Load-reducing therapy prevents development of arrhythmogenic right ventricular cardiomyopathy in plakoglobin-deficient mice

Endurance Training Provokes Arrhythmogenic Right Ventricular Cardiomyopathy Phenotype in Heterozygous Desmoglein-2 Mutants: Alleviation by Preload Reduction

Desmoglein-2 mutations are detected in 5-10% of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC). Endurance training accelerates the development of the ARVC phenotype, leading to earlier arrhythmic events. Homozygous Dsg2 mutant mice develop a severe ARVC-like phenotype. The phenotype of heterozygous mutant (Dsg2mt/wt) or haploinsufficient (Dsg20/wt) mice is still not well understood. To assess the effects of age and endurance swim training, we studied cardiac morphology and function in sedentary one-year-old Dsg2mt/wt and Dsg20/wt mice and in young Dsg2mt/wt mice exposed to endurance swim training. Cardiac structure was only occasionally affected in aged Dsg20/wt and Dsg2mt/wt mice manifesting as small fibrotic foci and displacement of Connexin 43. Endurance swim training increased the right ventricular (RV) diameter and decreased RV function in Dsg2mt/wt mice but not in wild types. Dsg2mt/wt hearts showed increased ventricular activation times and pacing-induced ventricular arrhythmia without obvious fibrosis or inflammation. Preload-reducing therapy during training prevented RV enlargement and alleviated the electrophysiological phenotype. Taken together, endurance swim training induced features of ARVC in young adult Dsg2mt/wt mice. Prolonged ventricular activation times in the hearts of trained Dsg2mt/wt mice are therefore a potential mechanism for increased arrhythmia risk. Preload-reducing therapy prevented training-induced ARVC phenotype pointing to beneficial treatment options in human patients.

Reduced plakoglobin increases the risk of sodium current defects and atrial conduction abnormalities in response to androgenic anabolic steroid abuse

Androgenic anabolic steroids (AAS) are commonly abused by young men. Male sex and increased AAS levels are associated with earlier and more severe manifestation of common cardiac conditions, such as atrial fibrillation, and rare ones, such as arrhythmogenic right ventricular cardiomyopathy (ARVC). Clinical observations suggest a potential atrial involvement in ARVC. Arrhythmogenic right ventricular cardiomyopathy is caused by desmosomal gene defects, including reduced plakoglobin expression. Here, we analysed clinical records from 146 ARVC patients to identify that ARVC is more common in males than females. Patients with ARVC also had an increased incidence of atrial arrhythmias and P wave changes. To study desmosomal vulnerability and the effects of AAS on the atria, young adult male mice, heterozygously deficient for plakoglobin (Plako+/- ), and wild type (WT) littermates were chronically exposed to 5α-dihydrotestosterone (DHT) or placebo. The DHT increased atrial expression of pro-hypertrophic, fibrotic and inflammatory transcripts. In mice with reduced plakoglobin, DHT exaggerated P wave abnormalities, atrial conduction slowing, sodium current depletion, action potential amplitude reduction and the fall in action potential depolarization rate. Super-resolution microscopy revealed a decrease in NaV 1.5 membrane clustering in Plako+/- atrial cardiomyocytes after DHT exposure. In summary, AAS combined with plakoglobin deficiency cause pathological atrial electrical remodelling in young male hearts. Male sex is likely to increase the risk of atrial arrhythmia, particularly in those with desmosomal gene variants. This risk is likely to be exaggerated further by AAS use. KEY POINTS: Androgenic male sex hormones, such as testosterone, might increase the risk of atrial fibrillation in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), which is often caused by desmosomal gene defects (e.g. reduced plakoglobin expression). In this study, we observed a significantly higher proportion of males who had ARVC compared with females, and atrial arrhythmias and P wave changes represented a common observation in advanced ARVC stages. In mice with reduced plakoglobin expression, chronic administration of 5α-dihydrotestosterone led to P wave abnormalities, atrial conduction slowing, sodium current depletion and a decrease in membrane-localized NaV 1.5 clusters. 5α-Dihydrotestosterone, therefore, represents a stimulus aggravating the pro-arrhythmic phenotype in carriers of desmosomal mutations and can affect atrial electrical function.

Management Strategies in Arrhythmogenic Cardiomyopathy across the Spectrum of Ventricular Involvement

Improved disease recognition through family screening and increased life expectancy with appropriate sudden cardiac death prevention has increased the burden of heart failure in arrhythmogenic cardiomyopathy (ACM). Heart failure management guidelines are well established but primarily focus on left ventricle function. A significant proportion of patients with ACM have predominant or isolated right ventricle (RV) dysfunction. Management of RV dysfunction in ACM lacks evidence but requires special considerations across the spectrum of heart failure regarding the initial diagnosis, subsequent management, monitoring for progression, and end-stage disease management. In this review, we discuss the unique aspects of heart failure management in ACM with a special focus on RV dysfunction.

Arrhythmogenic Cardiomyopathy: from Preclinical Models to Genotype-phenotype Correlation and Pathophysiology

Arrhythmogenic cardiomyopathy (ACM) is a hereditary myocardial disease characterized by the replacement of the ventricular myocardium with fibrous fatty deposits. ACM is usually inherited in an autosomal dominant pattern with variable penetrance and expressivity, which is mainly related to ventricular tachyarrhythmia and sudden cardiac death (SCD). Importantly, significant progress has been made in determining the genetic background of ACM due to the development of new techniques for genetic analysis. The exact molecular pathomechanism of ACM, however, is not completely clear and the genotype-phenotype correlations have not been fully elucidated, which are useful to predict the prognosis and treatment of ACM patients. Different gene-targeted and transgenic animal models, human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) models, and heterologous expression systems have been developed. Here, this review aims to summarize preclinical ACM models and platforms promoting our understanding of the pathogenesis of ACM and assess their value in elucidating the ACM genotype-phenotype relationship.

Chronic diastolic stretch unmasks conduction defects in an in vitro model of arrhythmogenic cardiomyopathy

We seek to elucidate the precise nature of mechanical loading that precipitates conduction deficits in a concealed-phase model of arrhythmogenic cardiomyopathy (ACM). ACM is a progressive disorder often resulting from mutations in desmosomal proteins. Exercise has been shown to worsen disease progression and unmask arrhythmia vulnerability, yet the underlying pathomechanisms may depend on the type and intensity of exercise. Because exercise causes myriad changes to multiple inter-dependent hemodynamic parameters, it is difficult to isolate its effects to specific changes in mechanical load. Here, we use engineered heart tissues (EHTs) with iPSC-derived cardiomyocytes expressing R451G desmoplakin, an ACM-linked mutation, which results in a functionally null model of desmoplakin (DSP). We also use a novel bioreactor to independently perturb tissue strain at different time points during the cardiac cycle. We culture EHTs under three strain regimes: normal physiological shortening; increased diastolic stretch, simulating high preload; and isometric culture, simulating high afterload. DSPR451G EHTs that have been cultured isometrically undergo adaptation, with no change in action potential parameters, conduction velocity, or contractile function, a phenotype confirmed by global proteomic analysis. However, when DSPR451G EHTs are subjected to increased diastolic stretch, they exhibit concomitant reductions in conduction velocity and the expression of connexin-43. These effects are rescued by inhibition of both lysosome activity and ERK signaling. Our results indicate that the response of DSPR451G EHTs to mechanical stimuli depends on the strain and the timing of the applied stimulus, with increased diastolic stretch unmasking conduction deficits in a concealed-phase model of ACM.

