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Background: Genes encoding sodium channel interacting proteins (ChIPs) have been identified as novel long QT syndrome (LQTS)-susceptibility genes. Approximately 25% of patients with LQTS remain genotype negative. ChIPs comprising the sodium channel macromolecular complex represent attractive candidates for disease susceptibility. Previously, in human jejunal circular smooth muscle, we demonstrated that syntrophin γ2 regulates sodium channel gating by a PDZ-domain interaction involving the C-terminus. In the heart, syntrophin α is more highly expressed than γ2, therefore, syntrophin α was evaluated as a possible LQTS-susceptibility ChIP. Methods: Comprehensive open reading frame/splice mutational analysis of syntrophin α was performed using PCR, DHPLC, and direct DNA sequencing on a cohort of 50 unrelated patients with LQT1–10 negative/phenotype positive LQTS (34 females; average age at diagnosis 26 ± 16 years; average QTc 531 ± 60.4 ms; QTc range 480 –759 ms). Mutations were engineered by site-directed mutagenesis and transiently expressed in HEK293 cells containing the stably-expressed SCN5A- encoded sodium channel α subunit (hNaV1.5). Results: Analysis of syntrophin α, encoded by SNTA1 , revealed 3 missense mutations in 2 patients (4%). A female diagnosed with LQTS at 13 years (QTc, 480 ms) with family history of autopsy-negative unexplained sudden death, was compound heterozygous for P74L/A257G while a male, diagnosed with LQTS at 18 years following syncopal episodes (QTc, 529 ms), hosted the A390V mutation. These mutations were absent in 600 reference alleles and A257G and A390V involved highly conserved residues. Functional studies revealed a marked leftward shift in sodium current activation for A257G and a significant rightward shift in channel inactivation for A390V-SNTA1. Both kinetic perturbations precipitated a ``gain-of-function” increase in the sodium channel window current. Conclusion: We provide the sentinel report of SNTA1 as a novel LQTS-susceptibility gene with a putative pathogenic mechanism involving a secondary ``gain-of-function” in the NaV1.5 sodium channel. Thus, CAV3-LQTS (LQT9), SCN4B-LQTS (LQT10), and now SNTA1-LQTS represent functional homologues with LQT3-like perturbations.

A-Kinase Anchoring Protein 9 (AKAP9), or Yotiao, binds to the carboxy-terminus (C-T) of the IKs channel alpha subunit KCNQ1 and recruits cAMP-dependent protein kinase A (PKA) and protein phosphatase 1 (PP1) to the channel to control its phosphorylation state. Previously, an inherited LQT1-causing mutation in the KCNQ1 C-T/Yotiao binding domain was shown to disrupt the complex and render the channel functionally insensitive to cAMP-dependent regulation. Despite the critical role of Yotiao in mediating this fundamental physiological response, the large size of the Yotiao protein (over 200 kD) has hindered patient screens and, to date, no disease-linked mutations have been found in this adaptor protein. The objectives of the present study were first to locate reciprocal binding site(s) for KCNQ1 on Yotiao and to test whether mutation(s) in the binding module(s) might cause LQTS. Using GST fusion protein pull down and immunoprecipitation (IP) techniques, we identified two regions in Yotiao necessary for binding to KCNQ1: one within the Yotiao N-terminus (residues 29 – 46), and a second within its C-terminus (1574 –1643). Targeted sequence analysis was then carried out in fifty clinically diagnosed but genotype negative LQTS patients in the coding regions for these two KCNQ1 binding domains in AKAP9-encoded Yotiao. This analysis identified a novel missense mutation, S1570L-Yotiao, present in two siblings diagnosed with LQTS but absent in the normal population. We found that the S1570L mutation, located close to the Yotiao C-T binding motif for KCNQ1, disrupted the interaction between the two proteins and significantly reduced both basal and exogenous cAMP-induced KCNQ1 phosphorylation. Perforated patch experiments in CHO cells revealed that expression of S1570L-Yotiao significantly reduced basal IKS channel activity and completely ablated the response of the IKs channel to cAMP plus the phosphatase inhibitor okadaic acid. These reconstituted cellular consequences of the inherited S1570L-Yotiao mutation are consistent with delayed repolarization of the ventricular action potential observed in the affected siblings. Thus, we have demonstrated for the first time a link between an inherited AKAP mutation and human disease, LQTS.

