The β-angle can help guide clinical decisions in the diagnostic work-up of patients suspected of Brugada syndrome: a validation study of the β-angle in determining the outcome of a sodium channel provocation test

AIMS

In patients with Brugada syndrome (BrS) but without spontaneous Type-1 electrocardiogram, several electrocardiographic characteristics have been studied, including the β-angle. Previous studies suggested that the β-angle might be useful in distinguishing BrS-patients from patients with only suggestive repolarization patterns without performing sodium channel blocker provocation testing. In this study, we aimed to determine the diagnostic value of the β-angle in patients suspected of BrS.

METHODS AND RESULTS

A large cohort (n = 1430) of consecutive patients who underwent provocation testing was evaluated. β-angles were measured in leads V1, V2, and their corresponding positions over the second and third intercostal space. Receiver-operating characteristic curves were constructed and the diagnostic accuracy of previously reported β-angle cut-offs were calculated and evaluated. The importance of the β-angle for predicting the provocation test outcome was determined using a prediction model constructed with logistic regression. The optimum β-angle cut-off in our cohort for ruling out a positive provocation test was 15°; sensitivities were 80-98% and negative predictive values were 79-96% among the right precordial leads. Previously reported β-angle cut-offs performed less well, indicated by lower Youden indices. In the optimism-corrected prediction model [C-statistic: 0.78 (95% CI: 0.75-0.81)], the β-angle had large value (Z-score: 2.1-10.3) and aided construction of a nomogram to predict test outcome.

CONCLUSION

To predict the outcome of provocation testing for BrS, the β-angle alone does not demonstrate strong diagnostic characteristics. However, the β-angle is an important variable to predict provocation test outcome and thus has added value.

Complex interactions in a novel SCN5A compound mutation associated with long QT and Brugada syndrome: Implications for Na+ channel blocking pharmacotherapy for de novo conduction disease

Background

The SCN5A mutation, P1332L, is linked to a malignant form of congenital long QT syndrome, type 3 (LQT3), and affected patients are highly responsive to the Na⁺ channel blocking drug, mexiletine. In contrast, A647D is an atypical SCN5A mutation causing Brugada syndrome. An asymptomatic male with both P1332L and A647D presented with varying P wave/QRS aberrancy and mild QTc prolongation which did not shorten measurably with mexiletine.

Objective

We characterized the biophysical properties of P1332L, A647D and wild-type (WT) Na⁺ channels as well as their combinations in order to understand our proband’s phenotype and to guide mexilitine therapy.

Methods

Na⁺ channel biophysics and mexilitine-binding kinetics were assessed using heterologous expression studies in CHO-K1 cells and human ventricular myocyte modeling.

Results

Compared to WT, P1332L channels displayed a hyperpolarizing shift in inactivation, slower inactivation and prominent late Na⁺ currents (I_Na). While A647D had no effect on the biophysical properties of I_Na, it reduced peak and late I_Na density when co-expressed with either WT or P1332L. Additionally, while P1332L channels had greater sensitivity to block by mexiletine compared to WT, this was reduced in the presence of A647D. Modelling studies revealed that mixing P1332L with A647D channels, action potential durations were shortened compared to P1332L, while peak I_Na was reduced compared to either A647D coexpressing with WT or WT alone.

Conclusions

While A647D mitigates the lethal LQT3 phenotype seen with P1332L, it also reduces mexilitine sensitivity and decreases I_Na density. These results explain our proband’s mild repolarization abnormality and prominent conduction defect in the atria and ventricles, but also suggest that expression of P1332L with A647D yields a novel disease phenotype for which mexiletine pharmacotherapy is no longer suitable.

Ajmaline blocks INa and IKr without eliciting differences between Brugada syndrome patient and control human pluripotent stem cell-derived cardiac clusters

The class Ia anti-arrhythmic drug ajmaline is used clinically to unmask latent type I ECG in Brugada syndrome (BrS) patients, although its mode of action is poorly characterised.

