Genetic characterization of KCNQ1 variants improves risk stratification in type 1 long QT syndrome patients.

AIMS: KCNQ1 mutations cause QTc prolongation increasing life-threatening arrhythmias risks. Heterozygous mutations [type 1 long QT syndrome (LQT1)] are common. Homozygous KCNQ1 mutations cause type 1 Jervell and Lange-Nielsen syndrome (JLNS) with deafness and higher sudden cardiac death risk. KCNQ1 variants causing JLNS or LQT1 might have distinct phenotypic expressions in heterozygous patients. The aim of this study is to evaluate QTc duration and incidence of long QT syndrome-related cardiac events according to genetic presentation. METHODS AND RESULTS: We enrolled LQT1 or JLNS patients with class IV/V KCNQ1 variants from our inherited arrhythmia clinic (September 1993 to January 2023). Medical history, ECG, and follow-up were collected. Additionally, we conducted a thorough literature review for JLNS variants. Survival curves were compared between groups, and multivariate Cox regression models identified genetic and clinical risk factors. Among the 789 KCNQ1 variant carriers, 3 groups were identified: 30 JLNS, 161 heterozygous carriers of JLNS variants (HTZ-JLNS), and 550 LQT1 heterozygous carriers of non-JLNS variants (HTZ-Non-JLNS). At diagnosis, mean age was 3.4 ± 4.7 years for JLNS, 26.7 ± 21 years for HTZ-JLNS, and 26 ± 21 years for HTZ-non-JLNS; 55.3% were female; and the mean QTc was 551 ± 54 ms for JLNS, 441 ± 32 ms for HTZ-JLNS, and 467 ± 36 ms for HTZ-Non-JLNS. Patients with heterozygous JLNS mutations (HTZ-JLNS) represented 22% of heterozygous KCNQ1 variant carriers and had a lower risk of cardiac events than heterozygous non-JLNS variant carriers (HTZ-Non-JLNS) [hazard ratio (HR) = 0.34 (0.22-0.54); P < 0.01]. After multivariate analysis, four genetic parameters were independently associated with events: haploinsufficiency [HR = 0.60 (0.37-0.97); P = 0.04], pore localization [HR = 1.61 (1.14-1.2.26); P < 0.01], C-terminal localization [HR = 0.67 (0.46-0.98); P = 0.04], and group [HR = 0.43 (0.27-0.69); P < 0.01]. CONCLUSION: Heterozygous carriers of JLNS variants have a lower risk of cardiac arrhythmic events than other LQT1 patients.

QT correction using Bazett's formula remains preferable in long QT syndrome type 1 and 2.

BACKGROUND: The heart rate (HR) corrected QT interval (QTc) is crucial for diagnosis and risk stratification in the long QT syndrome (LQTS). Although its use has been questioned in some contexts, Bazett's formula has been applied in most diagnostic and prognostic studies in LQTS patients. However, studies on which formula eliminates the inverse relation between QT and HR are lacking in LQTS patients. We therefore determined which QT correction formula is most appropriate in LQTS patients including the effect of beta blocker therapy and an evaluation of the agreement of the formulae when applying specific QTc limits for diagnostic and prognostic purposes. METHODS: Automated measurements from routine 12-lead ECGs from 200 genetically confirmed LQTS patients from two Swedish regions were included (167 LQT1, 33 LQT2). QT correction was performed using the Bazett, Framingham, Fridericia, and Hodges formulae. Linear regression was used to compare the formulae in all patients, and before and after the initiation of beta blocking therapy in a subgroup (n = 44). Concordance analysis was performed for QTc ≥ 480 ms (diagnosis) and ≥500 ms (prognosis). RESULTS: The median age was 32 years (range 0.1-78), 123 (62%) were female and 52 (26%) were children ≤16 years. Bazett's formula was the only method resulting in a QTc without relation with HR. Initiation of beta blocking therapy did not alter the result. Concordance analyses showed clinically significant differences (Cohen's kappa 0.629-0.469) for diagnosis and prognosis in individual patients. CONCLUSION: Bazett's formula remains preferable for diagnosis and prognosis in LQT1 and 2 patients.

