Genotype-phenotype correlations of KCNJ2 mutations in Japanese patients with Andersen-Tawil syndrome

Andersen-Tawil syndrome (ATS) is a rare inherited disorder characterized by periodic paralysis, mild dysmorphic features, and QT or QU prolongation with ventricular arrhythmias in electrocardiograms (ECGs). Mutations of KCNJ2, encoding the human inward rectifying potassium channel Kir 2.1, have been identified in patients with ATS. We aimed to clarify the genotype-phenotype correlations in ATS patients. We screened 23 clinically diagnosed ATS patients from 13 unrelated Japanese families. Ten different forms of KCNJ2 mutations were identified in the 23 ATS patients included in this study. Their ECGs showed normal QTc intervals and abnormal U waves with QUc prolongation and a variety of ventricular arrhythmias. Especially, bidirectional ventricular tachycardia (VT) was observed in 13 of 23 patients (57%). Periodic paralysis was seen in 13 of 23 carriers (57%), dysmorphic features in 17 (74%), and seizures during infancy in 4 (17%). Functional assays for the two novel KCNJ2 mutations (c. 200G>A (p. R67Q) and c. 436G>A (p. G146S)) displayed no functional inward rectifying currents in a heterologous expression system and showed strong dominant negative effects when co-expressed with wild-type KCNJ2 channels (91% and 84% reduction at -50 mV respectively compared to wild-type alone). Immunocytochemistry and confocal imaging revealed normal trafficking for mutant channels. In our study, all of the clinically diagnosed ATS patients had KCNJ2 mutations and showed a high penetrance with regard to the typical cardiac phenotypes: predominant U wave and ventricular arrhythmias, typically bidirectional VT.     

儿童Andersen-Tawil综合征1例并文献复习

目的分析1例Andersen-Tawil综合征（ATS）患儿的诊断和治疗经过,提高对ATS的认识。方法报道1例基因确诊ATS患儿的临床特征及诊疗过程,并进行文献复习。结果患儿,女,12岁10个月,因＂意识丧失3 h伴抽搐＂入院。患儿既往有发作性双下肢无力及不明原因胸闷史。入院前3 h患儿在参加智力竞赛时突然晕倒、意识丧失、口唇发绀伴肢体抽动。查体神志不清,眼窝凹陷、眼距略宽,心律不齐,四肢呈迟缓性麻痹,脊柱、四肢无畸形。实验室检查示血清钾一过性降低。ECG检查示室性颤动、室性心动过速和频发多形性室性期前收缩。入院后予机械通气,胺碘酮和美托洛尔抗心律失常治疗,疗效欠佳,心律失常反复发作。基因检测示KCNJ2杂合错义突变：c.899 G〉T hetero,GGC〉GTC,p.G300V,确诊为ATS。出院后1个月余在外院植入心律转复除颤器（ICD）,并加用氟卡尼100 mg.d-1口服治疗。治疗后患儿心律失常减少,迄今随访8个月余,未见抽搐及晕厥发作,目前继续随访中。结论 ATS以室性心律失常,周期性麻痹,轻度面部和（或）骨骼发育异常为特征。心源性晕厥及心跳骤停不常见,但可危及生命,需植入ICD治疗。KCNJ2基因突变有助确诊。     

Intravenous magnesium for cardiac arrhythmias: jack of all trades.

Intravenous magnesium has been used to prevent and treat many different types of cardiac arrhythmia. It has diverse electrophysiological actions on the conduction system of the heart; including prolonging sinus node recovery time, and reducing automaticity, atrioventricular nodal conduction, antegrade and retrograde conduction over an accessory pathway, and His-ventricular conduction. Intravenous magnesium can also homogenise transmural ventricular repolarisation. Because of its unique and diverse electrophysiological actions, intravenous magnesium has been reported to be useful in preventing atrial fibrillation and ventricular arrhythmias after cardiac and thoracic surgery; in reducing the ventricular response in acute onset atrial fibrillation, including for patients with Wolff-Parkinson-White syndrome; in the treatment of digoxin induced supraventricular and ventricular arrhythmias, multifocal atrial tachycardia, and polymorphic ventricular tachycardia or ventricular fibrillation from drug overdoses. Intravenous magnesium is, however, not useful in monomorphic ventricular tachycardia and shock-resistant ventricular fibrillation. Large randomised controlled studies are needed to confirm whether intravenous magnesium can improve patient centre outcomes in different cardiac arrhythmias.     

