Different underlying aetiologies in patients presenting with ventricular tachycardia fulfilling task force criteria for ARVC: initial suspicion based on the 12-lead electrocardiogram

Background

The Task Force Criteria (TFC) for ARVC are highly sensitive, but lack specificity. Patients with atypical RV-involvement (aRVi) may have different underlying aetiologies and prognosis, requiring specific therapeutic interventions.

Purpose

We aimed to evaluate the role of the baseline ECG for initial suspicion of aRVi.

Methods

From the Netherlands Heart Institute Arrhythmogenic Cardiomyopathy (NHI-ACM) registry, patients were selected who 1) fulfilled TFC for definite ARVC, 2) presented with sustained VT, 3) underwent genetic testing. The first available ECG after VT was evaluated for AV-conduction and the presence and surface area (SA) of an R'-wave in V1-V3. ECGs with AV-conduction disturbances or an R'-wave with SA ≥1.65 mm2 were classified as suspicious for `atypical RV-involvement' (aRVi-ECG).

Patients with ARVC-related pathogenic/likely pathogenic variant (P/LP+) were classified as “typical ARVC”. Data of patients without an ARVC-related pathogenic/likely pathogenic variant (P/LP−) were reviewed by an expert panel and classified as either “typical ARVC” or “suggestive for another aetiology” based on consensus.

Results

In total 124 P/LP+ patients and 35 P/LP− patients were included. Nineteen patients had an aRVi-ECG, which appeared significantly more predominant in the P/LP− group (11 (9%) P/LP+ vs. 8 (22%) P/LP−, p=0.019). Of the P/LP− patients, seventeen (49%) were classified as “suggestive for another aetiology” (e.g. myocarditis, ischemia, sarcoid), including all 8 patients with an aRVI-ECG.

Among P/LP+ patients with an aRVi-ECG, 46% carried the Arg14del phospolamban variant and 64% died, versus 15% and 18% of P/LP+ patients without aRVi-ECG, respectively (Table 1).

Conclusion

For patients presenting with sustained VT and fulfilling the TFC for ARVC diagnosis, a baseline ECG suggestive for atypical RV-involvement should raise suspicion for a different underlying aetiology in patients without an ARVC-related P/LP variant. In P/LP+ patients, an aRVi-ECG may identify those with poor outcome.

Funding Acknowledgement

Type of funding sources: None.

Life-long tailoring of diagnosis and management of patients with idiopathic ventricular fibrillation-future perspectives in research

The diagnosis and management of idiopathic ventricular fibrillation is challenging, as it requires extensive diagnostic testing and offers few curative options due to unknown underlying disease. The resulting population is a heterogeneous group of patients with a largely unknown natural history. Structural patient characterisation, follow-up and innovations in diagnostic testing can improve our understanding of the disease mechanisms of idiopathic ventricular fibrillation, detect underlying disease during follow-up and aid in therapeutic management. Recently, initiatives have been launched in the Netherlands to investigate the role of high-resolution non-invasive electrocardiographic imaging and genetic and familial screening in idiopathic ventricular fibrillation.

Dronedarone in patients with atrial fibrillation

Dronedarone is a recently developed new class III antiarrhythmic drug which possesses electrophysiological properties of all four Vaughan-Williams classes. An important difference with amiodarone is that it does not contain an iodine component and therefore lacks the iodine-related adverse effects. Based on currently available data, dronedarone can not be recommended as first-line therapy for either rhythm or rate control. We recommend to initiate rhythm or rate control with drugs as indicated in the 2006 guidelines of the ESC and other organisations. As amiodarone, dronedarone can be given to patients for whom standard drug therapy is not effective, or limited by (severe) side effects, although it is less effective than amiodarone. Nevertheless, it may be considered to give dronedarone initially to patients who would otherwise have received amiodarone, since the latter has more severe side effects than the former drug. The daily dosage of dronedarone is oral administration, 400 mg twice daily. Dronedarone is contraindicated in patients with impaired left ventricular function (NYHA class III/IV) and haemodynamic instability. (Neth Heart J 2010;18:370-3.).

Persistent precordial "hyperacute" T-waves signify proximal left anterior descending artery occlusion

OBJECTIVE

To describe patients with a distinct electrocardiogram (ECG) pattern without ST-segment elevation in the presence of an acute occlusion of the proximal left anterior descending (LAD) artery.

DESIGN

Single-centre observational study.

PATIENTS

Patients with acute anterior wall myocardial infarction who were referred for primary percutaneous coronary intervention (PCI) between 1998 and 2008.

RESULTS

We identified patients with a static, distinct ECG pattern without ST-segment elevation and an occlusion of the proximal LAD artery during urgent coronary angiography before PCI. Of 1890 patients who underwent primary PCI of the LAD artery, we could identify 35 patients (2%) with this distinct ECG pattern. The ECG showed ST-segment depression at the J-point of at least 1 mm in precordial leads with upsloping ST-segments continuing into tall, symmetrical T-waves. Patients with this distinct ECG pattern were younger, more often male and more often had hypercholesterolaemia compared to patients with anterior myocardial infarction and ST-segment elevation.

CONCLUSIONS

In patients presenting with chest pain, ST-segment depression at the J-point with upsloping ST-segments and tall, symmetrical T-waves in the precordial leads of the 12-lead ECG signifies proximal LAD artery occlusion. It is important for cardiologists and emergency care physicians to recognise this distinct ECG pattern, so they can triage such patients for immediate reperfusion therapy.