A novel mutation KCNQ1p.Thr312del is responsible for long QT syndrome type 1.

Patients with high-risk long QT syndrome (LQTS) mutations may experience life-threatening cardiac events. The present study sought to characterize a novel pathogenic mutation, KCNQ1p.Thr312del, in a Chinese LQT1 family. Clinical and genetic analyses were performed to identify this novel causative gene mutation in this LQTS family. Autosomal dominant inheritance of KCNQ1p.T312del was demonstrated in the three-generation pedigree. All mutation carriers presented with prolonged QT intervals and experienced recurrent syncope during exercise or emotional stress. The functional consequences of the mutant channel were investigated by computer homology modeling as well as whole-cell patch-clamp, western-blot and co-immunoprecipitation techniques using transfected mammalian cells. T312 is in the selectivity filter (SF) of the pore region of the KCNQ1-encoded channel. Homology modeling suggested that secondary structure was altered in the mutant SF compared with the wild-type (WT) SF. There were no significant differences in Kv7.1 expression, membrane trafficking or physical interactions with KCNE1-encoded subunits between the WT and mutant transfected channels. However, the KCNQ1p.T312del channels expressed in transfected cells were non-functional in the absence or presence of auxiliary KCNE1-subunits. Dominant-negative suppression of current density and decelerated activation kinetics were observed in cells expressing KCNQ1WT and KCNQ1p.T312del combined with KCNE1 (KCNQ1WT/p.T312del + KCNE1 channels). Those electrophysiological characteristics underlie the pathogenesis of this novel mutation and also suggest a high risk of cardiac events in patients carrying KCNQ1p.T312del. Although protein kinase A-dependent current increase was preserved, a significant suppression of rate-dependent current facilitation was noted in the KCNQ1WT/p.T312del + KCNE1 channels compared to the WT channels during 1- and 2-Hz stimulation, which was consistent with the patients' phenotype being triggered by exercise. Overall, KCNQ1p.Thr312del induces a loss of function in channel electrophysiology, and it is a high-risk mutation responsible for LQT1.

Dual LQT1 and HCM phenotypes associated with tetrad heterozygous mutations in KCNQ1, MYH7, MYLK2, and TMEM70 genes in a three-generation Chinese family.

AIMS: Hypertrophic cardiomyopathy (HCM) mainly results from autosomal-dominant inherited single heterozygous mutations in cardiac sarcomere genes. Contributions of multiple gene mutations to disease heterogeneity in a three-generation family were investigated. METHODS: Clinical, electrocardiographic (ECG), and echocardiographic examination in members of a three-generation Chinese family was followed by exon and boarding intron analysis of 96 genes in the proband using second-generation sequencing. The identified mutations were confirmed by bi-directional Sanger sequencing in all family members and 300 healthy controls. RESULTS: Four missense mutations were detected in the family. These were two novel MYH7-H1717Q and MYLK2-K324E mutations accompanied by the KCNQ1-R190W and TMEM70-I147T mutations. The proband carried all four mutations and showed overlapping HCM and LQT1 phenotypes. Five family members each carried two mutations. Subject II-2 only carried TMEM70-I147T. MYH7-H1717Q and TMEM70-I147T came from the paternal side, whereas KCNQ1-R190W and MYLK2-K324E came from the maternal side. Left ventricle mass indices in MYH7-H1717Q carriers were significantly higher than in non-H1717Q carriers (90.05 ± 7.33 g/m(2), 63.20 ± 4.53 g/m(2), respectively, P < 0.01). Four KCNQ1-R190W carriers showed QTc intervals that were significantly more prolonged than those in non-R190W carriers (472.25 ± 16.18 and 408.50 ± 7.66 ms, respectively, P < 0.05). All MYLK2-K324E carriers showed inverted ECG T waves. The subject with only a TMEM70-I147T mutation showed normal ECG and echocardiographs, suggesting that this had less pathological effects at least in this family. CONCLUSIONS: We demonstrate dual LQT1 and HCM phenotypes in this multiple LQT1- and HCM-related gene mutation carrier family for the first time and suggest that LQT-related gene mutations associate with QT interval prolongation and/or arrhythmia in HCM patients.

