The genetic background of arrhythmogenic right ventricular cardiomyopathy

Postmortem genetic analysis of 17 sudden cardiac deaths identified nonsense and frameshift variants in two cases of arrhythmogenic cardiomyopathy

Sudden death, or unexpected natural death of a healthy individual, is a serious problem in all nations. Sudden cardiac death (SCD) mainly due to ischemic heart diseases is the top cause of sudden death. However, there are pathophysiological conditions, referred to as sudden arrhythmic death syndrome, in which no apparent lesion can be identified even after complete conventional or ordinary autopsy. While postmortem genetic analyses have accumulated evidence about underlying genetic abnormality in such cases, the precise relationships between genetic background and the phenotype have been largely elusive. In this study, a retrospective investigation of 17 autopsy cases in which lethal arrhythmia was suspected to be the cause of death was carried out. Genetic analysis focusing on 72 genes reported to be associated with cardiac dysfunctions was performed, in combination with detailed histopathological and postmortem imaging examination, and a family study. As a result, in two cases of suspected arrhythmogenic cardiomyopathy (ACM), we found a nonsense variant in PKP2 and frameshift variant in TRPM4 gene. In contrast, the other 15 cases showed no morphological changes in the heart despite the presence of a frameshift variant and several missense variants, leaving the clinical significance of these variants obscure. The findings of the present study suggest that nonsense and frameshift variants could be involved in the morphological abnormality in cases of SCD due to ACM, while missense variants alone rarely contribute to massive structural changes in the heart.

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.

Predicting ventricular tachycardia circuits in patients with arrhythmogenic right ventricular cardiomyopathy using genotype-specific heart digital twins

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic cardiac disease that leads to ventricular tachycardia (VT), a life-threatening heart rhythm disorder. Treating ARVC remains challenging due to the complex underlying arrhythmogenic mechanisms, which involve structural and electrophysiological (EP) remodeling. Here, we developed a novel genotype-specific heart digital twin (Geno-DT) approach to investigate the role of pathophysiological remodeling in sustaining VT reentrant circuits and to predict the VT circuits in ARVC patients of different genotypes. This approach integrates the patient's disease-induced structural remodeling reconstructed from contrast-enhanced magnetic-resonance imaging and genotype-specific cellular EP properties. In our retrospective study of 16 ARVC patients with two genotypes: plakophilin-2 (PKP2, n = 8) and gene-elusive (GE, n = 8), we found that Geno-DT accurately and non-invasively predicted the VT circuit locations for both genotypes (with 100%, 94%, 96% sensitivity, specificity, and accuracy for GE patient group, and 86%, 90%, 89% sensitivity, specificity, and accuracy for PKP2 patient group), when compared to VT circuit locations identified during clinical EP studies. Moreover, our results revealed that the underlying VT mechanisms differ among ARVC genotypes. We determined that in GE patients, fibrotic remodeling is the primary contributor to VT circuits, while in PKP2 patients, slowed conduction velocity and altered restitution properties of cardiac tissue, in addition to the structural substrate, are directly responsible for the formation of VT circuits. Our novel Geno-DT approach has the potential to augment therapeutic precision in the clinical setting and lead to more personalized treatment strategies in ARVC.

Clinical and Genetic Characteristics of Arrhythmogenic Right Ventricular Cardiomyopathy Patients: A Single-Center Experience

Background

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited progressive cardiomyopathy. We aimed to define the long-term clinical outcome and genetic characteristics of patients and family members with positive genetic tests for ARVC in a single tertiary care cardiac center in Saudi Arabia.

Methods

We enrolled 46 subjects in the study, including 23 index-patients (probands) with ARVC based on the revised 2010 ARVC Task Force Criteria (TFC) and 23 family members who underwent a genetic test for the ARVC between 2016 and 2020.

Results

Of the probands, 17 (73.9%) were males with a mean age at presentation of 24.95 ± 13.9 years (7 to 55 years). Predominant symptoms were palpitations in 14 patients (60.9%), and syncope in 10 patients (43.47%). Sustained ventricular tachycardia (VT) was documented in 12 patients (52.2%). The mean left ventricular ejection fraction (LVEF) by echocardiogram was 52.81±6.311% (30-55%), and the mean right ventricular ejection fraction (RVEF) by cardiac MRI was 41.3±11.37% (23-64%). Implantable cardioverter-defibrillator (ICD) implantation was performed in 17 patients (73.9%), and over a mean follow-up of 13.65 ± 6.83 years, appropriate ICD therapy was noted in 12 patients (52.2%). Genetic variants were identified in 33 subjects (71.7%), 16 patients and 17 family members, with the most common variant of plakophilin 2 (PKP2) in 27 subjects (81.8%).

Conclusions

ARVC occurs during early adulthood in Saudi patients. It is associated with a significant arrhythmia burden in these patients. The PKP2 gene is the most common gene defect in Saudi patients, consistent with what is observed in other nations. We reported in this study two novel variants in PKP2 and desmocollin 2 (DSC2) genes. Genetic counseling is needed to include all first-degree family members for early diagnosis and management of the disease in our country.

Predicting Ventricular Tachycardia Circuits in Patients with Arrhythmogenic Right Ventricular Cardiomyopathy using Genotype-specific Heart Digital Twins

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic cardiac disease that leads to ventricular tachycardia (VT), a life-threatening heart rhythm disorder. Treating ARVC remains challenging due to the complex underlying arrhythmogenic mechanisms, which involve structural and electrophysiological (EP) remodeling. Here, we developed a novel genotype-specific heart digital twin (Geno-DT) approach to investigate the role of pathophysiological remodeling in sustaining VT reentrant circuits and to predict the VT circuits in ARVC patients of different genotypes. This approach integrates the patient's disease-induced structural remodeling reconstructed from contrast-enhanced magnetic-resonance imaging and genotype-specific cellular EP properties. In our retrospective study of 16 ARVC patients with two genotypes: plakophilin-2 (PKP2, n = 8) and gene-elusive (GE, n = 8), we found that Geno-DT accurately and non-invasively predicted the VT circuit locations for both genotypes (with 100%, 94%, 96% sensitivity, specificity, and accuracy for GE patient group, and 86%, 90%, 89% sensitivity, specificity, and accuracy for PKP2 patient group), when compared to VT circuit locations identified during clinical EP studies. Moreover, our results revealed that the underlying VT mechanisms differ among ARVC genotypes. We determined that in GE patients, fibrotic remodeling is the primary contributor to VT circuits, while in PKP2 patients, slowed conduction velocity and altered restitution properties of cardiac tissue, in addition to the structural substrate, are directly responsible for the formation of VT circuits. Our novel Geno-DT approach has the potential to augment therapeutic precision in the clinical setting and lead to more personalized treatment strategies in ARVC.

