The prevalence of left and right bundle branch block morphology ventricular tachycardia amongst patients with arrhythmogenic cardiomyopathy and sustained ventricular tachycardia: insights from the European Survey on Arrhythmogenic Cardiomyopathy

AIMS

In arrhythmogenic cardiomyopathy (ACM), sustained ventricular tachycardia (VT) typically displays a left bundle branch block (LBBB) morphology while a right bundle branch block (RBBB) morphology is rare. The present study assesses the VT morphology in ACM patients with sustained VT and their clinical and genetic characteristics.

METHODS AND RESULTS

Twenty-six centres from 11 European countries provided information on 954 ACM patients who had ≥1 episode of sustained VT spontaneously documented during patients' clinical course. Arrhythmogenic cardiomyopathy was defined according to the 2010 Task Force Criteria, and VT morphology according to the QRS pattern in V1. Overall, 882 (92.5%) patients displayed LBBB-VT alone and 72 (7.5%) RBBB-VT [alone in 42 (4.4%) or in combination with LBBB-VT in 30 (3.1%)]. Male sex prevalence was 79.3%, 88.1%, and 56.7% in the LBBB-VT, RBBB-VT, and LBBB + RBBB-VT groups, respectively (P = 0.007). First RBBB-VT occurred 5 years after the first LBBB-VT (46.5 ± 14.4 vs 41.1 ± 15.8 years, P = 0.011). An implanted cardioverter-defibrillator was more frequently implanted in the RBBB-VT (92.9%) and the LBBB + RBBB-VT groups (90%) than in the LBBB-VT group (68.1%) (P < 0.001). Mutations in PKP2 predominated in the LBBB-VT (65.2%) and the LBBB + RBBB-VT (41.7%) groups while DSP mutations predominated in the RBBB-VT group (45.5%). By multivariable analysis, female sex was associated with LBBB + RBBB-VT (P = 0.011) while DSP mutations were associated with RBBB-VT (P < 0.001). After a median follow-up of 103 (51-185) months, death occurred in 106 (11.1%) patients with no intergroup difference (P = 0.176).

CONCLUSION

RBBB-VT accounts for a significant proportion of sustained VTs in ACM. Sex and type of pathogenic mutations were associated with VT type, female sex with LBBB + RBBB-VT, and DSP mutation with RBBB-VT.

Diastolic Ventricular Interaction in Heart Failure With Preserved Ejection Fraction

Background

Exercise‐induced pulmonary hypertension is common in heart failure with preserved ejection fraction (HFpEF). We hypothesized that this could result in pericardial constraint and diastolic ventricular interaction in some patients during exercise.

Methods and Results

Contrast stress echocardiography was performed in 30 HFpEF patients, 17 hypertensive controls, and 17 normotensive controls (healthy). Cardiac volumes, and normalized radius of curvature (NRC) of the interventricular septum at end‐diastole and end‐systole, were measured at rest and peak‐exercise, and compared between the groups. The septum was circular at rest in all 3 groups at end‐diastole. At peak‐exercise, end‐systolic NRC increased to 1.47±0.05 (P<0.001) in HFpEF patients, confirming development of pulmonary hypertension. End‐diastolic NRC also increased to 1.54±0.07 (P<0.001) in HFpEF patients, indicating septal flattening, and this correlated significantly with end‐systolic NRC (ρ=0.51, P=0.007). In hypertensive controls and healthy controls, peak‐exercise end‐systolic NRC increased, but this was significantly less than observed in HFpEF patients (HFpEF, P=0.02 versus hypertensive controls; P<0.001 versus healthy). There were also small, non‐significant increases in end‐diastolic NRC in both groups (hypertensive controls, +0.17±0.05, P=0.38; healthy, +0.06±0.03, P=0.93). In HFpEF patients, peak‐exercise end‐diastolic NRC also negatively correlated (r=−0.40, P<0.05) with the change in left ventricular end‐diastolic volume with exercise (ie, the Frank‐Starling mechanism), and a trend was noted towards a negative correlation with change in stroke volume (r=−0.36, P=0.08).

