Arrhythmogenic Right Ventricular Cardiomyopathy Presenting as Clinical Myocarditis in Women

NFĸB signaling drives myocardial injury via CCR2+ macrophages in a preclinical model of arrhythmogenic cardiomyopathy

Nuclear factor κ-B (NFκB) is activated in iPSC-cardiac myocytes from patients with arrhythmogenic cardiomyopathy (ACM) under basal conditions, and inhibition of NFκB signaling prevents disease in Dsg2mut/mut mice, a robust mouse model of ACM. Here, we used genetic approaches and single-cell RNA-Seq to define the contributions of immune signaling in cardiac myocytes and macrophages in the natural progression of ACM using Dsg2mut/mut mice. We found that NFκB signaling in cardiac myocytes drives myocardial injury, contractile dysfunction, and arrhythmias in Dsg2mut/mut mice. NFκB signaling in cardiac myocytes mobilizes macrophages expressing C-C motif chemokine receptor-2 (CCR2+ cells) to affected areas within the heart, where they mediate myocardial injury and arrhythmias. Contractile dysfunction in Dsg2mut/mut mice is caused both by loss of heart muscle and negative inotropic effects of inflammation in viable muscle. Single nucleus RNA-Seq and cellular indexing of transcriptomes and epitomes (CITE-Seq) studies revealed marked proinflammatory changes in gene expression and the cellular landscape in hearts of Dsg2mut/mut mice involving cardiac myocytes, fibroblasts, and CCR2+ macrophages. Changes in gene expression in cardiac myocytes and fibroblasts in Dsg2mut/mut mice were dependent on CCR2+ macrophage recruitment to the heart. These results highlight complex mechanisms of immune injury and regulatory crosstalk between cardiac myocytes, inflammatory cells, and fibroblasts in the pathogenesis of ACM.

Role of genetics in inflammatory cardiomyopathy

Traditional cardiomyopathy paradigms segregate inflammatory etiologies from those caused by genetic variants. An identified or presumed trigger is implicated in acute myocarditis or chronic inflammatory cardiomyopathy but growing evidence suggests a significant proportion of patients have an underlying cardiomyopathy-associated genetic variant often even when a clear inflammatory trigger is identified. Recognizing a possible genetic contribution to inflammatory cardiomyopathy may have major downstream implications for both the patient and family. The presenting features of myocarditis (i.e. chest pain, arrhythmia, and/or heart failure) may provide insight into diagnostic considerations. One example is isolated cardiac sarcoidosis, a distinct inflammatory cardiomyopathy that carries diagnostic challenges and clinical overlap; genetic testing has increasingly reclassified cases of isolated cardiac sarcoidosis as genetic cardiomyopathy, notably altering management. On the other side, inflammatory presentations of genetic cardiomyopathies are likewise underappreciated and a growing area of investigation. Inflammation plays an important role in the pathogenesis of several familial cardiomyopathies, especially arrhythmogenic phenotypes. Given these clinical scenarios, and the implications on clinical decision making such as initiation of immunosuppression, sudden cardiac death prevention, and family screening, it is important to recognize when genetics may be playing a role.

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.

A case for genetic testing: Arrhythmogenic cardiomyopathy presenting as myocarditis

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy associated with fibrofatty tissue replacement of the ventricular tissue. The disease can cause ventricular dysfunction and arrhythmias and can increase the risk of sudden cardiac death. This cardiomyopathy can have variable clinical presentations, especially in the pediatric and young adult populations. In this report, we describe the case of an 18-year-old female with myocarditis as the initial presentation of ACM. She presented following a resuscitated cardiac arrest due to ventricular arrhythmia. On arrival, myocardial edema and delayed gadolinium enhancement were present on cardiac magnetic resonance imaging, with no ventricular changes observed, making the diagnosis consistent with myocarditis. Genetic testing revealed a pathogenic mutation in the desmoplakin gene consistent with ACM. Given the unconventional initial presentation of this patient's disease, early consideration of genetic testing may be beneficial to aid in the early diagnosis and management of ACM in young patients.

The role of genetic testing in suspected fulminant myocarditis: A case report

ACM is a rare hereditary heart disease characterized by a progressive fibro-fatty replacement of the myocardium that can affect either the right or the left ventricle or both. It is mainly caused by variants in the desmosome genes with autosomal dominant transmission and incomplete penetrance. The disease shows a wide spectrum of clinical manifestations, including ventricular arrhythmias, HF and myocarditis. The latter is considered a 'hot phase' in the natural history of the disease and must therefore be distinguished from the isolated AM, which is frequently due to viral infections. Our case report is an example of how an AM, as the first manifestation of the disease, helped to reach a diagnosis of ACM through the genetic analysis. In fact, the multi-parametric investigation, which also included CMR and EMB, revealed controversial aspects that led us to perform the genetic test. The latter revealed a heterozygous pathogenic variant in the PKP2 that was considered definitive proof of ACM.

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

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

Diagnostic delay in arrhythmogenic cardiomyopathy

AIMS

Diagnosis of arrhythmogenic cardiomyopathy (ACM) may be challenging, as it comprises diverse phenotypes (right dominant, biventricular, and left dominant), and each may overlap with other clinical entities. The issue of differential diagnosis with conditions mimicking ACM has been previously highlighted; however, a systematic analysis of ACM diagnostic delay, and of its clinical implications, is lacking.

METHODS AND RESULTS

Data of all ACM patients from three Italian Cardiomyopathy Referral Centres were reviewed to assess the time from first medical contact to definitive ACM diagnosis; a significant diagnostic delay was defined as a time to ACM diagnosis ≥2 years. Baseline characteristics and clinical course of patients with and without diagnostic delay were compared. Of 174 ACM patients, 31% experienced diagnostic delay, with a median time to diagnosis of 8 years (20% in right-dominant ACM, 33% in left-dominant ACM, and 39% in biventricular). Patients with diagnostic delay, when compared with those without, more frequently exhibited an ACM phenotype with left ventricular (LV) involvement (74 vs. 57%, P = 0.04) and a specific genetic background (none had plakophilin-2 variants). The most common initial (mis)diagnoses were dilated cardiomyopathy (51%), myocarditis (21%), and idiopathic ventricular arrhythmia (9%). At follow-up, all-cause mortality was greater in those with diagnostic delay (P = 0.03).