Identification of Low-Risk Adult Congenital LQTS Patients.

INTRODUCTION: To date, most risk stratification studies in long-QT syndrome (LQTS) have focused on identification of high-risk subjects. Current data on the long-term clinical course of low-risk adult LQTS patients are limited. METHODS AND RESULTS: Patients in this study were from the Rochester-based LQTS Registry. We hypothesized that long-term survival of LQT1-2 patients with QTc <500 milliseconds and no cardiac symptoms before age 20 (n = 523) would be similar to that of their unaffected genotype-negative family members (n = 1,134). Kaplan-Meier survival analysis and multivariate Cox proportional hazards regression models were used to evaluate the incidence and risk of all-cause mortality in the study population. The low-risk LQTS study group comprised 27% (523/1,919) of genetically confirmed LQTS Registry patients alive at age 20. The cumulative probability of all-cause mortality between age 20 and 65 was similar in the low-risk LQTS group and the genotype-negative control group (4.3% and 4.4%, respectively at age 65; P = 0.49 for overall difference). Multivariate analysis showed no significant difference in the risk of all-cause mortality between the 2 groups (HR = 0.89; 95% CI 0.33-2.43, P = 0.82). Consistent results were revealed in subgroup analyses in female and male LQTS patients and in patients with genetically identified LQT1 and LQT2 mutations. CONCLUSIONS: We identified a sizeable proportion of low-risk, adult LQTS patients with no cardiac symptoms before age 20 and QTc<500 milliseconds who had 45-year survival similar to unaffected family members.

Marked, transient, emotion-triggered QT accentuation in an adolescent female with type 1 long QT syndrome.

Type 1 long QT syndrome is the most common long QT syndrome genetic subtype. Exercise and emotional stress can precipitate sudden cardiac events in patients with type 1 long QT syndrome; however, the precise mechanism remains elusive. We report the case of a teenage girl with type 1 long QT syndrome secondary to a rare frameshift mutation (p. L191fs+90X) in the KCNQ1-encoded Kv7.1 potassium channel. During emotional distress, her continuous QTc recordings precipitously increased, peaking within minutes to 669 ms and then returning to baseline (520 ms) as she calmed without concomitant increase in heart rate. This is the first described case documenting transient, marked accentuation of the QTc interval in a long QT syndrome patient during emotional distress. Such events may be triggered by transient accentuation of the intrinsic perturbation in cardiac repolarisation and increase the risk of degeneration to a ventricular arrhythmia. This case illustrates the need improved understanding of the complex interaction between emotion and cardiac stability in patients with long QT syndrome.

Dominant-negative control of cAMP-dependent IKs upregulation in human long-QT syndrome type 1.

