Arrhythmogenic right ventricular cardiomyopathy/dysplasia: an update

Uncovering Inherited Cardiomyopathy With Human Induced Pluripotent Stem Cells

In the past decades, researchers discovered the contribution of genetic defects to the pathogenesis of primary cardiomyopathy and tried to explain the pathogenesis of these diseases by establishing a variety of disease models. Although human heart tissues and primary cardiomyocytes have advantages in modeling human heart diseases, they are difficult to obtain and culture in vitro. Defects developed in genetically modified animal models are notably different from human diseases at the molecular level. The advent of human induced pluripotent stem cells (hiPSCs) provides an unprecedented opportunity to further investigate the pathogenic mechanisms of inherited cardiomyopathies in vitro using patient-specific hiPSC-derived cardiomyocytes. In this review, we will make a summary of recent advances in in vitro inherited cardiomyopathy modeling using hiPSCs.

High risk of heart failure associated with desmoglein-2 mutations compared to plakophilin-2 mutations in arrhythmogenic right ventricular cardiomyopathy/dysplasia

BACKGROUND

Previous studies suggested that genetic status affects the clinical course of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) patients. The aim of this study was to compare the outcome of desmoglein-2 (DSG2) mutation carriers to those who carry the plakophilin-2 (PKP2) mutation, the most common ARVC/D-associated gene.

METHODS AND RESULTS

Consecutive ARVC/D patients carrying a pathogenic mutation in PKP2 or DSG2 were selected from a national ARVC/D registry. The cumulative freedom from sustained ventricular arrhythmia and cardiac transplantation/death from heart failure (HF) during follow-up was assessed, compared between PKP2 and DSG2, and predictors for ventricular arrhythmia and HF events determined. Overall, 118 patients from 78 families were included: 27 (23%) carried a DSG2 mutation and 91 (77%) a PKP2 mutation. There were no significant differences between DSG2 and PKP2 mutation carriers concerning gender, proband status, age at diagnosis, T-wave inversion, or right ventricular dysfunction at baseline. DSG2 patients displayed more frequent epsilon wave (37% vs. 17%, P = 0.048) and left ventricular dysfunction at diagnosis (54% vs. 10%, P < 0.001). During a median follow-up of 5.6 years (2.5-16), DSG2 and PKP2 mutation carriers displayed a similar risk of sustained ventricular arrhythmia (log-rank P = 0.20), but DSG2 mutation carriers were at higher risk of transplantation/HF-related death (log-rank P < 0.001). The presence of a DSG2 mutation vs. PKP2 mutation was a predictor of transplantation/HF-related death in univariate Cox analysis (P = 0.0005).

CONCLUSIONS

In this multicentre cohort, DSG2 mutation carriers were found to be at high risk of end-stage HF compared to PKP2 mutation carriers, supporting careful haemodynamic monitoring of these patients. The benefit of early HF treatment needs to be assessed in DSG2 carriers.

Neonatal Transplantation Confers Maturation of PSC-Derived Cardiomyocytes Conducive to Modeling Cardiomyopathy

Pluripotent stem cells (PSCs) offer unprecedented opportunities for disease modeling and personalized medicine. However, PSC-derived cells exhibit fetal-like characteristics and remain immature in a dish. This has emerged as a major obstacle for their application for late-onset diseases. We previously showed that there is a neonatal arrest of long-term cultured PSC-derived cardiomyocytes (PSC-CMs). Here, we demonstrate that PSC-CMs mature into adult CMs when transplanted into neonatal hearts. PSC-CMs became similar to adult CMs in morphology, structure, and function within a month of transplantation into rats. The similarity was further supported by single-cell RNA-sequencing analysis. Moreover, this in vivo maturation allowed patient-derived PSC-CMs to reveal the disease phenotype of arrhythmogenic right ventricular cardiomyopathy, which manifests predominantly in adults. This study lays a foundation for understanding human CM maturation and pathogenesis and can be instrumental in PSC-based modeling of adult heart diseases.

The Canadian Arrhythmogenic Right Ventricular Cardiomyopathy Registry: Rationale, Design, and Preliminary Recruitment

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a complex and clinically heterogeneous arrhythmic condition. Incomplete penetrance and variable expressivity are particularly evident in ARVC, making clinical decision-making challenging.

