Evaluation and Management of Chronic Thromboembolic Pulmonary Hypertension

Imaging of Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is pulmonary hypertension secondary to chronic obstruction of pulmonary arteries by organized thromboemboli. Echocardiography and Echocardiography and ventilation/perfusion (V/Q) scan are the initial screening examinations for CTEPH; the diagnosis is often missed on computed tomography (CT). Imaging findings of chronic thromboembolic pulmonary disease overlap with those of acute pulmonary embolism, and radiologists should evaluate for the presence of concurrent chronic disease in all cases of acute pulmonary embolism detected on CT pulmonary angiography. Conditions that can mimic CTEPH include in situ thrombus, vasculitis, pulmonary artery sarcoma, and fibrosing mediastinitis.

Association of insulin resistance surrogates with disease severity and adverse outcomes in chronic thromboembolic pulmonary hypertension: a multicenter cohort study

BACKGROUND

Chronic thromboembolic pulmonary hypertension (CTEPH) is a severely progressive disease that leads to right heart failure and death. Previous studies have shown that diabetes and insulin resistance (IR) are closely related to pulmonary hypertension, but the role of IR in patients with CTEPH remains unexplored. In this study, we investigated the relationship between four insulin resistance indices and disease severity, hemodynamic parameters, and adverse outcomes in patients with CTEPH.

METHODS

We conducted a multicenter, retrospective cohort study involving 516 patients diagnosed with CTEPH between January 2013 and December 2022. The metabolic score for IR (METS-IR), triglyceride to high-density lipoprotein cholesterol (TG/HDL-C) ratio, triglyceride and glucose (TyG) index, and triglyceride-glucose-body mass (TyG-BMI) index were used to quantify IR levels in patients with CTEPH. The primary endpoint events were clinical worsening. Multivariable Cox regression, restricted cubic splines, and receiver operating characteristic analyses were used to evaluate the predictive value of surrogates for IR.

RESULTS

Compared with in low to intermediate-low risk patients, the METS-IR (36.2 ± 6.7 vs. 37.7 ± 8.7, p = 0.038) and TyG-BMI index (204.0 ± 36.2 vs. 212.6 ± 46.5, p = 0.022) were significantly increased in high to intermediate-high risk patients. METS-IR correlated with markers of disease severity, such as World Health Organization functional class, 6-minute walk distance, and N-terminal pro-brain natriuretic peptide levels. During a mean of 2.5 years' follow-up, 110 participants experienced all-cause death or worsening condition. METS-IR independently predicted clinical worsening (hazard ratio: 1.27; 95% confidence interval 1.06-1.53 per 1.0-standard deviation increment, p = 0.009) after fully adjusting for covariates. Adding METS-IR to the COMPERA 2.0 risk score significantly improved its predictive ability, reclassification and discrimination ability.

CONCLUSIONS

METS-IR is an independent predictor of clinical worsening in patients with CTEPH. It offers a convenient marker for assessing disease severity and long-term outcomes in clinical risk assessment.

Interventional Strategies for Children with Progressive Pulmonary Hypertension Despite Optimal Therapy: An Official American Thoracic Society Clinical Practice Guideline

Background: Pulmonary hypertension in children is progressive with wide variability in prognosis. This document provides an evidence-based clinical practice guideline for the management of children with progressive pulmonary hypertension despite optimal therapy. Methods: A multidisciplinary panel identified pertinent questions regarding the management of children with pulmonary hypertension that has progressed despite optimal therapy, conducted systematic reviews of the relevant literature, and applied the Grading of Recommendations, Assessment, Development and Evaluation approach to develop clinical recommendations. Results: After reviewing the research evidence, the panel considered the balance of desirable (benefits) and undesirable (harms and burdens) effects of the interventions in each proposed question. Valuation of our main outcomes was also considered, together with resources required, equity, acceptability, and feasibility. Recommendations were developed for or against interventional strategies specific to children with pulmonary hypertension that has progressed despite optimal therapy. Conclusions: Although there is a growing population of children with pulmonary hypertension, there is a striking lack of empirical evidence regarding management of those whose disease has progressed despite optimal pharmacotherapy. The panel formulated and provided the rationale for clinical recommendations for or against interventional strategies on the basis of this limited empirical evidence, coupled with expert opinion, to aid clinicians in the management of these complex pediatric patients. In addition, we identified important areas for future research.

