Investigation on Sudden Unexpected Death in the Young (SUDY) in Europe: results of the European Heart Rhythm Association Survey.

The aims of this centre-based survey, promoted and disseminated by the European Heart Rhythm Association (EHRA) was to investigate the current practice for the investigation of Sudden Unexplained Death in the Young (SUDY) amongst European countries. An online questionnaire composed of 21 questions was submitted to the EHRA Research Network, European Cardiac Arrhythmia Genetics (ECGen) Focus Group members, and European Reference Network GUARD-Heart healthcare partners. There were 81 respondents from 24 European countries. The majority (78%) worked in a dedicated clinic focusing on families with inherited cardiac conditions and/or SUDY or had easy access to a nearby one. On average, an autopsy was performed in 43% of SUDY cases. Macroscopic examination of the body and all organs were completed in 71% of cases undergoing autopsy, and expert cardiac examination in 32%. Post-mortem genetic testing was requested on average in 37% of Sudden Arrhythmic Death Syndrome (SADS) cases, but not at all by 20% of survey respondents. Psychological support and bereavement counselling for SADS/SUDY families were available for ≤50% of participants. Whilst electrocardiogram (ECG) and echocardiography were largely employed to investigate SADS relatives, there was an inconsistent approach to the use of provocative testing with exercise ECG, sodium channel blocking drugs, and/or epinephrine and genetic testing. The survey highlighted a significant heterogeneity of service provision and variable adherence to current recommendations for the investigation of SUDY, partly attributable to the availability of dedicated units and specialist tests, genetic evaluation, and post-mortem examination.

Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome.

BACKGROUND: Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility. METHODS: We conducted genome-wide association studies followed by transethnic meta-analysis in 1656 unrelated patients with LQTS of European or Japanese ancestry and 9890 controls to identify susceptibility single nucleotide polymorphisms. We estimated the common variant heritability of LQTS and tested the genetic correlation between LQTS susceptibility and other cardiac traits. Furthermore, we tested the aggregate effect of the 68 single nucleotide polymorphisms previously associated with the QT-interval in the general population using a polygenic risk score. RESULTS: Genome-wide association analysis identified 3 loci associated with LQTS at genome-wide statistical significance (P<5×10-8) near NOS1AP, KCNQ1, and KLF12, and 1 missense variant in KCNE1(p.Asp85Asn) at the suggestive threshold (P<10-6). Heritability analyses showed that ≈15% of variance in overall LQTS susceptibility was attributable to common genetic variation (h2SNP 0.148; standard error 0.019). LQTS susceptibility showed a strong genome-wide genetic correlation with the QT-interval in the general population (rg=0.40; P=3.2×10-3). The polygenic risk score comprising common variants previously associated with the QT-interval in the general population was greater in LQTS cases compared with controls (P<10-13), and it is notable that, among patients with LQTS, this polygenic risk score was greater in patients who were genotype negative compared with those who were genotype positive (P<0.005). CONCLUSIONS: This work establishes an important role for common genetic variation in susceptibility to LQTS. We demonstrate overlap between genetic control of the QT-interval in the general population and genetic factors contributing to LQTS susceptibility. Using polygenic risk score analyses aggregating common genetic variants that modulate the QT-interval in the general population, we provide evidence for a polygenic architecture in genotype negative LQTS.

Determination and Interpretation of the QT Interval.