Understanding Arrhythmogenic Cardiomyopathy: Advances through the Use of Human Pluripotent Stem Cell Models

Cardiomyopathies (CMPs) represent a significant healthcare burden and are a major cause of heart failure leading to premature death. Several CMPs are now recognized to have a strong genetic basis, including arrhythmogenic cardiomyopathy (ACM), which predisposes patients to arrhythmic episodes. Variants in one of the five genes (PKP2, JUP, DSC2, DSG2, and DSP) encoding proteins of the desmosome are known to cause a subset of ACM, which we classify as desmosome-related ACM (dACM). Phenotypically, this disease may lead to sudden cardiac death in young athletes and, during late stages, is often accompanied by myocardial fibrofatty infiltrates. While the pathogenicity of the desmosome genes has been well established through animal studies and limited supplies of primary human cells, these systems have drawbacks that limit their utility and relevance to understanding human disease. Human induced pluripotent stem cells (hiPSCs) have emerged as a powerful tool for modeling ACM in vitro that can overcome these challenges, as they represent a reproducible and scalable source of cardiomyocytes (CMs) that recapitulate patient phenotypes. In this review, we provide an overview of dACM, summarize findings in other model systems linking desmosome proteins with this disease, and provide an up-to-date summary of the work that has been conducted in hiPSC-cardiomyocyte (hiPSC-CM) models of dACM. In the context of the hiPSC-CM model system, we highlight novel findings that have contributed to our understanding of disease and enumerate the limitations, prospects, and directions for research to consider towards future progress.

Evaluation of Left Ventricular Systolic Function Using Layer-Specific Strain in Rats Performing Endurance Exercise: A Pilot Study

OBJECTIVE

The functional characteristics of exercise-induced myocardial hypertrophy were studied in a rat model in conjunction with ultrasound layered strain technique to investigate the hidden changes in the heart brought about by exercise.

METHODS

Forty specific pathogen free (SPF) adult Sprague-Dawley rats were selected and randomly divided into two groups of 20 exercise and 20 control rats. The longitudinal and circumferential strain parameters were measured using the ultrasonic stratified strain technique. The differences between the two groups and the predictive effect of stratified strain parameters on left ventricular systolic function were analyzed.

RESULTS

The exercise group had significantly higher global endocardial myocardial longitudinal strain (GLSendo), global mid-myocardial global longitudinal strain (GLSmid) and global endocardial myocardial global longitudinal strain (GCSendo) values than the control group (p < 0.05). Even though global mid-myocardial circumferential strain (GCSmid) and global epicardial myocardial circumferential strain (GCSepi) were higher in the exercise group than in the control group, statistical significance was not reached (p > 0.05). Conventional echocardiography parameters were well correlated with GLSendo, GLSmid, and GCSendo (p < 0.05). GLSendo was the best predictor of left ventricular myocardial contractile performance in athletes determined using the receiver operating characteristic curve, with an area under the curve of 0.97, sensitivity of 95% and specificity of 90%.

CONCLUSION

Rats performing endurance exercise exhibited subclinical changes in the heart after prolonged high-intensity exercise. A stratified strain parameter, GLSendo, played an important role in the evaluation of LV systolic performance in exercising rats.

Dynamic mechanobiology of cardiac cells and tissues: Current status and future perspective

Mechanical forces impact cardiac cells and tissues over their entire lifespan, from development to growth and eventually to pathophysiology. However, the mechanobiological pathways that drive cell and tissue responses to mechanical forces are only now beginning to be understood, due in part to the challenges in replicating the evolving dynamic microenvironments of cardiac cells and tissues in a laboratory setting. Although many in vitro cardiac models have been established to provide specific stiffness, topography, or viscoelasticity to cardiac cells and tissues via biomaterial scaffolds or external stimuli, technologies for presenting time-evolving mechanical microenvironments have only recently been developed. In this review, we summarize the range of in vitro platforms that have been used for cardiac mechanobiological studies. We provide a comprehensive review on phenotypic and molecular changes of cardiomyocytes in response to these environments, with a focus on how dynamic mechanical cues are transduced and deciphered. We conclude with our vision of how these findings will help to define the baseline of heart pathology and of how these in vitro systems will potentially serve to improve the development of therapies for heart diseases.

Varied Presentation of Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C): A Case Series

Arrhythmogenic right ventricular dysplasia (ARVD) is a genetically predisposed form of cardiomyopathy that mainly affects young individuals resulting in fatal ventricular arrhythmias leading to sudden cardiac death. ARVD has 50% of cases that involve both the right ventricle (RV) and left ventricle (LV), but only a small number of cases involve an isolated left ventricle. In this case series, five patients (four males and one female) with a diagnosis of ARVD presented to our center with varied clinical presentations across a wide range of age groups. The MRI of all five cases showed dilated right atrium (RA)/RV with right ventricular free wall dyskinesia. Two-dimensional (2D) MRI showed aneurysmal outpouching with diffuse free wall enhancement. Automated implantable cardioverter defibrillator (AICD) was implanted uneventfully in all five patients, and the patients were discharged with oral medications such as low-dose diuretics, beta-blockers, spironolactone, angiotensin-converting enzymes (ACE) inhibitors, amiodarone, and anxiolytics. Until now, the patients were doing well on follow-up visits. The therapeutic management of patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) has evolved over the years and continues to be an important challenge. To further improve risk stratification and treatment of patients, more information is needed on natural history, long-term prognosis, and risk assessment. Special attention should be focused on the identification of patients who would benefit from implantable cardioverter-defibrillator (ICD) implantation in comparison to pharmacological and other nonpharmacological approaches.

Arrhythmogenic Cardiomyopathy: Exercise Pitfalls, Role of Connexin-43, and Moving beyond Antiarrhythmics

Arrhythmogenic Cardiomyopathy (ACM), a Mendelian disorder that can affect both left and right ventricles, is most often associated with pathogenic desmosomal variants that can lead to fibrofatty replacement of the myocardium, a pathological hallmark of this disease. Current therapies are aimed to prevent the worsening of disease phenotypes and sudden cardiac death (SCD). Despite the use of implantable cardioverter defibrillators (ICDs) there is no present therapy that would mitigate the loss in electrical signal and propagation by these fibrofatty barriers. Recent studies have shown the influence of forced vs. voluntary exercise in a variety of healthy and diseased mice; more specifically, that exercised mice show increased Connexin-43 (Cx43) expression levels. Fascinatingly, increased Cx43 expression ameliorated the abnormal electrical signal conduction in the myocardium of diseased mice. These findings point to a major translational pitfall in current therapeutics for ACM patients, who are advised to completely cease exercising and already demonstrate reduced Cx43 levels at the myocyte intercalated disc. Considering cardiac dysfunction in ACM arises from the loss of cardiomyocytes and electrical signal conduction abnormalities, an increase in Cx43 expression-promoted by low to moderate intensity exercise and/or gene therapy-could very well improve cardiac function in ACM patients.

Role of plakophilin-2 expression on exercise-related progression of arrhythmogenic right ventricular cardiomyopathy: a translational study

AIMS

Exercise increases arrhythmia risk and cardiomyopathy progression in arrhythmogenic right ventricular cardiomyopathy (ARVC) patients, but the mechanisms remain unknown. We investigated transcriptomic changes caused by endurance training in mice deficient in plakophilin-2 (PKP2cKO), a desmosomal protein important for intercalated disc formation, commonly mutated in ARVC and controls.

