Executive summary: HRS/EHRA/APHRS expert consensus statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes

Ajmaline Testing and the Brugada Syndrome

Brugada syndrome (BrS) diagnosis requires the presence of a typical type 1 ECG pattern. Owing to the spontaneous ECG variability, the real BrS prevalence in the general population remains unclear. The aim of the present study was to evaluate the prevalence of positive ajmaline challenge for BrS in a cohort of consecutive patients who underwent electrophysiological evaluation for different clinical reasons. All consecutive patients from 2008 to 2019 who underwent ajmaline testing were prospectively included. A total of 2,456 patients underwent ajmaline testing, 742 (30.2%) in the context of familial screening for BrS. In non-familial screening group (1,714) ajmaline testing resulted positive in 186 (10.9%). Indications for ajmaline testing were: suspicious BrS ECG in 23 cases (12.4%), palpitations in 27 (14.5%), syncope in 71 (38.2%), presyncope in 7 (3.8%), family history of sudden cardiac death in 18 (9.7%), documented ventricular arrhythmias in 12 (6.5%), unexplained cardiac arrest in 4 (2.2%), atrial fibrillation in 16 (8.5%), brady-arrhythmias in 1 (0.5%), and cerebrovascular accidents in 7 (3.7%). Compared with the overall population, ajmaline testing positive patients were younger (42.8 ± 15.5 vs 48.9 ± 20.4; p <0.001) and more frequently male (65.1% vs 56.3%; p = 0.023). Implantable cardioverter defibrillator was implanted in 84 patients (45.2%). During a median follow-up of 42.4 months, 12 appropriate shocks and 13 implantable cardioverter defibrillator related complications were reported. In conclusion, the BrS was diagnosed in an unexpected high proportion of patients that underwent ajmaline testing for a variety of cardiovascular symptoms. This can lead to an adequate counseling and clinical management in BrS patients.

The cardiac arrest centre for the treatment of sudden cardiac arrest due to presumed cardiac cause: aims, function, and structure: position paper of the ACVC association of the ESC, EAPCI, EHRA, ERC, EUSEM, and ESICM

Approximately 10% of patients resuscitated from out-of-hospital cardiac arrest (OHCA) survive to hospital discharge. Improved management to improve outcomes are required, and it is proposed that such patients should be preferentially treated in cardiac arrest centres (CACs). The minimum requirements of therapy modalities for the CAC are 24/7 availability of an on-site coronary angiography laboratory, an emergency department, an intensive care unit, imaging facilities, such as echocardiography, computed tomography, and magnetic resonance imaging, and a protocol outlining transfer of selected patients to CACs with additional resources (OHCA hub hospitals). These hub hospitals are regularly treating a high volume of patients and offer further treatment modalities. This consensus document describes the aims, the minimal requirements for therapeutic modalities and expertise, and the structure, of a CAC. It represents a consensus among the major European medical associations and societies involved in the treatment of OHCA patients.

Calmodulin mutations and life-threatening cardiac arrhythmias: insights from the International Calmodulinopathy Registry

AIMS

Calmodulinopathies are rare life-threatening arrhythmia syndromes which affect mostly young individuals and are, caused by mutations in any of the three genes (CALM 1-3) that encode identical calmodulin proteins. We established the International Calmodulinopathy Registry (ICalmR) to understand the natural history, clinical features, and response to therapy of patients with a CALM-mediated arrhythmia syndrome.

METHODS AND RESULTS

A dedicated Case Report File was created to collect demographic, clinical, and genetic information. ICalmR has enrolled 74 subjects, with a variant in the CALM1 (n = 36), CALM2 (n = 23), or CALM3 (n = 15) genes. Sixty-four (86.5%) were symptomatic and the 10-year cumulative mortality was 27%. The two prevalent phenotypes are long QT syndrome (LQTS; CALM-LQTS, n = 36, 49%) and catecholaminergic polymorphic ventricular tachycardia (CPVT; CALM-CPVT, n = 21, 28%). CALM-LQTS patients have extremely prolonged QTc intervals (594 ± 73 ms), high prevalence (78%) of life-threatening arrhythmias with median age at onset of 1.5 years [interquartile range (IQR) 0.1-5.5 years] and poor response to therapies. Most electrocardiograms (ECGs) show late onset peaked T waves. All CALM-CPVT patients were symptomatic with median age of onset of 6.0 years (IQR 3.0-8.5 years). Basal ECG frequently shows prominent U waves. Other CALM-related phenotypes are idiopathic ventricular fibrillation (IVF, n = 7), sudden unexplained death (SUD, n = 4), overlapping features of CPVT/LQTS (n = 3), and predominant neurological phenotype (n = 1). Cardiac structural abnormalities and neurological features were present in 18 and 13 patients, respectively.

CONCLUSION

Calmodulinopathies are largely characterized by adrenergically-induced life-threatening arrhythmias. Available therapies are disquietingly insufficient, especially in CALM-LQTS. Combination therapy with drugs, sympathectomy, and devices should be considered.

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

A Primary Prevention Clinical Risk Score Model for Patients With Brugada Syndrome (BRUGADA-RISK)

OBJECTIVES

The goal of this study was to develop a risk score model for patients with Brugada syndrome (BrS).

BACKGROUND

Risk stratification in BrS is a significant challenge due to the low event rates and conflicting evidence.

METHODS

A multicenter international cohort of patients with BrS and no previous cardiac arrest was used to evaluate the role of 16 proposed clinical or electrocardiogram (ECG) markers in predicting ventricular arrhythmias (VAs)/sudden cardiac death (SCD) during follow-up. Predictive markers were incorporated into a risk score model, and this model was validated by using out-of-sample cross-validation.

RESULTS

A total of 1,110 patients with BrS from 16 centers in 8 countries were included (mean age 51.8 ± 13.6 years; 71.8% male). Median follow-up was 5.33 years; 114 patients had VA/SCD (10.3%) with an annual event rate of 1.5%. Of the 16 proposed risk factors, probable arrhythmia-related syncope (hazard ratio [HR]: 3.71; p < 0.001), spontaneous type 1 ECG (HR: 3.80; p < 0.001), early repolarization (HR: 3.42; p < 0.001), and a type 1 Brugada ECG pattern in peripheral leads (HR: 2.33; p < 0.001) were associated with a higher risk of VA/SCD. A risk score model incorporating these factors revealed a sensitivity of 71.2% (95% confidence interval: 61.5% to 84.6%) and a specificity of 80.2% (95% confidence interval: 75.7% to 82.3%) in predicting VA/SCD at 5 years. Calibration plots showed a mean prediction error of 1.2%. The model was effectively validated by using out-of-sample cross-validation according to country.