Introduction: Unstable scar related ventricular tachycardia (VT) is a common problem after myocardial infarction. Aggressive ablation may be limited, however, by incomplete scar penetration with available RF energy delivery technologies. The purpose of this study was to test the feasibility of full thickness linear ablation of infarcted ventricular substrate with a high penetration virtual electrode needle based electrode system. Methods: Chronic infarcted (> 2months) mongrel dogs (35–40 kg) underwent percutaneous catheter ablation of the LV with a saline-injection needle catheter employing an 8 mm 20-GA tip. Constant power at 40W was delivered for 90 sec via the virtual electrode needle during infusion of saline 10 ml/h at 50°C. The lines were created under electroanatomic map guidance and intracardiac ultrasound (ICE). The ejection fraction was monitored immediately before and after the ablation. One week after ablation, the dogs where restudied using CARTO epicardial and endocardial voltage mapping and hemodynamic testing. Results: The ablation lines created by a virtual electrode energy delivery made in the antero-lateral wall showed mean length of 4.4±1.4 cm. The mean area of ablation per lesion in the endocardium, mid myocardium and epicardium was 1.1±1.0, 2.6±1.3 and 1.9±1.3 cm 2 (p<0.05) respectively, with a mean ablation depth of 1.5±0.5 cm. Sixty-four percent of the length of lesions were transmural and in non-transmural areas had an average depth of 90±16% of wall thickness. The mean number of gaps/line was 0.5±0.7 with a length of 0.6 cm. Ejection fraction was 50±14, 52±17 and 52±13% before, after and 1 week post ablation respectively. At one week the epicardial and endocardial areas of low bipolar voltage < 1.5mV and dense scar < 0.5mV in the Carto map were 11.4±1.2 and 7.9±6.1cm 2 respectively which measurements were confirmed at necropsy by macroscopic scar in the epicardium and endocardium of 11.8±4.3 and 6.6±4.1 cm 2 respectively. Conclusion: This new novel saline-injection needle catheter effectively creates continuous long transmural lines in the infarcted LV. These data also confirm that the macroscopic ablation lesions can be consistently and accurately monitored by 3D electroanatomical mapping in both endocardium and epicardium.

Background: In the ACUITY Trial, patients (pts) with chronic renal insufficiency (CRI) had significantly higher rates of ischemic events and major bleeding compared to pts without CRI at 30 days. Bivalirudin (Biv) monotherapy provided similar protection from ischemic events but with significantly less bleeding compared to heparin + a GPIIb/IIIa inhibitor (Hep+GPI). The impact of a Biv alone strategy on one year mortality is unknown. Methods: Pts with moderate and high risk acute coronary syndromes (ACS) were randomized to Hep + GPI, Biv + GPI, or Biv monotherapy. CRI was defined as baseline creatinine clearance (CrCl) <60 mL/min. We evaluated the impact of CRI and antithrombotic strategy on composite ischemia (death, MI, or revascularization) and mortality at one year. Results: Of the pts enrolled, 12,933 had baseline CrCl data: 2468 (19.1%) pts had CrCl ≥60 mL/min and 10,465 (80.9%) pts had CrCl <60 mL/min. Rates of major bleeding at 30 days in pts with CRI were significantly lower with Biv alone vs Hep+GPI (6.2% vs 9.8%, p<0.01). Pts with CRI had higher mortality at one year compared to those without CRI (8.7% vs 3.0%, p<0.001). There was no difference in composite ischemia for pts who received Biv monotherapy vs Hep + GPI (23.0% vs 21.4%, p=0.10). One year mortality by antithrombin strategy is shown in the Figure . Conclusions: CRI in pts with ACS is associated with higher rates of one year mortality. In these high risk pts, Biv monotherapy improved early clinical outcomes compared to Hep + GPI by reducing major bleeding, and resulted in similar rates of one year mortality. Cumulative Mortality at One Year, Patients with CRI