Chronic thromboembolic pulmonary hypertension: A comprehensive review of pathogenesis, diagnosis, and treatment strategies

Chronic thromboembolic pulmonary hypertension (CTEPH) is part of group 4 of the pulmonary hypertension (PH) classification and generally affects more than a third of patients referred to PH centers. It is a three-compartment disease involving proximal (lobar-to-segmental) and distal (subsegmental) pulmonary arteries that are obstructed by persistent fibrothrombotic material, and precapillary pulmonary arteries that can be affected as in pulmonary arterial hypertension. It is a rare complication of pulmonary embolism (PE), with an incidence of around 3% in PE survivors. The observed incidence of CTEPH in the general population is around six cases per million but could be three times higher than this, as estimated from PE incidence. However, a previous venous thromboembolic episode is not always documented. With advances in multimodality imaging and therapeutic management, survival for CTEPH has improved for both operable and inoperable patients. Advanced imaging with pulmonary angiography helps distinguish proximal from distal obstructive disease. However, right heart catheterization is of utmost importance to establish the diagnosis and hemodynamic severity of PH. The therapeutic strategy relies on a stepwise approach, starting with an operability assessment. Pulmonary endarterectomy (PEA), also known as pulmonary thromboendarterectomy, is the first-line treatment for operable patients. Growing experience and advances in surgical technique have enabled expansion of the distal limits of PEA and significant improvements in perioperative and mid- to long-term mortality. In patients who are inoperable or who have persistent/recurrent PH after PEA, medical therapy and/or balloon pulmonary angioplasty (BPA) are effective treatment options with favorable outcomes that are increasingly used. All treatment decisions should be made with a multidisciplinary team that includes a PEA surgeon, a BPA expert, and a chest radiologist.

Association of Fibrinogen Aα Thr312Ala (rs6050) Polymorphism with Venous Thrombosis and Chronic Thromboembolic Pulmonary Hypertension: A Meta-Analysis

BACKGROUND

Venous thromboembolism (VTE) comprises deep vein thrombosis (DVT) and pulmonary embolism (PE). Chronic thromboembolic pulmonary hypertension (CTEPH) typically arises from acute pulmonary embolism. The pathogenesis of them involves multiple risk factors such as genetic predisposition. However, the findings from these studies are not entirely consistent. This study aims to investigate the association between FGA rs6050 polymorphism and susceptibility to thrombotic diseases.

METHODS

We searched PubMed, OVID, Web of Science, Academic Search Ultimate, CNKI, and Wan Fang database. To assess the strength of associations, we calculated pooled odds ratios (ORs) and 95% confidence intervals (CIs) in different genetic models. Additionally, subgroup analyses, sensitivity analysis, and assessment of publication bias were also carried out.

RESULTS

A total of 11 studies, including 9 reported results on VTE (3856 individuals [1545 cases]) and 3 on CTEPH (761 participants [350 cases]), revealed a significant association between the rs6050 polymorphism and susceptibility to both VTE and CTEPH. The A allele was consistently linked to an elevated risk of VTE across all genetic models (allele, homozygote, heterozygote, recessive, and dominant model), while it was also associated with an increased risk of CTEPH under all genetic models excluding the recessive model. Furthermore, subgroup analysis among ethnic groups revealed a significant association between rs6050 polymorphisms and VTE in both Caucasians and Asians under all genetic models. In Africans, the association with VTE was only observed for rs6050 polymorphisms in dominant and heterozygous models.

CONCLUSIONS

The FGA rs6050 polymorphism is positively associated with susceptibility to VTE and CTEPH.

Post-Pulmonary Embolism Syndrome-A Diagnostic Dilemma and Challenging Management

Historically, research on pulmonary embolism (PE) management has focused on short-term outcomes, such as acute cardiovascular collapse, change in right ventricular function, and in-hospital mortality. However, long-standing functional impairments from acute PE occur in up to half of all patients. This chronic syndrome has been termed the post-PE syndrome, which describes patients who have persistent or worsening symptoms, functional limitations, and cardiorespiratory impairment not explained by a comorbid condition. Diagnosis and management are challenging, and post-PE syndrome remains an underrecognized and undertreated condition. This review seeks to increase awareness of the syndrome that affects a significant portion of PE survivors. The epidemiology, pathophysiology, and clinical features are discussed, followed by a description of imaging findings and management options across the entire spectrum of post-PE syndrome.

