Background: Aortic stenosis (AS) initiates a series of molecular alterations that predate cardiac remodeling and development of heart failure (HF). We hypothesized that integrating circulating mediators (proteome) from large-scale epidemiological cohorts with their cell-specific gene expression in the heart (transcriptome) may prioritize novel targets in human AS. Methods: Among individuals with severe AS, we measured the circulating proteome (Olink) and examined associations with myocardial structure/function (N=519), cardiac MRI-based tissue fibrosis (N=145), and clinical outcomes (N=802). We constructed proteomic signatures of cardiac remodeling and tested their association with mortality and HF in the UK Biobank (UKBB; N=36,668). We then examined a "remodeling proteome” prioritized by proteome-phenotype relations at the transcriptional level via single nuclear RNA-sequencing in 20 human hearts (11 with AS at the time of SAVR and 9 donor hearts unused for transplant). Results: We identified three principal components (PCs) of cardiac remodeling (across 12 echocardiographic measures in 503 patients with severe AS) loaded on cardiac morphology, systolic, and diastolic function traits. Proteins associated with these PCs specified both known and novel mediators of fibrosis, LVH, and oxidative stress. Proteomic signatures were strongly linked to mortality (AS cohort, UKBB) and incident HF (UKBB). At a myocardial level, we observed cell-specific differential gene expression, particularly prominent in fibroblasts, cardiomyocytes, and endothelial cells, featuring convergent fibrosis pathways ( WNT9A , ITGA6 , AGRN , CRIM1 , SEMA4C , LAYN, PTX3 , HMOX1 ) and metabolic-inflammatory signaling ( ENPP2/ATX, TNF), among others. Conclusions: Proteo-transcriptional prioritization in human AS identifies both known and novel targets that are mechanistically relevant to HF pathogenesis. Future integrative studies that link longitudinal circulating biomarkers in large-scale cohorts directly to myocardial tissue are warranted to inform pathways of HF progression.

Structural or electrophysiologic cardiac anomalies may compromise cardiac function, leading to sudden cardiac death (SCD). Genetic screening of families with severe cardiomyopathies underlines the role of genetic variations in cardiac-specific genes. The present study details the clinical and genetic characterization of a malignant dilated cardiomyopathy (DCM) case in a 1-year-old Mexican child who presented a severe left ventricular dilation and dysfunction that led to SCD. A total of 132 genes (48 structure- and 84 electrical-related genes) were examined by next generation sequencing to identify potential causative mutations in comparison to control population. In silico analysis identified only two deleterious heterozygous mutations within an evolutionarily well-conserved region of the sarcomeric genes ACTC1/cardiac actin (c.664G > A/p.Ala222Thr) and TTN/titin (c.33250G > A/p.Glu11084Lys). Further pedigree analysis revealed the father of the index case to carry with the TTN mutation. Surprisingly, the ACTC1 mutation was not harbored by any first-degree family member. Computational 3D modeling of the mutated proteins showed electrostatic and conformational shifts of cardiac actin compared to wild-type version, as well as changes in the stability of the compact/folded states of titin that normally contributes to avoid mechanic damage. In conclusion, our findings suggest a likely pathogenic de novo mutation in ACTC1 in coexpression of a TTN variant as possible causes of an early onset of a severe DCM and premature death. These results may increase the known clinical pathogenic variations that may critically alter the structure of the heart, whose fatality could be prevented when rapidly detected.

We have previously shown that the Myh6 promoter drives Cre expression in a subset of male germ line cells in three independent Myh6-Cre mouse lines, including two transgenic lines and one knock-in allele. In this study, we further compared the tissue-specificity of the two Myh6-Cre transgenic mouse lines, MDS Myh6-Cre and AUTR Myh6-Cre, through examining the expression of tdTomato (tdTom) red fluorescence protein in multiple internal organs, including the heart, brain, liver, lung, pancreas and brown adipose tissue. Our results show that MDS Myh6-Cre mainly activates tdTom reporter in the heart, whereas AUTR Myh6-Cre activates tdTom expression significantly in the heart, and in the cells of liver, pancreas and brain. In the heart, similar to MDS Myh6-Cre, AUTR Myh6-Cre activates tdTom in most cardiomyocytes. In the other organs, AUTR Myh6-Cre not only mosaically activates tdTom in some parenchymal cells, such as hepatocytes in the liver and neurons in the brain, but also turns on tdTom in some interstitial cells of unknown identity.