METHODS AND RESULTS

Exercise alone caused transcriptional downregulation of genes coding intercalated disk proteins. The changes converged with those in sedentary and in exercised PKP2cKO mice. PKP2 loss caused cardiac contractile deficit, decreased muscle mass and increased functional/transcriptomic signatures of apoptosis, despite increased fractional shortening and calcium transient amplitude in single myocytes. Exercise accelerated cardiac dysfunction, an effect dampened by pre-training animals prior to PKP2-KO. Consistent with PKP2-dependent muscle mass deficit, cardiac dimensions in human athletes carrying PKP2 mutations were reduced, compared to matched controls.

CONCLUSIONS

We speculate that exercise challenges a cardiomyocyte "desmosomal reserve" which, if impaired genetically (e.g., PKP2 loss), accelerates progression of cardiomyopathy.

Optimization of heart failure with reduced ejection fraction prognosis-modifying drugs: A 2021 heart failure expert consensus paper

Heart failure (HF) with reduced ejection fraction (HFrEF) is associated with high rates of hospitalization and death. It also has a negative impact on patients' functional capacity and quality of life, as well as on healthcare costs. In recent years, new HFrEF prognosis-modifying drugs have emerged, leading to intense debate within the international scientific community toward a paradigm shift for the management of HFrEF. In this article, we report the contribution of a Portuguese HF expert panel to the ongoing debate. Based on the most recently published clinical evidence, and the panel members' clinical judgment, three key principles are highlighted: (i) sacubitril/valsartan should be preferred as first-line therapy for HFrEF, instead of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker; (ii) the four foundation HFrEF drugs are the angiotensin receptor/neprilysin inhibitor, beta-adrenergic blocking agents, mineralocorticoid receptor antagonists, and sodium-glucose co-transporter 2 inhibitors, regardless of the presence of type-2 diabetes mellitus; (iii) these four HFrEF drug classes should be introduced over a short-term period of four to six weeks, guided by a safety protocol, followed by a dose up-titration period of 8 weeks.

Facts and Gaps in Exercise Influence on Arrhythmogenic Cardiomyopathy: New Insights From a Meta-Analysis Approach

Arrhythmogenic cardiomyopathy (ACM) is a genetic cardiac condition characterized by fibrofatty myocardial replacement, either at the right ventricle, at the left ventricle, or with biventricular involvement. Ventricular arrhythmias and heart failure represent its main clinical features. Exercise benefits on mental and physical health are worldwide recognized. However, patients with ACM appear to be an exception. A thorough review of the literature was performed in PubMed searching for original papers with the terms “ARVC AND sports/exercise” and “sudden cardiac death AND sports/exercise.” Additional papers were then identified through other sources and incorporated to the list. All of them had to be based on animal models or clinical series. Information was structured in a regular format, although some data were not available in some papers. A total of 34 papers were selected and processed regarding sports-related sudden cardiac death, pre-clinical models of ACM and sport, and clinical series of ACM patients engaged in sports activities. Eligible papers were identified to obtain pooled data in order to build representative figures showing the global incidence of the most important causes of sudden cardiac death in sports and the global estimates of life-threatening arrhythmic events in ACM patients engaged in sports. Tables and figures illustrate their major characteristics. The scarce points of controversy were discussed in the text. Fundamental concepts were summarized in three main issues: sports may accelerate ACM phenotype with either structural and/or arrhythmic features, restriction may soften the progression, and these rules also apply to phenotype-negative mutation carriers. Additionally, remaining gaps in the current knowledge were also highlighted, namely, the applicability of those fundamental concepts to non-classical ACM phenotypes since left dominant ACM or non-plakophillin-2 genotypes were absent or very poorly represented in the available studies. Hopefully, future research endeavors will provide solid evidence about the safest exercise dose for each patient from a personalized medicine perspective, taking into account a big batch of genetic, epigenetic, and epidemiological variables, for instance, in order to assist clinicians to provide a final tailored recommendation.

Optimization of heart failure with reduced ejection fraction prognosis-modifying drugs: A 2021 heart failure expert consensus paper

Heart failure (HF) with reduced ejection fraction (HFrEF) is associated with high rates of hospitalization and death. It also has a negative impact on patients' functional capacity and quality of life, as well as on healthcare costs. In recent years, new HFrEF prognosis-modifying drugs have emerged, leading to intense debate within the international scientific community toward a paradigm shift for the management of HFrEF. In this article, we report the contribution of a Portuguese HF expert panel to the ongoing debate. Based on the most recently published clinical evidence, and the panel members' clinical judgment, three key principles are highlighted: (i) sacubitril/valsartan should be preferred as first-line therapy for HFrEF, instead of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker; (ii) the four foundation HFrEF drugs are the angiotensin receptor/neprilysin inhibitor, beta-adrenergic blocking agents, mineralocorticoid receptor antagonists, and sodium-glucose co-transporter 2 inhibitors, regardless of the presence of type-2 diabetes mellitus; (iii) these four HFrEF drug classes should be introduced over a short-term period of four to six weeks, guided by a safety protocol, followed by a dose up-titration period of 8 weeks.

Arrhythmogenic cardiomyopathy: pathogenesis, pro-arrhythmic remodelling, and novel approaches for risk stratification and therapy

Arrhythmogenic cardiomyopathy (ACM) is a life-threatening cardiac disease caused by mutations in genes predominantly encoding for desmosomal proteins that lead to alterations in the molecular composition of the intercalated disc. ACM is characterized by progressive replacement of cardiomyocytes by fibrofatty tissue, ventricular dilatation, cardiac dysfunction, and heart failure but mostly dominated by the occurrence of life-threatening arrhythmias and sudden cardiac death (SCD). As SCD appears mostly in apparently healthy young individuals, there is a demand for better risk stratification of suspected ACM mutation carriers. Moreover, disease severity, progression, and outcome are highly variable in patients with ACM. In this review, we discuss the aetiology of ACM with a focus on pro-arrhythmic disease mechanisms in the early concealed phase of the disease. We summarize potential new biomarkers which might be useful for risk stratification and prediction of disease course. Finally, we explore novel therapeutic strategies to prevent arrhythmias and SCD in the early stages of ACM.

Early Preventive Treatment With Enalapril Improves Cardiac Function and Delays Mortality in Mice With Arrhythmogenic Right Ventricular Cardiomyopathy Type 5

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy type 5 (ARVC5) is an inherited cardiac disease with complete penetrance and an aggressive clinical course caused by mutations in TMEM43 (transmembrane protein 43). There is no cure for ARVC5 and palliative treatment is started once the phenotype is present. A transgenic mouse model of ARVC5 expressing human TMEM43-S358L (TMEM43mut) recapitulates the human disease, enabling the exploration of preventive treatments. The aim of this study is to determine whether preventive treatment with heart failure drugs (β-blockers, ACE [angiotensin-converting enzyme] inhibitors, mineralocorticoid-receptor antagonists) improves the disease course of ARVC5 in TMEM43mut mice.

METHODS

TMEM43mut male/female mice were treated with metoprolol (β-blockers), enalapril (ACE inhibitor), spironolactone (mineralocorticoid-receptor antagonist), ACE inhibitor + mineralocorticoid-receptor antagonist, ACE inhibitor + mineralocorticoid-receptor antagonist + β-blockers or left untreated. Drugs were initiated at 3 weeks of age, before ARVC5 phenotype, and serial ECG and echocardiograms were performed.

