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Pesco-Koplowitz L, Gintant G, Ward R, Heon D, Saulnier M, Heilbraun J. Drug-induced cardiac abnormalities in premature infants and neonates. Am Heart J 2018; 195:14-38. [PMID: 29224642 DOI: 10.1016/j.ahj.2017.07.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Accepted: 07/27/2017] [Indexed: 01/09/2023]
Abstract
The Cardiac Safety Research Consortium (CSRC) is a transparent, public-private partnership that was established in 2005 as a Critical Path Program and formalized in 2006 under a Memorandum of Understanding between the United States Food and Drug Administration and Duke University. Our continuing goal is to advance paradigms for more efficient regulatory science related to the cardiovascular safety of new therapeutics, both in the United States and globally, particularly where such safety questions add burden to innovative research and development. This White Paper provides a summary of discussions by a cardiovascular committee cosponsored by the CSRC and the US Food and Drug Administration (FDA) that initially met in December 2014, and periodically convened at FDA's White Oak headquarters from March 2015 to September 2016. The committee focused on the lack of information concerning the cardiac effects of medications in the premature infant and neonate population compared with that of the older pediatric and adult populations. Key objectives of this paper are as follows: Provide an overview of human developmental cardiac electrophysiology, as well as the electrophysiology of premature infants and neonates; summarize all published juvenile animal models relevant to drug-induced cardiac toxicity; provide a consolidated source for all reported drug-induced cardiac toxicities by therapeutic area as a resource for neonatologists; present drugs that have a known cardiac effect in an adult population, but no reported toxicity in the premature infant and neonate populations; and summarize what is not currently known about drug-induced cardiac toxicity in premature infants and neonates, and what could be done to address this lack of knowledge. This paper presents the views of the authors and should not be construed to represent the views or policies of the FDA or Health Canada.
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Kalik ZM, Mike JL, Slipski C, Wright M, Jalics JZ, Womble MD. Sex and regional differences in rabbit right ventricular L-type calcium current levels and mathematical modelling of arrhythmia vulnerability. Exp Physiol 2017; 102:804-817. [PMID: 28436171 DOI: 10.1113/ep085977] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 04/18/2017] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Regional variations of ventricular L-type calcium current (ICa-L ) amplitude may underlie the increased arrhythmia risk in adult females. Current amplitude variations have been described for the left ventricle but not for the right ventricle. What is the main finding and its importance? Adult female rabbit right ventricular base myocytes exhibit elevated ICa-L compared with female apex or male myocytes. Oestrogen upregulated ICa-L in cultured female myocytes. Mathematical simulations modelling long QT syndrome type 2 demonstrated that elevated ICa-L prolonged action potentials and induced early after-depolarizations. Thus, ventricular arrhythmias in adult females may be associated with an oestrogen-induced upregulation of ICa-L . Previous studies have shown that adult rabbit left ventricular myocytes exhibit sex and regional differences in L-type calcium current (ICa-L ) levels that contribute to increased female susceptibility to arrhythmogenic early after-depolarizations (EADs). We used patch-clamp recordings from isolated adult male and female rabbit right ventricular myocytes to determine apex-base differences in ICa-L density and used mathematical modelling to examine the contribution of ICa-L to EAD formation. Current density measured at 0 mV in female base myocytes was 67% higher than in male base myocytes and 55% higher than in female apex myocytes. No differences were observed between male and female apex myocytes, between male apex and base myocytes, or in the voltage dependences of ICa-L activation or inactivation. The role of oestrogen was investigated using cultured adult female right ventricular base myocytes. After 2 days, 17β-estradiol (1 nm) produced a 65% increase in ICa-L density compared with untreated control myocytes, suggesting an oestrogen-induced upregulation of ICa-L . Action potential simulations using a modified Luo-Rudy cardiomyocyte model showed that increased ICa-L density, at the level observed in female base myocytes, resulted in longer duration action potentials, and when combined with a 50% reduction of the rapidly inactivating delayed rectifier potassium current conductance to model long QT syndrome type 2, the action potential was accompanied by one or more EADs. Thus, we found higher levels of ICa-L in adult female right ventricle base myocytes and the upregulation of this current by oestrogen. Simulations of long QT syndrome type 2 showed that elevated ICa-L contributed to genesis of EADs.
