The concealed phase of arrhythmogenic right ventricular cardiomyopathy (ARVC) may initially manifest electrophysiologically. No studies have examined dynamic conduction/repolarization kinetics to distinguish benign right ventricular outflow tract ectopy (RVOT ectopy) from ARVC's early phase. We investigated dynamic endocardial electrophysiological changes that differentiate early ARVC disease expression from RVOT ectopy.
22 ARVC (12 definite based upon family history and mutation carrier status, 10 probable) patients without right ventricular structural anomalies underwent high-density non-contact mapping of the right ventricle. These were compared to data from 14 RVOT ectopy and 12 patients with supraventricular tachycardias and normal hearts. Endocardial & surface ECG conduction and repolarization parameters were assessed during a standard S1-S2 restitution protocol.
Definite ARVC without RV structural disease could not be clearly distinguished from RVOT ectopy during sinus rhythm or during steady state pacing. Delay in Activation Times at coupling intervals just above the ventricular effective refractory period (VERP) increased in definite ARVC (43±20 ms) more than RVOT ectopy patients (36±14 ms, p = 0.03) or Normals (25±16 ms, p = 0.008) and a progressive separation of the repolarisation time curves between groups existed. Repolarization time increases in the RVOT were also greatest in ARVC (definite ARVC: 18±20 ms; RVOT ectopy: 5±14, Normal: 1±18, p<0.05). Surface ECG correlates of these intracardiac measurements demonstrated an increase of greater than 48 ms in stimulus to surface ECG J-point pre-ERP versus steady state, with an 88% specificity and 68% sensitivity in distinguishing definite ARVC from the other groups. This technique could not distinguish patients with genetic predisposition to ARVC only (probable ARVC) from controls.
Significant changes in dynamic conduction and repolarization are apparent in early ARVC before detectable RV structural abnormalities, and were present to a lesser degree in probable ARVC patients. Investigation of dynamic electrophysiological parameters may be useful to identify concealed ARVC in patients without disease pedigrees by using endocardial electrogram or paced ECG parameters.
Left ventricular noncompaction (LVNC) is a myocardial disorder characterized by excessive left ventricular (LV) trabeculae. Current methods for quantification of LV trabeculae have limitations. The aim of this study is to describe a novel technique for quantifying LV trabeculation using cardiovascular magnetic resonance (CMR) and fractal geometry. Observing that trabeculae appear complex and irregular, we hypothesize that measuring the fractal dimension (FD) of the endocardial border provides a quantitative parameter that can be used to distinguish normal from abnormal trabecular patterns.
Fractal analysis is a method of quantifying complex geometric patterns in biological structures. The resulting FD is a unitless measure index of how completely the object fills space. FD increases with increased structural complexity. LV FD was measured using a box-counting method on CMR short-axis cine stacks. Three groups were studied: LVNC (defined by Jenni criteria), n=30(age 41±13; men, 16); healthy whites, n=75(age, 46±16; men, 36); healthy blacks, n=30(age, 40±11; men, 15).
In healthy volunteers FD varied in a characteristic pattern from base to apex along the LV. This pattern was altered in LVNC where apical FD were abnormally elevated. In healthy volunteers, blacks had higher FD than whites in the apical third of the LV (maximal apical FD: 1.253±0.005 vs. 1.235±0.004, p<0.01) (mean±s.e.m.). Comparing LVNC with healthy volunteers, maximal apical FD was higher in LVNC (1.392±0.010, p<0.00001). The fractal method was more accurate and reproducible (ICC, 0.97 and 0.96 for intra and inter-observer readings) than two other CMR criteria for LVNC (Petersen and Jacquier).
FD is higher in LVNC patients compared to healthy volunteers and is higher in healthy blacks than in whites. Fractal analysis provides a quantitative measure of trabeculation and has high reproducibility and accuracy for LVNC diagnosis when compared to current CMR criteria.