RESULTS

TMEM43mut mice treated with enalapril showed a significantly increased median survival compared with untreated mice (26 versus 21 weeks; P=0.003). Enalapril-treated mice also exhibited increased left ventricular ejection fraction at 4 months compared with controls (37.0% versus 24.9%; P=0.004), shorter QRS duration and reduced left ventricle fibrosis. Combined regimens including enalapril also showed positive effects. Metoprolol decreased QRS voltage prematurely and resulted in a nonsignificant decrease in left ventricular ejection fraction compared with untreated TMEM43mut mice.

CONCLUSIONS

Preventive enalapril-based regimens reduced fibrosis, improved ECG, echocardiographic parameters and survival of ARVC5 mice. Early metoprolol did not show positive effects and caused premature ECG abnormalities. Our findings pave the way to consider prophylactic enalapril in asymptomatic ARVC5 genetic carriers.

Beneficial effect of voluntary physical exercise in Plakophilin2 transgenic mice

Arrhythmogenic right ventricular cardiomyopathy is a hereditary, rare disease with an increased risk for sudden cardiac death. The disease-causing mutations are located within the desmosomal complex and the highest incidence is found in plakophilin2. However, there are other factors playing a role for the disease progression unrelated to the genotype such as inflammation or exercise. Competitive sports have been identified as risk factor, but the type and extend of physical activity as cofactor for arrhythmogenesis remains under debate. We thus studied the effect of light voluntary exercise on cardiac health in a mouse model. Mice with a heterozygous PKP2 loss-of-function mutation were given the option to exercise in a running wheel which was monitored 24 h/d. We analyzed structural and functional development in vivo by echocardiography which revealed that neither the genotype nor the exercise caused any significant structural changes. Ejection fraction and fractional shortening were not influenced by the genotype itself, but exercise did cause a drop in both parameters after 8 weeks, which returned to normal after 16 weeks of training. The electrophysiological analysis revealed that the arrhythmogenic potential was slightly higher in heterozygous animals (50% vs 18% in wt littermates) and that an additional stressor (isoprenaline) did not lead to an increase of arrhythmogenic events pre run or after 8 weeks of running but the vulnerability was increased after 16 weeks. Exercise-induced alterations in Ca handling and contractility of isolated myocytes were mostly abolished in heterozygous animals. No fibrofatty replacements or rearrangement of gap junctions could be observed. Taken together we could show that light voluntary exercise can cause a transient aggravation of the mutation-induced phenotype which is abolished after long term exercise indicating a beneficial effect of long term light exercise.

Pregnancy in arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is a rare heart muscle disease with a genetic background and autosomal dominant mode of transmission. The clinical manifestation is characterized by ventricular arrhythmias (VA), heart failure (HF) and the risk of sudden cardiac death (SCD). Pregnancy in young female patients with AC represents a challenging condition for the life and family planning of young affected women. In addition to genetic mechanisms that influence the complex pathophysiology of AC, experimental and clinical data have confirmed the pathogenetic role of strenuous exercise and competitive sports in the early onset and rapid progression of AC symptoms and complications. Pregnancy and exercise share a number of physiological aspects of adaptation. In AC, both result in ventricular volume overload and myocardial stretch. Therefore, pregnancy has been postulated as a potential risk factor for HF, VA, SCD, and pregnancy-related obstetric complications in patients with AC. However, the available evidence on pregnancy in AC does not confirm this hypothesis. In most women with AC, pregnancies are well tolerated, uneventful, and follow a benign course. Pregnancy-related symptoms (VA, syncope, HF) and mortality, as well as obstetric complications, are uncommon in AC patients and range in the order of background populations and cohorts with AC and no pregnancy. The number of completed pregnancies is not associated with an acceleration of AC pathology or an increased risk of VA or HF during pregnancy and follow-up. Accordingly, there is no medical indication to advise against pregnancy in patients with AC. Preconditions include stability of rhythm and hemodynamics at baseline, as well as clinical follow-ups and the availability of multidisciplinary expert consultation during pregnancy and postpartum. Genetic counseling is recommended prior to pregnancy for all couples and their families affected by AC.

Role of Exercise as a Modulating Factor in Arrhythmogenic Cardiomyopathy

PURPOSE OF REVIEW

The review addresses the role of exercise in triggering ventricular arrhythmias and promoting disease progression in arrhythmogenic cardiomyopathy (AC) patients and gene-mutation carriers, the differential diagnosis between AC and athlete's heart and current recommendations on exercise activity in AC.

RECENT FINDINGS

AC is an inherited heart muscle disease caused by genetically defective cell-to-cell adhesion structures (mainly desmosomes). The pathophysiological hallmark of the disease is progressive myocyte loss and replacement by fibro-fatty tissue, which creates the substrates for ventricular arrhythmias. Animal and human studies demonstrated that intense exercise, but not moderate physical activity, may increase disease penetrance, worsen the phenotype, and favor life-threatening ventricular arrhythmias. It has been proposed that in some individuals prolonged endurance sports activity may in itself cause AC (so-called exercise-induced AC). The studies agree that intense physical activity should be avoided in patients with AC and healthy gene-mutation carriers. However, low-to-moderate intensity exercise does not appear detrimental and these patients should not be entirely deprived from the many health benefits of physical activity.

Effect of preload reducing therapy on right ventricular size and function in patients with arrhythmogenic right ventricular cardiomyopathy

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an important cause of sudden cardiac death in young people and athletes. To date, no treatment has proven to slow the progression of the disease. Preload reducing agents such as nitrates and diuretics have shown promising results in preventing training-induced development of ARVC in a murine model.

OBJECTIVE

The purpose of this study was to describe our experience with preload reducing therapy in patients with ARVC and symptomatic right ventricular (RV) dysfunction.

METHODS

We performed retrospective chart review of prospectively collected registry data and included 20 patients with definite ARVC who had serial echocardiographic measurements and an implantable cardioverter-defibrillator. Six of the 20 patients with RV end-diastolic area (RVEDA) above median (>25 cm²) and New York Heart Association functional class II-IV symptoms were successfully treated with long-term isosorbide dinitrate 5-40 mg tid (at maximum tolerated dose) and hydrochlorothiazide-spironolactone 25-25 mg daily. The main outcomes of interest were RVEDA, RV fractional area change (FAC), and RV outflow tract measurements. Generalized estimating equations with repeated measures were used to identify the association between preload reducing agents and echocardiographic structural progression.

RESULTS

Patients who received preload reducing agents (n = 6) were older and had larger RVs with lower FAC at baseline. However, treatment with preload reducing agents was associated with less RVEDA enlargement during mean 3.3 (range 1-6.7) years of treatment in multivariate analysis (% change in RVEDA associated with treatment -7.71; 95% confidence interval -13.29 to -2.13; P = .007).

CONCLUSION

Preload reducing agents show promising results in slowing RV enlargement in patients with ARVC and show possible disease-modifying potential.

