Arrhythmogenic ventricular cardiomyopathy: A paradigm shift from right to biventricular disease

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

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

Basic and translational mechanisms in inflammatory arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a familial, nonischemic heart disease typically inherited via an autosomal dominant pattern (Nava et al., [1]; Wlodarska et al., [2]). Often affecting the young and athletes, early diagnosis of ACM can be complicated as incomplete penetrance with variable expressivity are common characteristics (Wlodarska et al., [2]; Corrado et al., [3]). That said, of the five desmosomal genes implicated in ACM, pathogenic variants in desmocollin-2 (DSC2) and desmoglein-2 (DSG2) have been discovered in both an autosomal-recessive and autosomal-dominant pattern (Wong et al., [4]; Qadri et al., [5]; Chen et al., [6]). Originally known as arrhythmogenic right ventricular dysplasia (ARVD), due to its RV prevalence and manifesting in the young, the disease was first described in 1736 by Giovanni Maria Lancisi in his book "De Motu Cordis et Aneurysmatibus" (Lancisi [7]). However, the first comprehensive clinical description and recognition of this dreadful disease was by Guy Fontaine and Frank Marcus in 1982 (Marcus et al., [8]). These two esteemed pathologists evaluated twenty-two (n = 22/24) young adult patients with recurrent ventricular tachycardia (VT) and RV dysplasia (Marcus et al., [8]). Initially, ARVD was thought to be the result of partial or complete congenital absence of ventricular myocardium during embryonic development (Nava et al., [9]). However, further research into the clinical and pathological manifestations revealed acquired progressive fibrofatty replacement of the myocardium (McKenna et al., [10]); and, in 1995, ARVD was classified as a primary cardiomyopathy by the World Health Organization (Richardson et al., [11]). Thus, now classifying ACM as a cardiomyopathy (i.e., ARVC) rather than a dysplasia (i.e., ARVD). Even more recently, ARVC has shifted from its recognition as a primarily RV disease (i.e., ARVC) to include left-dominant (i.e., ALVC) and biventricular subtypes (i.e., ACM) as well (Saguner et al., [12]), prompting the use of the more general term arrhythmogenic cardiomyopathy (ACM). This review aims to discuss pathogenesis, clinical and pathological phenotypes, basic and translational research on the role of inflammation, and clinical trials aimed to prevent disease onset and progression.

Management Strategies in Arrhythmogenic Cardiomyopathy across the Spectrum of Ventricular Involvement

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

Myocarditis as a trigger for the expression of biventricular arrhythmogenic cardiomyopathy in desmosomal gene mutation

Arrhythmogenic-cardiomyopathy (ACM) is an inherited heart disease with right, left, or biventricular (BVACM) involvement based on EKG, imaging, family history, and genetic testing. We present a 64-year-old woman with prior myocarditis and diagnosis of BVACM 29 years later. We propose myocarditis as a promoter of gene expression of plakophilin-2 mutation.

Progressive Reduction in Right Ventricular Contractile Function Due to Altered Actin Expression in an Aging Mouse Model of Arrhythmogenic Cardiomyopathy

BACKGROUND

Arrhythmogenic cardiomyopathy (ACM) is an inherited genetic disorder of desmosomal dysfunction, and plakophilin-2 (PKP2) has been reported to be the most common disease-causing gene when mutation-positive. In the early "concealed" phase, the ACM heart is at high risk of sudden cardiac death before cardiac remodeling occurs due to mistargeted ion channels and altered Ca²⁺ handling. However, the results of pathogenic PKP2 variants on myocyte contraction in ACM pathogenesis remain unknown.

METHODS

We studied the outcomes of a human truncating variant of PKP2 on myocyte contraction using a novel knock-in mouse model with insertion of thymidine in exon 5 of Pkp2, which mimics a familial case of ACM (PKP2-L404fsX5). We used serial echocardiography, electrocardiography, blood pressure measurements, histology, cardiomyocyte contraction, intracellular calcium measurements, and gene and protein expression studies.