A Case of Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a familial cardiac arrhythmia that is related to RYR2 or CASQ2 gene mutation. It occurs in patients with structurally normal heart and causes exercise-emotion-triggered syncope and sudden cardiac death. We experienced a case of CPVT in an 11 year-old female patient who was admitted for sudden cardiovascular collapse. The initial electrocardiogram (ECG) on emergency department revealed ventricular fibrillation. After multiple defibrillations, sinus rhythm was restored. However, recurrent ventricular fibrillation occurred during insertion of nasogastric tube without sedation in coronary care unit. On ECG monitoring, bidirectional ventricular tachycardia occurred with sinus tachycardia and then degenerated into ventricular fibrillation. To our knowledge, there has been no previous case report of CPVT triggered by sinus tachycardia in Korea. Therefore, we report the case as well as a review of the literature.     

Pathogenesis of lethal cardiac arrhythmias in Mecp2 mutant mice: implication for therapy in Rett syndrome

Rett syndrome is a neurodevelopmental disorder typically caused by mutations in methyl-CpG-binding protein 2 (MECP2) in which 26% of deaths are sudden and of unknown cause. To explore the hypothesis that these deaths may be due to cardiac dysfunction, we characterized the electrocardiograms in 379 people with Rett syndrome and found that 18.5% show prolongation of the corrected QT interval (QTc), an indication of a repolarization abnormality that can predispose to the development of an unstable fatal cardiac rhythm. Male mice lacking MeCP2 function, Mecp2(Null/Y), also have prolonged QTc and show increased susceptibility to induced ventricular tachycardia. Female heterozygous null mice, Mecp2(Null/+), show an age-dependent prolongation of QTc associated with ventricular tachycardia and cardiac-related death. Genetic deletion of MeCP2 function in only the nervous system was sufficient to cause long QTc and ventricular tachycardia, implicating neuronally mediated changes to cardiac electrical conduction as a potential cause of ventricular tachycardia in Rett syndrome. The standard therapy for prolonged QTc in Rett syndrome, β-adrenergic receptor blockers, did not prevent ventricular tachycardia in Mecp2(Null/Y) mice. To determine whether an alternative therapy would be more appropriate, we characterized cardiomyocytes from Mecp2(Null/Y) mice and found increased persistent sodium current, which was normalized when cells were treated with the sodium channel-blocking anti-seizure drug phenytoin. Treatment with phenytoin reduced both QTc and sustained ventricular tachycardia in Mecp2(Null/Y) mice. These results demonstrate that cardiac abnormalities in Rett syndrome are secondary to abnormal nervous system control, which leads to increased persistent sodium current. Our findings suggest that treatment in people with Rett syndrome would be more effective if it targeted the increased persistent sodium current to prevent lethal cardiac arrhythmias.     

Juvenile sudden death in a family with polymorphic ventricular arrhythmias caused by a novel RyR2 gene mutation: evidence of specific morphological substrates

We report on a family with a history of sudden death and effort-induced polymorphic ventricular arrhythmias. The index case was a 17-year-old boy who died suddenly and at postmortem had evidence of fibrofatty replacement in the right ventricular free wall, consistent with arrhythmogenic right ventricular cardiomyopathy, as well as calcium phosphate deposits within the myocytes. A molecular genetics investigation carried out in the paraffin-embedded myocardium of the subject and in blood samples of family members disclosed a missense mutation in exon 3 (230C-->T; A77V) of the cardiac ryanodine receptor type 2 gene. The carriers showed effort-induced polymorphic ventricular tachycardia in the setting of normal resting electrocardiogram and trivial echocardiographic abnormalities, consistent with catecholaminergic polymorphic ventricular tachycardia. The observation of both arrhythmogenic right ventricular cardiomyopathy type 2 and catecholaminergic polymorphic ventricular tachycardia in the same family suggests that the two entities might correspond to different degrees of phenotypic expression of the same disease. This experience underscores the importance of a precise autopsy diagnosis in the case of sudden cardiac death, including molecular genetics, and the mission of pathologists to guide further clinical investigation of family members.     

