Impact of DCM-Causing Genetic Background on Long-Term Response to Cardiac Resynchronization Therapy.

BACKGROUND: Patients with nonischemic dilated cardiomyopathy (DCM), severe left ventricular (LV) dysfunction, and complete left bundle branch block benefit from cardiac resynchronization therapy (CRT). However, a large heterogeneity of response to CRT is described. Several predictors of response to CRT have been identified, but the role of the underlying genetic background is still poorly explored. OBJECTIVES: In the present study, the authors sought to define differences in LV remodeling and outcome prediction after CRT when stratifying patients according to the presence or absence of DCM-causing genetic background. METHODS: From our center, 74 patients with DCM subjected to CRT and available genetic testing were retrospectively enrolled. Carriers of causative monogenic variants in validated DCM-causing genes, and/or with documented family history of DCM, were classified as affected by genetically determined disease (GEN+DCM) (n = 25). Alternatively, by idiopathic dilated cardiomyopathy (idDCM) (n = 49). The primary outcome was long-term LV remodeling and prevalence of super response to CRT (evaluated at 24-48 months after CRT); the secondary outcome was heart failure-related death/heart transplant/LV assist device. RESULTS: GEN+DCM and idDCM patients were homogeneous at baseline with the exception of QRS duration, longer in idDCM. The median follow-up was 55 months. Long-term LV reverse remodeling and the prevalence of super response were significantly higher in the idDCM group (27% in idDCM vs 5% in GEN+DCM; P = 0.025). The heart failure-related death/heart transplant/LV assist device outcome occurred more frequently in patients with GEN+DCM (53% vs 24% in idDCM; P = 0.028). CONCLUSIONS: Genotyping contributes to the risk stratification of patients with DCM undergoing CRT implantation in terms of LV remodeling and outcomes.

Brugada syndrome masked by complete left bundle branch block: A clinical and functional study of its association with the p.1449Y>H SCN5A variant.

SCN5A gene variants are associated with both Brugada syndrome and conduction disturbances, sometimes expressing an overlapping phenotype. Functional consequences of SCN5A variants assessed by patch-clamp electrophysiology are particularly beneficial for correct pathogenic classification and are related to disease penetrance and severity. Here, we identify a novel SCN5A loss of function variant, p.1449Y>H, which presented with high penetrance and complete left bundle branch block, totally masking the typical findings on the electrocardiogram. We highlight the possibility of this overlap combination that makes impossible an electrocardiographic diagnosis and, through a functional analysis, associate the p.1449Y>H variant to SCN5A pathogenicity.

Isolated left bundle branch block in the young: case reports and review of literature.

Isolated left bundle branch block (LBBB) aberrancy is exceedingly rare in the young and its clinical and genetic determinants remain poorly characterized. Furthermore, there is conflicting data on its natural history in the pediatric age group patients. We report the rare phenotype of isolated typical LBBB aberrancy in two healthy children, one of whom carried a likely pathogenic mutation in the coding exon 1 of NKX2-5 (p.Q22R, c.65A > G, rs201442000). Our findings suggest that isolated LBBB aberrancy could be non-progressive in some children, at least in the short term. However, given the paucity of data on this entity, we recommend continued long-term surveillance.

Malignant Arrhythmia with Variants of Desmocollin-2 and Desmoplakin Genes.

Malignant arrhythmia is a fast cardiac arrhythmia that can lead to a hemodynamic abnormality within a short time, most of which is ventricular tachycardia or ventricular fibrillation (VF), which should be managed in time. Both organic and nonorganic cardiac diseases have the potential to cause malignant arrhythmia. We report a noteworthy case of malignant arrhythmia in a teenager during exercise. Transthoracic echocardiography, cardiac magnetic resonance (CMR), electrophysiological study, magnetic resonance imaging of the brain, electroencephalography, chest X-ray, and blood tests were all normal. Twelve-lead electrocardiography showed incomplete right bundle branch block (IRBBB). Two heterozygous missense variants of the desmocollin-2 gene (DSC2, c.G2446A/p.V816M) and desmoplakin gene (DSP, c.G3620A/p.R1207K) were detected in the peripheral blood of this teenager and his father by genetic testing, which encoded a desmosomal protein that was related to arrhythmogenic right ventricular cardiomyopathy (ARVC). In these two rare variants, DSC2 V816M has been reported but uncertain significance, whereas DSP R1207K is never reported. Therefore, the two site variants in DSC2 and DSP genes are likely to become a new research focus for diagnosis and treatment of ARVC in the future. Meanwhile, this report emphasizes that, in addition to a standard set of laboratory tests and examinations, genetic testing may be useful for analyzing the causes of malignant arrhythmia.

Familial Clustering of Cardiac Conduction Defects and Pacemaker Insertion.