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Affiliation(s)
- Zane M Kalik
- Department of Biological Sciences, Youngstown State University, Youngstown, OH, USA
| | - Joshua L Mike
- Department of Mathematics and Statistics, Youngstown State University, Youngstown, OH, USA
| | - Cassandra Slipski
- Department of Biological Sciences, Youngstown State University, Youngstown, OH, USA
| | - Moriah Wright
- Department of Mathematics and Statistics, Youngstown State University, Youngstown, OH, USA
| | - Jozsi Z Jalics
- Department of Mathematics and Statistics, Youngstown State University, Youngstown, OH, USA
| | - Mark D Womble
- Department of Biological Sciences, Youngstown State University, Youngstown, OH, USA
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Yang Z, Prinsen JK, Bersell KR, Shen W, Yermalitskaya L, Sidorova T, Luis PB, Hall L, Zhang W, Du L, Milne G, Tucker P, George AL, Campbell CM, Pickett RA, Shaffer CM, Chopra N, Yang T, Knollmann BC, Roden DM, Murray KT. Azithromycin Causes a Novel Proarrhythmic Syndrome. Circ Arrhythm Electrophysiol 2017; 10:CIRCEP.115.003560. [PMID: 28408648 DOI: 10.1161/circep.115.003560] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 01/26/2017] [Indexed: 01/20/2023]
Abstract
BACKGROUND The widely used macrolide antibiotic azithromycin increases risk of cardiovascular and sudden cardiac death, although the underlying mechanisms are unclear. Case reports, including the one we document here, demonstrate that azithromycin can cause rapid, polymorphic ventricular tachycardia in the absence of QT prolongation, indicating a novel proarrhythmic syndrome. We investigated the electrophysiological effects of azithromycin in vivo and in vitro using mice, cardiomyocytes, and human ion channels heterologously expressed in human embryonic kidney (HEK 293) and Chinese hamster ovary (CHO) cells. METHODS AND RESULTS In conscious telemetered mice, acute intraperitoneal and oral administration of azithromycin caused effects consistent with multi-ion channel block, with significant sinus slowing and increased PR, QRS, QT, and QTc intervals, as seen with azithromycin overdose. Similarly, in HL-1 cardiomyocytes, the drug slowed sinus automaticity, reduced phase 0 upstroke slope, and prolonged action potential duration. Acute exposure to azithromycin reduced peak SCN5A currents in HEK cells (IC50=110±3 μmol/L) and Na+ current in mouse ventricular myocytes. However, with chronic (24 hour) exposure, azithromycin caused a ≈2-fold increase in both peak and late SCN5A currents, with findings confirmed for INa in cardiomyocytes. Mild block occurred for K+ currents representing IKr (CHO cells expressing hERG; IC50=219±21 μmol/L) and IKs (CHO cells expressing KCNQ1+KCNE1; IC50=184±12 μmol/L), whereas azithromycin suppressed L-type Ca++ currents (rabbit ventricular myocytes, IC50=66.5±4 μmol/L) and IK1 (HEK cells expressing Kir2.1, IC50=44±3 μmol/L). CONCLUSIONS Chronic exposure to azithromycin increases cardiac Na+ current to promote intracellular Na+ loading, providing a potential mechanistic basis for the novel form of proarrhythmia seen with this macrolide antibiotic.
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Affiliation(s)
- Zhenjiang Yang
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Joseph K Prinsen
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Kevin R Bersell
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Wangzhen Shen
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Liudmila Yermalitskaya
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Tatiana Sidorova
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Paula B Luis
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Lynn Hall
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Wei Zhang
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Liping Du
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Ginger Milne
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Patrick Tucker
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Alfred L George
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Courtney M Campbell
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Robert A Pickett
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Christian M Shaffer
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Nagesh Chopra
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Tao Yang
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Bjorn C Knollmann
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Dan M Roden
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN
| | - Katherine T Murray
- From the Department of Medicine and Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN.