CONCLUSION

Diagnostic delay is common in patients with ACM, particularly in the presence of LV involvement, and is associated with greater mortality at follow-up. Clinical suspicion and increasing use of tissue characterization by cardiac magnetic resonance in specific clinical settings are of key importance for the timely identification of ACM.

Recurrent Myocarditis in Patients With Desmosomal Pathogenic Variants: Is Self Antigen Presentation the Link?

Myocarditis is frequently associated with viral infections. Increasing evidence points to an association between myocarditis and inherited cardiomyopathies, though it is unclear whether myocarditis is a driver or an accessory. We present a primary vignette and case series highlighting recurrent myocarditis in patients later found to harbor pathogenic desmosomal variants and provide clinical and basic science context, exploring 2 potentially overlapping hypotheses: that stress induces cellular injury and death in structurally abnormal myocytes and that recurrent viral myocardial and truncated desomosomal protein byproducts as 2 hits could lead to loss of immune tolerance and subsequent autoreactivity.

Mechanisms of Innate Immune Injury in Arrhythmogenic Cardiomyopathy

Inhibition of nuclear factor kappa-B (NFκB) signaling prevents disease in Dsg2 mut/mut mice, a model of arrhythmogenic cardiomyopathy (ACM). Moreover, NFκB is activated in ACM patient-derived iPSC-cardiac myocytes under basal conditions in vitro . Here, we used genetic approaches and sequencing studies to define the relative pathogenic roles of immune signaling in cardiac myocytes vs. inflammatory cells in Dsg2 mut/mut mice. We found that NFκB signaling in cardiac myocytes drives myocardial injury, contractile dysfunction, and arrhythmias in Dsg2 mut/mut mice. It does this by mobilizing cells expressing C-C motif chemokine receptor-2 (CCR2+ cells) to the heart, where they mediate myocardial injury and arrhythmias. Contractile dysfunction in Dsg2 mut/mut mice is caused both by loss of heart muscle and negative inotropic effects of inflammation in viable muscle. Single nucleus RNA sequencing and cellular indexing of transcriptomes and epitomes (CITE-seq) studies revealed marked pro-inflammatory changes in gene expression and the cellular landscape in hearts of Dsg2 mut/mut mice involving cardiac myocytes, fibroblasts and CCR2+ cells. Changes in gene expression in cardiac myocytes and fibroblasts in Dsg2 mut/mut mice were modulated by actions of CCR2+ cells. These results highlight complex mechanisms of immune injury and regulatory crosstalk between cardiac myocytes, inflammatory cells, and fibroblasts in the pathogenesis of ACM.

BRIEF SUMMARY

We have uncovered a therapeutically targetable innate immune mechanism regulating myocardial injury and cardiac function in a clinically relevant mouse model of Arrhythmogenic Cardiomyopathy (ACM).

Cardiomyopathies in children: An overview

Paediatric cardiomyopathies form a heterogeneous group of disorders characterized by structural and electrical abnormalities of the heart muscle, commonly due to a gene variant of the myocardial cell structure. Mostly inherited as a dominant or occasionally recessive trait, they might be part of a syndromic disorder of underlying metabolic or neuromuscular defects or combine early developing extracardiac abnormalities (i.e., Naxos disease). The annual incidence of 1 per 100,000 children appears higher during the first two years of life. Dilated and hypertrophic cardiomyopathy phenotypes share an incidence of 60% and 25%, respectively. Arrhythmogenic right ventricular cardiomyopathy (ARVC), restrictive cardiomyopathy, and left ventricular noncompaction are less commonly diagnosed. Adverse events such as severe heart failure, heart transplantation, or death usually appear early after the initial presentation. In ARVC patients, high-intensity aerobic exercise has been associated with worse clinical outcomes and increased penetrance in at-risk genotype-positive relatives. Acute myocarditis in children has an incidence of 1.4-2.1 cases/per 100,000 children per year, with a 6-14% mortality rate during the acute phase. A genetic defect is considered responsible for the progression to dilated cardiomyopathy phenotype. Similarly, a dilated or arrhythmogenic cardiomyopathy phenotype might emerge with an episode of acute myocarditis in childhood or adolescence. This review provides an overview of childhood cardiomyopathies focusing on clinical presentation, outcome, and pathology.

Misdiagnosed myocarditis in arrhythmogenic cardiomyopathy induced by a homozygous variant of DSG2: a case report

Background

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy that is rarely diagnosed in infants or young children. However, some significant homozygous or compound heterozygous variants contribute to more severe clinical manifestations. In addition, inflammation of the myocardium and ventricular arrhythmia might lead to misdiagnosis with myocarditis. Here, we describe an 8-year-old patient who had been misdiagnosed with myocarditis. Timely genetic sequencing helped to identify this case as ACM induced by a homozygous variant of DSG2.

Case presentation

The proband of this case was an 8-year-old boy who initially presented with chest pain with an increased level of cardiac Troponin I. In addition, the electrocardiogram revealed multiple premature ventricular beats. Cardiac magnetic resonance revealed myocardial edema in the lateral ventricular wall and apex, indicating localized injuries of the myocardium. The patient was primarily suspected to have acute coronary syndrome or viral myocarditis. Whole-exome sequencing confirmed that the proband had a homozygous variation, c.1592T > G, of the DSG2 gene. This mutation site was regulated by DNA modification, which induced amino acid sequence changes, protein structure effects, and splice site changes. According to MutationTaster and PolyPhen-2 analyses, the variant was considered a disease-causing mutation. Next, we used SWISS-MODEL to illustrate the mutation site of p.F531C. The ensemble variance of p.F531C indicated the free energy changes after the amino acid change.