Polymorphisms in the cardiac sodium channel promoter displaying variant in vitro expression activity

Variable transcription of the cardiac sodium channel gene is a candidate mechanism determining arrhythmia susceptibility. We have previously cloned and characterized the core promoter and flanking region of SCN5A, encoding the cardiac sodium channel. Loss-of-function mutations in this gene have been reported in approximately 20% of patients with Brugada syndrome, an inherited cardiac electrical disorder associated with a high incidence of life-threatening arrhythmias. In this study, we identified DNA variants in the proximal 2.8 kb promoter region of SCN5A and determined their frequency in 1,121 subjects. This population consisted of 88 Brugada syndrome patients with no SCN5A coding region mutation, and 1,033 anonymized subjects from various ethnicities. Variant promoter activity was assayed in CHO cells and neonatal cardiomyocytes by transient transfection of promoter-reporter constructs. Single-nucleotide polymorphisms (SNPs) were identified at approximately 1/200 base pairs which are: 11 in the 5'-flanking region, 1 in exon 1, and 5 in intron 1. In addition, a haplotype consisting of two SNPs in complete linkage disequilibrium was identified. Minor allele frequencies were >5% in at least one ethnic panel at 5/19 polymorphic sites. In vitro functional analysis in cardiomyocytes identified four variants with significantly (P<0.05) reduced reporter activity (up to 63% reduction). The largest changes were seen with c.-225-1790 G>A, which reduced reporter activity by 62.8% in CHO cells and 55% in cardiomyocytes. From these results, we can conclude that the SCN5A core promoter includes multiple DNA polymorphisms with altered in vitro activity, further supporting the concept of interindividual variability in transcription of this cardiac ion channel gene.

[Catecholinergic ventricular tachycardia in children]

Catecholinergic ventricular tachycardia is an adrenergic induced polymorphic ventricular arrhythmia. It occurs in infancy and is responsible for syncope and sudden death in the absence of any morphological cardiac abnormality. Without treatment the mortality in catecholinergic ventricular tachycardia is very high. We report genetic and clinical data from 25 cases of catecholinergic ventricular tachycardia referred with syncope (n=19) or resuscitated sudden death during exercise (n=6). A family history from the 25 families identified 41 apparent subjects considered as being clinically affected, with an average age of 30 +/- 10 years (11 to 62 years). Analysis of the RyR2 gene showed mutations in 13 of the 25 cases and in 39 of apparent subjects. With betablocker treatment (nadolol: 1.6 +/- 0.15 mg/kg), 96% of patients remained asymptomatic over an average follow-up of between 7.5 +/- 1.5 years, although some of them continued to display polymorphic ventricular extrasystoles on exercise. Nevertheless, 12% of the cases suffered sudden death or further syncope during follow-up. An automatic defibrillator was implanted in 2 patients who had a RyR2 mutation. High dose betablockers are effective in preventing serious rhythm disturbance in children. In adolescence, implanting an automatic defibrillator should be discussed in cases with a history of syncope or resuscitated sudden death. We confirm the importance of genetic studies in these families at high risk of sudden death.

De novo mutation in the SCN5A gene associated with early onset of sudden infant death

BACKGROUND

Congenital long QT syndrome (LQTS), a cardiac ion channel disease, is an important cause of sudden cardiac death. Prolongation of the QT interval has recently been associated with sudden infant death syndrome, which is the leading cause of death among infants between 1 week and 1 year of age. Available data suggest that early onset of congenital LQTS may contribute to premature sudden cardiac death in otherwise healthy infants.

METHODS AND RESULTS

In an infant who died suddenly at the age of 9 weeks, we performed mutation screening in all known LQTS genes. In the surface ECG soon after birth, a prolonged QTc interval (600 ms(1/2)) and polymorphic ventricular tachyarrhythmias were documented. Mutational analysis identified a missense mutation (Ala1330Pro) in the cardiac sodium channel gene SCN5A, which was absent in both parents. Subsequent genetic testing confirmed paternity, thus suggesting a de novo origin. Voltage-clamp recordings of recombinant A1330P mutant channel expressed in HEK-293 cells showed a positive shift in voltage dependence of inactivation, a slowing of the time course of inactivation, and a faster recovery from inactivation.

CONCLUSIONS

In this study, we report a de novo mutation in the sodium channel gene SCN5A, which is associated with sudden infant death. The altered functional characteristics of the mutant channel was different from previously reported LQTS3 mutants and caused a delay in final repolarization. Even in families without a history of LQTS, de novo mutations in cardiac ion channel genes may lead to sudden cardiac death in very young infants.

Gating-dependent mechanisms for flecainide action in SCN5A-linked arrhythmia syndromes

BACKGROUND

Mutations in the cardiac sodium (Na) channel gene (SCN5A) give rise to the congenital long-QT syndrome (LQT3) and the Brugada syndrome. Na channel blockade by antiarrhythmic drugs improves the QT interval prolongation in LQT3 but worsens the Brugada syndrome ST-segment elevation. Although Na channel blockade has been proposed as a treatment for LQT3, flecainide also evokes "Brugada-like" ST-segment elevation in LQT3 patients. Here, we examine how Na channel inactivation gating defects in LQT3 and Brugada syndrome elicit proarrhythmic sensitivity to flecainide.

METHODS AND RESULTS

We measured whole-cell Na current (I(Na)) from tsA-201 cells transfected with DeltaKPQ, a LQT3 mutation, and 1795insD, a mutation that provokes both the LQT3 and Brugada syndromes. The 1795insD and DeltaKPQ channels both exhibited modified inactivation gating (from the closed state), thus potentiating tonic I(Na) block. Flecainide (1 micromol/L) tonic block was only 16.8+/-3.0% for wild type but was 58.0+/-6.0% for 1795insD (P<0.01) and 39.4+/-8.0% (P<0.05) for DeltaKPQ. In addition, the 1795insD mutation delayed recovery from inactivation by enhancing intermediate inactivation, with a 4-fold delay in recovery from use-dependent flecainide block.