RATIONALE: The mutation A341V in the S6 transmembrane segment of KCNQ1, the α-subunit of the slowly activating delayed-rectifier K(+) (I(Ks)) channel, predisposes to a severe long-QT1 syndrome with sympathetic-triggered ventricular tachyarrhythmias and sudden cardiac death. OBJECTIVE: Several genetic risk modifiers have been identified in A341V patients, but the molecular mechanisms underlying the pronounced repolarization phenotype, particularly during ß-adrenergic receptor stimulation, remain unclear. We aimed to elucidate these mechanisms and provide new insights into control of cAMP-dependent modulation of I(Ks). METHODS AND RESULTS: We characterized the effects of A341V on the I(Ks) macromolecular channel complex in transfected Chinese hamster ovary cells and found a dominant-negative suppression of cAMP-dependent Yotiao-mediated I(Ks) upregulation on top of a dominant-negative reduction in basal current. Phosphomimetic substitution of the N-terminal position S27 with aspartic acid rescued this loss of upregulation. Western blot analysis showed reduced phosphorylation of KCNQ1 at S27, even for heterozygous A341V, suggesting that phosphorylation defects in some (mutant) KCNQ1 subunits can completely suppress I(Ks) upregulation. Functional analyses of heterozygous KCNQ1 WT:G589D and heterozygous KCNQ1 WT:S27A, a phosphorylation-inert substitution, also showed such suppression. Immunoprecipitation of Yotiao with KCNQ1-A341V (in the presence of KCNE1) was not different from wild-type. CONCLUSIONS: Our results indicate the involvement of the KCNQ1-S6 region at/or around A341 in cAMP-dependent stimulation of I(Ks), a process that is under strong dominant-negative control, suggesting that tetrameric KCNQ1 phosphorylation is required. Specific long-QT1 mutations, including heterozygous A341V, disable this regulation.

Effect of beta-blockers on QT dynamics in the long QT syndrome: measuring the benefit.

AIMS: Beta-blockers are the standard of care for the treatment of long QT syndrome (LQTS), and have been shown to reduce recurrent syncope and mortality in patients with type 1 LQTS (LQT1). Although beta-blockers have minimal effect on the resting corrected QT interval, their effect on the dynamics of the non-corrected QT interval is unknown, and may provide insight into their protective effects. METHODS AND RESULTS: Twenty-three patients from eight families with genetically distinct mutations for LQT1 performed exercise stress testing before and after beta-blockade. One hundred and fifty-two QT, QTc, and Tpeak-Tend intervals were measured before starting beta-blockers and compared with those at matched identical cycle lengths following beta-blockade. Beta-blockers demonstrated heart-rate-dependent effects on the QT and QTc intervals. In the slowest heart rate tertile (<90 b.p.m.), beta-blockade increased the QT and QTc intervals (QT: 405 vs. 409 ms; P = 0.06; QTc: 459 vs. 464 ms; P = 0.06). In the fastest heart rate tertile (>100 b.p.m.), the use of beta-blocker was associated with a reduction in both the QT and QTc intervals (QT: 367 vs. 358 ms; P < 0.0001; QTc: 500 vs. 486 ms; P < 0.0001). The Tpeak-Tend interval showed minimal change at slower heart rates (<90 b.p.m.) (93 vs. 87 ms; P = 0.09) and at faster heart rates (>100 b.p.m.) (87 vs. 84 ms; P = NS) following beta-blockade. CONCLUSION: Beta-blockers have heart-rate-dependent effects on the QT and QTc intervals in LQTS. They appear to increase the QT and QTc intervals at slower heart rates and shorten them at faster heart rates during exercise.

The Romano-Ward syndrome--1964-2014: 50 years of progress.

This year marks the 50th anniversary of publication in the then Journal of the Irish Medical Association of the seminal work by Irish paediatrician Professor Conor Ward entitled 'A new familial Cardiac Syndrome in Children'. The condition soon became known by the eponym Romano-Ward Syndrome and is now recognised as the congenital Long QT Syndrome. Here we review the major developments in the field over the past fifty years, with special mention of the important contributions made by Irish researches.

Clinical characterization of type 1 long QT syndrome caused by C-terminus Kv7.1 variants.