RESULTS

Serial echocardiography of Pkp2 heterozygous (Pkp2-Het) mice revealed progressive failure of the right ventricle (RV) in animals older than three months of age. By contrast, left ventricular (LV) function remained normal. Electrocardiograms of six-month-old anesthetized Pkp2-Het mice showed normal baseline heart rates and QRS complexes. Cardiac responses to β-adrenergic agonist isoproterenol (2 mg.kg^-1) plus caffeine (120 mg.kg^-1) were also normal. However, adrenergic stimulation enhanced the susceptibility of Pkp2-Het hearts to tachyarrhythmia and sudden cardiac death. Histologic staining showed no significant fibrosis or adipocyte infiltration in the RVs and LVs of six- and twelve-month-old Pkp2-Het hearts. Contractility assessment of isolated myocytes demonstrated progressively reduced Pkp2-Het RV cardiomyocyte function consistent with RV failure measured by echocardiography. However, aging Pkp2-Het and control RV myocytes loaded with intracellular Ca²⁺ indicator Fura-2 showed comparable Ca²⁺ transients. Western blotting of Pkp2-RV homogenates revealed a 40% decrease in actin, while actin immunoprecipitation followed by a 2, 4-dinitrophenylhydrazine staining showed doubled oxidation level. This correlated with a 39% increase in troponin-I phosphorylation. In contrast, Pkp2-Het LV myocytes had normal contraction, actin expression and oxidation, and troponin-I phosphorylation. Finally, Western blotting of cardiac biopsies revealed actin expression was 40% decreased in RVs of end-stage ACM patients.

CONCLUSIONS

During the early "concealed" phase of ACM, reduced actin expression drives loss of RV myocyte contraction, contributing to progressive RV dysfunction.

Inflammation in the Pathogenesis of Arrhythmogenic Cardiomyopathy: Secondary Event or Active Driver?

Arrhythmogenic cardiomyopathy (ACM) is a rare inherited cardiac disease characterized by arrhythmia and progressive fibro-fatty replacement of the myocardium, which leads to heart failure and sudden cardiac death. Inflammation contributes to disease progression, and it is characterized by inflammatory cell infiltrates in the damaged myocardium and inflammatory mediators in the blood of ACM patients. However, the molecular basis of inflammatory process in ACM remains under investigated and it is unclear whether inflammation is a primary event leading to arrhythmia and myocardial damage or it is a secondary response triggered by cardiomyocyte death. Here, we provide an overview of the proposed players and triggers involved in inflammation in ACM, focusing on those studied using in vivo and in vitro models. Deepening current knowledge of inflammation-related mechanisms in ACM could help identifying novel therapeutic perspectives, such as anti-inflammatory therapy.

Autophagy and Endoplasmic Reticulum Stress during Onset and Progression of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is a heritable, potentially lethal disease without a causal therapy. AC is characterized by focal cardiomyocyte death followed by inflammation and progressive formation of connective tissue. The pathomechanisms leading to structural disease onset and progression, however, are not fully elucidated. Recent studies revealed that dysregulation of autophagy and endoplasmic/sarcoplasmic reticulum (ER/SR) stress plays an important role in cardiac pathophysiology. We therefore examined the temporal and spatial expression patterns of autophagy and ER/SR stress indicators in murine AC models by qRT-PCR, immunohistochemistry, in situ hybridization and electron microscopy. Cardiomyocytes overexpressing the autophagy markers LC3 and SQSTM1/p62 and containing prominent autophagic vacuoles were detected next to regions of inflammation and fibrosis during onset and chronic disease progression. mRNAs of the ER stress markers Chop and sXbp1 were elevated in both ventricles at disease onset. During chronic disease progression Chop mRNA was upregulated in right ventricles. In addition, reduced Ryr2 mRNA expression together with often drastically enlarged ER/SR cisternae further indicated SR dysfunction during this disease phase. Our observations support the hypothesis that locally altered autophagy and enhanced ER/SR stress play a role in AC pathogenesis both at the onset and during chronic progression.

MicroRNAs: From Junk RNA to Life Regulators and Their Role in Cardiovascular Disease

MicroRNAs (miRNAs) are single-stranded small non-coding RNA (18–25 nucleotides) that until a few years ago were considered junk RNA. In the last twenty years, they have acquired more importance thanks to the understanding of their influence on gene expression and their role as negative regulators at post-transcriptional level, influencing the stability of messenger RNA (mRNA). Approximately 5% of the genome encodes miRNAs which are responsible for regulating numerous signaling pathways, cellular processes and cell-to-cell communication. In the cardiovascular system, miRNAs control the functions of various cells, such as cardiomyocytes, endothelial cells, smooth muscle cells and fibroblasts, playing a role in physiological and pathological processes and seeming also related to variations in contractility and hereditary cardiomyopathies. They provide a new perspective on the pathophysiology of disorders such as hypertrophy, fibrosis, arrhythmia, inflammation and atherosclerosis. MiRNAs are differentially expressed in diseased tissue and can be released into the circulation and then detected. MiRNAs have become interesting for the development of new diagnostic and therapeutic tools for various diseases, including heart disease. In this review, the concept of miRNAs and their role in cardiomyopathies will be introduced, focusing on their potential as therapeutic and diagnostic targets (as biomarkers).