Conclusion

In summary, we reported a rare pediatric case initially presenting as myocarditis that transitioned into ACM during follow-up. A homozygous genetic variant of DSG2 was inherited in the proband. This study expanded the clinical feature spectrum of DSG2-associated ACM at an early age. Additionally, the presentation of this case emphasized the difference between homozygous and heterozygous variants of desmosomal genes in disease progression. Genetic sequencing screening could be helpful in distinguishing unexplained myocarditis in children.

Sex and gender differences in myocarditis and dilated cardiomyopathy: An update

In the past decade there has been a growing interest in understanding sex and gender differences in myocarditis and dilated cardiomyopathy (DCM), and the purpose of this review is to provide an update on this topic including epidemiology, pathogenesis and clinical presentation, diagnosis and management. Recently, many clinical studies have been conducted examining sex differences in myocarditis. Studies consistently report that myocarditis occurs more often in men than women with a sex ratio ranging from 1:2-4 female to male. Studies reveal that DCM also has a sex ratio of around 1:3 women to men and this is also true for familial/genetic forms of DCM. Animal models have demonstrated that DCM develops after myocarditis in susceptible mouse strains and evidence exists for this progress clinically as well. A consistent finding is that myocarditis occurs primarily in men under 50 years of age, but in women after age 50 or post-menopause. In contrast, DCM typically occurs after age 50, although the age that post-myocarditis DCM occurs has not been investigated. In a small study, more men with myocarditis presented with symptoms of chest pain while women presented with dyspnea. Men with myocarditis have been found to have higher levels of heart failure biomarkers soluble ST2, creatine kinase, myoglobin and T helper 17-associated cytokines while women develop a better regulatory immune response. Studies of the pathogenesis of disease have found that Toll-like receptor (TLR)2 and TLR4 signaling pathways play a central role in increasing inflammation during myocarditis and in promoting remodeling and fibrosis that leads to DCM, and all of these pathways are elevated in males. Management of myocarditis follows heart failure guidelines and there are currently no disease-specific therapies. Research on standard heart failure medications reveal important sex differences. Overall, many advances in our understanding of the effect of biologic sex on myocarditis and DCM have occurred over the past decade, but many gaps in our understanding remain. A better understanding of sex and gender effects are needed to develop disease-targeted and individualized medicine approaches in the future.

Role of cardiac magnetic resonance in the differential diagnosis between arrhythmogenic cardiomyopathy with left ventricular involvement and previous infectious myocarditis

AIMS

Arrhythmogenic cardiomyopathy with left ventricular involvement (ACM-LV), particularly in case of isolated left ventricular involvement (i.e. left dominant arrhythmogenic cardiomyopathy, LDAC) and previous infectious myocarditis (pIM) may have overlapping clinical and cardiac magnetic resonance (CMR) features. To date, there are no validated CMR criteria for the differential diagnosis between these conditions. The present study aimed to identify CMR characteristics to distinguish ACM-LV from pIM.

METHODS AND RESULTS

This observational, retrospective, single-centre study included 30 pIM patients and 30 ACM-LV patients. In ACM-LV patients CMR was performed at diagnosis; in patients with pIM, CMR was performed six months after acute infection. CMR analysis included quantitative assessment of left ventricle (LV) volumes, systolic function and wall thicknesses, qualitative and quantitative assessment of late gadolinium enhancement (LGE) sequences. Compared with pIM, ACM-LV patients showed slightly larger LV volumes, more frequent regional wall motion anomalies and reduced wall thicknesses. ACM-LV patients had higher amounts of LV LGE and extension. Notably, the LDAC subgroup had the highest amount of LV LGE. LV LGE amount > 15 g and a LV LGE percentage > 30% of LV mass discriminated ACM-LV from pIM with a 100% specificity. LGE segmental distribution was superimposable among the groups, except for septal segments that were more frequently involved in ACM-LV and LDAC patients.

CONCLUSIONS

A great extension of LV LGE (a cut-off of LGE >15 g and a percentage above 30% of LV LGE in relation to total myocardial mass) discriminates ACM-LV from pIM with extremely high specificity.

[A case of arrhythmogenic right ventricular cardiomyo-pathy associated with myocardial inflammation]

Recent years have been marked by a number of published reports that have shown a high frequency of signs of myocardial inflammation in patients with confirmed arrhythmogenic right ventricular cardiomyopathy (ARVC). This article presents a clinical case of typical phenotypic manifestations of ARVC associated with morphometric signs of subacute myocarditis. A 66-year-old man presented to the emergency department with signs of arrhythmogenic shock caused by ventricular tachycardia. Examination detected electrocardiographic signs of (ARVC), visualized signs of right ventricular dilatation, increased trabeculation, and wall fibrosis. Endomyocardial biopsy of the right ventricular wall showed degenerative alterations of cardiomyocytes with perivascular lymphocytic infiltration and areas of granulation tissue. New facts that evidence inflammatory alterations of the myocardium will still require specifying and reconsidering positions of expert consensuses on diagnostics and treatment of ARVC.

