Balloon pulmonary angioplasty reverse right ventricular remodelling and dysfunction in patients with inoperable chronic thromboembolic pulmonary hypertension: a systematic review and meta-analysis

Cone beam CT pulmonary angiography in balloon pulmonary angioplasty for chronic thromboembolic pulmonary hypertension during the program initiation period

AIM

Cone beam CT pulmonary angiography (CBCT-PA) has proven to be a valuable technique during balloon pulmonary angioplasty (BPA) for chronic thromboembolic pulmonary hypertension (CTEPH) in established centres. This study aimed to demonstrate the safety and efficacy of CBCT-PA-guided BPA for CTEPH during the initial period of a BPA program. CBCT-PA improves procedural accuracy by visualising distal thromboembolic lesions and providing real-time guidance, which is critical during program initiation.

MATERIALS AND METHODS

This single-centre, single-arm study prospectively evaluated patients with CTEPH undergoing BPA from 2017 to 2022. Outcomes of interest included pre-BPA and post-BPA 6-minute walking distance, New York Heart Association Functional Classification (NYHA-FC), mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), N-terminal pro B-type natriuretic peptide (NT-proBNP), and BPA-related adverse events (AEs). Statistical analysis compared pre-BPA and post-BPA results. CBCT-PA was used for three-dimensional (3D) vascular mapping and precise lesion targeting.

RESULTS

Ninety BPA sessions were performed on 19 patients under CBCT-PA guidance. Significant improvements were observed in mPAP (37.0 mmHg [interquartile range (IQR): 28.0-46.0] vs 25.5 [IQR: 22.8-31.5]; P<0.001), PVR (5.5 Wood units [IQR: 3.4-8.5] vs 3.3 [IQR: 2.7-4.6]; P < 0.001), NYHA-FC I-II rate (8 [42%] vs 18 [94%]; P = 0.04), and NT-proBNP (165 pg/mL [IQR: 82-1146] vs 127.0 [IQR: 57-216]; P = 0.014). Overall AE rate was 14.4%, and major AE rate was 7.7% (all Cardiovascular and Interventional Radiology Society of Europe [CIRSE] grade 3). The haemoptysis rate was 4.4%. No periprocedural deaths were reported.

CONCLUSION

BPA performed under CBCT-PA guidance appeared to be an effective and safe approach in the program's initial period, helping achieving similar results as established centres.

Right ventricular remodelling and long-term survival after pulmonary endarterectomy versus balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension

BACKGROUND

Pulmonary endarterectomy (PEA) is the treatment of choice for chronic thromboembolic pulmonary hypertension (CTEPH), while balloon pulmonary angioplasty (BPA) is an alternative for inoperable patients. We aimed to compare right ventricular (RV) remodelling and late survival after PEA and BPA.

METHODS

In this prospective observational cohort study, we performed echocardiography at baseline and follow-up in patients with CTEPH treated with PEA (n=54) or BPA (n=44) between 2011 and 2022.

RESULTS

Follow-up echocardiography was performed at 5 months (IQR 4-7) after PEA and 3 months (IQR 2-4) after the last BPA. Both groups showed significant improvements in left ventricular end-systolic eccentricity index, RV basal diameter and RV fractional area change (RV FAC). Tricuspid regurgitation pressure decreased by 26±18 mm Hg after PEA and 13±21 mm Hg after BPA (p=0.02 for between-group difference). Tricuspid annular systolic excursion (TAPSE) decreased by 4±5 mm after PEA but increased by 1±4 mm after BPA (p<0.001). The TAPSE/systolic pulmonary artery pressure ratio improved similarly in both groups. Five-year survival was 96% (95% CI 86% to 99%) for PEA and 79% (95% CI 61% to 89%) for BPA (p=0.25). Change in RV FAC was an independent predictor of survival (HR 0.9, 95% CI 0.82 to 0.99, p=0.03).

CONCLUSIONS

Both PEA and BPA led to significant RV reverse remodelling, with no clear evidence of a difference in survival rates. Improvement in RV function, particularly RV FAC, was associated with better outcomes, highlighting the importance of RV recovery in CTEPH treatment.

