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Background: Cardiac channelopathies are a heterogenous group of genetic heart diseases (GHDs) that affect cardiac ion channel function. The most prevalent among these are long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT) which predispose patients to potentially life threatening ventricular arrhythmias. Accurate and timely diagnosis is important for the management and risk stratification of the index case and identification of potentially at-risk relatives. Unfortunately, despite rising awareness of these GHDs, critical warning signs are overlooked. Objective: To describe the phenotypes of patients who present with a delayed or missed diagnosis of LQTS or CPVT. Methods: EMR data was reviewed for all patients evaluated and treated at Mayo Clinic between 2000-2023 who arrived with a mis- or delayed diagnosis of LQTS or CPVT. Data was abstracted for patient demographics, clinical characteristics, family history of SCD, and cardiac and genetic test results. Results: Overall, 47/2119 (2%) patients [33 (70%) female, mean age at correct diagnosis 26±18 years] diagnosed with LQTS (30; 2% of LQTS cohort) or CPVT (17; 7% of CPVT cohort) arrived with an outside misdiagnosis (37, 79%) or underdiagnosis (10, 21%). The most common misdiagnosis was epilepsy (20; 43%) or vasovagal syncope (14; 30%) and 3 CPVT patients (6%) were misdiagnosed with LQTS. Of the 10 underdiagnosed patients, 4 (40%) had QT prolongation, 4 (40%) family history of SCD, 3 (30%) bilateral deafness, and 1 (10%) fetal bradycardia and syndactyly. Overall, 40/47 (85%) were symptomatic (syncope: 29 [73%], seizures: 21 [53%], SCA: 10 [25%]) prior to diagnosis. Of note, 34/40 (85%) had symptoms with exertion, 5 (13%) at rest, and trigger was unknown in 1 (2%). Of the 7 asymptomatic patients (15%), 4 (57%) had QT prolongation and 4 (57%) had family history of SCD. In total, 20/47 patients (43%) had positive family history of SCD under 45 years of age. Overall, patients experienced a median delay in diagnosis of 8 years during which a median of 4 events (range: 1-150) occurred. As a result, an additional 29 family members of these patients received a delay in their diagnosis. Conclusions: Recognizing the signs and symptoms of patients with GHDs is important to reduce the ongoing burden of misdiagnosis or delayed diagnosis in LQTS and CPVT. The most important factors for suspicion of an inherited channelopathy are symptoms during exertion and family history of SCD.

Background: Long QT syndrome (LQTS) is a potentially lethal cardiac channelopathy. Among women with LQT2, the post-partum period has been considered high risk for cardiac events. However, whether this risk persists after establishing their diagnosis and implementing their LQT2-directed treatment program remains to be determined. Objective: To describe the management and outcomes of LQT2 women during the 9 months post-partum period. Methods: A retrospective analysis of 1869 patients with LQTS treated and evaluated at a tertiary center specializing in Genetic Heart Disease from January 2000 to November 2023 was performed to identify women with diagnosed and treated LQT2 who had a pregnancy during follow-up. Data were abstracted for patient demographics, clinical characteristics, symptomatic status, and treatment plans before and after pregnancy. Results: Overall, 30 pregnancies occurred in 22 women with LQT2. Their average QTc was 489 ± 34 ms with 7 patients (32%) having a resting QTc > 500 ms. Prior to their first post-partum period, 5/22 (23%) were symptomatic with 2 (9%) experiencing a LQT2-triggered sudden cardiac arrest (SCA). Before their post-partum period, their LQT2-directed therapy comprised preventative measures only in 7 (23%), drug therapy in 16 (53%), combination therapy in 7 (23%), and 10 women (43%) had an implantable cardioverter defibrillator (ICD). Pre-emptive treatment intensification was done for 24/30 post-partum periods. Only a single VF-terminating ICD therapy occurred in 1 (3%) of the 30 post-partum periods involving a 21-year-old with p.Lys610Asn-KCNH2 variant, QTc = 490 ms, and a pre-diagnosis presentation of seizures. Conclusion: Although the post-partum period is regarded as a ‘high risk’ window of time for women with LQT2, the risk of a LQT2-triggered cardiac event after diagnosis and implementation of contemporary therapies is very low. This designation of “high risk” among correctly diagnosed and treated women is misleading and generates inappropriate and unnecessary anxiety.

