Pathological findings of myocardium in a patient with cardiac conduction defect associated with an SCN5A mutation.

A 16-year-old Japanese man was admitted to our hospital because of syncope during exercise. His father and his younger brother had permanent pacemaker implantation because of sick sinus syndrome. Several examinations revealed first-degree atrioventricular block, complete right bundle branch block, sick sinus syndrome, and ventricular tachycardia with normal cardiac function. As no abnormalities were evident on coronary angiography, right ventricular endomyocardial biopsy was performed. It showed myocardial disarrangement and lipofuscin accumulation in hypertrophic myocytes. Moreover, electron microscopy showed a few degenerative myocytes, Z-band streaming, disarrangement, increased small capillaries with Weibel-Palade bodies in endothelial cells, and endothelial proliferations. Genetic analysis of the proband, his father, and his younger brother revealed a missense mutation, D1275N, in SCN5A, a gene which encodes sodium ion channel protein, are related to cardiomyopathy and arrhythmia. The proband was diagnosed with a cardiac conduction defect (CCD) and underwent permanent pacemaker implantation. These pathological findings suggest various myocardial changes presented in CCD patients with a missense mutation, D1275N, in SCN5A.

Clinical Manifestations and Long-Term Mortality in Lamin A/C Mutation Carriers From a Japanese Multicenter Registry.

BACKGROUND: Mutation in the lamin A/C gene (LMNA) is associated with several cardiac phenotypes, such as cardiac conduction disorders (CCD), atrial arrhythmia (AA), malignant ventricular arrhythmia (MVA) and left ventricular dysfunction (LVD), leading to sudden cardiac death (SCD) and/or end-stage heart failure. We investigated how these phenotypes are associated with each other and which of them are most important for total mortality. Methods and Results: A multicenter registry included 110 LMNA mutation carriers (age, 43±15 years, male: 62%) from 60 families. After genetic diagnosis of LMNA mutation (missense: 27%, non-missense: 73%), patients or subjects were followed to evaluate the manifestations of their phenotypes and the risk of total mortality; 90 patients could be followed (median: 5 [0-35] years). Prevalence of the 4 clinical phenotypes was significantly increased during follow-up. Among these phenotypes, AA was significantly associated with MVA. CCD was significantly associated with LVD. LVD, meanwhile, was significantly associated with CCD and MVA. Male sex was significantly associated with MVA. Furthermore, during follow-up, 17 patients died: 12 end-stage heart failure, 4 SCD and 1 stroke. LVD was the only independent predictor for all-cause death (OR: 41.7, 95% CI: 4.1-422.3; P=0.0016). CONCLUSIONS: Several cardiac phenotypes were age-dependently increased in LMNA mutation carriers, suggesting that ICD or CRT-D could suppress SCD after middle age; however, LVD leading to end-stage heart failure was the only independent predictor for total mortality.

Gene-Based Risk Stratification for Cardiac Disorders in LMNA Mutation Carriers.

BACKGROUND: Mutations in LMNA (lamin A/C), which encodes lamin A and C, typically cause age-dependent cardiac phenotypes, including dilated cardiomyopathy, cardiac conduction disturbance, atrial fibrillation, and malignant ventricular arrhythmias. Although the type of LMNA mutations have been reported to be associated with susceptibility to malignant ventricular arrhythmias, the gene-based risk stratification for cardiac complications remains unexplored. METHODS AND RESULTS: The multicenter cohort included 77 LMNA mutation carriers from 45 families; cardiac disorders were retrospectively analyzed. The mean age of patients when they underwent genetic testing was 45±17, and they were followed for a median 49 months. Of the 77 carriers, 71 (92%) were phenotypically affected and showed cardiac conduction disturbance (81%), low left ventricular ejection fraction (<50%; 45%), atrial arrhythmias (58%), and malignant ventricular arrhythmias (26%). During the follow-up period, 9 (12%) died, either from end-stage heart failure (n=7) or suddenly (n=2). Genetic analysis showed truncation mutations in 58 patients from 31 families and missense mutations in 19 patients from 14 families. The onset of cardiac disorders indicated that subjects with truncation mutations had an earlier occurrence of cardiac conduction disturbance and low left ventricular ejection fraction, than those with missense mutations. In addition, the truncation mutation was found to be a risk factor for the early onset of cardiac conduction disturbance and the occurrence of atrial arrhythmias and low left ventricular ejection fraction, as estimated using multivariable analyses. CONCLUSIONS: The truncation mutations were associated with manifestation of cardiac phenotypes in LMNA-related cardiomyopathy, suggesting that genetic analysis might be useful for diagnosis and risk stratification.

Progressive Atrial Conduction Defects Associated With Bone Malformation Caused by a Connexin-45 Mutation.

