 19 of 25 patients (76%). A vortical flow was observed in all but two patients (92%) on 4D flow images, and vortex duration showed good correlation with the mPAP (r = 0.805; p < 0.0001). Youden index analysis showed that a vortex duration of 8.6% of the cardiac cycle provided a 95% sensitivity and an 83% specificity to detect PH. Reliability for the measurement of vortex duration was excellent for both intra-observer ICC = 0.823 and inter-observer ICC = 0.788. Vortex duration could be a useful parameter to non-invasively estimate mPAP in patients with suspected CTEPH.

Characteristics of Right Ventricular Blood Flow in Patients With Chronic Thromboembolic Pulmonary Hypertension: An Analysis With 4-Dimensional Flow Cardiovascular Magnetic Resonance Imaging

Background

Blood flow is closely related to function, but currently, the relationship of right ventricular (RV) blood flow components with RV function and hemodynamics in patients with chronic thromboembolic pulmonary hypertension (CTEPH) remains unclear. Our objective is to qualify RV function with 4-dimensional flow cardiovascular magnetic resonance (4D-Flow CMR) imaging and to investigate the correlation between RV flow and hemodynamics in patients with CTEPH.

Methods

Retrospective enrollment included 67 patients with CTEPH (mean age 47.8±14.2 years, 47 men) who underwent CMR and right heart catheterization (RHC) within 2 days. RHC was used to evaluate hemodynamics. RV flow components including the percentages of direct flow (PDF), retained inflow (PRI), delayed ejection flow (PDEF), and residual volume (PRVo) were quantified on 4D-Flow sequence. RV functional metrics were determined with the CINE balanced steady-state free precession sequence. The sum of PDF and PDEF was compared with RV eject fraction (RVEF). The correlation among RV flow components, RV functional metrics and hemodynamics was analyzed with spearman correlation analysis.

Results

The median (interquartile range) of RVEF, PDF, PDEF, PRI, and PRVo, respectively was 35.5% (18.2, 45.6%), 18% (8.4, 21.4%), 15.1% (13.5, 19.0%), 15.9% (13.8, 20.8%), and 50.6% (35.6, 60.4%). The sum of PDF and PDEF is 35.1% (24.8, 46.6%), which was similar to RVEF (z = 0.58, p = 0.561). PDF negatively correlated with right ventricular end-systolic volume index (RVESVI), right ventricular myocardial mass index (RVMI) and right ventricular global longitudinal strain (r = −0.61, −0.65, −0.64, p &lt; 0.001). PRVo positively correlated with RVESVI and RVMI (r = 0.50, 0.58, p &lt; 0.001). PDF negatively correlated with pulmonary vascular resistance (PVR) (r = −0.72, p &lt; 0.001) while it positively correlated with cardiac output (CO) and cardiac index (CI) (r = 0.64 &amp; 0.52, p &lt; 0.001). PRVo positively correlated with mean pulmonary pressure and PVR (r = 0.57&amp;0.54, p &lt; 0.001). Total five patients died in the perioperative period. RVEF in the deceased patients was similar to survivors (z = −1.163, p = 0.092). In comparison with the survivors, RVPDF in the deceased patients significantly reduced (z = −2.158, p = 0.029) while RVPDEF, RVPRI, and RVPRVo in deceased patients were similar to survivors.

Conclusion

4D-Flow CMR can provide simultaneous quantification of RV function and hemodynamics in the assessment of CTEPH without breath-holding. The reduced PDF and increased PRVo were the main characteristics of RV flow in CTEPH.

Diagnostic test accuracy of artificial intelligence analysis of cross-sectional imaging in pulmonary hypertension: a systematic literature review

OBJECTIVES

To undertake the first systematic review examining the performance of artificial intelligence (AI) applied to cross-sectional imaging for the diagnosis of acquired pulmonary arterial hypertension (PAH).

METHODS

Searches of Medline, Embase and Web of Science were undertaken on 1 July 2020. Original publications studying AI applied to cross-sectional imaging for the diagnosis of acquired PAH in adults were identified through two-staged double-blinded review. Study quality was assessed using the Quality Assessment of Diagnostic Accuracy Studies and Checklist for Artificial Intelligence in Medicine frameworks. Narrative synthesis was undertaken following Synthesis Without Meta-Analysis guidelines. This review received no funding and was registered in the International Prospective Register of Systematic Reviews (ID:CRD42020196295).

