Background Long QT syndrome (LQTS) is characterized by a prolonged QT interval on the electrocardiogram (ECG), a risk for sudden cardiac death. A simple 'rule of thumb' method states that if a patient's heart rate is between 60-100 bpm, the QT interval should not be more than half the R-R interval. The clinical accuracy of this method has not been tested in the elderly. Objectives To determine if the 'rule of thumb' to calculate QT interval prolongation, is accurate, compared to the corrected QT interval calculated using Bazett's formula. Secondary objectives include the prevalence of long QT and risk factors for QT prolongation. Methods The QT interval was calculated using Bazett's formula, and the 'rule of thumb' method, from ECG's collected from patients over 60 years old, on their first visit to a geriatric clinical service. Only data from patients with heart rates in the range 60-100 were analyzed. Medications and electrolyte levels were recorded. Results A total of 1000 ECGs were collected. 776 ECGs were included in the study. Prevalence of prolonged QT interval was 37.8% using Bazett's formula. Compared to Bazett's formula, the 'rule of thumb' method had a sensitivity of 65.2% and a specificity of 96.9%. ECG computer analysis calculated QTc was available for 42.5% of the cases and had a sensitivity of 58.1% and specificity of 95.3% compared to Bazett's formula. Of the 23.3% of patients taking medications known to prolong the QT interval only 38.6% had a prolonged QT interval. There was a significant association between QT interval prolongation and hypokalaemia. Conclusion The 'rule of thumb' method to determine QT interval prolongation, has high specificity but low sensitivity. This bedside measure is similar in accuracy to QT determination using an ECG computer analysis calculation in this population of older persons. / MT 2019

Indiana University-Purdue University Indianapolis (IUPUI) / The cardiac voltage-gated sodium channel α subunit Nav1.5 generates the cardiac sodium current, which is essential for the initiation and propagation of the cardiac action potentials. Mutations of SCN5A, the gene that encodes Nav1.5, have been well documented to cause long-QT syndrome (LQTs) by disrupting channel inactivation and increasing late sodium current. Previous studies have revealed the importance of the intracellular loop region between transmembrane domain III and IV of sodium channel α subunit in regulating the fast inactivation. A recent clinical case study reported an infant patient with LQTs carrying a phenylalanine (F) deletion at amino acid 1486 of the Nav1.5 channel. This study reported that the patient showed severe cardiac arrhythmia reflected as LQTs and subsequent ventricular tachycardia, which was refractory to antiarrhythmic drug lidocaine treatment. Therefore, it was hypothesized that the deletion of F1486 on Nav1.5 would substantially alter electrophysiological properties of the channel and reduce the potency of lidocaine on sodium channel. Using HEK293 cells and neonatal rat cardiomyocytes, the F1486del channel was functionally characterized by whole-cell patch clamp techniques. Studies revealed that the deletion of F1486 causes a combination of changes including a loss-of-function alteration reflected as a substantial reduction of peak current density and a number of gain-of-function alterations including reduced channel inactivation, substantial augmentation of late sodium current, and an increase in ramp current. In addition, lidocaine sensitivity was dramatically reduced. By contrast, the voltage for half maximal activation (V1/2) and the time constant for channel deactivation for the F1486del channel were identical to the wild type channels. Using neonatal rat cardiomyocytes, we were able to study the functional consequence of F1484del on action potential duration (APD). Cardiomyocytes expressing F1486del channel have substantial APD prolongation and prominent spontaneous early afterdepolarizations, which likely underlie the subsequent LQTs in the patient. Taken together, despite the reduction in peak current density, the substantial gain-of-function changes are sufficient to cause the APD prolongation, which is a prominent characteristic of LQTs. These findings provide knowledge for understanding the relationships between sodium channel structure, pharmacology and the physiological consequence of sodium channel mutations that underlie LQT3.