Cardiothoracic Imaging for Outcome Prediction in Chronic Thromboembolic Pulmonary Hypertension after Pulmonary Endarterectomy or Balloon Pulmonary Angioplasty: A Scoping Review

There has been a rapid expansion in centers performing balloon pulmonary angioplasty (BPA) and pulmonary thromboendarterectomy (PTE) for chronic thromboembolic pulmonary hypertension (CTEPH). The purpose of this scoping review was to identify cardiothoracic imaging predictors of outcomes and to identify gaps to address in future work. A scoping review was conducted using the framework outlined by Arksey and O'Malley and Levac et al. in MEDLINE and EMBASE. The study protocol was preregistered in OSF Registries and performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews (PRISMA-ScR) guidelines. There were 1117 identified studies, including 48 involving pulmonary thromboendarterectomy (n = 25) and balloon pulmonary angioplasty (n = 23). CT was the most common preoperative imaging modality used (n = 21) and CT level of disease was the most reported imaging predictor of outcomes for pulmonary thromboendarterectomy. Although must studies evaluated hemodynamic improvements, imaging was of additional use in predicting clinically significant procedural complications after balloon pulmonary angioplasty, as well as mortality and long-term outcome after pulmonary endarterectomy. Predictors reported in MRI and digital subtraction angiography were less commonly reported and warrant multicenter validation. Cardiothoracic imaging may predict clinically significant outcomes after balloon pulmonary angioplasty and pulmonary thromboendarterectomy. Radiologists involved in the assessment of CTEPH patients should be aware of key predictors and future investigations could focus on multicenter validation and new technologies.

Imaging of chronic thromboembolic pulmonary hypertension before, during and after balloon pulmonary angioplasty

Balloon pulmonary angioplasty (BPA) has recently been elevated as a class I recommendation for the treatment of inoperable or residual chronic thromboembolic pulmonary hypertension (CTEPH). Proper patient selection, procedural safety, and post-procedural evaluation are crucial in the management of these patients, with imaging work-up playing a pivotal role. Understanding the diagnostic and therapeutic imaging algorithms of CTEPH, the imaging features of patients amenable to BPA, all imaging findings observed during and immediately after the procedure and the changes observed during the follow-up is crucial for all interventional radiologists involved in the care of patients with CTEPH. This article illustrates the imaging work-up of patients with CTEPH amenable to BPA, the imaging findings observed before, during and after BPA, and provides a detailed description of all imaging modalities available for CTEPH evaluation.

Effects of right ventricular remodeling in chronic thromboembolic pulmonary hypertension on the outcomes of balloon pulmonary angioplasty: a 2D-speckle tracking echocardiography study

BACKGROUND

Balloon pulmonary angioplasty (BPA) improves the prognosis of chronic thromboembolic pulmonary hypertension (CTEPH). Right ventricle (RV) is an important predictor of prognosis in CTEPH patients. 2D-speckle tracking echocardiography (2D-STE) can evaluate RV function. This study aimed to evaluate the effectiveness of BPA in CTEPH patients and to assess the value of 2D-STE in predicting outcomes of BPA.

METHODS

A total of 76 patients with CTEPH underwent 354 BPA sessions from January 2017 to October 2022. Responders were defined as those with mean pulmonary artery pressure (mPAP) ≤ 30 mmHg or those showing ≥ 30% decrease in pulmonary vascular resistance (PVR) after the last BPA session, compared to baseline. Logistic regression analysis was performed to identify predictors of BPA efficacy.

RESULTS

BPA resulted in a significant decrease in mPAP (from 50.8 ± 10.4 mmHg to 35.5 ± 11.9 mmHg, p < 0.001), PVR (from 888.7 ± 363.5 dyn·s·cm-5 to 545.5 ± 383.8 dyn·s·cm-5, p < 0.001), and eccentricity index (from 1.3 to 1.1, p < 0.001), and a significant increase in RV free wall longitudinal strain (RVFWLS: from 15.7% to 21.0%, p < 0.001). Significant improvement was also observed in the 6-min walking distance (from 385.5 m to 454.5 m, p < 0.001). After adjusting for confounders, multivariate analysis showed that RVFWLS was the only independent predictor of BPA efficacy. The optimal RVFWLS cutoff value for predicting BPA responders was 12%.