Establishment of mouse models for severe pulmonary hypertension through 'double-hit' strategies

Mouse models are crucial for understanding pulmonary hypertension (PH) mechanisms and developing therapies, but existing mouse models under hypoxia only exhibit mild PH. To address this, we established a double-hit model combining unilateral pneumonectomy (LPx) or left pulmonary artery ligation (LPAL) with hypoxia exposure in C57BL/6 mice. Our detailed haemodynamic and histological evaluations post-surgery demonstrated pronounced elevations in right ventricular systolic pressure (RVSP) (LPAL: 41.1 ± 4.63 mmHg, P = 0.005; LPx: 38.4 ± 2.95 mmHg, P = 0.002; Sham: 32.1 ± 2.21 mmHg) and pulmonary vascular wall thickness (LPAL: 56.9 ± 3.34%, P = 0.02; LPx: 54.3 ± 4.65%, P = 0.04; Sham: 44.8 ± 3.76%) compared to hypoxia-exposed sham-operated controls, reflecting a more severe PH phenotype. These novel models, which exhibit haemodynamic alterations akin to the established hypoxia with SU5416-induced PH model as per published data, could offer a substantial contribution to future PH research and therapeutic development.

Clinical Profile and Outcomes of Pulmonary Embolism in Central Iran: A Retrospective Cohort Study

BACKGROUND

Pulmonary embolism (PE) is a significant public health concern. This retrospective cohort study examines the clinical profiles and outcomes of patients diagnosed with PE at a medical center in central Iran, aiming to identify mortality predictors during hospitalization and follow-up.

METHODS

Data from 109 patients diagnosed with PE were analyzed, with a median follow-up of 23 months. The collected information included demographic and clinical characteristics, laboratory findings, treatment protocols, and outcomes. Logistic regression and Kaplan-Meier survival analysis were used to identify independent mortality predictors and assess survival impact.

RESULTS

The mean age was 59.2 years (±19.7), with 51.4% male. Common symptoms included dyspnea (86%) and chest pain (53%), with non-massive PE being the most prevalent (63%). Independent mortality predictors identified were age (odds ratio [OR] 1.065 per year, P<0.001), female sex (OR 4.421, P=0.009), and PE severity (OR 0.262, P=0.023). Kaplan-Meier analysis showed reduced survival probabilities in females (P=0.009), those with provoked PE (P=0.002), patients over 65 (P=0.016), and individuals with comorbidities (P=0.018). In-hospital mortality was 10.1%, linked to provoked massive PE, absence of thrombolytic therapy, and reduced left ventricular ejection fraction (LVEF).

CONCLUSION

In this cohort, age, sex, and PE severity were significant mortality predictors, while provoked PE, advanced age, and comorbidities were associated with lower mid-term survival probabilities.

A new perspective on targeting pulmonary arterial hypertension: Programmed cell death pathways (Autophagy, Pyroptosis, Ferroptosis)

Pulmonary arterial hypertension (PAH) is a severe cardiovascular disease characterized by elevated pulmonary vascular resistance, progressive increases in pulmonary artery pressures, ultimately leading to right-sided heart failure, and potentially mortality. Pulmonary vascular remodeling is pivotal in PAH onset and progression. While targeted drug therapies have notably ameliorated PAH prognosis, current medications primarily focus on vascular vasodilation, with limited ability to reverse pulmonary vascular remodeling fundamentally, resulting in suboptimal patient prognoses. Cellular death in pulmonary vasculature, once thought to be confined to apoptosis and necrosis, has evolved with the identification of pyroptosis, autophagy, and ferroptosis, revealing their association with vascular injury in PAH. These novel forms of regulated cellular death impact reactive oxygen species (ROS) generation, calcium stress, and inflammatory cascades, leading to pulmonary vascular cell loss, exacerbating vascular injury, and mediating adverse remodeling, inflammation, immune anomalies, and current emerging mechanisms (such as endothelial-mesenchymal transition, abnormal energy metabolism, and epigenetic regulation) in the pathogenesis of PAH. This review comprehensively delineates the roles of autophagy, pyroptosis, and ferroptosis in PAH, elucidating recent advances in their involvement and regulation of vascular injury. It juxtaposes their distinct functions in PAH and discusses the interplay of these programmed cell deaths in pulmonary vascular injury, highlighting the benefits of combined targeted therapies in mitigating pulmonary arterial hypertension-induced vascular injury, providing novel insights into targeted treatments for pulmonary arterial hypertension.