DSP-Related Cardiomyopathy as a Distinct Clinical Entity? Emerging Evidence from an Italian Cohort

Variants in desmoplakin gene (DSP MIM *125647) have been usually associated with Arrhythmogenic Cardiomyopathy (ACM), or Dilated Cardiomyopathy (DCM) inherited in an autosomal dominant manner. A cohort of 18 probands, characterized as heterozygotes for DSP variants by a target Next Generation Sequencing (NGS) cardiomyopathy panel, was analyzed. Cardiological, genetic data, and imaging features were retrospectively collected. A total of 16 DSP heterozygous pathogenic or likely pathogenic variants were identified, 75% (n = 12) truncating variants, n = 2 missense variants, n = 1 splicing variant, and n = 1 duplication variant. The mean age at diagnosis was 40.61 years (IQR 31-47.25), 61% of patients being asymptomatic (n = 11, New York Heart Association (NYHA) class I) and 39% mildly symptomatic (n = 7, NYHA class II). Notably, 39% of patients (n = 7) presented with a clinical history of presumed myocarditis episodes, characterized by chest pain, myocardial enzyme release, 12-lead electrocardiogram abnormalities with normal coronary arteries, which were recurrent in 57% of cases (n = 4). About half of the patients (55%, n = 10) presented with a varied degree of left ventricular enlargement (LVE), four showing biventricular involvement. Eleven patients (61%) underwent implantable cardioverter defibrillator (ICD) implantation, with a mean age of 46.81 years (IQR 36.00-64.00). Cardiac magnetic resonance imaging (CMRI) identified in all 18 patients a delayed enhancement (DE) area consistent with left ventricular (LV) myocardial fibrosis, with a larger localization and extent in patients presenting with recurrent episodes of myocardial injury. These clinical and genetic data confirm that DSP-related cardiomyopathy may represent a distinct clinical entity characterized by a high arrhythmic burden, variable degrees of LVE, Late Gadolinium Enhancement (LGE) with subepicardial distribution and episodes of myocarditis-like picture.

Desmoplakin cardiomyopathy—an inherited cardiomyopathy presenting with recurrent episodes of acute myocardial injury

We present two female patients with recurrent episodes of myocardial injury, consisting of acute chest pain and elevated cardiac markers without coronary artery disease. Cardiovascular magnetic resonance imaging identified extensive late gadolinium enhancement suggestive of an inherited cardiomyopathy. Genetic testing showed heterozygous pathogenic variants in the desmoplakin (DSP) gene, the gene coding for the desmoplakin protein, a structural protein found in the cardiac desmosome. Pathogenic variants in the DSP gene are associated with dilated and arrhythmogenic cardiomyopathy. DSP cardiomyopathies may cause recurring myocardial injury mimicking an acute coronary syndrome or myocarditis. Cardiac magnetic resonance imaging is key in its diagnosis due to its specifying imaging features. Genetic testing is essential for the evaluation and confirmation of the diagnosis.

Analysis of digitalized ECG signals based on artificial intelligence and spectral analysis methods specialized in ARVC

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease that appears between the second and forth decade of a patient's life, being responsible for 20% of sudden cardiac deaths before the age of 35. The effective and punctual diagnosis of this disease based on electrocardiograms (ECGs) could have a vital role in reducing premature cardiovascular mortality. In our analysis, we first outline the digitalization process of paper-based ECG signals enhanced by a spatial filter aiming to eliminate dark regions in the dataset's images that do not correspond to ECG waveform, producing undesirable noise. Next, we propose the utilization of a low-complexity convolutional neural network for the detection of an arrhythmogenic heart disease, that has not been studied through the usage of deep learning methodology to date, achieving high classification accuracy, namely 99.98% training and 98.6% testing accuracy, on a disease the major identification criterion of which are infinitesimal millivolt variations in the ECG's morphology, in contrast with other arrhythmogenic abnormalities. Finally, by performing spectral analysis we investigate significant differentiations in the field of frequencies between normal ECGs and ECGs corresponding to patients suffering from ARVC. In 16 out of the 18 frequencies where we encounter statistically significant differentiations, the normal ECGs are characterized by greater normalized amplitudes compared to the abnormal ones. The overall research carried out in this article highlights the importance of integrating mathematical methods into the examination and effective diagnosis of various diseases, aiming to a substantial contribution to their successful treatment.

Genotype-phenotype Correlates in Arrhythmogenic Cardiomyopathies

PURPOSE OF THE REVIEW

The definition of arrhythmogenic cardiomyopathy (ACM) has expanded beyond desmosomal arrhythmogenic right ventricular cardiomyopathy (ARVC) to include other genetic cardiomyopathies with a significant arrhythmia burden. Emerging data on genotype-phenotype correlations has led recent consensus guidelines to urge genetic testing as a critical component of not only diagnosis but also management of ACM.

RECENT FINDINGS

Plakophilin-2 (PKP2) ARVC/ACM is most likely to meet ARVC Task Force Criteria with right sided involvement and ventricular arrhythmias, while desmoplakin (DSP) ACM may have a normal electrocardiogram (ECG) and has a subepicardial LV scar pattern. Extra-desmosomal ACM including ACM associated with transmembrane protein 43 and phospholamban variants may have characteristic ECG patterns and biventricular cardiomyopathy. Lamin A/C and SCN5A cardiomyopathy often have heart block on ECG with DCM, but are distinct from DCM in that they have significantly elevated arrhythmic risk. Newer genes, especially filamin-C (FLNC) also may have distinct imaging scar patterns, arrhythmia risk, and risk predictors. Recognition of these key differences have implications for clinical management and reinforce the importance of genetic testing in the diagnosis and the emerging opportunities for genotype-specific management of ACM patients.

Arrhythmogenic Right Ventricular Cardiomyopathy Accompanied by Chronic Myocarditis

Patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) classically present with ventricular arrhythmias and less commonly heart failure. ARVC is an inherited cardiomyopathy and generally based on a variant of desmosomal genes. Recently, the association between myocardial inflammation and ARVC has been a matter of great concern. We encountered a patient with ARVC who had a desmoglein-2 mutation with advanced right ventricular failure accompanying a preserved left ventricular function. Concomitant right ventricular myocarditis was detected four years after the diagnosis of ARVC. ARVC and myocarditis might have a deep pathophysiological association, at least in some cases.

Genetic Architecture of Acute Myocarditis and the Overlap With Inherited Cardiomyopathy

BACKGROUND

Acute myocarditis is an inflammatory condition that may herald the onset of dilated cardiomyopathy (DCM) or arrhythmogenic cardiomyopathy (ACM). We investigated the frequency and clinical consequences of DCM and ACM genetic variants in a population-based cohort of patients with acute myocarditis.