CONCLUSIONS

This multicenter study identified 4 risk factors for VA/SCD in a primary prevention BrS population. A risk score model was generated to quantify risk of VA/SCD in BrS and inform implantable cardioverter-defibrillator prescription.

Predicting cardiac electrical response to sodium-channel blockade and Brugada syndrome using polygenic risk scores

Aims

Sodium-channel blockers (SCBs) are associated with arrhythmia, but variability of cardiac electrical response remains unexplained. We sought to identify predictors of ajmaline-induced PR and QRS changes and Type I Brugada syndrome (BrS) electrocardiogram (ECG).

Methods and results

In 1368 patients that underwent ajmaline infusion for suspected BrS, we performed measurements of 26 721 ECGs, dose–response mixed modelling and genotyping. We calculated polygenic risk scores (PRS) for PR interval (PRS_PR), QRS duration (PRS_QRS), and Brugada syndrome (PRS_BrS) derived from published genome-wide association studies and used regression analysis to identify predictors of ajmaline dose related PR change (slope) and QRS slope. We derived and validated using bootstrapping a predictive model for ajmaline-induced Type I BrS ECG. Higher PRS_PR, baseline PR, and female sex are associated with more pronounced PR slope, while PRS_QRS and age are positively associated with QRS slope (P < 0.01 for all). PRS_BrS, baseline QRS duration, presence of Type II or III BrS ECG at baseline, and family history of BrS are independently associated with the occurrence of a Type I BrS ECG, with good predictive accuracy (optimism-corrected C-statistic 0.74).

Conclusion

We show for the first time that genetic factors underlie the variability of cardiac electrical response to SCB. PRS_BrS, family history, and a baseline ECG can predict the development of a diagnostic drug-induced Type I BrS ECG with clinically relevant accuracy. These findings could lead to the use of PRS in the diagnosis of BrS and, if confirmed in population studies, to identify patients at risk for toxicity when given SCB.

Prognostic value and prevalence of complete right bundle branch block in an elderly population: a community-based 10-year prospective study

Complete right bundle branch block (CRBBB) occurs in 0.2% to 1.3% of the general population, but its prognostic significance in the geriatric population is unknown. We prospectively investigated the prevalence and prognostic value of CRBBB in individuals aged ≥65 years in a community-based population in Taiwan. A total of 5,830 community-dwelling individuals were prospectively recruited from 7 regions across Taiwan starting in December 2008 through March 2013. Those aged ≥65 years were included in the analysis (N=3,383). All subjects underwent a home visit and standardized medical exams and were followed up annually until the end of April 2019; cause of death was documented by citizen death records. The mean age of the study cohort was 73.5±5.9 years (65-104), and 47.21% were men. Among these individuals, 171 (5.05%) had CRBBB; the prevalence was higher in men (7.08%) than in women (3.25%). Subjects with CRBBB were older than those without CRBBB (75.4±6.5 vs. 73.4±5.9), and the frequency of CRBBB increased with age. Survival analysis revealed that all-cause mortality and cardiac mortality were similar in individuals with and without CRBBB during a mean follow-up of 92.6±23.6 months. CRBBB is not associated with increased risk of mortality in the geriatric population.

Vasospastic angina and overlapping cardiac disorders in patients resuscitated from cardiac arrest

BACKGROUND

Vasospastic angina (VSA) reportedly accounts for one form of sudden cardiac arrest (SCA). Intracoronary acetylcholine (ACh) testing is useful for diagnosing VSA although invasive provocation testing after SCA is a clinical challenge. In addition, even if the ACh test is positive, any causal relationship between VSA and SCA is often unclear because patients with VSA may have other underlying cardiac disorders.

METHODS

A total of 20 patients without overt structural heart disease who had been fully resuscitated from SCA were included. All patients underwent the ACh provocation test and scrutiny such as cardiac computed tomography or magnetic resonance imaging. Patients were followed up for all-cause death or recurrent SCA including appropriate implantable cardioverter defibrillator therapy.

RESULTS

An ACh provocation test was performed 20 ± 17 days after cardiac arrest. Fifteen out of 20 (75.0%) patients had a positive ACh test and 2 (10.0%) had adverse events such as ventricular tachycardia and transient cardiogenic shock during the test. In patients with a positive ACh test, 6 of 15 (40.0%) patients had other overlapping cardiac disorders such as long QT syndrome, Brugada syndrome, cardiac sarcoidosis, myocarditis, or cardiomyopathy. Long-term prognosis was not different regardless of a positive ACh test or the presence of other cardiac disorders overlapping with VSA.

CONCLUSIONS

Three-quarters of the patients who had been resuscitated from SCA had a positive ACh test. Further examinations revealed other overlapping cardiac disorders in addition to VSA in 40% of patients with a positive ACh test.

Cardiac phenotype in ATP1A3-related syndromes: A multicenter cohort study

OBJECTIVE

To define the risks and consequences of cardiac abnormalities in ATP1A3-related syndromes.

METHODS

Patients meeting clinical diagnostic criteria for rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) with ATP1A3 genetic analysis and at least 1 cardiac assessment were included. We evaluated the cardiac phenotype in an Atp1a3 knock-in mouse (Mashl^+/-) to determine the sequence of events in seizure-related cardiac death.

RESULTS

Ninety-eight patients with AHC, 9 with RDP, and 3 with CAPOS (63 female, mean age 17 years) were included. Resting ECG abnormalities were found in 52 of 87 (60%) with AHC, 2 of 3 (67%) with CAPOS, and 6 of 9 (67%) with RDP. Serial ECGs showed dynamic changes in 10 of 18 patients with AHC. The first Holter ECG was abnormal in 24 of 65 (37%) cases with AHC and RDP with either repolarization or conduction abnormalities. Echocardiography was normal. Cardiac intervention was required in 3 of 98 (≈3%) patients with AHC. In the mouse model, resting ECGs showed intracardiac conduction delay; during induced seizures, heart block or complete sinus arrest led to death.

CONCLUSIONS

We found increased prevalence of ECG dynamic abnormalities in all ATP1A3-related syndromes, with a risk of life-threatening cardiac rhythm abnormalities equivalent to that in established cardiac channelopathies (≈3%). Sudden cardiac death due to conduction abnormality emerged as a seizure-related outcome in murine Atp1a3-related disease. ATP1A3-related syndromes are cardiac diseases and neurologic diseases. We provide guidance to identify patients potentially at higher risk of sudden cardiac death who may benefit from insertion of a pacemaker or implantable cardioverter-defibrillator.