Background. Acquired long QT syndrome (aLQTS) is a reversible condition characterized by a pathological prolongation of the QT interval that can lead to a polymorphic ventricular tachycardia known as Torsades de Pointe and sudden cardiac death. Identifying the incidence, onset, and risk factors for aLQTS in intensive care init (ICU) populations has not been studied and may help clinicians develop safe monitoring guidelines to identify patients early preventing devastating outcomes. Objective. The objective of this study was to determine the frequency, temporal onset of occurrence, frequency of medications and host risk factors for aLQTS in an ICU. Method. In a retrospective chart review of 88 subjects, hourly electrocardiographic data collected in an ICU were analyzed for baseline, first long, longest, and final corrected QT intervals (QTc) using Bazett's formula. aLQTS was defined as a QTc interval ≥ 500 milliseconds (ms) or a change in QTc of ≥ 60 ms from baseline. Host risk factors were collected from the physician's dictated history and physicals and nursing admission databases. Names and timing of each medication administered were collected from the medication record. Results. aLQTS occurred in 52.3% of the ICU sample. All subjects positive for aLQTS (n=46) had a mean onset of 7.4 ± 9.4 hours from ICU admission. Subjects who developed aLQTS after ICU admission (n=32) had a mean onset of 10.6 ± 9.5 hours; 14 were positive on ICU admission. A statistically significant difference was noted in subjects receiving QT prolonging medications positive for aLQTS (63.5%, n=33) compared with subjects negative for aLQTS (36.5%, n=19), (X²[1] = 6.38, p = .012). Thirteen subjects (28.3%) developed aLQTS in the absence of a known QT interval prolonging medication. No host risk factors were found to have a significant difference between groups positive and negative for aLQTS. Conclusions. aLQTS was present in approximately one-half of the sample. Approximately a quarter of the subjects developed aLQTS in the absence of a known QT prolonging medication, indicating the importance of frequent QTc monitoring in all patients in ICUs. Larger studies to determine common host risk factors associated with aLQTS in ICU populations are warranted.

Commonly prescribed small molecule drugs can have net-positive and well-understood safety profiles when prescribed individually, but unexpected consequences when taken at the same time. Detection of these drug-drug interactions (DDIs) continues to be a critical and unmet area of translational research. The Centers for Disease Control and Prevention (CDC) estimate that one third of Americans are concurrently taking two or more prescription drugs, and DDIs are estimated to be responsible for 17% of all drug adverse events. The consequences of DDIs can be relatively minor (headache, skin rash) or much more severe (bleeding, liver toxicity). At a cellular level, DDIs can occur as a result of both drugs competing for metabolism (known as pharmacokinetic interactions) or targeting the same protein target or biological pathway (pharmacodynamic interactions). Clinical trials typically focus on the effects of individual drugs, leaving DDIs to usually be discovered only after the drugs have been approved. One of the most carefully studied drug adverse events is long QT syndrome (LQTS), an unexpected change in the heart's electrical activity that can lead to a potentially fatal ventricular tachycardia known as torsades de pointes (TdP). Some patients have genetic mutations that lead to congenital forms of LQTS, while drug-induced LQTS typically occurs via block of the hERG potassium channel (KCNH2) responsible for ventricular repolarization. After a number of high profile drugs were withdrawn from the market due to discovered risk of TdP, the FDA issued guidelines so that pharmaceutical companies could anticipate and test for this side effect before a new drug is approved. These recommendations have helped prevent new QT-prolonging drugs from entering the market, but nonetheless over 180 approved drugs have been associated with drug-induced LQTS. While information on individual QT-prolonging drugs is thus readily available to clinicians, little has remained known about DDIs (QT-DDIs). There are many more commonly prescribed drugs that are safe when given individually but could increase TdP risk when administered together. This troubling situation is compounded by the fact that traditional post-market surveillance algorithms are poorly equipped to sensitively and specifically detect DDIs. Data science – the application of rigorous analytical methods to large datasets – offers an opportunity for predicting previously unknown QT-DDIs. Some biomedical datasets (such as drug-target binding affinities and experiments to determine protein-protein interactions) have been collected explicitly for research, while other valuable datasets (such as electronic health records) were initially recorded for billing purposes. Each data modality has its own important set of advantages and disadvantages, and integrative data science approaches can incorporate multiple types of data to help account for these limitations. In this thesis we develop new data sciences techniques that combine clinical, biological, chemical, and genetic data. These approaches are explicitly designed to be robust to biased and missing data. We apply these new methodologies to (1) predict new QT-DDIs, (2) validate them experimentally, and (3) investigate their molecular and genetic mechanisms. We exemplify this approach in the discovery of a previously unknown QT-DDI between ceftriaxone (cephalosporin antibiotic) and lansoprazole (proton pump inhibitor); importantly, both drugs have no cardiac indications and are safe when given individually. The clinical data mining, drug target prediction, biological network analysis, genetic ancestry prediction, and experimental validation methods described in this thesis form the basis for a comprehensive pipeline to predict QT-DDIs rapidly and robustly. They also provide an opportunity for further enriching our understanding of LQTS biology and ultimately enabling the design of safer drugs.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 192-211).