Introduction: Long QT syndrome (LQTS) is a potentially life-threatening genetic heart disease. Patients with LQTS may also have co-existent mental health illnesses that may benefit from psychiatric medications. However, because many of these medications have QT-prolonging potential (www.crediblemeds.org), many of these patients receive suboptimal mental health care. Objective: To evaluate the frequency, management, and incidence of breakthrough cardiac events (BCEs) in patients with LQTS and concomitant mental health issues treated with psychiatric medications. Methods: A retrospective review was conducted on patients cared for in Mayo Clinic's Windland Smith Rice Genetic Heart Rhythm Clinic between 2000 and 2024 focusing on patients with LQTS and a concomitant psychiatric diagnosis requiring medication with known, possible or conditional risk of torsades de pointes (TdP). Electronic medical records were reviewed for data. BCEs were defined as LQTS-triggered syncope, seizures, appropriate ICD therapy, sudden cardiac arrest (SCA), or sudden cardiac death (SCD). Patients with missing information were excluded. Results: Overall, 195 /1899 LQTS patients [10%, 86 (43%) with LQT1, 83 (42%) with LQT2, and 16 (8%) with LQT3] had a concomitant psychiatric diagnosis requiring medication [150 female (76%), mean age at diagnosis 27 ± 18 years, median follow-up time 6.6 years (IQR 2.9-13)]. The most common psychiatric conditions were depression (71%), anxiety (62%), and ADHD (9%). The mean duration of therapy was 3.36 +/- 3.48 years and the most common medications used were fluoxetine (26%), sertraline (14%), and escitalopram (11%). There was no significant difference in QTc after starting the first psychiatric medication when compared to baseline (473 ± 33 vs 474 ± 35 ms, p=0.6). Prior to their LQTS diagnosis and while therefore untreated, 61/195 (31%) had at least 1 LQTS-associated cardiac event. This occurred in the setting of a psychiatric drug in 7 patients (11%). Following LQTS diagnosis and treatment, 14/195 patients (7%) have experienced a non-lethal BCE of which only 3/14 (21%) while on psychiatric medications. Conclusions: Although avoidance of medications with known QT-prolonging potential is prudent, attention to patient’s overall well-being besides just their LQTS must be given. After correct diagnosis and treatment, LQTS patients with concomitant mental health issues may be safely and effectively treated with medications known to prolong QTc.

AbstractIntroductionLong QT syndrome (LQTS) is a cardiac channelopathy characterized by QT prolongation and a potential for arrhythmic syncope, sudden cardiac arrest or deaths (SCA/SCD). It has been speculated that patients with LQTS might have a primary sinoatrial node (SAN) phenotype of chronotropic insufficiency (CI). This has not been demonstrated convincingly before because of the potentially confounding effects of beta blocker (BB) therapy. Herein, we set out to determine whether untreated patients with LQTS demonstrate intrinsic CI.Methods and ResultsA retrospective review of all treadmill exercise stress tests (TEST) was performed on patients with one of the three most common LQTS genotypes: LQT1, LQT2, and LQT3. For each patient, the first TEST completed while off BB was analyzed. Patients with prior left cardiac sympathetic denervation (LCSD) therapy were excluded. CI was defined as having an age‐ and gender‐predicted peak heart rate (HR) < 85% and/or a predicted HR reserve (HRR) < 80%. Overall, 463 LQTS patients (245 LQT1, 125 LQT2, and 93 LQT3) were included (267 female [58%]; mean age at time of TEST [29 ± 17 years]). Mean % predicted peak HR for all LQTS patients was 87.6% (range 42.9% ‐ 119.1%) and mean % predicted HRR was 80% (range 19.1% ‐ 153%). Overall, half of all LQTS patients (n = 234; 51%) displayed CI; 64% of patients with LQT1 (n = 157), 37% with LQT2 (n = 46), and 33% with LQT3 (n = 31). Patients with LQT1 were most likely to exhibit CI compared to patients with LQT2 (p < .0001) and LQT3 (p < .0001). CI was significantly more common in LQT1 compared to controls (p < .0001), while there was no difference between LQT2 (p = .5) or LQT3 and controls (p > .9). Presence of CI was not a predictor of LQTS‐associated symptoms, BB side effects or likelihood of future breakthrough cardiac events (BCE).ConclusionsPatients with LQTS, particularly LQT1, demonstrate a SAN phenotype of CI. If assessing BB therapy effect by impact on peak HR, the patient's pretreatment peak HR, rather than an age‐ and gender‐predicted maximum HR, should be used.