CONCLUSIONS

We have linked 2 inactivation gating defects ("closed-state" fast inactivation and intermediate inactivation) to flecainide sensitivity in patients carrying LQT3 and Brugada syndrome mutations. These results provide a mechanistic rationale for predicting proarrhythmic sensitivity to flecainide based on the identification of specific SCN5A inactivation gating defects.

K(ATP) channel opening during ischemia: effects on myocardial noradrenaline release and ventricular arrhythmias

Cardioprotection by K(ATP) channel openers during ischemia is well documented although ill understood. Proarrhythmic effects may be an important drawback. K(ATP) channel modulation influences neurotransmitter release during ischemia in brain synaptosomes. Therefore, we studied the effects of K(ATP) channel modulation on myocardial noradrenaline release and arrhythmias in ischemic rabbit hearts. Isolated rabbit hearts were perfused according to Langendorff and stimulated. Local electrograms were recorded and K+-selective electrodes were inserted in the left ventricular free wall. Cromakalim (3 microM) or glibenclamide (3 microM) was added 20 min prior to induction of global ischemia. After 15, 20, or 30 min of ischemia, hearts were reperfused and noradrenaline content of the first 100 ml of reperfusate was measured. Cromakalim (n = 16) prevented the second rise of extracellular [K(+)] in accordance with its cardioprotective effect. Cromakalim significantly reduced noradrenaline release after 15 min (mean, 169 +/- SEM 97 pmol/gr dry weight vs. control 941 +/- 278; p < 0.05) and 20 min of ischemia (230 +/- 125 pmol/gr dry wt vs. control 1,460 +/- 433; p < 0.05), but after 30 min of ischemia, the difference in noradrenaline release was no longer significant (cromakalim 2,703 +/- 1,195 pmol/gr dry wt vs. control 5,413 +/- 1,310; p = 0.08). Ventricular fibrillation or ventricular tachycardia occurred in 10 of 13 control hearts (77%) (n = 19), in six of 10 glibenclamide-treated hearts (60%) (n = 15), and in six of 14 cromakalim-treated hearts (43%) (p = NS). Cromakalim significantly accelerated onset of ventricular tachycardia or fibrillation (mean +/- SEM onset after 12.5 +/- 1.6 min ischemia vs. control 16.2 +/- 0.7 min; p < 0.05). Noradrenaline release occurred only in cromakalim-treated hearts with early-onset arrhythmias whereas no noradrenaline release was observed in cromakalim-treated hearts without ventricular tachycardia or fibrillation. Our results show that activation of the K(ATP) channel by cromakalim during ischemia reduces myocardial noradrenaline release and postpones the onset of irreversible damage, contributing to the cardioprotective potential of K(ATP) openers during myocardial ischemia.

Possible bradycardic mode of death and successful pacemaker treatment in a large family with features of long QT syndrome type 3 and Brugada syndrome

INTRODUCTION

We recently identified a novel mutation of SCN5A (1795insD) in a large family with features of both long QT syndrome type 3 and the Brugada syndrome. The purpose of this study was to detail the clinical features and efficacy of pacemaker therapy in preventing sudden death in this family.

METHODS AND RESULTS

The study group consisted of 116 adult family members: 60 carriers (29 males) and 56 noncarriers (28 males) of the mutant gene. Investigations included 24-hour Holter monitoring, ergometry, and electrophysiologic studies. Mean, lowest, and highest heart rate were lower in the carriers, but heart rate variability was comparable. In carriers, disproportional QT prolongation was present during bradycardia. No complex ventricular ectopy was recorded, and there were fewer isolated premature beats (both ventricular and atrial) in carriers. All patients were asymptomatic, except for two individuals who experienced syncope; in one of these patients, asystolic episodes (up to 9 sec) were repeatedly recorded. Prolonged HV intervals were present in 5 of 6 patients. Thirty carriers received a prophylactic backup pacemaker. During median follow-up of 4.5 years (range 0.0 to 22.6), their survival rate was 100%. There were five sudden deaths among the remaining 30 carriers without a pacemaker (P = 0.019).

CONCLUSION

This family with a high incidence of nocturnal sudden death is characterized by bradycardia-dependent QT prolongation, intrinsic sinus node dysfunction, and generalized conduction abnormalities. There is a striking absence of complex ventricular ectopy, and pacemaker implantation was effective in preventing sudden death. These findings raise the possibility of a bradycardic rather than tachycardic mode of death.

Adenosine induced ventricular arrhythmias in the emergency room

While adenosine effectively terminates most supraventricular tachycardias (SVT), rare case reports have demonstrated its proarrhythmic potential, including induction of ventricular tachycardia (VT). The aim of this study was to define the proarrhythmic effects of adenosine in a large, unselected population. During a 5-year period, adenosine was used (average dose 9.7 mg) in the emergency room to manage 187 episodes of tachycardia in 127 patients. In two thirds of the cases, adenosine induced ventricular ectopy following successful termination of SVT, including premature ventricular complexes (PVC) and nonsustained VT. The adenosine induced PVCs and VT were transient and self-terminating. More than half had a right bundle branch block morphology with a superior axis that suggested an origin in the inferior left ventricular septum. In conclusion, although adenosine is commonly used in clinical practice to treat SVTs, we found that it induced PVCs and VT in two thirds of the patients. The high incidence of ventricular arrhythmias following adenosine infusion was surprising but did not require further intervention. These arrhythmias appeared to frequently originate from the inferior left ventricular septum, suggesting that this area may be particularly susceptible to the proarrhythmic effects of adenosine.

