Complex Arrhythmia Syndrome in a Knock-In Mouse Model Carrier of the N98S Calm1 Mutation.

BACKGROUND: Calmodulin mutations are associated with arrhythmia syndromes in humans. Exome sequencing previously identified a de novo mutation in CALM1 resulting in a p.N98S substitution in a patient with sinus bradycardia and stress-induced bidirectional ventricular ectopy. The objectives of the present study were to determine if mice carrying the N98S mutation knocked into Calm1 replicate the human arrhythmia phenotype and to examine arrhythmia mechanisms. METHODS: Mouse lines heterozygous for the Calm1N98S allele (Calm1N98S/+) were generated using CRISPR/Cas9 technology. Adult mutant mice and their wildtype littermates (Calm1+/+) underwent electrocardiographic monitoring. Ventricular de- and repolarization was assessed in isolated hearts using optical voltage mapping. Action potentials and whole-cell currents and [Ca2+]i, as well, were measured in single ventricular myocytes using the patch-clamp technique and fluorescence microscopy, respectively. The microelectrode technique was used for in situ membrane voltage monitoring of ventricular conduction fibers. RESULTS: Two biologically independent knock-in mouse lines heterozygous for the Calm1N98S allele were generated. Calm1N98S/+ mice of either sex and line exhibited sinus bradycardia, QTc interval prolongation, and catecholaminergic bidirectional ventricular tachycardia. Male mutant mice also showed QRS widening. Pharmacological blockade and activation of ß-adrenergic receptors rescued and exacerbated, respectively, the long-QT phenotype of Calm1N98S/+ mice. Optical and electric assessment of membrane potential in isolated hearts and single left ventricular myocytes, respectively, revealed ß-adrenergically induced delay of repolarization. ß-Adrenergic stimulation increased peak density, slowed inactivation, and left-shifted the activation curve of ICa.L significantly more in Calm1N98S/+ versus Calm1+/+ ventricular myocytes, increasing late ICa.L in the former. Rapidly paced Calm1N98S/+ ventricular myocytes showed increased propensity to delayed afterdepolarization-induced triggered activity, whereas in situ His-Purkinje fibers exhibited increased susceptibility for pause-dependent early afterdepolarizations. Epicardial mapping of Calm1N98S/+ hearts showed that both reentry and focal mechanisms contribute to arrhythmogenesis. CONCLUSIONS: Heterozygosity for the Calm1N98S mutation is causative of an arrhythmia syndrome characterized by sinus bradycardia, QRS widening, adrenergically mediated QTc interval prolongation, and bidirectional ventricular tachycardia. ß-Adrenergically induced ICa.L dysregulation contributes to the long-QT phenotype. Pause-dependent early afterdepolarizations and tachycardia-induced delayed afterdepolarizations originating in the His-Purkinje network and ventricular myocytes, respectively, constitute potential sources of arrhythmia in Calm1N98S/+ hearts.

Genome-wide screening of functional long noncoding RNAs in the epicardial adipose tissues of atrial fibrillation.

Atrial fibrillation (AF) is the most common arrhythmias, and patients with AF are facing increased risk of heart failure and ischemic stroke. However, the AF pathogenesis, especially the long noncoding RNAs (lncRNA)-related mechanism, has not been fully understood. In this study, we collected RNA sequencing data of the epicardial adipose tissues (EAT) from 6 AF and 6 sinus rhythm (SR) to identify the differentially expressed protein-coding genes (PCGs) and lncRNAs. Functionally, the differentially expressed PCGs were significantly enriched in bone development disease, chronic kidney failure, and kidney disease. Particularly, we found that homeobox (HOX) genes, especially the antisense RNAs, HOTAIRM1, HOXA-AS2 and HOXB-AS2, were significantly downregulated in EAT of AF. The biological function predictions for the dysregulated lncRNAs revealed that TNF signaling pathway was the most frequent pathway that the lncRNAs might participate in. In addition, SNHG16 and RP11-471B22.2 might participate in TGF-beta signaling and ECM-receptor interaction by interacting with the proteins involved in the pathways, respectively. Collectively, we provided some potentially pathogenic lncRNAs in AF, which might be useful for the related researchers to study their functionality and develop new therapeutics.