Conclusions

Exercise pulmonary hypertension causes substantial diastolic ventricular interaction on exercise in some patients with HFpEF, and this restriction to left ventricular filling by the right ventricle exacerbates the pre‐existing impaired Frank‐Starling response in these patients.

Update on hypertrophic cardiomyopathy and a guide to the guidelines

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disorder, affecting 1 in 500 individuals worldwide. Existing epidemiological studies might have underestimated the prevalence of HCM, however, owing to limited inclusion of individuals with early, incomplete phenotypic expression. Clinical manifestations of HCM include diastolic dysfunction, left ventricular outflow tract obstruction, ischaemia, atrial fibrillation, abnormal vascular responses and, in 5% of patients, progression to a 'burnt-out' phase characterized by systolic impairment. Disease-related mortality is most often attributable to sudden cardiac death, heart failure, and embolic stroke. The majority of individuals with HCM, however, have normal or near-normal life expectancy, owing in part to contemporary management strategies including family screening, risk stratification, thromboembolic prophylaxis, and implantation of cardioverter-defibrillators. The clinical guidelines for HCM issued by the ACC Foundation/AHA and the ESC facilitate evaluation and management of the disease. In this Review, we aim to assist clinicians in navigating the guidelines by highlighting important updates, current gaps in knowledge, differences in the recommendations, and challenges in implementing them, including aids and pitfalls in clinical and pathological evaluation. We also discuss the advances in genetics, imaging, and molecular research that will underpin future developments in diagnosis and therapy for HCM.

Standing on the Shoulders of Giants: J.A.P. Paré and the Birth of Cardiovascular Genetics

Sudden death and stroke afflicted a family from rural Quebec with such frequency as to be called the Coaticook curse by the local community. In Montreal in the late 1950s, a team of physicians led by J.A.P. Paré investigated this family for inherited cardiovascular disease. Their efforts resulted in an extensive and now classic description of familial hypertrophic cardiomyopathy. A quarter of a century later, the same family was the subject of linkage analysis and direct sequencing, culminating in the isolation of a mutation in the gene encoding the β myosin heavy chain. MYH7 was the first gene implicated in a cardiovascular disease, which paved the way for identification of mutations in other heritable disorders, mechanistic studies, and clinical applications, such as predictive testing. The present era of cardiovascular genomics arguably had its inception in the clinical observations of Dr Paré and his colleagues more than 50 years ago.

Insights and challenges in hypertrophic cardiomyopathy, 2012

We present a contemporary overview of hypertrophic cardiomyopathy (HCM), incorporating recent thinking on disease mechanisms and advances in therapy. Clinical, pathological, genetic, and mechanistic definitions of HCM are discussed. The genetic profile of HCM in both adults and children is explored to the extent of present knowledge. The spectrum of morphological and histological abnormalities in HCM is reviewed, including involvement of the right ventricle, which is less widely recognised. Morbidity and mortality from HCM may result from diastolic dysfunction, ischaemia, left ventricular outflow tract obstruction, mitral regurgitation, supraventricular and ventricular arrhythmia, or--less commonly--progression to "burnt out" disease or sudden cardiac death (SCD). Defibrillators offer an efficacious means of averting SCD, but are not without their complications, underscoring the importance of identifying at-risk cases. We address the strengths and weaknesses of prognostication based on readily obtainable clinical markers, and discuss the integration of auxiliary approaches such as genotyping, cardiovascular magnetic resonance, and fractionation analysis into existing risk stratification guidelines. Finally, we provide an update on the pharmacological and interventional management of HCM, including the advent of disease-modifying therapy.

