Regional septal hinge-point injury contributes to adverse biventricular interactions in pulmonary hypertension

Adverse remodelling in tetralogy of Fallot: From risk factors to imaging analysis and future perspectives

Although contemporary outcomes of initial surgical repair of tetralogy of Fallot (TOF) are excellent, the survival of adult patients remains significantly lower than that of the normal population due to the high incidence of heart failure, ventricular arrhythmias, and sudden cardiac death. The underlying mechanisms are only partially understood but involve an adverse biventricular response, so-called remodelling, to key stressors such as right ventricular (RV) pressure-and/or volume-overload, myocardial fibrosis, and electro-mechanical dyssynchrony. In this review, we explore risk factors and mechanisms of biventricular remodelling, from histological to electro-mechanical aspects, and the role of imaging in their assessment. We discuss unsolved challenges and future directions to better understand and treat the long-term sequelae of this complex congenital heart disease.

Myocardial Fibrosis in Pediatric Patients With Ebstein's Anomaly

BACKGROUND

Left ventricular dysfunction in Ebstein's anomaly (EA) is associated with higher mortality. The health of the left ventricular myocardium in children and adolescents with EA has not been investigated in detail.

METHODS

Patients with unrepaired EA who had undergone cardiac magnetic resonance imaging including T1 mapping were retrospectively reviewed. Patients were compared with age- and sex-matched controls. EA severity index was calculated using volumetric measurements at end diastole ([right atrial+atrialized right ventricular volumes]/[functional right ventricular+left atrial+left ventricular volumes]). Global circumferential and radial strain and as well as strain rate were examined using cardiac magnetic resonance feature tracking.

RESULTS

Twelve EA patients and an equal number of controls were included. Functional and atrialized right ventricular end-diastolic volumes were 84±15 and 21±13 mL/m², respectively. Late gadolinium enhancement, confined to the right ventricle, was found in 2 patients (16%). Left ventricular native T1 values and extracellular volume fractions were higher in patients compared with controls (1026±47 versus 956±40 ms, P=0.0004 and 28.5±3.4% versus 22.5±2.6%, P<0.001, respectively). Native T1 times correlated inversely with patients' age, body surface area, and O₂ saturations (r=-0.63, -0.62, and -0.91, respectively; P=0.02, P=0.02, and P<0.0001, respectively). EA severity index ranged between 0.15 and 0.94 and correlated with T1 values (r=0.76, P=0.003). Native T1 correlated with global circumferential strain (r=0.58, P=0.04) but not ejection fraction (EF). EA patients had reduced maximum oxygen uptake (Vo₂max). Vo₂max correlated inversely with T1 values (r=-0.79, P=0.01).

CONCLUSIONS

Children and adolescents with EA experience an abnormal degree of diffuse myocardial fibrosis. Its association with O₂ saturation points toward a role of hypoxemia in the pathogenesis of fibrosis. Larger and prospective studies are needed to evaluate the value of T1 mapping for risk stratification and monitoring in EA.

Asymmetric Regional Work Contributes to Right Ventricular Fibrosis, Inefficiency, and Dysfunction in Pulmonary Hypertension versus Regurgitation

BACKGROUND

Right ventricular (RV) pressure loading from pulmonary hypertension (PH) and volume loading from pulmonary regurgitation (PR) lead to RV dysfunction, a critical determinant of clinical outcomes, but their impact on regional RV mechanics and fibrosis is poorly characterized. The aim of this study was to test the hypothesis that regional myocardial mechanics and efficiency in RV pressure and volume loading are associated with RV fibrosis and dysfunction.

METHODS

Eight PH, six PR, and five sham-control rats were studied. The PH rat model was induced using Sugen5416, a vascular endothelial growth factor receptor 2 inhibitor, combined with chronic hypoxia. PR rats were established by surgical laceration of the pulmonary valve leaflets. Six (n = 4) or 9 (n = 4) weeks after Sugen5416 and hypoxia and 12 weeks after PR surgery, myocardial strain and RV pressure were measured and RV pressure-strain loops generated. We further studied RV regional mechanics in 11 patients with PH. Regional myocardial work was calculated as the pressure-strain loop area (mm Hg ∙ %). Regional myocardial work efficiency was quantified through wasted work (ratio of systolic lengthening to shortening work). The relation of regional myocardial work to RV fibrosis and dysfunction was analyzed.