Exercise restores dysregulated gene expression in a mouse model of arrhythmogenic cardiomyopathy

AIMS

Arrhythmogenic cardiomyopathy (ACM) is a myocardial disease caused mainly by mutations in genes encoding desmosome proteins ACM patients present with ventricular arrhythmias, cardiac dysfunction, sudden cardiac death, and a subset with fibro-fatty infiltration of the right ventricle predominantly. Endurance exercise is thought to exacerbate cardiac dysfunction and arrhythmias in ACM. The objective was to determine the effects of treadmill exercise on cardiac phenotype, including myocyte gene expression in myocyte-specific desmoplakin (Dsp) haplo-insufficient (Myh6-Cre:DspW/F) mice.

METHODS AND RESULTS

Three months old sex-matched wild-type (WT) and Myh6-Cre:DspW/F mice with normal cardiac function, as assessed by echocardiography, were randomized to regular activity or 60 min of daily treadmill exercise (5.5 kJ work per run). Cardiac myocyte gene expression, cardiac function, arrhythmias, and myocardial histology, including apoptosis, were analysed prior to and after 3 months of routine activity or treadmill exercise. Fifty-seven and 781 genes were differentially expressed in 3- and 6-month-old Myh6-Cre:DspW/F cardiac myocytes, compared to the corresponding WT myocytes, respectively. Genes encoding secreted proteins (secretome), including inhibitors of the canonical WNT pathway, were among the most up-regulated genes. The differentially expressed genes (DEGs) predicted activation of epithelial-mesenchymal transition (EMT) and inflammation, and suppression of oxidative phosphorylation pathways in the Myh6-Cre:DspW/F myocytes. Treadmill exercise restored transcript levels of two-third (492/781) of the DEGs and the corresponding dysregulated transcriptional and biological pathways, including EMT, inflammation, and secreted inhibitors of the canonical WNT. The changes were associated with reduced myocardial apoptosis and eccentric cardiac hypertrophy without changes in cardiac function.

CONCLUSION

Treadmill exercise restored transcript levels of the majority of dysregulated genes in cardiac myocytes, reduced myocardial apoptosis, and induced eccentric cardiac hypertrophy without affecting cardiac dysfunction in a mouse model of ACM. The findings suggest that treadmill exercise has potential beneficial effects in a subset of cardiac phenotypes in ACM.

Arrhythmogenic Right Ventricular Cardiomyopathy in Pediatric Patients: An Important but Underrecognized Clinical Entity

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy characterized by fibrofatty infiltration of predominantly the right ventricular (RV) myocardium. Affected patients typically present as young adults with hemodynamically stable ventricular tachycardia, although pediatric cases are increasingly recognized. These young subjects often have a more severe phenotype with a high risk of sudden cardiac death (SCD) and progression toward heart failure. Diagnosis of ARVC is made by combining multiple sources of information as prescribed by the consensus-based Task Force Criteria. The description of Naxos disease, a fully penetrant autosomal recessive disorder that is associated with ARVC and a cutaneous phenotype of palmoplantar keratoderma and wooly hair facilitated the identification of the genetic cause of ARVC. At present, approximately 60% of patients are found to carry a pathogenic variant in one of five genes associated with the cardiac desmosome. The incomplete penetrance and variable expressivity of these variants however implies an important role for environmental factors, of which participation in endurance exercise is a strong risk factor. Since there currently is no definite cure for ARVC, disease management is directed toward symptom reduction, delay of disease progression, and prevention of SCD. This clinically focused review describes the spectrum of ARVC among children and adolescents, the genetic architecture underlying this disease, the cardio-cutaneous syndromes that led to its identification, and current diagnostic and therapeutic strategies in pediatric ARVC subjects.

Genetic Animal Models for Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy has been clinically defined since the 1980s and causes right or biventricular cardiomyopathy associated with ventricular arrhythmia. Although it is a rare cardiac disease, it is responsible for a significant proportion of sudden cardiac deaths, especially in athletes. The majority of patients with arrhythmogenic cardiomyopathy carry one or more genetic variants in desmosomal genes. In the 1990s, several knockout mouse models of genes encoding for desmosomal proteins involved in cell-cell adhesion revealed for the first time embryonic lethality due to cardiac defects. Influenced by these initial discoveries in mice, arrhythmogenic cardiomyopathy received an increasing interest in human cardiovascular genetics, leading to the discovery of mutations initially in desmosomal genes and later on in more than 25 different genes. Of note, even in the clinic, routine genetic diagnostics are important for risk prediction of patients and their relatives with arrhythmogenic cardiomyopathy. Based on improvements in genetic animal engineering, different transgenic, knock-in, or cardiac-specific knockout animal models for desmosomal and nondesmosomal proteins have been generated, leading to important discoveries in this field. Here, we present an overview about the existing animal models of arrhythmogenic cardiomyopathy with a focus on the underlying pathomechanism and its importance for understanding of this disease. Prospectively, novel mechanistic insights gained from the whole animal, organ, tissue, cellular, and molecular levels will lead to the development of efficient personalized therapies for treatment of arrhythmogenic cardiomyopathy.

Pathophysiological Mechanisms of Premature Ventricular Complexes

Premature ventricular complexes (PVCs) are the most common ventricular arrhythmia. Despite the high prevalence, the cause of PVCs remains elusive in most patients. A better understanding of the underlying pathophysiological mechanism may help to steer future research. This review aims to provide an overview of the potential pathophysiological mechanisms of PVCs and their differentiation.

Fibrosis in Arrhythmogenic Cardiomyopathy: The Phantom Thread in the Fibro-Adipose Tissue

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart disorder, predisposing to malignant ventricular arrhythmias leading to sudden cardiac death, particularly in young and athletic patients. Pathological features include a progressive loss of myocardium with fibrous or fibro-fatty substitution. During the last few decades, different clinical aspects of ACM have been well investigated but still little is known about the molecular mechanisms that underlie ACM pathogenesis, leading to these phenotypes. In about 50% of ACM patients, a genetic mutation, predominantly in genes that encode for desmosomal proteins, has been identified. However, the mutation-associated mechanisms, causing the observed cardiac phenotype are not always clear. Until now, the attention has been principally focused on the study of molecular mechanisms that lead to a prominent myocardium adipose substitution, an uncommon marker for a cardiac disease, thus often recognized as hallmark of ACM. Nonetheless, based on Task Force Criteria for the diagnosis of ACM, cardiomyocytes death associated with fibrous replacement of the ventricular free wall must be considered the main tissue feature in ACM patients. For this reason, it urges to investigate ACM cardiac fibrosis. In this review, we give an overview on the cellular effectors, possible triggers, and molecular mechanisms that could be responsible for the ventricular fibrotic remodeling in ACM patients.

2019 HRS expert consensus statement on evaluation, risk stratification, and management of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an arrhythmogenic disorder of the myocardium not secondary to ischemic, hypertensive, or valvular heart disease. ACM incorporates a broad spectrum of genetic, systemic, infectious, and inflammatory disorders. This designation includes, but is not limited to, arrhythmogenic right/left ventricular cardiomyopathy, cardiac amyloidosis, sarcoidosis, Chagas disease, and left ventricular noncompaction. The ACM phenotype overlaps with other cardiomyopathies, particularly dilated cardiomyopathy with arrhythmia presentation that may be associated with ventricular dilatation and/or impaired systolic function. This expert consensus statement provides the clinician with guidance on evaluation and management of ACM and includes clinically relevant information on genetics and disease mechanisms. PICO questions were utilized to evaluate contemporary evidence and provide clinical guidance related to exercise in arrhythmogenic right ventricular cardiomyopathy. Recommendations were developed and approved by an expert writing group, after a systematic literature search with evidence tables, and discussion of their own clinical experience, to present the current knowledge in the field. Each recommendation is presented using the Class of Recommendation and Level of Evidence system formulated by the American College of Cardiology and the American Heart Association and is accompanied by references and explanatory text to provide essential context. The ongoing recognition of the genetic basis of ACM provides the opportunity to examine the diverse triggers and potential common pathway for the development of disease and arrhythmia.