Long QT syndrome type 1 and 2 patients respond differently to arrhythmic triggers: The TriQarr in vivo study

BACKGROUND

In patients with long QT syndrome (LQTS), swimming and loud noises have been identified as genotype-specific arrhythmic triggers in LQTS type 1 (LQTS1) and LQTS type 2 (LQTS2), respectively.

OBJECTIVE

The purpose of this study was to compare LQTS group responses to arrhythmic triggers.

METHODS

LQTS1 and LQTS2 patients were included. Before and after beta-blocker intake, electrocardiograms were recorded as participants (1) were exposed to a loud noise of ∼100 dB; and (2) had their face immersed into cold water.

RESULTS

Twenty-three patients (9 LQTS1, 14 LQTS2) participated. In response to noise, LQTS groups showed similarly increased heart rate, but LQTS2 patients had corrected QT interval (Fridericia formula) (QTcF) prolonged significantly more than LQTS1 patients (37 ± 8 ms vs 15 ± 6 ms; P = .02). After intake of beta-blocker, QTcF prolongation in LQTS2 patients was significantly blunted and similar to that of LQTS1 patients (P = .90). In response to simulated diving, LQTS groups experienced a heart rate drop of ∼28 bpm, which shortened QTcF similarly in both groups. After intake of beta-blockers, heart rate dropped to 28 ± 2 bpm in LQTS1 patients and 20 ± 3 bpm in LQTS2, resulting in a slower heart rate in LQTS1 compared with LQTS2 (P = .01). In response, QTcF shortened similarly in LQTS1 and LQTS2 patients (57 ± 9 ms vs 36 ± 7 ms; P = .10).

CONCLUSION

When exposed to noise, LQTS2 patients had QTc prolonged significantly more than did LQTS1 patients. Importantly, beta-blockers reduced noise-induced QTc prolongation in LQTS2 patients, thus demonstrating the protective effect of beta-blockers. In response to simulated diving, LQTS groups responded similarly, but a slower heart rate was observed in LQTS1 patients during simulated diving after beta-blocker intake.

Usefulness of subcutaneous implantable cardioverter-defibrillator therapy in patients with Brugada syndrome

Implantable cardioverter-defibrillators (ICDs) are the main therapy to prevent sudden cardiac death in patients with Brugada syndrome (BrS). The subcutaneous ICD (S-ICD) can eliminate lead-associated complications compared with transvenous ICD (TV-ICD). However, S-ICD is susceptible to T-wave oversensing (TWOS) and may result in more frequent inappropriate shocks in patients with BrS. This study aimed to compare inappropriate shocks between TV-ICD and S-ICD in patients with BrS. We enrolled 32 patients with BrS (including one woman; mean age 52 ± 18 years) who were implanted with ICD (23 TV-ICDs and 9 S-ICDs) between January 2002 and November 2018 in Oita University Hospital. We carried out a standard surface electrocardiogram (ECG) screening tests in both supine and standing positions prior to S-ICD implantation. The patients received routine clinical review every month and device monitoring every 4 months. The period of follow-up was 129 ± 51 months. Six patients with BrS and TV-ICDs experienced inappropriate shocks (26%) with their ICD therapy. In contrast, two patients with BrS and S-ICDs experienced inappropriate shocks (22%). There was no significant difference between the two groups (P = 0.82). Although one case in the S-ICD group experienced TWOS-induced inappropriate shock, SMART Pass (new high-pass filter) prevented the subsequent recurrence of inappropriate shocks during ICD therapy. Our results suggest that S-ICD is not inferior to TV-ICD in the incidence of inappropriate shocks. SMART Pass may be a useful tool to prevent inappropriate ICD shocks by TWOS in patients with BrS.

Lack of association between mitochondrial DNA haplogroups J and T and clinical manifestation in Russian patients with Brugada syndrome

Brugada syndrome (BrS) is an inherited disorder characterized by specific ST segment elevation in the right precordial leads, pseudo right bundle branch block, and a high risk of sudden cardiac death due to ventricular tachycardia. It was initially described as a monogenic disorder with an autosomal dominant mode of inheritance. It is hypothesized that modifying genetic factors, in addition to disease-causing mutations, may significantly contribute to the clinical symptoms and the risk of sudden cardiac death. These modifying factors can include mitochondrial DNA (mtDNA) variants. In particular, combination of mtDNA m.T4216C, m.A11251G, m.C15452A and m.T16126C variants (defining haplogroups T and J), is considered to be a factor that promotes manifestation of BrS manifestation, with no pro-arrhythmic effects. The aim of the present study was to confirm the reported association of BrS with MtDNA variants in a cohort of Russian patients. mtDNA haplogroups were genotyped in 47 Russian BrS probands and the prevalence of common mtDNA haplogroups was compared with the general population in European part of Russia. The distribution and prevalence of all but the J mtDNA haplogroups were comparable in BrS probands and the general Russian population. The mitochondrial J haplogroup was not found in the BrS cohort. In conclusion, it was shown that the mtDNA polymorphism, m.T4216C (haplogroups J and T) does not contribute significantly to the clinical manifestation of BrS in Russian patients.

Prolonged left ventricular contraction duration in apical segments as a marker of arrhythmic risk in patients with long QT syndrome

AIMS

Long QT syndrome (LQTS) is an inherited cardiac ion channelopathy predisposing to life-threatening ventricular arrhythmias and sudden cardiac death. The aim of this study was to investigate left ventricular mechanical abnormalities in LQTS patients and establish a potential role of strain as a marker of arrhythmic risk.

METHODS AND RESULTS

We included 47 patients with genetically confirmed LQTS (22 LQT1, 20 LQT2, 3 LQT3, and 2 SCN3B) and 25 healthy controls. A history of cardiac events was present in 30 LQTS subjects. Tissue Doppler and speckle tracking echocardiography were performed and contraction duration was measured by radial and longitudinal strain. The radial strain characteristic was subdivided into two planes - the basal and the apical. Left ventricular ejection fraction and global longitudinal strain were normal in LQTS patients. Mean contraction duration was longer in LQTS patients compared with controls in regard to basal radial strain (491 ± 57 vs. 437 ± 55 ms, P < 0.001), apical radial strain (450 ± 53 vs. 407 ± 53 ms, P = 0.002), and longitudinal strain (445 ± 34 vs. 423 ± 43 ms, P = 0.02). Moreover, contraction duration obtained from apical radial strain analysis was longer in symptomatic compared with asymptomatic LQTS mutation carriers (462 ± 49 vs. 429 ± 55 ms, P = 0.024), as well as in subject with mutations other than LQT1 considered to be at higher risk (468 ± 50 vs. 429 ± 49 ms, P = 0.01).