BACKGROUND: Long QT syndrome (LQTS) is associated with potentially fatal arrhythmias. Treatment is very effective, but its diagnosis may be challenging. Importantly, different methods are used to assess the QT interval, which makes its recognition difficult. QT experts advocate manual measurements with the tangent or threshold method. However, differences between these methods and their performance in LQTS diagnosis have not been established. We aimed to assess similarities and differences between these 2 methods for QT interval analysis to aid in accurate QT assessment for LQTS. METHODS: Patients with a confirmed pathogenic variant in KCNQ1(LQT1), KCNH2(LQT2), or SCN5A(LQT3) genes and their family members were included. Genotype-positive patients were identified as LQTS cases and genotype-negative family members as controls. ECGs were analyzed with both methods, providing inter- and intrareader validity and diagnostic accuracy. Cutoff values based on control population's 95th and 99th percentiles, and LQTS-patients' 1st and 5th percentiles were established based on the method to correct for heart rate, age, and sex. RESULTS: We included 1484 individuals from 265 families, aged 33±21 years and 55% females. In the total cohort, QTTangent was 10.4 ms shorter compared with QTThreshold (95% limits of agreement±20.5 ms, P<0.0001). For all genotypes, QTTangent was shorter than QTThreshold ( P<0.0001), but this was less pronounced in LQT2. Both methods yielded a high inter- and intrareader validity (intraclass correlation coefficient >0.96), and a high diagnostic accuracy (area under the curve >0.84). Using the current guideline cutoff (QTc interval 480 ms), both methods had similar specificity but yielded a different sensitivity. QTc interval cutoff values of QTTangent were lower compared with QTThreshold and different depending on the correction for heart rate, age, and sex. CONCLUSION: The QT interval varies depending on the method used for its assessment, yet both methods have a high validity and can both be used in diagnosing LQTS. However, for diagnostic purposes current guideline cutoff values yield different results for these 2 methods and could result in inappropriate reassurance or treatment. Adjusted cutoff values are therefore specified for method, correction formula, age, and sex. In addition, a freely accessible online probability calculator for LQTS ( www.QTcalculator.org ) has been made available as an aid in the interpretation of the QT interval.

Incidence and predictors of implantable cardioverter-defibrillator therapy and its complications in idiopathic ventricular fibrillation patients.

AIMS: Idiopathic ventricular fibrillation (IVF) is a rare cause of sudden cardiac arrest. Implantable cardioverter-defibrillator (ICD) implantation is currently the only treatment option. Limited data are available on the prevalence and complications of ICD therapy in these patients. We sought to investigate ICD therapy and its complications in patients with IVF. METHODS AND RESULTS: Patients were selected from a national registry of IVF patients. Patients in whom no underlying diagnosis was found during follow-up were eligible for inclusion. Recurrence of ventricular arrhythmia (VA) was derived from medical and ICD records, electrogram records of ICD therapies were used to differentiate between appropriate or inappropriate interventions. Independent predictors for appropriate ICD shock were calculated using cox regression. In 217 IVF patients, recurrence of sustained VAs occurred in 66 patients (30%) during a median follow-up period of 6.1 years. Ten patients died (4.6%). Thirty-eight patients (17.5%) experienced inappropriate ICD therapy, and 32 patients (14.7%) had device-related complications. Symptoms before cardiac arrest [hazard ratio (HR): 2.51, 95% confidence interval (CI): 1.48-4.24], signs of conduction disease (HR: 2.27, 95% CI: 1.15-4.47), and carrier of the DPP6 risk haplotype (HR: 3.24, 1.70-6.17) were identified as independent predictors of appropriate shock occurrence. CONCLUSION: Implantable cardioverter-defibrillator therapy is an effective treatment in IVF, treating recurrences of potentially lethal VAs in approximately one-third of patients during long-term follow-up. However, device-related complications and inappropriate shocks were also frequent. We found significant predictors for appropriate ICD therapy. This may imply that these patients require additional management to prevent recurrent events.

Clinical Aspects of Type 3 Long-QT Syndrome: An International Multicenter Study.