We identified two different inherited mutations in KCNH2 gene, or human ether-a-go-go related gene (hERG), which are linked to Long QT Syndrome. The first mutation was in a 1-day-old infant, whereas the second was in a 14-year-old girl. The two KCNH2 mutations were transiently transfected into either human embryonic kidney (HEK) cells or human induced pluripotent stem-cell derived cardiomyocytes. We performed associated multiscale computer simulations to elucidate the arrhythmogenic potentials of the KCNH2 mutations. Genetic screening of the first and second index patients revealed a heterozygous missense mutation in KCNH2, resulting in an amino acid change (P632L) in the outer loop of the channel and substitution at position 428 from serine to proline (S428P), respectively. Heterologous expression of P632L and S428P into HEK cells produced no hERG current compared to the wild type (WT). Moreover, the co-transfection of WT and P632L yielded no hERG current; however, the co-transfection of WT and S428P yielded partial hERG current. Action potentials were prolonged in a complete or partial blockade of hERG current from computer simulations which was more severe in Purkinje than ventricular myocytes. Three dimensional simulations revealed a higher susceptibility to reentry in the presence of hERG current blockade. Our experimental findings suggest that both P632L and S428P mutations may impair the KCNH2 gene. The Purkinje cells exhibit a more severe phenotype than ventricular myocytes, and the hERG current blockade renders the ventricles an arrhythmogenic substrate from computer modeling.

ABSTRACTCardiac allograft vasculopathy (CAV) is the leading cause of late allograft failure and mortality after heart transplantation. As current standards of diagnosis and treatment of CAV have significant limitations, understanding cell-specific responses may prove critical for developing improved detection strategies and novel therapeutics. This study is the first to successfully utilize human endomyocardial biopsy (EMB) samples to isolate large numbers of intact nuclei for single-nuclear transcriptomics. These data also lay the groundwork for ongoing experiments to study serial, routinely-collected EMB specimens after heart transplantation to identify novel biomarkers and pathways through which early CAV pathogenesis can be interrupted, thereby prolonging allograft survival.

Cardiac arrhythmias are responsible for 200-300 thousand deaths/year. Despite considerable research effort, much remains to be elucidated concerning the underlying mechanisms of arrhythmogenesis. Mutations in transient receptor potential melastatin 4 (TRPM4), a widely expressed Ca 2+ -activated nonselective cation channel, have been associated with causing cardiac arrhythmias. However, direct genotype-phenotype correlation of arrhythmogenic TRPM4 mutant variants are often complicated, as this channel is not primary to the cardiac action potential. Here, we assessed the electrophysiological and post-transcriptional molecular properties of a single mutation (R892C)-TRPM4 associated with short QT syndrome (SQTS) and a triple mutation (R250C|A432T|G582S)-TRPM4 associated with long QT syndrome (LQTS), using stably transfected HEK293 cells. Overall, protein expression of the triple mutant was found to be significantly reduced, with increased proteasomal degradation, but enhanced SUMOylation, as compared to either WT or the single R892 mutant TRPM4 channel. Consequently, expression of R250C|A432T|G582S-TRPM4 was significantly lower at the cellular membrane than either R892C- and WT-TRPM4. In contrast, while total expression of TRPM4 was not significantly different between WT and the R892C single mutant, although the R892C exhibited increase aggregation. Patch-clamp cellular electrophysiology experiments indicated that both single and triple TRPM4 mutant channels could be activated by lower Ca 2+ concentrations compared to WT. However, R892C-TRPM4 channels inactivated faster, while R250C|A432T|G582S-TRPM4 channels inactivated much slower compared to WT. These data as obtained in our homologous recombinant overexpression system reveal that while the R892C-TRPM4 mutant variant exhibited normal-to-higher levels of expression and increased Ca 2+ -activation sensitivity, its tendency to aggregate combined with faster inactivation can result in overall loss-of-function compared to WT, correlative with SQTS. Conversely, while the R250C|A432T|G582S-TRPM4 mutant variant exhibited reduced expression and perturbed trafficking, its increased Ca 2+ -activation sensitivity and slow inactivation can result in overall gain-of-function compared to WT, correlative with LQTS.