Cardiomyopathy; Heart failure; Trabeculation
Abnormalities in Z-disc proteins cause hypertrophic (HCM), dilated (DCM) and/or restrictive cardiomyopathy (RCM), but disease-causing mechanisms are not fully understood. Myopalladin (MYPN) is a Z-disc protein expressed in striated muscle and functions as a structural, signaling and gene expression regulating molecule in response to muscle stress. MYPN was genetically screened in 900 patients with HCM, DCM and RCM, and disease-causing mechanisms were investigated using comparative immunohistochemical analysis of the patient myocardium and neonatal rat cardiomyocytes expressing mutant MYPN. Cardiac-restricted transgenic (Tg) mice were generated and protein–protein interactions were evaluated. Two nonsense and 13 missense MYPN variants were identified in subjects with DCM, HCM and RCM with the average cardiomyopathy prevalence of 1.66%. Functional studies were performed on two variants (Q529X and Y20C) associated with variable clinical phenotypes. Humans carrying the Y20C-MYPN variant developed HCM or DCM, whereas Q529X-MYPN was found in familial RCM. Disturbed myofibrillogenesis with disruption of α-actinin2, desmin and cardiac ankyrin repeat protein (CARP) was evident in rat cardiomyocytes expressing MYPNQ529X. Cardiac-restricted MYPNY20C Tg mice developed HCM and disrupted intercalated discs, with disturbed expression of desmin, desmoplakin, connexin43 and vinculin being evident. Failed nuclear translocation and reduced binding of Y20C-MYPN to CARP were demonstrated using in vitro and in vivo systems. MYPN mutations cause various forms of cardiomyopathy via different protein–protein interactions. Q529X-MYPN causes RCM via disturbed myofibrillogenesis, whereas Y20C-MYPN perturbs MYPN nuclear shuttling and leads to abnormal assembly of terminal Z-disc within the cardiac transitional junction and intercalated disc.
Cardiovascular magnetic resonance (CMR) is commonly used in patients with suspected arrhythmogenic right ventricular cardiomyopathy (ARVC) based on ECG, echocardiogram and Holter. However, various diseases may present with clinical characteristics resembling ARVC causing diagnostic dilemmas. The aim of this study was to explore the role of CMR in the differential diagnosis of patients with suspected ARVC.
657 CMR referrals suspicious for ARVC in a single tertiary referral centre were analysed. Standardized CMR imaging protocols for ARVC were performed. Potential ARVC mimics were grouped into: 1) displacement of the heart, 2) right ventricular overload, and 3) non ARVC-like cardiac scarring. For each, a judgment of clinical impact was made.
Twenty patients (3.0%) fulfilled imaging ARVC criteria. Thirty (4.6%) had a potential ARVC mimic, of which 25 (3.8%) were considered clinically important: cardiac displacement (n=17), RV overload (n=7) and non-ARVC like myocardial scarring (n=4). One patient had two mimics; one patient had dual pathology with important mimic and ARVC. RV overload and scarring conditions were always thought clinically important whilst the importance of cardiac displacement depended on the degree of displacement from severe (partial absence of pericardium) to epiphenomenon (minor kyphoscoliosis).
Some patients referred for CMR with suspected ARVC fulfil ARVC imaging criteria (3%) but more have otherwise unrecognised diseases (4.6%) mimicking potentially ARVC. Clinical assessment should reflect this, emphasising the assessment and/or exclusion of potential mimics in parallel with the detection of ARVC major and minor criteria.
Cardiovascular magnetic resonance; Arrhythmogenic right ventricular cardiomyopathy; Differential diagnosis; Mimics
During the past two decades, numerous disease-causing genes for different cardiomyopathies have been identified. These discoveries have led to better understanding of disease pathogenesis and initial steps in the application of mutation analysis in the evaluation of affected individuals and their family members. As knowledge of the genetic abnormalities, and insight into cellular and organ biology has grown, so has appreciation of the level of complexity of interaction between genotype and phenotype across disease states. What were initially thought to be one-to-one gene-disease correlates have turned out to display important relational plasticity dependent in large part on the genetic and environmental backgrounds into which the genes of interest express. The current state of knowledge with regard to genetics of cardiomyopathy represents a starting point to address the biology of disease, but is not yet developed sufficiently to supplant clinically based classification systems or, in most cases, to guide therapy to any significant extent. Future work will of necessity be directed towards elucidation of the biological mechanisms of both rare and common gene variants and environmental determinants of plasticity in the genotype–phenotype relationship with the ultimate goal of furthering our ability to identify, diagnose, risk stratify, and treat this group of disorders which cause heart failure and sudden death in the young.