Alterations in potassium channel gene expression in atria of patients with persistent and paroxysmal atrial fibrillation: differential regulation of protein and mRNA levels for K+ channels

OBJECTIVES

Our purpose was to determine whether patients with persistent atrial fibrillation (AF) and patients with paroxysmal AF show alterations in potassium channel expression.

BACKGROUND

Persistent AF is associated with a sustained shortening of the atrial action potential duration and atrial refractory period. Underlying molecular changes have not been studied in humans. We investigated whether a changed gene expression of specific potassium channels is associated with these changes in patients with persistent AF and in patients with paroxysmal AF.

METHODS

Right atrial appendages were obtained from 8 patients with paroxysmal AF, 10 with persistent AF and 18 matched controls in sinus rhythm. All controls underwent coronary artery bypass surgery, whereas most AF patients underwent Cox's MAZE surgery (atrial arrhythmia surgery to cure AF) (n = 12). All patients had normal left ventricular function. mRNA (ribonucleic acid) levels were measured by semiquantitative polymerase chain reaction and protein content by Western blotting.

RESULTS

mRNA levels of transient outward channel (Kv4.3), acetylcholine-dependent potassium channel (Kir3.4) and ATP-dependent potassium channel (Kir6.2) were reduced in patients with persistent AF (-35%, -47% and -36%, respectively, p < 0.05), whereas only Kv4.3 mRNA level was reduced in patients with paroxysmal AF (-29%, p = 0.03). No changes were found for Kv1.5 and HERG mRNA levels in either group. Protein levels of Kv4.3, Kv1.5 and Kir3.1 were reduced both in patients with persistent AF (-39%, -84% and -47%, respectively, p < 0.05) and in those with paroxysmal AF (-57%, -64%, and -40%, respectively, p < 0.05).

CONCLUSIONS

Persistent AF is accompanied by reductions in mRNA and protein levels of several potassium channels. In patients with paroxysmal AF these reductions were observed predominantly at the protein level and not at the mRNA level, suggesting a post-transcriptional regulation.

Diagnosis and long-term follow-up of the Brugada syndrome in patients with idiopathic ventricular fibrillation

AIMS

Some patients with idiopathic ventricular fibrillation may suffer from the Brugada syndrome. The diagnostic criteria for the Brugada syndrome are uncertain and arbitrarily set. Therefore, we studied the prevalence of the Brugada syndrome using various diagnostic criteria and long-term follow-up in 37 idiopathic ventricular fibrillation patients.

METHODS AND RESULTS

Idiopathic ventricular fibrillation was diagnosed after thorough clinical evaluation in 37 survivors of an out-of-hospital cardiac arrest referred to our institute (UMC Utrecht). Retrospectively, nine patients (24%, group I) were classified as potentially having the Brugada syndrome based on the presence of (in)complete right bundle branch block and ST-segment elevation in leads V(1)-V(3)of > or =1 mm. Only three patients (8%, group II) showed (in)complete right bundle branch block and > or =2 mm ST-segment elevation. With the intermittent presence of these ECG features and/or their (re)appearance with class I antiarrhythmic drugs included as criteria, the percentage of the Brugada syndrome was attenuated in group I (2/37; 5%) and group II (1/37; 3%). Sixteen (43%) of all idiopathic ventricular fibrillation patients (mean follow-up 77+/-41 months) had a recurrent episode of syncope, ventricular tachyarrhythmias or sudden death. Recurrence rate was 3/9 (33%) in Brugada patients group I, 2/3 (66%) in group II and 13/28 (46%) in patients without the Brugada syndrome (P=ns).

CONCLUSIONS

Depending on the diagnostic criteria used, the Brugada syndrome was observed in 3% to 24% of patients with idiopathic ventricular fibrillation, underlining the importance of defining the precise diagnostic criteria in these patients. For all idiopathic ventricular fibrillation patients, the ventricular tachyarrhythmia recurrence rate was substantial during an average follow-up of more than 6 years.

A sodium-channel mutation causes isolated cardiac conduction disease

Cardiac conduction disorders slow the heart rhythm and cause disability in millions of people worldwide. Inherited mutations in SCN5A, the gene encoding the human cardiac sodium (Na+) channel, have been associated with rapid heart rhythms that occur suddenly and are life-threatening; however, a chief function of the Na+ channel is to initiate cardiac impulse conduction. Here we provide the first functional characterization of an SCN5A mutation that causes a sustained, isolated conduction defect with pathological slowing of the cardiac rhythm. By analysing the SCN5A coding region, we have identified a single mutation in five affected family members; this mutation results in the substitution of cysteine 514 for glycine (G514C) in the channel protein. Biophysical characterization of the mutant channel shows that there are abnormalities in voltage-dependent 'gating' behaviour that can be partially corrected by dexamethasone, consistent with the salutary effects of glucocorticoids on the clinical phenotype. Computational analysis predicts that the gating defects of G514C selectively slow myocardial conduction, but do not provoke the rapid cardiac arrhythmias associated previously with SCN5A mutations.

Genotype-phenotype correlation in the long-QT syndrome: gene-specific triggers for life-threatening arrhythmias

BACKGROUND

The congenital long-QT syndrome (LQTS) is caused by mutations on several genes, all of which encode cardiac ion channels. The progressive understanding of the electrophysiological consequences of these mutations opens unforeseen possibilities for genotype-phenotype correlation studies. Preliminary observations suggested that the conditions ("triggers") associated with cardiac events may in large part be gene specific.