MicroRNAs in Hypertrophic, Arrhythmogenic and Dilated Cardiomyopathy

MicroRNAs (miRNAs) are a class of non-coding RNAs of about 20 nucleotides in length, involved in the regulation of many biochemical pathways in the human body. The level of miRNAs in tissues and circulation can be deregulated because of altered pathophysiological mechanisms; thus, they can be employed as biomarkers for different pathological conditions, such as cardiac diseases. This review summarizes published findings of these molecular biomarkers in the three most common structural cardiomyopathies: human dilated, arrhythmogenic and hypertrophic cardiomyopathy.

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

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

Altered Electrical, Biomolecular, and Immunologic Phenotypes in a Novel Patient-Derived Stem Cell Model of Desmoglein-2 Mutant ARVC

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a progressive heart condition which causes fibro-fatty myocardial scarring, ventricular arrhythmias, and sudden cardiac death. Most cases of ARVC can be linked to pathogenic mutations in the cardiac desmosome, but the pathophysiology is not well understood, particularly in early phases when arrhythmias can develop prior to structural changes. Here, we created a novel human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model of ARVC from a patient with a c.2358delA variant in desmoglein-2 (DSG2). These DSG2-mutant (DSG2^Mut) hiPSC-CMs were compared against two wildtype hiPSC-CM lines via immunostaining, RT-qPCR, Western blot, RNA-Seq, cytokine expression and optical mapping. Mutant cells expressed reduced DSG2 mRNA and had altered localization of desmoglein-2 protein alongside thinner, more disorganized myofibrils. No major changes in other desmosomal proteins were noted. There was increased pro-inflammatory cytokine expression that may be linked to canonical and non-canonical NFκB signaling. Action potentials in DSG2^Mut CMs were shorter with increased upstroke heterogeneity, while time-to-peak calcium and calcium decay rate were reduced. These were accompanied by changes in ion channel and calcium handling gene expression. Lastly, suppressing DSG2 in control lines via siRNA allowed partial recapitulation of electrical anomalies noted in DSG2^Mut cells. In conclusion, the aberrant cytoskeletal organization, cytokine expression, and electrophysiology found DSG2^Mut hiPSC-CMs could underlie early mechanisms of disease manifestation in ARVC patients.

Right ventricular dysplasia in the elderly: a case report from autopsy

Right ventricular dysplasia (RVD) is a rare disease of the heart that primarily affects the right ventricle. It is a clinical and pathological entity that presents classically with palpitations, syncope, or even sudden death. It presents rarely in the elderly. Where sudden death is the first and only presentation, an autopsy is required to make the diagnosis. However, the pathomorphological features of RVD can easily be overlooked or missed at autopsy. We report the case of a 68-year-old male with the past medical history of hypertension, gout and inflammatory bowel syndrome. He was admitted on account of difficulty in breathing, abdominal swelling and reduced urination. Physical examination revealed hypertension with cardiac murmurs, widespread crepitations, distended abdomen and lower limb oedema. Provisional diagnoses of acute-on-chronic kidney disease and congestive cardiac failure secondary to hypertensive heart disease, precipitated by probable gastrointestinal infection were made. While on admission, he had an episode of syncope. Electrocardiogram revealed bigeminy and bradycardic sinus rhythm with unifocal ventricular premature contraction. He died on the 8^th week of admission. Autopsy revealed an enlarged heart weighing 600gm; there was thinning of the apical aspect of the right ventricular wall with subtotal fibrofatty replacement. Microscopic examination revealed a transmural replacement of cardiac myocytes by fibroadipose tissue extending inwards, in the most parts, from the epicardium to the endocardial surface. Our aim is to increase the awareness of these pathomorphological features among anatomic/forensic pathologists.

Arrhythmogenic Right Ventricular Cardiomyopathy Presenting as Clinical Myocarditis in Women

Patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) classically initially present with ventricular arrhythmias or, less commonly, heart failure. Myocardial inflammation has been implicated in pathogenesis, but clinical myocarditis in ARVC is less described. We therefore studied clinical myocarditis as an initial ARVC presentation, and hypothesized that these patients have distinct clinical and genetic characteristics. Using the Johns Hopkins ARVC Registry, we identified 12 patients (all female, median age 20) referred between 2014 and 2019 diagnosed with myocarditis at presentation who were subsequently diagnosed with ARVC by Task Force Criteria. Majority presented with chest pain (n = 7, 58%) or ventricular arrhythmia (n = 3, 25%). All patients had troponin elevations and left ventricular (LV) function was reduced in 5 (42%). Magnetic resonance imaging demonstrated LV delayed gadolinium enhancement and/or pericardial enhancement in 10 (83%); only 3 (25%) patients had right ventricular abnormalities. Pathogenic genetic variants were identified in 11 (92%) patients: 10 desmoplakin (DSP) and 1 desmoglein-2 (DSG2). Thus, nearly 1/3 (10/32, 31%) of overall DSP ARVC patients were originally diagnosed with myocarditis. Patients were diagnosed with ARVC 1.8 years (IQR 2.7 years) after presentation and 8 (75%) patients did not meet Task Force Criteria without genetic testing. ARVC diagnosis led to an additional 5 (42%) patients referred for implantable cardiac defibrillator and 17 family member diagnoses. In conclusion, ARVC may initially present as myocarditis and these patients have distinct characteristics including female gender, LV involvement and DSP gene variants. Genetic testing is key to ARVC diagnosis and should be considered in select myocarditis patients.

Arrhythmogenic Cardiomyopathy: Molecular Insights for Improved Therapeutic Design

Arrhythmogenic cardiomyopathy (ACM) is an inherited disorder characterized by structural and electrical cardiac abnormalities, including myocardial fibro-fatty replacement. Its pathological ventricular substrate predisposes subjects to an increased risk of sudden cardiac death (SCD). ACM is a notorious cause of SCD in young athletes, and exercise has been documented to accelerate its progression. Although the genetic culprits are not exclusively limited to the intercalated disc, the majority of ACM-linked variants reside within desmosomal genes and are transmitted via Mendelian inheritance patterns; however, penetrance is highly variable. Its natural history features an initial “concealed phase” that results in patients being vulnerable to malignant arrhythmias prior to the onset of structural changes. Lack of effective therapies that target its pathophysiology renders management of patients challenging due to its progressive nature, and has highlighted a critical need to improve our understanding of its underlying mechanistic basis. In vitro and in vivo studies have begun to unravel the molecular consequences associated with disease causing variants, including altered Wnt/β-catenin signaling. Characterization of ACM mouse models has facilitated the evaluation of new therapeutic approaches. Improved molecular insight into the condition promises to usher in novel forms of therapy that will lead to improved care at the clinical bedside.

An autoantibody identifies arrhythmogenic right ventricular cardiomyopathy and participates in its pathogenesis

Aims

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by right ventricular myocardial replacement and life-threatening ventricular arrhythmias. Desmosomal gene mutations are sometimes identified, but clinical and genetic diagnosis remains challenging. Desmosomal skin disorders can be caused by desmosomal gene mutations or autoantibodies. We sought to determine if anti-desmosome antibodies are present in subjects with ARVC.

Methods and results

We evaluated ARVC subjects and controls for antibodies to cardiac desmosomal cadherin proteins. Desmoglein-2 (DSG2), desmocollin-2, and N-cadherin proteins on western blots were exposed to sera, in primary and validation cohorts of subjects and controls, as well as the naturally occurring Boxer dog model of ARVC. We identified anti-DSG2 antibodies in 12/12 and 25/25 definite ARVC cohorts and 7/8 borderline subjects. Antibody was absent in 11/12, faint in 1/12, and absent in 20/20 of two control cohorts. Anti-DSG2 antibodies were present in 10/10 Boxer dogs with ARVC, and absent in 18/18 without. In humans, the level of anti-DSG2 antibodies correlated with the burden of premature ventricular contractions (r = 0.70), and antibodies caused gap junction dysfunction, a common feature of ARVC, in vitro. Anti-DSG2 antibodies were present in ARVC subjects regardless of whether an underlying mutation was identified, or which mutation was present. A disease-specific DSG2 epitope was identified.

Conclusion

Anti-DSG2 antibodies are a sensitive and specific biomarker for ARVC. The development of autoimmunity as a result of target-related mutations is unique. Anti-DSG2 antibodies likely explain the cardiac inflammation that is frequently identified in ARVC and may represent a new therapeutic target.

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.

Arrhythmogenic Ventricular Cardiomyopathy Associated With Fibromuscular Dysplasia of Ostial Right Main Coronary Artery

In this article, we report the autopsy findings of a 23-year-old woman, who was found unconscious at home by her relatives. During the transportation to the hospital, the woman was handed over to the ambulance personnel, who were the first to provide cardiopulmonary resuscitation. In the hospital, after an hour-lasting asystole, the heart activity was restored. Prolonged cardiac arrest led to hypoxic brain injury, which resulted in a persistent coma. Examinations carried out during hospitalization detected hypokinetic interventricular septum, frequent ventricular extrasystoles and ventricular fibrillation. The patient died within 35 hours of admission to the hospital. Gross findings of the heart included a noticeable increase of the adipose tissue in the right ventricular wall, where histologically focal myocardial atrophy with focal transmural lipomatosis reaching endocardium were detected. Death was attributed to arrhythmogenic ventricular cardiomyopathy. Pathogenic variants in JUP gene and KCNH2 gene confirmed the diagnosis. Other finding of note was fibromuscular dysplasia of ostial right main coronary artery causing a significant luminal narrowing.