RESULTS

Searches returned 476 citations. Three retrospective observational studies, published between 2016 and 2020, were selected for data-extraction. Two methods applied to cardiac-MRI demonstrated high diagnostic accuracy, with the best model achieving AUC=0.90 (95% CI: 0.85-0.93), 89% sensitivity and 81% specificity. Stronger results were achieved using cardiac-MRI for classification of idiopathic PAH, achieving AUC=0.97 (95% CI: 0.89-1.0), 96% sensitivity and 87% specificity. One study reporting CT-based AI demonstrated lower accuracy, with 64.6% sensitivity and 97.0% specificity.

CONCLUSIONS

Automated methods for identifying PAH on cardiac-MRI are emerging with high diagnostic accuracy. AI applied to cross-sectional imaging may provide non-invasive support to reduce diagnostic delay in PAH. This would be helped by stronger solutions in other modalities.

ADVANCES IN KNOWLEDGE

There is a significant shortage of research in this important area. Early detection of PAH would be supported by further research advances on the promising emerging technologies identified.

k-t accelerated multi-VENC 4D flow MRI improves vortex assessment in pulmonary hypertension

BACKGROUND

4D flow imaging can be used to evaluate vortex formation in the pulmonary artery seen in patients with pulmonary hypertension. We evaluated if a k-t accelerated multi-VENC (velocity encoding) 4D flow acquisition improves image quality, inter-reader agreement and correlation with hemodynamic parameters.

METHODS

A total of 14 patients with pulmonary hypertension (5 females, 9 males; mean age 61 ± 16 years) underwent 4D flow MRI (magnetic resonance imaging) and right heart catheterization. In addition to that, 13 healthy volunteers (2 females, 11 males, mean age 33 ± 12 years) also underwent 4D flow MRI. Multi- and single-VENC datasets were reconstructed and evaluated for vortex formation and vortex duration by two blinded readers and image quality was rated on a 5-point scale.

RESULTS

Both readers rated image quality as significantly higher on multi-VENC datasets (3.96 ± 0.71 vs. 2.56 ± 0.93, p < 0.001; 4.70 ± 0.61 vs. 4.07 ± 0.92, p = 0.003). Inter-reader correlation for vortex duration quantification was higher on multi-VENC datasets compared to single-VENC datasets (r = 0.63 vs. r = 0.44). No significant correlation was found between vortex duration and mean pulmonary artery pressure in patients with PH.

CONCLUSION

Multi-VENC 4D flow MRI significantly improves image quality and inter-reader agreement for the evaluation of vortex formation in the pulmonary artery.

Computational simulation-derived hemodynamic and biomechanical properties of the pulmonary arterial tree early in the course of ventricular septal defects

Untreated ventricular septal defects (VSDs) can lead to pulmonary arterial hypertension (PAH) characterized by elevated pulmonary artery (PA) pressure and vascular remodeling, known as PAH associated with congenital heart disease (PAH-CHD). Though previous studies have investigated hemodynamic effects on vascular mechanobiology in late-stage PAH, hemodynamics leading to PAH-CHD initiation have not been fully quantified. We hypothesize that abnormal hemodynamics from left-to-right shunting in early stage VSDs affects PA biomechanical properties leading to PAH initiation. To model PA hemodynamics in healthy, small, moderate, and large VSD conditions prior to the onset of vascular remodeling, computational fluid dynamics simulations were performed using a 3D finite element model of a healthy 1-year-old's proximal PAs and a body-surface-area-scaled 0D distal PA tree. VSD conditions were modeled with increased pulmonary blood flow to represent degrees of left-to-right shunting. In the proximal PAs, pressure, flow, strain, and wall shear stress (WSS) increased with increasing VSD size; oscillatory shear index decreased with increasing VSD size in the larger PA vessels. WSS was higher in smaller diameter vessels and increased with VSD size, with the large VSD condition exhibiting WSS >100 dyn/cm[Formula: see text], well above values typically used to study dysfunctional mechanotransduction pathways in PAH. This study is the first to estimate hemodynamic and biomechanical metrics in the entire pediatric PA tree with VSD severity at the stage leading to PAH initiation and has implications for future studies assessing effects of abnormal mechanical stimuli on endothelial cells and vascular wall mechanics that occur during PAH-CHD initiation and progression.