Our aims were to identify ajmaline's mode of action in human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs), and establish a simple BrS hiPSC platform to test whether differences in ajmaline response could be determined between BrS patients and controls.

Control hiPSCs were differentiated into spontaneously contracting cardiac clusters. It was found using multi electrode array (MEA) that ajmaline treatment significantly lengthened cluster activation-recovery interval. Patch clamping of single CMs isolated from clusters revealed that ajmaline can block both I_Na and I_Kr.

Following generation of hiPSC lines from BrS patients (absent of pathogenic SCN5A sodium channel mutations), analysis of hiPSC-CMs from patients and controls revealed that differentiation and action potential parameters were similar. Comparison of cardiac clusters by MEA showed that ajmaline lengthened activation-recovery interval consistently across all lines.

We conclude that ajmaline can block both depolarisation and repolarisation of hiPSC-CMs at the cellular level, but that a more refined integrated tissue model may be necessary to elicit differences in its effect between BrS patients and controls.

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hiPSC lines generated and differentiated from BrS patients lacking SCN5A mutations

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Ajmaline lengthens the activation-recovery interval of hPSC cardiac clusters

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Ajmaline effect consistent between BrS patient and control hPSC cardiac clusters

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Patch clamp analysis of hiPSC-CMs reveals ajmaline blocks both I_Na and I_Kr

A novel NaV1.5 voltage sensor mutation associated with severe atrial and ventricular arrhythmias

BACKGROUND

Inherited autosomal dominant mutations in cardiac sodium channels (NaV1.5) cause various arrhythmias, such as long QT syndrome and Brugada syndrome. Although dozens of mutations throughout the protein have been reported, there are few reported mutations within a voltage sensor S4 transmembrane segment and few that are homozygous. Here we report analysis of a novel lidocaine-sensitive recessive mutation, p.R1309H, in the NaV1.5 DIII/S4 voltage sensor in a patient with a complex arrhythmia syndrome.

METHODS AND RESULTS

We expressed the wild type or mutant NaV1.5 heterologously for analysis with the patch-clamp and voltage clamp fluorometry (VCF) techniques. p.R1309H depolarized the voltage-dependence of activation, hyperpolarized the voltage-dependence of inactivation, and slowed recovery from inactivation, thereby reducing the channel availability at physiologic membrane potentials. Additionally, p.R1309H increased the "late" Na(+) current. The location of the mutation in DIIIS4 prompted testing for a gating pore current. We observed an inward current at hyperpolarizing voltages that likely exacerbates the loss-of-function defects at resting membrane potentials. Lidocaine reduced the gating pore current.

CONCLUSIONS

The p.R1309H homozygous NaV1.5 mutation conferred both gain-of-function and loss-of-function effects on NaV1.5 channel activity. Reduction of a mutation-induced gating pore current by lidocaine suggested a therapeutic mechanism.

[Electrical storm in Brugada syndrome successfully treated with isoproterenol. Report of a case]

We report a 22-year-old male who experienced several episodes of syncope within a timeframe of few hours. In the emergency room, multiple ventricular fibrillation episodes where documented along with a type 1 Brugada ECG pattern. Isoproterenol in continuous infusion was started, normalizing the ECG and avoiding further arrhythmia recurrences. The patient was implanted with an automated defibrillator and discharged 3 days after admission.

Long-term pharmacological therapy of Brugada syndrome: is J-wave attenuation a marker of drug efficacy?

We herein describe two patients with Brugada syndrome in whom J-waves were successfully modified by drugs. Case 1 was a 54-year-old man who presented with repeated ventricular fibrillations (VF) and J-point elevation in the right precordial and lateral leads. After administration of cilostazol (200 mg/d), J-waves disappeared and coved-type ST-segment elevation changed to a saddleback-type for 25 months. Case 2 was a 31-year-old man who presented with a VF storm and J-point elevation in the lateral leads. After administration of quinidine (300 mg/d), J-waves and coved-type ST-segment elevation disappeared for 20 months. J-wave disappearance and coved-type ST-segment elevation were followed by VF suppression, probably due to transient outward potassium current (Ito) suppression.