Novel role of the clustered miR-23b-3p and miR-27b-3p in enhanced expression of fibrosis-associated genes by targeting TGFBR3 in atrial fibroblasts.

Atrial fibrillation (AF) is the most common type of arrhythmia in cardiovascular diseases. Atrial fibrosis is an important pathophysiological contributor to AF. This study aimed to investigate the role of the clustered miR-23b-3p and miR-27b-3p in atrial fibrosis. Human atrial fibroblasts (HAFs) were isolated from atrial appendage tissue of patients with sinus rhythm. A cell model of atrial fibrosis was achieved in Ang-II-induced HAFs. Cell proliferation and migration were detected. We found that miR-23b-3p and miR-27b-3p were markedly increased in atrial appendage tissues of AF patients and in Ang-II-treated HAFs. Overexpression of miR-23b-3p and miR-27b-3p enhanced the expression of collagen, type I, alpha 1 (COL1A1), COL3A1 and ACTA2 in HAFs without significant effects on their proliferation and migration. Luciferase assay showed that miR-23b-3p and miR-27b-3p targeted two different sites in 3'-UTR of transforming growth factor (TGF)-ß1 receptor 3 (TGFBR3) respectively. Consistently, TGFBR3 siRNA could increase fibrosis-related genes expression, along with the Smad1 inactivation and Smad3 activation in HAFs. Additionally, overexpression of TGFBR3 could alleviate the increase of COL1A1, COL3A1 and ACTA2 in HAFs after transfection with miR-23b-3p and miR-27b-3p respectively. Moreover, Smad3 was activated in HAFs in response to Ang-II treatment and inactivation of Smad3 attenuated up-regulation of miR-23b-3p and miR-27b-3p in Ang-II-treated HAFs. Taken together, these results suggest that the clustered miR-23b-3p and miR-27b-3p consistently promote atrial fibrosis by targeting TGFBR3 to activate Smad3 signalling in HAFs, suggesting that miR-23b-3p and miR-27b-3p are potential therapeutic targets for atrial fibrosis.

[Diagnosis and treatment of kidney involvement in plasma cell diseases : Renal involvement in multiple myeloma and monoclonal gammopathies]. / Diagnose und Therapie der Nierenbeteiligung bei Plasmazellerkrankungen : Renale Beteiligung bei multiplem Myelom und monoklonalen Gammopathien.

BACKGROUND: Kidney involvement is a common complication in patients with plasma cell diseases. OBJECTIVE: This article outlines the spectrum of renal involvement in plasma cell dyscrasia and describes diagnostic and therapeutic measures to guide clinical management. MATERIAL AND METHODS: Evaluation and discussion of the current literature as well as existing guidelines and recommendations of professional societies. RESULTS: The clinical manifestations of renal involvement in plasma cell disorders are heterogeneous and range from acute cast nephropathy in multiple myeloma to rare forms of glomerulonephritis. The term monoclonal gammopathy of renal significance (MGRS) was introduced to describe kidney involvement caused by monoclonal gammopathy but without evidence for underlying malignancy. Light chain cast nephropathy is the most common renal manifestation in multiple myeloma, whereas monoclonal immunoglobulin deposition disease (MIDD) and renal light chain (AL) amyloidosis can be found in multiple myeloma and MGRS. Decisive is the extended hematological diagnostics in order to exclude the presence of a hematological neoplasm. The treatment of renal involvement in monoclonal gammopathies involves the reduction of the plasma cell clone with cytoreductive treatment. The reduction of the monoclonal protein in serum is prognostically relevant for the renal response to treatment. In the case of histological evidence of a light chain cast nephropathy, high cut-off dialysis is recommended to reduce the free light chains in serum. CONCLUSION: The spectrum of renal manifestations in plasma cell dyscrasia has been expanded, particularly since the introduction of the term MGRS. Diagnostic and therapeutic management remain an interdisciplinary challenge.

A novel 'splice site' HCN4 Gene mutation, c.1737+1 G>T, causes familial bradycardia, reduced heart rate response, impaired chronotropic competence and increased short-term heart rate variability.