METHODS AND RESULTS

We identified 670 LQTS patients of known genotype (LQT1, n=371; LQT2, n=234; LQT3, n=65) who had symptoms (syncope, cardiac arrest, sudden death) and examined whether 3 specific triggers (exercise, emotion, and sleep/rest without arousal) differed according to genotype. LQT1 patients experienced the majority of their events (62%) during exercise, and only 3% occurred during rest/sleep. These percentages were almost reversed among LQT2 and LQT3 patients, who were less likely to have events during exercise (13%) and more likely to have events during rest/sleep (29% and 39%). Lethal and nonlethal events followed the same pattern. Corrected QT interval did not differ among LQT1, LQT2, and LQT3 patients (498, 497, and 506 ms, respectively). The percent of patients who were free of recurrence with ss-blocker therapy was higher and the death rate was lower among LQT1 patients (81% and 4%, respectively) than among LQT2 (59% and 4%, respectively) and LQT3 (50% and 17%, respectively) patients.

CONCLUSIONS

Life-threatening arrhythmias in LQTS patients tend to occur under specific circumstances in a gene-specific manner. These data allow new insights into the mechanisms that relate the electrophysiological consequences of mutations on specific genes to clinical manifestations and offer the possibility of complementing traditional therapy with gene-specific approaches.

[The heartache of muscular dystrophy]

Duchenne and Becker muscular dystrophy are caused by a mutation in the dystrophin gene, located on the short arm of the X chromosome. Three so called dystrophinopathy patients, a women aged 54 and two men aged 23 and 21 years, suffered from a severe dilated cardiomyopathy. Such a cardiomyopathy can develop in both carriers and patients. In addition, it is often more important for prognosis than muscle weakness. For these two reasons it is important to screen both groups for (early) cardiological abnormalities. If these are present, regular follow-up is necessary to start timely therapy. When cardiological investigations yield normal results, it is advised to screen carriers with a five-year interval. Dystrophinopathy patients should be checked every year, because the cardiomyopathy sometimes develops and deteriorates over a short period of time. Patients with dilated cardiomyopathy and with a positive family history for dilated cardiomyopathy, muscle weakness or high serum creatine kinase activity should be screened for a mutation in the dystrophin gene.

[From gene to disease; ion channel proteins and the long QT syndrome]

The long QT syndrome is characterised by QT prolongation on the ECG, repeated syncope and sudden cardiac death. QT prolongation is the result of delayed repolarisation at the cellular level, secondary to dysfunctioning ion channels. Ventricular arrhythmias underlie syncope and death. At least six genes, all encoding (parts of) ion channels, are causally involved. A molecular diagnosis is often feasible and can be reached reasonably straightforwardly, based on the clinical (family) history and the ECG pattern.

Novel KCNQ1 and HERG missense mutations in Dutch long-QT families

Congenital long QT syndrome (cLQTS) is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncopes, seizure, or sudden death. LQTS can occur either as an autosomal dominant (Romano Ward) or as an autosomal recessive disorder (Jervell and Lange-Nielsen syndrome). Mutations in at least five genes have been associated with the LQTS. Four genes, encoding cardiac ion channels, have been identified. The most common forms of LQTS are due to mutations in the potassium-channel genes KCNQ1 and HERG. We have screened 24 Dutch LQTS families for mutations in KCNQ1 and HERG. Fourteen missense mutations were identified. Eight of these missense mutations were novel: three in KCNQ1 and five in HERG. Novel missense mutations in KCNQ1 were Y184S, S373P, and W392R and novel missense mutations in HERG were A558P, R582C, G604S, T613M, and F640L. The KCNQ1 mutation G189R and the HERG mutation R582C were detected in two families. The pathogenicity of the mutations was based on segregation in families, absence in control individuals, the nature of the amino acid substitution, and localization in the protein. Genotype-phenotype studies indicated that auditory stimuli as trigger of cardiac events differentiate LQTS2 and LQTS1. In LQTS1, exercise was the predominant trigger. In addition, a number of asymptomatic gene defect carriers were identified. Asymptomatic carriers are still at risk of the development of life-threatening arrhythmias, underlining the importance of DNA analyses for unequivocal diagnosis of patients with LQTS.

Genomic organisation and chromosomal localisation of two members of the KCND ion channel family, KCND2 and KCND3

To follow a candidate gene approach for the involvement of the KCND2 and KCND3 genes (Kv4.2 and Kv4.3) in the pathogenesis of the long QT syndrome (LQTS) and Brugada syndrome, it is necessary to determine the genomic organisation of KCND2 and KCND3. We therefore resolved the intron-exon boundaries and flanking intronic sequences and found that KCND2 consisted of six exons and KCND3 of seven exons. Subsequently, we designed the oligonucleotide primers needed for amplifying the coding exons of both KCND2 and KCND3 and established conditions for polymerase chain reaction amplification of each exon from genomic DNA. Furthermore, the chromosomal localisation of KCND2 and KCND3 was determined as 7q31 and 1p13.2, respectively. This information should facilitate the systematic screening of KCND2 and KCND3 exons for mutations in (inherited) arrhythmia syndromes, such as LQTS and Brugada.

