Renin-Angiotensin-Aldosterone System Inhibitors for Right Ventricular Dysfunction in Tetralogy of Fallot: Quo Vadis?

Right ventricular dysfunction following surgical repair of tetralogy of Fallot: Molecular pathways and therapeutic prospects

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease (CHD). Although surgical correction of TOF is possible, patients often face challenges related to right ventricle dysfunction (RVD) post-surgery, which can significantly impact their long-term survival. The causes of RVD in TOF patients are complex, involving both the unique structural characteristics of the TOF heart and damage resulting from surgical interventions. Residual anatomical issues following TOF repair are often unavoidable, placing the RV under stress and leading to the activation of multiple molecular pathways. This review comprehensively outlines the causes of RVD in patients after TOF surgery, particularly focusing the molecular pathways that contribute to RVD, including established signaling pathways as well as emerging pathways identified through transcriptomic analysis of RV myocardium in TOF patients. We also highlight the features of these molecular pathways concerning RVD, as well as the influence of gender disparities on these molecular pathways. By interpreting the causes and molecular mechanisms underlying RVD after TOF surgery, this review provides new insights for managing RVD in repaired TOF, potentially paving the way for targeted therapies aimed at improving long-term outcomes for those affected by RVD.

Right Ventricular Remodeling in Complex Congenital Heart Disease

In congenital heart diseases (CHDs) of moderate to great complexity involving the right ventricle (RV), the morphologic RV can be exposed to significant stressors across the lifespan, either in a biventricular circulation in a subpulmonary or subaortic position or as part of a univentricular circulation. These include pressure and/or volume overload, hypoxia, ischemia, and periprocedural surgical stress, leading to remodeling, maladaptation, dilation, hypertrophy, and dysfunction. In this review we examine the macroscopic remodeling of the RV in various forms of CHD and explore remodeling trajectories, along with the effects of surgeries and residual lesion repair, in tetralogy of Fallot, Ebstein anomaly, congenitally corrected transposition of the great arteries, transposition of the great arteries with atrial switch surgery, and single ventricle palliated by Fontan. In addition, the role of metabolism, genetic markers, and imaging criteria of RV remodeling are explored. Finally, the optimal timing for addressing residual lesions in CHD through surgery or percutaneous interventions is discussed, along with advanced heart failure management strategies and medical therapy aimed at preventing further RV dilation and/or systolic deterioration or promoting reverse remodeling.

Tetralogy of Fallot Across the Lifespan: A Focus on the Right Ventricle

Tetralogy of Fallot is a cyanotic congenital heart disease, for which various surgical techniques allow patients to survive to adulthood. Currently, the natural history of corrected tetralogy of Fallot is underlined by progressive right ventricular (RV) failure due to pulmonic regurgitation and other residual lesions. The underlying cellular mechanisms that lead to RV failure from chronic volume overload are characterized by microvascular and mitochondrial dysfunction through various regulatory molecules. On a clinical level, these cardiac alterations are commonly manifested as exercise intolerance. The degree of exercise intolerance can be objectified and aid in prognostication through cardiopulmonary exercise testing. The timing for reintervention on residual lesions contributing to RV volume overload remains controversial; however, interval assessment of cardiac function and volumes by echocardiography and magnetic resonance imaging may be helpful. In patients who develop clinically important RV failure, clinicians should aim to maintain a euvolemic state through the use of diuretics while paying particular attention to preload and kidney function. In patients who develop signs of cardiogenic shock from right heart failure, stabilization through the use of inotropes and pressor is indicated. In special circumstances, the use of mechanical support may be appropriate. However, cardiologists should pay particular attention to residual lesions that may impact the efficacy of the selected device.

LCZ696 (sacubitril/valsartan) inhibits pulmonary hypertension induced right ventricular remodeling by targeting pyruvate dehydrogenase kinase 4

BACKGROUND

Right ventricular (RV) function is a major prognostic factor in patients with cardiopulmonary disease. Effective medical therapies are available for left heart failure, but they are usually less effective or even ineffective in right heart failure. Here, we tested the hypothesis that LCZ696 (sacubitril/valsartan) can attenuate pressure overload-induced RV remodeling by inhibiting pyruvate dehydrogenase kinase 4 (PDK4).