Role of cardiovascular magnetic resonance in pediatric pulmonary hypertension-novel concepts and imaging biomarkers

Pulmonary hypertension (PH) in children is a heterogenous disease of the small pulmonary arteries characterized by a progressive increase in pulmonary vascular resistance. Despite adequate medical therapy, long-term pressure overload is frequently associated with a progressive course leading to right ventricular failure and ultimately death. Invasive hemodynamic assessment by cardiac catheterization is crucial for initial diagnosis, risk stratification and therapeutic strategy. Although echocardiography remains the most important imaging modality for the assessment of right ventricular function and pulmonary hemodynamics, cardiovascular magnetic resonance (CMR) has emerged as a valuable non-invasive imaging technique that enables comprehensive evaluation of biventricular performance, blood flow, morphology and the myocardial tissue. In this review, we summarize the principles and applications of CMR in the evaluation of pediatric PH patients and present an update about novel CMR based concepts and imaging biomarkers that may provide further diagnostic, therapeutic and prognostic information.

The role of 4D flow MRI for clinical applications in cardiovascular disease: current status and future perspectives

Magnetic resonance imaging (MRI) four-dimensional (4D) flow is a type of phase-contrast (PC) MRI that uses blood flow encoded in 3 directions, which is resolved relative to 3 spatial and temporal dimensions of cardiac circulation. It can be used to simultaneously quantify and visualize hemodynamics or morphology disorders. 4D flow MRI is more comprehensive and accurate than two-dimensional (2D) PC MRI and echocardiography. 4D flow MRI provides numerous hemodynamic parameters that are not limited to the basic 2D parameters, including wall shear stress (WSS), pulse wave velocity (PWV), kinetic energy, turbulent kinetic energy (TKE), pressure gradient, and flow component analysis. 4D flow MRI is widely used to image many parts of the body, such as the neck, brain, and liver, and has a wide application spectrum to cardiac diseases and large vessels. This present review aims to summarize the hemodynamic parameters of 4D flow MRI technology and generalize their usefulness in clinical practice in relation to the cardiovascular system. In addition, we note the improvements that have been made to 4D flow MRI with the application of new technologies. The application of new technologies can improve the speed of 4D flow, which would benefit clinical applications.

Evaluation and management of patients with chronic thromboembolic pulmonary hypertension - consensus statement from the ISHLT

ISHLT members have recognized the importance of a consensus statement on the evaluation and management of patients with chronic thromboembolic pulmonary hypertension. The creation of this document required multiple steps, including the engagement of the ISHLT councils, approval by the Standards and Guidelines Committee, identification and selection of experts in the field, and the development of 6 working groups. Each working group provided a separate section based on an extensive literature search. These sections were then coalesced into a single document that was circulated to all members of the working groups. Key points were summarized at the end of each section. Due to the limited number of comparative trials in this field, the document was written as a literature review with expert opinion rather than based on level of evidence.

Circulation derived from 4D flow MRI correlates with right ventricular dysfunction in patients with tetralogy of Fallot