BACKGROUND: Variants in the KCNQ1 gene, encoding the α-subunit of the slow component of delayed rectifier K+ channel Kv7.1, cause long QT syndrome (LQTS) type 1. The location of variants may be one of the factors in determining prognosis. However, detailed genotype-phenotype relationships associated with C-terminus variants remain unelucidated. OBJECTIVE: We investigated the clinical characteristics and variant-specific arrhythmic risks in patients with LQTS carrying Kv7.1 C-terminus variants. METHODS: The study comprises 202 consecutive patients with LQTS (98 probands and 104 family members) who carry a rare heterozygous variant in the Kv7.1 C-terminus. Their clinical characteristics and arrhythmic events were investigated. RESULTS: We identified 36 unique C-terminus variants (25 missense and 11 non-missense). The p.R366W variant was identified in 8 families, and p.T587M was identified in 21 families in large numbers from northwestern Japan. As for the location of the variant, we found that the variants in highly conserved regions and nonhelical domains were associated with longer QTc intervals compared with the variants in other regions. Both p.R366W and p.T587M variants are located in the highly conserved and functionally pivotal regions close to helices A and D, which are associated with calmodulin binding and channel assembly (tetramerization), respectively. The probands carrying p.T587M and p.R366W variants had worse arrhythmia outcomes compared with those with other C-terminus variants. The haplotype analysis of p.T587M families was suggestive of a founder effect. CONCLUSION: The arrhythmic risk of C-terminus variants in Kv7.1 in LQTS is not homogeneous, and locations of variants can be a determining factor for prognosis.

Patient-specific induced pluripotent stem-cell models for long-QT syndrome.

BACKGROUND: Long-QT syndromes are heritable diseases associated with prolongation of the QT interval on an electrocardiogram and a high risk of sudden cardiac death due to ventricular tachyarrhythmia. In long-QT syndrome type 1, mutations occur in the KCNQ1 gene, which encodes the repolarizing potassium channel mediating the delayed rectifier I(Ks) current. METHODS: We screened a family affected by long-QT syndrome type 1 and identified an autosomal dominant missense mutation (R190Q) in the KCNQ1 gene. We obtained dermal fibroblasts from two family members and two healthy controls and infected them with retroviral vectors encoding the human transcription factors OCT3/4, SOX2, KLF4, and c-MYC to generate pluripotent stem cells. With the use of a specific protocol, these cells were then directed to differentiate into cardiac myocytes. RESULTS: Induced pluripotent stem cells maintained the disease genotype of long-QT syndrome type 1 and generated functional myocytes. Individual cells showed a "ventricular," "atrial," or "nodal" phenotype, as evidenced by the expression of cell-type­specific markers and as seen in recordings of the action potentials in single cells. The duration of the action potential was markedly prolonged in "ventricular" and "atrial" cells derived from patients with long-QT syndrome type 1, as compared with cells from control subjects. Further characterization of the role of the R190Q­KCNQ1 mutation in the pathogenesis of long-QT syndrome type 1 revealed a dominant negative trafficking defect associated with a 70 to 80% reduction in I(Ks) current and altered channel activation and deactivation properties. Moreover, we showed that myocytes derived from patients with long-QT syndrome type 1 had an increased susceptibility to catecholamine-induced tachyarrhythmia and that beta-blockade attenuated this phenotype. CONCLUSIONS: We generated patient-specific pluripotent stem cells from members of a family affected by long-QT syndrome type 1 and induced them to differentiate into functional cardiac myocytes. The patient-derived cells recapitulated the electrophysiological features of the disorder. (Funded by the European Research Council and others.)

Mutation location effect on severity of phenotype during exercise testing in type 1 long-QT syndrome: impact of transmembrane and C-loop location.

BACKGROUND: Targeted mutation site-specific differences have correlated C-loop missense mutations with worse outcomes and increased benefit of beta-blockers in LQT1. This observation has implicated the C-loop region as being mechanistically important in the altered response to sympathetic stimulation known to put patients with LQT1 at risk of syncope and sudden cardiac death. OBJECTIVE: The objective of this study was to determine if there is mutation site-specific response to sympathetic stimulation and beta-blockers using exercise testing. METHODS: This study is a retrospective review of LQT1 patients undergoing exercise testing at 3 academic referral centers. RESULTS: A total of 123 patients (age 28 ± 17 years, 59 male) were studied including 34 patients (28%) with C-loop mutations. There were no significant differences in supine, standing, peak exercise and 1-minute recovery QTc duration between patients with C-loop mutations and patients with alternate mutation sites. In 37 patients that underwent testing on and off beta-blockers, beta-blocker use was associated with a significant reduction in supine, standing and peak exercise QTc. This difference was not seen in the small group of patients (7/37) with C-loop mutations. There was no difference in QTc at 1 and 4 minutes into recovery. CONCLUSIONS: Genetically confirmed LQT1 patients in this study cohort with C-loop mutations did not demonstrate the expected increase in QTc in response to exercise, or resultant response to beta-blocker. The apparent increased risk of cardiac events associated with C-loop mutation sites and the marked benefit received from beta-blocker therapy are not reflected by exercise-mediated effects on QTc in this study population.