METHODS

Pediatric and adult cardiologists, geneticists, genetic counsellors, ethicists, nurses, and qualitative researchers are collaborating to create the Canadian ARVC registry using a web-based clinical database. Biological samples will be banked and systematic analysis will be performed to examine potentially causative mutations, variants, and biomarkers. Outcomes will include syncope, ventricular arrhythmias, defibrillator therapies, heart failure, and mortality.

RESULTS

Preliminary recruitment has enrolled 365 participants (aged 42.7 ± 17.1 years; 50% women), including 129 probands and 236 family members. Previous cardiac arrest occurred in 28 (8%) participants, syncope occurred in 43 (12%) participants, and 46% of probands had a family history of sudden death. Overall yield of genetic testing was 36% for a disease-causing mutation and 20% for a variant of unknown significance. Target enrollment is 1000 affected patients and 500 unaffected family member controls over 7 years. The cross-sectional and longitudinal data collected in this manner will allow a robust assessment of the natural history and clinical course of genetic subtypes.

CONCLUSIONS

The Canadian ARVC Registry will create a population-based cohort of patients and their families to inform clinical decisions regarding patients with ARVC.

Long-Term Clinical Outcome of Arrhythmogenic Right Ventricular Cardiomyopathy in Individuals With a p.S358L Mutation in TMEM43 Following Implantable Cardioverter Defibrillator Therapy

Background—

We previously showed a survival benefit of the implantable cardioverter defibrillator (ICD) in males with arrhythmogenic right ventricular cardiomyopathy caused by a p.S358L mutation in TMEM43 . We present long-term data (median follow-up 8.5years) after ICD for primary (PP) and secondary prophylaxis in males and females, determine whether ICD discharges for ventricular tachycardia/ventricular fibrillation were equivalent to an aborted death, and assess relevant clinical predictors.

Methods and Results—

We studied 24 multiplex families segregating an autosomal dominant p.S358L mutation in TMEM43 . We compared survival in 148 mutation carriers with an ICD to 148 controls matched for age, sex, disease status, and family. Of 80 male mutation carriers with ICDs (median age at implantation 31 years), 61 (76%) were for PP; of 68 females (median age at implantation 43 years), 66 (97%) were for PP. In males, irrespective of indication, survival was better in the ICD groups compared with control groups (relative risk 9.3 [95% confidence interval 3.3–26] for PP and 9.7 [95% confidence interval 3.2–29.6] for secondary prophylaxis). For PP females, the relative risk was 3.6 (95% confidence interval 1.3–9.5). ICD discharge-free survival for ventricular tachycardia/ventricular fibrillation ≥240 beats per minute was equivalent to the control survival rate. Ectopy (≥1000 premature ventricular complexes/24 hours) was the only independent clinical predictor of ICD discharge in males, and no predictor was identified in females.

Conclusions—

ICD therapy is indicated for PP in postpubertal males and in females ≥30 years with the p.S358L TMEM43 mutation. ICD termination of rapid ventricular tachycardia/ventricular fibrillation can reasonably be considered an aborted death.

Maturation-Based Model of Arrhythmogenic Right Ventricular Dysplasia Using Patient-Specific Induced Pluripotent Stem Cells

Cellular reprogramming of somatic cells to patient-specific induced pluripotent stem cells (iPSCs) enables in-vitro modeling of human cardiac disorders for pathogenic and therapeutic investigations. However, using iPSC-derived cardiomyocytes (iPSC-CMs) to model an adult-onset heart disease remains challenging because of the uncertainty regarding the ability of relatively immature iPSC-CMs to fully recapitulate adult disease phenotypes. Arrhythmogenic right ventricular dysplasia (ARVD) is an inherited cardiomyopathy characterized by pathological fibrofatty infiltration and cardiomyocyte (CM) loss predominantly in the right ventricle (RV), leading to heart failure and lethal arrhythmias. Over 50% of affected individuals have desmosome gene mutations, most commonly inPKP2encoding plakophilin-2. Using Yamanaka's pluripotent factors, we generated iPSC lines from ARVD patients withPKP2mutations. We first developed a method to induce metabolic maturation of iPSC-CMs and showed that induction of adult-like metabolic energetics from an embryonic/glycolytic state is essential to model an adult-onset cardiac disease using patient-specific iPSCs. Furthermore, we showed that coactivation of normal peroxisome proliferator-activated receptor (PPAR)-α and abnormal PPARγ pathways in ARVD iPSC-CMs resulted in exaggerated CM lipogenesis, CM apoptosis, Na(+)channel downregulation and defective intracellular calcium handling, recapitulating the pathological signatures of ARVD. Using this model, we revealed novel pathogenic insights that metabolic derangement in an adult-like metabolic milieu underlies ARVD pathologies, enabling us to propose novel disease-modifying therapeutic strategies.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D)