Right ventricular dysplasia: management and treatment in light of current evidence

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare cardiovascular disease that predisposes to ventricular arrhythmias potentially leading to sudden cardiac death (SCD). ARVC varies considerably with multiple clinical presentations, ranging from no symptoms to cardiac arrhythmias to SCD. ARVC prevalence is not well known, but the estimated prevalence in the general population is 1:5000. Diagnosis of ARVC can be made by using the Revised European Society of Cardiology criteria for ARVC that includes ventricular structural and functional changes, ECG abnormalities, arrhythmias, family and genetic factors. The management of ARVC is focused on prevention of lethal events such as SCD. Implantable cardioverter defibrillator placement is the only proven mortality benefit in treatment of ARVC. Other treatment strategies include medications such as beta blockers and antiarrhythmics, radiofrequency ablation, surgery, cardiac transplantation, and lifestyle changes. All these interventions help in symptomatic treatment but none of them have proved to decrease mortality rates. ARVC is a progressive disease that leads to SCD if not treated appropriately. Management of these diseases has been a challenge for physicians. With the advent of technology and many new drugs/devices under clinical investigation, this might change in the future. However, while advances in technologies have helped elucidate many aspects of these diseases, many mysteries still remain of this unique disease. With continued research, we can expect more cost-effective and patient-friendly drug therapies and ablation techniques to be developed in the near future.

Blockade of the renin-angiotensin-aldosterone system in patients with arrhythmogenic right ventricular dysplasia: A double-blind, multicenter, prospective, randomized, genotype-driven study (BRAVE study)

Arrhythmogenic right ventricular dysplasia (ARVD) is a rare cardiomyopathy characterized by the progressive replacement of cardiomyocytes by fatty and fibrous tissue in the right ventricle (RV). These infiltrations lead to cardiac electrical instability and ventricular arrhythmia. Current treatment for ARVD is empirical and essentially based on treatment of arrhythmia. Thus, there is no validated treatment that will prevent the deterioration of RV function in patients with ARVD. The aim of the BRAVE study is to evaluate the effect of ramipril, an angiotensin-converting enzyme inhibitor, on ventricular myocardial remodeling and arrhythmia burden in patients with ARVD. Despite the fact that myocardial fibrosis is one of the structural hallmarks of ARVD, no study has tested an antifibrotic drug in ARVD patients. The trial is a double-blind, parallel, multicenter, prospective, randomized, phase 4 drug study. Patients will be randomized into 2 groups, ramipril or placebo. The 120 patients (60 per group) will be enrolled by 26 centers in France. Patients will be followed up every 6 months for 3 years. The 2 co-primary endpoints are defined as the difference of telediastolic RV volume measured by magnetic resonance imaging between baseline and 3 years of follow-up, and the change in arrhythmia burden during the 3 years of follow-up. A decrease in RV and/or left ventricular deterioration and in arrhythmia burden are expected in ARVD patients treated with ramipril. This reduction will improve quality of life of patients and will reduce the number of hospitalizations and the risk of terminal heart failure.

Heart Failure Is Common and Under-Recognized in Patients With Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia

BACKGROUND

Heart failure (HF) prevalence in arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) varies depending on study cohort and is not well characterized. This study sought to determine prevalence and predictors of HF in ARVC/D.

METHODS AND RESULTS

Clinical HF, defined as at least 1 HF sign or symptom, was retrospectively adjudicated for 289 patients meeting ARVC/D Task Force Criteria. HF was present in 142 patients (49%): 113 had isolated RV involvement and 29 had evidence of LV dysfunction. Average age of HF onset was 40±14 years. Most commonly reported symptoms were exertional dyspnea (78%) and fatigue (73%). Only 40% (n=57/142) had signs of volume overload. Left-sided HF signs were rare. Patients with clinical HF before ARVC/D diagnosis (n=31) were older (P=0.005) and met fewer Task Force Criteria (P=0.013) than those who developed HF after ARVC/D presentation. Female sex (odds ratio, 2.2; 95% confidence interval, 1.21-4.01; P=0.01) and lateral precordial T-wave inversions (odds ratio, 9.87; 95% confidence interval, 1.07-91.1; P=0.043) were associated with increased odds of HF. Additionally, patients with symptomatic LV dysfunction had higher odds of lateral precordial T-wave inversions (odds ratio, 18.4; 95% confidence interval, 2.92-116.18; P=0.002). Patients with HF were more likely to undergo heart transplantation (15/142 versus 1/147; P<0.001) or die during study follow-up period (7 versus 0; P=0.007).

CONCLUSIONS

HF symptoms, especially exertional dyspnea, are common in ARVC/D; yet, classic left-sided signs are typically absent and less than half have evidence of volume overload. Given the unique predominately right-sided phenotype, a large portion of patients with HF may be under-recognized.

Mast Cells Granular Contents Are Crucial for Deep Vein Thrombosis in Mice

RATIONALE

Deep vein thrombosis (DVT) and its complication pulmonary embolism have high morbidity reducing quality of life and leading to death. Cellular mechanisms of DVT initiation remain poorly understood.

OBJECTIVE

We sought to determine the role of mast cells (MCs) in DVT initiation and validate MCs as a potential target for DVT prevention.

METHODS AND RESULTS

In a mouse model, DVT was induced by partial ligation (stenosis) of the inferior vena cava. We demonstrated that 2 strains of mice deficient for MCs were completely protected from DVT. Adoptive transfer of in vitro differentiated MCs restored thrombosis. MCs were present in the venous wall, and the number of granule-containing MCs decreased with thrombosis. Pharmacological depletion of MCs granules or prevention of MC degranulation also reduced DVT. Basal plasma levels of von Willebrand factor and recruitment of platelets to the inferior vena cava wall after DVT induction were reduced in MC-deficient mice. Stenosis application increased plasma levels of soluble P-selectin in wild-type but not in MC-deficient mice. MC releasate elevated ICAM-1 (intercellular adhesion molecule-1) expression on HUVEC (human umbilical vein endothelial cells) in vitro. Topical application of compound 48/80, an MC secretagogue, or histamine, a Weibel-Palade body secretagogue from MCs, potentiated DVT in wild-type mice, and histamine restored thrombosis in MC-deficient animals.

CONCLUSIONS

MCs exacerbate DVT likely through endothelial activation and Weibel-Palade body release, which is, at least in part, mediated by histamine. Because MCs do not directly contribute to normal hemostasis, they can be considered potential targets for prevention of DVT in humans.