Genome-wide association study identifies loci influencing concentrations of liver enzymes in plasma

Concentrations of liver enzymes in plasma are widely used as indicators of liver disease. We carried out a genome-wide association study in 61,089 individuals, identifying 42 loci associated with concentrations of liver enzymes in plasma, of which 32 are new associations (P = 10(-8) to P = 10(-190)). We used functional genomic approaches including metabonomic profiling and gene expression analyses to identify probable candidate genes at these regions. We identified 69 candidate genes, including genes involved in biliary transport (ATP8B1 and ABCB11), glucose, carbohydrate and lipid metabolism (FADS1, FADS2, GCKR, JMJD1C, HNF1A, MLXIPL, PNPLA3, PPP1R3B, SLC2A2 and TRIB1), glycoprotein biosynthesis and cell surface glycobiology (ABO, ASGR1, FUT2, GPLD1 and ST3GAL4), inflammation and immunity (CD276, CDH6, GCKR, HNF1A, HPR, ITGA1, RORA and STAT4) and glutathione metabolism (GSTT1, GSTT2 and GGT), as well as several genes of uncertain or unknown function (including ABHD12, EFHD1, EFNA1, EPHA2, MICAL3 and ZNF827). Our results provide new insight into genetic mechanisms and pathways influencing markers of liver function.

Familial evaluation in arrhythmogenic right ventricular cardiomyopathy: impact of genetics and revised task force criteria

BACKGROUND

With recognition of disease-causing genes in arrhythmogenic right ventricular cardiomyopathy, mutation analysis is being applied.

METHODS AND RESULTS

The role of genotyping in familial assessment for arrhythmogenic right ventricular cardiomyopathy was investigated, including the prevalence of mutations in known causal genes, the penetrance and expressivity in genotyped families, and the utility of the 2010 Task Force criteria in clinical diagnosis. Clinical and molecular genetic evaluation was performed in 210 first-degree and 45 second-degree relatives from 100 families. In 51 families, the proband was deceased. The living probands had a high prevalence of ECG abnormalities (89%) and ventricular arrhythmia (78%) and evidence of more severe disease than relatives. Definite or probable causal mutations were found in 58% of families and 73% of living probands, of whom 28% had an additional desmosomal variant (ie, mutation or polymorphism). Ninety-three relatives had a causal mutation; 33% fulfilled the 2010 criteria, whereas only 19% satisfied the 1994 version (P=0.03). An additional desmosomal gene variant was found in 10% and was associated with a 5-fold increased risk of developing penetrant disease (odds ratio, 4.7; 95% confidence interval, 1.1 to 20.4; P=0.04).

CONCLUSIONS

Arrhythmogenic right ventricular cardiomyopathy is a genetically complex disease characterized by marked intrafamilial phenotype diversity. Penetrance is definition dependent and is greater with the 2010 criteria compared with the 1994 criteria. Relatives harboring >1 genetic variant had significantly increased risk of developing clinical disease, potentially an important determinant of the phenotypic heterogeneity seen within families with arrhythmogenic right ventricular cardiomyopathy.

Genetics of Dilated Cardiomyopathy: Risk of Conduction Defects and Sudden Cardiac Death

Dilated cardiomyopathy is familial in at least 40--60% of cases and causal mutations have been identified in more than 40 different genes. Mutations in lamin A/C (LMNA) and desmosomal components appear associated with increased risk of sudden cardiac death, the latter in the context of left-dominant arrhythmogenic cardiomyopathy. Specific clinical features may be valuable in identifying patients with these mutations. Routine sequencing of all the genes implicated in dilated cardiomyopathy may not be cost-effective at present. Targeted mutation screening of LMNA and desmosomal components is recommended and may facilitate prognostication and management.

Mutational Heterogeneity, Modifier Genes, and Environmental Influences Contribute to Phenotypic Diversity of Arrhythmogenic Cardiomyopathy

Background—

Arrhythmogenic cardiomyopathy is one of the leading causes of sudden cardiac death in the ≤35-year age group. The broad phenotypic spectrum encompasses left-dominant and biventricular subtypes, characterized by early left ventricular involvement, as well as the classic right-dominant form, better known as arrhythmogenic right ventricular cardiomyopathy. Mendelian inheritance patterns are accompanied by incomplete penetrance and variable expressivity, the latter manifesting as diversity in morphology, arrhythmic burden, and clinical outcomes.