Left cardiac sympathetic denervation for catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia is a potentially lethal disease characterized by adrenergically mediated ventricular arrhythmias manifested especially in children and teenagers. Beta-blockers are the cornerstone of therapy, but some patients do not have a complete response to this therapy and receive an implantable cardioverter-defibrillator (ICD). Given the nature of catecholaminergic polymorphic ventricular tachycardia, ICD shocks may trigger new arrhythmias, leading to the administration of multiple shocks. We describe the long-term efficacy of surgical left cardiac sympathetic denervation in three young adults with catecholaminergic polymorphic ventricular tachycardia, all of whom had symptoms before the procedure and were symptom-free afterward.     

Ventricular arrhythmias in patients with hypertensive left ventricular hypertrophy

In patients with hypertension, a pattern of left ventricular hypertrophy on the electrocardiogram is associated with a risk of sudden death in excess of the risk attributable to hypertension alone. We therefore investigated the frequency of complex ventricular arrhythmias by means of 48-hour ambulatory electrocardiographic monitoring in 100 treated hypertensive patients, of whom 50 had electrocardiographic evidence of left ventricular hypertrophy and 50 did not, and in 50 normotensive controls. The groups were matched for age, sex, and smoking habits, and the two hypertensive groups were matched for blood-pressure levels before and after antihypertensive therapy. Nonsustained ventricular tachycardia, defined as greater than or equal to 3 complexes at a rate greater than or equal to 120 beats per minute, occurred in 14 (28 percent) of the 50 patients with an electrocardiographic pattern of left ventricular hypertrophy, in 4 (8 percent) of the 50 patients without hypertrophy (P less than 0.05), and in 1 (2 percent) of the control subjects. Eight of the 50 patients (16 percent) with hypertrophy had episodes of nonsustained ventricular tachycardia longer than 5 complexes, whereas no patients without hypertrophy and no controls had such episodes. The group with nonsustained ventricular tachycardia was characterized by a high left ventricular mass on echocardiography and a high prevalence of ST-T abnormalities on electrocardiography. Ventricular tachycardia was not closely related to blood-pressure levels, nor was it associated with diuretic therapy or hypokalemia. The clinical importance of these arrhythmias is uncertain. Nevertheless, our data suggest that complex ventricular arrhythmias occur commonly in hypertensive patients with left ventricular hypertrophy and may contribute to the higher incidence of sudden death in these patients.     

Variants in NAA15 cause pediatric hypertrophic cardiomyopathy

The NatA N‐acetyltransferase complex is important for cotranslational protein modification and regulation of multiple cellular processes. The NatA complex includes the core components of NAA10, the catalytic subunit, and NAA15, the auxiliary component. Both NAA10 and NAA15 have been associated with neurodevelopmental disorders with overlapping clinical features, including variable intellectual disability, dysmorphic facial features, and, less commonly, congenital anomalies such as cleft lip or palate. Cardiac arrhythmias, including long QT syndrome, ventricular tachycardia, and ventricular fibrillation were among the first reported cardiac manifestations in patients with NAA10‐related syndrome. Recently, three individuals with NAA10‐related syndrome have been reported to also have hypertrophic cardiomyopathy (HCM). The general and cardiac phenotypes of NAA15‐related syndrome are not as well described as NAA10‐related syndrome. Congenital heart disease, including ventricular septal defects, and arrhythmias, such as ectopic atrial tachycardia, have been reported in a small proportion of patients with NAA15‐related syndrome. Given the relationship between NAA10 and NAA15, we propose that HCM is also likely to occur in NAA15‐related disorder. We present two patients with pediatric HCM found to have NAA15‐related disorder via exome sequencing, providing the first evidence that variants in NAA15 can cause HCM.     