Animal models of arrhythmogenic right ventricular cardiomyopathy: what have we learned and where do we go? Insight for therapeutics

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare genetically-determined cardiac heart muscle disorder characterized by fibro-fatty replacement of the myocardium that results in heart failure and sudden cardiac death (SCD), predominantly in young males. The disease is often caused by mutations in genes encoding proteins of the desmosomal complex, with a significant minority caused by mutations in non-desmosomal proteins. Existing treatment options are based on SCD prevention with the implantable cardioverter defibrillator, antiarrhythmic drugs, and anti-heart failure medication. Heart transplantation may also be required and there is currently no cure. Several genetically modified animal models have been developed to characterize the disease, assess its progression, and determine the influence of potential environmental factors. These models have also been very valuable for translational therapeutic approaches, to screen new treatment options that prevent and/or reverse the disease. Here, we review the available ARVC animal models reported to date, highlighting the most important pathophysiological findings and discussing the effect of treatments tested so far in this setting. We also describe gaps in our knowledge of the disease, with the goal of stimulating research and improving patient outcomes.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy is an inherited cardiomyopathy characterised by ventricular arrhythmias and an increased risk of sudden cardiac death. Arrhythmogenic right ventricular dysplasia/cardiomyopathy diagnosis is based on criteria that take into account electrical and structural cardiac abnormalities, as well as mutation analysis. Appropriate pharmacological therapy and the prevention of sudden death with implantable defibrillators are important in the management of these patients. Exercise is considered an important environmental factor for the development and progression of the disease.

Murine Electrophysiological Models of Cardiac Arrhythmogenesis

Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.

Molecular disturbance underlies to arrhythmogenic cardiomyopathy induced by transgene content, age and exercise in a truncated PKP2 mouse model

Arrhythmogenic cardiomyopathy (ACM) is a disorder characterized by a progressive ventricular myocardial replacement by fat and fibrosis, which lead to ventricular arrhythmias and sudden cardiac death. Mutations in the desmosomal gene Plakophilin-2 (PKP2) accounts for >40% of all known mutations, generally causing a truncated protein. In a PKP2-truncated mouse model, we hypothesize that content of transgene, endurance training and aging will be determinant in disease progression. In addition, we investigated the molecular defects associated with the phenotype in this model. We developed a transgenic mouse model containing a truncated PKP2 (PKP2-Ser329) and generated three transgenic lines expressing increasing transgene content. The pathophysiological features of ACM in this model were assessed. While we did not observe fibro-fatty replacement, ultrastructural defects were exhibited. Moreover, we observed transgene content-dependent development of structural (ventricle dilatation and dysfunction) and electrophysiological anomalies in mice (PR interval and QRS prolongation and arrhythmia induction). In concordance with pathological defects, we detected a content reduction and remodeling of the structural proteins Desmocollin-2, Plakoglobin, native Plakophilin-2, Desmin and β-Catenin as well as the electrical coupling proteins Connexin 43 and cardiac sodium channel (Nav1.5). Surprisingly, we observed structural but not electrophysiological abnormalities only in trained and old mice. We demonstrated that truncated PKP2 provokes ACM in the absence of fibro-fatty replacement in the mouse. Transgene dose is essential to reveal the pathology, whereas aging and endurance training trigger limited phenotype. Molecular abnormalities underlay the structural and electrophysiological defects.

Cardiac disease and arrhythmogenesis: Mechanistic insights from mouse models

The mouse is the second mammalian species, after the human, in which substantial amount of the genomic information has been analyzed. With advances in transgenic technology, mutagenesis is now much easier to carry out in mice. Consequently, an increasing number of transgenic mouse systems have been generated for the study of cardiac arrhythmias in ion channelopathies and cardiomyopathies. Mouse hearts are also amenable to physical manipulation such as coronary artery ligation and transverse aortic constriction to induce heart failure, radiofrequency ablation of the AV node to model complete AV block and even implantation of a miniature pacemaker to induce cardiac dyssynchrony. Last but not least, pharmacological models, despite being simplistic, have enabled us to understand the physiological mechanisms of arrhythmias and evaluate the anti-arrhythmic properties of experimental agents, such as gap junction modulators, that may be exert therapeutic effects in other cardiac diseases. In this article, we examine these in turn, demonstrating that primary inherited arrhythmic syndromes are now recognized to be more complex than abnormality in a particular ion channel, involving alterations in gene expression and structural remodelling. Conversely, in cardiomyopathies and heart failure, mutations in ion channels and proteins have been identified as underlying causes, and electrophysiological remodelling are recognized pathological features. Transgenic techniques causing mutagenesis in mice are extremely powerful in dissecting the relative contributions of different genes play in producing disease phenotypes. Mouse models can serve as useful systems in which to explore how protein defects contribute to arrhythmias and direct future therapy.

Arrhythmogenic Cardiomyopathy: Electrical and Structural Phenotypes

This overview gives an update on the molecular mechanisms, clinical manifestations, diagnosis and therapy of arrhythmogenic cardiomyopathy (ACM). ACM is mostly hereditary and associated with mutations in genes encoding proteins of the intercalated disc. Three subtypes have been proposed: the classical right-dominant subtype generally referred to as ARVC/D, biventricular forms with early biventricular involvement and left-dominant subtypes with predominant LV involvement. Typical symptoms include palpitations, arrhythmic (pre)syncope and sudden cardiac arrest due to ventricular arrhythmias, which typically occur in athletes. At later stages, heart failure may occur. Diagnosis is established with the 2010 Task Force Criteria (TFC). Modern imaging tools are crucial for ACM diagnosis, including both echocardiography and cardiac magnetic resonance imaging for detecting functional and structural alternations. Of note, structural findings often become visible after electrical alterations, such as premature ventricular beats, ventricular fibrillation (VF) and ventricular tachycardia (VT). 12-lead ECG is important to assess for depolarisation and repolarisation abnormalities, including T-wave inversions as the most common ECG abnormality. Family history and the detection of causative mutations, mostly affecting the desmosome, have been incorporated in the TFC, and stress the importance of cascade family screening. Differential diagnoses include idiopathic right ventricular outflow tract (RVOT) VT, sarcoidosis, congenital heart disease, myocarditis, dilated cardiomyopathy, athlete's heart, Brugada syndrome and RV infarction. Therapeutic strategies include restriction from endurance and competitive sports, β-blockers, antiarrhythmic drugs, heart failure medication, implantable cardioverter-defibrillators and endocardial/epicardial catheter ablation.

Central role for GSK3β in the pathogenesis of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is characterized by redistribution of junctional proteins, arrhythmias, and progressive myocardial injury. We previously reported that SB216763 (SB2), annotated as a GSK3β inhibitor, reverses disease phenotypes in a zebrafish model of ACM. Here, we show that SB2 prevents myocyte injury and cardiac dysfunction in vivo in two murine models of ACM at baseline and in response to exercise. SB2-treated mice with desmosome mutations showed improvements in ventricular ectopy and myocardial fibrosis/inflammation as compared with vehicle-treated (Veh-treated) mice. GSK3β inhibition improved left ventricle function and survival in sedentary and exercised Dsg2^mut/mut mice compared with Veh-treated Dsg2^mut/mut mice and normalized intercalated disc (ID) protein distribution in both mutant mice. GSK3β showed diffuse cytoplasmic localization in control myocytes but ID redistribution in ACM mice. Identical GSK3β redistribution is present in ACM patient myocardium but not in normal hearts or other cardiomyopathies. SB2 reduced total GSK3β protein levels but not phosphorylated Ser 9-GSK3β in ACM mice. Constitutively active GSK3β worsens ACM in mutant mice, while GSK3β shRNA silencing in ACM cardiomyocytes prevents abnormal ID protein distribution. These results highlight a central role for GSKβ in the complex phenotype of ACM and provide further evidence that pharmacologic GSKβ inhibition improves cardiomyopathies due to desmosome mutations.

