Arrhythmogenic right ventricular cardiomyopathy a still underrecognized clinic entity. Trends Cardiovasc Med. 1997;7:84-90. [PMID: 21235869 DOI: 10.1016/s1050-1738(97)00011-x]

Concealed cardiomyopathy as an emerging cause of sudden cardiac arrest and sudden cardiac death

The inherited cardiomyopathies exhibit a broad spectrum of disease, with some patients remaining asymptomatic throughout life, while, for others, the first symptom of disease is sudden cardiac death at a young age. The risk of malignant ventricular arrhythmia in these conditions has traditionally been linked to the degree of structural myocardial abnormalities and functional impairment. However, recent advances in genetic testing and knowledge of the genetic basis of the diseases have led to the identification of concealed cardiomyopathy, in which sudden cardiac arrest or sudden cardiac death occurs in the absence of observable clinical features of cardiomyopathy, with a diagnosis being made only after the identification of a causative genetic variant. Increased awareness of concealed cardiomyopathy, a better understanding of mechanisms of arrhythmia and identification of risk modulators will be vital to improve care for families with concealed cardiomyopathy.

Cardiovascular Involvement in Pediatric FLNC Variants: A Case Series of Fourteen Patients

Filamin C is a protein specifically expressed in myocytes and cardiomyocytes and is involved in several biological functions, including sarcomere contractile activity, signaling, cellular adhesion, and repair. FLNC variants are associated with different disorders ranging from striated muscle (myofibrillar distal or proximal) myopathy to cardiomyopathies (CMPs) (restrictive, hypertrophic, and dilated), or both. The outcome depends on functional consequences of the detected variants, which result either in FLNC haploinsufficiency or in an aberrant protein, the latter affecting sarcomere structure leading to protein aggregates. Cardiac manifestations of filaminopathies are most often described as adult onset CMPs and limited reports are available in children or on other cardiac spectrums (congenital heart defects-CHDs, or arrhythmias). Here we report on 13 variants in 14 children (2.8%) out of 500 pediatric patients with early-onset different cardiac features ranging from CMP to arrhythmias and CHDs. In one patient, we identified a deletion encompassing FLNC detected by microarray, which was overlooked by next generation sequencing. We established a potential genotype-phenotype correlation of the p.Ala1186Val variant in severe and early-onset restrictive cardiomyopathy (RCM) associated with a limb-girdle defect (two new patients in addition to the five reported in the literature). Moreover, in three patients (21%), we identified a relatively frequent finding of long QT syndrome (LQTS) associated with RCM (n = 2) and a hypertrabeculated left ventricle (n = 1). RCM and LQTS in children might represent a specific red flag for FLNC variants. Further studies are warranted in pediatric cohorts to delineate potential expanding phenotypes related to FLNC.

A novel murine model for arrhythmogenic cardiomyopathy points to a pathogenic role of Wnt signalling and miRNA dysregulation

AIMS

Arrhythmogenic cardiomyopathy (AC) is one of the most common inherited cardiomyopathies, characterized by progressive fibro-fatty replacement in the myocardium. Clinically, AC manifests itself with ventricular arrhythmias, syncope, and sudden death and shows wide inter- and intra-familial variability. Among the causative genes identified so far, those encoding for the desmosomal proteins plakophilin-2 (PKP2), desmoplakin (DSP), and desmoglein-2 (DSG2) are the most commonly mutated. So far, little is known about the molecular mechanism(s) behind such a varied spectrum of phenotypes, although it has been shown that the causative mutations not only lead to structural abnormalities but also affect the miRNA profiling of cardiac tissue. Here, we aimed at studying the pathogenic effects of a nonsense mutation of the desmoglein-2 gene, both at the structural level and in terms of miRNA expression pattern.

METHODS AND RESULTS

We generated transgenic mice with cardiomyocyte-specific overexpression of a FLAG-tagged human desmoglein-2 harbouring the Q558* nonsense mutation found in an AC patient. The hearts of these mice showed signs of fibrosis, decrease in desmosomal size and number, and reduction of the Wnt/β-catenin signalling. Genome-wide RNA-Seq performed in Tg-hQ hearts and non-transgenic hearts revealed that 24 miRNAs were dysregulated in transgenic animals. Further bioinformatic analyses for selected miRNAs suggested that miR-217-5p, miR-499-5p, and miR-708-5p might be involved in the pathogenesis of the disease.

CONCLUSION

Down-regulation of the canonical Wnt/β-catenin signalling might be considered a common key event in the AC pathogenesis. We identified the miRNA signature in AC hearts, with miR-708-5p and miR-217-5p being the most up-regulated and miR-499-5p the most down-regulated miRNAs. All of them were predicted to be involved in the regulation of the Wnt/β-catenin pathway and might reveal the potential pathophysiology mechanisms of AC, as well as be useful as therapeutic targets for the disease.

Bradyarrhythmias in Arrhythmogenic Right Ventricular Cardiomyopathy

Less is known about bradyarrhythmias in arrhythmogenic right ventricular cardiomyopathy (ARVC). This cross-sectional study aimed to assess the prevalence and clinical significance of bradyarrhythmias in ARVC. From May 1995 to December 2017, bradyarrhythmias including sick sinus syndrome, atrioventricular block, and intraventricular conductional block (ICB) were investigated in 522 ARVC patients. A total of 169 patients (32.4%) presented with bradyarrhythmias including sick sinus syndrome in18 (3.5%), atrioventricular block in 56 (10.7%), and ICB in 118 patients (22.6%). Multivariate analysis showed right atrial dilation increased the risk of bradyarrhythmias (odds ratio [OR] 1.641, 95% confidence interval [CI] 1.081 to 2.492, p= 0.020). Bradyarrhythmias were not associated with death and heart transplantation. In patients with bradyarrhythmias, female gender, left atrial diameter >40 mm, and New York Heart Association Ⅲ/Ⅳ increased the risk of death and heart transplantation (hazards ratio [HR] = 2.790, 95% CI 1.220 to 6.377, p = 0.015; HR = 4.913, 95% CI 2.058 to 11.730, p <0.001; HR = 3.223, 95% CI 1.246 to 8.340, p = 0.016). Among the 23 patients who underwent device implantation, left atrial diameter >40mm was associated with death and heart transplantation (HR = 9.523, 95% CI 1.587 to 57.126, p = 0.014). In conclusion, bradyarrhythmias were commonly seen in ARVC, and ICB was the most common type. Female, left atrial diameter >40 mm, and NYHA class were associated with death and heart transplantation.