CONCLUSIONS

BPA was found to reduce pulmonary artery pressure, reverse RV remodeling, and improve exercise capacity. RVFWLS obtained by 2D-STE was an independent predictor of BPA outcomes. Our study may provide a meaningful reference for interventional therapy of CTEPH.

Efficacy of balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension patients with pulmonary comorbidity

Background

Balloon pulmonary angioplasty (BPA) is an established treatment for inoperable chronic thromboembolic pulmonary hypertension (CTEPH), but its efficacy in CTEPH patients with a pulmonary comorbidity has not been well-studied. Here, we compared post-BPA outcomes between CTEPH patients with and without chronic pulmonary disease at baseline and analyzed predictors of BPA success.

Methods

From August 2017 to October 2022, 62 patients with inoperable CTEPH who underwent BPA were consecutively enrolled and grouped based on the presence of a pulmonary comorbidity at baseline. All patients underwent transthoracic echocardiography, pulmonary function tests, and right heart catheterization. Pre- and post-BPA data were evaluated to identify factors that influence the success of BPA.

Results

Among the 62 CTEPH patients, BPA was considered successful in 50 patients and unsuccessful in 12 patients. Responders to BPA had better exercise capacity and right heart function at baseline, but no differences in hemodynamic or respiratory function were detected between the groups. In CTEPH patients with chronic pulmonary disease (n = 14), BPA significantly improved mean pulmonary arterial pressure, pulmonary vascular resistance and right heart function parameters. Only CTEPH patients without chronic pulmonary disease (n = 48) exhibited significant improvement in 6-minute walk distance and respiratory function. Multivariate logistic regression analysis showed that pulmonary comorbidity at baseline was independently associated with the efficacy of BPA.

Conclusions

BPA provided significantly improvements in hemodynamics and right heart function in CTEPH patients, independent of pulmonary comorbidity at baseline. However, pulmonary comorbidity can negatively impact post-BPA outcomes.

Optimal short-term outcomes in balloon pulmonary angioplasty: the minimum frequency of three sessions annually

BACKGROUND

Balloon pulmonary angioplasty (BPA) is typically performed in a sequential manner.

OBJECTIVES

This study aimed to determine the lowest frequency of BPA for patients who could not reach treatment goals in a short period.

DESIGN

Retrospective cohort.

METHODS

We retrospectively enrolled 186 BPA-treated patients diagnosed with chronic thromboembolic pulmonary hypertension. According to the accumulative number of performed BPA sessions or treated pulmonary vessels or the ratio of the number of treated pulmonary vessels/the number of baseline lesions (T/P) prior to the initial occurrence of clinical outcome or censored date, we divided patients into different groups. The principal outcome was clinical worsening.

RESULTS

After stratifying patients by the number of performed BPA sessions, most baseline parameters were comparable among groups. During follow-up, 31 (16.7%) of 186 patients experienced clinical worsening. The 6-month cumulative clinical worsening-free survival rates of ⩾2 performed sessions group were significantly higher than that of 1 performed session group. The 12-month cumulative rates of clinical worsening-free survival exhibited a declining pattern in the subsequent sequence: ⩾3, 2, and 1 performed BPA sessions, and this trend persisted when follow-up time exceeded 12 months. The 6-, 12-, and 24-month cumulative clinical worsening-free survival rates were comparable between patients with 3 and ⩾4 performed BPA sessions. Similar results were also observed when stratifying patients by the accumulative number of treated pulmonary vessels (⩽8, 9-16, ⩾17) and T/P (⩽0.789, 0.790-1.263, ⩾1.264).

CONCLUSION

To achieve optimal short-term outcomes, patients might need to undergo ⩾2 BPA sessions or have ⩾9 pulmonary vessels treated or have T/P ⩾0.790 within 6 months, and undergo ⩾3 BPA sessions or have ⩾17 pulmonary vessels treated or have T/P ⩾1.264 within 12 months.

Outcome of moderate-severe tricuspid regurgitation after pulmonary endarterectomy or balloon pulmonary angioplasty

INTRODUCTION AND OBJECTIVES

The management of persistent moderate-severe tricuspid regurgitation (TR) in patients with chronic thromboembolic pulmonary hypertension after treatment with pulmonary endarterectomy (PEA) or balloon pulmonary angioplasty (BPA) is not well defined. This study aimed to analyze the progression and predictors of significant persistent postintervention TR and its prognostic impact.