CONCLUSION

Myocardial contraction duration is prolonged for both radial and longitudinal directions in LQTS patients. Regional left ventricular function analysis may contribute to risk stratification. Apical radial deformation seems to select subjects at higher risk of arrhythmic events.

GSTM3 variant is a novel genetic modifier in Brugada syndrome, a disease with risk of sudden cardiac death

BACKGROUND

Brugada syndrome (BrS) is a rare inherited disease causing sudden cardiac death (SCD). Copy number variants (CNVs) can contribute to disease susceptibility, but their role in Brugada syndrome (BrS) is unknown. We aimed to identify a CNV associated with BrS and elucidated its clinical implications.

METHODS

We enrolled 335 unrelated BrS patients from 2000 to 2018 in the Taiwanese population. Microarray and exome sequencing were used for discovery phase whereas Sanger sequencing was used for the validation phase. HEK cells and zebrafish were used to characterize the function of the CNV variant.

FINDINGS

A copy number deletion of GSTM3 (chr1:109737011-109737301, hg38) containing the eighth exon and the transcription stop codon was observed in 23.9% of BrS patients versus 0.8% of 15,829 controls in Taiwan Biobank (P < 0.001), and 0% in gnomAD. Co-segregation analysis showed that the co-segregation rate was 20%. Patch clamp experiments showed that in an oxidative stress environment, GSTM3 down-regulation leads to a significant decrease of cardiac sodium channel current amplitude. Ventricular arrhythmia incidence was significantly greater in gstm3 knockout zebrafish at baseline and after flecainide, but was reduced after quinidine, consistent with clinical observations. BrS patients carrying the GSTM3 deletion had higher rates of sudden cardiac arrest and syncope compared to those without (OR: 3.18 (1.77-5.74), P<0.001; OR: 1.76 (1.02-3.05), P = 0.04, respectively).

INTERPRETATION

This GSTM3 deletion is frequently observed in BrS patients and is associated with reduced I_Na, pointing to this as a novel potential genetic modifier/risk predictor for the development of the electrocardiographic and arrhythmic manifestations of BrS.

FUNDING

This work was supported by the Ministry of Science and Technology (107-2314-B-002-261-MY3 to J.M.J. Juang), and by grants HL47678, HL138103 and HL152201 from the National Institutes of Health to CA.

Diagnostic yield and long-term outcome of nonischemic sudden cardiac arrest survivors and their relatives: Results from a tertiary referral center

BACKGROUND

Cardiac arrest may be the first manifestation of most inherited cardiac diseases. International guidelines recommend screening of relatives of sudden cardiac arrest (SCA) survivors if an inherited cardiac disorder is suspected.

OBJECTIVE

The purpose of this study was to assess the prevalence and spectrum of inherited cardiac diseases and the long-term outcome in a consecutive cohort of nonischemic SCA survivors (probands) and their relatives.

METHODS

This retrospective study consecutively included probands and their relatives referred to our tertiary center for family screening between 2005 and 2018. All participants underwent a systematic workup and follow-up protocol. Data were retrieved from medical records.

RESULTS

We included 155 probands (age 41.2 ± 15.5 years; 61% male) and 282 relatives (age 35.7 ± 18.8 years; 51% male). Mean follow-up was 7.1 years for probands and 4.4 years for relatives. We identified an inherited cardiac disease in 76 (49%) probands and 42 (15%) relatives. An implantable cardioverter-defibrillator was inserted in 147 (95%) probands and 9 (3%) relatives. During follow-up, 4 (3%) probands and 3 (1%) relatives died, and 37 probands and 2 relatives received appropriate shock therapy. All relatives received genetic counseling, and 18 (6%) relatives started pharmacologic treatment during follow-up.

CONCLUSION

Systematic workup of nonischemic SCA survivors and their relatives identified an inherited cardiac disease in 49% of referred probands and 15% of their relatives. The favorable long-term prognosis of diagnosed relatives probably not only reflects lower age but also the effects of early diagnosis, treatment, and follow-up. These findings support systematic workup of SCA survivors and their relatives.

The role of rare compound heterozygous events in autism spectrum disorder

The identification of genetic variants underlying autism spectrum disorders (ASDs) may contribute to a better understanding of their underlying biology. To examine the possible role of a specific type of compound heterozygosity in ASD, namely, the occurrence of a deletion together with a functional nucleotide variant on the remaining allele, we sequenced 550 genes in 149 individuals with ASD and their deletion-transmitting parents. This approach allowed us to identify additional sequence variants occurring in the remaining allele of the deletion. Our main goal was to compare the rate of sequence variants in remaining alleles of deleted regions between probands and the deletion-transmitting parents. We also examined the predicted functional effect of the identified variants using Combined Annotation-Dependent Depletion (CADD) scores. The single nucleotide variant-deletion co-occurrence was observed in 13.4% of probands, compared with 8.1% of parents. The cumulative burden of sequence variants (n = 68) in pooled proband sequences was higher than the burden in pooled sequences from the deletion-transmitting parents (n = 41, X2 = 6.69, p = 0.0097). After filtering for those variants predicted to be most deleterious, we observed 21 of such variants in probands versus 8 in their deletion-transmitting parents (X2 = 5.82, p = 0.016). Finally, cumulative CADD scores conferred by these variants were significantly higher in probands than in deletion-transmitting parents (burden test, β = 0.13; p = 1.0 × 10-5). Our findings suggest that the compound heterozygosity described in the current study may be one of several mechanisms explaining variable penetrance of CNVs with known pathogenicity for ASD.

Management of cardiac conduction abnormalities and arrhythmia in aircrew

Cardiovascular diseasesⁱ are the most common cause of loss of flying licence globally, and cardiac arrhythmia is the main disqualifier in a substantial proportion of aircrew. Aircrewⁱⁱ often operate within a demanding physiological environment, that potentially includes exposure to sustained acceleration (usually resulting in a positive gravitational force, from head to feet (+Gz)) in high performance aircraft. Aeromedical assessment is complicated further when trying to discriminate between benign and potentially significant rhythm abnormalities in aircrew, many of whom are young and fit, have a resultant high vagal tone, and among whom underlying cardiac disease has a low prevalence. In cases where a significant underlying aetiology is plausible, extensive investigation is often required and where appropriate should include review by an electrophysiologist. The decision regarding restriction of flying activity will be dependent on several factors including the underlying arrhythmia, associated pathology, risk of incapacitation and/or distraction, the type of aircraft operated, and the specific flight or mission criticality of the role performed by the individual aircrew.