When signalling goes wrong: pathogenic variants in structural and signalling proteins causing cardiomyopathies

Cardiomyopathies are a diverse group of cardiac disorders with distinct phenotypes, depending on the proteins and pathways affected. A substantial proportion of cardiomyopathies are inherited and those will be the focus of this review article. With the wide application of high-throughput sequencing in the practice of clinical genetics, the roles of novel genes in cardiomyopathies are recognised. Here, we focus on a subgroup of cardiomyopathy genes [TTN, FHL1, CSRP3, FLNC and PLN, coding for Titin, Four and a Half LIM domain 1, Muscle LIM Protein, Filamin C and Phospholamban, respectively], which, despite their diverse biological functions, all have important signalling functions in the heart, suggesting that disturbances in signalling networks can contribute to cardiomyopathies.

Arrhythmogenic right-ventricular cardiomyopathy: molecular genetics into clinical practice in the era of next generation sequencing

Sudden death, ventricular arrhythmia and heart failure are common features in arrhythmogenic right-ventricular cardiomyopathy (ARVC), an inheritable heart muscle disease, characterized by clinical and genetic heterogeneity. So far, 13 disease genes have been identified, responsible for around 60% of all ARVC cases. In this review, we summarize the main clinical and pathological aspects of ARVC, focusing on the importance of the genetic testing and the application of the new sequencing techniques referred to next generation sequencing technology.

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.

Arrhythmogenic right ventricular cardiomyopathy in pregnancy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is predominantly a genetically determined heart muscle disorder that is characterized by fibro-fatty replacement of the right ventricular (RV) myocardium.(1)) The clinical spectrum of ARVC may represent from asymptomatic premature ventricular complexes to ventricular tachycardia (VT) and sudden cardiac death (SCD). It is a well-known leading cause of SCD in young adults.(2,3))There is no general consensus on the management of ARVC in pregnancy, and the preferred mode of delivery is uncertain. Herein, we report a case of ARVC diagnosed at 20 weeks of gestation following a sustained VT and treated with an implantable cardiac defibrillator (ICD). We also reviewed the current knowledge and approach to ARVC in pregnancy since the literature on this condition is based on case reports.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC/D): A Systematic Literature Review

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a genetic form of cardiomyopathy (CM) usually transmitted with an autosomal dominant pattern. It primary affects the right ventricle (RV), but may involve the left ventricle (LV) and culminate in biventricular heart failure (HF), life threatening ventricular arrhythmias and sudden cardiac death (SCD). It accounts for 11%-22% of cases of SCD in the young athlete population. Pathologically is characterized by myocardial atrophy, fibrofatty replacement and chamber dilation. Diagnosis is often difficult due to the nonspecific nature of the disease and the broad spectrum of phenotypic variations. Therefore consensus diagnostic criteria have been developed and combined electrocardiography, echocardiography, cardiac magnetic resonance imaging (CMRI) and myocardial biopsy. Early detection, family screening and risk stratification are the cornerstones in the diagnostic evaluation. Implantable cardioverter-defibrillator (ICD) implantation, ablative procedures and heart transplantation are currently the main therapeutic options.

Sudden cardiac death due to arrhythmogenic right ventricular cardiomyopathy and cystic tumor of the AV node

An 18-year-old white male collapsed suddenly in his home and died. At autopsy, the right ventricle of the decedent was noted to be dilated with marked thinning of the wall focally. Microscopically, the myocardium of the right ventricle was noted to be significantly thinned focally, where transmural infiltration with fibroadipose tissue was noted. Depending on the criteria utilized to render such a diagnosis, these findings were consistent with arrhythmogenic right ventricular cardiomyopathy (ARVC). Subsequent microscopic examination of the SA and AV node, however, revealed the presence of a cystic tumor of the AV node (CTAVN), a known cause of sudden death from arrhythmia. The case represents the first reported case of ARVC and CTAVN occurring together in the same individual.

Functional effects of the TMEM43 Ser358Leu mutation in the pathogenesis of arrhythmogenic right ventricular cardiomyopathy

Background

The Ser358Leu mutation in TMEM43, encoding an inner nuclear membrane protein, has been implicated in arrhythmogenic right ventricular cardiomyopathy (ARVC). The pathogenetic mechanisms of this mutation are poorly understood.

Methods

To determine the frequency of TMEM43 mutations as a cause of ARVC, we screened 11 ARVC families for mutations in TMEM43 and five desmosomal genes previously implicated in the disease. Functional studies were performed in COS-7 cells transfected with wildtype, mutant, and 1:2 wildtype:mutant TMEM43 to determine the effect of the Ser358Leu mutation on the stability and cellular localization of TMEM43 and other nuclear envelope and desmosomal proteins, assessed by solubility assays and immunofluorescence imaging. mRNA expression was assessed of genes potentially affected by dysfunction of the nuclear lamina.