Fever-induced QTc prolongation and ventricular arrhythmias in individuals with type 2 congenital long QT syndrome.

Type 2 congenital long QT syndrome (LQT-2) is linked to mutations in the human ether a-go-go-related gene (HERG) and is characterized by rate-corrected QT interval (QTc) prolongation, ventricular arrhythmias, syncope, and sudden death. Recognized triggers of these cardiac events include emotional and acoustic stimuli. Here we investigated the repeated occurrence of fever-induced polymorphic ventricular tachycardia and ventricular fibrillation in 2 LQT-2 patients with A558P missense mutation in HERG. ECG analysis showed increased QTc with fever in both patients. WT, A558P, and WT+A558P HERG were expressed heterologously in HEK293 cells and were studied using biochemical and electrophysiological techniques. A558P proteins showed a trafficking-deficient phenotype. WT+A558P coexpression caused a dominant-negative effect, selectively accelerated the rate of channel inactivation, and reduced the temperature-dependent increase in the WT current. Thus, the WT+A558P current did not increase to the same extent as the WT current, leading to larger current density differences at higher temperatures. A similar temperature-dependent phenotype was seen for coexpression of the trafficking-deficient LQT-2 F640V mutation. We postulate that the weak increase in the HERG current density in WT-mutant coassembled channels contributes to the development of QTc prolongation and arrhythmias at febrile temperatures and suggest that fever is a potential trigger of life-threatening arrhythmias in LQT-2 patients.

ß-blockers protect against dispersion of repolarization during exercise in congenital long-QT syndrome type 1.

INTRODUCTION: ß-Blocker therapy reduces syncope and sudden death in long-QT syndrome type 1 (LQT1), but the mechanism of protection is incompletely understood. This study tested the hypothesis that ß-blockade reduces QT prolongation and dispersion of repolarization, measured as the T peak-to-end interval (T(pe) ), during exercise and recovery in LQT1 patients. METHODS AND RESULTS: QT and T(pe) were measured in 10 LQT1 patients (33 ± 13 years) and 35 normal subjects (32 ± 12 years) during exercise tests on and off ß-blockade. In LQT1 patients, ß-blockade reduced QT (391 ± 25 milliseconds vs 375 ± 26 milliseconds, P = 0.04 during exercise; 419 ± 41 milliseconds vs 391 ± 39 milliseconds, P = 0.02 during recovery) and markedly reduced T(pe) (91 ± 26 milliseconds vs 67 ± 19 milliseconds, P = 0.03 during exercise; 103 ± 26 milliseconds vs 78 ± 11 milliseconds, P = 0.02 during recovery). In contrast, in normal subjects, ß-blockade had no effect on QT (320 ± 17 milliseconds vs 317 ± 16 milliseconds, P = 0.29 during exercise; 317 ± 13 milliseconds vs 315 ± 14 milliseconds, P = 0.15 during recovery) and mildly reduced T(pe) (69 ± 13 milliseconds vs 61 ± 11 milliseconds, P = 0.01 during exercise; 77 ± 19 milliseconds vs. 68 ± 14 milliseconds, P < 0.001 during recovery). CONCLUSION: In LQT1 patients, ß-blockers reduced QT and T(pe) during exercise and recovery, supporting the theory that ß-blocker therapy protects LQT1 patients by reducing dispersion of repolarization during exercise and recovery.

Bupivacaine destabilizes action potential duration in cellular and computational models of long QT syndrome 1.