Approximately 50% of all heart failure (HF) diagnoses can be classified as HF with preserved ejection fraction (HFpEF). HFpEF is more prevalent in females compared with males, but the underlying mechanisms are unknown. We previously showed that pressure overload (PO) in male felines induces a cardiopulmonary phenotype with essential features of human HFpEF. The goal of this study was to determine if slow progressive PO induces distinct cardiopulmonary phenotypes in females and males in the absence of other pathological stressors. Female and male felines underwent aortic constriction (banding) or sham surgery after baseline echocardiography, pulmonary function testing, and blood sampling. These assessments were repeated at 2 and 4 mo postsurgery to document the effects of slow progressive pressure overload. At 4 mo, invasive hemodynamic studies were also performed. Left ventricle (LV) tissue was collected for histology, myofibril mechanics, extracellular matrix (ECM) mass spectrometry, and single-nucleus RNA sequencing (snRNAseq). The induced pressure overload (PO) was not different between sexes. PO also induced comparable changes in LV wall thickness and myocyte cross-sectional area in both sexes. Both sexes had preserved ejection fraction, but males had a slightly more robust phenotype in hemodynamic and pulmonary parameters. There was no difference in LV fibrosis and ECM composition between banded male and female animals. LV snRNAseq revealed changes in gene programs of individual cell types unique to males and females after PO. Based on these results, both sexes develop cardiopulmonary dysfunction but the phenotype is somewhat less advanced in females. NEW & NOTEWORTHY We performed a comprehensive assessment to evaluate the effects of slow progressive pressure overload on cardiopulmonary function in a large animal model of heart failure with preserved ejection fraction (HFpEF) in males and females. Functional and structural assessments were performed at the organ, tissue, cellular, protein, and transcriptional levels. This is the first study to compare snRNAseq and ECM mass spectrometry of HFpEF myocardium from males and females. The results broaden our understanding of the pathophysiological response of both sexes to pressure overload. Both sexes developed a robust cardiopulmonary phenotype, but the phenotype was equal or a bit less robust in females.

Cardiac arrhythmias are responsible for 200-300 thousand deaths/year. Despite considerable research effort, much remains to be elucidated concerning the underlying mechanisms of arrhythmogenesis. Mutations in transient receptor potential melastatin 4 (TRPM4), a widely expressed Ca 2+ -activated nonselective cation channel, have been associated with causing cardiac arrhythmias. However, direct genotype-phenotype correlation of arrhythmogenic TRPM4 mutant variants are often complicated, as this channel is not primary to the cardiac action potential. Here, we assessed the electrophysiological and post-transcriptional molecular properties of a single mutation (R892C)-TRPM4 associated with short QT syndrome (SQTS) and a triple mutation (R250C|A432T|G582S)-TRPM4 associated with long QT syndrome (LQTS), using stably transfected HEK293 cells. Overall, protein expression of the triple mutant was found to be significantly reduced, with increased proteasomal degradation, but enhanced SUMOylation, as compared to either WT or the single R892 mutant TRPM4 channel. Consequently, expression of R250C|A432T|G582S-TRPM4 was significantly lower at the cellular membrane than either R892C- and WT-TRPM4. In contrast, while total expression of TRPM4 was not significantly different between WT and the R892C single mutant, although the R892C exhibited increase aggregation. Patch-clamp cellular electrophysiology experiments indicated that both single and triple TRPM4 mutant channels could be activated by lower Ca 2+ concentrations compared to WT. However, R892C-TRPM4 channels inactivated faster, while R250C|A432T|G582S-TRPM4 channels inactivated much slower compared to WT. These data as obtained in our homologous recombinant overexpression system reveal that while the R892C-TRPM4 mutant variant exhibited normal-to-higher levels of expression and increased Ca 2+ -activation sensitivity, its tendency to aggregate combined with faster inactivation can result in overall loss-of-function compared to WT, correlative with SQTS. Conversely, while the R250C|A432T|G582S-TRPM4 mutant variant exhibited reduced expression and perturbed trafficking, its increased Ca 2+ -activation sensitivity and slow inactivation can result in overall gain-of-function compared to WT, correlative with LQTS.