Results

Three novel mutations in previously documented desmosomal genes, but no mutations in TMEM43, were identified. COS-7 cells transfected with mutant TMEM43 exhibited no change in desmosomal stability. Stability and nuclear membrane localization of mutant TMEM43 and of lamin B and emerin were normal. Mutant TMEM43 did not alter the expression of genes located on chromosome 13, previously implicated in nuclear envelope protein mutations leading to skeletal muscular dystrophies.

Conclusions

Mutant TMEM43 exhibits normal cellular localization and does not disrupt integrity and localization of other nuclear envelope and desmosomal proteins. The pathogenetic role of TMEM43 mutations in ARVC remains uncertain.

Arrhythmogenic right ventricular cardiomyopathy: a survey of the investigations at the University of Padua

The purpose of this paper is to review the history of the clinico-pathologic investigations performed at the University of Padua on an old morbid entity ("parchment heart"), which, in the 1960s, led to the clinical description of the disease, in the 1980s to the revival of the scientific interest, and in the mid 1990s to the understanding of the genetic background. All the steps of the progressive knowledge are reviewed: necropsy of young people who died suddenly, in vivo diagnosis by ECG, echocardiography, angiocardiography, endomyocardial biopsy, nuclear magnetic resonance, and diagnostic criteria. Familial occurrence with autosomic dominant transmission and various penetrance was documented. Gene defects were recently mapped both to chromosome 14q23-q24 and 1q42-q43, thus providing evidence for genetic heterogeneity. The pathologic substrates of arrhythmogenic right ventricular cardiomyopathy pointed to an acquired progressive myocardial atrophy with fibro-fatty replacement of dying myocytes. Nowadays the disease is definitively regarded as a primary myocardial disorder and it has been included in the revised WHO classification of cardiomyopathies.

Insect ryanodine receptors: molecular targets for novel pest control chemicals

Ryanodine receptors (RyRs) are a distinct class of ligand-gated calcium channels controlling the release of calcium from intracellular stores. They are located on the sarcoplasmic reticulum of muscle and the endoplasmic reticulum of neurons and many other cell types. Ryanodine, a plant alkaloid and an important ligand used to characterize and purify the receptor, has served as a natural botanical insecticide, but attempts to generate synthetic commercial analogues of ryanodine have proved unsuccessful. Recently two classes of synthetic chemicals have emerged resulting in commercial insecticides that target insect RyRs. The phthalic acid diamide class has yielded flubendiamide, the first synthetic ryanodine receptor insecticide to be commercialized. Shortly after the discovery of the phthalic diamides, the anthranilic diamides were discovered. This class has produced the insecticides Rynaxypyr and Cyazypyr. Here we review the structure and functions of insect RyRs and address the modes of action of phthalic acid diamides and anthranilic diamides on insect ryanodine receptors. Particularly intersting is the inherent selectivity both chemical classes exhibit for insect RyRs over their mammalian counterparts. The future prospects for RyRs as a commercially-validated target site for insect control chemicals are also considered.

Arrhythmogenic right ventricular cardiomyopathy in athletes: diagnosis, management, and recommendations for sport activity

This article examines the role of arrhythmogenic right ventricular cardiomyopathy/dysplasia in causing sudden death in young competitive athletes and suggests a prevention strategy based on identification of affected athletes at preparticipation screening. Systematic cardiovascular screening (including 12-lead ECG) of all subjects embarking on sports activity has the potential to identify those athletes at risk and to reduce mortality.

Molecular cardiology and genetics in the 21st century--a primer

The terminology and technology of molecular genetics and recombinant DNA have become an essential part of academic cardiology and will soon be applied at the bedside. The treatise includes a brief summary of the essentials of the DNA molecule, the more common techniques, and their application to genetics and molecular cardiology. It is written to be understood by physicians, scientists, and paramedical personnel who would not necessarily have a background in molecular biology. Inherent in the DNA molecule are three properties fundamental to all of the diagnostic and therapeutic applications, namely, the ability of DNA to separate into single strands, recombine (annealment or hybridization), and the presence of the negative charge enables DNA fragments to be separated easily by electrophoresis. Genetic linkage analysis of a family with an inherited disease enables one to identify the gene without knowing its protein product. Over 50 diseases in cardiology due to single-gene disorders have been identified and multiple mutations have been detected. The new therapeutic frontier will be stem cells and nuclear transfer. Identification of genes responsible for coronary artery disease made possible by genome-wide single nucleotide polymorphism (SNP) mapping techniques paves the way for personalized medicine.

Differentiating arrhythmogenic right ventricular cardiomyopathy from right ventricular outflow tract ventricular tachycardia using multilead QRS duration and axis

BACKGROUND

Ventricular tachycardia (VT) resulting from arrhythmogenic right ventricular cardiomyopathy (ARVC) may be difficult to differentiate from idiopathic right ventricular outflow tract (RVOT) VT.

OBJECTIVES

The purpose of this study was to investigate the hypothesis that QRS characteristics would be different in ARVC because of altered conduction through abnormal myocardium.

METHODS

In 24 RVOT VT patients (18 women and 6 men; age 42 +/- 10 years) and 20 ARVC patients (12 women and 8 men; age 38 +/- 14 years), mean QRS duration, frontal plane axis, and precordial R-wave transition were measured in 12-lead ECGs recorded during VT.

RESULTS

Mean QRS duration was longer in all 12 leads in ARVC patients. A significant difference was noted in leads I, III, aVL, aVF, V(1), V(2), and V(3) (P <.05). Leads I and aVL had the largest mean difference between ARVC and RVOT VT patients of 17.6 +/- 4.7 ms and 15.8 +/- 7.5 ms, respectively (P <.0001). Lead I QRS duration > or =120 ms had a sensitivity of 100%, specificity 46%, positive predictive value 61%, and negative predictive value 100% for ARVC. The area under the receiver operating characteristic (ROC) curve was 0.89. The addition of mean QRS axis <30 degrees (R<S in lead III) to the above criterion increased specificity for ARVC to 100%. QRS duration remained sensitive and specific in the subgroup of nine ARVC ECGs with an inferior axis (ROC area 0.82). R-wave transition was not different between groups.