The intercalated disc: a unique organelle for electromechanical synchrony in cardiomyocytes

The intercalated disc (ID) is a highly specialized structure that connects cardiomyocytes via mechanical and electrical junctions. Although described in some detail by light microscopy in the 19th century, it was in 1966 that electron microscopy images showed that the ID represented apposing cell borders and provided detailed insight into the complex ID nanostructure. Since then, much has been learned about the ID and its molecular composition, and it has become evident that a large number of proteins, not all of them involved in direct cell-to-cell coupling via mechanical or gap junctions, reside at the ID. Furthermore, an increasing number of functional interactions between ID components are emerging, leading to the concept that the ID is not the sum of isolated molecular silos but an interacting molecular complex, an "organelle" where components work in concert to bring about electrical and mechanical synchrony. The aim of the present review is to give a short historical account of the ID's discovery and an updated overview of its composition and organization, followed by a discussion of the physiological implications of the ID architecture and the local intermolecular interactions. The latter will focus on both the importance of normal conduction of cardiac action potentials as well as the impact on the pathophysiology of arrhythmias.

Genetic Testing for Cardiomyopathy in Japan 2022: Current Status and Issues of Precision Medicine

Although many causative genes for primary cardiomyopathy have been identified, the use of genetic testing in routine practice is limited in Japan presently. Genetic diagnosis has been reported to be useful for early diagnosis through cascade genetic screening in the family, differentiating secondary cardiomyopathies, and predicting prognosis in some patients; nonetheless, the acquisition of genetic information for cardiomyopathy is stagnating in actual clinical practice. There seem to be a number of reasons for this phenomenon, and although the use of next-generation sequencers has resolved some of the past issues, the importance of pathogenicity studies of variants that are identified is growing. To ensure that patients with cardiomyopathy and their relatives can receive precision medicine, the results of genetic analysis linked to clinical information need to be collected, and a database of variants in Japanese people needs to be established.

Evaluation of autoantibodies to desmoglein-2 in dogs with and without cardiac disease

Autoantibodies to desmoglein-2 have been associated with arrhythmogenic right ventricular cardiomyopathy (ARVC) in people. ARVC is a common disease in the Boxer dog. The role of anti-desmoglein-2 antibodies in Boxers with ARVC and correlation with disease status or severity is unknown. This prospective study is the first to evaluate dogs of various breeds and cardiac disease state for anti-desmoglein-2 antibodies. The sera of 46 dogs (10 ARVC Boxers, 9 healthy Boxers, 10 Doberman Pinschers with dilated cardiomyopathy, 10 dogs with myxomatous mitral valve disease, and 7 healthy non-Boxer dogs) were assessed for antibody presence and concentration via Western blotting and densitometry. Anti-desmoglein-2 antibodies were detected in all dogs. Autoantibody expression did not differ between study groups and there was no correlation with age or body weight. In dogs with cardiac disease, there was weak correlation with left ventricular dilation (r = 0.423, p = 0.020) but not left atrial size (r = 0.160, p = 0.407). In ARVC Boxers there was strong correlation with the complexity of ventricular arrhythmias (r = 0.841, p = 0.007) but not total number of ectopic beats (r = 0.383, p = 0.313). Anti-desmoglein-2 antibodies were not disease specific in the studied population of dogs. Correlation with some measures of disease severity requires further study with larger populations.

Application of Size Exclusion Chromatography with Multi-Angle Light Scattering in the Analytical Development of a Preclinical Stage Gene Therapy Program

To provide safe recombinant adeno-associated viruses (rAAV) to patients, scalable manufacturing processes are required. However, these processes may introduce impurities that impact the performance and quality of the final drug product. Empty rAAV capsids are product-related impurities. Regulatory guidance requires that accurate analytical methods be implemented early in product development to measure the level of empty capsids. A process confirmation vector, produced from 200L production, was used to develop and optimize a size exclusion chromatography with UV and multi-angle light scattering (SEC-MALS) method. Vector produced from a 500L production was used to assess the full-to-empty ratio using the following analytical methods: sedimentation velocity analytical ultracentrifugation (SV-AUC), ddPCR with capsid ELISA, bulk absorbance at 260nm/280nm, cryogenic electron microscopy (cryo-EM), and SEC-MALS. This test article was used for a 30-day, non-Good Laboratory Practices (GLP) animal study that assessed biodistribution of the product (STRX-330). SEC-MALS outperformed the other methods and correlated well with SV-AUC values of full-to-empty particles. In addition, SEC-MALS agreed with ddPCR and ELISA measurements for Vector Genomes (VG)/mL and Capsid Particles (CP)/mL, respectively. SEC-MALS was linear, accurate, and precise while achieving chromatography quality control (QC) recommendations. Compared to other stability-indicating assays, SEC-MALS performed similarly to ddPCR, capsid ELISA, and infectivity assays in accelerated stress studies. In response to alkaline, but not acidic stress, SEC-MALS indicated distinct changes in the DNA content of the monomer AAV peak for STRX-330, which was supported by ddPCR data. Conversely, acidic treatment resulted in more aggregated vector, but didn't impact the DNA content. This work indicates that SEC-MALS is a valuable analytical tool in the analytical development and quality control testing of AAV. In addition, this work suggests SEC-MALS can provide fundamental understanding of AAV in response to environmental stress. This may impact steps of the manufacturing process to minimize conditions that reduce performance.

Type 2 Diabetes in Obesity: A Systems Biology Study on Serum and Adipose Tissue Proteomic Profiles

Obesity is associated with metabolic disorders such as insulin resistance and type 2 diabetes mellitus (T2DM), further increasing an already heightened cardiovascular risk. Here, amongst obese class III bariatric surgery patients, we have investigated the effect of T2DM in serum and in two, same patient, adipose tissue (AT) depots through proteomic profile expression analyses. Serum and AT samples from subcutaneous (SAT) and visceral (VAT) fat were collected during bariatric surgery. Bead-based targeted multiplex assay systems were used to simultaneously detect and quantify multiple targets in serum samples (targeted proteomics) and analyze changes in adipokine serum composition. AT samples were assessed through an untargeted proteomics approach. Through a systems biology analysis of the proteomic data, information on the affected biological pathways was acquired. In obese class III individuals, the presence of T2DM induced a significantly higher systemic release of ghrelin, GLP-1, glucagon, MMP3, BAFF, chitinase 3-like 1, TNF-R1 and TNF-R2, and a lower systemic release of IL-8. SAT and VAT proteomes belonging to the same patient showed significant differences in local protein content. While the proteins upregulated in VAT were indicative of metabolic dysregulation, SAT protein upregulation suggested adequate endocrine regulation. The presence of T2DM significantly affected VAT protein composition through the upregulation of dysregulating metabolic pathways, but SAT protein composition was not significantly modified. Our results show that T2DM induces metabolic dysregulation in obese individuals with changes in systemic marker levels and impairment of proteostasis in VAT but not in SAT.