Molecular Pathophysiology of Chronic Thromboembolic Pulmonary Hypertension: A Clinical Update from a Basic Research Perspective

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare but severe condition characterized by persistent obstruction and vascular remodeling in the pulmonary arteries following an acute pulmonary embolism (APE). Although APE is a significant risk factor, up to 25% of CTEPH cases occur without a history of APE or deep vein thrombosis, complicating the understanding of its pathogenesis. Herein, we carried out a narrative review discussing the mechanisms involved in CTEPH development, including fibrotic thrombus formation, pulmonary vascular remodeling, and abnormal angiogenesis, leading to elevated pulmonary vascular resistance and right heart failure. We also outlined how the disease's pathophysiology reveals both proximal and distal pulmonary artery obstruction, contributing to the development of pulmonary hypertension. We depicted the risk factors predicting CTEPH, including thrombotic history, hemostatic disorders, and certain medical conditions. We finally looked at the molecular mechanisms behind the role of endothelial dysfunction, gene expression alterations, and inflammatory processes in CTEPH progression and detection. Despite these insights, there is still a need for improved diagnostic tools, biomarkers, and therapeutic strategies to enhance early detection and management of CTEPH, ultimately aiming to reduce diagnostic delay and improve patient outcomes.

Chronic thromboembolic pulmonary disease

Chronic thromboembolic pulmonary hypertension is a complication of pulmonary embolism and a treatable cause of pulmonary hypertension. The pathology is a unique combination of mechanical obstruction due to failure of clot resolution, and a variable degree of microvascular disease, that both contribute to pulmonary vascular resistance. Accordingly, multiple treatments have been developed to target the disease components. However, accurate diagnosis is often delayed. Evaluation includes high-quality imaging modalities, necessary for disease confirmation and for appropriate treatment planning. All patients with chronic thromboembolic pulmonary disease, and especially those with pulmonary hypertension, should be referred to expert centres for multidisciplinary team decision on treatment. The first decision remains assessment of operability, and the best improvement in symptoms and survival is achieved by the mechanical therapies, pulmonary endarterectomy and balloon pulmonary angioplasty. With the advances in multimodal therapies, excellent outcomes can be achieved with 3-year survival of >90%.

Tricuspid annular plane systolic excursion to pulmonary artery systolic pressure ratio in chronic thromboembolic pulmonary hypertension improves with balloon pulmonary angioplasty

Right ventricle (RV)-to-pulmonary artery (PA) coupling measured by the ratio of echocardiography-derived tricuspid annular plane systolic excursion (TAPSE) and pulmonary artery systolic pressure (PASP) is a meaningful prognostic marker in pulmonary hypertension (PH). It's unclear if balloon pulmonary angioplasty (BPA) treatment of chronic thromboembolic pulmonary hypertension (CTEPH) alters RV-PA coupling measured by TAPSE/PASP. We reviewed CTEPH patients treated with BPA at our institution who had a transthoracic echocardiogram (TTE) before BPA and a follow-up TTE at any point during BPA. TAPSE was obtained from the initial and lattermost TTE; hemodynamics were obtained before each BPA session. Between March 2015 to October 2023, there were 228 patients treated with BPA. After excluding post-PTE patients and those without PH, 67 were included. Initial TAPSE/PASP was 0.39 ± 0.21 mm/mmHg. Using previously defined TAPSE/PASP tertiles in PH (<0.19, 0.19-0.32, >0.32 mm/mmHg), there were 6 patients (9%) in low, 30 (45%) in middle, and 31 (46%) in the high tertiles at baseline. The lower TAPSE/PASP tertiles had more severe baseline hemodynamics (p < 0.001) compared to the high TAPSE/PASP cohort. At follow-up, TAPSE/PASP improved to 0.47 ± 0.20 mm/mmHg (p = 0.023), with 2 (3%), 13 (19%), and 52 (78%) patients in the low, middle, high TAPSE/PASP tertiles, respectively. As patients progress through BPA sessions, the TAPSE/PASP ratio increases, possibly reflecting improved RV mechanics and RV-PA coupling. TAPSE/PASP ratio as a marker of RV-PA coupling can improve with BPA treatment and may be an important measure to follow during treatment of CTEPH.