CONCLUSION

QRS duration is longer in ARVC compared with RVOT VT. An algorithm combining lead I QRS duration for sensitivity and axis for specificity is useful for differentiating the two tachycardia substrates.

Improved delineation of morphological features of arrhythmogenic right ventricular cardiomyopathy with the use of contrast-enhanced echocardiography

A case of an already diagnosed arrhythmogenic right ventricular cardiomyopathy in which the use of contrast improved the echocardiographic characterization of morphologic abnormalities of the right ventricle is reported.

Molecular genetics of sudden cardiac death in small animals - a review

Sudden cardiac death in small animals is uncommon but often occurs due to cardiac conduction defects or myocardial diseases. Primary cardiac conduction defects are mainly caused by mutations in genes involved in impulse conduction processes (e.g., gap-junction genes and transcription factors) or repolarisation processes (e.g., ion-channel genes), whereas primary cardiomyopathies are mainly caused by defective force generation or force transmission due to gene mutations in either sarcomeric or cytoskeleton proteins. Although over 50 genes have been identified in humans directly or indirectly related to sudden cardiac death, no genetic aetiologies have been identified in small animals. Sudden cardiac deaths have been also reported in German Shepherds and Boxers. A better understanding of molecular genetic aetiologies for sudden cardiac death will be required for future study toward unveiling aetiology in sudden cardiac death in small animals.

Arrhythmogenic right ventricular cardiomyopathy type 6 (ARVC6): support for the locus assignment, narrowing of the critical region and mutation screening of three candidate genes

Background

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a heritable disorder characterized by progressive degeneration of right ventricular myocardium, arrhythmias and an increased risk of sudden death at a young age. By linkage analysis, ARVC type 6 was previously mapped to a 10.6 cM region on chromosome 10p12-p14 in a large North American kindred. To date, the genetic defect that causes ARVC6 has not been identified.

Methods

We identified a South African family of 13 members with ARVC segregating as an autosomal dominant disorder. The diagnosis of ARVC was based on international diagnostic criteria. All available family members were genotyped with microsatellite markers at six known ARVC loci, and positional candidate gene screening was performed.

Results

Genetic linkage and haplotype analysis provided lod scores that are highly suggestive of linkage to the ARVC6 locus on chromosome 10p12-p14, and the narrowing of the critical region to ~2.9 Mb. Two positional candidate genes (ITG8 and FRMD4A) were screened in which defects could possibly disrupt cell-cell adhesion. A non-positional candidate gene with apoptosis inducing properties, LAMR1P6 (laminin receptor 1 pseudogene 6) was also screened. Direct sequencing of DNA from affected individuals failed to detect disease-causing mutations in the exonic sequences of the three genes investigated.

Conclusion

The narrowing of the ARVC6 critical region may facilitate progress towards the identification of the gene that is involved in ARVC. Identification of the causative genes for ARVC will contribute to the understanding of the pathogenesis and management of this poorly understood condition.

The impact of implantable cardioverter-defibrillator therapy on survival in autosomal-dominant arrhythmogenic right ventricular cardiomyopathy (ARVD5)

OBJECTIVES

We sought to determine the impact of implantable cardioverter-defibrillator (ICD) therapy in patients with familial arrhythmogenic right ventricular cardiomyopathy (ARVC).

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy is a cause of sudden cardiac death, which may be prevented by ICD.

METHODS

We studied 11 families in which a 3p25 deoxyribonucleic acid (DNA) haplotype at locus ARVD5 segregated with disease and compared mortality in subjects who received an ICD with that in control subjects who were matched for age, gender, ARVC status, and family. Subjects (n = 367) at 50% a priori risk of inheriting ARVC were classified as high risk (HR) (n = 197), low risk (n = 92), or unknown (n = 78) on the basis of clinical events, DNA haplotyping, and/or pedigree position. Forty-eight HR subjects (30 males, [median age 32 years] and 18 females [median age 41 years]) were followed after ICD (secondary to ventricular tachycardia [VT] in 27%). Survival was compared with 58 HR control subjects who were alive at the same age to-the-day at which the ICD subject received the device.

RESULTS

In the HR group, 50% of males were dead by 39 years and females by 71 years: relative risk of death was 5.1 (95% confidence interval 3 to 8.5) for males. The five-year mortality rate after ICD in males was zero compared with 28% in control subjects (p = 0.009). Within five years, the ICD fired for VT in 70% and for VT >240 beats/min in 30%, with no difference in discharge rate when analyzed by ICD indication.

CONCLUSIONS

The unknown mutation at the ARVD5 locus causing ARVC results in high mortality. Risk stratification using genetic haplotyping and ICD therapy produced improved survival for males.

Use of signal-averaged electrocardiography in the evaluation of arrhythmogenic right ventricular cardiomyopathy in Boxers

OBJECTIVE

To assess signal-averaged electrocardiography (SAECG) for evaluation of Boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC) and identify dogs at risk for sudden death (SD) or death related to congestive heart failure (CHF).

DESIGN

Prospective study.

ANIMALS

94 Boxers with ARVC and 49 clinically normal non-Boxers (controls).

PROCEDURE

Boxers were screened for ARVC, and severity was estimated by use of echocardiography, 24-hour ambulatory ECG, and SAECG. Statistical evaluation was performed to identify significant differences in SAECG variables relative to clinical outcome, frequency of ventricular arrhythmias, and systolic function. Sensitivity, specificity, and positive and negative predictive values were evaluated for each SAECG variable for occurrence of SD or death related to CHF. Late potentials were also evaluated as a predictor of cardiac-related death.