Engineered Heart Slice Model of Arrhythmogenic Cardiomyopathy Using Plakophilin-2 Mutant Myocytes

IMPACT STATEMENT

Genetic heart diseases such as arrhythmogenic cardiomyopathy (AC), a common genetic cause of sudden cardiac death, can be modeled using patient-specific induced pluripotent stem cell-derived cardiac myocytes (CMs). However, it is important to culture these cells in a multicellular syncytium with exposure to surrounding matrix cues to create more accurate and robust models of the disease due to the importance of cell-cell and cell-matrix interactions. The engineered heart slice, constructed by seeding CMs on intact decellularized matrix slices, allows molecular and functional studies on an aligned multilayered syncytium of CMs. This study reveals the potential for an improved disease-in-a-dish model of AC.

Fifty Years of Ventricular Tachycardia in a Single Patient

We report a patient who first presented during childhood in the early 1960's with several episodes of ventricular tachycardia (VT) and we describe her management which reflected the best medical knowledge at the time. She then presented more than 50 years later, again with VT, at which time a definitive diagnosis of the underlying cause was made. Her case illustrates the evolution in the understanding and management of VT over the past 50 years. This in turn reflects the clinical and technological advances in the management of cardiovascular disease over time.

Arrhythmogenic cardiomyopathy: what blood can reveal?

Blood, serum and plasma represent accessible sources of data about physiological and pathologic status. In arrhythmogenic cardiomyopathy (ACM), circulating nucleated cells are routinely used for detection of germinal genetic mutations. In addition, different biomarkers have been proposed for diagnostic purposes and for monitoring disease progression, including inflammatory cytokines, markers of myocardial dysfunction and damage, and microRNAs. This review summarizes the current information that can be retrieved from the blood of ACM patients and considers the future prospects. Improvements in current knowledge of circulating factors may provide noninvasive means to simplify and improve the diagnosis, prognosis prediction, and management of ACM patients.

Endomyocardial biopsy in patients with acute myocarditis, idiopathic dilated cardiomyopathy, and arrhythmogenic right ventricular dysplasia

Endomyocardial biopsy (EMB) is useful for the diagnosis of myocarditis, cardiac sarcoidosis, and non-ischemic cardiomyopathy. In this mini-review, we discuss the diagnostic potential of EMB in cases of acute/chronic-active myocarditis, sarcoidosis, idiopathic dilated cardiomyopathy and arrhythmogenic right ventricular dysplasia. We also summarize the complications caused by endomyocardial biopsy procedures. Importantly, we finally review the emerging molecular biology technologies as well as biological engineering techniques that can help improve the diagnostic accuracy of EMB to diagnose myocarditis and cardiomyopathies, promoting the management of these diseases.

Cell models of arrhythmogenic cardiomyopathy: advances and opportunities

Arrhythmogenic cardiomyopathy is a rare genetic disease that is mostly inherited as an autosomal dominant trait. It is associated predominantly with mutations in desmosomal genes and is characterized by the replacement of the ventricular myocardium with fibrous fatty deposits, arrhythmias and a high risk of sudden death. In vitro studies have contributed to our understanding of the pathogenic mechanisms underlying this disease, including its genetic determinants, as well as its cellular, signaling and molecular defects. Here, we review what is currently known about the pathogenesis of arrhythmogenic cardiomyopathy and focus on the in vitro models that have advanced our understanding of the disease. Finally, we assess the potential of established and innovative cell platforms for elucidating unknown aspects of this disease, and for screening new potential therapeutic agents. This appraisal of in vitro models of arrhythmogenic cardiomyopathy highlights the discoveries made about this disease and the uses of these models for future basic and therapeutic research.

Summary:In vitro models of ACM provide insights into the molecular mechanisms of this disease. This reappraisal offers a comprehensive vision of past discoveries and constitutes a tool for future research.