Methods and Results—

To investigate the role of mutational heterogeneity, genetic modifiers and environmental influences in arrhythmogenic cardiomyopathy, we studied phenotype variability in 9 quantitative traits among an affected-only sample of 231 cases from 48 families. Heritability was estimated by variance component analysis as a guide to the combined influence of mutational and genetic background heterogeneity. Nested ANOVA was used to distinguish mutational and genetic modifier effects. Heritability estimates ranged from 20% to 77%, being highest for left ventricular ejection fraction and right–to–left ventricular volume ratio and lowest for the ventricular arrhythmia grade, suggesting differing genetic and environmental contributions to these traits. ANOVA models indicated a predominant mutation effect for the left ventricular lesion score, an indicator of the extent of fat and late enhancement on cardiovascular magnetic resonance. In contrast, the modifier genetic effect appeared significant for right ventricular end-diastolic volume, ejection fraction, and lesion score; left ventricular ejection fraction; ventricular volume ratio; and arrhythmic events.

Conclusions—

Systematic investigation of modifier genes and environmental influences will be pivotal to understanding clinical diversity in arrhythmogenic cardiomyopathy, refining prognostication, and developing targeted therapies.

Genetics of restrictive cardiomyopathy

Restrictive physiology, a severe form of diastolic dysfunction, is characteristically observed in the setting of constrictive pericarditis and myocardial restriction. The latter is commonly due to systemic diseases, some of which are inherited as mendelian traits (eg, hereditary amyloidosis), while others are multifactorial (eg, sarcoidosis). When restrictive physiology occurs as an early and dominant feature of a primary myocardial disorder, it may be termed restrictive cardiomyopathy. In the past decade, clinical and genetic studies have demonstrated that restrictive cardiomyopathy as such is part of the spectrum of sarcomeric disease and frequently coexists with hypertrophic cardiomyopathy in affected families.

Arrhythmogenic cardiomyopathy: etiology, diagnosis, and treatment

Arrhythmogenic right ventricular cardiomyopathy (ARVC) has a prevalence of at least 1 in 1000, is a leading cause of sudden cardiac death in people aged < or =35 years, and accounts for up to 10% of deaths from undiagnosed cardiac disease in the <65 age group. The classic form of the disease has an early predilection for the right ventricle, but recognition of left-dominant and biventricular subtypes has prompted proposal of the broader term arrhythmogenic cardiomyopathy. The clinical profile of the disease bridges the gap between the cardiomyopathies and inherited arrhythmia syndromes. The early "concealed" phase is characterized by propensity toward ventricular tachyarrhythmia in the setting of well-preserved morphology, histology, and ventricular function. As the disease progresses, however, myocyte loss, inflammation, and fibroadiposis become evident. Up to 40% of cases harbor rare variants in genes encoding components of the desmosome, specialized intercellular junctions that confer mechanical strength to cardiac and epithelial tissue, and may also participate in signaling networks. Phenotypic heterogeneity and the nonspecific nature of associated features complicate clinical diagnosis, which requires multipronged cardiovascular investigation rather than a single test. Development of a prospectively validated risk-stratification algorithm for the full disease spectrum remains the foremost clinical challenge.

Left-dominant arrhythmogenic cardiomyopathy: an under-recognized clinical entity

OBJECTIVES

We sought to investigate the clinical-genetic profile of left-dominant arrhythmogenic cardiomyopathy (LDAC).

BACKGROUND

In the absence of coronary disease and left ventricular (LV) systolic dysfunction, lateral T-wave inversion and arrhythmia of LV origin are often considered benign. Similarly, chest pain with enzyme release might be attributed to viral myocarditis. We hypothesized that these abnormalities might be manifestations of the "left-dominant" subtype of arrhythmogenic right ventricular cardiomyopathy.

METHODS

The 42-patient cohort was established through clinical evaluation of individuals with unexplained (infero)lateral T-wave inversion, arrhythmia of LV origin, and/or proven LDAC/idiopathic myocardial fibrosis in the family.