Acute cardiac injury is prevalent in critical COVID-19 and associated with increased mortality. Its etiology remains debated, as initially presumed causes - myocarditis and cardiac necrosis - have proved uncommon. To elucidate the pathophysiology of COVID-19-associated cardiac injury, we conducted a prospective study of the first 69 consecutive COVID-19 decedents at CUIMC in New York City. Of 6 acute cardiac histopathologic features, presence of microthrombi was the most commonly detected among our cohort. We tested associations of cardiac microthrombi with biomarkers of inflammation, cardiac injury, and fibrinolysis and with in-hospital antiplatelet therapy, therapeutic anticoagulation, and corticosteroid treatment, while adjusting for multiple clinical factors, including COVID-19 therapies. Higher peak erythrocyte sedimentation rate and C-reactive protein were independently associated with increased odds of microthrombi, supporting an immunothrombotic etiology. Using single-nuclei RNA-sequencing analysis on 3 patients with and 4 patients without cardiac microthrombi, we discovered an enrichment of prothrombotic/antifibrinolytic, extracellular matrix remodeling, and immune-potentiating signaling among cardiac fibroblasts in microthrombipositive, relative to microthrombi-negative, COVID-19 hearts. Non-COVID-19, nonfailing hearts were used as reference controls. Our study identifies a specific transcriptomic signature in cardiac fibroblasts as a salient feature of microthrombi-positive COVID-19 hearts. Our findings warrant further mechanistic study as cardiac fibroblasts may represent a potential therapeutic target for COVID-19-associated cardiac microthrombi.

the LV unipolar lead with appropriate sensing, impedance, and capture thresholds with the new RV lead.Conclusion: This patient was referred for system revision for inadequate sensing on her ICD lead, however, after DFTs we determined that she had suffered a conductor fracture in the lead, which also raised questions about her unipolar epicardial LV lead.Revision of the RV lead, although not for the original problem prompting referral, fixed her system.