BACKGROUND: The most important molecular determinant of heart rate regulation in sino-atrial pacemaker cells includes hyperpolarization-activated, cyclic nucleotide-gated ion channels, the major isoform of which is encoded by the HCN4 gene. Mutations affecting the HCN4 gene are associated primarily with sick sinus syndrome. METHODS AND RESULTS: A novel c.1737+1 G>T 'splice-site' HCN4 mutation was identified in a large family with familial bradycardia which co-segregated with the disease providing a two-point LOD score of 4.87. Twelve out of the 22 investigated family members [4 males, 8 females average age 36 (SD 6) years] were considered as clinically affected (heart rate<60/min on resting ECG). Minimum [36 (SD 7) vs. 47 (SD 5) bpm, p=0.0087) and average heart rates [62 (SD 8) vs. 73 (SD 8) bpm, p=0.0168) were significantly lower in carriers on 24-hour Holter recordings. Under maximum exercise test carriers achieved significantly lower heart rates than non-carrier family members, and percent heart rate reserve and percent corrected heart rate reserve were significantly lower in carriers. Applying rigorous criteria for chronotropic incompetence a higher number of carriers exhibited chronotropic incompetence. Parameters, characterizing short-term variability of heart rate (i.e. rMSSD and pNN50%) were increased in carrier family members, even after normalization for heart rate, in the 24-hour ECG recordings with the same relative increase in 5-minute recordings. CONCLUSIONS: The identified novel 'splice site' HCN4 gene mutation, c.1737+1 G>T, causes familial bradycardia and leads to reduced heart rate response, impaired chronotropic competence and increased short-term heart rate variability in the mutation carriers.

Allostery modulates the beat rate of a cardiac pacemaker.

The S672R mutation in heart cell ion channels leads to low heart rates and arrhythmia by an unknown route. A multifaceted NMR analysis now demonstrates that this mutant impacts allosteric coupling in domains inside of the cell to change channel activation, providing a mechanistic explanation for phenotypic outcomes.

Free energy landscape remodeling of the cardiac pacemaker channel explains the molecular basis of familial sinus bradycardia.

The hyperpolarization-activated and cyclic nucleotide-modulated ion channel (HCN) drives the pacemaker activity in the heart, and its malfunction can result in heart disorders. One such disorder, familial sinus bradycardia, is caused by the S672R mutation in HCN, whose electrophysiological phenotypes include a negative shift in the channel activation voltage and an accelerated HCN deactivation. The outcomes of these changes are abnormally low resting heart rates. However, the molecular mechanism underlying these electrophysiological changes is currently not fully understood. Crystallographic investigations indicate that the S672R mutation causes limited changes in the structure of the HCN intracellular gating tetramer, but its effects on protein dynamics are unknown. Here, we utilize comparative S672R versus WT NMR analyses to show that the S672R mutation results in extensive perturbations of the dynamics in both apo- and holo-forms of the HCN4 isoform, reflecting how S672R remodels the free energy landscape for the modulation of HCN4 by cAMP, i.e. the primary cyclic nucleotide modulator of HCN channels. We show that the S672R mutation results in a constitutive shift of the dynamic auto-inhibitory equilibrium toward inactive states of HCN4 and broadens the free-energy well of the apo-form, enhancing the millisecond to microsecond dynamics of the holo-form at sites critical for gating cAMP binding. These S672R-induced variations in dynamics provide a molecular basis for the electrophysiological phenotypes of this mutation and demonstrate that the pathogenic effects of the S672R mutation can be rationalized primarily in terms of modulations of protein dynamics.

HCN4 mutations in multiple families with bradycardia and left ventricular noncompaction cardiomyopathy.

BACKGROUND: Familial forms of primary sinus bradycardia have sometimes been attributed to mutations in HCN4, SCN5A, and ANK2. In these studies, no structural cardiac alterations were reported in mutation carriers. However, a cluster of reports in the literature describe patients presenting with sinus bradycardia in association with left ventricular noncompaction cardiomyopathy (LVNC), pointing to a shared genetic cause. OBJECTIVES: This study sought to identify the genetic defect underlying the combined clinical presentation of bradycardia and LVNC, hypothesizing that these 2 clinical abnormalities have a common genetic cause. METHODS: Exome sequencing was carried out in 2 cousins from the index family that were affected by the combined bradycardia-LVNC phenotype; shared variants thus identified were subsequently overlaid with the chromosomal regions shared among 5 affected family members that were identified using single nucleotide polymorphism array analysis. RESULTS: The combined linkage analysis and exome sequencing in the index family identified 11 novel variants shared among the 2 affected cousins. One of these, p.Gly482Arg in HCN4, segregated with the combined bradycardia and LVNC phenotype in the entire family. Subsequent screening of HCN4 in 3 additional families with the same clinical combination of bradycardia and LVNC identified HCN4 mutations in each. In electrophysiological studies, all found HCN4 mutations showed a more negative voltage dependence of activation, consistent with the observed bradycardia. CONCLUSIONS: Although mutations in HCN4 have been previously linked to bradycardia, our study provides the first evidence to our knowledge that mutations in this ion channel gene also may be associated with structural abnormalities of the myocardium.