[Long QT-interval syndrome and investigation of heritability: psychological reactions in three generations in one family]

DNA diagnostics were carried out in a family after the long QT interval syndrome had been diagnosed in one of its members. The psychic reactions to this testing were different from those seen in other hereditary diseases such as Huntington's disease. This was probably due to the sudden and unexpected occurrence of the arrhythmia. The family members in whom clinical and DNA diagnostics gave purely negative findings were not relieved, owing to solidarity with the affected relatives. Their partners did not understand this response. The anxiety and concern of the gene carriers had nothing to do with their own health status but with that of their carrier children. These parents were in need of educational counselling and advice. The results of clinical and DNA diagnostics affected the family relationships: in carriers the feeling of closeness grew, while the non-carriers were afraid of loss of family closeness.

Two distinct congenital arrhythmias evoked by a multidysfunctional Na(+) channel

The congenital long-QT syndrome (LQT3) and the Brugada syndrome are distinct, life-threatening rhythm disorders linked to autosomal dominant mutations in SCN5A, the gene encoding the human cardiac Na(+) channel. It is believed that these two syndromes result from opposite molecular effects: LQT3 mutations induce a gain of function, whereas Brugada syndrome mutations reduce Na(+) channel function. Paradoxically, an inherited C-terminal SCN5A mutation causes affected individuals to manifest electrocardiographic features of both syndromes: QT-interval prolongation (LQT3) at slow heart rates and distinctive ST-segment elevations (Brugada syndrome) with exercise. In the present study, we show that the insertion of the amino acid 1795insD has opposite effects on two distinct kinetic components of Na(+) channel gating (fast and slow inactivation) that render unique, simultaneous effects on cardiac excitability. The mutation disrupts fast inactivation, causing sustained Na(+) current throughout the action potential plateau and prolonging cardiac repolarization at slow heart rates. At the same time, 1795insD augments slow inactivation, delaying recovery of Na(+) channel availability between stimuli and reducing the Na(+) current at rapid heart rates. Our findings reveal a novel molecular mechanism for the Brugada syndrome and identify a new dual mechanism whereby single SCN5A mutations may evoke multiple cardiac arrhythmia syndromes by influencing diverse components of Na(+) channel gating function. The full text of this article is available at http://www.circresaha.org.

Premature ventricular contractions during triggered imaging with ultrasound contrast

BACKGROUND

Premature ventricular contractions (PVCs) were observed during triggered second harmonic imaging of a contrast agent for myocardial perfusion assessment, with continuous infusion of the contrast agent. Further investigation into the relation of this phenomenon to both ultrasound energy and the contrast agent was carried out during a subsequent bolus-versus-infusion study.

METHODS AND RESULTS

Two open-label studies in healthy male volunteers were performed. The initial study was a dose-response study in 10 subjects, which compared 3 infusion rates. Each volunteer received 3 continuous infusions with different infusion rates of the contrast agent for either 10 (n = 6) or 20 (n = 4) minutes. End-systolic triggered imaging with a mechanical index (MI) of 1.5 was used throughout this part of the study. The second study compared bolus injection with a continuous infusion in 9 volunteers, with a single-dose level but different imaging modalities: end-systolic and end-diastolic triggered imaging at MIs of both 1.1 and 1.5. Spontaneous baseline PVCs were uncommon: 10 in 344 minutes (0.03 PVC/min, maximal 1 PVC/min) of baseline imaging. During end-diastolic triggering, no increase in PVCs was seen, irrespective of MI. A significant increase to 1.06 PVC/min (P <.001) was seen during end-systolic imaging with an MI of 1.5, but not with an MI of 1.1. The increase in PVC rate was dose-dependent in the initial study.

CONCLUSION

Imaging of contrast agents with high acoustic pressures can cause PVCs if end-systolic triggering is used. This effect is related to both the dose of contrast agent and acoustic pressure. It does not occur during end-diastolic triggered imaging. Precautionary measures would include using lower MIs or end-diastolic triggering.

A single Na(+) channel mutation causing both long-QT and Brugada syndromes

Mutations in SCN5A, the gene encoding the cardiac Na(+) channel, have been identified in 2 distinct diseases associated with sudden death: one form of the long-QT syndrome (LQT(3)) and the Brugada syndrome. We have screened SCN5A in a large 8-generation kindred characterized by a high incidence of nocturnal sudden death, and QT-interval prolongation and the "Brugada ECG" occurring in the same subjects. An insertion of 3 nucleotides (TGA) at position 5537, predicted to cause an insertion of aspartic acid (1795insD) in the C-terminal domain of the protein, was linked to the phenotype and was identified in all electrocardiographically affected family members. ECGs were obtained from 79 adults with a defined genetic status (carriers, n=43; noncarriers, n=36). In affected individuals, PR and QRS durations and QT intervals are prolonged (P<0.0001 for all parameters). ST segment elevation in the right precordial leads is present as well (P<0.0001). Twenty-five family members died suddenly, 16 of them during the night. Expression of wild-type and mutant Na(+) channels in Xenopus oocytes revealed that the 1795insD mutation gives rise to a 7.3-mV negative shift of the steady-state inactivation curve and an 8.1-mV positive shift of the steady-state activation curve. The functional consequence of both shifts is likely to be a reduced Na(+) current during the upstroke of the action potential. LQT(3) and Brugada syndrome are allelic disorders but may also share a common genotype.

Human SCN5A gene mutations alter cardiac sodium channel kinetics and are associated with the Brugada syndrome

BACKGROUND

Primary dysrhythmias other than those associated with the long QT syndrome, are increasingly recognized. One of these are represented by patients with a history of resuscitation from cardiac arrest but without any structural heart disease. These patients exhibit a distinct electrocardiographic (ECG) pattern consisting of a persistent ST-segment elevation in the right precordial leads often but not always accompanied by a right bundle branch block (Brugada syndrome). This syndrome is associated with a high mortality rate and has been shown to display familial occurrence.