Introduction : Type 1 catecholaminergic polymorphic ventricular tachycardia (CPVT1) is pursuant to mutations in the RyR2- encoded cardiac ryanodine receptor. Recently, we discovered nearly as many CPVT1-causing mutations as LQT3-causing mutations in a large cohort of unrelated LQTS referral patients. Here, we examine potential predictors of RyR2 genotype (CPVT1) among LQTS referral patients. Methods : Previously, comprehensive mutational analysis of the LQT1–10 susceptibility genes was completed for 541 unrelated patients (358 females, average age at diagnosis = 24 years, average QTc = 482 ms) referred for LQTS genetic testing. Using PCR, DHPLC, and DNA sequencing, we performed targeted analysis of RyR2 involving 44 exons (8–15, 37–49, 83–105) for the 260 unrelated referrals (172 females, average age at diagnosis = 25 years, average QTc = 470 ms) that remained “genotype-negative” following LQTS genetic testing. Results : Overall, 22 distinct RyR2 mutations (19 novel) were seen in 23 (8.8%, 12 females, average age at diagnosis = 22 ±14 years) unrelated “genotype-negative” LQTS individuals. Compared to patients with either genetically proven LQTS or the remaining genotype negative cohort, the RyR2 -positive cohort had significantly lower average QTc (419 ms vs 494 ms, p =2.4 ×10 −6 ; vs 472 ms, p = 0.005) and was more likely to experience either syncope (88% vs 66%, p = 0.06 vs 53%, p = 0.008) or cardiac arrest (56% vs 23%, p = 0.006 vs 17%, p = 0.001). Overall, 123 of the 541 LQTS referrals (23%) exhibited exertion-induced cardiac events (68 LQTS gene positive; 42 gene negative, and 13 RyR2-positive). Every RyR2 -positive case with an exertionally-triggered event had a QTc ≤ 460 ms, compared to only 17% of LQTS gene positive cases (p = 0.1 × 10 −8 ) and 24% of LQT1 cases. None of the exertion-induced LQTS gene positive cases had a QTc ≤ 420 ms. Conclusions: Failure to distinguish CPVT from LQTS can be a fatal mistake, as individuals with CPVT1 have a more severe phenotype and are much less protected by beta blocker therapy than those with LQT1. CPVT1, rather than concealed LQT1, should lead the differential diagnosis in the setting of syncope/cardiac arrest during exercise and a normal resting QTc.

Background: The hallmark of Long QT Syndrome (LQTS) is a prolongation of the ventricular electrical action potential caused by mutations involving key cardiac ion channels on the surface membrane of ventricular myocytes. Different mutations are associated with specific modes of arrhythmia initiation and distinct changes in cardiac rhythm prior to these events. We hypothesized that some LQTS-causing mutations might involve the sinus node, leading to aberrations in cardiac rhythm. To test this hypothesis, we examined the features of cardiac rhythm in 23 genotyped patients with LQTS and 14 matched controls (C) using Holter ECG data (6hrs). Methods: QRS-complexes were identified using custom software and verified by an experienced ECG reader; series of sinus beats were extracted and gaps in time series were linearly interpolated. The mean, max, and min heart rate (HR), the time (SD, SDNN, SDANN, RMSSD, pNN50) and frequency-domain (Total (TP), Very low (VLF), Low (LF), High (HF) frequency powers, and LF/HF) indices of heart rate variability (HRV) were calculated in each 5-min interval and over the entire recording. The short-long-short irregularity was examined using the novel multiscale rhythmogenetic analysis (MRA), which quantifies changes in the HRV indices during the transition from one time-scale window to another. Results: The maximum heart rate was slower in LQTS than in C (101±13 and 119±19bpm, p=0.001). The high-frequency power (HF) was lower in LQTS than in C (80±76 and 113±58ms 2 , p<0.05). However, the short-term irregularity (quantified by the difference in RMSSD between the 75ms and 2000ms time scales) was 4 times greater in LQTS compared to C (p=0.003). Inclusion or exclusion of two patents who were on β-blockers did not change the results. Conclusions: LQTS is associated with specific changes in cardiac rhythm, including: diminished acceleration capacity, decreased high-frequency power, and enhanced short-long-short irregularity. This suggests that LQTS involves channel modifications in the sinus node, which might contribute to arrhythmogenesis. Rhythm characterization in genetic sub-types of LQTS might improve arrhythmia risk stratification in this heterogeneous patient population.