We used 4D-flow MRI to investigate circulation, an area integral of vorticity, in the main pulmonary artery (MPA) as a new hemodynamic parameter for assessing patients with a repaired Tetralogy of Fallot (TOF). We evaluated the relationship between circulation, right ventricular (RV) function and the pulmonary regurgitant fraction (PRF). Twenty patients with a repaired TOF underwent cardiac MRI. Flow-sensitive 3D-gradient sequences were used to obtain 4D-flow images. Vortex formation in the MPA was visualized, with short-axis and longitudinal vorticities calculated by software specialized for 4D flow. The RV indexed end-diastolic/end-systolic volumes (RVEDVi/RVESVi) and RV ejection fraction (RVEF) were measured by cine MRI. The PR fraction (PRF) and MPA area were measured by 2D phase-contrast MRI. Spearman ρ values were determined to assess the relationships between circulation, RV function, and PRF. Vortex formation in the MPA occurred in 15 of 20 patients (75%). The longitudinal circulation (11.7 ± 5.1 m²/s) was correlated with the RVEF (ρ = − 0.85, p = 0.0002), RVEDVi (ρ = 0.62, p = 0.03), and RVESVi (ρ = 0.76, p = 0.003) after adjusting for the MPA size. The short-axis circulation (9.4 ± 3.4 m²/s) in the proximal MPA was positively correlated with the MPA area (ρ = 0.61, p = 0.004). The relationships between the PRF and circulation or RV function were not significant. Increased longitudinal circulation in the MPA, as demonstrated by circulation analysis using 4D flow MRI, was related to RV dysfunction in patients with a repaired TOF.

Cardiovascular Magnetic Resonance in Right Heart and Pulmonary Circulation Disorders

Right heart and pulmonary circulation disorders are generally caused by right ventricle (RV) pressure overload, volume overload, and cardiomyopathy, and they are associated with distinct clinical courses and therapeutic approaches, although they often may coexist. Cardiac magnetic resonance (CMR) provides a noninvasive accurate and reproducible multiplanar anatomic and functional assessment, tissue characterization, and blood flow evaluation of the right heart and pulmonary circulation. This article reviews the current status of the CMR, the most recent techniques, the new parameters and their clinical utility in diagnosis, prognosis, and therapeutic management in the right heart and pulmonary circulation disorders.

From Early Morphometrics to Machine Learning-What Future for Cardiovascular Imaging of the Pulmonary Circulation?

Imaging plays a cardinal role in the diagnosis and management of diseases of the pulmonary circulation. Behind the picture itself, every digital image contains a wealth of quantitative data, which are hardly analysed in current routine clinical practice and this is now being transformed by radiomics. Mathematical analyses of these data using novel techniques, such as vascular morphometry (including vascular tortuosity and vascular volumes), blood flow imaging (including quantitative lung perfusion and computational flow dynamics), and artificial intelligence, are opening a window on the complex pathophysiology and structure-function relationships of pulmonary vascular diseases. They have the potential to make dramatic alterations to how clinicians investigate the pulmonary circulation, with the consequences of more rapid diagnosis and a reduction in the need for invasive procedures in the future. Applied to multimodality imaging, they can provide new information to improve disease characterization and increase diagnostic accuracy. These new technologies may be used as sophisticated biomarkers for risk prediction modelling of prognosis and for optimising the long-term management of pulmonary circulatory diseases. These innovative techniques will require evaluation in clinical trials and may in themselves serve as successful surrogate end points in trials in the years to come.

Update on noninvasive imaging of right ventricle dysfunction in pulmonary hypertension

Pulmonary hypertension (PH) is a progressive disease affecting patients across the life span. The pathophysiology primarily involves the pulmonary vasculature and right ventricle (RV), but eventually affects the left ventricular (LV) function as well. Safe, accurate imaging modalities are critical for diagnosis, serial monitoring, and tailored therapy. While cardiac catheterization remains the conventional modality for establishing diagnosis and serial monitoring, noninvasive imaging has gained considerable momentum in providing accurate assessment of the entire RV-pulmonary axis. In this state-of-the-art review, we will discuss the most recent developments in echocardiography, magnetic resonance imaging, and computed tomography in PH evaluation from pediatric to adult population.

A Proof of Concept of a Non-Invasive Image-Based Material Characterization Method for Enhanced Patient-Specific Computational Modeling

PURPOSE

Computational models of cardiovascular structures rely on their accurate mechanical characterization. A validated method able to infer the material properties of patient-specific large vessels is currently lacking. The aim of the present study is to present a technique starting from the flow-area (QA) method to retrieve basic material properties from magnetic resonance (MR) imaging.