Differences in Brugada Syndrome Patients Through Ventricular Repolarization Analysis During Sleep

Brugada syndrome (BS) is a genetic pathology that might cause sudden cardiac death (SCD) in patients with a structurally normal heart. Repolarization disorders have been postulated as a potential substrate for triggering cardiac arrhythmia in BS, that usually occur at rest or during sleep. In this paper, we have characterized ventricular repolarization markers during sleep on patients suffering from BS. To this end, standard 12-lead ECG recordings were analyzed in a population of 110 BS patients (25 symptomatic). The QT and the T-wave peak to T-wave end intervals (respectively QT and Tpe) were assessed from lead V5. The linear relationship between these markers and the instantaneous heart rate period (RR interval) are determined during each hour and for the whole sleep period. From the models obtained, corrected QT and Tpe measures were then estimated for each patient at 60 beats/min (QT₆₀ and Tpe₆₀) and at the mean heart rate observed during the involved time interval (QT_HR and Tpe_HR). Results show larger values for symptomatic patients in all markers, with significant differences with respect to the asymptomatic group in the case of Tpe (Tpe₆₀: p = 0.0012; Tpe_HR: p = 0.0014). Moreover, the temporal profiles of these markers reveal major differences among BS subgroups during the last 3 hours of sleep, where symptomatic patients presented increased QT_60/HR (p = 0.01) and Tpe_60/HR (p <; 0.001), as compared to the initial sleep hours. We conclude that BS patients present different repolarization properties according to their symptomatology, especially during the final stage of sleep.

Dynamic changes in ventricular depolarization during exercise in patients with Brugada syndrome

Brugada syndrome (BS) is a genetic pathological condition associated with a high risk for sudden cardiac death (SCD). Ventricular depolarization disorders have been suggested as a potential electrophysiological mechanism associated with high SCD risk on patients with BS. This paper aims to characterize the dynamic changes of ventricular depolarization observed during physical exercise in symptomatic and asymptomatic BS patients. To this end, cardiac ventricular depolarization features were automatically extracted from 12-lead ECG recordings acquired during standardized exercise stress test in 110 BS patients, of whom 25 were symptomatic. Conventional parameters were evaluated, including QRS duration, R and S wave amplitudes (AR, AS), as well as QRS morphological features, such as up-stroke and down-stroke slopes of the R and S waves (UR, DR and US). The effects of physical exercise and recovery on the dynamics of these markers were assessed in both BS populations. Features showing significantly different dynamics between the studied groups were used alone and in combination with the clinical characteristics of the patients in a logistic regression analysis. Results show larger changes in the second half of the QRS complex through AS and US measured in the right precordial leads for asymptomatic patients, especially during recovery, when the vagal tone is more pronounced. Multivariate analysis involving both types of features resulted in a reduced model of three relevant features (ΔAS in lead V2, Sex and heart rate recovery, HRR), which achieved a suitable discrimination performance between groups; sensitivity = 80% and specificity = 75% (AUC = 83%). However, after controlling the model for possible confounding factors, only one feature (ΔAS) remained meaningful. This adjusted model significantly improved the overall discrimination performance by up to: sensitivity = 84% and specificity = 100% (AUC = 94%). The study highlights the importance of physical exercise test to unmask differentiated behaviors between symptomatic and asymptomatic BS patients through depolarization dynamic analysis. This analysis together with the obtained model may help to identify asymptomatic patients at low or high risk of future cardiac events, but it should be confirmed by further prospective studies.

Mothers with long QT syndrome are at increased risk for fetal death: findings from a multicenter international study

BACKGROUND

Most fetal deaths are unexplained. Long QT syndrome is a genetic disorder of cardiac ion channels. Affected individuals, including fetuses, are predisposed to sudden death. We sought to determine the risk of fetal death in familial long QT syndrome, in which the mother or father carries the long QT syndrome genotype. In addition, we assessed whether risk differed if the long QT syndrome genotype was inherited from the mother or father.

OBJECTIVE

This was a retrospective review of pregnancies in families with the 3 most common heterozygous pathogenic long QT syndrome genotypes in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3), which occur in approximately 1 in 2000 individuals. The purpose of our study was to compare pregnancy and birth outcomes in familial long QT syndrome with the normal population and between maternal and paternal carriers of the long QT syndrome genotype. We hypothesized that fetal death before (miscarriage) and after (stillbirths) 20 weeks gestation would be increased in familial long QT syndrome compared with the normal population and that the parent of origin would not affect birth outcomes.

STUDY DESIGN

Our study was a multicenter observational case series of 148 pregnancies from 103 families (80 mothers, 23 fathers) with familial long QT syndrome (60 with LQT1, 29 with LQT2, 14 with LQT3) who were recruited from 11 international centers with expertise in hereditary heart rhythm diseases, pediatric and/or adult electrophysiology, and high-risk pregnancies. Clinical databases from these sites were reviewed for long QT syndrome that occurred in men or women of childbearing age (18-40 years). Pregnancy outcomes (livebirth, stillbirth, and miscarriage), birthweights, and gestational age at delivery were compared among long QT syndrome genotypes and between maternal vs paternal long QT syndrome-affected status with the use of logistic regression analysis.

RESULTS

Most offspring (80%; 118/148) were liveborn at term; 66% of offspring (73/110) had long QT syndrome. Newborn infants of mothers with long QT syndrome were delivered earlier and, when the data were controlled for gestational age, weighed less than newborn infants of long QT syndrome fathers. Fetal arrhythmias were observed rarely, but stillbirths (fetal death at >20 weeks gestation) were 8 times more frequent in long QT syndrome (4% vs approximately 0.5%); miscarriages (fetal death at ≤20 weeks gestation) were 2 times that of the general population (16% vs 8%). The likelihood of fetal death was significantly greater with maternal vs paternal long QT syndrome (24.4% vs 3.4%; P=.036). Only 10% of all fetal deaths underwent postmortem long QT syndrome testing; 2 of 3 cases were positive for the family long QT syndrome genotype.

CONCLUSION

This is the first report to demonstrate that mothers with long QT syndrome are at increased risk of fetal death and to uncover a previously unreported cause of stillbirth. Our results suggest that maternal effects of long QT syndrome channelopathy may cause placental or myometrial dysfunction that confers increased susceptibility to fetal death and growth restriction in newborn survivors, regardless of long QT syndrome status.