RESULTS

In rats, PH and PR induced similar RV dilatation, but fractional area change (%) was lower in PH than in PR. RV lateral wall work was asymmetrically higher in PH compared with sham, while septal work was similar to sham. In PR, lateral and septal work were symmetrically higher versus sham. Myocardial wasted work ratio was asymmetrically increased in the PH septum versus sham. Fibrosis in the RV lateral wall, but not septum, was higher in PH than PR. RV fibrosis burden was linearly related to regional work and to measures of RV systolic and diastolic function but not to wasted myocardial work ratio. Patients with PH demonstrated similar asymmetric and inefficient regional myocardial mechanics.

CONCLUSIONS

Asymmetric RV work and increased wasted septal work in experimental PH are associated with RV fibrosis and dysfunction. Future investigation should examine whether assessment of asymmetric regional RV work and efficiency can predict clinical RV failure and influence patient management.

The role of regenerative therapy in the treatment of right ventricular failure: a literature review

Right ventricular (RV) failure is a commonly encountered problem in patients with congenital heart disease but can also be a consequence of left ventricular disease, primary pulmonary hypertension, or RV-specific cardiomyopathies. Improved survival of the aforementioned pathologies has led to increasing numbers of patients suffering from RV dysfunction, making it a key contributor to morbidity and mortality in this population. Currently available therapies for heart failure were developed for the left ventricle (LV), and there is clear evidence that LV-specific strategies are insufficient or inadequate for the RV. New therapeutic strategies are needed to address this growing clinical problem, and stem cells show significant promise. However, to properly evaluate the prospects of a potential stem cell-based therapy for RV failure, one needs to understand the unique pathophysiology of RV dysfunction and carefully consider available data from animal models and human clinical trials. In this review, we provide a comprehensive overview of the molecular mechanisms involved in RV failure such as hypertrophy, fibrosis, inflammation, changes in energy metabolism, calcium handling, decreasing RV contractility, and apoptosis. We also summarize the available preclinical and clinical experience with RV-specific stem cell therapies, covering the broad spectrum of stem cell sources used to date. We describe two different scientific rationales for stem cell transplantation, one of which seeks to add contractile units to the failing myocardium, while the other aims to augment endogenous repair mechanisms and/or attenuate harmful remodeling. We emphasize the limitations and challenges of regenerative strategies, but also highlight the characteristics of the failing RV myocardium that make it a promising target for stem cell therapy.

Animal models of right heart failure

Right heart failure may be the ultimate cause of death in patients with acute or chronic pulmonary hypertension (PH). As PH is often secondary to other cardiovascular diseases, the treatment goal is to target the underlying disease. We do however know, that right heart failure is an independent risk factor, and therefore, treatments that improve right heart function may improve morbidity and mortality in patients with PH. There are no therapies that directly target and support the failing right heart and translation from therapies that improve left heart failure have been unsuccessful, with the exception of mineralocorticoid receptor antagonists. To understand the underlying pathophysiology of right heart failure and to aid in the development of new treatments we need solid animal models that mimic the pathophysiology of human disease. There are several available animal models of acute and chronic PH. They range from flow induced to pressure overload induced right heart failure and have been introduced in both small and large animals. When initiating new pre-clinical or basic research studies it is key to choose the right animal model to ensure successful translation to the clinical setting. Selecting the right animal model for the right study is hence important, but may be difficult due to the plethora of different models and local availability. In this review we provide an overview of the available animal models of acute and chronic right heart failure and discuss the strengths and limitations of the different models.