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a progressive genetic cardiomyopathy characterized by progressive fatty and fibrous replacement of ventricular myocardium. The clinical presentation is marked by ventricular arrhythmias, some fatal. The disease has evolved from a primary electrical/electrophysiological disorder (in the 1980s-1990s) to a diagnostic imaging conundrum (in the 2000s) to the current day understanding of a genetic cardiomyopathy caused by defects in cell-cell adhesion proteins or intracellular signaling components. The pathogenesis, clinical presentation, and the genetics of the disease are discussed in this review.

Studying arrhythmogenic right ventricular dysplasia with patient-specific iPSCs

Cellular reprogramming of somatic cells to patient-specific induced pluripotent stem cells (iPSCs) enables in vitro modelling of human genetic disorders for pathogenic investigations and therapeutic screens. However, using iPSC-derived cardiomyocytes (iPSC-CMs) to model an adult-onset heart disease remains challenging owing to the uncertainty regarding the ability of relatively immature iPSC-CMs to fully recapitulate adult disease phenotypes. Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited heart disease characterized by pathological fatty infiltration and cardiomyocyte loss predominantly in the right ventricle, which is associated with life-threatening ventricular arrhythmias. Over 50% of affected individuals have desmosome gene mutations, most commonly in PKP2, encoding plakophilin-2 (ref. 9). The median age at presentation of ARVD/C is 26 years. We used previously published methods to generate iPSC lines from fibroblasts of two patients with ARVD/C and PKP2 mutations. Mutant PKP2 iPSC-CMs demonstrate abnormal plakoglobin nuclear translocation and decreased β-catenin activity in cardiogenic conditions; yet, these abnormal features are insufficient to reproduce the pathological phenotypes of ARVD/C in standard cardiogenic conditions. Here we show that induction of adult-like metabolic energetics from an embryonic/glycolytic state and abnormal peroxisome proliferator-activated receptor gamma (PPAR-γ) activation underlie the pathogenesis of ARVD/C. By co-activating normal PPAR-alpha-dependent metabolism and abnormal PPAR-γ pathway in beating embryoid bodies (EBs) with defined media, we established an efficient ARVD/C in vitro model within 2 months. This model manifests exaggerated lipogenesis and apoptosis in mutant PKP2 iPSC-CMs. iPSC-CMs with a homozygous PKP2 mutation also had calcium-handling deficits. Our study is the first to demonstrate that induction of adult-like metabolism has a critical role in establishing an adult-onset disease model using patient-specific iPSCs. Using this model, we revealed crucial pathogenic insights that metabolic derangement in adult-like metabolic milieu underlies ARVD/C pathologies, enabling us to propose novel disease-modifying therapeutic strategies.

Perioperative management of hereditary arrhythmogenic syndromes

Patients with inherited cardiac channel disorders are at high risk of perioperative lethal arrhythmias. Preoperative control of symptoms and a multidisciplinary approach are required for a well-planned management. Good haemodynamic monitoring, adequate anaesthesia and analgesia, perioperative maintenance of normocarbia, normothermia, and normovolaemia are important. In congenital long QT syndrome, torsades de pointes should be prevented with magnesium sulphate infusion and avoidance of drugs such as droperidol, succinylcholine, ketamine, and ondansetron. Propofol and epidural anaesthesia represent safe choices, while caution is needed with volatile agents. In Brugada syndrome, β-blockers, α-agonists, and cholinergic drugs should be avoided, while isoproterenol reverses the ECG changes. Propofol, thiopental, and volatiles have been used uneventfully. In congenital sick sinus syndrome, severe bradycardia resistant to atropine may require isoproterenol or epinephrine. Anaesthetics with vagolytic properties are preferable, while propofol and vecuronium should be given with caution due to risk of inducing bradyarrhythmias. Neuraxial anaesthesia should produce the least autonomic imbalance. Arrhythmogenic right ventricular dysplasia/cardiomyopathy induces ventricular tachyarrhythmias, which should be treated with β-blockers. Generally, β-adrenergic stimulation and catecholamine release should be avoided. Halothane and pancuronium are contraindicated, while large doses of local anaesthetics and epinephrine should be avoided in neuraxial blocks. In catecholaminergic polymorphic ventricular tachycardia, β-blocker treatment should be continued perioperatively. Catecholamine release and β-agonists, such as isoproterenol, should be avoided. Propofol and remifentanil are probably safe, while halothane and pancuronium are contraindicated. Regional anaesthesia, without epinephrine, is relatively safe. In suspicious cardiac deaths, postmortem examination and familial screening are recommended.