METHODS

This single-center observational study included 72 patients undergoing PEA and 20 who completed a BPA program with a previous diagnosis of chronic thromboembolic pulmonary hypertension and moderate-to-severe TR.

RESULTS

The postintervention prevalence of moderate-to-severe TR was 29%, with no difference between the PEA- or BPA-treated groups (30.6% vs 25% P=.78). Compared with patients with absent-mild postprocedure TR, those with persistent TR had higher mean pulmonary arterial pressure (40.2±1.9 vs 28.5±1.3mmHg P <.001), pulmonary vascular resistance (472 [347-710] vs 282 [196-408] dyn.s/cm5; P <.001), and right atrial area (23.0 [21-31] vs 16.0 [14.0-20.0] P <.001). The variables independently associated with persistent TR were pulmonary vascular resistance> 400 dyn.s/cm5 and postprocedure right atrial area> 22cm2. No preintervention predictors were identified. The variables associated with increased 3-year mortality were residual TR and mean pulmonary arterial pressure> 30mmHg.

CONCLUSIONS

Residual moderate-to-severe TR following PEA-PBA was associated with persistently high afterload and unfavorable postintervention right chamber remodeling. Moderate-to-severe TR and residual pulmonary hypertension were associated with a worse 3-year prognosis.

Impact of Balloon Pulmonary Angioplasty on Right Ventricular Function in Patients With Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) can develop in some patients after an acute pulmonary embolism. The disease is characterized by the conversion of emboli into fibrotic thrombi that chronically impede normal circulation through the pulmonary arteries and increase pulmonary vascular resistance. Over time, this increases right ventricular (RV) afterload and strains the RV. The RV compensates by undergoing cardiomyocyte hypertrophy and RV dilation that can maintain stroke volume. However, these adaptations eventually decrease cardiac output and lead to right heart failure. Balloon pulmonary angioplasty has been developed as a treatment option for CTEPH by systematically disrupting thrombosed vessels and improving blood flow throughout the pulmonary circulation. This ultimately reverses the structural maladaptation's seen in CTEPH and improves RV function.

Balloon pulmonary angioplasty for chronic thromboembolic pulmonary hypertension: a clinical consensus statement of the ESC working group on pulmonary circulation and right ventricular function

The current treatment algorithm for chronic thromboembolic pulmonary hypertension (CTEPH) as depicted in the 2022 European Society of Cardiology (ESC)/European Respiratory Society (ERS) guidelines on the diagnosis and treatment of pulmonary hypertension (PH) includes a multimodal approach of combinations of pulmonary endarterectomy (PEA), balloon pulmonary angioplasty (BPA) and medical therapies to target major vessel pulmonary vascular lesions, and microvasculopathy. Today, BPA of >1700 patients has been reported in the literature from centers in Asia, the US, and also Europe; many more patients have been treated outside literature reports. As BPA becomes part of routine care of patients with CTEPH, benchmarks for safe and effective care delivery become increasingly important. In light of this development, the ESC Working Group on Pulmonary Circulation and Right Ventricular Function has decided to publish a document that helps standardize BPA to meet the need of uniformity in patient selection, procedural planning, technical approach, materials and devices, treatment goals, complications including their management, and patient follow-up, thus complementing the guidelines. Delphi methodology was utilized for statements that were not evidence based. First, an anatomical nomenclature and a description of vascular lesions are provided. Second, treatment goals and definitions of complete BPA are outlined. Third, definitions of complications are presented which may be the basis for a standardized reporting in studies involving BPA. The document is intended to serve as a companion to the official ESC/ERS guidelines.

Should We Change the Target of Therapy in Pulmonary Hypertension?