RESULTS

Differences were detected in SAECG variables on the basis of clinical outcome, systolic function, and frequency of ventricular arrhythmias. More severely affected dogs had significantly more abnormal SAECG findings. The presence of late potentials, defined as 2 abnormal root mean square values (of 4), was associated with high sensitivity, specificity, and negative predictive value for cardiac-related SD or death secondary to CHF CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that SAECG is a useful noninvasive diagnostic test to evaluate dogs affected with ARVC and identify individuals at risk for cardiac-related death.

Molecular genetic basis of sudden cardiac death

This article outlines the up-to-date understanding of the molecular basis of disorders that cause sudden death. Several arrhythmic disorders that cause sudden death have been well-described at the molecular level, including the long QT syndromes and Brugada syndrome; this article reviews the current scientific knowledge of these diseases. Hypertrophic cardiomyopathy, a myocardial disorder that causes sudden death also has been well-studied. Finally, a disorder in which myocardial abnormalities and rhythm abnormalities coexist, arrhythmogenic right ventricular dysplasia, is described.

Causes of sudden cardiac death in young Australians

OBJECTIVES

To determine the causes of sudden cardiac death in people aged 35 years or younger.

DESIGN AND SETTING

A review of all autopsies performed between 1 January 1994 and 31 December 2002 at a major Sydney forensic medicine department serving an area with over 2 million people.

MAIN OUTCOME MEASURES

Incidence of various types of cardiac disease causing sudden death in those aged <or= 35 years; proportion of deaths in which no cause was found at autopsy.

RESULTS

There were 10 199 autopsies performed during the study period. Of these, 2986 (29.2%) deaths occurred in people aged <or= 35 years; 193 were classified as sudden cardiac deaths. The cause of sudden death in this group was not established in 60 (31%), and was presumed to be due to primary arrhythmogenic disorders. Coronary artery disease occurred in 46 (24%), hypertrophic cardiomyopathy/unexplained left ventricular hypertrophy in 29 (15%), and myocarditis in 23 (12%).

CONCLUSIONS

Unexplained deaths, presumed to result from sudden primary arrhythmogenic causes, occur in young Australians with structurally normal hearts. That underlying disease-causing genetic defects may be involved has clinical implications for family members.

Lamr1 functional retroposon causes right ventricular dysplasia in mice

Arrhythmogenic right ventricular dysplasia (ARVD) is a hereditary cardiomyopathy that causes sudden death in the young. We found a line of mice with inherited right ventricular dysplasia (RVD) caused by a mutation of the gene laminin receptor 1 (Lamr1). This locus contained an intron-processed retroposon that was transcribed in the mice with RVD. Introduction of a mutated Lamr1 gene into normal mice by breeding or by direct injection caused susceptibility to RVD, which was similar to that seen in the RVD mice. An in vitro study of cardiomyocytes expressing the product of mutated Lamr1 showed early cell death accompanied by alteration of the chromatin architecture. We found that heterochromatin protein 1 (HP1) bound specifically to mutant LAMR1. HP1 is a dynamic regulator of heterochromatin sites, suggesting that mutant LAMR1 impairs a crucial process of transcriptional regulation. Indeed, mutant LAMR1 caused specific changes to gene expression in cardiomyocytes, as detected by gene chip analysis. Thus, we concluded that products of the Lamr1 retroposon interact with HP1 to cause degeneration of cardiomyocytes. This mechanism may also contribute to the etiology of human ARVD.

Circumstances of death and gross and microscopic observations in a series of 200 cases of sudden death associated with arrhythmogenic right ventricular cardiomyopathy and/or dysplasia

BACKGROUND

Sudden death is a possible consequence of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). Prevalence of ARVC/D in unexpected sudden cardiac death (USCD), however, remains imprecise, as do circumstances of death and ARVC/D-associated gross and microscopic findings, especially His bundle anomalies.

METHODS AND RESULTS

We reviewed 14 000 forensic autopsies required by judicial authorities from January 1980 to January 1999 in a 2 000 000-resident area. Age, gender, and circumstances of death were recorded. Hearts were examined macroscopically and microscopically. In this series, the ARVC/D group accounted for 200 consecutive cases (10.4%) of USCD, including 108 males and 92 females (average age 32.5 and 34.5 years, respectively). Nearly one third of deaths occurred during the fourth decade of life. Circumstances of death were various, but 75.6% occurred during everyday life events (at home, 63.1%; in the street, 6.6%; or at work, 6.1%); only 7 cases (3.5%) occurred during sports activity. Nineteen cases (9.5%) happened during the perioperative period. Adipose infiltration of the right ventricle was either isolated (20%) or associated with fibrosis (74.5%) and lymphocytes (5.5%). A total of 14.5% of cases had cardiac hypertrophy, assessed by an increase in heart weight and/or left ventricular wall thickness. In most cases, the His bundle and its branches were abnormal either because of infiltration of adipose tissue (8.1%), fibrosis (54.3%), or both (5.6%).

CONCLUSIONS

In ARVC/D, both sexes are equally affected, and there is a peak of risk during the fourth decade. Death most frequently occurs during sedentary activity. His abnormalities and left ventricular hypertrophy may be associated with ARVC/D.

Arrhythmogenic Right Ventricular Dysplasia in the Elderly

Arrhythmogenic right ventricular dysplasia (ARVD) is a form of cardiomyopathy characterized by fibrofatty infiltration of the right ventricle that leads to cardiac arrhythmias, usually sustained ventricular tachycardia or ventricular fibrillation. ARVD typically becomes recognized in young adults. The authors report a case of an octogenarian in whom third-degree atrioventricular block, low cardiac output syndrome, and failure to capture the pacer stimuli developed. ARVD was diagnosed at autopsy based on fibrofatty replacement of the right ventricle. To date, this case represents the oldest patient ever diagnosed with ARVD reported in the literature.