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20673号 / 医博第4283号 / 新制||医||1024(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 長船 健二, 教授 横出 正之, 教授 山下 潤 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(医学) / 甲第24802号 / 医博第4994号 / 新制||医||1067(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 石見 拓, 教授 近藤 尚己, 教授 湊谷 謙司 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Thesis (DMed (Medicine. Internal Medicine))--University of Stellenbosch, 2007. / Background Although great progress has been made in defining genes conferring the majority of genetic risk in Long QT Syndrome (LQTS) patients, there remains a substantial challenge to explain the widely observed variability in disease expression and phenotype severity, even among family members, sharing the same mutation. Identifying clinical and genetic variables capable of influencing/predicting the clinical phenotype of LQTS patients would allow a more accurate risk stratification, important for determining prognosis, selecting patients for the most appropriate therapy, and counseling asymptomatic mutation carriers (MCs). To address these questions an Italian LQT2 family and a South African Founder LQT1 population have been used. Methods and Results Italian LQT2 family. The proband, a 44-yr-old white woman, presented with ventricular fibrillation and cardiac arrest. Intermittent QT prolongation was subsequently observed and LQT2 was diagnosed following the identification of a missense KCNH2 mutation (A1116V). The proband also carried the common KCNH2 polymorphism K897T on the non-mutant allele. Relatives who carried A1116V without K897T were asymptomatic but some exhibited transient mild QTc prolongation suggesting latent disease. Expression studies in Chinese Hamster Ovary (CHO) cells, demonstrated that the presence of KCNH2-K897T is predicted to exaggerate the IKr reduction caused by the A1116V mutation. These data explain why symptomatic LQTS occurred only in the proband carrying both alleles. South African LQT1 population. The study population involved 320 subjects, 166 MCs and 154 non mutation carriers (NMCs). Off ß-blocker therapy, MCs had a wide range of QTc values (406-676 ms) and a QTc>500 ms was associated with increased risk for cardiac events (OR=4.22; 95%CI 1.12-15.80; p=0.033). We also found that MCs with a heart rate <73 bpm were at significantly lower risk (OR=0.23; 95%CI 0.06-0.86; p=0.035). In a subgroup of patients Baroreflex Sensitivity (BRS) was determined both in presence and absence of ß-blocker therapy. BRS, analyzed in subjects in the 2nd and 3rd age quartiles (age 26-47) to avoid the influence of age, was lower among asymptomatic than symptomatic MCs (11.8±3.5 vs 20.1±10.9 ms/mmHg, p<0.05). A BRS in the lower tertile carried a lower risk of cardiac events (OR 0.13, 95%CI 0.02-0.96; p<0.05). This study also unexpectedly determined that KCNQ1-A341V was associated with greater risk than that reported for large databases of LQT1 patients: A341V MCs were more symptomatic by age 40 (79% vs 30%) and became symptomatic earlier (7±4 vs 13±9 years), both p<0.001. Accordingly, functional studies of KCNQ1-A341V in CHO cells with KCNE1, identified a dominant negative effect of the mutation on wild-type channels. Conclusion Our findings indicate that risk stratification for LQTS patients must be more individually tailored and may have to take into account the specific mutation and probably additional clinical and genetic variables capable of influencing/predicting the clinical phenotype of LQTS patients. As a matter of fact, we have provided evidence that a common KCNH2 polymorphism may modify the clinical expression of a latent LQT2 mutation and the availability of an extended kindred with a common mutation allowed us to highlight that KCNQ1-A341V is associated with an unusually severe clinical phenotype and to identify two autonomic markers, HR and BRS, as novel risk factors.