Impact of an expert-derived, quick hands-on tool on classifying pulmonary hypertension in chest computed tomography: a study on inexperienced readers using RAPID-CT-PH

PURPOSE

To test the inter-reader agreement in classifying pulmonary hypertension (PH) on chest contrast-enhanced computed tomography (CECT) between a consensus of two cardio-pulmonary-devoted radiologists (CRc) and inexperienced readers (radiology residents, RRs) when using a CECT-based quick hands-on tool built upon PH imaging literature, i.e., the "Rapid Access and Practical Information Digest on Computed Tomography for PH-RAPID-CT-PH".

MATERIAL AND METHODS

The observational study retrospectively included 60 PH patients who underwent CECT between 2015 and 2022. Four RRs independently reviewed all CECTs and classified each case into one of the five PH groups per the 2022 ESC/ERS guidelines. While RR3 and RR4 (RAPID-CT-PH group) used RAPID-CT-PH, RR1 and RR2 (control group) did not. RAPID-CT-PH and control groups' reports were compared with CRc using unweighted Cohen's Kappa (k) statistics. RRs' report completeness and reporting time were also compared using the Wilcoxon-Mann-Whitney test.

RESULTS

The inter-reader agreement in classifying PH between the RAPID-CT-PH group and CRc was substantial (k = 0.75 for RR3 and k = 0.65 for RR4); while, it was only moderate for the control group (k = 0.57 for RR1 and k = 0.49 for RR2). Using RAPID-CT-PH resulted in significantly higher report completeness (all p < 0.0001) and significantly lower reporting time (p < 0.0001) compared to the control group.

CONCLUSION

RRs using RAPID-CT-PH showed a substantial agreement with CRc on CECT-based PH classification. RAPID-CT-PH improved report completeness and reduced reporting time. A quick hands-on tool for classifying PH on chest CECT may help inexperienced radiologists effectively contribute to the PH multidisciplinary team.

Sex differences in Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is an underdiagnosed sequela of acute pulmonary embolism with varied clinical presentation causing significant morbidity among the affected population. There exist important differences in the occurrence, clinical features and diagnosis of CTEPH between men and women, with women carrying a greater predisposition for the disease. Ongoing studies have also pointed out variations among men and women, in the treatment offered and long-term outcomes including mortality. This focused review article highlights important sex-associated differences in multiple aspects of CTEPH including its epidemiology, clinical features, diagnosis, treatment and outcomes as reported in current literature and highlights the need for future research to facilitate a clearer understanding of these differences.

The Importance of Topographical Recognition of Pulmonary Arteries in Diagnostics and Treatment of CTEPH, Based on an Analysis of a Dissected Case Model-A Pilot Study

BACKGROUND

Knowledge of the anatomy of pulmonary arteries is essential in many invasive procedures concerning pulmonary circulation. In the diagnosis and treatment of chronic thromboembolic pulmonary hypertension (CTEPH), two-dimensional (2D) pulmonary angiography is used. Recognizing the topographic course of the pulmonary arteries and understanding the status in three dimensions (3D) is paramount. This study aimed to evaluate and describe the branching variant of pulmonary arteries in a single case, as well as morphological parameters of the segmental arteries, like length, diameter and branching angles.

METHODS

One pair of embalmed human cadaver lungs was dissected by a scalpel and surgical forceps and was measured up to the subsegmental arteries.

RESULTS

The diameters (ranging from 3.04 to 9.29 mm) and lengths (ranging from 9.09 to 53.91 mm) of the pulmonary segmental arteries varied. The proximal branching angles were wide and close to perpendicular, while distally, the angles between the segmental and subsegmental arteries were narrower (30-45°). Upon evaluating the branching, rare variations were identified and delineated, notably in the lower lobes of both lungs.

CONCLUSIONS

Utilizing knowledge and data in clinical settings is instrumental for effectively diagnosing and treating CTEPH. Further research is required to explore the complications in invasive procedures related to various anatomical variations.