Anaesthetic management of abdominal hysterectomy in patient with congenital sinus node dysfunction.

A 45 years old woman having dysfunctional uterine bleeding was scheduled for total abdominal hysterectomy with bilateral salpingo-oophorectomy under general anaesthesia. On pre-operative anaesthesia assessment, she was found to have junctional rhythm at rate of 44 beats/minute with bigeminies and pre-mature ventricular contractions on ECG. On further evaluation, she was diagnosed as having congenital sinus node dysfunction on the basis of 24 hours Holter monitoring. She was asymptomatic, no prior comorbidity and belonged to functional class one. General anaesthesia was successfully managed by vigilance, invasive monitoring, standby transcutaneous and transvenous pacemakers; use of cardiostable and vagolytic anaesthetic agents like Etomidate, Atracurium and Pethidine during the procedure and for postoperative pain management. Transcutaneous external pacing pads were placed just after induction of anaesthesia, their functional apability was confirmed and was ready for use if needed. The transcutaneous and transvenous pacemakers were on backup and both were not required. Patient was successfully managed and was discharged home on third postoperative day with uneventful hospital course. The elective pacemaker implantation was therefore not required.

Association of congenital, diffuse electrical disease in children with normal heart: sick sinus syndrome, intraventricular conduction block, and monomorphic ventricular tachycardia.

INTRODUCTION: Rhythm disturbances in children with structurally normal hearts are usually associated with abnormalities in cardiac ion channels. The phenotypic expression of these abnormalities ("channelopathies") includes: long and short QT syndromes, Brugada syndrome, congenital sick sinus syndrome, catecholaminergic polymorphic ventricular tachycardia, Lènegre-Lev disease, and/or different degrees of cardiac conduction disease. METHODS: The study group consisted of three male patients with sick sinus syndrome, intraventricular conduction disease, and monomorphic sustained ventricular tachycardia. Clinical data and results of electrocardiography, Holter monitoring, electrophysiology, and echocardiography are described. RESULTS: In all patients, the ECG during sinus rhythm showed right bundle branch block and long QT intervals. First-degree AV block was documented in two subjects, and J point elevation in one. A pacemaker was implanted in all cases due to symptomatic bradycardia (sick sinus syndrome). Atrial tachyarryhthmias were observed in two patients. The common characteristic ventricular arrhythmia was a monomorphic sustained ventricular tachycardia, inducible with ventricular stimulation and sensitive to lidocaine. In one patient, radiofrequency catheter ablation was successfully performed. No structural abnormalities were found in echocardiography in the study group. CONCLUSION: Common clinical and ECG features suggest a common pathophysiology in this group of patients with congenital severe electrical disease.

[Congenital sick sinus syndrome in a healthy heart: case report]. / L'atteinte congenitale binodale du tissu de conduction sur coeur sain. A propos d'un cas.

Isolated congenital sick sinusal syndrome on non harmed heart is a rare affection. Its association with an atrio-ventricular block is exceptional. The authors report a case of a 19 year-old patient, with an early history of bradycardia, hospitalised for effort intolerance. His electrocardiogram reveals a high degree sino-atrial block replaced by a junctional rhythm at 30/mn. During Treadmill test, the sinusal acceleration is satisfactory and an effort atrio-ventricular block was present. He later had a definitive stimulation under DDDR. This report shows that the sinusal node, in the same way as the atrio-ventricular node may be injured by congenital dysimmunitary process. The coexistence of these two conductive troubles worsen the prognosis and should lead more often to the practice of definitive stimulation by the only mode DDDR.

Congenital sick sinus syndrome caused by recessive mutations in the cardiac sodium channel gene (SCN5A).