RESULTS

Patients presented from adolescence to age >80 years with arrhythmia or chest pain but not heart failure. Desmosomal mutations were identified in 8 of 24 families (15 of 33 patients). Magnetic resonance findings included LV late-enhancement in a subepicardial/midwall distribution, corresponding to fibrofatty replacement and fibrosis on histopathology. Fifty percent had previously been misdiagnosed with viral myocarditis, dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy, or idiopathic ventricular tachycardia. Arrhythmic events included presentation with ventricular fibrillatory arrest in 1 patient and 2 instances of sudden cardiac death during follow-up.

CONCLUSIONS

Arrhythmogenic cardiomyopathy is distinguished from DCM by a propensity towards arrhythmia exceeding the degree of ventricular dysfunction. The left-dominant subtype is under-recognized owing to misattribution to other disorders and lack of specific diagnostic criteria. Clinicians are alerted to the possibility of LDAC in patients of any age with unexplained arrhythmia of LV origin, (infero)lateral T-wave inversion, apparent DCM (with arrhythmic presentation), or myocarditis (chest pain and enzyme rise with unobstructed coronary arteries).

Role of genetic analysis in the management of patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a recognized cause of sudden cardiac death, which may be prevented by timely detection and intervention. Clinical diagnosis of ARVC is fraught with difficulties in both index cases and relatives owing to the nonspecific nature of associated features, diverse phenotypic manifestations, and a lack of conspicuous abnormalities in the early, "concealed" phase. During the past 7 years, researchers have isolated causative mutations in several components of the desmosome, shedding light on the molecular mechanisms underlying the disease and offering the promise of genetic testing as a diagnostic tool. Sequence analysis is likely to be the mainstay of genotyping in ARVC because of marked allelic heterogeneity, frequent "private" mutations, and digenicity in a minority, highlighting the importance of comprehensive genetic screening. The main technical obstacle to implementation of genotyping in clinical practice will be the prohibitive costs of performing sequence analysis of a genomic region exceeding 40 kb. Nevertheless, the success rate of genotyping in ARVC is of the order of 40%, and key clinical applications include confirmatory testing of index cases to facilitate interpretation of borderline investigations and cascade screening of families. The latter is particularly attractive in ARVC, because age-related penetrance otherwise demands lifelong clinical reassessment of extended families. A role for genetic analysis in prognostication is more tenuous at present, but increasing identification of individuals with early and familial disease underscores the need for a definitive risk stratification algorithm in this population.

Clinical and genetic characterization of families with arrhythmogenic right ventricular dysplasia/cardiomyopathy provides novel insights into patterns of disease expression

BACKGROUND

According to clinical-pathological correlation studies, the natural history of arrhythmogenic right ventricular dysplasia/cardiomyopathy is purported to progress from localized to global right ventricular dysfunction, followed by left ventricular (LV) involvement and biventricular pump failure. The inevitable focus on sudden death victims and transplant recipients may, however, have created a skewed perspective of a genetic disease. We hypothesized that unbiased representation of the spectrum of disease expression in arrhythmogenic right ventricular dysplasia/cardiomyopathy would require in vivo assessment of families in a genetically heterogeneous population.

METHODS AND RESULTS

A cohort of 200 probands and relatives satisfying task force or modified diagnostic criteria for arrhythmogenic right ventricular dysplasia/cardiomyopathy underwent comprehensive clinical evaluation. Desmosomal mutations were identified in 39 individuals from 20 different families. Indices of structural severity correlated with advancing age and were increased in long-term endurance athletes. Fulfillment of modified criteria indicated phenotypically mild disease, whereas asymptomatic status did not. In >80%, ECG, rhythm monitoring, and/or gadolinium-enhanced cardiovascular magnetic resonance were suggestive of LV involvement, the extent of which often was marked among individuals with chain-termination mutations and/or desmoplakin disease. Three patterns of disease expression were identified: (1) classic, with isolated right ventricular disease or LV involvement in association with significant right ventricular impairment; (2) left dominant, with early and prominent LV manifestations and relatively mild right-sided disease; and (3) biventricular, characterized by parallel involvement of both ventricles.