Critical assessment of secondary findings in genes linked to primary arrhythmia syndromes

As comprehensive sequencing technologies gain widespread use, questions about so-called secondary findings (SF) require urgent consideration. The American College of Medical Genetics and Genomics has recommended to report SF in 59 genes (ACMG SF v2.0) including four actionable genes associated with inherited primary arrhythmia syndromes (IPAS) such as catecholaminergic polymorphic ventricular tachycardia, long QT syndrome, and Brugada syndrome. Databases provide conflicting results for the purpose of identifying pathogenic variants in SF associated with IPAS at a level of sufficient evidence for clinical return. As IPAS account for a significant proportion of sudden cardiac deaths (SCD) in young and apparently healthy individuals, variant interpretation has a great impact on diagnosis and prevention of disease. Of 6381 individuals, 0.4% carry pathogenic variants in one of the four actionable genes related to IPAS: RYR2, KCNQ1, KCNH2, and SCN5A. Comparison of the databases ClinVar, Leiden Open-source Variant Database, and Human Gene Mutation Database showed impactful differences (0.2% to 1.3%) in variant interpretation improvable by expert-curation depending on database and classification system used. These data further highlight the need for international consensus regarding the variant interpretation, and subsequently management of SF in particular with regard to treatable arrhythmic disorders with increased risk of SCD.

[Brugada syndrome : Risk stratification and prevention of sudden cardiac death]

Brugada syndrome is ion channelopathy defined by coved type ST-elevation in at least one right precordial ECG lead. Patients may suffer from ventricular tachycardia/fibrillation, which may cause syncope or sudden cardiac death. The majority of patients are likely to remain asymptomatic throughout life. A correct ECG diagnosis remains challenging. The implantable cardioverter/defibrillator (ICD) is the only established therapy to protect against sudden cardiac death. Thus, individual risk stratification is of major clinical relevance in primary prevention. The present article gives an update on current risk stratification and novel therapeutic options apart from ICD therapy.

Brugada syndrome: A comprehensive review of pathophysiological mechanisms and risk stratification strategies

Brugada syndrome (BrS) is an inherited ion channel channelopathy predisposing to ventricular arrhythmias and sudden cardiac death. Originally believed to be predominantly associated with mutations in SCN5A encoding for the cardiac sodium channel, mutations of 18 genes other than SCN5A have been implicated in the pathogenesis of BrS to date. Diagnosis is based on the presence of a spontaneous or drug-induced coved-type ST segment elevation. The predominant electrophysiological mechanism underlying BrS remains disputed, commonly revolving around the three main hypotheses based on abnormal repolarization, depolarization or current-load match. Evidence from computational modelling, pre-clinical and clinical studies illustrates that molecular abnormalities found in BrS lead to alterations in excitation wavelength (λ), which ultimately elevates arrhythmic risk. A major challenge for clinicians in managing this condition is the difficulty in predicting the subset of patients who will suffer from life-threatening ventricular arrhythmic events. Several repolarization risk markers have been used thus far, but these neglect the contributions of conduction abnormalities in the form of slowing and dispersion. Indices incorporating both repolarization and conduction based on the concept of λ have recently been proposed. These may have better predictive values than the existing markers. Current treatment options include pharmacological therapy to reduce the occurrence of arrhythmic events or to abort these episodes, and interventions such as implantable cardioverter-defibrillator insertion or radiofrequency ablation of abnormal arrhythmic substrate.

Current Controversies and Challenges in Brugada Syndrome

More than three decades since its initial description in 1993, Brugada syndrome remains engulfed in controversy. This review aims to shed light on the main challenges surrounding the diagnostic pathway and criteria, risk stratification of asymptomatic patients, pharmacological and interventional risk modification strategies as well as our current pathophysiological understanding of the disease.

Prediction and Prevention of Sudden Death in the Brugada Syndrome

Sudden cardiac death (SCD) secondary to sudden cardiac arrest (SCA) is a leading cause of death in the United States, claiming over a quarter million lives annually, and is directly responsible for 50% of all cardiovascular mortality. Brugada Syndrome (BrS) is an arrhythmogenic cardiovascular channelopathy that predisposes asymptomatic patients who have no identified disease to a high-risk of SCD/SCA as their first cardiac event/disease manifestation. Limited progress has been made in risk prediction of SCA and SCD, with the greatest challenge being the ability to identify the small high-risk subgroups concealed within the larger general population. In conclusion, accurate identification of high-risk asymptomatic BrS patients (through multiparametric risk scores composed of reliable and validated unambiguous clinical variables and biomarkers) may hold utility in improving current SCD prediction algorithms, and the appropriate primary prevention therapy may prove valuable in reducing risk of sudden death for this patient population. This systematic review aims to comprehensively summarize qualitative evidence that explore proposed clinical, electrocardiographic, electrophysiological, and genetic markers for risk stratification of patients with BrS phenotype, and to discuss the best available contemporary evidence regarding therapeutic approach.

The Use of Succinylcholine in Brugada Syndrome: A Case Report and Discussion of Literature

We describe a patient with a major depression and a newly discovered Brugada syndrome, who was successfully treated with 35 electroconvulsive therapy sessions using succinylcholine as muscle relaxant. We discuss the use of succinylcholine in patients with Brugada syndrome.

Ventricular conduction delay as marker of risk in Brugada Syndrome. Results from the analysis of clinical and electrocardiographic features of a large cohort of patients

BACKGROUND

Brugada Syndrome is a genetic arrhythmogenic disease with a variable clinical spectrum. The role of clinical and ECG parameters in the risk stratification is still uncertain.

AIMS

In a large cohort of Brugada patients we analysed clinical and ECG features to determine the variables with prognostic value for the occurrence of a first documented arrhythmic event and for recurrences.

METHODS

We enrolled 614 patients, subdivided into 3 groups according to their clinical presentation: 531 (88%) asymptomatic, 69 (10%) with previous unexplained syncope and 14 (2%) with aborted sudden death. We also compared the ECG characteristics of patients with a single documented arrhythmic event (either at presentation or at follow-up, 17 patients), with those of patients with arrhythmic recurrences (13 patients).

RESULTS

The event rate was 1.3% in the asymptomatic patients and 15% among patients with unexplained syncope (median follow-up 6 years), p < 0.0001. In both groups a QRS duration ≥110 ms in lead II and/or V6 and/or S wave duration ≥40 ms in lead I and/or II were significant risk factors for the occurrence and timing of events at follow-up. The same ECG risk factors were also significantly associated with arrhythmic recurrences.