BACKGROUND: Risk stratification in patients with type 3 long-QT syndrome (LQT3) by clinical and genetic characteristics and effectiveness of ß-blocker therapy has not been studied previously in a large LQT3 population. METHODS: The study population included 406 LQT3 patients with 51 sodium channel mutations; 391 patients were known to be event free during the first year of life and were the focus of our study. Clinical, electrocardiographic, and genetic parameters were acquired for patients from 7 participating LQT3 registries. Cox regression analysis was used to evaluate the independent contribution of clinical, genetic, and therapeutic factors to the first occurrence of time-dependent cardiac events (CEs) from age 1 to 41 years. RESULTS: Of the 391 patients, 118 (41 males, 77 females) patients (30%) experienced at least 1 CE (syncope, aborted cardiac arrest, or long-QT syndrome-related sudden death), and 24 (20%) suffered from LQT3-related aborted cardiac arrest/sudden death. The risk of a first CE was directly related to the degree of QTc prolongation. Cox regression analysis revealed that time-dependent ß-blocker therapy was associated with an 83% reduction in CEs in females (P=0.015) but not in males (who had many fewer events), with a significant sex × ß-blocker interaction (P=0.04). Each 10-ms increase in QTc duration up to 500 ms was associated with a 19% increase in CEs. Prior syncope doubled the risk for life-threatening events (P<0.02). CONCLUSIONS: Prolonged QTc and syncope predispose patients with LQT3 to life-threatening CEs. However, ß-blocker therapy reduces this risk in females; efficacy in males could not be determined conclusively because of the low number of events.

Yield of molecular and clinical testing for arrhythmia syndromes: report of 15 years' experience.

BACKGROUND: Sudden cardiac death is often caused by inherited arrhythmia syndromes, particularly if it occurs at a young age. In 1996, we started a cardiogenetics clinic aimed at diagnosing such syndromes and providing timely (often presymptomatic) treatment to families in which such syndromes or sudden cardiac death existed. We studied the yield of DNA testing for these syndromes using a candidate-gene approach over our 15 years of experience. METHODS AND RESULTS: We analyzed the yield of DNA testing. In subanalyses, we studied differences in the yield of DNA testing over time, between probands with isolated or familial cases and between probands with or without clear disease-specific clinical characteristics. In cases of sudden unexplained death (antemortem or postmortem analysis of the deceased not performed or providing no diagnosis), we analyzed the yield of cardiological investigations. Among 7021 individuals who were counseled, 6944 from 2298 different families (aged 41 ± 19 years; 49% male) were analyzed. In 702 families (31%), a possible disease-causing mutation was detected. Most mutations were found in families with long-QT syndrome (47%) or hypertrophic cardiomyopathy (46%). Cascade screening revealed 1539 mutation-positive subjects. The mutation detection rate decreased over time, in part because probands with a less severe phenotype were studied, and was significantly higher in familial than in isolated cases. We counseled 372 families after sudden unexplained death; in 29% of them (n=108), an inherited arrhythmia syndrome was diagnosed. CONCLUSIONS: The proportion of disease-causing mutations found decreased over time, in part because probands with a less severe phenotype were studied. Systematic screening of families identified many (often presymptomatic) mutation-positive subjects.

Targeted sequence capture and GS-FLX Titanium sequencing of 23 hypertrophic and dilated cardiomyopathy genes: implementation into diagnostics.

BACKGROUND: Genetic evaluation of cardiomyopathies poses a challenge. Multiple genes are involved but no clear genotype-phenotype correlations have been found so far. In the past, genetic evaluation for hypertrophic (HCM) and dilated (DCM) cardiomyopathies was performed by sequential screening of a very limited number of genes. Recent developments in sequencing have increased the throughput, enabling simultaneous screening of multiple genes for multiple patients in a single sequencing run. OBJECTIVE: Development and implementation of a next generation sequencing (NGS) based genetic test as replacement for Sanger sequencing. METHODS AND RESULTS: In order to increase the number of genes that can be screened in a shorter time period, we enriched all exons of 23 of the most relevant HCM and DCM related genes using on-array multiplexed sequence capture followed by massively parallel pyrosequencing on the GS-FLX Titanium. After optimisation of array based sequence capture it was feasible to reliably detect a large panel of known and unknown variants in HCM and DCM patients, whereby the unknown variants could be confirmed by Sanger sequencing. CONCLUSIONS: The rate of detection of (pathogenic) variants in both HCM and DCM patients was increased due to a larger number of genes studied. Array based target enrichment followed by NGS showed the same accuracy as Sanger sequencing. Therefore, NGS is ready for implementation in a diagnostic setting.