CONCLUSIONS

LV involvement in arrhythmogenic right ventricular dysplasia/cardiomyopathy may precede the onset of significant right ventricular dysfunction. Recognition of disease variants with early and/or predominant LV involvement supports adoption of the broader term arrhythmogenic cardiomyopathy.

Desmoglein-2 mutations in arrhythmogenic right ventricular cardiomyopathy: a genotype-phenotype characterization of familial disease

AIMS

Mutations in the desmoglein-2 (DSG2) gene have been reported in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) but clinical information regarding the associated phenotype is at present limited. In this study, we aimed to clinically characterize probands and family members carrying a DSG2 mutation.

METHODS AND RESULTS

We investigated 86 Caucasian ARVC patients for mutations in DSG2 by direct sequencing and detected eight novel mutations in nine probands. Clinical evaluation of family members with DSG2 mutations demonstrated penetrance of 58% using Task Force criteria, or 75% using proposed modified criteria. Morphological abnormalities of the right ventricle were evident in 66% of gene carriers, left ventricular (LV) involvement in 25%, and classical right precordial T-wave inversion only in 26%. Sustained ventricular arrhythmia was present in 8% and a family history of sudden death/aborted sudden death in 66%.

CONCLUSION

Mutations in DSG2 display a high degree of penetrance. Disease expression was of variable severity with LV involvement a prominent feature. The low prevalence of classical ECG changes highlights the need to expand current diagnostic criteria to take account of LV disease, childhood disease expression, and incomplete penetrance.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy associated with mutations in the desmosomal gene desmocollin-2

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited myocardial disorder associated with arrhythmias, heart failure, and sudden death. To date, mutations in four genes encoding major desmosomal proteins (plakoglobin, desmoplakin, plakophilin-2, and desmoglein-2) have been implicated in the pathogenesis of ARVD/C. We screened 77 probands with ARVD/C for mutations in desmocollin-2 (DSC2), a gene coding for a desmosomal cadherin. Two heterozygous mutations--a deletion and an insertion--were identified in four probands. Both mutations result in frameshifts and premature truncation of the desmocollin-2 protein. For the first time, we have identified mutations in desmocollin-2 in patients with ARVD/C, a finding that is consistent with the hypothesis that ARVD/C is a disease of the desmosome.

Cardiovascular magnetic resonance in arrhythmogenic right ventricular cardiomyopathy revisited: comparison with task force criteria and genotype

OBJECTIVES

We sought to assess the utility of cardiovascular magnetic resonance (CMR) in the evaluation of arrhythmogenic right ventricular cardiomyopathy (ARVC) in relation to diagnostic criteria and genotype.

BACKGROUND

Timely diagnosis of ARVC is difficult as clinical findings may be subtle and nonspecific in early disease. The role of CMR is controversial owing to the absence of a standardized protocol, insufficient experience with the modality, and inherent difficulties in imaging the right ventricle.

METHODS

Comprehensive CMR examination was performed in 232 patients undergoing evaluation for suspected ARVC. CMR outcomes were compared with: 1) prospective clinical diagnosis using Task Force guidelines, with and without the proposed modifications for familial ARVC; and 2) gene-carrier status in 35 individuals from genotyped families.

RESULTS

CMR studies were positive in all 64 patients who prospectively fulfilled Task Force criteria, resulting in 100% sensitivity. Specificity in relation to Task Force criteria was low (29%). Of the 119 apparent false positives detected by CMR, however, 63 fulfilled modified diagnostic criteria for familial ARVC and 7 were obligate gene carriers, suggesting that CMR frequently identifies individuals with early disease, in whom Task Force criteria are relatively insensitive. This was borne out by evaluation of genotyped individuals (26 gene-positive and 9 gene-negative), in whom CMR had a sensitivity of 96% and a specificity of 78%.

CONCLUSIONS

CMR is a valuable component of the diagnostic workup for ARVC when performed with a dedicated protocol by specialists with experience in analysis of volumes, right ventricular wall motion, and delayed-enhancement imaging.