BACKGROUND: The etiopathogenesis of electrocardiographic bundle branch and atrioventricular blocks is not fully understood. We investigated familial clustering of cardiac conduction defects and pacemaker insertion in the FHS (Framingham Heart Study). Additionally, we assessed familial clustering of pacemaker insertion in the Danish general population. METHODS: In FHS, we used multivariable-adjusted logistic regression models to investigate the association of parental atrioventricular block (PR interval, ≥0.2 s), complete bundle branch block (QRS, ≥0.12 s), or pacemaker insertion with the occurrence of cardiac conduction abnormalities in their offspring. The Danish nationwide administrative registries were interrogated to assess the relations of parental pacemaker insertion with offspring pacemaker insertion. RESULTS: In FHS (n=371 cases with first-degree atrioventricular block, complete bundle branch block, or pacemaker insertion, and 1471 age- and sex-matched controls), individuals with at least 1 affected parent with a conduction defect had a 1.65-fold odds (odds ratio, 95% CI, 1.32-2.07) for manifesting an atrioventricular block and a 1.62-fold odds (95% CI, 1.08-2.42) for developing a complete bundle branch block. If at least 1 parent had any electrocardiographic conduction defect or pacemaker insertion, the offspring had a 1.62-fold odds (95% CI, 1.31-2.00) for experiencing any of these conditions. In Denmark (n=2 824 199 individuals; 5397 incident pacemaker implantations), individuals with at least 1 first-degree relative with history of pacemaker insertion had a multivariable-adjusted 1.68-fold (incidence rate ratio, 95% CI, 1.49-1.89) risk of undergoing a pacemaker insertion. If the affected relative was ≤45 years of age, the incidence rate ratio was markedly increased to 51.0 (95% CI, 32.7-79.9). CONCLUSIONS: Cardiac conduction blocks and risk for pacemaker insertion cluster within families. A family history of conduction system disturbance or pacemaker insertion should trigger increased awareness of a similar propensity in other family members, especially so when the conduction system disease occurs at a younger age.

Electro-vectorcardiographic demonstration of bifascicular block associated with ventricular preexcitation.

Down syndrome occurs more frequently in the offsprings of older pregnant women and may be associated with atrioventricular septal defect. This refers to a broad spectrum of malformations characterized by a deficiency of the atrioventricular septum and abnormalities of the atrioventricular valves caused by an abnormal fusion of the superior and inferior endocardial cushions with the midportion of the atrial septum and the muscular portion of the ventricular septum.

Left bundle branch block in Duchenne muscular dystrophy: Prevalence, genetic relationship and prognosis.

BACKGROUND: Duchenne muscular dystrophy (DMD) is an inherited myogenic disorder due to mutations in the dystrophin gene on chromosome Xp21.1. We designed this study to determine the prevalence of left bundle branch block (LBBB), whether there is a relationship between LBBB and genetic pattern, and to assess predictive factors for acute cardiac events and mortality in adult DMD patients. METHODS: We reviewed the charts of DMD followed at the Home Mechanical Ventilation Unit of the Raymond Poincare University Hospital. RESULTS: A total of 121 patients, aged from 18 to 41 years have been included in our study. Median vital capacity (VC) was 12% [7; 19.5] of predicted. Almost all patients were on home mechanical ventilation (95%). LBBB was present in 15 patients (13%); among them, 10 disclosed exonic deletions. After a median follow up of 6 years, 21 patients (17%) experienced acute heart failure (AHF), 7 patients (6%) supraventricular arrhythmia, 3 patients (2.4%) ventricular tachycardia, 4 patients (3%) significant electrical disturbances. LBBB was significantly associated with cardiac events (OR = 12.7; 95%CI [3.78-42.7]; p <0.0001) and mortality (OR = 4.4; 95%CI [1.44-13.7]; p 0.009). Presence of residual dystrophin protein was not associated with significant less cardiac events. Age and LVEF were also predictive factors for cardiac events and mortality. CONCLUSION: LBBB is relatively frequent in DMD and is a major predictive factor for cardiac events and mortality. Presence of residual dystrophin protein was not associated with a lower incidence of cardiac events.

A mutant HCN4 channel in a family with bradycardia, left bundle branch block, and left ventricular noncompaction.

We found that a female infant presenting with left bundle branch block and left ventricular noncompaction carries uninvestigated gene mutations HCN4(G811E), SCN5A(L1988R), DMD(S2384Y), and EMD(R203H). Here, we explored the possible pathogenicity of HCN4(G811E), which results in a G811E substitution in hyperpolarization-activated cyclic nucleotide-gated channel 4, the main subunit of the cardiac pacemaker channel. Voltage-clamp measurements in a heterologous expression system of HEK293T cells showed that HCN4(G811E) slightly reduced whole-cell HCN4 channel conductance, whereas it did not affect the gating kinetics, unitary conductance, or cAMP-dependent modulation of voltage-dependence. Immunocytochemistry and immunoblot analysis showed that the G811E mutation did not impair the membrane trafficking of the channel subunit in the heterologous expression system. These findings indicate that HCN4(G811E) may not be a monogenic factor to cause the cardiac disorders.