METHODS

The proposed method was developed and tested, first, in silico and then in vitro. In silico, fluid-structure interaction (FSI) simulations of flow within a deformable pipe were run with varying elastic modules (E) between 0.5 and 32 MPa. The proposed QA-based formulation was assessed and modified based on the FSI results to retrieve E values. In vitro, a compliant phantom connected to a mock circulatory system was tested within MR scanning. Images of the phantom were acquired and post-processed according to the modified formulation to infer E of the phantom. Results of in vitro imaging assessment were verified against standard tensile test.

RESULTS

In silico results from FSI simulations were used to derive the correction factor to the original formulation based on the geometrical and material characteristics. In vitro, the modified QA-based equation estimated an average E = 0.51 MPa, 2% different from the E derived from tensile tests (i.e. E = 0.50 MPa).

CONCLUSION

This study presented promising results of an indirect and non-invasive method to establish elastic properties from solely MR images data, suggesting a potential image-based mechanical characterization of large blood vessels.

Patient-Adaptive Magnetic Resonance Oximetry: Comparison With Invasive Catheter Measurement of Blood Oxygen Saturation in Patients With Cardiovascular Disease

BACKGROUND

The current standard method to measure intracardiac oxygen (O₂ ) saturation is by invasive catheterization. Accurate noninvasive blood O₂ saturation by MRI could potentially reduce the duration and risk of invasive diagnostic procedures.

PURPOSE

To noninvasively determine blood oxygen saturation in the heart with MRI and compare the accuracy with catheter measurements.

STUDY TYPE

Prospective.

SUBJECTS

Thirty-two patients referred for right heart catheterization (RHC) and five healthy subjects.

FIELD STRENGTH/SEQUENCE

T2-prepared single-shot balanced steady-state free-precession at 1.5T.

ASSESSMENT

MR signals in venous and arterial blood, hematocrit, and arterial O₂ saturation from a pulse oximeter were jointly processed to fit the Luz-Meiboom model and estimate blood O₂ saturation in the right heart. Interstudy reproducibility was evaluated in volunteers and patients. Interobserver reproducibility among three readers was assessed using data from volunteers and 10 patients. Accuracy of MR oximetry was compared to RHC in all patients.

STATISTICAL TESTS

Coefficient of variation, intraclass correlation coefficient, Bland-Altman analysis, Pearson's correlation.

RESULTS

The coefficient of variation for interstudy reproducibility of O₂ saturation was 2.6% on average in volunteers and 3.2% in patients. Interobserver reproducibility among three observers yielded intraclass correlation coefficients of 0.81 and 0.87 respectively for RV and MPA O₂ saturation. O₂ saturation (y = 0.85x + 0.13, R = 0.78) and (a-v)O₂ difference (y = 0.71x + 0.90, R = 0.69) by MR and RHC were significantly correlated (N = 32, P < 0.05 in both cases) in patients. MR slightly overestimated O₂ saturation compared to RHC with 2% ± 5% bias and limits of agreement between -7% and 12%.

DATA CONCLUSION

MR oximetry is repeatable and reproducible. Good agreement was shown between MR and catheter venous O₂ saturation and (a-v)O₂ difference in a cohort whose venous O₂ ranged from abnormally low to high levels, with most values in the normal physiological range.

LEVEL OF EVIDENCE

2.

TECHNICAL EFFICACY STAGE

2.

Simulation of unsteady blood flows in a patient-specific compliant pulmonary artery with a highly parallel monolithically coupled fluid-structure interaction algorithm

Computational fluid dynamics (CFD) is increasingly used to study blood flows in patient-specific arteries for understanding certain cardiovascular diseases. The techniques work quite well for relatively simple problems but need improvements when the problems become harder when (a) the geometry becomes complex (eg, a few branches to a full pulmonary artery), (b) the model becomes more complex (eg, fluid-only to coupled fluid-structure interaction), (c) both the fluid and wall models become highly nonlinear, and (d) the computer on which we run the simulation is a supercomputer with tens of thousands of processor cores. To push the limit of CFD in all four fronts, in this paper, we develop and study a highly parallel algorithm for solving a monolithically coupled fluid-structure system for the modeling of the interaction of the blood flow and the arterial wall. As a case study, we consider a patient-specific, full size pulmonary artery obtained from computed tomography (CT) images, with an artificially added layer of wall with a fixed thickness. The fluid is modeled with a system of incompressible Navier-Stokes equations, and the wall is modeled by a geometrically nonlinear elasticity equation. As far as we know, this is the first time the unsteady blood flow in a full pulmonary artery is simulated without assuming a rigid wall. The proposed numerical algorithm and software scale well beyond 10 000 processor cores on a supercomputer for solving the fluid-structure interaction problem discretized with a stabilized finite element method in space and an implicit scheme in time involving hundreds of millions of unknowns.