Are disease-specific patient-reported outcomes measures (PROMs) used in cardiogenetics? A systematic review.

Patient-reported outcome measures (PROMs) are used to facilitate patient-centered care (PCC). While studies in patients with cardiac conditions have revealed poorer health-related quality of life (HRQoL) and elevated emotional stress, studies in inherited cardiac conditions (ICC) seem rare. A systematic review evaluated which (specific domains of) PROMs are used in patients with ICC. From three databases (PubMed, PsychINFO, and Web of Science) quantitative studies investigating PROMs in patients with ICC were included. A Cochrane-based assessment tool was used to evaluate quality and potential risk of bias per subdomain. Data from 17 eligible articles were extracted. Among the included studies, risk of bias was predominantly high (35%) or unclear (30%). Most (n = 14) studies used a generic health status measure (SF-36, SF-12); 3 studies used a disease-specific PROM (KCCQ- cardiomyopathy and MLFHQ-heart failure). In addition to HRQoL measures, several studies used affective psychological measures (i.e., HADS, CAQ-18, IES-R, and IPQ). The mental health component of the PROMs showed lower scores overall in patients with ICC compared to population norms. Nine studies using HADS and GAD-7/PHQ-9 showed a prevalence of clinically significant anxiety (17-47%) and depression levels (8.3-28%) that were higher than the population norm (8.3% and 6.3%, respectively). HRQoL in patients with ICC is primarily assessed with generic PROMs. Results further confirmed high psychological morbidity in this population. Generic PROMS measures evaluate overall health status, but lack sensitivity to ICC-specific factors like heredity-related concerns. We propose developing a PROM specific for ICC to optimize PCC.

Mutations in cytoplasmic loops of the KCNQ1 channel and the risk of life-threatening events: implications for mutation-specific response to ß-blocker therapy in type 1 long-QT syndrome.

BACKGROUND: ß-Adrenergic stimulation is the main trigger for cardiac events in type 1 long-QT syndrome (LQT1). We evaluated a possible association between ion channel response to ß-adrenergic stimulation and clinical response to ß-blocker therapy according to mutation location. METHODS AND RESULTS: The study sample comprised 860 patients with genetically confirmed mutations in the KCNQ1 channel. Patients were categorized into carriers of missense mutations located in the cytoplasmic loops (C loops), membrane-spanning domain, C/N terminus, and nonmissense mutations. There were 27 aborted cardiac arrest and 78 sudden cardiac death events from birth through 40 years of age. After multivariable adjustment for clinical factors, the presence of C-loop mutations was associated with the highest risk for aborted cardiac arrest or sudden cardiac death (hazard ratio versus nonmissense mutations=2.75; 95% confidence interval, 1.29-5.86; P=0.009). ß-Blocker therapy was associated with a significantly greater reduction in the risk of aborted cardiac arrest or sudden cardiac death among patients with C-loop mutations than among all other patients (hazard ratio=0.12; 95% confidence interval, 0.02-0.73; P=0.02; and hazard ratio=0.82; 95% confidence interval, 0.31-2.13; P=0.68, respectively; P for interaction=0.04). Cellular expression studies showed that membrane spanning and C-loop mutations produced a similar decrease in current, but only C-loop mutations showed a pronounced reduction in channel activation in response to ß-adrenergic stimulation. CONCLUSIONS: Patients with C-loop missense mutations in the KCNQ1 channel exhibit a high risk for life-threatening events and derive a pronounced benefit from treatment with ß-blockers. Reduced channel activation after sympathetic activation can explain the increased clinical risk and response to therapy in patients with C-loop mutations.

Variants in the 3' untranslated region of the KCNQ1-encoded Kv7.1 potassium channel modify disease severity in patients with type 1 long QT syndrome in an allele-specific manner.