Despite the evolution of drug therapy in pulmonary arterial hypertension and the more aggressive treatment approach according to the guidelines, patients continue to have unacceptable mortality rates. Furthermore, specific drug therapy alone in chronic thromboembolic pulmonary hypertension also does not seem to have any beneficial impact on survival. As the function of the right ventricle (RV) determines the prognosis of patients with pulmonary hypertension, the treatment strategy should focus on modifying factors involved in RV dysfunction. Although some previous reports demonstrated that the survival of patients with pulmonary hypertension was associated with mPAP, nevertheless, mPAP is still not considered as a target of therapy. There are many examples of effective mPAP lowering with early and aggressive drug therapy in pulmonary arterial hypertension, or with interventions in chronic thromboembolic pulmonary hypertension. This effective mPAP reduction can lead to reverse RV remodeling, and thus, improvement in survival. In this article, the importance of mPAP lowering is stated, as well as why the change of our current strategy and considering mPAP reduction as the target of therapy could make pulmonary hypertension a chronic but not fatal disease.

Balloon Pulmonary Angioplasty for Chronic Thromboembolic Pulmonary Hypertension: Clinical Outcomes

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare major vessel pulmonary vascular disease that is characterised by fibrotic obstructions deriving from an organised clot. Recent advances in treatments for CTEPH have significantly improved outcomes. Apart from classical surgical pulmonary endarterectomy, balloon pulmonary angioplasty (BPA) and vasodilator drugs that were tested in randomised controlled trials of non-operable patients are now available. In Europe, CTEPH affects males and females equally. In the first European CTEPH Registry, women with CTEPH underwent pulmonary endarterectomy less frequently than men, especially at low-volume centres. In Japan, CTEPH is more common in females and is predominantly treated by BPA. More data on gender-specific outcomes are expected from the results of the International BPA Registry (NCT03245268).

A Comprehensive Assessment of Right Ventricular Function in Chronic Thromboembolic Pulmonary Hypertension

While chronic thromboembolic pulmonary hypertension (CTEPH) results from macroscopic and microscopic obstruction of the pulmonary vascular bed, the function of the right ventricle (RV) and increased RV afterload are the main determinants of its symptoms and prognosis. In this review, we assess RV function in patients diagnosed with CTEPH with a focus on the contributions of RV afterload and dysfunction to the pathogenesis of this disease. We will also discuss changes in RV function and geometry in response to treatment, including medical therapy, pulmonary endarterectomy, and balloon pulmonary angioplasty.

Cardiopulmonary disease as sequelae of long-term COVID-19: Current perspectives and challenges

COVID-19 infection primarily targets the lungs, which in severe cases progresses to cytokine storm, acute respiratory distress syndrome, multiorgan dysfunction, and shock. Survivors are now presenting evidence of cardiopulmonary sequelae such as persistent right ventricular dysfunction, chronic thrombosis, lung fibrosis, and pulmonary hypertension. This review will summarize the current knowledge on long-term cardiopulmonary sequelae of COVID-19 and provide a framework for approaching the diagnosis and management of these entities. We will also identify research priorities to address areas of uncertainty and improve the quality of care provided to these patients.

The original and two new derivative versions of the COMPERA 2.0 risk assessment model: useful tools for guiding balloon pulmonary angioplasty

Background

The COMPERA 2.0 4-stratum (4-S) risk score has been demonstrated superior over the 3-stratum (3-S) one in patients with pulmonary arterial hypertension and medically managed patients with chronic thromboembolic pulmonary hypertension (CTEPH). We aimed to determine the prognostic value of the original 4-S and 3-S COMPERA 2.0 risk score and two new derivative versions in CTEPH patients who underwent balloon pulmonary angioplasty (BPA).

Methods

We retrospectively enrolled 175 BPA-treated patients with CTEPH. We assessed the risk stratification before and after each BPA session of CTEPH patients by the original 4-S and 3-S COMPERA 2.0 risk score (by rounding decimal to the nearest integer) and two new proposed derivative versions: the modified version (by rounding decimal to the next integer) and a hybrid version that fuses the original and modified versions. The primary endpoint was clinical worsening events. The secondary outcomes were achieving low-risk profile and mean pulmonary arterial pressure (mPAP) < 30 mmHg at follow-up. We used the Kaplan–Meier curve analysis to assess the survival differences between stratified patients. The comparative model’s performance was evaluated in terms of discrimination by Harrell’s C-index.