Radiofrequency catheter ablation of hemodynamically unstable ventricular tachycardia associated with systemic sclerosis

Systemic sclerosis (SS) is a connective tissue disease and cardiac involvement is common. Primary cardiac involvement such as conduction system disturbances and arrhythmias can also occur. However, reports of sustained ventricular tachycardia (VT) are rare. We report a case of catheter ablation of sustained ventricular tachycardia in a patient with systemic sclerosis using a conventional mapping system. A 64-yr-old woman with a 10-yr history of SS was referred for management of her ventricular tachycardia. There was no structural abnormality in cardiac chambers. However, electrophysiologic study revealed electrical substrate of ventricular tachycardia which could be ablated with pacemapping and substrate mapping. This case demonstrated successful conventional mapping and catheter ablation in a hemodynamically unstable patient with SS.     

A novel long-QT 5 gene mutation in the C-terminus (V109I) is associated with a mild phenotype

Mutations in the human minK gene KCNE1 have been linked to autosomal dominant and autosomal recessive long-QT (LQT) syndrome, a cardiac condition predisposing to ventricular arrhythmias. minK and KvLQT1, the LQT1 gene product, form a native cardiac K+ channel that regulates the slowly delayed rectifier potassium current I(Ks). We used single-strand conformation polymorphism and sequencing techniques to identify novel KCNE1 mutations in patients with a congenital LQT syndrome of unknown genetic origin. In 150 unrelated index patients a missense mutation (V109I) was identified that significantly reduced the wild-type I(Ks) current amplitude (by 36%) when coexpressed with KvLQT1 in Xenopus oocytes. Other biophysical properties of the I(Ks) channel were not altered. Since we observed incomplete penetrance (only one of two mutation carriers could be diagnosed by clinical criteria), and the family's history was unremarkable for sudden cardiac death, the 109I allele most likely causes a mild phenotype. This finding may have implications for the occurrence of "acquired" conditions for ventricular arrhythmias and thereby the potential cardiac risk for asymptomatic mutation carriers still remains to be determined.     

Functional and clinical characterization of a mutation in KCNJ2 associated with Andersen-Tawil syndrome

Background

Andersen‐Tawil syndrome (ATS) is a rare inherited disorder, characterised by periodic paralysis, cardiac dysarrhythmias, and dysmorphic features, and is caused by mutations in the gene KCNJ2, which encodes the inward rectifier potassium channel, Kir2.1. This study sought to analyse KCNJ2 in patients with familial ATS and to determine the functional characteristics of the mutated gene.

Methods and results

We screened a family with inherited ATS for the mutation in KCNJ2, using direct DNA sequencing. A missense mutation (T75R) of Kir2.1, located in the highly conserved cytoplasmic N‐terminal domain, was identified in three affected members of this family. Using the Xenopus oocyte expression system and whole cell voltage clamp analyses, we found that the T75R mutant was non‐functional and possessed a strong dominant negative effect when co‐expressed with the same amount of wild type Kir2.1. Transgenic (Tg) mice expressing the mutated form of Kir2.1 in the heart had prolonged QTc intervals compared with mice expressing the wild type protein. Ventricular tachyarrhythmias were observed in 5 of 14 T75R‐Tg mice compared with 1 of 7 Wt‐Tg and none of 6 non‐transgenic littermates. In three of five T75R‐Tg mice with ventricular tachycardia, their ECG disclosed bidirectional tachycardia as in our proband.

Conclusions

The in vitro studies revealed that the T75R mutant of Kir2.1 had a strong dominant negative effect in the Xenopus oocyte expression system. It still preserved the ability to co‐assemble and traffic to the cell membrane in mammalian cells. For in vivo studies, the T75R‐Tg mice had bidirectional ventricular tachycardia after induction and longer QT intervals.     