BACKGROUND: Inherited cardiac conduction disease is a rare bradyarrhythmia associated with mutations in various genes that affect action potential propagation. It is often characterized by isolated conduction disturbance of the His-Purkinje system, but it is rarely described as a syndromic form. OBJECTIVES: The authors sought to identify the genetic defect in families with a novel bradyarrhythmia syndrome associated with bone malformation. METHODS: The authors genetically screened 15 European cases with genotype-negative de novo atrioventricular (AV) block and their parents by trio whole-exome sequencing, plus 31 Japanese cases with genotype-negative familial AV block or sick sinus syndrome by targeted exon sequencing of 457 susceptibility genes. Functional consequences of the mutation were evaluated using an in vitro cell expression system and in vivo knockout mice. RESULTS: The authors identified a connexin-45 (Cx45) mutation (p.R75H) in 2 unrelated families (a de novo French case and a 3-generation Japanese family) who presented with progressive AV block, which resulted in atrial standstill without ventricular conduction abnormalities. Affected individuals shared a common extracardiac phenotype: a brachyfacial pattern, finger deformity, and dental dysplasia. Mutant Cx45 expressed in Neuro-2a cells showed normal hemichannel assembly and plaque formation. However, Lucifer yellow dye transfer and gap junction conductance between cell pairs were severely impaired, which suggested that mutant Cx45 impedes gap junction communication in a dominant-negative manner. Tamoxifen-induced, cardiac-specific Cx45 knockout mice showed sinus node dysfunction and atrial arrhythmia, recapitulating the intra-atrial disturbance. CONCLUSIONS: Altogether, the authors showed that Cx45 mutant p.R75H is responsible for a novel disease entity of progressive atrial conduction system defects associated with craniofacial and dentodigital malformation.

Echocardiographic estimation of left atrial pressure in beagle dogs with experimentally-induced mitral valve regurgitation.

Non-invasive and immediate estimation of left atrial pressure (LAP) is very useful for the management of mitral regurgitation (MR), and many reports have assessed echocardiographic estimations of LAP to date. However, it has been unclear of which examination and evaluate article possess the best accuracy for the MR severity. The present research aims to establish the echocardiographic estimation equation of LAP that is well applicable for clinical MR dogs. After the chordae tendineae rupture was experimentally induced via left atriotomy in six healthy beagle dogs (three males and three females, two years old, weighing between 9.8 to 12.8 kg), a radio telemetry transmitter catheter was inserted, which allows the continuous recordings of LAP without the use of sedation. Approximately 5 weeks after the surgery, echocardiographic examination, indirect blood pressure measurement, measurement of plasma atrial natriuretic peptide (ANP) and LAP measurement by way of the radio telemetry system was performed simultaneously. Subsequently, simple linear regression equations between LAP and each variable were obtained, and the equations were evaluated whether to be applicable for clinical MR dogs. As a result, the ratio of early diastolic mitral flow to early diastolic lateral mitral annulus velocity (E/Ea) had the strongest correlation as maximum LAP=7.03*(E/Ea)-54.86 (r=0.74), and as mean LAP=4.94*(E/Ea)-40.37 (r=0.70) among the all variables. Therefore, these two equations associated with E/Ea should bring more precise and instant estimations of maximum and mean LAP in clinical MR dogs.

Heart-specific small subunit of myosin light chain phosphatase activates rho-associated kinase and regulates phosphorylation of myosin phosphatase target subunit 1.

Phosphorylation of myosin regulatory light chain (MLC) plays a regulatory role in muscle contraction, and the level of MLC phosphorylation is balanced by MLC kinase and MLC phosphatase (MLCP). MLCP consists of a catalytic subunit, a large subunit (MYPT1 or MYPT2), and a small subunit. MLCP activity is regulated by phosphorylation of MYPTs, whereas the role of small subunit in the regulation remains unknown. We previously characterized a human heart-specific small subunit (hHS-M(21)) that increased the sensitivity to Ca(2+) in muscle contraction. In this study, we investigated the role of hHS-M(21) in the regulation of MLCP phosphorylation. Two isoforms of hHS-M(21), hHS-M(21)A and hHS-M(21)B, preferentially bound the C-terminal one-third region of MYPT1 and MYPT2, respectively. Amino acid substitutions at a phosphorylation site of MYPT1, Ser-852, impaired the binding of MYPT1 and hHS-M(21). The hHS-M(21) increased the phosphorylation level of MYPT1 at Thr-696, which was attenuated by Rho-associated kinase (ROCK) inhibitors and small interfering RNAs for ROCK. In addition, hHS-M(21) bound ROCK and enhanced the ROCK activity. These findings suggest that hHS-M(21) is a heart-specific effector of ROCK and plays a regulatory role in the MYPT1 phosphorylation at Thr-696 by ROCK.

Cardiovascular effects of right ventricle-pulmonary artery valved conduit implantation in experimental pulmonic stenosis.

Right ventricle (RV)-pulmonary artery (PA) valved conduit (RPVC) implantation decreases RV systolic pressure in pulmonic stenosis (PS) by forming a bypass route between the RV and the PA. The present study evaluates valved conduits derived from canine aortae in a canine model of PS produced by pulmonary artery banding (PAB). Pulmonary stenosis was elicited using PAB in 10 conditioned beagles aged 8 months. Twelve weeks after PAB, the dogs were assigned to one group that did not undergo surgical intervention and another that underwent RPVC using denacol-treated canine aortic valved grafts (PAB+RPVC). Twelve weeks later, the rate of change in the RV-PA systolic pressure gradient was significantly decreased in the PAB+RPVC, compared with the PAB group (60.5 +/- 16.7% vs. 108.9 +/- 22.9%; p<0.01). In addition, the end-diastolic RV free wall thickness (RVFWd) was significantly reduced in the PAB+RPVC, compared with the PAB group (8.2 +/- 0.2 vs. 9.4 +/- 0.7 mm; p<0.05). Thereafter, regurgitation was not evident beyond the conduit valve and the decrease in RV pressure overload induced by RPVC was confirmed. The present results indicate that RPVC can be performed under a beating heart without cardiopulmonary bypass and adapted to dogs with various types of PS, including "supra valvular" PS or PS accompanied by dysplasia of the pulmonary valve. Therefore, we consider that this method is useful for treating PS in small animals.