From the sarcomere to the nucleus: role of genetics and signaling in structural heart disease

The identification of genetic mutations underlying familial structural heart disease has provided exciting new insights into how alterations in structural components of the cardiomyocyte lead to different forms of cardiomyopathy. Specifically, mutations in components of the sarcomere are frequently associated with hypertrophic cardiomyopathy, whereas mutations in cytoskeletal proteins lead to dilated cardiomyopathy. In addition, extrinsic stresses such as hypertension and valvular disease can produce myocardial remodeling that is very similar to that observed in genetic cardiomyopathy. For myocardial remodeling to occur, changes in gene expression must occur; therefore, changes in contractile function or wall stress must be communicated to the nucleus via signal transduction pathways. The identity of these signaling pathways has become a key question in molecular biology. Numerous signaling molecules have been implicated in the development of hypertrophy and failure, including the beta-adrenergic receptor, G alpha(q) and downstream effectors, mitogen-activated protein kinase pathways, and the Ca(2+)-regulated phosphatase, calcineurin. In the past it has been difficult to discern which signaling molecules actually contributed to disease progression in vivo; however, the development of numerous transgenic and knockout mouse models of cardiomyopathy is now allowing the direct testing of stimulatory and inhibitory molecules in the mouse heart. From this work it has been possible to identify signaling molecules and pathways that are required for different aspects of disease progression in vivo. In particular, a number of signaling pathways have now been identified that may be key regulators of changes in myocardial structure and function in response to mutations in structural components of the cardiomyocyte. Myocardial structure and signal transduction are now merging into a common field of research that will lead to a more complete understanding of the molecular mechanisms that underly heart disease.

Molecular Mechanisms of Inherited Cardiomyopathies

Cardiomyopathies are diseases of heart muscle that may result from a diverse array of conditions that damage the heart and other organs and impair myocardial function, including infection, ischemia, and toxins. However, they may also occur as primary diseases restricted to striated muscle. Over the past decade, the importance of inherited gene defects in the pathogenesis of primary cardiomyopathies has been recognized, with mutations in some 18 genes having been identified as causing hypertrophic cardiomyopathy (HCM) and/or dilated cardiomyopathy (DCM). Defining the role of these genes in cardiac function and the mechanisms by which mutations in these genes lead to hypertrophy, dilation, and contractile failure are major goals of ongoing research. Pathophysiological mechanisms that have been implicated in HCM and DCM include the following: defective force generation, due to mutations in sarcomeric protein genes; defective force transmission, due to mutations in cytoskeletal protein genes; myocardial energy deficits, due to mutations in ATP regulatory protein genes; and abnormal Ca2+ homeostasis, due to altered availability of Ca2+ and altered myofibrillar Ca2+ sensitivity. Improved understanding that will result from these studies should ultimately lead to new approaches for the diagnosis, prognostic stratification, and treatment of patients with heart failure.

Molecular genetic basis of sudden cardiac death

In this review, the up-to-date understanding of the molecular basis of disorders causing sudden death will be described. Two arrhythmic disorders causing sudden death have recently been well described at the molecular level, the long QT syndromes (LQTS) and Brugada syndrome, and in this article we will review the current scientific knowledge of each disease. A third disorder, hypertrophic cardiomyopathy (HCM), a myocardial disorder causing sudden death, has also been well studied. Finally, a disorder in which both myocardial abnormalities and rhythm abnormalities coexist, arrhythmogenic right ventricular dysplasia (ARVD) will also be described. The role of the pathologist in these studies will be highlighted.

Genomic organization and isoform-specific tissue expression of human NAPOR (CUGBP2) as a candidate gene for familial arrhythmogenic right ventricular dysplasia

Neuroblastoma apoptosis-related RNA-binding protein (NAPOR; HGMW-approved symbol CUGBP2) is a newly discovered gene prominently induced during apoptosis, suggesting that it plays a role during apoptosis. We have found that it is encoded by a gene located on chromosome 10p13-p14 between Généthon markers D10S547 and D10S223, a region to which we have recently localized a gene responsible for arrhythmogenic right ventricular dysplasia (ARVD). To examine its possible role in the pathogenesis of ARVD, we determined the genomic organization of the human NAPOR gene including its exon-intron boundaries and the putative promoter sequence, which provide a plausible mechanism for its alternative mRNA splicing. We also demonstrated that three isoforms of the NAPOR transcript were differently expressed, with NAPOR-3 being nearly neuron specific while the other two forms were ubiquitously expressed. The expression of NAPOR is differentially regulated during development. Finally, we screened the members of the ARVD family for mutations and identified two DNA sequence variants in the protein-coding exons of NAPOR, neither of which was responsible for ARVD. While the function of NAPOR remains to be elucidated, our current characterization of the NAPOR gene will be valuable for further clinical and functional study.