Morphological and Functional Characteristics of Animal Models of Myocardial Fibrosis Induced by Pressure Overload

Myocardial fibrosis is characterized by excessive deposition of myocardial interstitial collagen, abnormal distribution, and excessive proliferation of fibroblasts. According to the researches in recent years, myocardial fibrosis, as the pathological basis of various cardiovascular diseases, has been proven to be a core determinant in ventricular remodeling. Pressure load is one of the causes of myocardial fibrosis. In experimental models of pressure-overload-induced myocardial fibrosis, significant increase in left ventricular parameters such as interventricular septal thickness and left ventricular posterior wall thickness and the decrease of ejection fraction are some of the manifestations of cardiac damage. These morphological and functional changes have a serious impact on the maintenance of physiological functions. Therefore, establishing a suitable myocardial fibrosis model is the basis of its pathogenesis research. This paper will discuss the methods of establishing myocardial fibrosis model and compare the advantages and disadvantages of the models in order to provide a strong basis for establishing a myocardial fibrosis model.

Relation between right ventricular wall stress, fibrosis, and function in right ventricular pressure loading

Right ventricle (RV) pressure loading can lead to RV fibrosis and dysfunction. We previously found increased RV, septal hinge-point and left ventricle (LV) fibrosis in experimental RV pressure loading. However, the relation of RV wall stress to biventricular fibrosis and dysfunction is incompletely defined. Rabbits underwent progressive pulmonary artery banding (PAB) over 3 wk with hemodynamics, echocardiography, and myocardial samples obtained at a terminal experiment at 6 wk. An additional group received PAB and treatment with an endothelin receptor antagonist. The endocardial and epicardial borders of short-axis echo images were traced and analyzed with invasive pressures to yield regional end-diastolic (ED) and end-systolic (ES) wall stress. To increase clinical translation, computer model-derived wall stress was compared with Laplace wall stress. The relation of wall stress with fibrosis (picrosirius red staining) and ventricular function was analyzed. ED wall stress in all regions and RV and LV free-wall ES wall stress were increased in PAB rabbits versus sham animals. Laplace wall stress correlated well with computational models. In PAB, fibrosis was highest in the RV free wall, then septal hinge regions, and lowest in the septum and LV free wall. Fibrosis was moderately related to ED (r = 0.47, P = 0.0011), but not ES wall stress. RV ED wall stress was strongly related to echo indexes of function (strain rate: r = 0.71, P = 0.048; E', r = -0.75, P = 0.0077; tricuspid annular plane systolic excursion: r = 0.85, P = 0.0038) and RV fractional area change (r = 0.77, P = 0.027). ED, more than ES, wall stress is related moderately to fibrosis and strongly to function in experimental RV pressure loading, especially at the septal hinge-point regions, where fibrosis is prominent. This suggests that wall stress partially links RV pressure loading, fibrosis, and dysfunction and may be useful to follow clinically.NEW & NOTEWORTHY Biventricular fibrosis and dysfunction impact outcomes in RV pressure loading, but their relation to wall stress is poorly defined. Using a pulmonary artery band rabbit model, we entered echocardiography and catheter data into a computer model to yield regional end-diastolic (EDWS) and end-systolic (ESWS) wall stress. EDWS, more than ESWS, correlated with fibrosis and dysfunction, especially at the fibrosis-intense septal hinge-point regions. Thus, wall stress may be clinically useful in linking RV pressure loading to regional fibrosis and dysfunction.

Early Left Ventricular Involvement Detected by Cardiovascular Magnetic Resonance Feature Tracking in Arrhythmogenic Right Ventricular Cardiomyopathy: The Effects of Left Ventricular Late Gadolinium Enhancement and Right Ventricular Dysfunction

Background

Left ventricular (LV) involvement is common in arrhythmogenic right ventricular cardiomyopathy (ARVC). We aim to evaluate LV involvement in ARVC patients by cardiovascular magnetic resonance feature tracking.