Appropriateness guidelines for inferior vena cava filter utilization: A contemporary review

Concern regarding the exponential increase in optional utilization of inferior vena cava filters (IVCFs) in the early 2000s with a persistent low retrieval rate nationwide has resulted in increased scrutiny regarding clinical application of IVCFs. IVCFs are used in a variety of clinical scenarios, ranging from thromboembolic protection in patients with deep venous thrombosis and contraindication to anticoagulation to prophylactic deployment in multitrauma and critically ill patients. Evidence supporting IVCFs as mechanical thromboembolic protection in certain clinical scenarios has been established through evidenced-based guidelines. As an adjunct to evidence-based guidelines, appropriateness criteria to address specific clinical scenarios and facilitate clinical decision making when considering placement of an IVCF have been developed. In this review, current evidence-based and appropriateness guidelines are summarized.

Chronic Thromboembolic Pulmonary Hypertension: Clinical and Imaging Evaluation

Chronic thromboembolic pulmonary hypertension (CTEPH) is a complication of pulmonary embolism and is an important cause of pulmonary hypertension. As a clinical entity, it is frequently underdiagnosed with prolonged diagnostic delays. This study reviews the clinical and radiographic findings associated with CTEPH to improve awareness and recognition. Strengths and limitations of multiple imaging modalities are reviewed. Accompanying images are provided to supplement the text and provide examples of important findings for the reader.

Systemic Sclerosis-Associated Pulmonary Arterial Hypertension: From Bedside to Bench and Back Again

Systemic sclerosis (SSc) is a heterogeneous disease characterized by autoimmunity, vasculopathy, and fibrosis which affects the skin and internal organs. One key aspect of SSc vasculopathy is pulmonary arterial hypertension (SSc-PAH) which represents a leading cause of morbidity and mortality in patients with SSc. The pathogenesis of pulmonary hypertension is complex, with multiple vascular cell types, inflammation, and intracellular signaling pathways contributing to vascular pathology and remodeling. In this review, we focus on shared molecular features of pulmonary hypertension and those which make SSc-PAH a unique entity. We highlight advances in the understanding of the clinical and translational science pertinent to this disease. We first review clinical presentations and phenotypes, pathology, and novel biomarkers, and then highlight relevant animal models, key cellular and molecular pathways in pathogenesis, and explore emerging treatment strategies in SSc-PAH.

Progressive Dyspnea on Exertion in an 82-Year-Old

An older patient with hereditary hemorrhagic telangiectasia and right lower lobe segmental pulmonary embolism presented with dyspnea that had worsened over 5 years; physical examination and laboratory testing showed jugular venous distension, a cardiac systolic murmur, right ventricular heave, bilateral lower extremity edema to the knees, and elevated brain-type natriuretic peptide level. What is the diagnosis and what would you do next?

Chronic Thromboembolic Pulmonary Hypertension: A Review of the Multifaceted Pathobiology

Chronic thromboembolic pulmonary disease results from the incomplete resolution of thrombi, leading to fibrotic obstructions. These vascular obstructions and additional microvasculopathy may lead to chronic thromboembolic pulmonary hypertension (CTEPH) with increased pulmonary arterial pressure and pulmonary vascular resistance, which, if left untreated, can lead to right heart failure and death. The pathobiology of CTEPH has been challenging to unravel due to its rarity, possible interference of results with anticoagulation, difficulty in selecting the most relevant study time point in relation to presentation with acute pulmonary embolism (PE), and lack of animal models. In this article, we review the most relevant multifaceted cross-talking pathogenic mechanisms and advances in understanding the pathobiology in CTEPH, as well as its challenges and future direction. There appears to be a genetic background affecting the relevant pathological pathways. This includes genetic associations with dysfibrinogenemia resulting in fibrinolysis resistance, defective angiogenesis affecting thrombus resolution, and inflammatory mediators driving chronic inflammation in CTEPH. However, these are not necessarily specific to CTEPH and some of the pathways are also described in acute PE or deep vein thrombosis. In addition, there is a complex interplay between angiogenic and inflammatory mediators driving thrombus non-resolution, endothelial dysfunction, and vascular remodeling. Furthermore, there are data to suggest that infection, the microbiome, circulating microparticles, and the plasma metabolome are contributing to the pathobiology of CTEPH.