BACKGROUND: Long QT syndrome is a lethal arrhythmia syndrome, frequently caused by rare loss-of-function variants in the potassium channel encoded by KCNH2 . Variant classification is difficult, often because of lack of functional data. Moreover, variant-based risk stratification is also complicated by heterogenous clinical data and incomplete penetrance. Here we sought to test whether variant-specific information, primarily from high-throughput functional assays, could improve both classification and cardiac event risk stratification in a large, harmonized cohort of KCNH2 missense variant heterozygotes. METHODS: We quantified cell-surface trafficking of 18 796 variants in KCNH2 using a multiplexed assay of variant effect (MAVE). We recorded KCNH2 current density for 533 variants by automated patch clamping. We calibrated the strength of evidence of MAVE data according to ClinGen guidelines. We deeply phenotyped 1458 patients with KCNH2 missense variants, including QTc, cardiac event history, and mortality. We correlated variant functional data and Bayesian long QT syndrome penetrance estimates with cohort phenotypes and assessed hazard ratios for cardiac events. RESULTS: Variant MAVE trafficking scores and automated patch clamping peak tail currents were highly correlated (Spearman rank-order ρ=0.69; n=433). The MAVE data were found to provide up to pathogenic very strong evidence for severe loss-of-function variants. In the cohort, both functional assays and Bayesian long QT syndrome penetrance estimates were significantly predictive of cardiac events when independently modeled with patient sex and corrected QT interval (QTc); however, MAVE data became nonsignificant when peak tail current and penetrance estimates were also available. The area under the receiver operator characteristic curve for 20-year event outcomes based on patient-specific sex and QTc (area under the curve, 0.80 [0.76–0.83]) was improved with prospectively available penetrance scores conditioned on MAVE (area under the curve, 0.86 [0.83–0.89]) or attainable automated patch clamping peak tail current data (area under the curve, 0.84 [0.81–0.88]). CONCLUSIONS: High-throughput KCNH2 variant MAVE data meaningfully contribute to variant classification at scale, whereas long QT syndrome penetrance estimates and automated patch clamping peak tail current measurements meaningfully contribute to risk stratification of cardiac events in patients with heterozygous KCNH2 missense variants.

BACKGROUND: Genetic testing for cardiac channelopathies is the standard of care. However, many rare genetic variants remain classified as variants of uncertain significance (VUS) due to lack of epidemiological and functional data. Whether deep protein language models may aid in VUS resolution remains unknown. Here, we set out to compare how 2 deep protein language models perform at VUS resolution in the 3 most common long-QT syndrome–causative genes compared with the gold-standard patch clamp. METHODS: A total of 72 rare nonsynonymous VUS (9 KCNQ1, 19 KCNH2 , and 50 SCN5A ) were engineered by site-directed mutagenesis and expressed in either HEK293 cells or TSA201 cells. Whole-cell patch-clamp technique was used to functionally characterize these variants. The protein language models, evolutionary scale modeling, version 1b and AlphaMissense, were used to predict the variant effect of missense variants and compared with patch clamp. RESULTS: Considering variants in all 3 genes, the evolutionary scale modeling, version 1b model had a receiver operating characteristic curve–area under the curve of 0.75 ( P =0.0003). It had a sensitivity of 88% and a specificity of 50%. AlphaMissense performed well compared with patch-clamp with an receiver operating characteristic curve-area under the curve of 0.85 ( P <0.0001), sensitivity of 80%, and specificity of 76%. CONCLUSIONS: Deep protein language models aid in VUS resolution with high sensitivity but lower specificity. Thus, these tools cannot fully replace functional characterization but can aid in reducing the number of variants that may require functional analysis.