Heterogeneous response of J-wave syndromes to beta-adrenergic stimulation

BACKGROUND

Inferolateral early repolarization (ER) and Brugada syndrome manifest with J waves. Isoproterenol suppresses recurrent ventricular arrhythmias while reducing J waves in both disorders.

OBJECTIVE

To characterize the effect of isoproterenol on J waves.

METHODS

We analyzed the impact of isoproterenol on J waves in 20 patients with Brugada-type electrocardiogram (Br group) and 38 patients with ER (ER group).

RESULTS

In the ER group, J waves were present in inferior leads in 32 patients (84%) and in lateral leads in 23 patients (61%). Isoproterenol increased the heart rate by 75 beats/min in the ER group and by 71 beats/min in the Br group (P = .20). The incidences of persistent (≤ 0.05-mV decrease), decreased, and normalized J waves (residual J wave ≤ 0.05 mV) were 20%, 80%, and 0% for Br group patients and 29%, 8%, and 63% for ER group patients, respectively (P <.001). Within the ER group, inferior J waves persisted in 34% of the cases, decreased in 9%, and normalized in 56% whereas lateral J waves always normalized (P <.001). Baseline QRS width was broader in ER group patients with persistent J waves (90 ms vs 80 ms; P = .003) and was unchanged with isoproterenol (90 ms; P = .19), whereas it decreased in the remaining patients (75 ms; P <.001).

CONCLUSIONS

J-wave syndromes have distinct regional sensitivity to beta-adrenergic stimulation. J waves may persist in a subset of patients with right precordial and inferior J waves but never in lateral location. This heterogeneous response to isoproterenol may indicate distinctive mechanisms for Brugada and ER patterns, including depolarization abnormalities or ion channel sensitivity.

Effect of sodium-channel blockade on early repolarization in inferior/lateral leads in patients with idiopathic ventricular fibrillation and Brugada syndrome

BACKGROUND

A high incidence of early repolarization (ER) pattern in the inferolateral leads has been reported in patients with idiopathic ventricular fibrillation (IVF). Brugada syndrome (BS) is characterized by J-point or ST-segment elevation in the right precordial leads and ventricular fibrillation, and some patients with BS also have ER in the inferolateral leads.

OBJECTIVE

To compare the clinical characteristics and effects of sodium-channel blockade on ER between IVF patients with ER (early repolarization syndrome [ERS]) and BS patients with or without ER.

METHODS

Fourteen patients with ERS and 21 patients with BS were included in this study. ER was defined as an elevation of at least 0.1 mV from baseline in the QRS-T junction in the inferorolateral leads. Provocative tests with sodium-channel blockers were conducted in all patients with ERS to distinguish ERS from BS.

RESULTS

In the ERS group, all patients were male and most patients experienced ventricular fibrillation during sleep or low activity (79%). ER was attenuated by sodium-channel blockers in most patients with ERS (13/14, 93%) and BS (5/5, 100%), whereas ST-segment elevation was augmented in the right precordial leads in the BS group. The rates of positive late potentials were significantly higher in the BS group (60%) than in the ERS group (7%) (P <.01).

CONCLUSIONS

Some similarities were observed between ERS and BS, including gender, arrhythmia triggers, and response of ER to sodium-channel blockers. Unlike the ST segment in the right precordial leads in BS, ER was attenuated in patients with both ERS and BS, suggesting a differential mechanism between ER in the inferolateral leads and ST elevation in the right precordial leads.