Neonatal complex arrhythmias possibly related to a TTN mutation.

We describe a neonate born with complex arrhythmias that included concurrent atrial and ventricular tachycardias. Genetic testing demonstrated a mutation in the TTN gene, which codes for titin, a large protein found in striated muscle sarcomeres. The complex arrhythmias were successfully treated with amiodarone and flecainide. The patient remains asymptomatic with normal biventricular function. We speculate that the complex arrhythmias and TTN gene mutation may be related.

Wide QRS in a 2-month infant associated with recurrent ventricular tachycardia: A case of Brugada-like syndrome.

We report the case of a 2-month old infant who experienced recurrent sustained ventricular tachycardia (VT) in a structurally normal heart. Resting electrocardiogram (ECG) showed wide QRS with a complete right bundle branch bloc (RBBB) morphology. There was no family history of syncope or sudden death, but the ECGs of the father and the brother showed incomplete RBBB with negative T waves on V1 lead. This case seems to fit well with the newly defined entity of Brugada-like syndrome with a highly suspected genetic underlying disposition.

An investigation of the association of the H558R polymorphism of the SCN5A gene with idiopathic cardiac conduction disorders.

AIM: The aim of this study was to investigate the predictive value of the rs1805124 polymorphism of the SCN5A gene with regard to idiopathic cardiac conduction disorders. RESULTS: The AG genotype frequency was significantly higher in patients with an atrioventricular block (61,2%±6,0%) compared with healthy control subjects (34,8%±2,3%), p<0.0001. The AG genotype frequencies among patients with only idiopathic complete right bundle-branch block (CRBBB) (54,2%±5,5%) and those with both CLBBB and LAH (50%±5,1) were significantly higher than in the control group (34,8%±2,3%), p<0.005. CONCLUSIONS: The AG genotype of the H558R (rs1805124) polymorphism of the SCN5A gene is a genetic predictor of idiopathic disorders of atrioventricular and intraventricular conduction.

p.Y1449C SCN5A mutation associated with overlap disorder comprising conduction disease, Brugada syndrome, and atrial flutter.

Mutations in the SCN5A gene, which encodes the cardiac sodium channel, have been associated with cardiac arrhythmia syndromes and conduction disease. Specific SCN5A mutations had initially been considered to cause specific phenotypes. More recently, some SCN5A mutations have been associated with overlap syndromes, characterized by phenotypic heterogeneity within and between mutation carriers. Here we report and associate the presence of the p.Y1449C SCN5A mutation in a single family with a spectrum of cardiac phenotypes including conduction disease, Brugada syndrome and atrial arrhythmias, for the first time to our knowledge.

A mutation in the Z-line Cypher/ZASP protein is associated with arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an important cause of malignant arrhythmia and sudden death particularly in young people. Although it is considered a desmosomal disease, mutations in non-desmosomal genes have also been identified. We report on a family where a mutation in LDB3 is associated with this condition. The index case and first and second degree relatives underwent a complete clinical evaluation: physical examination, electrocardiography (ECG), signal-averaged ECG, 2D echocardiogram, cardiac magnetic resonance and 24-h monitoring. After ruling out mutations in the five desmosomal genes, genetic testing by means of Next Generation Sequencing was carried out on the proband. A heterozygous missense mutation in LDB3 c.1051A>G was identified. This result was confirmed by subsequent Sanger DNA sequencing. Another six carriers were identified amongst her relatives. Three subjects fulfilled the criteria for a definitive diagnosis of ARVC and one reached a borderline diagnosis. In conclusion, this is the first family with ARVC where a mutation in LDB3 is associated with ARVC. Next generation sequencing arises as a particular useful tool to point to new causative genes in ARVC.

[The Role of Transcriptional Factor Gene TBX5 in Development of Disorders of Cadiac Conduction].

In order to study relationship between development of idiopathic atrioventricular (AV) and intraventricular disorders of cardiac conduction (DCC) with single nucleotide polymorphism (SNP) of TBX5 gene we examined 260 persons with primary DCC (71 patients with abnormal AV conduction, 84 and 105 patients with disordered conduction along right and left brunches of His bundle, respectively) as well as 257 individuals without cardiovascular diseases (control group). Patients were divided into subgroups depending on nosology, age, and sex. Diagnosis was verified by standard cardiological methods and retrospective analysis of available results of previous examinations. Molecular-genetic study of DNA was used for identification of genotype of TBX5 gene SNP. The results indicated significant preponderance of rare GG genotype (CNP-marker rs3825214) of TBX5 gene in the group of patients with left bundle branch block and in the subgroup of women with this pathology. These data suggest that presence of GG genotype (rs3825214) of TBX5 gene increases probability of development of idiopathic DCC along left bundle branch mainly in women.