AIMS: Heterozygous mutations in KCNQ1 cause type 1 long QT syndrome (LQT1), a disease characterized by prolonged heart rate-corrected QT interval (QTc) and life-threatening arrhythmias. It is unknown why disease penetrance and expressivity is so variable between individuals hosting identical mutations. We aimed to study whether this can be explained by single nucleotide polymorphisms (SNPs) in KCNQ1's 3' untranslated region (3'UTR). METHODS AND RESULTS: This study was performed in 84 LQT1 patients from the Academic Medical Center in Amsterdam and validated in 84 LQT1 patients from the Mayo Clinic in Rochester. All patients were genotyped for SNPs in KCNQ1's 3'UTR, and six SNPs were found. Single nucleotide polymorphisms rs2519184, rs8234, and rs10798 were associated in an allele-specific manner with QTc and symptom occurrence. Patients with the derived SNP variants on their mutated KCNQ1 allele had shorter QTc and fewer symptoms, while the opposite was also true: patients with the derived SNP variants on their normal KCNQ1 allele had significantly longer QTc and more symptoms. Luciferase reporter assays showed that the expression of KCNQ1's 3'UTR with the derived SNP variants was lower than the expression of the 3'UTR with the ancestral SNP variants. CONCLUSION: Our data indicate that 3'UTR SNPs potently modify disease severity in LQT1. The allele-specific effects of the SNPs on disease severity and gene expression strongly suggest that they are functional variants that directly alter the expression of the allele on which they reside, and thereby influence the balance between proteins stemming from either the normal or the mutant KCNQ1 allele.

Diagnostic Accuracy of the Standing Test in Adults Suspected for Congenital Long-QT Syndrome.

Background An elegant bedside provocation test has been shown to aid the diagnosis of long-QT syndrome (LQTS) in a retrospective cohort by evaluation of QT intervals and T-wave morphology changes resulting from the brief tachycardia provoked by standing. We aimed to prospectively determine the potential diagnostic value of the standing test for LQTS. Methods and Results In adults suspected for LQTS who had a standing test, the QT interval was assessed manually and automated. In addition, T-wave morphology changes were determined. A total of 167 controls and 131 genetically confirmed patients with LQTS were included. A prolonged heart rate-corrected QT interval (QTc) (men ≥430 ms, women ≥450 ms) at baseline before standing yielded a sensitivity of 61% (95% CI, 47-74) in men and 54% (95% CI, 42-66) in women, with a specificity of 90% (95% CI, 80-96) and 89% (95% CI, 81-95), respectively. In both men and women, QTc≥460 ms after standing increased sensitivity (89% [95% CI, 83-94]) but decreased specificity (49% [95% CI, 41-57]). Sensitivity further increased (P<0.01) when a prolonged baseline QTc was accompanied by a QTc≥460 ms after standing in both men (93% [95% CI, 84-98]) and women (90% [95% CI, 81-96]). However, the area under the curve did not improve. T-wave abnormalities after standing did not further increase the sensitivity or the area under the curve significantly. Conclusions Despite earlier retrospective studies, a baseline ECG and the standing test in a prospective evaluation displayed a different diagnostic profile for congenital LQTS but no unequivocal synergism or advantage. This suggests that there is markedly reduced penetrance and incomplete expression in genetically confirmed LQTS with retention of repolarization reserve in response to the brief tachycardia provoked by standing.

Sodium channelopathies: do we really understand what's going on?

Long-QT syndrome, Brugada syndrome, and conduction disease may be caused by mutations in the cardiac sodium channel gene SCN5A, and from the ECG one can already presume either a gain- or a loss-of-function defect. We describe a family harboring 2 SCN5A mutations: the ΔKPQ mutation, the "classical" gain-of-function mutation associated with Long-QT syndrome, and the I1660V mutation, a loss-of-function mutation associated with Brugada syndrome. However, we were surprised by the result of genetic testing in this family. One son who carried the ΔKPQ mutation but not the I1660V mutation did not show the expected Long-QT phenotype but, unexpectedly, showed a conduction disease/Brugada phenotype.

Diagnostic accuracy of the response to the brief tachycardia provoked by standing in children suspected for long QT syndrome.