Sudden Cardiac Death in the Young: A Strategy for Prevention by Targeted Evaluation

The annual incidence of sudden cardiac death (SCD) in the general population is estimated as 1 in a 1,000. Since survival rates from out-of-hospital cardiac arrests are poor, primary prevention is key to reducing the burden of SCD in the community. Prominent causes of SCD include ischaemic heart disease, anomalous coronary arteries, and the primary myocardial diseases: hypertrophic cardiomyopathy, dilated cardiomyopathy, and ar rhythmogenic right ventricular cardiomyopathy (ARVC). In 4% of sudden deaths in the 16-64 age group, post-mortem examination fails to identify a cause, yielding a default diagnosis of sudden arrhythmic death syndrome (SADS). The inherited arrhythmia syndromes (long QT, short QT, and Brugada syndromes, and familial catecholaminergic polymorphic ventricular tachycardia) may be implicated in SADS, owing to their propensity for producing ventricular tachyarrhythmia in the structurally normal heart. Monogenic disorders therefore predominate as causes of SCD in the young. The advent of effective therapies for these diseases, particularly implantable cardioverter defibrillators, has prompted calls for universal screening to enable timely diagnosis of occult cardiac disease. Since prospective cardiac assessment of the general population is not feasible, the solution may be to target high-risk subgroups, namely, patients with cardiac symptoms, relatives of SCD victims, and competitive athletes. The recommended preliminary work-up includes a 12-lead ECG, signal-averaged ECG, transthoracic echocardiogram, exercise test, and ambulatory ECG monitoring. Cardiovascular magnetic resonance is a useful adjunct in patients with suspected ARVC or anomalous coronary arteries. Provocative challenge with a sodium challenge blocker may be of value in unmasking the Brugada syndrome. Identification of disease-causing mutations in affected individuals facilitates cascade screening of families.

Novel mutation in desmoplakin causes arrhythmogenic left ventricular cardiomyopathy

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a familial heart muscle disease characterized by structural, electrical, and pathological abnormalities of the right ventricle (RV). Several disease loci have been identified. Mutations in desmoplakin have recently been isolated in both autosomal-dominant and autosomal-recessive forms of ARVC. Primary left ventricular (LV) variants of the disease are increasingly recognized. We report on a large family with autosomal-dominant left-sided ARVC.

METHODS AND RESULTS

The proband presented with sudden cardiac death and fibrofatty replacement of the LV myocardium. The family was evaluated. Diagnosis was based on modified diagnostic criteria for ARVC. Seven had inferior and/or lateral T-wave inversion on ECG, LV dilatation, and ventricular arrhythmia, predominantly extrasystoles of LV origin. Three had sustained ventricular tachycardia; 7 had late potentials on signal-averaged ECG. Cardiovascular magnetic resonance imaging in 4 patients revealed wall-motion abnormalities of the RV and patchy, late gadolinium enhancement in the LV, suggestive of fibrosis. Linkage confirmed cosegregation to the desmoplakin intragenic marker D6S2975. A heterozygous, single adenine insertion (2034insA) in the desmoplakin gene was identified in affected individuals only. A frameshift introducing a premature stop codon with truncation of the rod and carboxy terminus of desmoplakin was confirmed by Western blot analysis.

CONCLUSIONS

We have described a new dominant mutation in desmoplakin that causes left-sided ARVC, with arrhythmias of LV origin, lateral T-wave inversion, and late gadolinium enhancement in the LV on magnetic resonance images. Truncation of the carboxy terminus of desmoplakin and consequent disruption of intermediate filament binding may account for the predominant LV phenotype.

Clinical Expression of Plakophilin-2 Mutations in Familial Arrhythmogenic Right Ventricular Cardiomyopathy

Background— Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiac disorder characterized by loss of cardiomyocytes and their replacement by adipose and fibrous tissue. It is considered a disease of cell adhesion because mutations in desmosomal genes, desmoplakin and plakoglobin, have been implicated in the pathogenesis of ARVC. In a recent report, mutations in plakophilin-2, a gene highly expressed in cardiac desmosomes, have been shown to cause ARVC.