Clinical diagnosis and management strategies in arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a myocardial disease, often familial, that is characterized by fibro-fatty replacement of the right ventricular (RV) myocardium. The most common clinical manifestations of ARVC consists of ventricular arrhythmias of RV origin, which may lead to sudden death mostly in young people and athletes, electrocardiograph depolarization/repolarization changes mostly localized to right precordial leads, and global and/or regional dysfunction and structural alterations of the RV. The diagnosis of ARVC may be difficult due to several problems with the specificity of the electrocardiograph abnormalities, the different potential etiologies of ventricular arrhythmias with a left bundle branch morphology, the assessment of the RV structure and function, and the interpretation of endomyocardial biopsy findings. Therefore, standardized diagnostic criteria have been proposed by the Study Group on ARVC of the European Society of Cardiology. According to these guidelines, the diagnosis of ARVC is based on the presence of major and minor criteria encompassing electrocardiograph, arrhythmic, morphofunctional, histopathologic, and genetic factors. Because the assessment of sudden death risk in patients with ARVC is still not well established, there are no precise guidelines to determine which are the patients who need to be treated and which is the best management approach. The therapeutic options include beta blockers, antiarrhythmic drugs, catheter ablation, and implantable cardioverter defibrillator. The implantable defibrillator is the most effective safe-guard against arrhythmic sudden death. However, its precise role in changing natural history of ARVC by preventing sudden and nonsudden death needs to be evaluated by a prospective study of a large series of patients. In patients in whom ARVC has progressed to severe RV or biventricular systolic dysfunction with risk of thromboembolic complications, treatment consists of current therapy for heart failure including anticoagulant therapy. In case of refractory congestive heart failure, the patients may become candidates for heart transplantation.

Genetics of brugada, long QT, and arrhythmogenic right ventricular dysplasia syndromes

This article outlines the up-to-date understanding of the molecular basis of primary ventricular arrhythmias. Two disorders have recently been well described at the molecular level, the long QT syndromes and Brugada syndrome, and this article reviews the current scientific knowledge of each disease. A third disorder, arrhythmogenic right ventricular dysplasia, which is on the cusp of understanding, will also be described.

Apoptotic cell death in arrhythmogenic right ventricular cardiomyopathy: a comparative study with idiopathic sustained ventricular tachycardia

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a specific heart muscle disease of unknown etiology characterized by fatty and fibrofatty replacement of the right ventricular myocardium. It often manifests life-threatened ventricular arrhythmias. Previous studies have hypothesized that myocyte apoptosis contributes to the myocyte cell loss and fatty change in ARVC and may be induced by recurrent ventricular tachycardia (VT). We examined whether these progressive pathological changes result from apoptotic cell death in both autopsied and biopsied right ventricular myocardium from 35 patients with ARVC by using in situ terminal deoxynucleotidyl transferase assay (TUNEL) and agarose gel electrophoresis. We also studied the biopsied myocardium from 30 patients with idiopathic sustained VT whose origin was the outflow tract of the right ventricle. TUNEL-positive cells indicating DNA fragments were observed in some cardiomyocytes and fibroblasts in ARVC, but the numbers of TUNEL-positive myocytes were very low in idiopathic VT. DNA laddering was confirmed in two autopsied cases in ARVC, but not in a non-cardiac case who died. These results suggest that at least some cardiomyocytes and fibroblasts are subjected to apoptosis in ARVC, leading to the loss of myocardium with characteristic pathological changes and subsequently progressive cardiomyopathy. Furthermore, the apoptotic process may not result from myocardial ischemia due to repetitive VT.

Spontaneously occurring arrhythmogenic right ventricular cardiomyopathy in the domestic cat: A new animal model similar to the human disease

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary myocardial disease of incompletely resolved pathogenesis and is a largely unappreciated cause of sudden death in the young.

METHODS AND RESULTS

Clinical features of 12 domestic cats with ARVC (7 male; 1 to 20 years old, mean 7.3+/-5.2 years) were right-sided congestive heart failure (n=8), supraventricular tachyarrhythmias (n=5), ventricular tachycardia (n=3), polymorphic ventricular arrhythmias (n=6), and right bundle-branch block (n=5). ARVC was suspected in all 8 cats examined with echocardiography by marked enlargement of the right ventricle (RV) and right atrium and tricuspid regurgitation. Eight died of cardiovascular disease and 4 died of noncardiac conditions. At autopsy, hearts of ARVC cats were characterized grossly by moderate-to-severe RV cavity enlargement and wall thinning (n=12) and apical aneurysm formation (n=6). Histology demonstrated pronounced RV lesions in all 12 ARVC cats, including marked myocardial injury (myocyte death and atrophy) and repair (fibrous and/or fatty replacement). Injury and repair were also evident in the left ventricle (LV) in 10 cats, and 2 had involvement of both atria. Myocarditis was present in 10 of the 12 ARVC cats. Apoptosis was detected in 9 ARVC cats (mean apoptotic index, 28+/-23% RV, 21+/-19% LV, and 17+/-15% ventricular septum) but not in controls.

CONCLUSIONS

In the common domestic cat, we identified a clinically relevant cardiomyopathy that closely mimics ARVC in humans. This unique feline model of human disease will be relevant to defining pathogenesis and investigating mechanisms responsible for disease progression in ARVC.

Human protein tyrosine phosphatase-like gene: expression profile, genomic structure, and mutation analysis in families with ARVD

The mouse protein tyrosine phosphatase-like gene (Ptpla) was recently cloned and data suggested that it plays a role in myogenesis and cardiogenesis. The human homologue (PTPLA) was mapped to chromosome 10p13-14, a region where we have mapped a locus responsible for arrhythmogenic right ventricular dysplasia (ARVD). As a positional candidate gene, we characterized PTPLA by determining its tissue expression, its genomic structure, and we also screened for mutations in the ARVD patients. Northern analysis demonstrated PTPLA is preferentially expressed in both adult and fetal heart. A much lower expression was detected in skeletal and smooth muscle tissues. Virtually no expression was observed in other tissues. The protein-encoding sequences of PTPLA consist of seven exons. A sequence variation (Lys64Gln) was found in all the affecteds in a large ARVD family. However, the same variant was also detected in normal control subjects (three alleles/100 chromosomes). Thus, the variant (Lys64Gln) is not responsible for ARVD in our family and is a benign polymorphism. Nevertheless, its tissue-specific expression in the developing and adult heart suggest PTPLA has a role in regulating cardiac development, differentiation, or other cellular events. The genomic structure and intragenic polymorphism of PTPLA should be useful for further clinical and genetic studies such as gene targeting of PTPLA.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy: need for an international registry. European Society of Cardiology and the Scientific Council on Cardiomyopathies of the World Heart Federation