BACKGROUND: Adult long QT syndrome (LQTS) patients have inadequate corrected QT interval (QTc) shortening and an abnormal T-wave response to the sudden heart rate acceleration provoked by standing. In adults, this knowledge can be used to aid an LQTS diagnosis and, possibly, for risk stratification. However, data on the diagnostic value of the standing test in children are currently limited. OBJECTIVE: To determine the potential value of the standing test to aid LQTS diagnostics in children. METHODS: In a prospective cohort including children (≤18 years) who had a standing test, comprehensive analyses were performed including manual and automated QT interval assessments and determination of T-wave morphology changes. RESULTS: We included 47 LQTS children and 86 control children. At baseline, the QTc that identified LQTS children with a 90% sensitivity was 435 ms, which yielded a 65% specificity. A QTc ≥ 490 ms after standing only slightly increased sensitivity (91%, 95% confidence interval [CI]: 80%-98%) and slightly decreased specificity (58%, 95% CI: 47%-70%). Sensitivity increased slightly more when T-wave abnormalities were present (94%, 95% CI: 82%-99%; specificity 53%, 95% CI: 42%-65%). When a baseline QTc ≥ 440 ms was accompanied by a QTc ≥ 490 ms and T-wave abnormalities after standing, sensitivity further increased (96%, 95% CI: 85%-99%) at the expense of a further specificity decrease (41%, 95% CI: 30%-52%). Beat-to-beat analysis showed that 30 seconds after standing, LQTS children had a greater increase in heart rate compared to controls, which was more evidently present in LQTS boys and LQTS type 1 children. CONCLUSION: In children, the standing test has limited additive diagnostic value for LQTS over a baseline electrocardiogram, while T-wave abnormalities after standing also have limited additional value. The standing test for LQTS should only be used with caution in children.

Genetic testing in cardiovascular diseases.

PURPOSE OF REVIEW: To review the current state and different aspects, including the yield, of genetic counseling and genetic testing in inherited heart disease. RECENT FINDINGS: The number of counselees is growing rapidly all over the world, and the first studies about patients' perspectives and follow-up have been published. Progress has been made by gene-specific studies on long QT syndrome to judge the relevance of detected mutations in the specific domains. SUMMARY: With the increasing identification of associated genes and available techniques in molecular testing of the inherited heart diseases, the diagnostic yield of mutation analysis is growing rapidly. To determine the relevance of all these mutations, ongoing research is needed. Furthermore, the process of genetic counseling can be optimized and extended with cascade screening, which leads to identifying patients at risk and timely treatment.

The role of the epinephrine test in the diagnosis and management of children suspected of having congenital long QT syndrome.

The epinephrine test has been shown to be a powerful tool to predict the genotype of congenital long QT syndrome (LQTS). The aim of this study was to evaluate its role in the diagnosis and management of LQTS in children. The test (using the Shimizu protocol) was conducted in patients with some evidence of LQTS but in whom clinical and management decisions were challenging (n = 41, age 9.6 +/- 3.9 years, 19 female). LQT1, LQT2, and negative responses to epinephrine were obtained in 16, 5, and 20 subjects, respectively. LQTS gene positivity was obtained in two subjects. Beta-blocker therapy was started in all subjects with a positive epinephrine response (n = 21) and in some negative responders because of their strong LQTS phenotype (n = 10). No therapy was given to the subset with less convincing features of LQTS who had also responded negatively to epinephrine (n = 10). Follow-up for 3.0 +/- 2 years was uneventful in both management groups. Due to the discordance with genotyping, the epinephrine test cannot be used to diagnose genotype-positive LQTS but when used in combination with phenotype assessment and genetic screening, it could enable better management decisions.

Heart Rate Recovery After Exercise Is Associated With Arrhythmic Events in Patients With Catecholaminergic Polymorphic Ventricular Tachycardia.