Sick sinus syndrome (SSS) describes an arrhythmia phenotype attributed to sinus node dysfunction and diagnosed by electrocardiographic demonstration of sinus bradycardia or sinus arrest. Although frequently associated with underlying heart disease and seen most often in the elderly, SSS may occur in the fetus, infant, and child without apparent cause. In this setting, SSS is presumed to be congenital. Based on prior associations with disorders of cardiac rhythm and conduction, we screened the alpha subunit of the cardiac sodium channel (SCN5A) as a candidate gene in ten pediatric patients from seven families who were diagnosed with congenital SSS during the first decade of life. Probands from three kindreds exhibited compound heterozygosity for six distinct SCN5A alleles, including two mutations previously associated with dominant disorders of cardiac excitability. Biophysical characterization of the mutants using heterologously expressed recombinant human heart sodium channels demonstrate loss of function or significant impairments in channel gating (inactivation) that predict reduced myocardial excitability. Our findings reveal a molecular basis for some forms of congenital SSS and define a recessive disorder of a human heart voltage-gated sodium channel.

Congenital sick sinus syndrome with breath holding and severe syncope episodes during infancy. A case report.

Sick sinus syndrome is a rare cause of bradycardia in children without structural heart disease. A case of profound sinus bradycardia, sinus arrest with junctional escape, and pauses in a two-year-old infant with breath-holding and syncope episodes is presented. As a result of these clinical symptoms and electrocardiographic findings, the patient with sick sinus syndrome underwent implantation of transvenous ventricular pacemaker. He has been well and asymptomatic since the insertion of the pacemaker. In the differential diagnosis of an infant with breath-holding and syncope episodes, when these symptoms in particular cannot be explained by other common reasons, sick sinus syndrome should be kept in mind. This case also illustrates the importance of electrocardiographic studies for the diagnosis.

[Sinus node dysfunction in children without heart defect]. / Sinusknotendysfunktion bei Kindern ohne Herzfehler.

Sinus node dysfunction (SND) is a rare cause of bradycardia in children without structural heart disease. The clinical and diagnostic findings in 4 children with this condition are described. Two of them presented with symptoms, in one arrhythmias had been noted before birth, and a routine physical examination had revealed bradycardia in another. Age at onset of either clinical symptoms or bradycardia ranged from 0 to 11 1/2 years. Routine and 24-h-electrocardiograms showed atrioventricular junctional rhythms with minimal rates of 25/min and episodes of asystole with a maximal duration of 10.3 s. Other electrocardiographic abnormalities such as first degree atrioventricular block, ventricular extrasystoles or tachycardia were common findings. Electrophysiological studies were performed in 3 cases and confirmed the diagnosis of SND. A permanent pacemaker was inserted in 2 children; medical treatment did not have any long-term effect. During a follow-up period of 5 to 13 years there were no complications. In summary, SND in childhood can be assessed by Holter monitoring with high reliability. Electrophysiological studies are not necessary and of limited value. Therapeutic policies and prognostic statements are difficult to establish due to the small number of cases so far described. Permanent cardiac pacing, however, is unavoidable in symptomatic children.

[Sick sinus syndrome in children with a "healthy heart". Apropos of 2 cases with direct endocavitory tracing of the sino-atrial block]. / Maladie du sinus chez l'enfant à "coeur sain". A propos de deux cas avec enregistrement direct endocavitaire du bloc sino-auriculaire.

The sinus disease in children with "healthy hearts" is exceptional, and has never been documented by tracing of the sinus node. We are reporting two cases of two children, aged 4 and 14 years. An electrophysiological exploration with measurement of the direct activity of the sinus node, illustrates in one case the mechanism of sinus dysfunction. A review from the literature and our cases specifies some of the characteristics of this disease: 1) there are two forms: sporadic (case n. 1) 59 published cases, and familial (case n. 2) 28 published cases in 13 families; 2) the familial forms have a dominant autosomic transmission with variable penetration; 3) the disease may occur during the first days of life, suggesting a congenital origin (from the pathology findings, this disease may be one of the causes of the unexplained sudden death syndrome in infants; 4) association to atrio-ventricular conduction disorders and atrial and ventricular rhythm disorders; 5) frequent indication of stimulators, emphasizing the severity of this disease with a more severe course in sporadic forms (7 deaths in 59 cases).