METHODS AND RESULTS

Pharmacological sodium channel blockade elicits or worsens the electrocardiographic features associated with this syndrome. Hence, a candidate gene approach directed towards SCN5A, the gene encoding the alpha-subunit of the cardiac sodium channel, was followed in six affected individuals. In two patients missense mutations were identified in the coding region of the gene: R1512W in the DIII-DIV cytoplasmic linker and A1924T in the C-terminal cytoplasmic domain. In two other patients mutations were detected near intron/exon junctions. To assess the functional consequences of the R1512W and A1924T mutations, wild-type and mutant sodium channel proteins were expressed in Xenopus oocytes. Both missense mutations affected channel function, most notably a 4-5 mV negative voltage shift of the steady-state activation and inactivation curves in R1512W and a 9 mV negative voltage shift of the steady-state activation curve in A1924T, measured at 22 degrees C. Recovery from inactivation was slightly prolonged for R1512W channels. The time dependent kinetics of activation and inactivation at -20 mV were not significantly affected by either mutation.

CONCLUSIONS

Two SCN5A mutations associated with the Brugada syndrome, significantly affect cardiac sodium channel characteristics. The alterations seem to be associated with an increase in inward sodium current during the action potential upstroke.

[Presymptomatic screening after a sudden cardiac death in the family]

Sudden cardiac death without ischaemic heart disease may be due to a hereditary heart disease with an autosomal dominant heredity. The occurrence, if any, of sudden death in such a family is a main indicator for the risk of sudden cardiac death in other family members. Cardiological and/or genetic investigation may reveal a hereditary disease in relatives without symptoms. Of some of these pathological conditions, the corresponding chromosomal localizations and sometimes the gene mutations have been identified. The psychic burden of family investigation and the socio-economic consequences (insurances, occupation, family relationships) are potentially heavy. Prophylactic treatment of asymptomatic persons in whom a gene mutation is established may comprise advice about lifestyle (e.g. avoidance of peak exercise in patients with hypertrophic cardiomyopathy), medication (e.g. beta-receptor blockers in patients with a long QT interval) or implantation of a pacemaker or internal defibrillator (e.g. in asymptomatic persons with the Brugada syndrome, a form of right bundle branch block). Presymptomatic investigation must be performed multidisciplinary.

Cardiac involvement in carriers of Duchenne and Becker muscular dystrophy

A cross-sectional study in a cohort of DNA proven carriers of Duchenne (DMD) and Becker (BMD) muscular dystrophy was undertaken with the following objectives: (1) to estimate the frequency of electrocardiographic (ECG) and echocardiographic abnormalities; (2) to establish the proportion of carriers with dilated cardiomyopathy and (3) to assess possible associations between dilated cardiomyopathy and genotype. One hundred and twenty nine DMD and BMD carriers, aged 18-60 years, were traced through the files of the central register kept at the department of Human Genetics in Leiden. Investigations included full medical history, physical examination, ECG and two-dimensional and M-mode echocardiographic examination. Forty-seven percent had ECG changes. Thirty-six percent (DMD 41%, BMD 27%) had at least one abnormality as is usually found in the male patients. Echocardiographic examination was abnormal in 36% (DMD 38%, BMD 34%). Dilated cardiomyopathy was found in seven DMD carriers (8%), and in none of BMD carriers. In addition, 18% had left ventricle dilatation (DMD 19%, BMD 16%). Only 38% had a completely normal investigation of the heart. We found no association between genotype and cardiac manifestations. Our study underlines that cardiac involvement is part of the dystrophinopathies. Carriers should be told about the increased risk of this complication when asking genetic advice. It also implicates that a complete cardiological evaluation should be performed at least once in all carriers. If left ventricle dilatation or dilated cardiomyopathy is present a yearly follow up is needed, in order to start timely therapy.

Signs and symptoms of Duchenne muscular dystrophy and Becker muscular dystrophy among carriers in The Netherlands: a cohort study

BACKGROUND

Carriers of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) may show muscle weakness or dilated cardiomyopathy. Studies focusing on skeletal-muscle involvement were done before DNA analysis was possible. We undertook a cross-sectional study in a population of definite carriers to estimate the proportion and to assess the clinical profile of carriers with symptoms. We also assessed a possible correlation between genotype and phenotype.

METHODS

Carriers of DMD and BMD, aged 18-60 years, were traced through the files of the central register kept at the Department of Human Genetics in Leiden, Netherlands. For each carrier who agreed to participate a medical history was taken, and muscle-strength assessment by hand-held dynamometry and manual muscle testing and cardiological assessment were done.

FINDINGS

129 carriers of muscular dystrophy (85 DMD, 44 BMD) participated in the study. In 90 women from 52 (70%) families, 37 different mutations were found. 28 (22%) women had symptoms. 22 (17%) had muscle weakness, varying from mild to moderately severe. Muscle weakness was found in carriers of DMD and BMD, but dilated cardiomyopathy was found only in seven (8%) carriers of DMD, of whom one had concomitant muscle weakness. There was an unexpectedly high proportion of left-ventricle dilation (18%). No genotype-phenotype correlation was found.

INTERPRETATION

Clinical manifestation of muscle weakness, dilated cardiomyopathy, or both can be found in about a fifth of carriers of DMD and BMD. If left-ventricle dilation is taken into account, the proportion of carriers with symptoms is even higher, amounting to 40%.