BACKGROUND: Risk stratification in catecholaminergic polymorphic ventricular tachycardia remains ill defined. Heart rate recovery (HRR) immediately after exercise is regulated by autonomic reflexes, particularly vagal tone, and may be associated with symptoms and ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia. Our objective was to evaluate whether HRR after maximal exercise on the exercise stress test (EST) is associated with symptoms and ventricular arrhythmias. METHODS: In this retrospective observational study, we included patients ≤65 years of age with an EST without antiarrhythmic drugs who attained at least 80% of their age- and sex-predicted maximal HR. HRR in the recovery phase was calculated as the difference in heart rate (HR) at maximal exercise and at 1 minute in the recovery phase (ΔHRR1'). RESULTS: We included 187 patients (median age, 36 years; 68 [36%] symptomatic before diagnosis). Pre-EST HR and maximal HR were equal among symptomatic and asymptomatic patients. Patients who were symptomatic before diagnosis had a greater ΔHRR1' after maximal exercise (43 [interquartile range, 25-58] versus 25 [interquartile range, 19-34] beats/min; P<0.001). Corrected for age, sex, and relatedness, patients in the upper tertile for ΔHRR1' had an odds ratio of 3.4 (95% CI, 1.6-7.4) of being symptomatic before diagnosis (P<0.001). In addition, ΔHRR1' was higher in patients with complex ventricular arrhythmias at EST off antiarrhythmic drugs (33 [interquartile range, 22-48] versus 27 [interquartile range, 20-36] beats/min; P=0.01). After diagnosis, patients with a ΔHRR1' in the upper tertile of its distribution had significantly more arrhythmic events as compared with patients in the other tertiles (P=0.045). CONCLUSIONS: Catecholaminergic polymorphic ventricular tachycardia patients with a larger HRR following exercise are more likely to be symptomatic and have complex ventricular arrhythmias during the first EST off antiarrhythmic drug.

Clinical aspects of type-1 long-QT syndrome by location, coding type, and biophysical function of mutations involving the KCNQ1 gene.

BACKGROUND: Type-1 long-QT syndrome (LQTS) is caused by loss-of-function mutations in the KCNQ1-encoded I(Ks) cardiac potassium channel. We evaluated the effect of location, coding type, and biophysical function of KCNQ1 mutations on the clinical phenotype of this disorder. METHODS AND RESULTS: We investigated the clinical course in 600 patients with 77 different KCNQ1 mutations in 101 proband-identified families derived from the US portion of the International LQTS Registry (n=425), the Netherlands' LQTS Registry (n=93), and the Japanese LQTS Registry (n=82). The Cox proportional hazards survivorship model was used to evaluate the independent contribution of clinical and genetic factors to the first occurrence of time-dependent cardiac events from birth through age 40 years. The clinical characteristics, distribution of mutations, and overall outcome event rates were similar in patients enrolled from the 3 geographic regions. Biophysical function of the mutations was categorized according to dominant-negative (> 50%) or haploinsufficiency (< or = 50%) reduction in cardiac repolarizing I(Ks) potassium channel current. Patients with transmembrane versus C-terminus mutations (hazard ratio, 2.06; P<0.001) and those with mutations having dominant-negative versus haploinsufficiency ion channel effects (hazard ratio, 2.26; P<0.001) were at increased risk for cardiac events, and these genetic risks were independent of traditional clinical risk factors. CONCLUSIONS: This genotype-phenotype study indicates that in type-1 LQTS, mutations located in the transmembrane portion of the ion channel protein and the degree of ion channel dysfunction caused by the mutations are important independent risk factors influencing the clinical course of this disorder.

Phenotypic variability in Caucasian and Japanese patients with matched LQT1 mutations.