The effect of connexin40 deficiency on ventricular conduction system function during development.

AIMS: The aim of this study was to characterize ventricular activation patterns in normal and connexin40-deficient mice in order to dissect the role of connexin40 in developing the conduction system. METHODS AND RESULTS: We performed optical mapping of epicardial activation between ED9.5-18.5 and analysed ventricular activation patterns and times of left ventricular activation. Mouse embryos deficient for connexin40 were compared with normal and heterozygous littermates. Morphology of the primary interventricular ring (PIR) was delineated with the help of T3-LacZ transgene. Four major types of ventricular activation patterns characterized by primary breakthrough in different parts of the heart were detected during development: PIR, left ventricular apex, right ventricular apex, and dual right and left ventricular apices. Activation through PIR was frequently present at the early stages until ED12.5. From ED14.5, the majority of hearts showed dual left and right apical breakthrough, suggesting functionality of both bundle branches. Connexin40-deficient embryos showed initially a delay in left bundle branch function, but the right bundle branch block, previously described in the adults, was not detected in ED14.5 embryos and appeared only gradually with 80% penetrance at ED18.5. CONCLUSION: The switch of function from the early PIR conduction pathway to the mature apex to base activation is dependent upon upregulation of connexin40 expression in the ventricular trabeculae. The early function of right bundle branch does not depend on connexin40. Quantitative analysis of normal mouse embryonic ventricular conduction patterns will be useful for interpretation of effects of mutations affecting the function of the cardiac conduction system.

Mutational spectrum in the Ca(2+)--activated cation channel gene TRPM4 in patients with cardiac conductance disturbances.

Very recently, mutations in the TRPM4 gene have been identified in four pedigrees as the cause of an autosomal dominant form of cardiac conduction disease. To determine the role of TRPM4 gene variations, the relative frequency of TRPM4 mutations and associated phenotypes was assessed in a cohort of 160 unrelated patients with various types of inherited cardiac arrhythmic syndromes. In eight probands with atrioventricular block or right bundle branch block--five familial cases and three sporadic cases--a total of six novel and two published TRPM4 mutations were identified. In patients with sinus node dysfunction, Brugada syndrome, or long-QT syndrome, no mutations were found. The novel mutations include six amino acid substitutions and appeared randomly distributed through predicted TRPM4 protein. In addition, eight polymorphic sites including two in-frame deletions were found. Mutations separated from polymorphisms by absence in control individuals and familial cosegregation in some families. In summary, TRPM4 gene mutations appear to play a major role in cardiac conduction disease but not for other related syndromes so far. The phenotypes are variable and clearly suggestive of additional factors modulating the disease phenotype in some patients.

Clinical and genetic investigation of a Japanese family with cardiac fabry disease. Identification of a novel α-galactosidase A missense mutation (G195V).

Fabry disease is an X-linked lysosomal storage disorder caused by mutations of the α-galactosidase A gene (GLA), and the disease is a relatively prevalent cause of left ventricular hypertrophy mimicking idiopathic hypertrophic cardiomyopathy. We assessed clinically 5 patients of a three-generation family and also searched for GLA mutations in 10 family members. The proband had left ventricular hypertrophy with localized thinning in the basal posterior wall and late gadolinium enhancement (LGE) in the near-circumferential wall in cardiovascular magnetic resonance images and her sister had vasospastic angina pectoris without organic stenosis of the coronary arteries. LGE notably appeared in parallel with decreased α-galactosidase A activity and increased NT-pro BNP in our patients. We detected a new GLA missense mutation (G195V) in exon 4, resulting in a glycine-to-valine substitution. Of the 10 family members, 5 family members each were positive and negative for this mutation. These new data extend our clinical and molecular knowledge of GLA gene mutations and confirm that a novel missense mutation in the GLA gene is important not only for a precise diagnosis of heterozygous status, but also for confirming relatives who are negative for this mutation.

Arrhythmogenic right ventricular cardiomyopathy in boxers.

Arrhythmogenic right ventricular cardiomyopathy, formerly termed boxer cardiomyopathy, is a familial primary myocardial disease that is prevalent in boxers. Unique histopathologic changes in the myocardium lead to conduction abnormalities that typically manifest as ventricular tachyarrhythmias with left bundle branch block morphology. Affected dogs can be asymptomatic or may have syncope and/or exercise intolerance. Diagnosis can be difficult, and indications for antiarrhythmic therapy are not always clear. A small number of dogs present with systolic dysfunction and/or congestive heart failure. Screening in asymptomatic breeding dogs was difficult until the recent development of genetic testing.