METHODS

Adult male C57 mice were subjected to transverse aortic constriction (TAC), pulmonary artery constriction (PAC), or sham surgery. Bioinformatics analysis was used to screen for common differentially expressed genes (DEGs) between TAC and PAC. Chemical compounds targeting DEGs were predicted by molecular docking analysis. Effects of LCZ696 on PAC-induced RV remodeling and the associated PDK4-related mechanisms were investigated.

RESULTS

We found 60 common DEGs between PAC and TAC, and Pdk4 was one of the downregulated DEGs. From 47 chemical compounds with potential cardiovascular activity and PDK4 protein binding ability, we selected LCZ696 to treat PAC-induced RV remodeling because of its high docking score for binding PDK4. Compared with vehicle-treated PAC mice, LCZ696-treated mice had significantly smaller RV wall thickness and RV diameters, less myocardial fibrosis, lower expression of PDK4 protein, and less phosphorylation of glycogen synthase kinase-3β (p-GSK3β). In PAC mice, overexpression of Pdk4 blocked the inhibitory effect of LCZ696 on RV remodeling, whereas conditional knockout of Pdk4 attenuated PAC-induced RV remodeling.

CONCLUSIONS

Pdk4 is a common therapeutic target for pressure overload-induced left ventricular and RV remodeling, and LCZ696 attenuates RV remodeling by downregulating Pdk4 and inhibiting PDK4/p-GSK3β signal.

Avalanches in cardiology

Sudden cardiac death (SCD) accounts for 15%–60% of mortality in patients with heart disease. Generally, this has been attributed to ventricular tachyarrhythmia. However, ventricular tachyarrhythmia has been documented or strongly suspected on clinical grounds in a relatively small proportion of SCD patients (8%–50%). Attempted prophylaxis of SCD by implantation of cardioverter-defibrillator is associated with variable success in different subsets of high-risk cardiac patients (30%–70%). A significant number of SCD, therefore, appear to be due to catastrophic circulatory failure. Multiple interdependent compensatory mechanisms help to maintain circulation in advanced cardiac disease. Rapid, unexpected, and massive breakdown of the compensated state can be precipitated by small and often imperceptible triggers. The initial critical but stable state followed by rapid circulatory failure and death has been considered to be analogous to snow avalanches. It is typically described in patients with left ventricular (LV) dysfunction (ischemic or nonischemic). It is now recognized that SCD can also happen in conditions where the right ventricle (RV) takes the brunt of the hemodynamic load. Advanced pulmonary arterial hypertension and operated patients of tetralogy of Fallot with pulmonary regurgitation are of particular interest to pediatric cardiologists. A large amount of data is available on LV changes and mechanics, while relatively little information is available on the mechanisms of RV adaptation to increased load and RV failure. Whether the triggers and the decompensatory processes are similar for the two ventricles is a moot point. This article highlights the currently available knowledge on the pathophysiology of SCD in RV overload states, with special reference to RV adaptive and decompensatory mechanisms, and therapeutic measures that can potentially interrupt the vicious downward course (cardiac avalanches).

Impaired right and left ventricular function and relaxation induced by pulmonary regurgitation are not reversed by tardive antifibrosis treatment

Pulmonary regurgitation (PR) after repair of tetralogy of Fallot (rTOF) is associated with progressive right (RV) and left (LV) ventricular dysfunction and fibrosis. However, angiotensin II receptor blockade therapy has shown mixed and often disappointing results. The aim of this study was to serially assess changes in biventricular remodeling, dysfunction, and interactions in a rat model of isolated severe PR and to study the effects of angiotensin II receptor blockade. PR was induced in Sprague-Dawley rats by leaflet laceration. Shams (n = 6) were compared with PR (n = 5) and PR + losartan treatment (n = 6). In the treatment group, oral losartan (50 mg·kg^-1·day^-1) was started 6 wk after PR induction and continued for 6 wk until the terminal experiment. In all groups, serial echocardiography was performed every 2 wk until the terminal experiment where biventricular myocardium was harvested and analyzed for fibrosis. PR and PR + losartan rats experienced early progressive RV dilatation by 2 wk which then stabilized. RV systolic dysfunction occurred from 4 wk after insult and gradually progressed. In PR rats, RV dilatation caused diastolic LV compression and impaired relaxation. PR rats developed increased RV fibrosis compared with shams. Although losartan decreased RV fibrosis, RV dilatation and dysfunction were not improved. This suggests that RV dilatation is an early consequence of PR and affects LV relaxation. RV dysfunction may progress independent of further remodeling. Reduced RV fibrosis was not associated with improved RV function and may not be a viable therapeutic target in rTOF with predominant RV volume loading.NEW & NOTEWORTHY The time-course of RV dilatation and the mechanisms of biventricular dysfunction caused by PR have not been well characterized and the effect of losartan in volume-overloaded RV remains controversial. Our findings suggest that severe PR induces early onset of RV dilatation and dysfunction with little progression after the first 4 wk. The RV dilatation distorts LV geometry with associated impaired LV relaxation. Losartan reduced RV fibrosis but did not reverse RV dilatation and dysfunction.