METHODS

This was a population-based cohort of 336 consecutive patients with acute myocarditis enrolled in London and Maastricht. All participants underwent targeted DNA sequencing for well-characterized cardiomyopathy-associated genes with comparison to healthy controls (n=1053) sequenced on the same platform. Case ascertainment in England was assessed against national hospital admission data. The primary outcome was all-cause mortality.

RESULTS

Variants that would be considered pathogenic if found in a patient with DCM or ACM were identified in 8% of myocarditis cases compared with <1% of healthy controls (P=0.0097). In the London cohort (n=230; median age, 33 years; 84% men), patients were representative of national myocarditis admissions (median age, 32 years; 71% men; 66% case ascertainment), and there was enrichment of rare truncating variants (tv) in ACM-associated genes (3.1% of cases versus 0.4% of controls; odds ratio, 8.2; P=0.001). This was driven predominantly by DSP-tv in patients with normal LV ejection fraction and ventricular arrhythmia. In Maastricht (n=106; median age, 54 years; 61% men), there was enrichment of rare truncating variants in DCM-associated genes, particularly TTN-tv, found in 7% (all with left ventricular ejection fraction <50%) compared with 1% in controls (odds ratio, 3.6; P=0.0116). Across both cohorts over a median of 5.0 years (interquartile range, 3.9-7.8 years), all-cause mortality was 5.4%. Two-thirds of deaths were cardiovascular, attributable to worsening heart failure (92%) or sudden cardiac death (8%). The 5-year mortality risk was 3.3% in genotype-negative patients versus 11.1% for genotype-positive patients (Padjusted=0.08).

CONCLUSIONS

We identified DCM- or ACM-associated genetic variants in 8% of patients with acute myocarditis. This was dominated by the identification of DSP-tv in those with normal left ventricular ejection fraction and TTN-tv in those with reduced left ventricular ejection fraction. Despite differences between cohorts, these variants have clinical implications for treatment, risk stratification, and family screening. Genetic counseling and testing should be considered in patients with acute myocarditis to help reassure the majority while improving the management of those with an underlying genetic variant.

Acute Myocarditis Associated With Desmosomal Gene Variants

BACKGROUND

The risk of adverse cardiovascular events in patients with acute myocarditis (AM) and desmosomal gene variants (DGV) remains unknown.

OBJECTIVES

The purpose of this study was to ascertain the risk of death, ventricular arrhythmias, recurrent myocarditis, and heart failure (main endpoint) in patients with AM and pathogenic or likely pathogenetic DGV.

METHODS

In a retrospective international study from 23 hospitals, 97 patients were included: 36 with AM and DGV (DGV[+]), 25 with AM and negative gene testing (DGV[-]), and 36 with AM without genetics testing. All patients had troponin elevation plus findings consistent with AM on histology or at cardiac magnetic resonance (CMR). In 86 patients, CMR changes in function and structure were re-assessed at follow-up.

RESULTS

In the DGV(+) AM group (88.9% DSP variants), median age was 24 years, 91.7% presented with chest pain, and median left ventricular ejection fraction (LVEF) was 56% on CMR (P = NS vs the other 2 groups). Kaplan-Meier curves demonstrated a higher risk of the main endpoint in DGV(+) AM compared with DGV(-) and without genetics testing patients (62.3% vs 17.5% vs 5.3% at 5 years, respectively; P &lt; 0.0001), driven by myocarditis recurrence and ventricular arrhythmias. At follow-up CMR, a higher number of late gadolinium enhanced segments was found in DGV(+) AM.

CONCLUSIONS

Patients with AM and evidence of DGV have a higher incidence of adverse cardiovascular events compared with patients with AM without DGV. Further prospective studies are needed to ascertain if genetic testing might improve risk stratification of patients with AM who are considered at low risk.

Accordion sign in COVID 19 related acute myocarditis, an old sign for a novel context? A cardiac magnetic resonance case series report study

INTRODUCTION

The COVID-19 pandemic is related to a higher incidence of myocarditis; we present a case series of seven patients, admitted with COVID-19 related acute myocarditis, evaluated with cardiac magnetic resonance imaging, showing an altered profile of the free wall of the right ventricle, no longer present after six months follow-up.

MATERIALS AND METHODS

Seven patients have been evaluated for COVID-19 related acute myocarditis, all patients have been evaluated with cardiac magnetic resonance imaging both in the acute setting and after six months follow-up.

RESULTS

In the acute phase, myocarditis was confirmed in keeping with the current diagnostic criteria. In five out of seven cases, the presence of a crinkling profile of the free wall of the right ventricle was observed; at six months follow up, remission in four out of the five cases and a significant reduction in the remaining case, of the previously described findings, was observed.

CONCLUSIONS

Crinkling appearance in the profile of the free wall of the right ventricle, detectable with cardiac magnetic resonance imaging, might represent a morphological feature present in the acute setting of COVID-19 related myocarditis; several underlying physiopathological mechanisms are conceivable. Further studies are needed to confirm this correlation, define the underlying mechanisms and the prognostic implication related to it. This is the first report in the literature that has considered such findings to the best of our knowledge.