BACKGROUND: Ethnic differences may affect the phenotypic expression of genetic disorders. However, data regarding the effect of ethnicity on outcome in patients with genetic cardiac disorders are limited. We compared the clinical course of Caucasian and Japanese long QT type-1 (LQT1) patients who were matched for mutations in the KCNQ1 gene. METHODS: The study population comprised 62 Caucasian and 38 Japanese LQT1 patients from the International LQTS Registry who were identified as having six identical KCNQ1 mutations. The biophysical function of the mutations was categorized into dominant-negative (> 50%) or haploinsufficiency (< or =50%) reduction in cardiac repolarizing IKs potassium channel current. The primary end point of the study was the occurrence of a first cardiac event from birth through age 40 years. RESULTS: Japanese patients had a significantly higher cumulative rate of cardiac events (67%) than Caucasian patients (39%; P = 0.01). The respective frequencies of dominant negative mutations in the two ethnic groups were 63% and 28% (P < 0.001). In multivariate analysis, Japanese patients had an 81% increase in the risk of cardiac events (P = 0.06) as compared with Caucasians. However, when the biophysical function of the mutations was included in the multivariate model, the risk associated with Japanese ethnicity was no longer evident (HR = 1.05; P = 0.89). Harboring a dominant negative mutation was shown to be the most powerful and significant predictor of outcome (HR = 3.78; P < 0.001). CONCLUSIONS: Our data indicate that ethnic differences in the clinical expression of LQTS can be attributed to the differences in frequencies of the specific mutations within the two populations.

Gain-of-function mutation in SCN5A causes ventricular arrhythmias and early onset atrial fibrillation.

BACKGROUND: Mutations in SCN5A, the gene encoding the α-subunit of the cardiac sodium channel (NaV1.5), are associated with a broad spectrum of inherited cardiac arrhythmia disorders. The purpose of this study was to identify the genetic and functional determinants underlying a Dutch family that presented with a combined phenotype of ventricular arrhythmias with a likely adrenergic component, either in isolation or in combination with a mildly decreased heart function and early onset (<55years) atrial fibrillation. METHODS AND RESULTS: We performed next generation sequencing in the proband of a two-generation Dutch family and demonstrated a novel missense mutation in SCN5A-(p.M1851V) which co-segregated with the clinical phenotype in the family. We functionally evaluated the putative genetic defect by patch clamp electrophysiological studies in human embryonic kidney cells transfected with mutant or wild-type Nav1.5. The current inactivation was slower and recovery from inactivation was faster in SCN5A-M1851V channels. The voltage dependence of inactivation was shifted towards more positive potentials and consequently, a larger TTX-sensitive window current was observed in SCN5A-M1851V channels. Furthermore, a higher upstroke velocity was observed for the SCN5A-M1851V channels, while the depolarization voltage was more negative, both indicating increased excitability. CONCLUSIONS: This mutation leads to a gain-of-function mechanism based on increased channel availability and increased window current, fitting the observed clinical phenotype of (likely adrenergic-induced) ventricular arrhythmias and atrial fibrillation. These findings further expand the range of cardiac arrhythmias associated with mutations in SCN5A.

Effect of Age and Sex on the QTc Interval in Children and Adolescents With Type 1 and 2 Long-QT Syndrome.

BACKGROUND: In congenital long-QT syndrome, age, sex, and genotype have been associated with cardiac events, but their effect on the trend in QTc interval has never been established. We, therefore, aimed to assess the effect of age and sex on the QTc interval in children and adolescents with type 1 (LQT1) and type 2 (LQT2) long-QT syndrome. METHODS AND RESULTS: QTc intervals of 12-lead resting electrocardiograms were determined, and trends over time were analyzed using a linear mixed-effects model. The study included 278 patients with a median follow-up of 4 years (interquartile range, 1-9) and a median number of 6 (interquartile range, 2-10) electrocardiograms per patient. Both LQT1 and LQT2 male patients showed QTc interval shortening after the onset of puberty. In LQT2 male patients, this was preceded by a progressive QTc interval prolongation. In LQT1, after the age of 12 years, male patients had a significantly shorter QTc interval than female patients. In LQT2, during the first years of life and from 14 to 26 years, male patients had a significantly shorter QTc interval than female patients. On the contrary, between 5 and 14 years, LQT2 male patients had significantly longer QTc interval than LQT2 female patients. CONCLUSIONS: There is a significant effect of age and sex on the QTc interval in long-QT syndrome, with a unique pattern per genotype. The age of 12 to 14 years is an important transitional period. In the risk stratification and management of long-QT syndrome patients, clinicians should be aware of these age-, sex-, and genotype-related trends in QTc interval and especially the important role of the onset of puberty.