MicroRNA-130a Regulation of Desmocollin 2 in a Novel Model of Arrhythmogenic Cardiomyopathy

BACKGROUND

MicroRNAs are small noncoding RNA molecules that play a critical role in regulating physiological and disease processes. Recent studies have now recognized microRNAs as an important player in cardiac arrhythmogenesis. Molecular insight into arrhythmogenic cardiomyopathy (AC) has primarily focused on mutations in desmosome proteins. To our knowledge, models of AC due to microRNA dysregulation have not been reported. Previously, we reported on miR-130a mediated down-regulation of Connexin43.

OBJECTIVE

Here, we investigate miR-130a-mediated translational repression of Desmocollin2 (DSC2), as it has a predicted target site for miR-130a. DSC2 is an important protein for cell adhesion, which has been shown to be dysregulated in human AC.

METHOD & RESULTS

After induction of miR-130a, transgenic mice demonstrated right ventricular dilation. Surface ECG revealed spontaneous premature ventricular complexes confirming an arrhythmogenic phenotype in αMHC-miR130a mice. Using total protein from whole ventricular lysate, western blot analysis demonstrated an 80% reduction in DSC2 levels in transgenic myocardium. Furthermore, immunofluorescent staining confirmed downregulation of DSC2 in transgenic compared with littermate control myocardium. In transgenic hearts, histologic findings revealed fibrosis and lipid accumulation within both ventricles. To validate DSC2 as a direct target of miR-130a, we performed in vitro target assays in 3T3 fibroblasts, known to express miR-130a. Using a luciferase reporter fused to the 3UTR of DSC2 compared with a control, we found a 42% reduction in luciferase activity with the DSC2 3UTR. This reduction was reversed upon selective inhibition of miR-130a.

CONCLUSION

Overexpression of miR-130a results in a disease phenotype characteristic of AC and therefore, may serve as potential model for microRNA-induced AC.

Multi-Scale Assessments of Cardiac Electrophysiology Reveal Regional Heterogeneity in Health and Disease

The left and right ventricles of the four-chambered heart have distinct developmental origins and functions. Chamber-specific developmental programming underlies the differential gene expression of ion channel subunits regulating cardiac electrophysiology that persists into adulthood. Here, we discuss regional specific electrical responses to genetic mutations and cardiac stressors, their clinical correlations, and describe many of the multi-scale techniques commonly used to analyze electrophysiological regional heterogeneity.

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.

Genetic and epigenetic regulation of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is most commonly characterized as a disease of the intercalated disc that promotes abnormal cardiac conduction. Previously, arrhythmogenic cardiomyopathy was frequently referred to as arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D); however, genotype-phenotype studies have defined a broader phenotypic spectrum; with the identification of left-dominant and biventricular subtypes. Molecular insight into AC has primarily focused on mutations in desmosomal proteins and the downstream signaling pathways; however, desmosomal gene mutations can only be identified in approximately 50% of patients with AC. Animal and cellular studies have shown that in addition to abnormal biomechanical properties from changes in desmosome function, crosstalk from the desmosome to the nucleus, gap junctions, and ion channels are implicated in the pathobiology of AC. In this review, we highlight some of the newly identified genetic and epigenetic mechanisms that may lead to the development of AC including the role of the Hippo pathway and microRNAs. This article is part of a Special Issue entitled: Genetic and epigenetic control of heart failure - edited by Jun Ren & Megan Yingmei Zhang.

Left Ventricular Function in Children and Adolescents With Arrhythmogenic Right Ventricular Cardiomyopathy

The aim of this study was to determine if left ventricular (LV) contractility is reduced in children with arrhythmogenic right ventricular cardiomyopathy (ARVC). For this retrospective study, children and adolescents undergoing a workup for ARVC were characterized according to the revised Task Force Criteria (rTFC). LV strain, rotation, and torsion were measured by feature-tracking cardiovascular magnetic resonance imaging (CMR). Of 142 pediatric patients, 41% had no, 23% possible, 20% borderline, and 16% definite ARVC. LV ejection fraction (EF) did not differ between rTFC categories. Patients in higher rTFC categories had lower right ventricular (RV) EF z-scores (Z-), higher Z-RV end-diastolic volumes (EDVs) and larger Z-LVEDVs (p <0.001, p = 0.002 and 0.013, respectively). LV global circumferential strain was lower in higher rTFC categories (p = 0.018). Z-LVEDV correlated with Z-RVEDV, and Z-LVEF correlated with Z-RVEF (r = 0.69 and r = 0.55, both p <0.001). Z-LVEF and Z-RVEF correlated with LV global circumferential strain (r = 0.48 and r = 0.46, both p <0.001). Forty-eight patients (34%) underwent follow-up CMR investigations after a mean of 3.2 ± 1.9 (0.4 to 8.4) years. A decrease of Z-LVEF over time correlated with that of Z-RVEF (r = 0.35), and Z-LVEDV increase correlated with Z-RVEDV increase (r = 0.57). In conclusion, LV myocardial dysfunction is present in young patients with suspected ARVC. Progressive LV dysfunction assessed by conventional CMR and feature-tracking and enlargement over time parallel adverse remodeling of the RV.