Abstract Background and Aims Type 1 long QT syndrome (LQT1) is caused by pathogenic variants in the KCNQ1-encoded Kv7.1 potassium channels, which pathologically prolong ventricular action potential duration (APD). Herein, the pathologic phenotype in transgenic LQT1 rabbits is rescued using a novel KCNQ1 suppression-replacement (SupRep) gene therapy. Methods KCNQ1-SupRep gene therapy was developed by combining into a single construct a KCNQ1 shRNA (suppression) and an shRNA-immune KCNQ1 cDNA (replacement), packaged into adeno-associated virus serotype 9, and delivered in vivo via an intra-aortic root injection (1E10 vg/kg). To ascertain the efficacy of SupRep, 12-lead electrocardiograms were assessed in adult LQT1 and wild-type (WT) rabbits and patch-clamp experiments were performed on isolated ventricular cardiomyocytes. Results KCNQ1-SupRep treatment of LQT1 rabbits resulted in significant shortening of the pathologically prolonged QT index (QTi) towards WT levels. Ventricular cardiomyocytes isolated from treated LQT1 rabbits demonstrated pronounced shortening of APD compared to LQT1 controls, leading to levels similar to WT (LQT1-UT vs. LQT1-SupRep, P &lt; .0001, LQT1-SupRep vs. WT, P = ns). Under β-adrenergic stimulation with isoproterenol, SupRep-treated rabbits demonstrated a WT-like physiological QTi and APD90 behaviour. Conclusions This study provides the first animal-model, proof-of-concept gene therapy for correction of LQT1. In LQT1 rabbits, treatment with KCNQ1-SupRep gene therapy normalized the clinical QTi and cellular APD90 to near WT levels both at baseline and after isoproterenol. If similar QT/APD correction can be achieved with intravenous administration of KCNQ1-SupRep gene therapy in LQT1 rabbits, these encouraging data should compel continued development of this gene therapy for patients with LQT1.

Abstract Background Short QT syndrome type 1 (SQT1) is a genetic channelopathy characterized by gain-of-function variants in the KCNH2-encoded potassium channel underlying the IKr current, leading to a pathologically shortened cardiac action potential duration (APD). Patients with SQT1 manifest shortening of the QT duration on 12-lead ECG and are prone to cardiac arrhythmias that can culminate in sudden cardiac death. Purpose To investigate the effect of a KCNH2-specific suppression-replacement (KCNH2-SupRep) gene therapy on the pathogenic phenotype in transgenic SQT1 rabbits. Methods A novel dual-component KCNH2-SupRep gene therapy was developed by combining a custom-designed KCNH2 shRNA (suppression) and an shRNA-immune (shIMM) KCNH2 cDNA (replacement) into AAV9. In vivo AAV9-mediated KCNH2-SupRep / sham treatment was performed by intra-aortic root injection of the KCNH2-SupRep AAV9 (1E10 vg/kg) / NaCl 0.9% during balloon occlusion using a Swan Ganz catheter. Three weeks after administration, 12-lead ECGs were assessed in adult transgenic SQT1 (KCNH2-N588K, gain of IKr due to impaired inactivation) and wild-type (WT) rabbits to determine the effect of KCNH2-SupRep / sham treatment on the rabbit’s QTc duration and QT index. Patch-clamp recordings were performed in isolated ventricular cardiomyocytes (CMs) to evaluate the effect of KCNH2-SupRep / sham treatment on the CM’s action potential duration at 90% repolarization (APD90). Results After in vivo AAV9-mediated KCNH2-SupRep gene therapy injection (1E10 vg/kg) in 7 SQT1 rabbits, QTc duration and QT index significantly increased in all SQT1 rabbits (QTc: untreated(UT)-SQT1: 153.2±3.8ms vs treated-SQT1: 166.5±4.6ms, p=0.0002, N=7 each; QTi: UT-SQT1: 92.5±1.9% vs treated-SQT1: 99.7±2.7%, p=0.0007, N=7 each), reaching a QT index of ~100% typically observed in WT rabbits. No such changes were observed in the sham-SQT1 rabbits. Furthermore, cardiomyocytes isolated from 7 SQT1 rabbits that received in vivo SupRep gene therapy demonstrated APD90 prolongation closer to WT rabbits compared to UT-SQT1 and sham-SQT1 rabbits (APD90: UT-SQT1: 314.2±11.9ms, WT: 404.5±13.8ms, treated-SQT1: 362.9±10.6ms; UT-SQT1 vs WT: p&lt;0.0001; UT-SQT1 vs treated-SQT1: p=0.019; WT vs Treated-SQT1: p=0.031). In line with these observations, first IKr measurements demonstrate smaller IKr currents in SupRep-SQT1 than in sham-SQT1 CMs. Conclusion In vivo KCNH2-SupRep gene therapy normalizes the pathologically shortened QTc duration and QT index in transgenic SQT1 rabbits. Moreover, KCNH2-SupRep treatment prolongs APD90 in SQT1 compared to UT-SQT1 and sham-SQT1 reaching levels closer to WT.