Dilated cardiomyopathy and chronic cardiac inflammation: Pathogenesis, diagnosis and therapy

Dilated cardiomyopathy (DCM) is typically defined by left ventricular dilation and systolic dysfunction in the absence of a clear precipitant. Idiopathic disease is common; up to 50% of patients with DCM have no cause found despite imaging, genetic and biopsy assessments. Treatment remains focused on managing symptoms, reducing the risk of sudden cardiac death and ameliorating the structural and electrical complications of disease progression. In the absence of aetiology-specific treatments, the condition remains associated with a poor prognosis; mortality is approximately 40% at 10 years. The role of immune-mediated inflammatory injury in the development and progression of DCM was first proposed over 30 years ago. Despite the subsequent failures of three large clinical trials of immunosuppressive treatment (ATTACH, RENEWAL and the Myocarditis Treatment Trial), evidence for an abnormal adaptive immune response in DCM remains significant. In this review, we summarise and discuss available evidence supporting immune dysfunction in DCM, with a specific focus on cellular immunity. We also highlight current clinical and experimental treatments. We propose that the success of future immunosuppressive treatment trials in DCM will be dependent on the deep immunophenotyping of patients, to identify those with active inflammation and/or an abnormal immune response who are most likely to respond to therapy.

Modern genomic techniques in the identification of genetic causes of cardiomyopathy

Over the past three decades numerous disease-causing genes have been linked to the pathogenesis of heritable cardiomyopathies, but many causal genes are yet to be identified. Next-generation sequencing (NGS) platforms have revolutionised clinical testing capacity in familial cardiomyopathy. In this review, we summarise how NGS technologies have advanced our understanding of genetic non-syndromic cardiomyopathy over the last decade. First, 26 putative new disease-causing genes have been identified to date, mostly from whole-exome sequencing, and some of which (FLNC, MTO1, HCN4) have had a considerable clinical impact and are now included in routine diagnostic gene panels. Second, we consider challenges in variant interpretation and the importance of large-scale NGS population control cohorts for this purpose. Third, an emerging role of common variation in some forms of genetic cardiomyopathy is being elucidated through recent studies which have illustrated an additive effect of numerous polymorphic loci on cardiac parameters; this may explain phenotypic variability and low rates of genetic diagnosis from sequencing studies. Finally, we discuss the clinical utility of genetic testing in cardiomyopathy in Western settings, where NGS panel testing of core disease genes is currently recommended with possible implications for patient management. Given the findings of recent studies, whole-exome or whole-genome sequencing should be considered in patients of non-European ancestry with clearly familial disease, or severe paediatric disease, when no result is obtained on panel sequencing. The clinical utility of polygenic risk assessment needs to be investigated further in patients with unexplained dilated cardiomyopathy and hypertrophic cardiomyopathy in whom a pathogenic variant is not identified.

"Orphan" Connexin43 in Plakophilin-2 Deficient Hearts Revealed by Volume Electron Microscopy

Previous studies revealed an abundance of functional Connexin43 (Cx43) hemichannels consequent to loss of plakophilin-2 (PKP2) expression in adult murine hearts. The increased Cx43-mediated membrane permeability is likely responsible for excess entry of calcium into the cells, leading to an arrhythmogenic/cardiomyopathic phenotype. The latter has translational implications to the molecular mechanisms of inheritable arrhythmogenic right ventricular cardiomyopathy (ARVC). Despite functional evidence, visualization of these "orphan" (i.e., non-paired in a gap junction configuration) Cx43 hemichannels remains lacking. Immuno-electron microscopy (IEM) remains an extremely powerful tool to localize, with nanometric resolution, a protein within its native structural landscape. Yet, challenges for IEM are to preserve the antigenicity of the molecular target and to provide access for antibodies to reach their target, while maintaining the cellular/tissue ultrastructure. Fixation is important for maintaining cell structure, but strong fixation and vigorous dehydration (as it is routine for EM) can alter protein structure, thus impairing antigen-antibody binding. Here, we implemented a method to combine pre-embedding immunolabeling (pre-embedding) with serial block-face scanning electron microscopy (SBF-SEM). We utilized a murine model of cardiomyocyte-specific, Tamoxifen (TAM) activated knockout of PKP2. Adult hearts were harvested 14 days post-TAM, at this time hearts present a phenotype of concealed ARVC (i.e., an arrhythmogenic phenotype but no overt structural disease). Thick (200 µm) vibratome slices were immunolabelled for Cx43 and treated with nanogold or FluoroNanogold, coupled with a silver enhancement. Left or right ventricular free walls were dissected and three-dimensional (3D) localization of Cx43 in cardiac muscle was performed using SBF-SEM. Reconstructed images allowed us to visualize the entire length of gap junction plaques, seen as two parallel, closely packed strings of Cx43-immunoreactive beads at the intercalated disc. In contrast, in PKP2-deficient hearts we observed bulging of the intercellular space, and entire areas where only one of the two strings could be observed, indicating the presence of orphan Cx43. We conclude that pre-embedding and SBF-SEM allowed visualization of cardiac Cx43 plaques in their native environment, providing for the first time a visual complement of functional data indicating the presence of orphan Cx43 hemichannels resulting from loss of desmosomal integrity in the heart.

The microtubule cytoskeleton in cardiac mechanics and heart failure

The microtubule network of cardiac muscle cells has unique architectural and biophysical features to accommodate the demands of the working heart. Advances in live-cell imaging and in deciphering the 'tubulin code' have shone new light on this cytoskeletal network and its role in heart failure. Microtubule-based transport orchestrates the growth and maintenance of the contractile apparatus through spatiotemporal control of translation, while also organizing the specialized membrane systems required for excitation-contraction coupling. To withstand the high mechanical loads of the working heart, microtubules are post-translationally modified and physically reinforced. In response to stress to the myocardium, the microtubule network remodels, typically through densification, post-translational modification and stabilization. Under these conditions, physically reinforced microtubules resist the motion of the cardiomyocyte and increase myocardial stiffness. Accordingly, modified microtubules have emerged as a therapeutic target for reducing stiffness in heart failure. In this Review, we discuss the latest evidence on the contribution of microtubules to cardiac mechanics, the drivers of microtubule network remodelling in cardiac pathologies and the therapeutic potential of targeting cardiac microtubules in acquired heart diseases.

Arrhythmogenic right ventricular cardiomyopathy presenting as heart failure in a child

Arrhythmogenic right ventricular cardiomyopathy is an uncommon diagnosis in the paediatric population, most commonly presenting with arrhythmia. We report an 11-year-old male presenting with right heart failure due to biventricular systolic dysfunction found to have arrhythmogenic right ventricular cardiomyopathy with de novo Desmin and MYH7 mutations.