Clinical aspects of the early repolarization syndrome: a 2011 update

Recent studies suggest that the electrocardiographic (ECG) finding of J-point ST-elevation, the early repolarization syndrome, is not as benign as earlier believed. Three important articles published in 2008/2009 suggest that this finding in the inferolateral leads of the ECG may be representing a risk for subsequent ventricular fibrillation. Although these retrospective studies do justify a careful evaluation of persons with this electrocardiographic pattern, especially of those with syncope or ventricular arrhythmias and/or family history of sudden cardiac death, it seems to be unjustified to consider it today to be a marker for high risk for sudden cardiac deaths in a general population. Even in athletes, early repolarization was found to increase only minimally their arrhythmic risk. In spite of certain similarities with the Brugada syndrome, their association is far from being proved. Prospective studies and further electrophysiological and genetic information will help to clarify the clinical significance of this syndrome.

Automatic continuous ECG monitoring system for over-drug detection in Brugada Syndrome

This paper is concerned with the automatic control of drug administration in patients suffering from Brugada Syndrome (BS). Drugs such as flecainide, procainamide, ajmaline and pilsicainide should be administrated under carefully controlled electrocardiogram (ECG) monitoring given that the treatment must be stopped if some ECG disturbing conditions appear. These conditions are, among others the development of premature ventricular contraction (PVC), atrial fibrillation (AF) and the widening of the QRS wave. The proposed system can detect these abnormalities by using a pattern recognition approach based on Hidden Markov Models (HMM) with features extracted from three scales of the Wavelet Transform (WT). Performances higher than 98% were reached regarding the classification of normal and abnormal pulses. The system was trained and tested mainly in data from the standard MIT-BIH arrhythmia database.

Monitoring the safety of antiepileptic medication in a child with Brugada syndrome

We report the case of an 8 year old boy presenting with episodes of decreased consciousness. As the boy's father died of a sudden cardiac death (SCD) at the age of 31 years, among other causes a Brugada syndrome (BS) was suspected. The boy was further examined at the UZ Brussels Heart Rhythm Management Center. The intravenous administration of ajmaline confirmed a BS without ventricular arrhythmias. Syncope in children can be an imminent sign of BS. BS is a life threatening condition that can deteriorate into SCD. The boy presented with episodes of lowered consciousness, transpiration and paleness. Readmission for further investigation was required. Clinical observation and continuous registered EEG during sleep showed multiple epileptical incidents. Hence the child was diagnosed with new onset epilepsy. For initiation of antiepileptic therapy, the patient was admitted at the pediatric intensive care unit (PICU). Close clinical observation and cardiovascular monitoring with continuous 12-lead ECG registration were performed during orally administered sodium valproic acid. During this anticonvulsive treatment in a child with documented BS no significant alterations in ECG-findings were observed. In this particular patient sodium valproic acid treatment can be estimated as a safe anticonvulsive therapy.

Putative druggable targets for selective enhancement of cardiac conduction

Putative druggable targets to selectively enhance cardiac conduction can be considered from the level of the ion channels determining the initiation and duration of the cardiac action potential to the gap junction proteins responsible for optimal cellular electrical coupling. Nature has provided a number of inherited disorders of conduction, the pathophysiology of which offer novel insights into future therapeutic targets. This review will focus upon the potential cellular and molecular targets for drug development based upon our knowledge of their pathophysiological impact.

The Brugada syndrome: update 2006

Over the last 14 years - since the Brugada syndrome was first recognized as a distinct clinical/electrocardiographical entity - a considerable number of papers have been published on its various aspects. It has been defined as the combination of a typical ST-segment elevation in the right precordial leads and a predisposition for malignant ventricular arrhythmias occurring in the absence of structural heart disease. From the outset, controversy arose about the diagnostic criteria to be applied. This issue has been clarified since the announcement of a first (2002) and second (2005) consensus report. Our review will discuss the clinical characteristics and different possible pathophysiological mechanisms underlying the specific ECG-abnormalities and susceptibility for malignant arrhythmias. Nowadays, the main issue of discussion revolves essentially around its prognostic features, especially in asymptomatic patients. This review will compare the results of different follow-up studies and yields a possible explanation for the differences in event rates and in the identification of useful sudden-death predictors. Finally, the most recent data concerning new diagnostic techniques, gene identification and future therapeutic options will also be discussed.