Thesis (MScMedSc)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Long QT syndrome (LQTS) is a cardiac repolarization disorder affecting every 1:2000-1:3000 individuals. This disease is characterized by a prolonged QT interval on the surface electrocardiogram (ECG) of patients. Symptoms of LQTS range from dizziness and syncope to more severe symptoms such as seizures and sudden cardiac death (SCD). Clinical features of LQTS are a result of the precipitations of Torsades de Pointes, which is a polymorphic form of ventricular tachycardia. A number of genetic forms of LQTS have been identified with more than 700 mutations in 12 different genes leading to disease pathogenesis. However it has been estimated that approximately 25% of patients with compelling LQTS have no mutations within the known LQT genes. This proves to be problematic since treatment regimens depend on the genetic diagnosis of affected individuals. Of the known mutated genes, KCNE2 is associated with LQT6. KCNE2 encodes the beta-subunit of potassium ion channel proteins. These proteins contain cytoplasmic C-terminal domains in which many mutations have been identified. We hypothesize that genes encoding KCNE2-interacting proteins might be identified as disease-causing or modifying genes. The present study aimed to use yeast two-hybrid (Y2H) methodology to screen a pre-transformed cardiac cDNA library in order to identify putative interactors of the C-terminal of KCNE2. Through specific selection methods the number of KCNE2 ligands was reduced from 296 to 83. These interactors were sequenced and 14 were identified as putative interacting proteins. False positive ligands were excluded based on their function and subcellular location. Ultimately three strong candidate ligands were selected for further analysis: Alpha-B crystallin (CRYAB), Filamin C (FLNC) and voltage-dependent anion-selective channel protein 1 (VDAC1). Three-dimensional (3D) co-localization and co-immunoprecipitation were used to verify these proposed interactions and succeeded in doing so. The genes encoding verified interactors will be screened in our SA panel of LQT patients, to potentially identify novel LQT causative or modifying genes. Furthermore, the interactions verified in the present study may shed some light on the mechanism of pathogenesis of LQT causative mutations in KCNE2. / AFRIKAANSE OPSOMMING: Lang QT-sindroom (LQTS) is 'n hart her-polariserende siekte wat elke 1:2000-1:3000 individue affekteer. Hierdie siekte word gekenmerk deur 'n lang QT-interval op die oppervlak elektrokardiogram (EKG) van pasiënte. Simptome van LQTS wissel van duiseligheid en floutes tot meer ernstige simptome soos stuiptrekkings of aanvalle en skielike kardiale dood (SKD). Kliniese kenmerke van LQTS is 'n gevolg van die neerslag van Torsades de Pointes; 'n polimorfiese vorm van ventrikulêre tagikardie. Verskeie genetiese vorms van LQTS is geïdentifiseer met meer as 700 mutasies in 12 verskillende gene wat lei tot siekte patogenese. Dit is ergter beraam dat ongeveer 25% van pasiënte met dwingende LQTS geen mutasies in die bekend LQT gene besit nie. Dit is problematies aangesien siekte behandeling af hang van die genetiese diagnose van geaffekteerde individue. Een van die bekende gemuteerde gene is KCNE2 wat verband hou met LQT6. KCNE2 kodeer die beta-subeenheid van kalium ioonkanaal proteïene. Hierdie proteïene bevat sitoplasmiese C-terminale waarin baie mutasies alreeds geïdentifiseer is. Ons veronderstel dat gene wat proteïene kodeer wat met KCNE2 interaksie toon, geïdentifiseer kan word as siekte veroorsaakende of wysigings gene. Die huidige studie het die gis twee-hibried metode gebruik om 'n vooraf-getransformeerde hart cDNS biblioteek te sif om vermeende protein interaksies van die C-terminaal van KCNE2 te identifiseer. Deur middel van seleksie metodes is die aantal KCNE2 ligande verminder van 296 tot 83. Die identiteit van die proteïene is bekend gemaak deur volgorderbepaling waarna 14 geïdentifiseer is as proteïene wat moontlik interaksie kan toon met KCNE2. Vals positiewe ligande is uitgesluit op grond van hul funksie en subsellulêre lokasering. Drie kandidaat ligande is gekies vir verdere analise: Alfa-B crystallin (CRYAB), Filamin C (FLNC) en spanning-afhanklike anioon-selektiewe kanaal proteïen 1 (VDAC1). Drie-dimensionele (3D) mede-lokalisering en mede-immunopresipitasie tegnieke is gebruik om hierdie voorgestelde interaksies te verifieer en het geslaag om dit te doen. Die gene wat geverifieerde proteïene kodeer, sal gekeur word in ons Suid-Afrikaanse paneel van LQT pasiënte om sodoende potensieel nuwe LQT veroorsakende of wysigings gene te identifiseer. Verder kan die geverifieer interaksies in die huidige studie lig werp op die meganisme van die ontstaan van LQT veroorsakende mutasies in KCNE2. / Harry Crossley Foundation (South Africa) / Stellenbosch University / South African Council for Scientific and Industrial Research / Stella and Paul Loewenstein Charitable and Educational Trust