CONCLUSIONS

The arrhythmic risk of Brugada patients is related not only to the symptoms at presentation, but also to the presence of a ventricular conduction delay (QRS duration ≥ 110 ms and/or S wave duration ≥ 40 ms). The ECG conduction parameters also affect the timing of events and recurrences.

Genetic variants of alcohol-metabolizing enzymes in Brugada syndrome: Insights into syncope after drinking alcohol

BACKGROUND

Patients with Brugada syndrome (BrS) are known to have arrhythmic events after alcohol drinking and are recommended to avoid its excessive intake. Mechanisms underlying the alcohol-induced cardiac events are however unknown. This study aimed to test the hypothesis whether activity of alcohol-metabolizing enzymes determines fatal arrhythmic events after drinking alcohol.

METHODS

A total of 198 Japanese patients with BrS were enrolled in this study. These patients were classified into symptomatic (n = 90) and asymptomatic (n = 108) groups. The former was divided into an alcohol-related group (syncope after alcohol drinking, n = 16) and an alcohol-unrelated group (n = 74). Polymerase chain reaction was performed to determine genetic variants of genes encoding alcohol dehydrogenase 1B (ADH1B) and aldehyde dehydrogenase 2 (ALDH2).

RESULTS

The genotype distribution for ALDH2 was not significantly different between symptomatic and asymptomatic groups and between alcohol-related and alcohol-unrelated groups. The genotype distribution for ADH1B was not significantly different between symptomatic and asymptomatic groups, but the genotype ADH1B His/His was significantly more prevalent in the alcohol-related group than in the alcohol-unrelated group (81.3% vs 50%, P = .023). In multivariate logistic regression analysis, the genotype of ADH1B His/His was independently associated with syncope after alcohol drinking (odds ratio, 5.746; 95% confidence interval, 1.580-28.421; P = .007).

CONCLUSIONS

Arrhythmic events after alcohol drinking was associated with enhanced activity of alcohol-metabolizing enzyme ADH1B in our cohort of BrS. Therefore, the lifestyle change to avoid the excessive alcohol intake deserves attention.

Post mortem genetic test, the clinical diagnosis is not fade with the death of the patient

In up to one-third of cases of sudden death, the medico-legal autopsy finding is inconclusive, and the option to perform a molecular autopsy is covered in international guidelines. The importance of postmortem genetic testing lies in its ability to identify hereditary diseases, often those with an autosomal dominant transmission pattern, and, through consultations and screening of relatives, to identify family members with a pathogenic mutation, who are often asymptomatic, providing an opportunity to change the course of their lives. The authors present three clinical cases that highlight the importance of postmortem genetic studies and family studies, as well as the integration of the data obtained in a cardiology consultation, which may be for arrhythmology, coronary disease or cardiomyopathy, depending on the specific condition. This could modify the course of the disease in many relatives.

Ventricular conduction stability test: a method to identify and quantify changes in whole heart activation patterns during physiological stress

AIMS

Abnormal rate adaptation of the action potential is proarrhythmic but is difficult to measure with current electro-anatomical mapping techniques. We developed a method to rapidly quantify spatial discordance in whole heart activation in response to rate cycle length changes. We test the hypothesis that patients with underlying channelopathies or history of aborted sudden cardiac death (SCD) have a reduced capacity to maintain uniform activation following exercise.

METHODS AND RESULTS

Electrocardiographical imaging (ECGI) reconstructs >1200 electrograms (EGMs) over the ventricles from a single beat, providing epicardial whole heart activation maps. Thirty-one individuals [11 SCD survivors; 10 Brugada syndrome (BrS) without SCD; and 10 controls] with structurally normal hearts underwent ECGI vest recordings following exercise treadmill. For each patient, we calculated the relative change in EGM local activation times (LATs) between a baseline and post-exertion phase using custom written software. A ventricular conduction stability (V-CoS) score calculated to indicate the percentage of ventricle that showed no significant change in relative LAT (<10 ms). A lower score reflected greater conduction heterogeneity. Mean variability (standard deviation) of V-CoS score over 10 consecutive beats was small (0.9 ± 0.5%), with good inter-operator reproducibility of V-CoS scores. Sudden cardiac death survivors, compared to BrS and controls, had the lowest V-CoS scores post-exertion (P = 0.011) but were no different at baseline (P = 0.50).

CONCLUSION

We present a method to rapidly quantify changes in global activation which provides a measure of conduction heterogeneity and proof of concept by demonstrating SCD survivors have a reduced capacity to maintain uniform activation following exercise.

Association between PR Interval, First-degree atrioventricular block and major arrhythmic events in patients with Brugada syndrome - Systematic review and meta-analysis

BACKGROUND

Risk stratification in patients with asymptomatic Brugada Syndrome is challenging, and despite recent advances, there is no clear evidence. The first-degree atrioventricular block was hypothesized to be a predictor of arrhythmic events. Measurement of the PR interval and diagnosing atrioventricular block from surface ECG is easy, noninvasive, and cost-effective. We aimed to assess the latest evidence on PR interval or first-degree atrioventricular block and major arrhythmic events related to Brugada Syndrome.

METHODS

We performed a comprehensive search in PubMed for "atrioventricular block" OR "PR interval" and "Brugada syndrome." We included studies that have a component of PR interval and/or first-degree atrioventricular block and major arrhythmic events related to Brugada Syndrome including syncope/VT/VF/appropriate ICD shocks/ICD implantation.

RESULTS

We included 1526 subjects from 7 studies. Pooled mean difference of PR interval in 4 studies showed a significant difference [MD 10.77 ms (2.97-18.57) P = 0.007, moderate-high heterogeneity I2 = 53% P = 0.08]. On sensitivity analysis by removing a study, it became MD 6.50 ms [1.97-11.03], P = 0.005, heterogeneity I2 = 0% P = 0.52. Indicating that PR interval was prolonged by small margin. Pooled analysis of the association between a first-degree atrioventricular block and major arrhythmic events was significant [OR 3.33 (2.02-5.50) P < 0.001, low heterogeneity I2 = 0% P = 0.57].

CONCLUSION

First-degree AV block is associated with more frequent major arrhythmic events in Brugada syndrome patients. PR interval seemed to be prolonged but is yet to be determined whether the PR interval association is still significant if it did not cross the first-degree AVB threshold.