Decreased Expression of Plakophilin-2 and αT-Catenin in Arrhythmogenic Right Ventricular Cardiomyopathy: Potential Markers for Diagnosis

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a hereditary disease of the heart muscle. Clinical challenges remain, however, in identifying patients with ARVC in the early or concealed stages with subtle clinical manifestations. Therefore, we wanted to identify potential targets by immunohistochemical (IHC) analysis in comparison with controls. Pathogenic mutations were identified in 11 of 37 autopsied patients with ARVC. As observed from IHC analysis of the RV, expression of αT-catenin and plakophilin-2 is significantly decreased in autopsied patients with ARVC as compared to controls, and the decreased expression is consistent in patients with and without pathogenic mutations. Furthermore, ARVC specimens demonstrated a reduced localization of αT-catenin, desmocollin-2, desmoglein-2, desmoplakin, and plakophilin-2 on intercalated discs. These findings have been validated by comparing RV specimens obtained via endomyocardial biopsy between patients with ARVC and those without. The pathogenic mutation was present in 3 of 5 clinical patients with ARVC. In HL-1 myocytes, siRNA was used to knockdown CTNNA3, and western blotting analysis demonstrated that the decline in αT-catenin expression was accompanied by a significant decline in the expression of plakophilin-2. The aforementioned effect was directed towards protein degradation rather than mRNA stability. Plakophilin-2 expression decreases concurrently with the decline in CTNNA3 expression. Therefore, the expression of αT-catenin and plakophilin-2 could be potential surrogates for the diagnosis of ARVC.

Genetic Evaluation of Late-Onset Hypertrophic Cardiomyopathy: An Autobiographical Case Report

Cardiomyopathy, also known as a pathology with a cardiovascular cause, can be further differentiated into multiple categories including genetic. Strong correlations between genetic mutations in sarcomeric proteins and presentation of cardiomyopathies have been made. This case report describes the clinical diagnosis of my late-onset hypertrophic cardiomyopathy, which was brought upon by symptoms of chest pain and palpitations that started approximately two years ago and had mostly gone unnoticed during this period. As a geneticist, I decided to undergo genetic test upon diagnosis. These tests found a heterozygous variant of uncertain significance (VUS) in the ALPK3 gene, c.399dup (p.Gly134ArgfsTer30), and a heterozygous c.7552G>A (p.Val2518Ile) VUS in the desmoplakin (DSP) gene. This autobiographical case report hopes to shed light on the importance of genetic screening in the search for the etiology of clinical symptoms.

Arrhythmogenic right ventricular cardiomyopathy in Bulldogs: Evaluation of clinical and histopathologic features, progression, and outcome in 71 dogs (2004-2016)

OBJECTIVES

This study aimed to characterize the clinical and histopathological features of arrhythmogenic right ventricular cardiomyopathy (ARVC) in English Bulldogs, American Bulldogs, and Bulldog-type mixed breed dogs and assess affected Bulldogs for a striatin gene mutation previously reported in Boxers with ARVC.

ANIMALS

Seventy-one Bulldogs fit the inclusion criteria. Genetic analysis was performed on five dogs. Cardiac post-mortem evaluations were performed on two dogs.

METHODS

Medical records from a single veterinary cardiology group (CVCA) were retrospectively evaluated. Tissue and blood samples were submitted for histopathological analysis and genetic testing in select patients.

RESULTS

Presenting complaints included syncope (38%), arrhythmia (81.7%), or murmur (34.2%) documented on examination. On presentation, congestive heart failure (CHF) was diagnosed in 22 (31%) dogs, and 58 (81.7%) had ventricular arrhythmias. On bivariable analyses, the two-dimensional (2D) left atrial-to-aortic root ratio (LA:Ao) was the only prognostic variable significantly associated with survival time. Dogs with 2D LA:Ao below the mean (1.41) had longer median survival to all-cause mortality (12 months; 95% confidence interval [CI] 6.0-15.0 months) than those with 2D LA:Ao above the mean (four months; 95% CI 2.0-6.0 months; p=0.0384). Most dogs (54%) died from cardiac disease, with 42.1% experiencing sudden death. The median time from diagnosis to cardiac death was four months.

CONCLUSIONS

Arrhythmogenic right ventricular cardiomyopathy affects Bulldogs with both arrhythmogenic and dilated-type phenotypes. Despite variable arrhythmia severity and predominantly right-sided involvement in many dogs, an increase in left atrial size was the only significant predictor of mortality in this sample of dogs.

A Novel Diagnostic Score Integrating Atrial Dimensions to Differentiate between the Athlete's Heart and Arrhythmogenic Right Ventricular Cardiomyopathy

Objective: The 2010 Task Force Criteria (TFC) have not been tested to differentiate ARVC from the athlete’s heart. Moreover, some criteria are not available (myocardial biopsy, genetic testing, morphology of ventricular tachycardia) or subject to interobserver variability (right ventricular regional wall motion abnormalities) in clinical practice. We hypothesized that atrial dimensions are useful and robust to differentiate between both entities and proposed a new diagnostic score based upon readily available parameters including echocardiographic atrial dimensions. Methods: In this observational study, 21 patients with definite ARVC were matched for age, gender and body mass index to 42 athletes. Based on ROC analysis, the following parameters were included in the score: indexed right/left atrial volumes ratio (RAVI/LAVI ratio), NT-proBNP, RVOT measurements (PLAX and PSAX BSA-corrected), tricuspid annular motion (TAM), precordial TWI and depolarization abnormalities according to TFC. Results: ARVC patients had a higher RAVI/LAVI ratio (1.76 ± 1.5 vs. 0.87 ± 0.2, p < 0.001), lower right ventricular function (fac: 29 ± 10.1 vs. 42.2 ± 5%, p < 0.001; TAM: 19.8 ± 5.4 vs. 23.8 ± 3.8 mm, p = 0.001) and higher serum NT-proBNP levels (345 ± 612 vs. 48 ± 57 ng/L, p < 0.001). Our score showed a good performance, which is comparable to the 2010 TFC using those parameters, which are available in routine clinical practice (AUC93%, p < 0.001 (95%CI 0.874–0.995) vs. AUC97%, p < 0.001 (95%CI 0.93–1.00). A score of 6/12 points yielded a specificity of 91% and an improved sensitivity of 67% for ARVC diagnosis as compared to a sensitivity of 41% for the abovementioned readily available 2010 TFC. Conclusions: ARVC patients present with significantly larger RA compared to athletes, resulting in a greater RAVI/LAVI ratio. Our novel diagnostic score includes readily available clinical parameters and has a high diagnostic accuracy to differentiate between ARVC and the athlete’s heart.

Arrhythmogenic right ventricular cardiomyopathy in dogs

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited myocardial disease seen in dogs, cats, and humans. A common entity in Boxers and the related English bulldog, the disease is characterized by fatty or fibrofatty replacement of the myocardium, ventricular arrhythmias, and the potential for syncope or sudden death. In some individuals, concomitant left ventricular involvement results in systolic dysfunction and a progression to congestive heart failure. The clinical and pathological characteristics of ARVC share many similarities in dogs and humans, and Boxers serve as an important spontaneous model of the disease. Although multiple mechanisms have been implicated in the pathogenesis of ARVC, the disease is ultimately considered to be a disorder of the desmosome. Multiple causal genetic mutations have been identified in people, and over 50% of affected humans have an identifiable mutation in desmosomal proteins. To date, only a single genetic mutation has been associated with ARVC in Boxer dogs. Other as-yet-undiscovered genetic mutations and epigenetic modifiers of the disease are likely. Treatment of ARVC in dogs is focused on controlling ventricular arrhythmias and associated clinical signs. This article will review the pathophysiology, clinical diagnosis, treatment, and prognosis of ARVC in the dog.