Introduction: Approximately 50% of all heart failure (HF) diagnoses can be classified as HF with preserved ejection fraction (HFpEF), which has no FDA approved therapies. HFpEF is more prevalent in females compared to males, but the underlying mechanisms for the development as a sex-based disorder are unknown. We previously described how slow progressive pressure overload (PO) in male felines recapitulates the HFpEF phenotype but have not investigated the female phenotype. Hypothesis: Females will develop a less severe HFpEF phenotype compared to males under the same pathological stress. Methods & Results: Male (m) and female (f) domestic short felines (age 2mo) underwent aortic constriction (m: n=11; f: n=10) using a customized pre-shaped band or a sham procedure (m: n=7; f: n=7). Before surgery (baseline), there was no difference in body weight (BW) between groups and lung compliance was not different. Echocardiography revealed no significant difference in the ratio of left atrium to aortic root (LA/Ao), LA ejection fraction (LA EF), left ventricle (LV) ejection fraction, LV wall-thickness, and E/A ratio. By 4mo post-surgery, both males and females had developed cardiac dysfunction and decreased lung compliance. At this time, females had significantly smaller BWs than males. Despite the difference in BW, LV wall thickness and changes in E/A ratio were similar in both sexes in banded vs. shams. Importantly, LV EF did not change in any group. There was a decrease in LA EF and increased LA/Ao in all banded animals. Invasive hemodynamics at 4mo post-surgery showed no differences between sexes for the systolic pressure gradient generated by aortic banding. Banded males had higher LV end-diastolic pressure vs. banded females (m: 15.0±2.7mmHg; f: 8.1±1.9mmHg). However, there was a trend towards prolongation of tau and lower dp/dt min in banded females, suggestive of abnormal relaxation. There were no differences between banded males and females in heart weight/BW or cardiomyocyte cross-sectional area and both developed fibrosis. Conclusions: Exposure of male and female felines to PO resulted in similar cardiac hypertrophy, fibrosis, and decreased lung compliance. Females had lower LVEDP than males suggesting they may be protected from diastolic dysfunction.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are used for genetic models of cardiac diseases. We report an arrhythmia syndrome consisting of Early Repolarization Syndrome (ERS) and Short QT Syndrome (SQTS). The index patient (MMRL1215) developed arrhythmia-mediated syncope after electrocution and was found to carry six mutations. Functional alterations resulting from these mutations were examined in patient-derived hiPSC-CMs. Electrophysiological recordings were made in hiPSC-CMs from MMRL1215 and healthy controls. ECG analysis of the index patient showed slurring of the QRS complex and QTc = 326 ms. Action potential (AP) recordings from MMRL1215 myocytes showed slower spontaneous activity and AP duration was shorter. Field potential recordings from MMRL1215 hiPSC-CMs lack a “pseudo” QRS complex suggesting reduced inward current(s). Voltage clamp analysis of ICa showed no difference in the magnitude of current. Measurements of INa reveal a 60% reduction in INa density in MMRL1215 hiPSC-CMs. Steady inactivation and recovery of INa was unaffected. mRNA analysis revealed ANK2 and SCN5A are significantly reduced in hiPSC-CM derived from MMRL1215, consistent with electrophysiological recordings. The polygenic cause of ERS/SQTS phenotype is likely due to a loss of INa due to a mutation in PKP2 coupled with and a gain of function in IK,ATP due to a mutation in ABCC9.

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.

Background. We report an inherited cardiac arrhythmia syndrome consisting of Brugada and Early Repolarization Syndrome associated with variants in SCN9A, PXDNL, and FKBP1B. The proband inherited the 3 mutations and exhibited palpitations and arrhythmia-mediated syncope, whereas the parents and sister, who carried one or two of the mutations, were asymptomatic. Methods and Results. We assessed the functional impact of these mutations in induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) derived from the proband and an unaffected family member. Current and voltage clamp recordings, as well as confocal microscopy analysis of Ca2+ transients, were evaluated in hiPSC-CMs from the proband and compared these results with hiPSC-CMs from undiseased controls. Genetic analysis using next-generation DNA sequencing revealed heterozygous mutations in SCN9A, PXDNL, and FKBP1B in the proband. The proband displayed right bundle branch block and exhibited episodes of syncope. The father carried a mutation in FKBP1B, whereas the mother and sister carried the SCN9A mutation. None of the 3 family members screened developed cardiac events. Action potential recordings from control hiPSC-CM showed spontaneous activity and a low upstroke velocity. In contrast, the hiPSC-CM from the proband showed irregular spontaneous activity. Confocal microscopy of the hiPSC-CM of the proband revealed low fluorescence intensity Ca2+ transients that were episodic in nature. Patch-clamp measurements in hiPSC-CM showed no difference in INa but reduced ICa in the proband compared with control. Coexpression of PXDNL-R391Q with SCN5A-WT displayed lower INa density compared to PXDNL-WT. In addition, coexpression of PXDNL-R391Q with KCND3-WT displayed significantly higher Ito density compared to PXDNL-WT. Conclusion. SCN9A, PXDNL, and FKBP1B variants appeared to alter spontaneous activity in hiPSC-CM. Only the proband carrying all 3 mutations displayed the ERS/BrS phenotype, whereas one nor two mutations alone did not produce the clinical phenotype. Our results suggest a polygenic cause of the BrS/ERS arrhythmic phenotype due to mutations in these three gene variants caused a very significant loss of function of INa and ICa and gain of function of Ito.

