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      Inherited arrhythmias: The cardiac channelopathies

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          Abstract

          Ion channels in the myocardial cellular membrane are responsible for allowing the cardiac action potential. Genetic abnormalities in these channels can predispose to life-threatening arrhythmias. We discuss the basic science of the cardiac action potential; outline the different clinical entities, including information regarding overlapping diagnoses, touching upon relevant genetics, new innovations in screening, diagnosis, risk stratification, and management. The special considerations of sudden unexplained death and sudden infant death syndrome are discussed. Scientists and clinicians continue to reconcile the rapidly growing body of knowledge regarding the molecular mechanisms and genetics while continuing to improve our understanding of the various clinical entities and their diagnosis and management in clinical setting. Two separate searches were run on the National Center for Biotechnology Information's website. The first using the term cardiac channelopathies was run on the PubMed database using filters for time (published in past 5 years) and age (birth-18 years), yielding 47 results. The second search using the medical subject headings (MeSH) database with the search terms “Long QT Syndrome” (MeSH) and “Short QT Syndrome” (MeSH) and “Brugada Syndrome” (MeSH) and “Catecholaminergic Polymorphic Ventricular Tachycardia” (MeSH), applying the same filters yielded 467 results. The abstracts of these articles were studied, and the articles were categorized and organized. Articles of relevance were read in full. As and where applicable, relevant references and citations from the primary articles where further explored and read in full.

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          Most cited references46

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          Risk stratification in Brugada syndrome: results of the PRELUDE (PRogrammed ELectrical stimUlation preDictive valuE) registry.

          The PRELUDE (PRogrammed ELectrical stimUlation preDictive valuE) prospective registry was designed to assess the predictive accuracy of sustained ventricular tachycardia/ventricular fibrillation (VTs/VF) inducibility and to identify additional predictors of arrhythmic events in Brugada syndrome patients without history of VT/VF. Brugada syndrome is a genetic disease associated with increased risk of sudden cardiac death. Even though its value has been questioned, inducibility of VTs/VF is widely used to select candidates to receive a prophylactic implantable defibrillator, and its accuracy has never been addressed in prospective studies with homogeneous enrolling criteria. Patients with a spontaneous or drug-induced type I electrocardiogram (ECG) and without history of cardiac arrest were enrolled. The registry included 308 consecutive individuals (247 men, 80%; median age 44 years, range 18 to 72 years). Programmed electrical stimulation was performed at enrollment, and patients were followed-up every 6 months. During a median follow-up of 34 months, 14 arrhythmic events (4.5%) occurred (13 appropriate shocks of the implantable defibrillator, and 1 cardiac arrest). Programmed electrical stimulation performed with a uniform and pre-specified protocol induced ventricular tachyarrhythmias in 40% of patients: arrhythmia inducibility was not a predictor of events at follow-up (9 of 14 events occurred in noninducible patients). History of syncope and spontaneous type I ECG (hazard ratio [HR]: 4.20), ventricular refractory period <200 ms (HR: 3.91), and QRS fragmentation (HR: 4.94) were significant predictors of arrhythmias. Our data show that VT/VF inducibility is unable to identify high-risk patients, whereas the presence of a spontaneous type I ECG, history of syncope, ventricular effective refractory period <200 ms, and QRS fragmentation seem useful to identify candidates for prophylactic implantable cardioverter defibrillator. Copyright © 2012 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.
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            Impact of genetics on the clinical management of channelopathies.

            There are few areas in cardiology in which the impact of genetics and genetic testing on clinical management has been as great as in cardiac channelopathies, arrhythmic disorders of genetic origin related to the ionic control of the cardiac action potential. Among the growing number of diseases identified as channelopathies, 3 are sufficiently prevalent to represent significant clinical and societal problems and to warrant adequate understanding by practicing cardiologists: long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and Brugada syndrome. This review will focus selectively on the impact of genetic discoveries on clinical management of these 3 diseases. For each disorder, we will discuss to what extent genetic knowledge and clinical genetic test results modify the way cardiologists should approach and manage affected patients. We will also address the optimal use of genetic testing, including its potential limitations and the potential medico-legal implications when such testing is not performed. We will highlight how important it is to understand the ways that genotype can affect clinical manifestations, risk stratification, and responses to the therapy. We will also illustrate the close bridge between molecular biology and clinical medicine, and will emphasize that consideration of the genetic basis for these heritable arrhythmia syndromes and the proper use and interpretation of clinical genetic testing should remain the standard of care. Copyright © 2013. Published by Elsevier Inc.
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              Induced pluripotent stem cells used to reveal drug actions in a long QT syndrome family with complex genetics

              Understanding the basis for differential responses to drug therapies remains a challenge despite advances in genetics and genomics. Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to investigate the pharmacology of disease processes in therapeutically and genetically relevant primary cell types in vitro and to interweave clinical and basic molecular data. We report here the derivation of iPSCs from a long QT syndrome patient with complex genetics. The proband was found to have a de novo SCN5A LQT-3 mutation (F1473C) and a polymorphism (K897T) in KCNH2, the gene for LQT-2. Analysis of the biophysics and molecular pharmacology of ion channels expressed in cardiomyocytes (CMs) differentiated from these iPSCs (iPSC-CMs) demonstrates a primary LQT-3 (Na+ channel) defect responsible for the arrhythmias not influenced by the KCNH2 polymorphism. The F1473C mutation occurs in the channel inactivation gate and enhances late Na+ channel current (INaL) that is carried by channels that fail to inactivate completely and conduct increased inward current during prolonged depolarization, resulting in delayed repolarization, a prolonged QT interval, and increased risk of fatal arrhythmia. We find a very pronounced rate dependence of INaL such that increasing the pacing rate markedly reduces INaL and, in addition, increases its inhibition by the Na+ channel blocker mexiletine. These rate-dependent properties and drug interactions, unique to the proband’s iPSC-CMs, correlate with improved management of arrhythmias in the patient and provide support for this approach in developing patient-specific clinical regimens.
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                Author and article information

                Journal
                Ann Pediatr Cardiol
                Ann Pediatr Cardiol
                APC
                Annals of Pediatric Cardiology
                Medknow Publications & Media Pvt Ltd (India )
                0974-2069
                0974-5149
                Sep-Dec 2015
                : 8
                : 3
                : 210-220
                Affiliations
                [1]Department of Pediatrics, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire, USA
                [1 ]Department of Pediatric Cardiology, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire, USA
                Author notes
                Address for correspondence: Dr. Shashank P Behere, Department of Pediatrics, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire 03766, USA. E-mail: shashibehere@ 123456gmail.com
                Article
                APC-8-210
                10.4103/0974-2069.164695
                4608198
                fa725a68-07b5-4dab-8601-ea0c5c927b1d
                Copyright: © 2015 Annals of Pediatric Cardiology

                This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

                History
                Categories
                Review Article

                Cardiovascular Medicine
                brugada syndrome,cardiac channelopathy,catecholaminergic polymorphic ventricular tachycardia,long qt syndrome,short qt syndrome

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