Myocarditis-like Episodes in Patients with Arrhythmogenic Cardiomyopathy: A Systematic Review on the So-Called Hot-Phase of the Disease

Arrhythmogenic cardiomyopathy (ACM) is a genetically determined myocardial disease, characterized by myocytes necrosis with fibrofatty substitution and ventricular arrhythmias that can even lead to sudden cardiac death. The presence of inflammatory cell infiltrates in endomyocardial biopsies or in autoptic specimens of ACM patients has been reported, suggesting a possible role of inflammation in the pathophysiology of the disease. Furthermore, chest pain episodes accompanied by electrocardiographic changes and troponin release have been observed and defined as the “hot-phase” phenomenon. The aim of this critical systematic review was to assess the clinical features of ACM patients presenting with “hot-phase” episodes. According to PRISMA guidelines, a search was run in the PubMed, Scopus and Web of Science electronic databases using the following keywords: “arrhythmogenic cardiomyopathy”; “myocarditis” or “arrhythmogenic cardiomyopathy”; “troponin” or “arrhythmogenic cardiomyopathy”; and “hot-phase”. A total of 1433 titles were retrieved, of which 65 studies were potentially relevant to the topic. Through the application of inclusion and exclusion criteria, 9 papers reporting 103 ACM patients who had experienced hot-phase episodes were selected for this review. Age at time of episodes was available in 76% of cases, with the mean age reported being 26 years ± 14 years (min 2–max 71 years). Overall, 86% of patients showed left ventricular epicardial LGE. At the time of hot-phase episodes, 49% received a diagnosis of ACM (Arrhythmogenic left ventricular cardiomyopathy in the majority of cases), 19% of dilated cardiomyopathy and 26% of acute myocarditis. At the genetic study, Desmoplakin (DSP) was the more represented disease-gene (69%), followed by Plakophillin-2 (9%) and Desmoglein-2 (6%). In conclusion, ACM patients showing hot-phase episodes are usually young, and DSP is the most common disease gene, accounting for 69% of cases. Currently, the role of “hot-phase” episodes in disease progression and arrhythmic risk stratification remains to be clarified.

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

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

Myocarditis or inherited disease? - The multifaceted presentation of arrhythmogenic cardiomyopathy

INTRODUCTION

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is now usually referred to as arrhythmogenic cardiomyopathy (ACM) because of the possible left and biventricular affection. In recent years, it has been shown that early-stage ACM, especially in women carrying a disease-causing variant in the DSP gene, may present with clinical signs of myocarditis.

CASE PRESENTATION

The female patient was diagnosed with myocarditis based on arrhythmia and findings on magnetic resonance imaging at the age of 24 years. An additional performed myocardial biopsy confirmed a lymphocytic inflammatory reaction. Subsequently, the patient experienced cardiac arrest because of ventricular fibrillation and was resuscitated. As a result, she received an implantable cardioverter defibrillator, and repeated ablations of recurrent ventricular tachycardia were performed. After four years, molecular genetic testing identified the heterozygous, likely pathogenic nonsense variant c.4789G > T, p.(Glu1597*) in DSP (NM_004415.4). Based on this finding, ACM could be diagnosed, and a heart transplantation was performed only a few months later because of rapid disease progression.

DISCUSSION

Truncating variants in DSP have been associated with fulminant progression of arrhythmia. However, the currently used ARVC task force criteria are inadequate to detect DSP-associated ACM with left dominant presentation. Moreover, the initial diagnosis of myocarditis may distract from a more extensive search for other causes. Consequently, in cases of recurrent or unusually prolonged myocarditis, especially if present without detected pathogens, molecular genetic testing should be considered.

Arrhythmias as Presentation of Genetic Cardiomyopathy

There is increasing evidence regarding the prevalence of genetic cardiomyopathies, for which arrhythmias may be the first presentation. Ventricular and atrial arrhythmias presenting in the absence of known myocardial disease are often labelled as idiopathic, or lone. While ventricular arrhythmias are well-recognized as presentation for arrhythmogenic cardiomyopathy in the right ventricle, the scope of arrhythmogenic cardiomyopathy has broadened to include those with dominant left ventricular involvement, usually with a phenotype of dilated cardiomyopathy. In addition, careful evaluation for genetic cardiomyopathy is also warranted for patients presenting with frequent premature ventricular contractions, conduction system disease, and early onset atrial fibrillation, in which most detected genes are in the cardiomyopathy panels. Sudden death can occur early in the course of these genetic cardiomyopathies, for which risk is not adequately tracked by left ventricular ejection fraction. Only a few of the cardiomyopathy genotypes implicated in early sudden death are recognized in current indications for implantable cardioverter defibrillators which otherwise rely upon a left ventricular ejection fraction ≤0.35 in dilated cardiomyopathy. The genetic diagnoses impact other aspects of clinical management such as exercise prescription and pharmacological therapy of arrhythmias, and new therapies are coming into clinical investigation for specific genetic cardiomyopathies. The expansion of available genetic information and implications raises new challenges for genetic counseling, particularly with the family member who has no evidence of a cardiomyopathy phenotype and may face a potentially negative impact of a genetic diagnosis. Discussions of risk for both probands and relatives need to be tailored to their numeric literacy during shared decision-making. For patients presenting with arrhythmias or cardiomyopathy, extension of genetic testing and its implications will enable cascade screening, intervention to change the trajectory for specific genotype-phenotype profiles, and enable further development and evaluation of emerging targeted therapies.

Evidence of Failed Resolution Mechanisms in Arrhythmogenic Inflammation, Fibrosis and Right Heart Disease

Inflammation is a complex program of active processes characterized by the well-orchestrated succession of an initiation and a resolution phase aiming to promote homeostasis. When the resolution of inflammation fails, the tissue undergoes an unresolved inflammatory status which, if it remains uncontrolled, can lead to chronic inflammatory disorders due to aggravation of structural damages, development of a fibrous area, and loss of function. Various human conditions show a typical unresolved inflammatory profile. Inflammatory diseases include cancer, neurodegenerative disease, asthma, right heart disease, atherosclerosis, myocardial infarction, or atrial fibrillation. New evidence has started to emerge on the role, including pro-resolution involvement of chemical mediators in the acute phase of inflammation. Although flourishing knowledge is available about the role of specialized pro-resolving mediators in neurodegenerative diseases, atherosclerosis, obesity, or hepatic fibrosis, little is known about their efficacy to combat inflammation-associated arrhythmogenic cardiac disorders. It has been shown that resolvins, including RvD1, RvE1, or Mar1, are bioactive mediators of resolution. Resolvins can stop neutrophil activation and infiltration, stimulate monocytes polarization into anti-inflammatory-M2-macrophages, and activate macrophage phagocytosis of inflammation-debris and neutrophils to promote efferocytosis and clearance. This review aims to discuss the paradigm of failed-resolution mechanisms (FRM) potentially promoting arrhythmogenicity in right heart disease-induced inflammatory status.