Immunoreactive signal for the desmosomal protein plakoglobin (γ-catenin) is reduced at cardiac intercalated disks in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), a highly arrhythmogenic condition caused by mutations in genes encoding desmosomal proteins. Previously, we observed a “false positive” case in which plakoglobin signal was reduced in a patient initially thought to have ARVC but who actually had cardiac sarcoidosis. Sarcoidosis can masquerade clinically as ARVC, but has not previously been associated with altered desmosomal proteins.
Methods and Results
We observed marked reduction in immunoreactive signal for plakoglobin at cardiac myocyte junctions in patients with sarcoidosis and giant cell myocarditis, both highly arrhythmogenic forms of myocarditis associated with granulomatous inflammation. In contrast, plakoglobin signal was not depressed in lymphocytic (non-granulomatous) myocarditis. To determine whether cytokines might promote dislocation of plakoglobin from desmosomes, we incubated cultures of neonatal rat ventricular myocytes with selected inflammatory mediators. Brief exposure to low concentrations of IL-17, TNFα and IL-6, cytokines implicated in granulomatous myocarditis, caused translocation of plakoglobin from cell-cell junctions to intracellular sites, whereas other potent cytokines implicated in non-granulomatous myocarditis had no effect, even at much high concentrations. We also observed myocardial expression of IL-17 and TNFα, and elevated serum levels of inflammatory mediators including IL-6R, IL-8, MCP1 and MIP1β in ARVC patients (all p<0.0001 compared with controls).
These results suggest novel disease mechanisms involving desmosomal proteins in granulomatous myocarditis and implicate cytokines, perhaps derived in part from the myocardium, in disruption of desmosomal proteins and arrhythmogenesis in ARVC.
plakoglobin; desmosome; sarcoidosis; giant cell myocarditis; cytokines
Anecdotal observations suggest that sub-clinical electrophysiological manifestations of arrhythmogenic right ventricular cardiomyopathy (ARVC) develop before detectable structural changes ensue on cardiac imaging. To test this hypothesis, we investigated a murine model with conditional cardiac genetic deletion of one desmoplakin allele (DSP ±) and compared the findings to patients with non-diagnostic features of ARVC who carried mutations in desmoplakin.
Methods and results
Murine: the DSP (±) mice underwent electrophysiological, echocardiographic, and immunohistochemical studies. They had normal echocardiograms but delayed conduction and inducible ventricular tachycardia associated with mislocalization and reduced intercalated disc expression of Cx43. Sodium current density and myocardial histology were normal at 2 months of age. Human: ten patients with heterozygous mutations in DSP without overt structural heart disease (DSP+) and 12 controls with supraventricular tachycardia were studied by high-density electrophysiological mapping of the right ventricle. Using a standard S1–S2 protocol, restitution curves of local conduction and repolarization parameters were constructed. Significantly greater mean increases in delay were identified particularly in the outflow tract vs. controls (P< 0.01) coupled with more uniform wavefront progression. The odds of a segment with a maximal activation–repolarization interval restitution slope >1 was 99% higher (95% CI: 13%; 351%, P= 0.017) in DSP+ vs. controls. Immunostaining revealed Cx43 mislocalization and variable Na channel distribution.
Desmoplakin disease causes connexin mislocalization in the mouse and man preceding any overt histological abnormalities resulting in significant alterations in conduction–repolarization kinetics prior to morphological changes detectable on conventional cardiac imaging. Haploinsufficiency of desmoplakin is sufficient to cause significant Cx43 mislocalization. Changes in sodium current density and histological abnormalities may contribute to a worsening phenotype or disease but are not necessary to generate an arrhythmogenic substrate. This has important implications for the earlier diagnosis of ARVC and risk stratification.