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Abstract
Brugada syndrome is an inherited disease characterized by an increased risk of sudden cardiac death owing to ventricular arrhythmias in the absence of structural heart disease. Since the first description of the syndrome >20 years ago, considerable advances have been made in our understanding of the underlying mechanisms involved and the strategies to stratify at-risk patients. The development of repolarization-depolarization abnormalities in patients with Brugada syndrome can involve genetic alterations, abnormal neural crest cell migration, improper gap junctional communication, or connexome abnormalities. A common phenotype observed on the electrocardiogram of patients with Brugada syndrome might be the result of different pathophysiological mechanisms. Furthermore, risk stratification of this patient cohort is critical, and although some risk factors for Brugada syndrome have been frequently reported, several others remain unconfirmed. Current clinical guidelines offer recommendations for patients at high risk of developing sudden cardiac death, but the management of those at low risk has not yet been defined. In this Review, we discuss the proposed mechanisms that underlie the development of Brugada syndrome and the current risk stratification and therapeutic options available for these patients.
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Affiliation(s)
- Juan Sieira
- Heart Rhythm Management Centre, UZ Brussel-VUB, Brussels, Laarbeeklaan 101, 1090 Brussels, Belgium.,Cardiology Department, University Hospital Erasme, Route de Lennik 808, 1070 Brussels, Belgium
| | - Gregory Dendramis
- Heart Rhythm Management Centre, UZ Brussel-VUB, Brussels, Laarbeeklaan 101, 1090 Brussels, Belgium.,Cardiovascular Division, University Hospital "Paolo Giaccone", Via Del Vespro 127. 90127 Palermo, Italy
| | - Pedro Brugada
- Heart Rhythm Management Centre, UZ Brussel-VUB, Brussels, Laarbeeklaan 101, 1090 Brussels, Belgium
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Brugada J, Blom N, Sarquella-Brugada G, Blomstrom-Lundqvist C, Deanfield J, Janousek J, Abrams D, Bauersfeld U, Brugada R, Drago F, de Groot N, Happonen JM, Hebe J, Yen Ho S, Marijon E, Paul T, Pfammatter JP, Rosenthal E. Pharmacological and non-pharmacological therapy for arrhythmias in the pediatric population: EHRA and AEPC-Arrhythmia Working Group joint consensus statement. ACTA ACUST UNITED AC 2013; 15:1337-82. [DOI: 10.1093/europace/eut082] [Citation(s) in RCA: 217] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Cardiomyocyte calcium cycling in a naturally occurring German shepherd dog model of inherited ventricular arrhythmia and sudden cardiac death. J Vet Cardiol 2013; 15:5-14. [PMID: 23434243 DOI: 10.1016/j.jvc.2012.07.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 03/30/2012] [Accepted: 07/16/2012] [Indexed: 11/22/2022]
Abstract
OBJECTIVE To further characterize arrhythmic mechanisms in German shepherd dogs (GSDs) affected with inherited ventricular arrhythmias by evaluating intracellular calcium cycling and expression of calcium handling genes. ANIMALS Twenty five GSDs, 9 backcross dogs, and 6 normal mongrel dogs (controls) were studied. The GSDs and backcross dogs were from a research colony of inherited ventricular arrhythmias. The control research dogs were purchased. METHODS Action potentials (APs) and pseudo-electrocardiograms (ECG) were recorded from left ventricular (LV) wedge preparations of GSDs and normal dogs. Midmyocardial (Mid) LV cells from GSDs and normal mongrels were isolated by enzymatic digestion. Cells were either field stimulated or voltage clamped and calcium transients were measured by confocal microscopy using the indicator Fluo-3AM. Expression of calcium handling genes was measured by quantitative RT-PCR. RESULTS Mean calcium transient decay (tau) was not different between affected GSDs and control dogs, but striking cell-to-cell variability for tau was observed within affected GSDs and between affected GSDs and controls (P < 0.0001 each); within-dog variability accounted for 75% of total variability. Calcium sparks and afterdepolarizations occurred in GSD but not control cells. ATP2A2/SERCA2a expression was significantly reduced (P = 0.0063) in affected GSDs and inversely correlated (P = 0.0006) with severity of ventricular arrhythmias. CONCLUSIONS German shepherd dogs with inherited ventricular arrhythmias have electrophysiologic abnormalities in calcium cycling associated with reduced ATP2A2/SERCA2a expression. These animals provide a unique opportunity to study calcium remodeling at the genetic and molecular level in familial ventricular arrhythmias.