Methods and Results

Sixty‐eight patients with ARVC and 30 controls were prospectively enrolled. ARVC patients were divided into 2 subgroups: the preserved LV ejection fraction (LVEF) group (LVEF ≥55%, n=27) and the reduced LVEF group (LVEF <55%, n=41). Cardiovascular magnetic resonance with late gadolinium enhancement (LGE) and cardiovascular magnetic resonance feature tracking were performed in all subjects. LV global and regional (basal, mid, apical) peak strain (PS) in radial, circumferential and longitudinal directions were assessed, respectively. Right ventricular global PS in three directions were also analyzed. Compared with the controls, LV global and regional PS were all significantly impaired in the reduced LVEF group (all P<0.05). However, only LV global longitudinal PS as well as mid and apical longitudinal PS were impaired in the preserved LVEF group (all P<0.05), and all these parameters were significantly associated with right ventricular global radial PS (r=−0.47, −0.47, and −0.49, respectively, all P<0.001). The reduced LVEF group showed significantly higher prevalence of LGE (95.10% versus 63.00%, P=0.002) than the preserved LVEF group. Moreover, LV radial PS was significantly reduced in LV segments with LGE (33.15±20.42%, n=46) than those without LGE (41.25±15.98%, n=386) in the preserved LVEF group (P=0.016).

Conclusions

In patients with ARVC, cardiovascular magnetic resonance feature tracking could detect early LV dysfunction, which was associated with LV myocardial LGE and right ventricular dysfunction.

Dacomitinib, a new pan-EGFR inhibitor, is effective in attenuating pulmonary vascular remodeling and pulmonary hypertension

Accumulating evidence suggests that epidermal growth factor receptor (EGFR) plays a role in the progression of pulmonary arterial hypertension (PAH). Clinically-approved epidermal growth factor inhibitors such as gefitinib, erlotinib, and lapatinib have been explored for PAH. However, None of them were able to attenuate PAH. So, we explored the role of dacomitinib, a new pan-EGFR inhibitor, in PAH. Adult male Sprague-Dawley rats were used to study hypoxia- or monocrotaline-induced right ventricular remodeling as well as systolic function and hemodynamics using echocardiography and a pressure-volume admittance catheter. Morphometric analyses of lung vasculature and pressure-volume vessels were performed. Immunohistochemical staining, flow cytometry, and viability, as well as scratch-wound, and Boyden chamber migration assays were used to identify the roles of dacomitinib in pulmonary artery smooth muscle cells (PASMCs). The results revealed that dacomitinib has a significant inhibitory effect on the thickening of the media, adventitial collagen increased. Dacomitinib also has a significant role in attenuating pulmonary artery pressure and right ventricular hypertrophy. Additionally, dacomitinib inhibits hypoxia-induced proliferation, migration, autophagy and cell cycle progression through PI3K-AKT-mTOR signaling in PASMCs. Our study indicates that dacomitinib inhibited hypoxia-induced cell cycle progression, proliferation, migration, and autophagy of PASMCs, thereby attenuating pulmonary vascular remodeling and development of PAH via the PI3K-AKT-mTOR signaling pathway. Overall, dacomitinib may serve as new potential therapeutic for the treatment of PAH.

Regional septal hinge-point injury contributes to adverse biventricular interactions in pulmonary hypertension

Death and morbidity in pulmonary arterial hypertension (PAH) are often due to right ventricular (RV) failure and associated left ventricular (LV) dysfunction. We investigated regional myocardial remodeling and function as the basis for adverse ventricular‐ventricular interactions in experimental chronic RV pressure overload. Two distinct animal models were studied: A rabbit model of increased RV pressure‐load through progressive pulmonary artery banding A rat model of monocrotaline (MCT)‐induced pulmonary arterial hypertension (PAH). Regional myocardial function was assessed by speckle‐tracking strain echocardiography and ventricular pressures measured by catheterization before termination. Regional RV and LV myocardium was analyzed for collagen content, apoptosis and pro‐fibrotic signaling gene and protein expression. Although the RV developed more fibrosis than the LV; in both models the LV was substantially affected. In both ventricles, particularly the LV, fibrosis developed predominantly at the septal hinge‐point regions in association with decreased regional and global circumferential strain, reduced global RV and LV function and up‐regulation of regional transforming growth factor‐β1 (TGFβ1) and apoptosis signaling. A group of PAH rats who received the TGFβ blocker SB431542 showed improved RV function and reduced regional hinge‐point myocardial fibrosis. RV pressure‐loading and PAH lead to biventricular TGFβ1 signaling, fibrosis and apoptosis, predominantly at the septal hinge‐point regions, in association with regional myocardial dysfunction. This suggests that altered geometry and wall stress lead to adverse RV‐LV interactions through the septal hinge‐points to induce LV fibrosis and dysfunction.