Dilated cardiomyopathy: a new insight into the rare but common cause of heart failure

Heart failure is a global health burden responsible for high morbidity and mortality with a prevalence of greater than 60 million individuals worldwide. One of the major causes of heart failure is dilated cardiomyopathy (DCM), characterized by associated systolic dysfunction. During the last few decades, there have been remarkable advances in our understanding about the genetics of dilated cardiomyopathy. The genetic causes were initially thought to be associated with mutations in genes encoding proteins that are localized to cytoskeleton and sarcomere only; however, with the advancement in mechanistic understanding, the roles of ion channels, Z-disc, mitochondria, nuclear proteins, cardiac transcription factors (e.g., NKX-2.5, TBX20, GATA4), and the factors involved in calcium homeostasis have also been identified and found to be implicated in both familial and sporadic DCM cases. During past few years, next-generation sequencing (NGS) has been established as a diagnostic tool for genetic analysis and it has added significantly to the existing candidate gene list for DCM. The animal models have also provided novel insights to develop a better treatment strategy based on phenotype-genotype correlation, epigenetic and phenomic profiling. Most of the DCM biomarkers that are used in routine genetic and clinical testing are structural proteins, but during the last few years, the role of mi-RNA has also emerged as a biomarker due to their accessibility through noninvasive methods. Our increasing genetic knowledge can improve the clinical management of DCM by bringing clinicians and geneticists on one platform, thereby influencing the individualized clinical decision making and leading to precision medicine.

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.

Sudden cardiac death: A comparative review of humans, dogs and cats

Sudden death is one of the most common causes of death in humans in Western countries. Approximately 85% of these cases are of cardiac origin. In dogs and cats, sudden cardiac death (SCD) also commonly occurs, but fewer pathophysiological and prevalence data are available. Both structural, primarily 'electrical' and ischemic heart diseases are known to cause SCD, many of which share similar underlying arrhythmogenic mechanisms between humans and companion animals. As for underlying genetics, numerous mutations on multiple loci have been related to SCD in humans, but only a few mutations associated with dilated cardiomyopathy and SCD have been identified in dogs, e.g. in the phospholamban and titin genes. Information published from human medicine can therefore inform future veterinary studies, but also dogs and cats could act as spontaneous models of SCD in humans. Further research in both fields is therefore warranted to better understand the pathophysiology, genetics, and prevention of SCD.

Sudden Cardiac Death-A New Insight Into Potentially Fatal Genetic Markers

Sudden cardiac death (SCD) is an unexpected and dramatic event. It draws special attention especially in young, seemingly healthy athletes. Our scientific paper is based on the death of a young, 23-year-old professional footballer, who died on the football field after a two-year history of cardiac symptoms. In this study we analyzed clinical, ECG and laboratory data, as well as results of genetic testing analysis in family members. To elucidate potential genetic etiology of SCD in this family, our analysis included 294 genes related to various cardiac conditions.

The Time Has Come to Explore Plasma Biomarkers in Genetic Cardiomyopathies

For patients with hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) or arrhythmogenic cardiomyopathy (ACM), screening for pathogenic variants has become standard clinical practice. Genetic cascade screening also allows the identification of relatives that carry the same mutation as the proband, but disease onset and severity in mutation carriers often remains uncertain. Early detection of disease onset may allow timely treatment before irreversible changes are present. Although plasma biomarkers may aid in the prediction of disease onset, monitoring relies predominantly on identifying early clinical symptoms, on imaging techniques like echocardiography (Echo) and cardiac magnetic resonance imaging (CMR), and on (ambulatory) electrocardiography (electrocardiograms (ECGs)). In contrast to most other cardiac diseases, which are explained by a combination of risk factors and comorbidities, genetic cardiomyopathies have a clear primary genetically defined cardiac background. Cardiomyopathy cohorts could therefore have excellent value in biomarker studies and in distinguishing biomarkers related to the primary cardiac disease from those related to extracardiac, secondary organ dysfunction. Despite this advantage, biomarker investigations in cardiomyopathies are still limited, most likely due to the limited number of carriers in the past. Here, we discuss not only the potential use of established plasma biomarkers, including natriuretic peptides and troponins, but also the use of novel biomarkers, such as cardiac autoantibodies in genetic cardiomyopathy, and discuss how we can gauge biomarker studies in cardiomyopathy cohorts for heart failure at large.

Sex Differences in Right Ventricular Dysfunction: Insights From the Bench to Bedside

There are inherent distinctions in right ventricular (RV) performance based on sex as females have better RV function than males. These differences are magnified and have very important prognostic implications in two RV-centric diseases, pulmonary hypertension (PH), and arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). In both PH and ARVC/D, RV dysfunction results in poor patient outcomes. However, there are no currently approved therapies specifically targeting the failing RV, an important unmet need for these two life-threatening disorders. In this review, we highlight human data demonstrating divergent RV phenotypes in healthy, PH, and ARVC/D patients based on sex. Furthermore, we discuss the links between estrogen (the female predominant sex hormone), testosterone (the male predominant sex hormone), and dehydroepiandrosterone (a precursor hormone for multiple sex hormones in males and females) and RV function in both disorders. To provide potential mechanistic insights into sex differences in RV function, we review data that investigate how sex hormones combat or contribute to pathophysiological changes in the RV. Finally, we highlight the ongoing clinical trials in pulmonary arterial hypertension targeting estrogen and dehydroepiandrosterone signaling. Hopefully, a greater understanding of the factors that promote superior RV function in females will lead to novel therapeutic approaches to combat RV dysfunction in PH and ARVC/D.

Epigenetic profiling of Italian patients identified methylation sites associated with hereditary transthyretin amyloidosis

Hereditary transthyretin (TTR) amyloidosis (hATTR) is a rare life-threatening disorder caused by amyloidogenic coding mutations located in TTR gene. To understand the high phenotypic variability observed among carriers of TTR disease-causing mutations, we conducted an epigenome-wide association study (EWAS) assessing more than 700,000 methylation sites and testing epigenetic difference of TTR coding mutation carriers vs. non-carriers. We observed a significant methylation change at cg09097335 site located in Beta-secretase 2 (BACE2) gene (standardized regression coefficient = -0.60, p = 6.26 × 10-8). This gene is involved in a protein interaction network enriched for biological processes and molecular pathways related to amyloid-beta metabolism (Gene Ontology: 0050435, q = 0.007), amyloid fiber formation (Reactome HSA-977225, q = 0.008), and Alzheimer's disease (KEGG hsa05010, q = 2.2 × 10-4). Additionally, TTR and BACE2 share APP (amyloid-beta precursor protein) as a validated protein interactor. Within TTR gene region, we observed that Val30Met disrupts a methylation site, cg13139646, causing a drastic hypomethylation in carriers of this amyloidogenic mutation (standardized regression coefficient = -2.18, p = 3.34 × 10-11). Cg13139646 showed co-methylation with cg19203115 (Pearson's r2 = 0.32), which showed significant epigenetic differences between symptomatic and asymptomatic carriers of amyloidogenic mutations (standardized regression coefficient = -0.56, p = 8.6 × 10-4). In conclusion, we provide novel insights related to the molecular mechanisms involved in the complex heterogeneity of hATTR, highlighting the role of epigenetic regulation in this rare disorder.