Results

All versions of COMPERA 2.0 4-S model outperformed the 3-S one in discriminating the differences in echocardiographic and hemodynamic parameters and clinical worsening-free survival rates. The original and hybrid 4-S model could independently predict the primary and secondary endpoints, and the hybrid version seemed to perform better. The first BPA session could significantly improve risk profiles, and these changes were associated with the likelihood of experiencing clinical worsening events, achieving a low-risk profile and mPAP < 30 mmHg at follow-up. The number of BPA sessions required to achieve low risk/mPAP < 30 mmHg increased as the baseline risk score escalated.

Conclusions

The COMPERA 2.0 4-S model outperformed the 3-S one in BPA-treated patients with CTEPH. The 4-S model, especially its hybrid version, could be used to predict clinical outcome before the initiation of BPA and monitor treatment response.

Update on balloon pulmonary angioplasty for treatment of chronic thromboembolic pulmonary hypertension

PURPOSE OF REVIEW

To provide an update on balloon pulmonary angioplasty (BPA) for the treatment of chronic thromboembolic pulmonary hypertension (CTEPH), a pulmonary vascular disease that is characterized by fibro-thrombotic material mechanically obliterating major pulmonary arteries, resulting in increased pulmonary vascular resistance (PVR), progressive pulmonary hypertension (PH) combined with a microscopic pulmonary vasculopathy [1▪▪], right ventricular (RV) failure [2] and premature death.

RECENT FINDINGS

Data from a most recent CTEPH European registry (2015 and 2016) suggest significantly improved survival [3▪] of CTEPH patients compared with survival in the eighties [4], or with data from 2007 and 2009 [5]. Pulmonary endarterectomy (PEA) is still the gold-standard therapy for CTEPH [6,7]. However, only around two thirds of all CTEPH patients are amenable to surgery [3▪,5]. Patients not suitable for PEA and treated conservatively have a poor prognosis [8]. BPA may have a role for this particular group of patients. [9-11]. Currently, BPA programs are available in many countries, with excellent results at expert centers [12-15,16▪,17,18▪▪]. Based on recent data, BPA seems to have a greater impact on symptomatic and hemodynamic improvement than medical therapy with riociguat alone [15].

SUMMARY

The evidence favoring BPA is growing, but there is still a lack of published controlled trials. In addition, treatment concepts including indication, technical performance, use of PH-targeted medication, and the concept of follow-up vary between centers. In addition, there is a significant learning curve impacting outcomes [13]. The data from the International BPA registry will provide answers for some of the open questions.

An Update on the Management of Acute High-Risk Pulmonary Embolism

Hemodynamic instability and right ventricular (RV) dysfunction are the key determinants of short-term prognosis in patients with acute pulmonary embolism (PE). High-risk PE encompasses a wide spectrum of clinical situations from sustained hypotension to cardiac arrest. Early recognition and treatment tailored to each individual are crucial. Systemic fibrinolysis is the first-line pulmonary reperfusion therapy to rapidly reverse RV overload and hemodynamic collapse, at the cost of a significant rate of bleeding. Catheter-directed pharmacological and mechanical techniques ensure swift recovery of echocardiographic parameters and may possess a better safety profile than systemic thrombolysis. Further clinical studies are mandatory to clarify which pulmonary reperfusion strategy may improve early clinical outcomes and fill existing gaps in the evidence.

Right ventricle remodeling in chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is an underdiagnosed, but potentially curable pulmonary vascular disease. The increased pulmonary vascular resistance in CTEPH is caused by unresolved proximal thrombus and secondary microvasculopathy in the pulmonary vasculature, leading to adaptive and maladaptive remodeling of the right ventricle (RV), eventual right heart failure, and death. Knowledge on the RV remodeling process in CTEPH is limited. The progression to RV failure in CTEPH is a markedly slower process. A detailed understanding of the pathophysiology and underlying mechanisms of RV remodeling may facilitate early diagnosis and the development of targeted therapy. While ultrasound, magnetic resonance imaging, right heart catheterization, and serum biomarkers have been used to assess cardiac function, the current treatment strategies reduce the afterload of the right heart, but are less effective in improving the maladaptive remodeling of the right heart. This review systematically summarizes the current knowledge on adaptive and maladaptive remodeling of the right heart in CTEPH from molecular mechanisms to clinical practice.