Anaesthesia for patients with arrhythmogenic right ventricular dysplasia

Arrhythmogenic right ventricular dysplasia (ARVD) is an inherited heart muscle disease. Myocyte apoptosis and fibro-fatty scar tissue predisposes patients to malignant ventricular arrhythmias. Patients may present to variety of surgical procedures with diagnosed ARVD. Surgical insult, catecholamine surge and physiological disturbance can be hazardous on the vulnerable myocardium and may result in life-threatening ventricular tachycardia or sudden cardiac death in the perioperative period. Anaesthetists have particular role in perioperative management of this patient population, meticulous perioperative planning, close haemodynamic monitoring and maintenance of physiological stability throughout helps to avoid devastating perioperative loss.

A 43-Year-Old Man With Daytime Sleepiness and a Heart Murmur

A 43-year-old man was referred to our tertiary sleep center for the initiation of sleep apnea treatment. A prior diagnostic overnight polysomnography (Fig 1) had revealed an apnea-hypopnea index (AHI) of 22/h of sleep. The apneas were predominantly central (central AHI, 18.2/h; obstructive AHI, 3.8/h), more pronounced in the supine position (AHI supine, 36.6/h; AHI nonsupine, 11/h) and during non-rapid eye movement (non-REM) sleep (REM, 15.8/h; non-REM, 23.5/h). A continuous positive airway pressure (CPAP) trial in an outpatient setting had failed, as the fixed CPAP of 11 cm H₂O was not tolerated by the patient because of a feeling of lightheadedness when wearing the mask. At referral, the patient complained about falling asleep in front of the computer in the afternoons despite regular bedtimes and 7 to 8 h of sleep per night. His Epworth Sleepiness Scale score was 11. He had no significant past history including cardiopulmonary disease. He was not taking any medication but had noticed a slow decline in general physical performance in the last year, with dyspnea (New York Heart Association class I) after running distances of 1 to 2 km. He had never experienced syncope. His family history was unremarkable.

Sudden death after major head and neck cancer surgery due to undetected arrhythmogenic right ventricle cardiomyopathy (ARVC)

BACKGROUND

Oral squamous cell carcinoma is the sixth most frequent malignancy in Austria. The incidence of arrhythmogenic right ventricle dysplasia (ARVC), an important cause of sudden cardiac death, is estimated at 1:5000 to 1:1000.

CASE REPORT

We present a case of a 75-year-old woman who underwent major oncologic surgery for T4aN0M0 maxillary squamous cell carcinoma and reconstruction with a scapular-latissimus dorsi microvascular flap. The patient died suddenly during her postoperative care. Autopsy revealed pericardiac tamponade due to rupture of the right ventricular wall. Histologic examination showed ARVC in a sample taken directly from the ruptured area. Cause of death was secondary arrhythmia originating from the ARVC. The arrhythmia had led to rupture of the right ventricular wall and sudden cardiac death.

DISCUSSION

As per our current knowledge, no cases of maxillary cancer and ARVC as co-morbidities have been reported in the literature. The patient had been given anti-arrhythmia treatment for previously detected atrial fibrillation, which could have been why the arrhythmia was not apparent on the electrocardiogram. Thus, although the appropriate preoperative diagnostics were performed according to current oncologic and anesthesiology guidelines, the potentially lethal cardiac condition of the patient could not be detected.

The role of mutations in the SCN5A gene in cardiomyopathies

The SCN5A gene encodes the alpha-subunit of the Nav1.5 ion channel protein, which is responsible for the sodium inward current (INa). Since 1995 several hundred mutations in this gene have been found to be causative for inherited arrhythmias including Long QT syndrome, Brugada syndrome, cardiac conduction disease, sudden infant death syndrome, etc. As expected these syndromes are primarily electrical heart diseases leading to life-threatening arrhythmias with an "apparently normal heart". In 2003 a new form of dilated cardiomyopathy was identified associated with mutations in the SCN5A gene. Recently mutations have been also found in patients with arrhythmogenic right ventricular cardiomyopathy and atrial standstill. The purpose of this review is to outline and analyze the following four topics: 1) SCN5A genetic variants linked to different cardiomyopathies; 2) clinical manifestations of the known mutations; 3) possible molecular mechanisms of myocardial remodeling; and 4) the potential implications of gene-specific treatment for those disorders. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

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

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

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

AIMS

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Arrhythmogenic Noncompaction Cardiomyopathy: Is There an Echocardiographic Phenotypic Overlap of Two Distinct Cardiomyopathies?