Desmoglein 2 mutant mice develop cardiac fibrosis and dilation

Desmosomes are cell–cell adhesion sites and part of the intercalated discs, which couple adjacent cardiomyocytes. The connection is formed by the extracellular domains of desmosomal cadherins that are also linked to the cytoskeleton on the cytoplasmic side. To examine the contribution of the desmosomal cadherin desmoglein 2 to cardiomyocyte adhesion and cardiac function, mutant mice were prepared lacking a part of the extracellular adhesive domain of desmoglein 2. Most live born mutant mice presented normal overall cardiac morphology at 2 weeks. Some animals, however, displayed extensive fibrotic lesions. Later on, mutants developed ventricular dilation leading to cardiac insufficiency and eventually premature death. Upon histological examination, cardiomyocyte death by calcifying necrosis and replacement by fibrous tissue were observed. Fibrotic lesions were highly proliferative in 2-week-old mutants, whereas the fibrotic lesions of older mutants showed little proliferation indicating the completion of local muscle replacement by scar tissue. Disease progression correlated with increased mRNA expression of c-myc, ANF, BNF, CTGF and GDF15, which are markers for cardiac stress, remodeling and heart failure. Taken together, the desmoglein 2-mutant mice display features of dilative cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, an inherited human heart disease with pronounced fibrosis and ventricular arrhythmias that has been linked to mutations in desmosomal proteins including desmoglein 2.

[Arrhytmogenic right ventricle--prognostic significance of exercise test]

The authors summarize the present knowledge on arrhythmogenic right ventricular cardiomyopathy/dysplasia. Limited data are available about natural history of asymptomatic patients with arrhythmogenic right ventricle cardiomyopathy/dysplasia, who have a ventricular tachycardia during exercise test. A 25-year old female patient was treated with osteosynthesis because of ankle injury. Cardiology consultation was performed because of an abnormal ECG. Physical examination was normal. ECG showed a normal sinus rhythm, left axis deviation, negative T waves in leads II, III, aVF and V2-V6. Chest X-ray and laboratory findings were normal. Echocardiography showed normal left ventricular ejection fraction along with inferior akinesis and dilated right ventricle. Bicycle exercise test revealed a good exercise tolerability (9 MET), and after sporadic ventricular extra systoles ventricular tachycardia developed lasting for 3 minutes, which spontaneously stopped after aborting the test and performed abdominal strain. MRI was performed which has shown normal left ventricular size, wall motion and ejection fraction and depressed right ventricle function (ejection fraction 31.6%) enlarged right ventricular end-systolic and diastolic volumes, hypo-akinetic regions without aneurysm and bulging. No contrast enhancement was seen in the thin right ventricular wall. According to abnormal ECG and MRI findings arrhythmogenic right ventricle cardiomyopathy/dysplasia was diagnosed. No ICD implantation was indicated because the patient was asymptomatic, and no sudden cardiac death occurred in the family. Three month later the patient was found dead. At autopsy the right ventricular chamber was markedly enlarged, with multiple translucent areas of fatty accumulation accompanied with extended myocytes loss. There was a characteristic triangle dysplasia: the inflow, outflow tracts and apical areas. The coronaries were free of atherosclerosis. Mallory's phosphotungstic acid-hematoxilin stain demonstrated the presence of fibrosis within the scattered myocardium.

CONCLUSION

malignant ventricular arrhythmia provoked by exercise test in an asymptomatic arrhythmogenic right ventricle cardiomyopathy/dysplasia patient with negative family history should be an indication for ICD implantation.

Genetic Testing for Cardiac Arrhythmias: Ready for Prime Time?

Despite the heterogeneity of substrates and clinical expressivity, genetic testing has a direct impact on clinical practice: it allows a specific diagnosis, including silent carriers (ie, asymptomatic diagnosis) and, in select diseases, the identification of a mutation has major impact for risk stratification and treatment of patients. This article addresses the role of genetic testing for each of the most epidemiologically relevant inherited arrhythmogenic diseases, specifically long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy.