Introduction: Cardiac arrhythmias are generally associated with abnormal mutations in ion channel genes. Epilepsy is a disorder of neuronal function, which also involves abnormal channel function. Our Hypothesis: now increasing by demonstration that the etiologies of Brugada syndrome (BrS) and epilepsy may partly overlap. However, only a few genetic studies have addressed a possible link between cardiac and neural channelopathies. Methods: The suspected case and family were underwent thorough medical examination. Fifteen candidate genes were screened for ion channels by direct sequencing. Ion channel variants were cloned by site-directed mutagenesis and studied using patch clamp and confocal microscopy techniques in TSA201 cells. Results: A 36 y/o male with epilepsy showing typical type 1 Brugada pattern ECG during flecainide challenge test and under antiepileptic medication (valproic acid). Cardiac evaluation included a normal echocardiogram and exercise stress test. We identified two mutations (D2130N and A1717G) in CACNA1C and one in KCNE2 (T10M). All mutations are highly conserved. The variants in CACNA1C were located in C terminal and the one in KCNE2 was in N terminal. Functional studies in CACNA1C mutants were co-expressed with CACNB2b and CACNA2D1 . At 0 mV, peak ICa densities were reduced by 85% and 70% in D2130N and A1717G vs. WT respectively. Significant kinetic alterations included a negative shift in V1/2 of inactivation, and positive shift in V1/2 of activation, for D2130N and A1717G, respectively. Confocal study showed D2130N and A1717G conjugated to YFP trafficked normally to the cell membrane. We found a gain-of-function in Ito current when T10M- KCNE2 was co-expressed with KCND3 channels by 55% relative to WT. Conclusion: Our results suggest for the first time that several mutations in CACNA1C leads to a loss of function in ICa and thus can contribute to the development of BrS phenotype. T10M- KCNE2 produces a gain of function in Ito, which further aggravates BrS. Meanwhile, as previously reported, T10M- KCNE2 also produces a loss-of-function of IKr, so it is reasonable to deduce that the mutation is probably responsible for the epilepsy. It once again provides the evidence that anti-epilepsy drug could unmask potential Brugada ECG.

OBJECTIVES:This study sought to evaluate the phenotypic and functional expression of an apparent hotspot mutation associated with short QT syndrome (SQTS).BACKGROUND:SQTS is a rare channelopathy associated with a high risk of life-threatening arrhythmias and sudden cardiac death (SCD).METHODS:Probands diagnosed with SQTS and their family members were evaluated clinically and genetically. KCNH2 wild-type (WT) and mutant genes were transiently expressed in HEK293 cells, and currents were recorded using whole-cell patch clamp and action potential (AP) clamp techniques.RESULTS:KCNH2-T618I was identified in 18 members of 7 unrelated families (10 men; median age: 24.0 years). All carriers showed 100% penetrance with variable expressivity. Eighteen members in 7 families had SCD. The average QTc intervals of probands and all carriers was 294.1 ± 23.8 ms and 313.2 ± 23.8 ms, respectively. Seven carriers received an implantable cardioverter-defibrillator. Quinidine with adequate plasma levels was effective in prolonging QTc intervals among 5 cases, but 3 cases still had premature ventricular contraction or nonsustained ventricular tachycardia. Bepridil successfully prevented drug-refractory ventricular fibrillation in 1 case with 19-ms prolongation of the QTc interval. Functional studies with KCNE2 revealed a significant increase of IKr (rapidly activating delayed rectifier potassium channel) tail-current density in homozygous (119.0%) and heterozygous (74.6%) expression compared with WT. AP clamp recordings showed IKr was larger, and peak repolarizing current occurred earlier in mutant versus WT channels.CONCLUSIONS:We reported the clinical characteristics and biophysical properties of the highly frequent mutation that contributes to genetically identified SQTS probands. These findings extend our understanding of the spectrum of KCNH2 channel defects in SQTS.