Pathogenesis of cardiac conduction disorders in children genetic and histopathologic aspects

Fetal dysrhythmias are usually transient. Abnormal fetal rates and rhythms during labor are "functional." Fetal dysrhythmias may be associated with congenital heart disease and fetal hydrops. Bradycardia is usually related to fetal distress; supraventricular tachycardia, atrial flutter, and atrial fibrillation may be associated with severe congestive heart failure. Ventricular fibrillation is rare in the fetus and infant and is usually associated with myocardial necrosis with perimembranous septal defect; the nonbranching atrioventricular (AV) bundle may have an aberrant position and result in cardiac arrhythmia. Wolff-Parkinson-White syndrome with conduction abnormalities and left ventricular hypertrophy (LVH) is due to an accessory pathway that bypasses the AV sulcus and results in faster conduction. Carnitine deficiency may be primary or secondary and may result in cardiac arrhythmia. Histiocytoid cardiomyopathy is characterized by cardiomegaly, incessant ventricular tachycardia, and frequently sudden death. Arrhythmogenic right ventricular dysplasia (ARVD) results in ventricular tachycardia and left bundle branch block. Noncompaction of the left ventricle predisposes to potentially fatal arrhythmias. Long Q-T syndromes (LQTS) are a heterogeneous group of disorders with many genetic mutations. Brugada syndrome is an autosomal dominant trait with right bundle branch block and ST elevation. Barth syndrome is an X-linked disorder with dilated cardiomyopathy, cyclic neutropenia and skeletal myopathy. Hypertrophic cardiomyopathy in infancy may be related to metabolic diseases, particularly glycogen storage diseases; the familial form predisposes to sudden death. Arrhythmias following cardiac surgery may occur after closure of a ventricular septal defect (VSD) or damage to the conduction system.     

Fever-induced QTc prolongation and ventricular fibrillation in a healthy young man

Long QT syndrome is associated with lethal tachyarrhythmia that can lead to syncope, seizure, and sudden death. Congenital long QT syndrome is a genetic disorder, characterized by delayed cardiac repolarization and prolongation of the QT interval on the electrocardiogram (ECG). Type 2 congenital long QT is linked to mutations in the human ether a go-go-related gene (HERG). There are environmental triggers of adverse cardiac events such as emotional and acoustic stimuli, but fever can also be a potential trigger of life-threatening arrhythmias in long QT syndrome type 2 patients. Herein, we report a healthy young man who experienced fever-induced polymorphic ventricular tachycardia and QT interval prolongation.     

Cardiac arrhythmias in aluminium phosphide poisoning studied by on continuous holter and cardioscopic monitoring

Variable incidences of cardiac arrhythmias (based on isolated 12 lead ECG records) have been reported in patients of aluminium phosphide (ALP) poisoning. We did continuous holter and cardioscopic monitoring in ICU in 30 patients of acute ALP poisoning. Supraventricular and ventricular ectopics were recorded in each and every patient. Life threatening ventricular tachycardia was recorded in 40% cases and ventricular fibrillation in 23.3% cases. Supraventricular tachycardia and atrial flutter/fibrillation occurred in 46.7% and 20% patients, respectively. ST-T changes simulating myocardial ischaemia were also present in all patients (S-T depression in 90%, S-T elevation in 10%). One-third of the patients developed variable degrees of heart block, IV amiodarone/xylocard could revert dangerous ventricular arrhythmias to sinus rhythm in 4 cases. Toxic myocarditis produced by phosphine seems to be responsible for the development of these arrhythmias.     

The acute effect of ajmaline on ventricular arrhythmia after cardiac surgery

The acute effect of ajmaline was investigated in the treatment of postoperative ventricular arrhythmias. Ajmaline (Glurytmal--Giulini Pharma GMBH) was applied intravenously in 15 patients suffering from ventricular premature beats (Lown II--IV/b), tachycardia and/or ventricular fibrillation after open heart surgery. Ajmaline infusion produced in 40% of the cases a total suppression and in 100% a significant improvement of malignant ventricular arrhythmia. In patients with recurrent and resistant ventricular tachycardia, ajmaline proved effective even when other antiarrhythmic drugs had failed. It was shown to be effective in reducing ventricular premature contractions and recurrent ventricular tachycardia after heart surgery, without haemodynamic side effects. Because of recurrent ventricular premature beats in 11 patients after acute ajmaline administration further oral application of prajmalium bitartarate (Neo-Gilurytmal) was necessary. The maintenance of these patients on oral ajmaline treatment seemed important.     