Desmosomal gene analysis in arrhythmogenic right ventricular dysplasia/cardiomyopathy: spectrum of mutations and clinical impact in practice

AIMS

Five desmosomal genes have been recently implicated in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) but the clinical impact of genetics remains poorly understood. We wanted to address the potential impact of genotyping.

METHODS AND RESULTS

Direct sequencing of the five genes (JUP, DSP, PKP2, DSG2, and DSC2) was performed in 135 unrelated patients with ARVD/C. We identified 41 different disease-causing mutations, including 28 novel ones, in 62 patients (46%). In addition, a genetic variant of unknown significance was identified in nine additional patients (7%). Distribution of genes was 31% (PKP2), 10% (DSG2), 4.5% (DSP), 1.5% (DSC2), and 0% (JUP). The presence of desmosomal mutations was not associated with familial context but was associated with young age, symptoms, electrical substrate, and extensive structural damage. When compared with other genes, DSG2 mutations were associated with more frequent left ventricular involvement (P = 0.006). Finally, complex genetic status with multiple mutations was identified in 4% of patients and was associated with more frequent sudden death (P = 0.047).

CONCLUSION

This study supports the use of genetic testing as a new diagnostic tool in ARVC/D and also suggests a prognostic impact, as the severity of the disease appears different according to the underlying gene or the presence of multiple mutations.

The importance of the family history in caring for families with long QT syndrome and dilated cardiomyopathy

In potentially inherited cardiac diseases, the family history is of great importance. We looked at the way cardiologists take a family history in patients with idiopathic dilated cardiomyopathy (DCM) or long QT syndrome (LQTS) and whether this led to screening of relatives or other follow-up. We performed retrospective cross-sectional analyses of adult index patients with DCM or LQTS in a general hospital (GH) or a University Medical Center (UMC). We identified 82 index patients with DCM (34 GH; 48 UMC) and 20 with LQTS (all UMC) between 1996 and 2005. Mean follow-up was 58 months. A family history was recorded in 90% of both LQTS and DCM patients most of the cases restricted to first-degree family members. The genetic aspects, counseling and screening of family members was discussed significantly more often with LQTS than DCM patients (all P < 0.05). Also follow-up (screening of family members, DNA analysis and referral) was performed significantly more often in LQTS than DCM patients. Cardiologists in the UMC referred DCM index patients for genetic counseling more often than those in the GH (25% vs. 6%; P < 0.05). Only a few index patients with DCM were referred to a clinical genetics department. One-third of DCM cases and nearly all LQTS cases are familial. Since early recognition and treatment may reduce morbidity and mortality we recommend cardiologists take a more thorough family history and always consider referring to a clinical genetics department in such index patients.

When is genetic testing useful in patients suspected to have inherited cardiac arrhythmias?

PURPOSE OF REVIEW

In this article, we will review the appropriate use of genetic testing in those patients suspected to have inherited arrhythmogenic diseases, with specific focus on the indications for testing and the expected probability of positive genotyping.

RECENT FINDINGS

Important advances have been made in the identification of new genes, associated mutations, and polymorphisms that modulate susceptibility of acquired arrhythmias. We will examine the most recent advances relevant to the rational application of genetic analysis, guided by genotype-phenotype correlations derived from disease and patient-specific evaluation, as well as discussing novel technologies and recently published cost-effectiveness data.

SUMMARY

Genetic analysis can be performed to identify the molecular substrate in those patients suspected to be affected by an inherited arrhythmogenic disease; however, the clinical usefulness of this information is often not straightforward. We hope to emphasize the concept that there is a significant difference in the impact of genetic testing within the various arrhythmogenic disorders, and the benefit of accessing genetic testing is not the same in all patients. The resultant integration between the expected yield of genetic screening and cost may allow the formation of criteria to prioritize access for those who could derive the most clinical benefit.

Role of genetic testing in arrhythmogenic right ventricular cardiomyopathy/dysplasia

In a cohort of patients with confirmed or suspected arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D), genetic testing is useful in confirming the diagnosis, particularly in individuals who do not completely fulfil Task Force criteria for the disease, thereby also enabling the adoption of preventive measures in family members. Due to the high percentage of novel mutations that are expected to be identified in ARVC/D, the use of genetic screening technology based on the identification of known mutations seems to have very restricted value. Our results support that the presence of certain genetic variations could play a role in the final phenotype of patients with ARVC/D, where single and compound mutation carriers would have more symptomatic forms of the disease and the polymorphism P366L could be associated to a more benign phenotype.