The evolving role of cardiac magnetic resonance in primary mitral regurgitation: ready for prime time?

A fifth of patients with primary degenerative mitral regurgitation continue to present with de novo ventricular dysfunction following surgery and higher rates of heart failure, morbidity, and mortality. This raises questions as to why the left ventricle (LV) might fail to recover and has led to support for better LV characterization; cardiac magnetic resonance (CMR) may play a role in this regard, pending further research and outcome data. CMR has widely acknowledged advantages, particularly in repeatability of measurements of volume and ejection fraction, yet recent guidelines relegate its use to cases where there is discordant information or poor-quality imaging from echocardiography because of the lack of data regarding the CMR-based ejection fraction threshold for surgery and CMR-based outcome data. This article reviews the current evidence regarding the role of CMR in an integrated surveillance and surgical timing programme.

The feasibility in estimating pulmonary vascular resistance by cardiovascular magnetic resonance in pulmonary hypertension: A systematic review and meta-analysis

PURPOSE

Cardiac magnetic resonance (CMR) is a substitute technique for noninvasively assessing pulmonary hemodynamics. Some preliminary studies have shown that CMR has the potential to quantify pulmonary vascular resistance (PVR). However, the evaluative value has not been well established. The purpose of the systematic review is to assess the feasibility of CMR in the measurement of PVR in patients with pulmonary hypertension (PH).

METHODS

Studies were retrieved from multiple databases. Methodological evaluation of CMR and right heart catheterization (RHC) in estimating PVR were obtained from included studies. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was used to assess the quality of studies. The results of comparisons of continuous variables are reported as weighted mean difference (WMD), together with the corresponding 95% confidence intervals (CIs). Summary correlation coefficient (r) values were extracted from each study, and 95% CIs were calculated after Fisher's z transformation. Sensitivity analysis was conducted to investigate potential heterogeneity.

RESULTS

A total of 15 studies were included in the systematic review, and 6 of these studies were included in the meta-analysis. The pooled WMD with fixed-effects analysis revealed no statistical significance between PVR-CMR and PVR-RHC in patients with PH (WMD = 0.278 WU; 95% CI: -0.415 to 0.972; p = 0.431). The pooled r value for all studies was 0.85 (95% CI: 0.81, 0.89), and notable heterogeneity was evident. The pooled r value after the exclusion of one heterogeneous article was 0.81 (95% CI: 0.74, 0.87) and was not significantly heterogeneous.

CONCLUSIONS

CMR and RHC have good consistency in the testing of PVR in the meta-analysis. The systematic review shows that completely noninvasive evaluation of PVR with CMR in patients with pH is feasible.

Endothelial Cell Reactive Oxygen Species and Ca2+ Signaling in Pulmonary Hypertension

Pulmonary hypertension (PH) refers to a disorder characterized by elevated pulmonary arterial pressure, leading to right ventricular overload and eventually right ventricular failure, which results in high morbidity and mortality. PH is associated with heterogeneous etiologies and distinct molecular mechanisms, including abnormal migration and proliferation of endothelial and smooth muscle cells. Although the exact details are not fully elucidated, reactive oxygen species (ROS) have been shown to play a key role in promoting abnormal function in pulmonary arterial smooth muscle and endothelial cells in PH. In endothelial cells, ROS can be generated from sources such as NADPH oxidase and mitochondria, which in turn can serve as signaling molecules in a wide variety of processes including posttranslational modification of proteins involved in Ca²⁺ homeostasis. In this chapter, we discuss the role of ROS in promoting abnormal vasoreactivity and endothelial migration and proliferation in various models of PH. Furthermore, we draw particular attention to the role of ROS-induced increases in intracellular Ca²⁺ concentration in the pathobiology of PH.