The Diagnostic Yield of Brugada Syndrome After Sudden Death With Normal Autopsy

BACKGROUND

Familial evaluation after a sudden death with negative autopsy (sudden arrhythmic death syndrome; SADS) may identify relatives at risk of fatal arrhythmias.

OBJECTIVES

This study aimed to assess the impact of systematic ajmaline provocation testing using high right precordial leads (RPLs) on the diagnostic yield of Brugada syndrome (BrS) in a large cohort of SADS families.

METHODS

Three hundred three SADS families (911 relatives) underwent evaluation with resting electrocardiogram using conventional and high RPLs, echocardiography, exercise, and 24-h electrocardiogram monitor. An ajmaline test with conventional and high RPLs was undertaken in 670 (74%) relatives without a familial diagnosis after initial evaluation. Further investigations were guided by clinical suspicion.

RESULTS

An inherited cardiac disease was diagnosed in 128 (42%) families and 201 (22%) relatives. BrS was the most prevalent diagnosis (n = 85, 28% of families; n = 140, 15% of relatives). Ajmaline testing was required to unmask the BrS in 97% of diagnosed individuals. The use of high RPLs showed a 16% incremental diagnostic yield of ajmaline testing by diagnosing BrS in an additional 49 families. There were no differences of the characteristics between individuals and families with a diagnostic pattern in the conventional and the high RPLs. On follow-up, a spontaneous type 1 Brugada pattern and/or clinically significant arrhythmic events developed in 17% (n = 25) of the concealed BrS cohort.

CONCLUSIONS

Systematic use of ajmaline testing with high RPLs increases substantially the yield of BrS in SADS families. Assessment should be performed in expert centers where patients are counseled appropriately for the potential implications of provocation testing.

The Taiwan Heart Registries: Its Influence on Cardiovascular Patient Care

Taiwanese heart registries for the main cardiovascular diseases have been conducted in the past 10 years, with the goal of examining the quality of cardiovascular patient care, which cannot be guaranteed by the universal Taiwan National Health Insurance. The results show suboptimal adherence to guideline recommendations. Door-to-balloon time and dual antiplatelet therapy use in acute coronary syndrome, standard medications for management of heart failure, low-density lipoprotein cholesterol levels in dyslipidemia, anticoagulant agent use in atrial fibrillation, and the understanding of sudden arrhythmia death syndrome were all found to be inadequate. However, all were improved, either by changing National Health Insurance policy or through continuous education for physicians and patients. Thus, specific cardiovascular disease registries could help examine the status of real-world practice, find inadequacies in guideline implementation and understanding of rare diseases, facilitate lobbying to policy makers and education for physicians and patients, and influence and improve cardiovascular patient care.

Next-generation sequencing using microfluidic PCR enrichment for molecular autopsy

Background

We aimed to determine the mutation yield and clinical applicability of “molecular autopsy” following sudden arrhythmic death syndrome (SADS) by validating and utilizing low-cost high-throughput technologies: Fluidigm Access Array PCR-enrichment with Illumina HiSeq 2000 next generation sequencing (NGS).

Methods

We validated and optimized the NGS platform with a subset of 46 patients by comparison with Sanger sequencing of coding exons of major arrhythmia risk-genes (KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, RYR2). A combined large multi-ethnic international SADS cohort was sequenced utilizing the NGS platform to determine overall molecular yield; rare variants identified by NGS were subsequently reconfirmed by Sanger sequencing.

Results

The NGS platform demonstrated 100% sensitivity for pathogenic variants as well as 87.20% sensitivity and 99.99% specificity for all substitutions (optimization subset, n = 46). The positive predictive value (PPV) for NGS for rare substitutions was 16.0% (27 confirmed rare variants of 169 positive NGS calls in 151 additional cases). The overall molecular yield in 197 multi-ethnic SADS cases (mean age 22.6 ± 14.4 years, 68% male) was 5.1% (95% confidence interval 2.0–8.1%), representing 10 cases carrying pathogenic or likely pathogenic risk-mutations.

Conclusions

Molecular autopsy with Fluidigm Access Array and Illumina HiSeq NGS utilizing a selected panel of LQTS/BrS and CPVT risk-genes offers moderate diagnostic yield, albeit requiring confirmatory Sanger-sequencing of mutational variants.

Electronic supplementary material

The online version of this article (10.1186/s12872-019-1154-8) contains supplementary material, which is available to authorized users.

Herausforderung der Varianteninterpretation am Beispiel des Long-QT-Syndroms (LQTS)

Die „Next-generation Sequencing (NGS)“-Technologie ermöglicht es, alle bekannten LQTS-Gene in der Diagnostik parallel zu analysieren. Dies führt dazu, dass in zunehmendem Maße Varianten nachgewiesen werden, deren klinische Bedeutung unklar ist. Erschwerend macht sich hierbei bemerkbar, dass abgesehen von den drei gut beschriebenen Hauptgenen KCNQ1, KCNH2 und SCN5A, deren Varianten für ca. 70 % der Erkrankungsfälle verantwortlich sind, die Evidenz für eine ursächliche Beteiligung einiger „Nebengene“ nur mäßig oder umstritten ist. Um eine Flut unklarer Befunde zu vermeiden und die Notwendigkeit ausgedehnter familiärer Segregationsstudien zu begrenzen sowie Fehlinterpretationen vorzubeugen, sind eine fundierte Auswahl der zu analysierenden Gene sowie ein transparentes und allgemein anerkanntes System der Variantenklassifikation essenziell. Die ACMG-Richtlinien sind der derzeitige Konsens zur Klassifikation von Varianten. Allerdings zeigen sich bei der Anwendung Limitationen, sodass diese Richtlinien nur eine Basis darstellen, die durch differenziertere Systeme verbessert werden kann.

Bei den Bestrebungen nach einer personalisierten Medizin werden große Hoffnungen auf Genotyp-Phänotyp-Zusammenhänge gesetzt. In LQTS-Proteinen wurden einige funktionell relevante Regionen wie die Poren der Kalium- und Natriumkanäle, in denen Varianten tendenziell schwerwiegende Phänotypen hervorrufen, beschrieben. Darüber hinaus zeigen dominant-negative Varianten in der Regel stärkere Effekte als „loss-of-function“ (LoF)-Varianten. Dennoch ist eine differenzielle Therapie nur eingeschränkt möglich. Während Patienten mit Kaliumkanaldefekten mit β‑Blockern behandelt werden, profitieren Patienten mit „gain-of-function“ (GoF)-Varianten in SCN5A von Natriumkanalblockern.