Experimental Right Ventricular Hypertension Induces Regional β1-Integrin-Mediated Transduction of Hypertrophic and Profibrotic Right and Left Ventricular Signaling

BACKGROUND

Development of right ventricular (RV) hypertension eventually contributes to RV and left ventricular (LV) myocardial fibrosis and dysfunction. The molecular mechanisms are not fully elucidated.

METHODS AND RESULTS

Pulmonary artery banding was used to induce RV hypertension in rats in vivo. Then, we evaluated cardiac function and regional remodeling 6 weeks after pulmonary artery banding. To further elucidate mechanisms responsible for regional cardiac remodeling, we also mimicked RV hypertensive stress by cyclic mechanical stretching applied to confluent cultures of cardiac fibroblasts, isolated from the RV free wall, septal hinge points, and LV free wall. Echocardiography and catheter evaluation demonstrated that rats in the pulmonary artery banding group developed RV hypertension with leftward septal displacement, LV compression, and increased LV end-diastolic pressures. Picrosirius red staining indicated that pulmonary artery banding induced marked RV fibrosis and dysfunction, with prominent fibrosis and elastin deposition at the septal hinge points but less LV fibrosis. These changes were associated with proportionally increased expressions of integrin-β1 and profibrotic signaling proteins, including phosphorylated Smad2/3 and transforming growth factor-β1. Moreover, mechanically stretched fibroblasts also expressed significantly increased levels of α-smooth muscle actin, integrin-β1, transforming growth factor-β1, collagen I deposition, and wrinkle formation on gel assays, consistent with myofibroblast transformation. These changes were not observed in parallel cultures of mechanically stretched fibroblasts, preincubated with the integrin inhibitor (BTT-3033).

CONCLUSIONS

Experimentally induced RV hypertension triggers regional RV, hinge-point, and LV integrin β1-dependent mechanotransduction signaling pathways that eventually trigger myocardial fibrosis via transforming growth factor-β1 signaling. Reduced LV fibrosis and preserved global function, despite geometrical and pressure aberrations, suggest a possible elastin-mediated protective mechanism at the septal hinge points.

Growth Differentiation Factor 11 Promotes Abnormal Proliferation and Angiogenesis of Pulmonary Artery Endothelial Cells

Disordered proliferation and angiogenesis of pulmonary artery endothelial cells is an important stage in the development of pulmonary arterial hypertension. Recent studies revealed that GDF11 (growth differentiation factor 11) induces endothelial cells proliferation and migration; however, whether GDF11 is directly involved in the pathogenesis of pulmonary arterial hypertension remains unknown. Here, we found that GDF11 was significantly upregulated and activated in 2 experimental pulmonary arterial hypertension models and cultured pulmonary artery endothelial cells. Genetic ablation of gdf11 in endothelial cells rescued pulmonary arterial hypertension features, as demonstrated by right ventricle hypertrophy, right ventricular systolic pressure, hemodynamics, cardiac function, and vascular remodeling. Moreover, we found that hypoxia significantly increased cell cycle progression, proliferation, migration, adhesion, and tube formation, which were significantly inhibited by GDF11 small interfering RNA. These events could be reproduced using cultured pulmonary artery endothelial cells and were dependent on Smad signaling. Moreover, hypoxia-induced GDF11 expression was regulated by the transcription factor zinc finger protein 740, which assisted RNA polymerase in recognizing and binding to the GDF11 promoter sequence located at a site (-753/-744; CCCCCCCCAC) upstream of the gene. This study identified a novel growth and differentiation factor signaling pathway involved in the zinc finger protein 740/GDF11/transforming growth factor-β receptor I/Smad signaling axis and involved in pulmonary artery endothelial cells proliferation and angiogenesis. These results provide critical insights for the development of novel therapeutic strategies for pulmonary arterial hypertension involving components of the GDF11 signaling system.