BACKGROUND: The effects of the local anesthetic bupivacaine on cardiac action potentials (APs) are mainly attributed to inhibition of cardiac Na(+) channels. The relevance of its ability to also induce high-affinity blockade of human ether-à-gogo-related gene (hERG) channels is unclear. We investigated whether this interaction may functionally become more significant in cellular and computational models of long (L)QT syndromes. METHODS: Left ventricular cardiomyocytes were isolated from adult guinea pig hearts, and bupivacaine-induced effects on APs were investigated using the patch-clamp technique. LQT-like states were pharmacologically induced by either blocking I(Ks) (LQT1-like, 10 µmol/L chromanol 293B), or I(Kr) (LQT2-like, 10 µmol/L E4031). Computational analysis of bupivacaine's effects was based on the Luo-Rudy dynamic model. RESULTS: Bupivacaine induced dose-dependent AP shortening in control myocytes. However, in the presence of 1 to 30 µmol/L bupivacaine, a high variability in AP duration with AP prolongations of up to 40% was observed. This destabilizing effect on AP duration was significantly increased in LQT1-like but not in LQT2-like myocytes. Similarly, the incidence of AP prolongations in the presence of 3 µmol/L bupivacaine was significantly increased from 6% in control myocytes to 24% in LQT1-like but not in LQT2-like myocytes. Computational modeling supported the concept that this bupivacaine-induced AP instability and the AP prolongations in the control and LQT1-like myocytes were caused by inhibition of hERG channels. CONCLUSIONS: This study provides evidence that bupivacaine induces inhibition of hERG channels, which is functionally silent under normal conditions but will become more relevant in LQT1-like states in which repolarization relies to a larger degree on hERG channels. Interactions with ion channels other than cardiac Na(+) channels may, therefore, determine the net cardiac effects of bupivacaine when the normal balance of ionic currents is altered.

NOS1AP polymorphisms reduce NOS1 activity and interact with prolonged repolarization in arrhythmogenesis.

AIMS: NOS1AP single-nucleotide polymorphisms (SNPs) correlate with QT prolongation and cardiac sudden death in patients affected by long QT syndrome type 1 (LQT1). NOS1AP targets NOS1 to intracellular effectors. We hypothesize that NOS1AP SNPs cause NOS1 dysfunction and this may converge with prolonged action-potential duration (APD) to facilitate arrhythmias. Here we test (i) the effects of NOS1 inhibition and their interaction with prolonged APD in a guinea pig cardiomyocyte (GP-CMs) LQT1 model; (ii) whether pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from LQT1 patients differing for NOS1AP variants and mutation penetrance display a phenotype compatible with NOS1 deficiency. METHODS AND RESULTS: In GP-CMs, NOS1 was inhibited by S-Methyl-L-thiocitrulline acetate (SMTC) or Vinyl-L-NIO hydrochloride (L-VNIO); LQT1 was mimicked by IKs blockade (JNJ303) and ß-adrenergic stimulation (isoproterenol). hiPSC-CMs were obtained from symptomatic (S) and asymptomatic (AS) KCNQ1-A341V carriers, harbouring the minor and major alleles of NOS1AP SNPs (rs16847548 and rs4657139), respectively. In GP-CMs, NOS1 inhibition prolonged APD, enhanced ICaL and INaL, slowed Ca2+ decay, and induced delayed afterdepolarizations. Under action-potential clamp, switching to shorter APD suppressed 'transient inward current' events induced by NOS1 inhibition and reduced cytosolic Ca2+. In S (vs. AS) hiPSC-CMs, APD was longer and ICaL larger; NOS1AP and NOS1 expression and co-localization were decreased. CONCLUSION: The minor NOS1AP alleles are associated with NOS1 loss of function. The latter likely contributes to APD prolongation in LQT1 and converges with it to perturb Ca2+ handling. This establishes a mechanistic link between NOS1AP SNPs and aggravation of the arrhythmia phenotype in prolonged repolarization syndromes.