Association of Premature Ventricular Contraction Burden on Serial Holter Monitoring With Arrhythmic Risk in Patients With Arrhythmogenic Right Ventricular Cardiomyopathy

IMPORTANCE

A high burden of premature ventricular contractions (PVCs) at disease diagnosis has been associated with an overall higher risk of ventricular arrhythmias in arrhythmogenic right ventricular cardiomyopathy (ARVC). Data regarding dynamic modification of PVC burden at follow-up with Holter monitoring and its impact on arrhythmic risk in ARVC are scarce.

OBJECTIVE

To describe changes in the PVC burden and to assess whether serial Holter monitoring is dynamically associated with sustained ventricular arrhythmias during follow-up in patients with ARVC.

DESIGN, SETTINGS, AND PARTICIPANTS

In this cohort study, patients with a definite ARVC diagnosis, available Holter monitoring results at disease diagnosis, and at least 2 additional results of Holter monitoring during follow-up were enrolled from 6 ARVC registries in North America and Europe. Data were collected from June 1 to September 15, 2021.

MAIN OUTCOMES AND MEASURES

The association between prespecified variables retrieved at each Holter monitoring follow-up (ie, overall PVC burden; presence of sudden PVC spikes, defined as absolute increase in PVC burden ≥5000 per 24 hours or a relative ≥75% increase, with an absolute increase of ≥1000 PVCs; presence of nonsustained ventricular tachycardia [NSVT]; and use of β-blockers and class III antiarrhythmic drugs) and sustained ventricular arrhythmias occurring within 12 months after that Holter examination was assessed using a mixed logistical model.

RESULTS

In 169 enrolled patients with ARVC (mean [SD] age, 36.3 [15.0] years; 95 men [56.2%]), a total of 723 Holter examinations (median, 4 [IQR, 4-5] per patient) were performed during a median follow-up of 54 (IQR, 42-63) months and detected 75 PVC spikes and 67 sustained ventricular arrhythmias. The PVC burden decreased significantly from the first to the second Holter examination (mean, 2906 [95% CI, 1581-4231] PVCs per 24 hours; P < .001). A model including 24-hour PVC burden (odds ratio [OR] 1.50 [95% CI, 1.10-2.03]; P = .01), PVC spikes (OR, 6.20 [95 CI, 2.74-13.99]; P < .001), and NSVT (OR, 2.29 [95% CI, 1.10-4.51]; P = .03) at each follow-up Holter examination was associated with sustained ventricular arrhythmia occurrence in the following 12 months.

CONCLUSIONS AND RELEVANCE

These findings suggest that in patients with ARVC, changes in parameters derived from each Holter examination performed during follow-up are associated with the risk of sustained ventricular arrhythmias within 12 months of disease diagnosis.

Arrhythmogenic Right Ventricular Cardiomyopathy and Differential Diagnosis with Diseases Mimicking Its Phenotypes

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease, which is characterized by fibro-fatty replacement of predominantly the right ventricle (RV). The disease can result in ventricular tachyarrhythmias and sudden cardiac death. Our understanding of the pathophysiology and clinical expressivity of ARVC has been continuously evolving. The diagnosis can be challenging due to its variable expressivity, incomplete penetrance and the lack of specific diagnostic criteria. Idiopathic RV outflow tract tachycardia, Brugada Syndrome, athlete’s heart, dilated cardiomyopathy, myocarditis, cardiac sarcoidosis, congenital aneurysms and diverticula may mimic clinical phenotypes of ARVC. This review aims to provide an update on the differential diagnosis of ARVC.

THE KEY-STONES OF RIGHT VENTRICULAR ARRHYTHMOGENIC CARDIOMYOPATHY-INDUCED MORPHOLOGICAL DISARRANGEMENT

Arrhythmogenic right ventricular cardiomyopathy is an urgent problem of modern cardiology. This myocardial remodeling manifests various desmosomopathies, channelopathies, and other mutations resulting in a violation of the coordinated heart work, particularly the myocardium. The incidence of this cardiomyopathy is not significant. Still, it is worth noting that athletes are at an increased risk of developing this disease, emphasizing the importance of studying this topic and its relevance from cardiologists and sports physicians. Moreover, the clinical pattern of this disease is heterogeneous. This pathology requires strengthening control and attention of medical personnel and constant improvement and optimization of diagnostic methods and treatment protocols. In this article, the pathophysiological mechanisms, molecular genetic aspects, and the dynamics of morphofunctional changes are represented in detail. Understanding the mechanisms of etiopathogenesis and the features of morphological changes observed in this cardiomyopathy and its more detailed study is fundamental in developing modern treatment methods to improve patients' quality and life expectancy.

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.

Desmosomes: emerging pathways and non-canonical functions in cardiac arrhythmias and disease

Desmosomes are critical adhesion structures in cardiomyocytes, with mutation/loss linked to the heritable cardiac disease, arrhythmogenic right ventricular cardiomyopathy (ARVC). Early studies revealed the ability of desmosomal protein loss to trigger ARVC disease features including structural remodeling, arrhythmias, and inflammation; however, the precise mechanisms contributing to diverse disease presentations are not fully understood. Recent mechanistic studies demonstrated the protein degradation component CSN6 is a resident cardiac desmosomal protein which selectively restricts cardiomyocyte desmosomal degradation and disease. This suggests defects in protein degradation can trigger the structural remodeling underlying ARVC. Additionally, a subset of ARVC-related mutations show enhanced vulnerability to calpain-mediated degradation, further supporting the relevance of these mechanisms in disease. Desmosomal gene mutations/loss has been shown to impact arrhythmogenic pathways in the absence of structural disease within ARVC patients and model systems. Studies have shown the involvement of connexins, calcium handling machinery, and sodium channels as early drivers of arrhythmias, suggesting these may be distinct pathways regulating electrical function from the desmosome. Emerging evidence has suggested inflammation may be an early mechanism in disease pathogenesis, as clinical reports have shown an overlap between myocarditis and ARVC. Recent studies focus on the association between desmosomal mutations/loss and inflammatory processes including autoantibodies and signaling pathways as a way to understand the involvement of inflammation in ARVC pathogenesis. A specific focus will be to dissect ongoing fields of investigation to highlight diverse pathogenic pathways associated with desmosomal mutations/loss.