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a heart muscle disease characterized by peculiar right ventricular involvement and electrical instability that precipitates ventricular arrhythmias and sudden death. The purpose of the present consensus report of the Study Group of the European Society of Cardiology and the Scientific Council on Cardiomyopathies of the World Heart Federation is to review the considerable progress in our understanding of the etiopathogenesis, morbid anatomy, and clinical presentation of ARVD/C since its first description in 1977. This article will focus on the important but still unanswered issues, mostly regarding risk stratification, clinical outcome, and management of affected patients. Because ARVD/C is relatively uncommon and any one center may have experience with only a few patients, an international registry is being established to accumulate information and enhance the numbers of patients that can be analyzed to answer the pending questions. The registry also will facilitate pathologic, molecular, and genetics research on the etiology and pathogenesis of the disease. Furthermore, availability of an international database will enhance awareness of this largely unrecognized condition among the medical community. Physicians are encouraged to enroll patients in the International Registry of ARVD/C.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy: need for an international registry. Study Group on Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy of the Working Groups on Myocardial and Pericardial Disease and Arrhythmias of the European Society of Cardiology and of the Scientific Council on Cardiomyopathies of the World Heart Federation

Arrhythmogenic right ventricular (RV) dysplasia/cardiomyopathy (ARVD/C) is a heart muscle disease characterized by peculiar RV involvement and electrical instability that precipitates ventricular arrhythmias and sudden death. The purpose of the present consensus report of the Study Group on ARVD/C of the Working Groups on Myocardial and Pericardial Disease and Arrhythmias of the European Society of Cardiology and of the Scientific Council on Cardiomyopathies of the World Heart Federation is to review the considerable progress in our understanding of the etiopathogenesis, morbid anatomy, and clinical presentation of ARVD/C since it first was described in 1977. The present article focuses on important but still unanswered issues, mostly regarding risk stratification, clinical outcome, and management of affected patients. Because ARVD/C is relatively uncommon and any one center may have experience with only a few patients, an international registry is being established to accumulate information and enhance the numbers of patients that can be analyzed and thus answer pending questions. The registry also will facilitate pathological, molecular, and genetics research on the causes and pathogenesis of the ARVD/C. Furthermore, availability of an international database will enhance awareness of this largely unrecognized condition among the medical community. Physicians are encouraged to enroll patients in the International Registry of ARVD/C.

The locus of a novel gene responsible for arrhythmogenic right-ventricular dysplasia characterized by early onset and high penetrance maps to chromosome 10p12-p14

Arrhythmogenic right-ventricular dysplasia (ARVD), a cardiomyopathy inherited as an autosomal-dominant disease, is characterized by fibro-fatty infiltration of the right-ventricular myocardium. Four loci for ARVD have been mapped in the Italian population, and recently the first locus was mapped in inhabitants of North America. None of the genes have been identified. We have now identified another North American family with early onset of ARVD and high penetrance. All of the children with the disease haplotype had pathological or clinical evidence of the disease at age <10 years. The family spans five generations, having 10 living and 2 dead affected individuals, with ARVD segregating as an autosomal-dominant disorder. Genetic linkage analysis excluded known loci, and a novel locus was identified on chromosome 10p12-p14. A peak two-point LOD score of 3.92 was obtained with marker D10S1664, at a recombination fraction of 0. Additional genotyping and haplotype analysis identified a shared region of 10.6 cM between marker D10S547 and D10S1653. Thus, a novel gene responsible for ARVD resides on the short arm of chromosome 10. This disease is intriguing, since it initiates exclusively in the right ventricle and exhibits pathological features of apoptosis. Chromosomal localization of the ARVD gene is the first step in identification of the genetic defect and the unraveling of the molecular basis responsible for the pathogenesis of the disease.

Arrhythmogenic Right Ventricular Dysplasia

Despite recurrences of ventricular tachycardia, patients with arrhythmogenic right ventricular dysplasia have a favorable prognosis with medical therapy. Because of the low incidence of arrhythmic death and the problems involved in identifying patients at high risk, it is difficult to evaluate the benefits of interventional therapies (ablation, surgery, and implantable cardioverter-defibrillators).

Clinical and pathologic study of two siblings with arrhythmogenic right ventricular cardiomyopathy

ARVC is a cardiomyopathy in which the right ventricular myocardium is replaced by fibroadipose tissue. Males are affected slightly more often than females and, in those cases which are familial, the pattern of inheritance is usually autosomal dominant with incomplete penetrance. We examined the hearts of two sisters, ages 17 and 14, with no family history of heart disease. The older sibling, who was previously considered healthy, died suddenly, while the younger sibling developed congestive heart failure and received a cardiac transplant. An autopsy of the older sibling and examination of the younger sibling's excised heart revealed severe examples of ARVC with minor differences. A thick cap of fibroadipose tissue covered most, if not all, of each right ventricle and was transmural in some areas. Microscopically, lelt ventricles contained extensive myocyte disarray and multifocal fibrosis. The coronary arteries displayed intimal hyperplasia with disruption of the internal elastic lamina, similar to fibromuscular dysplasia. These two cases comprise a unique familial grouping in a polymorphic disease. Despite the male predominance and autosomal dominant inheritance in ARVC, the only members affected in this family were female, and an autosomal dominant pattern of inheritance, even with incomplete penetrance, would be unusual. In addition, we identified changes in the coronary arteries similar to fibromuscular dysplasia and corroborated recently reported changes in the left ventricle of patients with ARVC, providing evidence that this disease, in its most severe form, involves the entire heart.