Lack of Contribution of p66shc to Pressure Overload-Induced Right Heart Hypertrophy

The leading cause of death in pulmonary arterial hypertension (PAH) is right ventricular (RV) failure (RVF). Reactive oxygen species (ROS) have been suggested to play a role in the development of RV hypertrophy (RVH) and the transition to RVF. The hydrogen peroxide-generating protein p66shc has been associated with left ventricular (LV) hypertrophy but its role in RVH is unclear. The purpose of this study was to determine whether genetic deletion of p66shc affects the development and/or progression of RVH and RVF in the pulmonary artery banding (PAB) model of RV pressure overload. The impact of p66shc on mitochondrial ROS formation, RV cardiomyocyte function, as well as on RV morphology and function were studied three weeks after PAB or sham operation. PAB in wild type mice did not affect mitochondrial ROS production or RV cardiomyocyte function, but induced RVH and impaired cardiac function. Genetic deletion of p66shc did also not alter basal mitochondrial ROS production or RV cardiomyocyte function, but impaired RV cardiomyocyte shortening was observed following PAB. The development of RVH and RVF following PAB was not affected by p66shc deletion. Thus, our data suggest that p66shc-derived ROS are not involved in the development and progression of RVH or RVF in PAH.

4HNE Impairs Myocardial Bioenergetics in Congenital Heart Disease-Induced Right Ventricular Failure

BACKGROUND

In patients with complex congenital heart disease, such as those with tetralogy of Fallot, the right ventricle (RV) is subject to pressure overload stress, leading to RV hypertrophy and eventually RV failure. The role of lipid peroxidation, a potent form of oxidative stress, in mediating RV hypertrophy and failure in congenital heart disease is unknown.

METHODS

Lipid peroxidation and mitochondrial function and structure were assessed in right ventricle (RV) myocardium collected from patients with RV hypertrophy with normal RV systolic function (RV fractional area change, 47.3±3.8%) and in patients with RV failure showing decreased RV systolic function (RV fractional area change, 26.6±3.1%). The mechanism of the effect of lipid peroxidation, mediated by 4-hydroxynonenal ([4HNE] a byproduct of lipid peroxidation) on mitochondrial function and structure was assessed in HL1 murine cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes.

RESULTS

RV failure was characterized by an increase in 4HNE adduction of metabolic and mitochondrial proteins (16 of 27 identified proteins), in particular electron transport chain proteins. Sarcomeric (myosin) and cytoskeletal proteins (desmin, tubulin) also underwent 4HNE adduction. RV failure showed lower oxidative phosphorylation (moderate RV hypertrophy, 287.6±19.75 versus RV failure, 137.8±11.57 pmol/[sec×mL]; P=0.0004), and mitochondrial structural damage. Using a cell model, we show that 4HNE decreases cell number and oxidative phosphorylation (control, 388.1±23.54 versus 4HNE, 143.7±11.64 pmol/[sec×mL]; P<0.0001). Carvedilol, a known antioxidant did not decrease 4HNE adduction of metabolic and mitochondrial proteins and did not improve oxidative phosphorylation.

CONCLUSIONS

Metabolic, mitochondrial, sarcomeric, and cytoskeletal proteins are susceptible to 4HNE-adduction in patients with RV failure. 4HNE decreases mitochondrial oxygen consumption by inhibiting electron transport chain complexes. Carvedilol did not improve the 4HNE-mediated decrease in oxygen consumption. Strategies to decrease lipid peroxidation could improve mitochondrial energy generation and cardiomyocyte survival and improve RV failure in patients with congenital heart disease.