Mutation-specific effects of lidocaine in Brugada syndrome

Brugada syndrome (BrS) is a hereditary cardiac disease characterized by right bundle-branch block, an elevation of the ST-segment in leads V1 through V3 on the electrocardiogram, and ventricular fibrillation that can lead to sudden cardiac death. Mutations in the cardiac sodium channel gene SCN5A, which encodes the alpha-subunit of the human cardiac voltage-dependent Na+ channel (Na(v)1.5), are identified in 15-30% of patients with BrS. Most SCN5A mutations lead to a 'loss-of-function' phenotype, reducing the Na+ current during the early phases of the action potential. Anti-arrhythmic drugs that affect Na+ channels typically block these Na+ channels, thereby exaggerating the ECG abnormalities and arrhythmogenicity in the BrS. However, the N406S mutation in SCN5A causes distinct gating defects and enhanced intermediate inactivation of Na+ channels, which led to unexpected pharmacological effects of lidocaine in a patient carrying this mutation. In the presence of the N406S mutation, use-dependent block by lidocaine is reduced and recovery from intermediate inactivation is hastened by lidocaine. These findings suggest that lidocaine may improve the Brugada phenotype in patients with N406S by increasing the availability of Na+ channels.

Ionic basis of pharmacological therapy in Brugada syndrome

An implantable cardioverter-defibrillator is considered the only effective therapy to terminate ventricular arrhythmias in symptomatic patients with Brugada syndrome. However, it does not prevent future arrhythmic episodes. Only antiarrhythmic drug therapy can prevent them. There have been several reports of a beneficial effect of oral quinidine in both asymptomatic and symptomatic patients. Other possible beneficial oral agents could be I(to) blockers. Intravenous isoproterenol has been reported to be especially useful in abolishing arrhythmic storms in emergency situations. Also, isolated case reports on the usefulness of cilostazol, sotalol, and mexiletine have been described. The present article reviews the mechanisms by which these drugs may act and their possible role in the pharmacotherapy of this disease.

A paradoxical effect of lidocaine for the N406S mutation of SCN5A associated with Brugada syndrome

BACKGROUND

Accelerated intermediate inactivation, which is caused by mutations in the cardiac voltage-gated sodium channel alpha-subunit gene (SCN5A), is one of the molecular mechanisms underlying Brugada syndrome. The N406S mutation associated with Brugada syndrome results in the accelerated intermediate inactivation, in addition to unique pharmacological characteristics.

METHODS

Functional sodium channels were expressed transiently in HEK293 cells by transfecting equally the alpha- and beta-subunit plasmids (1 microg/ml) and the sodium current were measured in whole-cell mode of patch-clamp recording.

RESULTS

Since the N406S mutant channel has a greatly reduced use-dependent block of lidocaine, we took the advantage of the mutant channel to examine the effect of lidocaine on intermediate inactivation using wild-type (WT) and N406S mutant channels recombinantly expressed in HEK293 cells. Lidocaine (100 microM) slowed the recovery from the fast inactivation similarly for WT and N406S. On the other hand, whereas lidocaine slowed the recovery from the intermediate inactivation for WT, lidocaine accelerated the recovery for N406S. Activity-dependent loss of channel availability by repetitive 500-ms pulses was more strongly enhanced and accelerated by lidocaine for WT, but lidocaine exerted little effect on the N406S channel.

CONCLUSION

We demonstrate that lidocaine may suppress Brugada syndrome associated with the N406S mutation by preventing the sodium channel from accumulating in the intermediate inactivation state.