Cardiac magnetic resonance in arrhythmogenic cardiomyopathies

Over the past few years, the approach to the 'arrhythmic patient' has profoundly changed. An early clinical presentation of arrhythmia is often accompanied by non-specific symptoms and followed by inconclusive electrocardiographic findings. In this scenario, cardiac magnetic resonance (CMR) has been established as a clinical tool of fundamental importance for a correct prognostic stratification of the arrhythmic patient. This technique provides a high-spatial-resolution tomographic evaluation of the heart, which allows studying accurately the ventricular volumes, identifying even segmental kinetic anomalies and properly detecting diffuse or focal tissue alterations through an excellent tissue characterization, while depicting different patterns of fibrosis distribution, myocardial edema or fatty substitution. Through these capabilities, CMR has a pivotal role for the adequate management of the arrhythmic patient, allowing the identification of those phenotypic manifestations characteristic of structural heart diseases. Therefore, CMR provides valuable information to reclassify the patient within the wide spectrum of potentially arrhythmogenic heart diseases, the definition of which remains the major determinants for both an adequate treatment and a poor prognosis. The purpose of this review study was to focus on the role of CMR in the evaluation of the main cardiac clinical entities associated with arrhythmogenic phenomena and to present a brief debate on the main pathophysiological mechanisms involved in the arrhythmogenesis process.

Missense variants in the spectrin repeat domain of DSP are associated with arrhythmogenic cardiomyopathy: A family report and systematic review

Rare loss of function variants in DSP, which codes for the desmosomal protein desmoplakin, have been implicated in dilated and arrhythmogenic right ventricular cardiomyopathies. We present a family with arrhythmogenic cardiomyopathy associated with a novel missense variant in DSP (NM_004415.4): c.877G>A, p.(Glu293Lys). The phenotype is characterized by predominant involvement of the left ventricle with systolic dysfunction, fibrosis, and life-threatening arrhythmias. We performed a systematic review of literature collecting all cardiomyopathy cases with rare missense variants in DSP. We demonstrate that the distribution of missense variants across the protein domains in cardiomyopathy cases differs from that in gnomAD (p = .04), with a case enrichment of rare missense variants in the spectrin repeat domain (36/78 [46%] in cases vs. 449/1495 [30%] in gnomAD; p = .004). Our findings highlight the predominance of cardiac arrhythmia and left ventricular involvement in desmoplakin cardiomyopathy and pinpoint to a potential mutation hotspot in DSP thereby facilitating missense variant interpretation in the diagnostic setting.

The importance of chain context in assessing small nucleotide variants in titin: in silico case study of the I10-I11 tandem and its arrhythmic right ventricular cardiomyopathy linked position T2580

Non-synonymous small nucleotide variations (nsSNVs) in the giant muscle protein, titin, have key roles in the development of several myopathologies. Although there is considerable motive to screen at-risk individuals for nsSNVs, to identify patients in early disease stages while therapeutic intervention is still possible, the clinical significance of most titin variations remains unclear. Therefore, there is a growing need to establish methods to classify nsSNVs in a simple, economic and rapid manner. Due to its strong correlation to arrhythmogenic right ventricular cardiomyopathy (ARVC), one particular mutation in titin-T2580I, located in the I10 immunoglobulin domain-has received considerable attention. Here, we use the I10-I11 tandem as a case study to explore the possible benefits of considering the titin chain context-i.e. domain interfaces-in the assessment of titin nsSNVs. Specifically, we investigate which exchanges mimic the conformational molecular phenotype of the T2580I mutation at the I10-I11 domain interface. Then, we computed a residue stability landscape for domains alone and in tandem to define a Domain Interface Score (DIS) which identifies several hotspot residues. Our findings suggest that the T2580 position is highly sensitive to exchange and that any variant found in this position should be considered with care. Furthermore, we conclude that the consideration of the higher order structure of the titin chain is important to gain accurate insights into the vulnerability of positions in linker regions and that titin nsSNV prediction benefits from a contextual analysis. Communicated by Ramaswamy H. Sarma.

The desmosome as a model for lipid raft driven membrane domain organization

Desmosomes are cadherin-based adhesion structures that mechanically couple the intermediate filament cytoskeleton of adjacent cells to confer mechanical stress resistance to tissues. We have recently described desmosomes as mesoscale lipid raft membrane domains that depend on raft dynamics for assembly, function, and disassembly. Lipid raft microdomains are regions of the plasma membrane enriched in sphingolipids and cholesterol. These domains participate in membrane domain heterogeneity, signaling and membrane trafficking. Cellular structures known to be dependent on raft dynamics include the post-synaptic density in neurons, the immunological synapse, and intercellular junctions, including desmosomes. In this review, we discuss the current state of the desmosome field and put forward new hypotheses for the role of lipid rafts in desmosome adhesion, signaling and epidermal homeostasis. Furthermore, we propose that differential lipid raft affinity of intercellular junction proteins is a central driving force in the organization of the epithelial apical junctional complex.

Plakophilin-2 Haploinsufficiency Causes Calcium Handling Deficits and Modulates the Cardiac Response Towards Stress

Human variants in plakophilin-2 (PKP2) associate with most cases of familial arrhythmogenic cardiomyopathy (ACM). Recent studies show that PKP2 not only maintains intercellular coupling, but also regulates transcription of genes involved in Ca2+ cycling and cardiac rhythm. ACM penetrance is low and it remains uncertain, which genetic and environmental modifiers are crucial for developing the cardiomyopathy. In this study, heterozygous PKP2 knock-out mice (PKP2-Hz) were used to investigate the influence of exercise, pressure overload, and inflammation on a PKP2-related disease progression. In PKP2-Hz mice, protein levels of Ca2+-handling proteins were reduced compared to wildtype (WT). PKP2-Hz hearts exposed to voluntary exercise training showed right ventricular lateral connexin43 expression, right ventricular conduction slowing, and a higher susceptibility towards arrhythmias. Pressure overload increased levels of fibrosis in PKP2-Hz hearts, without affecting the susceptibility towards arrhythmias. Experimental autoimmune myocarditis caused more severe subepicardial fibrosis, cell death, and inflammatory infiltrates in PKP2-Hz hearts than in WT. To conclude, PKP2 haploinsufficiency in the murine heart modulates the cardiac response to environmental modifiers via different mechanisms. Exercise upon PKP2 deficiency induces a pro-arrhythmic cardiac remodeling, likely based on impaired Ca2+ cycling and electrical conduction, versus structural remodeling. Pathophysiological stimuli mainly exaggerate the fibrotic and inflammatory response.

Calcium as a Key Player in Arrhythmogenic Cardiomyopathy: Adhesion Disorder or Intracellular Alteration?