Pharmacotherapy and other therapeutic modalities for managing Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is a genetically determined rare cardiomyopathy (1 in 5000 to 1 in 2000 in the general population), which can lead to ventricular arrhythmias and sudden death (SD). The classic form of the disease has a predilection for the right ventricle (RV), but recognition of left-dominant and biventricular variants led to the broader term "Arrhythmogenic Cardiomyopathy". The disease affects men more frequently than women and becomes clinically overt usually from the second to the fourth decade of life. Treatment consists of restriction of physical exercise, antiarrhythmic drugs, catheter ablation and ICD implantation. These treatments have the potential to change the natural history of the disease by protecting against SD and offering a good-quality and nearly normal life-expectancy. Antiarrhythmic drugs play an important role in terms of reduction of both the number and the complexity of arrhythmias, but they do not reduce the risk of SD. The results of catheter ablation are poor because of the high rate of VT recurrence. ICD should be reserved to selected patients after an accurate risk stratification. The clinical challenge is to improve risk stratification for better identification of those patients who most benefit from the above therapies. Unfortunately, a curative therapy is not yet available.

Sports in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy and desmosomal mutations

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a rare cardiomyopathy associated with life-threatening arrhythmias and an increased risk of sudden cardiac death. In addition to mutations in desmosomal genes, environmental factors such as exercise and sport have been implicated in the pathogenesis of the disease. Recent studies have shown that exercise may be associated with adverse outcomes in patients with ARVD/C. On the basis of current evidence, patients with ARVD/C are recommended to limit exercise irrespective of their mutation status. Some studies have suggested the presence of an entirely acquired form of the disease caused by exercise, which has been dubbed "exercise-induced ARVD/C."

Loss of plakoglobin immunoreactivity in intercalated discs in arrhythmogenic right ventricular cardiomyopathy: protein mislocalization versus epitope masking

AIMS

To examine the relevance and cause of reduced plakoglobin IF in intercalated discs for arrhythmogenic right ventricular cardiomyopathy (ARVC) and ARVC-like disease in mouse and human.

METHODS AND RESULTS

Normalized semi-quantitative IF measurements were performed in a standardized format in desmoglein 2-mutant mice with an ARVC-like phenotype (n = 6) and in cardiac biopsies from humans with ARVC and non-ARVC heart disease (n = 10). Reduced plakoglobin staining was detectable in ARVC only with one antibody directed against a defined epitope but not with three other antibodies reacting with different epitopes of plakoglobin.

CONCLUSIONS

Reduced plakoglobin staining in intercalated discs of heart tissue from human ARVC patients and in a murine ARVC model is caused by alterations in epitope accessibility and not by protein relocalization.

Arrhythmogenic right ventricular cardiomyopathy, clinical manifestations, and diagnosis

This review aims to give an update on the pathogenesis, clinical manifestations, and diagnosis of arrhythmogenic right ventricular cardiomyopathy (ARVC). Arrhythmogenic right ventricular cardiomyopathy is mainly an autosomal dominant inherited disease linked to mutations in genes encoding desmosomes or desmosome-related proteins. Classic symptoms include palpitations, cardiac syncope, and aborted cardiac arrest due to ventricular arrhythmias. Heart failure may develop in later stages. Diagnosis is based on the presence of major and minor criteria from the Task Force Criteria revised in 2010 (TFC 2010), which includes evaluation of findings from six different diagnostic categories. Based on this, patients are classified as having possible, borderline, or definite ARVC. Imaging is important in ARVC diagnosis, including both echocardiography and cardiac magnetic resonance imaging for detecting structural and functional abnormalities, but importantly these findings may occur after electrical alterations and ventricular arrhythmias. Electrocardiograms (ECGs) and signal-averaged ECGs are analysed for depolarization and repolarization abnormalities, including T-wave inversions as the most common ECG alteration. Ventricular arrhythmias are common in ARVC and are considered a major diagnostic criterion if originating from the RV inferior wall or apex. Family history of ARVC and detection of an ARVC-related mutation are included in the TFC 2010 and emphasize the importance of family screening. Electrophysiological studies are not included in the diagnostic criteria, but may be important for differential diagnosis including RV outflow tract tachycardia. Further differential diagnoses include sarcoidosis, congenital abnormalities, myocarditis, pulmonary hypertension, dilated cardiomyopathy, and athletic cardiac adaptation, which may mimic ARVC.

Inherited cardiomyopathies--Novel therapies

Cardiomyopathies arising due to a single gene defect represent various pathways that evoke adverse remodeling and cardiac dysfunction. While the gene therapy approach is slowly evolving and has not yet reached clinical "prime time" and gene correction approaches are applicable at the bench but not at the bedside, major advances are being made with molecular and drug therapies. This review summarizes the contemporary drugs introduced or being tested to help manage these unique disorders bearing a major impact on the quality of life and survival of the affected individuals. The restoration of the RNA reading frame facilitates the expression of partly functional protein to salvage or alleviate the disease phenotype. Chaperones are used to prevent the degradation of abnormal but still functional proteins, while other molecules are given for pathogen silencing, to prevent aggregation or to enhance clearance of protein deposits. The absence of protein may be managed by viral gene delivery or protein therapy. Enzyme replacement therapy is already a clinical reality for a series of metabolic diseases. The progress in molecular biology, based on the knowledge of the gene defect, helps generate small molecules and pharmaceuticals targeting the key events occurring in the malfunctioning element of the sick organ. Cumulatively, these tools augment the existing armamentarium of phenotype oriented symptomatic and evidence-based therapies for patients with inherited cardiomyopathies.

Treatment of Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia: An International Task Force Consensus Statement

Supplemental Digital Content is available in the text.

Relationship between arrhythmogenic right ventricular dysplasia and exercise

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is rare cardiomyopathy associated with life-threatening arrhythmias and increased risk of sudden cardiac death. In addition to mutations in desmosomal genes, environmental factors such as exercise have been implicated in the pathogenesis of the disease. Recent studies have shown that exercise may be associated with adverse outcomes in ARVD/C patients. Based on current evidence, ARVD/C patients are recommended to limit exercise irrespective of their mutation status. In addition, some studies have suggested the presence of an entirely acquired form of the disease caused by exercise that has been dubbed exercise-induced ARVD/C.

Circulating tumor cell clusters-associated gene plakoglobin and breast cancer survival

Breast cancer recurrence is a major cause of the disease-specific death. Circulating tumor cells (CTCs) are negatively associated with breast cancer survival. Plakoglobin, a cell adhesion protein, was recently reported as a determinant of CTCs types, single or clustered ones. Here, we aim to summarize the studies on the roles of plakoglobin and evaluate the association of plakoglobin and breast cancer survival. Plakoglobin as a key component in both cell adhesion and the signaling pathways was briefly reviewed first. Then the double-edge functions of plakoglobin in tumors and its association with CTCs and breast cancer metastasis were introduced. Finally, based on an open-access database, the association between plakoglobin and breast cancer survival was investigated using univariate and multivariate survival analyses. Plakoglobin may be a molecule functioning as a double-edge sword. Loss of plakoglobin expression leads to increased motility of epithelial cells, thereby promoting epithelial-mesenchymal transition and further metastasis of cancer. However, studies also show that plakoglobin can function as an oncogene. High expression of plakoglobin results in clustered tumor cells in circulation with high metastatic potential in breast cancer and shortened patient survival. Plakoglobin may be a potential prognostic biomarker that can be exploited to develop as a therapeutic target for breast cancer.