The mechanical contraction of the heart is tightly coupled to rapid and concerted electrical excitation of the cardiac muscle. This electrical activity is facilitated by a highly synchronized conduction system consisting of channels, pumps, and transporters that facilitate the flow of charged ions between cellular compartments, the cytoplasm, and the interstitial fluid between cells. The biophysical properties of these membrane proteins have been studied for many years, but their role in the generation of potentially lethal cardiac arrhythmias and their interactions with drugs remains an important field of research. The cardiac isoform of the voltage-gated Na+-channel, Nav1.5, has garnered widespread interest because of its role in the generation of electrical impulses in the cardiac myocyte, its association with congenital conduction disorders and acquired cardiac arrhythmias, and its unique pharmacological properties. The Congenital Long QT Syndrome Type 3 (LQT3) arises from heritable mutations in SCN5A - the gene encoding Nav1.5 - that disrupt the inactivation process responsible for imparting a refractory period and that often cause a sustained depolarizing late current (INaL). The gain of function depolarizing currents arising from LQT3 mutant channels cause a prolongation of the ventricular action potential and leave patients susceptible to asynchronous electrical activity, ventricular arrhythmias, and sudden cardiac death. The disruption of channel inactivation can arise through a wide range of modalities, including changes in inactivation voltage-dependence and kinetics, and has been shown to occur with varying degrees of severity. Because of this range of phenotypes there is heterogeneity in the risk factors for arrhythmia and sudden cardiac death and in the utility of Na+-channel blocking antiarrhythmic drugs. Moreover, INaL has been implicated as a proarrhythmic and potentiating factor in several acquired cardiac ailments including heart failure, ischemia, and hypertrophy. There is therefore a large unmet need for improved understanding of INaL and mechanisms of its selective inhibition, and LQT3 mutant channels provide a reliable experimental model for this class of cardiac arrhythmias. This study will employ a combination of electrophysiological and computational methods to unravel mechanisms by which mutant Nav1.5 produces pro-arrhythmic currents and the interactions of different disease-causing mutant channels with a set of clinically relevant antiarrhythmic drugs. Chapter 1 of this study presents a functional characterization of one LQT3 mutation, F1473C, that was discovered in a patient with severe QT prolongation, frequent ventricular arrhythmias, and a poor response to pharmacological intervention. This mutation gives rise to INaL by a mechanism that is functionally distinct from the mechanism discovered previously in the canonical LQT3 mutation, ΔKPQ (1505-1507del), and causes a unique response to channel inhibitors. In order to better understand the mechanisms of this divergent pharmacology, Chapter 2 presents the development of a series of computational models which explore the gating dysfunctions that cause INaL and how these pathological changes can influence the predicted safety and efficacy of pharmacological intervention. These models predict that the majority of mutation- specific drug effects can be attributed to differential mutant channel gating, but raise the possibility that mutations may directly alter the physical chemical interaction between drugs and channels. Finally, Chapter 3 presents an attempt to explore this possibility using an innovative chemical biology technique - the site-specific incorporation of unnatural amino acids - that allows for the measurement of precise chemical interactions hypothesized to vary in a mutation-dependent manner. The findings presented in this work promote the need for patient-specific screening of antiarrhythmic agents and lay the groundwork for the use of in silico systems analysis of cardiovascular pharmacology.