Abstract Background Long-QT syndrome type 1 (LQT1) is a genetic channelopathy characterized by loss-of-function variants in the repolarizing potassium channel KCNQ1/IKs which lead to QT-prolongation and predisposes patients to adverse events such as cardiac arrhythmias. Clincally, during catecholamine infusion or exercise stress test, patients with LQT1 present a paradoxical QT prolongation. Purpose To investigate whether a gene-therapy approach targeting the defective K+-channel, through a KCNQ1 suppression-and-replacement (SupRep) strategy, can restore the healthy phenotype at baseline and under catecholamine infusion in LQT1 transgenic rabbits. Methods Our proprietary dual component suppression-and-replacement (SupRep) gene therapy was created by combining a custom-designed KCNQ1 shRNA and a shRNA-immune (shIMM) KCNQ1 cDNA into AAV9. In vivo KCNQ1-SupRep gene therapy was performed by targeted intra-aortic root injection during balloon occlusion. Two or three weeks post gene therapy, 12-lead ECGs were assessed in adult transgenic LQT1 (KCNQ1-Y315S, loss-of IKs) and wild-type (WT) rabbits to determine the effect of SupRep gene therapy on QT-duration at baseline and under catecholamine infusion (10nM isoproterenol, 5mL/h). Ventricular cardiomyocytes (VCMs) were isolated to investigate the effect of SupRep gene therapy on action potential duration (APD) and calcium transients (Ca2+T) at baseline and under isoproterenol infusion. Results At the cellular level, VCMs isolated from SupRep treated LQT1 rabbits showed a significant shortening of the APD90 as compared to UT-LQT1 (p&lt;0.0001). At the whole animal level, at baseline, the QTi (%) of the UT-LQT1 transgenic rabbits (122±3) was significantly longer compared to the WT rabbits (105±2, p&lt;0.0001). Treatment with AAV9-KCNQ1-SupRep shortened significantly the QTi of the transgenic LQT1 rabbits as compared to the UT-LQT1 rabbits (111±2, p=0.0115). To further investigate the effect of SupRep gene therapy, 12-lead ECGs were obtained in UT-LQT1, sham-treated LQT1, SupRep-treated LQT1, and WT rabbits under ISO infusion. While reaching a 20% increase in heart rate during ISO stimulation, the UT-LQT1 and the sham treated LQT1 rabbits showed a marked QT prolongation, with ΔQTi of 31.4% and 24.5%, respectively, as compared to baseline. In contrast, the SupRep-treated LQT1 rabbit behaved nearly identical to the WT rabbit during ISO infusion, showing a ΔQTi of 16.9% as compared to 16.5% in the WT rabbit. Similarly, in contrast to the UT-LQT1, VCMs isolated from SupRep-treated LQT1 rabbits demonstrated a normalization of the APD and Ca2+T under ISO stimulation, showing a significantly shortened APD90 (p&lt;0.0001) and Ca2+T90 (p=0.0025) which was similar to what was observed in WT VCMs. Conclusion In vivo KCNQ1 suppression-and-replacement gene therapy normalizes the pathologically prolonged APD/QT interval and restores a physiological response to catecholamine infusion in treated LQT1 transgenic rabbits.