Methods and Results— We investigated 100 white patients with ARVC for mutations in plakophilin-2. Nine different mutations were identified by direct sequencing in 11 cases. Five of these mutations are novel (A733fsX740, L586fsX658, V570fsX576, R413X, and P533fsX561) and predicted to cause a premature truncation of the plakophilin-2 protein. Family studies showed incomplete disease expression in mutation carriers and identified a number of individuals who would be misdiagnosed with the existing International Task Force and modified diagnostic criteria for ARVC.

Conclusions— In this study, we provide new evidence that mutations in the desmosomal plakophilin-2 gene can cause ARVC. A systematic clinical evaluation of mutation carriers within families demonstrated variable phenotypic expression, even among individuals with the same mutation, and highlighted the need for a more accurate set of diagnostic criteria for ARVC.

Genetics of right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease that may result in arrhythmia, heart failure, and sudden death. The hallmark pathological findings are progressive myocyte loss and fibrofatty replacement, with a predilection for the right ventricle. However, variants of ARVC that preferentially affect the left ventricle are increasingly recognized. ARVC is distinguished from dilated cardiomyopathy by a propensity toward ventricular arrhythmia and sudden death in the absence of significant ventricular dysfunction. In the majority of families, ARVC shows autosomal dominant inheritance with incomplete penetrance. Recessive forms are also described, often in association with cutaneous disorders. Causative mutations have so far been identified in plakoglobin, desmoplakin, and plakophilin, all of which encode key components of the desmosome. Desmosomes are protein complexes that anchor intermediate filaments to the cytoplasmic membrane in adjoining cells, thereby forming a three-dimensional scaffolding that provides tissues with mechanical strength. Unraveling of the genetic etiology of ARVC has elicited a new model for pathogenesis. Impaired functioning of cell adhesion junctions during exposure to shear stress may lead to myocyte detachment and death, accompanied by inflammation and fibrofatty repair. At least three mechanisms contribute to the arrhythmic substrate: bouts of myocarditis, fibrous and adipose infiltrates that facilitate macroreentry, and gap junction remodeling secondary to altered mechanical coupling. The latter may underlie arrhythmogenicity in early disease. Although ARVC can be considered a disease of the desmosome, a variety of other genetic defects give rise to phenocopies, which may ultimately enhance our understanding of the broad phenotypic spectrum.

Arrhythmogenic right ventricular cardiomyopathy: clinical presentation, diagnosis, and management

Arrhythmogenic right ventricular cardiomyopathy, also known as right ventricular dysplasia, is a genetically determined heart muscle disease associated with arrhythmia, heart failure, and sudden death. Autosomal dominant inheritance is typical. The identification of causative mutations in cell adhesion proteins has shed new light on its pathogenesis. Fibrofatty replacement of the myocardium, the hallmark pathologic feature, may be a response to injury caused by myocyte detachment. Sudden death is often the first manifestation in probands, emphasizing the importance of evaluating asymptomatic relatives for the disease. Standardized guidelines facilitate the clinical diagnosis of right ventricular dysplasia. However, familial studies have highlighted the need to broaden the diagnostic criteria, which are highly specific but lack sensitivity for early disease. Modifications have been proposed for the diagnosis of right ventricular dysplasia in relatives. Early right ventricular dysplasia is characterized by a "concealed phase" in which electrocardiographic and imaging abnormalities are often absent, but patients may nonetheless be at risk for arrhythmic events. Detection at this stage remains a clinical challenge, underscoring the potential value of mutation analysis in identifying affected persons. Serial evaluation of patients with suspected right ventricular dysplasia is recommended as clinical features may develop during the follow-up period. The onset of symptoms such as palpitation or syncope may herald an active phase of a previously quiescent disease, during which patients are at increased risk for sudden death. Greater awareness of right ventricular dysplasia among physicians and judicious use of implantable cardioverter-defibrillators may help to prevent unnecessary deaths.