LocaLisa: new technique for real-time 3-dimensional localization of regular intracardiac electrodes

BACKGROUND

Estimation of the 3-dimensional (3D) position of ablation electrodes from fluoroscopic images is inadequate if a systematic lesion pattern is required in the treatment of complex arrhythmogenic substrates.

METHODS AND RESULTS

We developed a new technique for online 3D localization of intracardiac electrodes. Regular catheter electrodes are used as sensors for a high-frequency transthoracic electrical field, which is applied via standard skin electrodes. We investigated localization accuracy within the right atrium, right ventricle, and left ventricle by comparing measured and true interelectrode distances of a decapolar catheter. Long-term stability was analyzed by localization of the most proximal His bundle before and after slow pathway ablation. Electrogram recordings were unaffected by the applied electrical field. Localization data from 3 catheter positions, widely distributed within the right atrium, right ventricle, or left ventricle, were analyzed in 10 patients per group. The relationship between measured and true electrode positions was highly linear, with an average correlation coefficient of 0.996, 0.997, and 0.999 for the right atrium, right ventricle, and left ventricle, respectively. Localization accuracy was better than 2 mm, with an additional scaling error of 8% to 14%. After 2 hours, localization of the proximal His bundle was reproducible within 1.4+/-1.1 mm.

CONCLUSIONS

This new technique enables accurate and reproducible real-time localization of electrode positions in cardiac mapping and ablation procedures. Its application does not distort the quality of electrograms and can be applied to any electrode catheter.

Auditory stimuli as a trigger for arrhythmic events differentiate HERG-related (LQTS2) patients from KVLQT1-related patients (LQTS1)

OBJECTIVE

This study was performed to identify a possible relationship between genotype and phenotype in the congenital familial long QT syndrome (cLQTS).

BACKGROUND

The cLQTS, which occurs as an autosomal dominant or recessive trait, is characterized by QT-interval prolongation on the electrocardiogram and torsade de pointes arrhythmias, which may give rise to recurrent syncope or sudden cardiac death. Precipitators for cardiac events are exercise or emotion and occasionally acoustic stimuli.

METHODS

The trigger for cardiac events (syncope, documented cardiac arrhythmias, sudden cardiac death) was analyzed in 11 families with a familial LQTS and a determined genotype.

RESULTS

The families were subdivided in KVLQT1-related families (LQTS1, n = 5) and HERG (human ether-a-gogo-related gene)-related families (LQTS2, n = 6) based on single-strand conformation polymorphism analysis and sequencing. Whereas exercise-related cardiac events dominate the clinical picture of LQTS1 patients, auditory stimuli as a trigger for arrhythmic events were only seen in LQTS2 patients.

CONCLUSIONS

Arrhythmic events triggered by auditory stimuli may differentiate LQTS2 from LQTS1 patients.

Long-term (subacute) potassium treatment in congenital HERG-related long QT syndrome (LQTS2)

INTRODUCTION

Congenital long QT syndrome (LQTS) is subdivided according to the underlying gene defect. In LQTS2, an aberrant HERG gene that encodes the potassium channel IKr leads to insufficient IKr activity and delayed repolarization, causing ECG abnormalities and torsades de pointes (TdP). Increasing serum potassium levels by potassium infusion normalizes the ECG in LQTS2 because IKr activity varies with serum potassium levels.

METHODS AND RESULTS

In an LQTS2 patient who presented with TdP, we attempted to achieve a long-term (subacute) elevation of serum potassium by increased potassium intake and potassium-sparing drugs. However, due to renal potassium homeostasis, it was impossible to achieve a long-lasting rise of serum potassium above 4.0 mmol/L.

CONCLUSION

Although raising serum potassium reverses the ECG abnormalities in LQTS2, a long-lasting rise of serum potassium is only partially achievable because in the presence of normal renal function, potassium homeostasis limits the amount of serum potassium increase.

Molecular mechanisms of arrhythmias

Most arrhythmias occur in patients with structural heart disease, where anatomical factors play an important role. Patients without structural heart disease may also suffer from arrhythmias, and recently the genetic basis for such so-called idiopathic arrhythmias has been elucidated. In the congenital long QT syndrome, characterized by a prolonged QT interval, torsade de pointes and sudden death, three aberrant ionic currents have been identified, resulting in a prolongation of the ventricular action potential, which in its turn may cause early afterdepolarization and torsade de pointes. In LQTS1, mutations in the KvLQT1 gene reduce the slow component of the delayed rectifier Iks; in LQTS, mutations in the Human Ether a-go-go Related Gene (HERG) reduce the rapid component of the delayed rectifier Iks. Both potassium currents are important determinants of repolarization: a reduction in outward currents carried by K+ ions prolongs the action potential. In LQTS3, there are mutation in the NA+ channel gene (SCN5A) which causes the channel to inactivate incompletely; the persistent inward current carried by Na+ ions also prolongs the action potential. In the Brugada syndrome, characterized by right bundle branch block, ST elevation in V1-V3 and sudden death, mutations have been observed in the Na+ channel gene, but it is as yet unclear which functional changes in the NA+ channel are responsible for the typical ECG changes and the arrhythmias. Various cardiac disorders may lead to changes in gene expression that modify channel function. In hypertrophy, the ventricular action potential is prolonged by a decrease in the inward rectifier and the transient outward current. After prolonged episodes of rapid electrical activity, the atrial action potential is shortened, because of a reduction in the Iks type calcium current. Finally, many carriers of mutated genes display no abnormalities on the ECG. It is conceivable that such individuals may show excessive QT prolongation when taking cardiac or noncardiac drugs (such as neuroleptics, antidepressants, antihistamines, antimicrobials, antimalarials) that block potassium currents.