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.

Left Cardiac Sympathetic Denervation Monotherapy in Patients With Congenital Long QT Syndrome.

BACKGROUND: Videoscopic left cardiac sympathetic denervation (LCSD) is an effective antifibrillatory, minimally invasive therapy for patients with potentially life-threatening arrhythmia syndromes like long QT syndrome (LQTS). Although initially used primarily for treatment intensification following documented LQTS-associated breakthrough cardiac events while on beta-blockers, LCSD as 1-time monotherapy for certain patients with LQTS requires further evaluation. We are presenting our early experience with LCSD monotherapy for carefully selected patients with LQTS. METHODS: Among the 1400 patients evaluated and treated for LQTS, a retrospective review was performed on the 204 patients with LQTS who underwent LCSD at our institution since 2005 to identify the patients where the LCSD served as stand-alone, monotherapy. Clinical data on symptomatic status before diagnosis, clinical, and genetic diagnosis, and breakthrough cardiac events after diagnosis were analyzed to determine efficacy of LCSD monotherapy. RESULT: Overall, 64 of 204 patients (31%) were treated with LCSD alone (37 [58%] female, mean QTc 466±30 ms, 16 [25%] patients were symptomatic before diagnosis with a mean age at diagnosis 17.3±11.8 years, 5 had [8%] ≥1 breakthrough cardiac event after diagnosis, and mean age at LCSD was 21.1±11.4 years). The primary motivation for LCSD monotherapy was an unacceptable quality of life stemming from beta-blocker related side effects (ie, beta-blocker intolerance) in 56/64 patients (88%). The underlying LQTS genotype was LQT1 in 36 (56%) and LQT2 in 20 (31%). There were no significant LCSD-related surgical complications. With a mean follow-up of 2.7±2.4 years so far, only 3 patients have experienced a nonlethal, post-LCSD breakthrough cardiac event in 180 patient-years. CONCLUSIONS: LCSD may be a safe and effective stand-alone therapy for select patients who do not tolerate beta-blockers. However, LCSD is not curative and patient selection will be critical when potentially considering LCSD as monotherapy.

A computational analysis of the effect of sevoflurane in a human ventricular cell model of long QT syndrome: Importance of repolarization reserve in the QT-prolonging effect of sevoflurane.

The slowly and rapidly activating delayed rectifier K+ channels (IKs and IKr, respectively) contribute to the repolarization of ventricular action potential in human heart and thereby determine QT interval on an electrocardiogram. Loss-of-function mutations in genes encoding IKs and IKr cause type 1 and type 2 long QT syndrome (LQT1 and LQT2, respectively), accompanied by a high risk of malignant ventricular arrhythmias and sudden cardiac death. This study was designed to investigate which cardiac electrophysiological conditions exaggerate QT-prolonging and arrhythmogenic effects of sevoflurane. We used the O'Hara-Rudy dynamic model to reconstruct human ventricular action potential and a pseudo-electrocardiogram, and simulated LQT1 and LQT2 phenotypes by decreasing conductances of IKs and IKr, respectively. Sevoflurane, but not propofol, prolonged ventricular action potential duration and QT interval in wild-type, LQT1 and LQT2 models. The QT-prolonging effect of sevoflurane was more profound in LQT2 than in wild-type and LQT1 models. The potent inhibitory effect of sevoflurane on IKs was primarily responsible for its QT-prolonging effect. In LQT2 model, IKs was considerably enhanced during excessive prolongation of ventricular action potential duration by reduction of IKr and relative contribution of IKs to ventricular repolarization was markedly elevated, which appears to underlie more pronounced QT-prolonging effect of sevoflurane in LQT2 model, compared with wild-type and LQT1 models. This simulation study clearly elucidates the electrophysiological basis underlying the difference in QT-prolonging effect of sevoflurane among wild-type, LQT1 and LQT2 models, and may provide important information for developing anesthetic strategies for patients with long QT syndrome in clinical settings.