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart disease characterized by sudden death in young people and featured by fibro-adipose myocardium replacement, malignant arrhythmias, and heart failure. To date, no etiological therapies are available. Mutations in desmosomal genes cause abnormal mechanical coupling, trigger pro-apoptotic signaling pathways, and induce fibro-adipose replacement. Here, we discuss the hypothesis that the ACM causative mechanism involves a defect in the expression and/or activity of the cardiac Ca²⁺ handling machinery, focusing on the available data supporting this hypothesis. The Ca²⁺ toolkit is heavily remodeled in cardiomyocytes derived from a mouse model of ACM defective of the desmosomal protein plakophilin-2. Furthermore, ACM-related mutations were found in genes encoding for proteins involved in excitation‒contraction coupling, e.g., type 2 ryanodine receptor and phospholamban. As a consequence, the sarcoplasmic reticulum becomes more eager to release Ca²⁺, thereby inducing delayed afterdepolarizations and impairing cardiac contractility. These data are supported by preliminary observations from patient induced pluripotent stem-cell-derived cardiomyocytes. Assessing the involvement of Ca²⁺ signaling in the pathogenesis of ACM could be beneficial in the treatment of this life-threatening disease.

Autosomal-dominant biventricular arrhythmogenic cardiomyopathy in a large family with a novel in-frame DSP nonsense mutation

A novel autosomal-dominant in-frame deletion resulting in a nonsense mutation in the desmoplakin (DSP) gene was identified in association with biventricular arrhythmogenic cardiomyopathy across three generations of a large Caucasian family. Mutations that disrupt the function and structure of desmosomal proteins, including desmoplakin, have been extensively linked to familial arrhythmogenic right ventricular cardiomyopathy (ARVC). Analysis of data from 51 individuals demonstrated the previously undescribed variant p.Cys81Stop (c.243_251delCTTGATGCG) in DSP segregates with a pathogenic phenotype exhibiting variable penetrance and expressivity. The mutation's pathogenicity was first established due to two sudden cardiac deaths (SCDs), each with a biventricular cardiomyopathy identified on autopsy. Of the individuals who underwent genetic screening, 27 of 51 were heterozygous for the DSP mutation (29 total with two obligate carriers). Six of these were subsequently diagnosed with arrhythmogenic cardiomyopathy. An additional nine family members have a conduction disorder and/or myocardial structural changes characteristic of an evolving condition. Previous reports from both human patients and mouse studies proposed DSP mutations with a premature stop codon impart mild to no clinical symptoms. Loss of expression from the abnormal allele via the nonsense-mediated mRNA decay pathway has been implicated to explain these findings. We identified an autosomal-dominant DSP nonsense mutation in a large family that led to SCD and phenotypic expression of arrhythmogenic cardiomyopathy involving both ventricles. This evidence demonstrates the pathogenic significance of this type of desmosomal mutation and provides insight into potential clinical manifestations.

A case of desmoplakin mutation and delayed arrhythmogenic right ventricular cardiomyopathy/dysplasia after atrial septal defect closure

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a slow-developing cardiomyopathy characterized by ventricular arrhythmias and fibrofatty replacement of the right ventricular (RV) myocardium. Its clinical diagnosis is challenging because of its variable clinical presentation and low genetic penetrance. We describe the case of a 67-year-old man who was diagnosed as having ARVC/D with a desmoplakin mutation that appeared after occlusion of an atrial septal defect (ASD). He underwent patch closure surgery for ASD at the age of 54 years. Four years later, he underwent catheter ablation for multifocal atrial tachycardias. Because of pre-syncope and inducible sustained monomorphic ventricular tachycardia, an implantable cardioverter defibrillator was implanted. When he was admitted for worsening heart failure at the age of 61 years, the desmoplakin mutation was detected with progressive left ventricular (LV) dysfunction. Subsequently, he was diagnosed as having ARVC/D with RV dysfunction. At cardiac autopsy, characteristics of ARVC/D, including dilatation, fibrofatty changes in the right ventricle, and diffuse fibrosis in the left ventricle were detected. Along with the effect of RV dysfunction caused by ASD, the progression of LV dysfunction after ASD closure was also possibly caused by the disease progression of ARVC/D. Physicians should carefully assess the various states of ARVC/D. <Learning objective: Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a cardiomyopathy characterized by arrhythmias, fibrofatty replacement of the right ventricular (RV) myocardium, and slow progression to more diffuse ventricular dysfunction. This case involved an atrial septal defect (ASD) that promoted the RV failure and was complicated with delayed progression of ARVC/D after ASD closure. The present case suggests that physicians need to carefully assess the various states of ARVC/D.>.

Advanced Evolution of Pathogenesis Concepts in Cardiomyopathies

Cardiomyopathy is a group of heterogeneous cardiac diseases that impair systolic and diastolic function, and can induce chronic heart failure and sudden cardiac death. Cardiomyopathy is prevalent in the general population, with high morbidity and mortality rates, and contributes to nearly 20% of sudden cardiac deaths in younger individuals. Genetic mutations associated with cardiomyopathy play a key role in disease formation, especially the mutation of sarcomere encoding genes and ATP kinase genes, such as titin, lamin A/C, myosin heavy chain 7, and troponin T1. Pathogenesis of cardiomyopathy occurs by multiple complex steps involving several pathways, including the Ras-Raf-mitogen-activated protein kinase-extracellular signal-activated kinase pathway, G-protein signaling, mechanotransduction pathway, and protein kinase B/phosphoinositide 3-kinase signaling. Excess biomechanical stress induces apoptosis signaling in cardiomyocytes, leading to cell loss, which can induce myocardial fibrosis and remodeling. The clinical features and pathophysiology of cardiomyopathy are discussed. Although several basic and clinical studies have investigated the mechanism of cardiomyopathy, the detailed pathophysiology remains unclear. This review summarizes current concepts and focuses on the molecular mechanisms of cardiomyopathy, especially in the signaling from mutation to clinical phenotype, with the aim of informing the development of therapeutic interventions.

Characteristics of recurrent ventricular tachyarrhythmia after catheter ablation in patients with arrhythmogenic right ventricular cardiomyopathy

BACKGROUND

The reason for recurrence of ventricular arrhythmia (VA) after catheter ablation in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) is not clear.

METHODS

In this study, 91 ARVC patients (age, 47 ± 13 years; 47 men) who underwent catheter ablation for drug-refractory ventricular arrhythmia (VA) were enrolled. The patients were categorized into single or multiple procedures (n = 28). The baseline characteristics and electrophysiological features of the patients were examined to elucidate the reason of the VA recurrences.

RESULTS

A total of 186 VAs were induced during the index procedure and 176 (94.6%) were eliminated. Successful, partially successful, and failed ablations were achieved in 89.0%, 8.8%, and 2.2% of the patients, respectively. During a mean follow-up period of 32 ± 26 months, 35 patients had VA recurrences. Forty-two repeat procedures were performed for 81 induced VAs in 28 patients. Of the 42 repeat procedures, successful, partially successful, and failed ablations were achieved in 37, 4, and 1 of the procedures, respectively. Most of the recurrent VAs (70 [72.9%]) originated from the newly-developed circuits owing to the scar progression. The patients with repeat procedure had worsening right ventricular remodeling. The multivariate analysis revealed that history as endurance athlete significantly predicted the need of a repeat procedure in spite of the initially successful endocardial/epicardial ablation and negative inducibility (hazard ratio: 3.014, 95% confidence interval: 1.493-6.084, P = 0.002).