Arrhythmia; Conduction; ARVC; Repolarization; Desmosome; Desmoplakin
hypertrophic cardiomyopathy; sudden death; risk stratification
Familial hypertrophic cardiomyopathy (FHC) is an autosomal dominant disease, which in about 30% of the patients is caused by missense mutations in one allele of the β-myosin heavy chain (β-MHC) gene (MYH7). To address potential molecular mechanisms underlying the family-specific prognosis, we determined the relative expression of mutant versus wild-type MYH7-mRNA. We found a hitherto unknown mutation-dependent unequal expression of mutant to wild-type MYH7-mRNA, which is paralleled by similar unequal expression of β-MHC at the protein level. Relative abundance of mutated versus wild-type MYH7-mRNA was determined by a specific restriction digest approach and by real-time PCR (RT-qPCR). Fourteen samples from M. soleus and myocardium of 12 genotyped and clinically well-characterized FHC patients were analyzed. The fraction of mutated MYH7-mRNA in five patients with mutation R723G averaged to 66 and 68% of total MYH7-mRNA in soleus and myocardium, respectively. For mutations I736T, R719W and V606M, fractions of mutated MYH7-mRNA in M. soleus were 39, 57 and 29%, respectively. For all mutations, unequal abundance was similar at the protein level. Importantly, fractions of mutated transcripts were comparable among siblings, in younger relatives and unrelated carriers of the same mutation. Hence, the extent of unequal expression of mutated versus wild-type transcript and protein is characteristic for each mutation, implying cis-acting regulatory mechanisms. Bioinformatics suggest mRNA stability or splicing effectors to be affected by certain mutations. Intriguingly, we observed a correlation between disease expression and fraction of mutated mRNA and protein. This strongly suggests that mutation-specific allelic imbalance represents a new pathogenic factor for FHC.
Electronic supplementary material
The online version of this article (doi:10.1007/s00395-011-0205-9) contains supplementary material, which is available to authorized users.
Hypertrophic cardiomyopathy; Allelic imbalance; Cardiac β-myosin heavy chain; Myosin missense mutation; mRNA quantification
We sought to determine the impact of implantable cardioverter-defibrillator (ICD) therapy in patients with familial arrhythmogenic right ventricular cardiomyopathy (ARVC).
Arrhythmogenic right ventricular cardiomyopathy is a cause of sudden cardiac death, which may be prevented by ICD.
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.
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.
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.
PMID: 15680719 CAMSID: cams1792
Cellular adhesion mediated by cardiac desmosomes is a prerequisite for proper electric propagation mediated by gap junctions in the myocardium. However, the molecular principles underlying this interdependence are not fully understood.
The purpose of this study was to determine potential causes of right ventricular conduction abnormalities in a patient with borderline diagnosis of arrhythmogenic right ventricular cardiomyopathy.
To assess molecular changes, the patient's myocardial tissue was analyzed for altered desmosomal and gap junction (connexin43) protein levels and localization. In vitro functional studies were performed to characterize the consequences of the desmosomal mutations.
Loss of plakoglobin signal was evident at the cell junctions despite expression of the protein at control levels. Although the distribution of connexin43 was not altered, total protein levels were reduced and changes in phosphorylation were observed. The truncation mutant in desmocollin-2a is deficient in binding plakoglobin. Moreover, the ability of desmocollin-2a to directly interact with connexin43 was abolished by the mutation. No pathogenic potential of the desmoglein-2 missense change was identified.
The observed abnormalities in gap junction protein expression and phosphorylation, which precede an overt cardiac phenotype, likely are responsible for slow myocardial conduction in this patient. At the molecular level, altered binding properties of the desmocollin-2a mutant may contribute to the changes in connexin43. In particular, the newly identified interaction between the desmocollin-2a isoform and connexin43 provides novel insights into the molecular link between desmosomes and gap junctions.
Cardiomyopathy; Conduction; Connexin43; Desmocollin-2; Desmoglein-2; Desmosome; Functional studies; Gap junction; Mutation; Plakoglobin; ARVC, arrhythmogenic right ventricular cardiomyopathy; Cx43, connexin43; DAPI, 4′,6-diamidino-2-phenylindole; DSC2, desmocollin-2; DSG2, desmoglein-2; DSP, desmoplakin; GFP, green fluorescent protein; GST, glutathione-S-transferase; ICS, intracellular cadherin segment; PG, plakoglobin; PKP2, plakophilin-2; RV, right ventricle; YFP, yellow fluorescent protein
In 1994, an International Task Force proposed criteria for the clinical diagnosis of ARVC/D which facilitated recognition and interpretation of the frequently non-specific clinical features of ARVC/D. This enabled confirmatory clinical diagnosis in index cases through exclusion of phenocopies, and provided a standard upon which clinical research and genetic studies could be based. Structural, histological, electrocardiographic, arrhythmic, and familial features of the disease were incorporated into the criteria, subdivided into major and minor according to the specificity of their association with ARVC/D. At that time, clinical experience with ARVC/D was dominated by symptomatic index cases and sudden cardiac death victims: the overt and/or severe end of the disease spectrum. Consequently, the 1994 criteria were highly specific but lacked sensitivity for early and familial disease.