Background: Long QT syndrome (LQTS) is a potentially lethal yet highly treatable channelopathy underscored by marked heterogeneity that necessitates evidence-based and individualized therapeutic approaches. One such therapy is the implantable cardioverter defibrillator (ICD). Here, we sought to determine the percentage of patients (pts) with LQTS that received an ICD in our LQTS clinic and its short term outcomes. Methods: An IRB-approved, retrospective analysis of the electronic medical records of 167 LQT1, 113 LQT2, and 29 LQT3 pts evaluated in our LQTS Clinic with subset analysis of those implanted with an ICD in our institution from January 2000 to June 2007. Results: Forty-eight pts (15% of total, 33 females, 14 LQT1, 20 LQT2, and 14 LQT3) received an ICD. The average age at implant was 30 ± 12 years (range 8 – 52 years). Nearly two-thirds received an ICD as primary prevention. The QTc exceeded 500 ms in 18 (37.5%). With an average follow-up of 42 ± 32 months, 9 (19%) have had an appropriate, VF-terminating therapy including 3 with LQT1 and 6 with LQT2. Notably, 5 of the 6 LQT2 females have already received an appropriate ICD therapy whereas none of the LQT3 pts have received one. Secondary prevention indications (p = 0.006), LQT2 genotype (p = 0.03), QTc > 500 ms (p = 0.001), and surprisingly a negative family history (p = 0.0005) predicted those ICD pts most likely to receive an appropriate therapy. Importantly, none of the non-ICD treated pts (> 250) have died a LQT-related death during the same follow-up. Conversely, 9 pts have experienced an inappropriate shock including 6 with LQT3 and males were more likely to receive inappropriate therapies (p = 0.002). Conclusions: The majority of pts with LQTS can be treated effectively without an ICD. In this study, potentially life-saving therapies have been rendered so far at a 5– 6%/year rate. Inappropriate shocks occurred with similar frequency. Secondary prevention, genotype, and QTc predicted those ICD recipients most likely to receive appropriate therapy. Although LQT3 status is commonly associated with an ICD recommendation, so far none of the LQT3 positive ICD recipients have needed their device. Instead, the greatest “save” rate has occurred among the LQT2 positive females deemed at high risk.

Long QT syndrome (LQTS) is a heterogeneous group of channelopathies characterized by increased risk of potentially lethal ventricular arrhythmias. LQT1, LQT2, and LQT3 comprise 95% of genetically proven cases and exhibit a number of established genotype-phenotype correlations. The study aimed at examining the phenotypes of genotype-negative LQTS, accounting for ~25% of LQTS cases. An IRB-approved retrospective analysis was conducted on 56 patients (39 female, 25 ± 17 years) who, after genetic testing either in our sudden death genomics laboratory or with the commercially available Familion test, were negative for mutations in the 3 principal LQTS-susceptibility genes ( KCNQ1, KCNH2, and SCN5A), and the minor genes underlying LQT5 and LQT6. All had been diagnosed with LQTS, with a clinical diagnostic score of ≥ 3.5 or QTc ≥ 480 ms. The mean diagnostic score was 4.4 (95% CI 4.2 – 4.7); mean QTc was 525 ms (95% CI 508 – 543 ms). Two-thirds were symptomatic (syncope, cardiac arrest, and/or seizures) with exercise-triggered events in 10 (26%). Twenty-one (38%) had a family history of sudden cardiac arrest. ECG showed a T wave pattern suggestive of LQT1 in 32%, LQT2 in 43%, and LQT3 in 18%. In those with exercise-induced symptoms, the ECG was LQT2-like in 50% and LQT1-like in 30%. One patient had post-partum syncope with an LQT2-like ECG. None had an auditory trigger, but 3 patients, all with an LQT2-like ECG, had a family history of auditory-triggered events. One-third of the patients had received an ICD, 58% as secondary prevention. Over 2/3 were on beta-blockers. Among the 45 patients so far tested for mutations in minor LQTS-susceptibility genes, 2 had LQTS-causing mutations in ANKB (LQT4), 1 in SCN4B (LQT10), 1 in AKAP9 (LQT11) and 2 in SNTA1 (LQT12). Genotype-negative patients with a firm LQTS diagnosis show marked phenotypic heterogeneity, suggesting multiple underlying pathogenic pathways. Only a few patients have LQTS-causing mutations in minor genes after complete LQT1–12 genetic testing. Classifying genotype negative patients into LQT1-, LQT2-, or LQT3-like profiles may guide the discovery of novel genes encoding channel interacting proteins corresponding to those specific signaling pathways.