Helicity and Vorticity of Pulmonary Arterial Flow in Patients With Pulmonary Hypertension: Quantitative Analysis of Flow Formations

Background

Qualitative and quantitative flow hemodynamic indexes have been shown to reflect right ventricular (RV) afterload and function in pulmonary hypertension (PH). We aimed to quantify flow hemodynamic formations in pulmonary arteries using 4‐dimensional flow cardiac magnetic resonance imaging and the spatial velocity derivatives helicity and vorticity in a heterogeneous PH population.

Methods and Results

Patients with PH (n=35) and controls (n=10) underwent 4‐dimensional flow magnetic resonance imaging study for computation of helicity and vorticity in the main pulmonary artery (MPA), the right pulmonary artery, and the RV outflow tract. Helicity and vorticity were correlated with standard RV volumetric and functional indexes along with MPA stiffness assessed by measuring relative area change. Patients with PH had a significantly decreased helicity in the MPA (8 versus 32 m/s²; P<0.001), the right pulmonary artery (24 versus 50 m/s²; P<0.001), and the RV outflow tract–MPA unit (15 versus 42 m/s²; P<0.001). Vorticity was significantly decreased in patients with PH only in the right pulmonary artery (26 versus 45 1/s; P<0.001). Total helicity computed correlated with the cardiac magnetic resonance imaging–derived ventricular‐vascular coupling (−0.927; P<0.000), the RV ejection fraction (0.865; P<0.0001), cardiac output (0.581; P<0.0001), mean pulmonary arterial pressure (−0.581; P=0.0008), and relative area change measured at the MPA (0.789; P<0.0001).

Conclusions

The flow hemodynamic character in patients with PH assessed via quantitative analysis is considerably different when compared with healthy and normotensive controls. A strong association between helicity in pulmonary arteries and ventricular‐vascular coupling suggests a relationship between the mechanical and flow hemodynamic domains.

Diagnosis of chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is the only potentially curable form of pulmonary hypertension. Rapid and accurate diagnosis is pivotal for successful treatment. Clinical signs and symptoms can be nonspecific and risk factors such as history of venous thromboembolism may not always be present. Echocardiography is the recommended first diagnostic step. Cardiopulmonary exercise testing is a complementary tool that can help to identify patients with milder abnormalities and chronic thromboembolic disease, triggering the need for further investigation. Ventilation/perfusion (V'/Q') scintigraphy is the imaging methodology of choice to exclude CTEPH. Single photon emission computed tomography V'/Q' is gaining popularity over planar imaging. Assessment of pulmonary haemodynamics by right heart catheterisation is mandatory, although there is increasing interest in noninvasive haemodynamic evaluation. Despite the status of digital subtraction angiography as the gold standard, techniques such as computed tomography (CT) and magnetic resonance imaging are increasingly used for characterising the pulmonary vasculature and assessment of operability. Promising new tools include dual-energy CT, combination of rotational angiography and cone beam CT, and positron emission tomography. These innovative procedures not only minimise misdiagnosis, but also provide additional vascular information relevant to treatment planning. Further research is needed to determine how these modalities will fit into the diagnostic algorithm for CTEPH.

Unravelling cardiovascular disease using four dimensional flow cardiovascular magnetic resonance

Knowledge of normal and abnormal flow patterns in the human cardiovascular system increases our understanding of normal physiology and may help unravel the complex pathophysiological mechanisms leading to cardiovascular disease. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has emerged as a suitable technique that enables visualization of in vivo blood flow patterns and quantification of parameters that could potentially be of prognostic value in the disease process. In this review, current image processing tools that are used for comprehensive visualization and quantification of blood flow and energy distribution in the heart and great vessels will be discussed. Also, imaging biomarkers extracted from 4D flow CMR will be reviewed that have been shown to distinguish between normal and abnormal flow patterns. Furthermore, current applications of 4D flow CMR in the heart and great vessels will be discussed, showing its potential as an additional diagnostic modality which could aid in disease management and timing of surgical intervention.