Methods and Results
Revision of the diagnostic criteria provides guidance on the role of emerging diagnostic modalities and advances in the genetics of ARVC/D. The criteria have been modified to incorporate new knowledge and technology to improve diagnostic sensitivity, but with the important requisite of maintaining diagnostic specificity. The approach classifying structural, histological, electrocardiographic, arrhythmic, and genetic features of the disease as major and minor criteria has been maintained. In this modification of the Task Force Criteria, quantitative criteria are proposed and abnormalities are defined based on comparison with normal subject data.
The diagnosis of ARVC/D based on modification of the original Task Force criteria is a working framework to improve the diagnosis and management of this condition.
cardiomyopathy; diagnosis; echocardiography; electrocardiography; magnetic resonance imaging
In 1994, an International Task Force proposed criteria for the clinical diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) that facilitated recognition and interpretation of the frequently nonspecific clinical features of ARVC/D. This enabled confirmatory clinical diagnosis in index cases through exclusion of phenocopies and provided a standard on which clinical research and genetic studies could be based. Structural, histological, electrocardiographic, arrhythmic, and familial features of the disease were incorporated into the criteria, subdivided into major and minor categories according to the specificity of their association with ARVC/D. At that time, clinical experience with ARVC/D was dominated by symptomatic index cases and sudden cardiac death victims–the overt or severe end of the disease spectrum. Consequently, the 1994 criteria were highly specific but lacked sensitivity for early and familial disease.
Methods and Results
Revision of the diagnostic criteria provides guidance on the role of emerging diagnostic modalities and advances in the genetics of ARVC/D. The criteria have been modified to incorporate new knowledge and technology to improve diagnostic sensitivity, but with the important requisite of maintaining diagnostic specificity. The approach of classifying structural, histological, electrocardiographic, arrhythmic, and genetic features of the disease as major and minor criteria has been maintained. In this modification of the Task Force criteria, quantitative criteria are proposed and abnormalities are defined on the basis of comparison with normal subject data.
The present modifications of the Task Force Criteria represent a working framework to improve the diagnosis and management of this condition.
Clinical Trial Registration
clinicaltrials.gov Identifier: NCT00024505.
Arrhythmias, cardiac; Arrhythmogenic right ventricular cardiomyopathy/dysplasia; Death, sudden, cardiac; Diagnosis; Echocardiography; Electrocardiography; Magnetic resonance imaging
To evaluate arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) in affected families with desmosome mutations on the basis of the recently revised Task Force Criteria (TFC).
Methods and results
One hundred and three consecutive carriers of pathogenic desmosome mutations and 102 mutation-negative relatives belonging to 22 families with dominant and 14 families with recessive ARVC/D were evaluated according to the original and revised TFC. Serial cardiac assessment with 12-lead, signal-averaged, and 24 h ambulatory ECG and two-dimensional echocardiography was performed. Clinical events and outcome were prospectively analysed up to 24 years (median 4 years). With the revised criteria, 16 carriers were newly diagnosed on the basis of ECG abnormalities in 100%, ventricular arrhythmias in 79%, and functional/structural alterations in 31%, increasing diagnostic sensitivity from 57 to 71% (P = 0.001). Task Force Criteria specificity improved from 92 to 99% (P = 0.016). In dominant mutation carriers, penetrance changed significantly (61 vs. 42%, P = 0.001); no changes were observed in recessive homozygous carriers (97 vs. 97%, P = 1.00). Affected carriers according to the revised TFC (n = 73) had 12-lead ECG abnormalities in 96%, ventricular arrhythmias in 91%, and functional/structural alterations fulfilling echocardiographic criteria in 76%. Cumulative and event-free survival did not differ significantly between dominant and recessive affected carriers, being at 78.6 vs. 76 and 51.7 vs. 55.4%, respectively, by the age of 40 years.
Revised TFC increased diagnostic sensitivity particularly in dominant ARVC/D. Serial family evaluation may rely on electrocardiography which seems to have the best diagnostic utility particularly in early disease that is not detectable by two-dimensional echocardiography.
Cardiomyopathy; Arrhythmogenic right ventricular cardiomyopathy/dysplasia; Diagnostic criteria; Desmosome mutations