Clinical characteristics and risk stratification of desmoplakin cardiomyopathy

Aims

Desmoplakin (DSP) cardiomyopathy is an increasingly recognized form of arrhythmogenic cardiomyopathy. With a genotype-specific approach, we characterized the diagnosis, natural history, and risk for ventricular arrhythmia and heart failure in DSP cardiomyopathy.

Methods and results

We followed 91 individuals [45 probands, 34% male, median age 27.5 years (interquartile interval 20.0–43.9)] with pathogenic or likely pathogenic DSP variants for a median of 4.3 years. Regarding the ventricular involvement, left predominance was most common (n = 22, 28%) followed by bi-ventricular in 12 (15%) and right predominance in 5 (6%). Myocardial injury (chest pain, elevated troponin, normal coronary angiogram) occurred in 20 (22%) individuals. Incidence rates of sustained ventricular arrhythmia and heart failure (ventricular dysfunction ± symptoms) were 5.9 [95% confidence interval (CI): 3.9–9.1] and 6.7 (95% CI: 4.5–9.8) per 100 person-years, respectively. In univariate regression, myocardial injury was associated with sustained ventricular arrhythmia [hazard ratio (HR) 2.53, 95% CI: 1.05–6.11] and heart failure (HR 7.53, 95% CI: 3.10–18.26). After adjustment, left ventricular ejection fraction <35% and right ventricular dysfunction were prognostic for sustained ventricular arrhythmia while proband status and myocardial injury were prognostic for heart failure (all P < 0.05). The sensitivity of the arrhythmogenic right ventricular cardiomyopathy Task Force Criteria in diagnosing left dominant disease was 0.73; 5/22 (23%) of patients with sustained ventricular arrhythmias did not meet these criteria.

Conclusion

DSP cardiomyopathy affects both ventricles and carries high risk for ventricular arrhythmia and heart failure. Myocardial injury is associated with worse disease outcomes. Both diagnosis and risk stratification of DSP cardiomyopathy need refinement.

Desmoplakin cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy: two distinct forms of cardiomyopathy?

The confirmation of a hypothesis that desmoplakin-related (DSP) cardiomyopathy could represent a distinct clinical entity from the classical, RV-dominant, form of arrhythmogenic cardiomyopathy (ACM), most frequently caused by PKP2 mutations, would without any shadow of doubt signify a turning point in the history of this disease. The concept of gene-specific diseases underneath the umbrella diagnosis of ACM would bring fundamental changes not only in the clinical, diagnostic and therapeutic approach, but also in terms of risk stratification, pushing the scientific community towards a more patient-centred view of the disease, similarly to what has already been done in other inherited arrhythmogenic disease (e.g., Long QT Syndrome; LQTS). We provide a state-of-the-art review, starting with a brief historical framework to give the necessary context and better focus the question. Then, we proceed with a novel, genotype-tophenotype-based comparison of the most important aspects of DSP-related cardiomyopathy with the classical, RV-dominant ACM: this allows us to ascertain not only that the differences between the forms exist, but are also clinically relevant and actionable, leading to the underrecognition of the atypical, DSP-related, LV-dominant forms when applying the current diagnostic criteria. These findings will usher an exciting era, in which the scientific community will try to answer a range of questions, starting from the reasons why different desmosomal mutations cause such different phenotypes.

Anatomical-MRI Correlations in Adults and Children with Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare disease in which the right ventricular myocardium is replaced by islands of fibro-adipose tissue. Therefore, ventricular re-entry circuits can occur, predisposing the patient to ventricular tachyarrhythmias, as well as dilation of the right ventricle that eventually leads to heart failure. Although it is a rare disease with low prevalence in Europe and the United States, many patients are addressed disproportionately for cardiac magnetic resonance imaging (MRI). The most severe consequence of this condition is sudden cardiac death at a young age due to untreated cardiac arrhythmias. The purpose of this paper is to revise the magnetic resonance characteristics of ARVC, including the segmental contraction abnormalities, fatty tissue replacement, decrease of the ejection fraction, and the global RV dilation. Herein, we also present several recent improvements of the 2010 Task Force criteria that are not included within the ARVC diagnosis guidelines. In our opinion, these features will be considered in a future Task Force Consensus.

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.

Arrhythmogenic Left Ventricular Cardiomyopathy: Genotype-Phenotype Correlations and New Diagnostic Criteria

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart muscle disease characterized by loss of ventricular myocardium and fibrofatty replacement, which predisposes to scar-related ventricular arrhythmias and sudden cardiac death, particularly in the young and athletes. Although in its original description the disease was characterized by an exclusive or at least predominant right ventricle (RV) involvement, it has been demonstrated that the fibrofatty scar can also localize in the left ventricle (LV), with the LV lesion that can equalize or even overcome that of the RV. While the right-dominant form is typically associated with mutations in genes encoding for desmosomal proteins, other (non-desmosomal) mutations have been showed to cause the biventricular and left-dominant variants. This has led to a critical evaluation of the 2010 International Task Force criteria, which exclusively addressed the right phenotypic manifestations of ACM. An International Expert consensus document has been recently developed to provide upgraded criteria (“the Padua Criteria”) for the diagnosis of the whole spectrum of ACM phenotypes, particularly left-dominant forms, highlighting the use of cardiac magnetic resonance. This review aims to offer an overview of the current knowledge on the genetic basis, the phenotypic expressions, and the diagnosis of left-sided variants, both biventricular and left-dominant, of ACM.

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

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