The inheritance of premature ventricular excitation syndrome and the evolution of its clinical course according to prospective studies

Interest for the problem of inheritance of premature ventricular excitation syndrome (PVES) has grown significantly in the recent years due to an increase in the prevalence of paroxysmal supraventricular tachycardia and atrial fibrillation in the general population. Appearance of such cardiac arrhythmias in young people makes it necessary to include PVES in diagnostic search program. At the same time, the clinical picture of the disease may change with age and appearance of various cardiovascular pathology. A prospective study including 240 patients was undertaken to study the evolution of the clinical course of PVES. A 30-year observation showed that in 88% of PVES patients the number of forms and the degree of the severity of cardiac arrhythmias tended to grow. By the end of the study the prevalence of paroxysmal supraventricular tachycardia had decreased significantly, while the number of patients with atrial fibrillation had increased. Attacks of atrial fibrillation occurred in PVES at older age than paroxysmal tachycardia, and it was observed much more often in cases where PVES was combined with other heart diseases. Thus, the studies show that paroxysms of atrial fibrillation in PVES patients occur more often in the presence of different cardiovascular diseases, and that clinical manifestations of PVES are determined by the evolution of the associated diseases as well.     

Studies on faint attack due to arrhythmias with Holter electrocardiogram

Out of 1,400 Holter ECGs, 15 records revealed arrhythmias which would be responsible for faint attack, including 8 sick sinus syndrome with cardiac arrest, 4 non-sustained ventricular tachycardia (VT), 2 paroxysmal atrial fibrillation and 1 paroxysmal supraventricular tachycardia. All of cardiac arrest corresponding to faint attack lasted for longer than 4 sec, and an averaged duration of the arrest was 5.8 +/- 2.3 sec. This was significantly longer than that with no subjective symptoms, 3.4 +/- 0.7 sec. Duration and rate of VT did not show any significant relationship with faint attack. The result suggests that cardiac arrest is mostly responsible for arrhythmia-induced involvement of cerebral circulation and faint attack. It is also suggested that cardiac arrest longer than 4 sec should be extensively treated including pacemaker implantation.     

Ventricular histamine concentrations and arrhythmias during acute myocardial ischaemia in rats

The relation between ventricular histamine concentrations and the occurrence of early ventricular arrhythmias during acute myocardial ischaemia was investigated in pentobarbitone-anaesthetized rats. There was significant decrease in the left, but not the right, ventricular histamine level at 5 min following acute left coronary artery ligation. Pretreatment with rhodanine caused remarkable reduction in ventricular histamine concentrations as well as significantly lower incidence and slower onset of ventricular tachycardia and fibrillation resulting from acute myocardial ischaemia. On the contrary, aminoguanidine pretreatment did not significantly alter ventricular histamine levels nor did it influence the occurrence of early ventricular arrhythmias induced by coronary artery ligation. The responses of blood pressure and heart rate to acute coronary artery ligation were not noticeably affected by rhodanine or aminoguanidine pretreatment. These findings support the hypothesis that histamine release from cardiac tissues may contribute to the genesis of early ventricular arrhythmias, but not to the changes in blood pressure and heart rate, during acute myocardial ischaemia.     

恶性肿瘤病人132例心电图变化临床分析

目的:本文对恶性肿瘤病人心电图变化进行临床分析。方法:本文共记录262例心电图,其中132例为恶性肿瘤组,130例为正常人组,观察和比较两组心电图异常改变的例数和总体异常发生率。结果:恶性肿瘤组在窦速、T波改变、室性早搏、室性心动过速,肢导联低电压、电轴偏移等心电图异常事件发生的例数为44例,异常率为33%,正常人组心电图异常事件发生的例数11例,异常率为8%。结论:恶性肿瘤组心电图异常发生率较正常人组明显增高,并有恶性室性心律失常发生。