CONCLUSIONS

In spite of the initial complete VA elimination, history as an athlete was associated with scar progression, RV remodeling, and VA recurrences from the newly developed arrhythmogenic substrates/circuit in ARVC.

Four and a half LIM domain protein signaling and cardiomyopathy

Four and a half LIM domain (FHL) protein family members, FHL1 and FHL2, are multifunctional proteins that are enriched in cardiac muscle. Although they both localize within the cardiomyocyte sarcomere (titin N2B), they have been shown to have important yet unique functions within the context of cardiac hypertrophy and disease. Studies in FHL1-deficient mice have primarily uncovered mitogen-activated protein kinase (MAPK) scaffolding functions for FHL1 as part of a novel biomechanical stretch sensor within the cardiomyocyte sarcomere, which acts as a positive regulator of pressure overload-mediated cardiac hypertrophy. New data have highlighted a novel role for the serine/threonine protein phosphatase (PP5) as a deactivator of the FHL1-based biomechanical stretch sensor, which has implications in not only cardiac hypertrophy but also heart failure. In contrast, studies in FHL2-deficient mice have primarily uncovered an opposing role for FHL2 as a negative regulator of adrenergic-mediated signaling and cardiac hypertrophy, further suggesting unique functions targeted by FHL proteins in the "stressed" cardiomyocyte. In this review, we provide current knowledge of the role of FHL1 and FHL2 in cardiac muscle as it relates to their actions in cardiac hypertrophy and cardiomyopathy. A specific focus will be to dissect the pathways and protein-protein interactions that underlie FHLs' signaling role in cardiac hypertrophy as well as provide a comprehensive list of FHL mutations linked to cardiac disease, using evidence gained from genetic mouse models and human genetic studies.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) in clinical practice

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is an inherited myocardial disease characterized by fibro-fatty replacement of the right ventricular myocardium, and associated with paroxysmal ventricular arrhythmias and sudden cardiac death (SCD). It is currently the second most common cause of SCD after hypertrophic cardiomyopathy in young people <35 years of age, causing up to 20% of deaths in this patient population. This condition has a male preponderance and is more commonly found in individuals of Italian and Greek descent. To date, there is no single diagnostic test for ARVC/D and the diagnosis is made based on clinical, electrocardiographic, and radiological findings according to the Revised 2010 Task Force Criteria. In this review, we will discuss the mainstay treatment which includes pharmacotherapy, implantable cardioverter-defibrillator insertion for abortion of sudden cardiac death, and in the advanced stages of the disease cardiac transplantation.

Exploring digenic inheritance in arrhythmogenic cardiomyopathy

Background

Arrhythmogenic cardiomyopathy (ACM) is an inherited genetic disorder, characterized by the substitution of heart muscle with fibro-fatty tissue and severe ventricular arrhythmias, often leading to heart failure and sudden cardiac death. ACM is considered a monogenic disorder, but the low penetrance of mutations identified in patients suggests the involvement of additional genetic or environmental factors.

Methods

We used whole exome sequencing to investigate digenic inheritance in two ACM families where previous diagnostic tests have revealed a PKP2 mutation in all affected and some healthy individuals. In family members with PKP2 mutations we determined all genes that harbor variants in affected but not in healthy carriers or vice versa. We computationally prioritized the most likely candidates, focusing on known ACM genes and genes related to PKP2 through protein interactions, functional relationships, or shared biological processes.

Results

We identified four candidate genes in family 1, namely DAG1, DAB2IP, CTBP2 and TCF25, and eleven candidate genes in family 2. The most promising gene in the second family is TTN, a gene previously associated with ACM, in which the affected individual harbors two rare deleterious-predicted missense variants, one of which is located in the protein’s only serine kinase domain.

Conclusions

In this study we report genes that might act as digenic players in ACM pathogenesis, on the basis of co-segregation with PKP2 mutations. Validation in larger cohorts is still required to prove the utility of this model.

Electronic supplementary material

The online version of this article (10.1186/s12881-017-0503-7) contains supplementary material, which is available to authorized users.

Arrhythmogenic Cardiomyopathy: the Guilty Party in Adipogenesis

Arrhythmogenic cardiomyopathy (ACM) is a genetic cardiac condition characterized by the replacement of the ventricular myocardium with fibro-fatty tissue, by arrhythmias and sudden death. Adipogenesis in ACM is considered an aberrant remodeling following myocardial loss. Which cell type(s) is (are) responsible for the adipose replacement is still matter of debate. A systematic overview of the different cells that have been, over time, considered as main players in adipose replacement is provided. The comprehension of the cellular component giving rise to arrhythmogenic cardiomyopathy substrate defects may represent both an essential tool for mechanistic studies of disease pathogenesis and a novel possible therapeutic target.

Sudden cardiac death: focus on the genetics of channelopathies and cardiomyopathies

Sudden cardiac death (SCD) describes a natural and unexpected death from cardiac causes occurring within a short period of time (generally within 1 h of symptom onset) in the absence of any other potentially lethal condition. Most SCD-related diseases have a genetic basis; in particular congenital cardiac channelopathies and cardiomyopathies have been described as leading causes of SCD. Congenital cardiac channelopathies are primary electric disorders caused by mutations affecting genes encoding cardiac ion channels or associated proteins, whereas cardiomyopathies are related to mutations in genes encoding several categories of proteins, including those of sarcomeres, desmosomes, the cytoskeleton, and the nuclear envelope. The purpose of this review is to provide a general overview of the main genetic variants that have been linked to the major congenital cardiac channelopathies and cardiomyopathies. Functional alterations of the related proteins are also described.

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.

Molecular mechanisms in cardiomyopathy

Cardiomyopathies represent a heterogeneous group of diseases that negatively affect heart function. Primary cardiomyopathies specifically target the myocardium, and may arise from genetic [hypertrophic cardiomyopathy (HCM), arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D), mitochondrial cardiomyopathy] or genetic and acquired [dilated cardiomyopathy (DCM), restrictive cardiomyopathy (RCM)] etiology. Modern genomics has identified mutations that are common in these populations, while in vitro and in vivo experimentation with these mutations have provided invaluable insight into the molecular mechanisms native to these diseases. For example, increased myosin heavy chain (MHC) binding and ATP utilization lead to the hypercontractile sarcomere in HCM, while abnormal protein–protein interaction and impaired Ca2+ flux underlie the relaxed sarcomere of DCM. Furthermore, expanded access to genetic testing has facilitated identification of potential risk factors that appear through inheritance and manifest sometimes only in the advanced stages of the disease. In this review, we discuss the genetic and molecular abnormalities unique to and shared between these primary cardiomyopathies and discuss some of the important advances made using more traditional basic science experimentation.