The clinical diagnosis of right ventricular (RV) cardiomyopathies is often challenging. It is difficult to differentiate the isolated left ventricular (LV) noncompaction cardiomyopathy (NC) from biventricular NC or from coexisting arrhythmogenic ventricular cardiomyopathy (AC). There are currently few established morphologic criteria for the diagnosis other than RV dilation and presence of excessive regional trabeculation. The gross and microscopic changes suggest pathological similarities between, or coexistence of, RV-NC and AC. Therefore, the term arrhythmogenic right ventricular cardiomyopathy is somewhat misleading as isolated LV or biventricular involvement may be present and thus a broader term such as AC should be preferred. We describe an unusual case of AC associated with a NC in a 27-year-old man who had a history of permanent pacemaker 7 years ago due to second-degree atrioventricular block.

Relationship between arrhythmogenic right ventricular dysplasia and exercise

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

Cardiac and non-cardiac causes of T-wave inversion in the precordial leads in adult subjects: A Dutch case series and review of the literature

AIM: To describe the electrocardiographic (ECG) phenomena characterized by T-wave inversion in the precordial leads in adults and to highlight its differential diagnosis.

METHODS: A retrospective chart review of 8 adult patients who were admitted with ECG T-wave inversion in the anterior chest leads with or without prolongation of corrected QT (QTc) interval. They had different clinical conditions. Each patient underwent appropriate clinical assessment including investigation for myocardial involvement. Single and multimodality non-invasive, semi-invasive and invasive diagnostic approach were used to ascertain the diagnosis. The diagnostic assessment included biochemical investigation, cardiac and abdominal ultrasound, cerebral and chest computed tomography, nuclear medicine and coronary angiography.

RESULTS: Eight adult subjects (5 females) with a mean age of 66 years (range 51 to 82) are analyzed. The etiology of T-wave inversion in the precordial leads were diverse. On admission, all patients had normal blood pressure and the ECG showed sinus rhythm. Five patients showed marked prolongation of the QTc interval. The longest QTc interval (639 ms) was found in the patient with pheochromocytoma. Giant T-wave inversion (≥ 10 mm) was found in pheochromocytoma followed by electroconvulsive therapy and finally ischemic heart disease. The deepest T-wave was measured in lead V₃ (5 ×). In 3 patients presented with mild T-wave inversion (patients 1, 5 and 4 mm), the QTc interval was not prolonged (432, 409 and 424 msec), respectively.

CONCLUSION: T-wave inversion associated with or without QTc prolongation requires meticulous history taking, physical examination and tailored diagnostic modalities to reach rapid and correct diagnosis to establish appropriate therapeutic intervention.

Is cardiac MRI an effective test for arrhythmogenic right ventricular cardiomyopathy diagnosis?

AIM: To evaluate the referrals with suspected arrhythmogenic right ventricular cardiomyopathy (ARVC) and compare cardiac MR (cMR) findings against clinical diagnosis.

METHODS: A retrospective analysis of 114 (age range 16 to 83, males 55% and females 45%) patients referred for cMR with a suspected diagnosis of ARVC between May 2006 and February 2010 was performed after obtaining institutional approval for service evaluation. Reasons for referral including clinical symptoms and family history of sudden death, electrocardiogram and echo abnormalities, cMR findings, final clinical diagnosis and information about clinical management were obtained. The results of cMR were classified as major, minor, non-specific or negative depending on both functional and tissue characterisation and the cMR results were compared against the final clinical diagnosis.

RESULTS: The most common reasons for referral included arrhythmias (30%) and a family history of sudden death (20%). Of the total cohort of 114 patients: 4 patients (4%) had major cMR findings for ARVC, 13 patients (11%) had minor cMR findings, 2 patients had non-specific cMR findings relating to the right ventricle and 95 patients had a negative cMR. Of the 4 patients who had major cMR findings, 3 (75%) had a positive clinical diagnosis. In contrast, of the 13 patients who had minor cMR findings, only 2 (15%) had a positive clinical diagnosis. Out of the 95 negative patients, clinical details were available for 81 patients and none of them had ARVC. Excluding the 14 patients with no clinical data and final diagnosis, the sensitivity of the test was 100%, specificity 87%, positive predictive value 29% and the negative predictive value 100%.

CONCLUSION: CMR is a useful tool for ARVC evaluation because of the high negative predictive value as the outcome has a significant impact on the clinical decision-making.