Cardiac I Kr is a critical repolarizing current in the heart and a target for inherited and acquired long QT syndrome. Biochemical studies show that native I Kr channels are heteromers composed of both hERG 1a and 1b subunits, yet our current understanding of I Kr functional properties derives primarily from studies of homo-oligomers of the original hERG 1a isolate. The hERG 1a and 1b subunits are identical except at the amino (NH2) terminus, which in hERG 1b is much shorter and has a unique primary sequence. We compared the biophysical properties of currents produced by hERG 1a and 1a/1b channels expressed in HEK-293 cells at near-physiological temperatures. We found that heteromeric hERG 1a/1b currents are much larger than hERG 1a currents and conduct 80% more charge during an action potential. This surprising difference corresponds to a two-fold increase in the apparent rates of activation and recovery from inactivation, which reduces rectification and facilitates current rebound during repolarization. Kinetic modeling shows these gating differences account quantitatively for the differences in current amplitude between the two channel types. Depending on the action potential model used, loss of 1b predicts an increase in action potential duration of 27 ms (7%) or 41 ms (17%), respectively. Drug sensitivity was also different. Compared to homomeric 1a channels, heteromeric 1a/1b channels were inhibited by E-4031 with a slower time course and a corresponding four-fold positive shift in the IC 50 . Differences in current kinetics and drug sensitivity were modeled by “NH2 mode” gating with conformational states bound by the amino terminus in hERG 1a homomers but not 1a/1b heteromers. The importance of hERG 1b in vivo is supported by the identification of a 1b-specific A8V missense mutation in 1/269 unrelated genotype-negative LQTS patients and absent in 400 control alleles. Mutant 1bA8V expressed alone or with hERG 1a in HEK-293 cells nearly eliminated 1b protein. Thus, mutations specifically disrupting hERG 1b function are expected to reduce cardiac I Kr , prolong QT interval and enhance drug sensitivity, thus representing a potential mechanism underlying inherited or acquired LQTS.

Introduction: Left atrial appendage (LAA) flow depends largely on left ventricular compliance and may play a role in mediating the regulation of left atrial volume-pressure relationships. Hypothesis: We hypothesize that LAA emptying flow velocity (LAAEV) is a predictive factor of long-term outcomes (e.g. recurrent AF, stroke, and survival) after cardioversion for non-valvular AF. Method: We identified 3,251 consecutive patients with non-valvular AF who underwent successful TEE-guided electrical cardioversion (ECV) at our institution between May 2000 and March 2012. Successful ECV was defined as sinus rhythm at time of discharge from the cardioversion unit. Patients were monitored following their ECV procedure for first documentation of recurrent AF, stroke or death. Multivariate Cox proportional hazards models were used to identify independent predictors of long-term outcomes. Patients with >= moderate valvular regurgitation or stenosis were excluded. Results: Among the 3,251 patients who were successfully cardioverted to sinus rhythm, the mean (±SD) LAAEV was 38.43±23 cm/s and the median was 33 cm/s, (interquartile range [IQR], 20-50). Patients with LAAEV <=33 cm/s had higher CHA 2 DS 2 -VASc score (2.6±1.2 vs. 1.9±1.3, P =.009), larger LAVI (52.0±20.9 cc/m 2 vs. 43.3±13.6 cc/m 2 , P <.001) than those with LAAEV >33 cm/s. Pre or post-procedure antiarrhythmic drug use was similar between the two groups. During 1-year follow-up, patients with LAAEV <=33 cm/s had significantly higher rate of AF recurrence than those with LAAEV >33 cm/s (55% vs 45%, P <.001). Likewise, during a mean follow-up of 4.9±3.6 years, similar patterns in 5-year rates were observed for first recurrence of AF (81% vs 73%, P <.001), stroke (7% vs 4%, P =.003) and mortality (31% vs 23%, P <.001) for LAAEV <=33 vs > 33cm/s, respectively. Stepwise multivariate Cox regression analysis revealed that LAAEV <=33 cm/s, age, CHA 2 DS 2 -VASc score were independent predictors of AF recurrence, stroke and mortality. Conclusions: LAA emptying flow velocity is an effective and convenient method for risk stratification of patients undergoing cardioversion for AF. Our data showed that patients with reduced LAAEV have an increased risk for AF recurrence, stroke and death following electrical cardioversion.