Amitriptyline-induced Brugada pattern fails to respond to sodium bicarbonate

This report describes a Brugada electrocardiographic pattern after tricyclic antidepressant intoxication that fails to resolve following sodium bicarbonate treatment. A 50-year-old male ingested 13.6 grams of amitriptyline and presented in cardiopulmonary arrest. After initial resuscitation, the patient developed a Brugada electrocardiographic pattern. The pattern persisted despite intravenous administration of 700 mEq of sodium bicarbonate. Five hours after the last dose of sodium bicarbonate and 18 hours after initial presentation, the Brugada pattern resolved. No co-ingestants were ingested and an ischemic pattern was not seen on electrocardiogram. The serum amitriptyline level was >1000 ng/ml. Response of the tricyclic-induced Brugada pattern to sodium bicarbonate has not been previously reported.

Acute and chronic management in patients with Brugada syndrome associated with electrical storm of ventricular fibrillation

BACKGROUND

Some patients with Brugada syndrome experience an electrical storm of ventricular fibrillation (VF).

OBJECTIVE

The purpose of this study was to investigate the clinical, laboratory, electrocardiographic, and electrophysiologic characteristics, acute and subsequent chronic treatment, and follow-up data of patients with Brugada syndrome associated with electrical storm of VF.

METHODS

Sixty-seven patients with Brugada syndrome (65 men and 2 women, age 46 +/- 14 years) were divided into three groups: 7 patients with a history of electrical storm of VF (group I), 39 symptomatic patients with documented VF and/or syncope (group II), and 21 asymptomatic patients (group III). Electrical storm was defined as three or more episodes of VF per day recorded by the memory of an implantable cardioverter-defibrillator.

RESULTS

No significant differences were observed among the three groups with regard to clinical (age at diagnosis, familial history of sudden cardiac death), laboratory (SCN5A mutation and serum potassium level), electrocardiographic and electrophysiologic characteristics, and follow-up duration after diagnosis. However, arrhythmic events during follow-up after diagnosis and number of arrhythmic events per patient were significantly higher in group I compared with groups II and III. Isoproterenol infusion (0.003 +/- 0.003 microg/kg/min for 24 +/- 13 days) completely suppressed electrical storm of VF in all five patients treated and was successfully replaced with oral medications, including denopamine, quinidine, isoproterenol, cilostazol, and bepridil alone or in combination.

CONCLUSION

No specifically clinical, laboratory, electrocardiographic, and electrophysiologic characteristics were recognized in patients with Brugada syndrome associated with electrical storm of VF. Isoproterenol infusion was effective as an acute treatment in suppressing electrical storm of VF and was successfully replaced with chronic oral medications.

Low-dose isoproterenol for repetitive ventricular arrhythmia in patients with Brugada syndrome

AIMS

Arrhythmic storm or repetitive ventricular arrhythmia (VA) has been occasionally observed in Brugada syndrome (BS). A beta-adrenergic stimulator [isoproterenol (ISP)] has been reported to suppress this arrhythmic storm in sporadic cases. Accordingly, we investigated the antiarrhythmic effects of ISP infusion in consecutive BS patients with arrhythmic storm or repetitive VA.

METHODS AND RESULTS

Seven BS patients with arrhythmic storm were studied. Intravenous ISP was administered as a bolus injection (1-2 microg), followed by continuous infusion (0.15 microg/min). Arrhythmic storm or repetitive VA was suppressed immediately after the bolus administration of ISP, which was followed by continuous infusion of low-dose ISP for 1-3 days. In all patients, ST-elevation decreased in right precordial leads. In six of the seven patients, VA subsided after the discontinuance of ISP. RR interval was shortened and ST-elevation in right precordial leads was decreased after ISP bolus injection. ST-elevation in right precordial leads remained decreased during continuous ISP infusion, whereas the RR interval returned to the control level.

CONCLUSION

Continuous administration of low-dose ISP may be effective for the suppression of repetitive VA occurrence in patients with BS.