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Abstract
This case describes the prenatal diagnosis and integrated peripartum management of a foetus with 2:1 atrioventricular block and torsade de pointes due to congenital long QT syndrome. The unique issues related to the detection of intrauterine conduction abnormalities and ventricular arrhythmias, along with the immediate postnatal care, have been described as an interesting teaching case with successful outcome.
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van der Bijl P, Heradien M, Doubell A, Brink P. QTc prolongation prior to angiography predicts poor outcome and associates significantly with lower left ventricular ejection fractions and higher left ventricular end-diastolic pressures. Cardiovasc J Afr 2012. [PMID: 23192258 PMCID: PMC3721884 DOI: 10.5830/cvja-2012-060] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Background QT prolongation on the surface ECG is associated with sudden cardiac death. The cause of QT prolongation in ischaemic heart disease (IHD) patients remains unknown, but may be due to a complex interplay between genetic factors and impaired systolic and/or diastolic function through as yet unexplained mechanisms. It was hypothesised that QT prolongation before elective coronary angiography is associated with an increased mortality at six months. Methods Complete records of 321 patients who underwent coronary angiography were examined for QT interval corrected for heart rate (QTc), left ventricular ejection fraction (LVEF), left ventricular end-diastolic pressure (LVEDP) and known ischaemic heart disease risk factors. Patients were designated long QTc (LQTc) when they had prolonged QTc intervals or normal QTc (NQTc) when the QTc interval was normal. Patients with atrial fibrillation, bundle branch blocks, no ECG in the 24 hours before angiography, or a creatinine level > 200 μmol/l were excluded. Survival was determined telephonically at six months. Results Twenty-eight per cent of the total population had LQTc. During follow up, 15 patients (4.7%) died suddenly, 73% of whom had a LQTc. LQTc was significantly associated with mortality (LQTc 12% vs NQTc 1.7%; p < 0.01), and with lower but normal LVEF (LQTc 52.9 ± 15.4% vs NQTc 61.6 ± 13.6%; p < 0.01), higher LVEDP at LVEF > 45% (LQTc 19.2 ± 9.0 mmHg vs NQTc 15.95 ± 7.5 mmHg; p < 0.05), hypercholesterolaemia and a negative family history of IHD. Conclusion In patients with sinus rhythm and normal QRS width, QTc prolongation before coronary angiography predicted increased mortality at six months. QTc also associated strongly with left ventricular systolic and diastolic dysfunction, hypercholesterolaemia and a negative family history of IHD.
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Affiliation(s)
- P van der Bijl
- Division of Cardiology, Department of Medicine, Stellenbosch University and Tygerberg Academic Hospital, Western Cape, South Africa
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Abstract
Atrial fibrillation (AF) is rare in the pediatric population; however, there is increasing recognition that AF can be inherited. Long QT syndrome (LQTS), likewise, can be both acquired and inherited with mutations leading to abnormalities in cardiac ion channel function. Mutations in KCNQ1 are the most common cause of LQTS. Although rare, mutations in KCNQ1 also can cause familial AF. This report describes a child with a KCNQ1 missense mutation who uniquely expresses concomitant AF and LQTS. Due to the potential for increased morbidity and mortality, young patients who present with AF and a family history suggestive of inherited arrhythmias should trigger further investigation for LQTS and subsequent familial genetic counseling.
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Abstract
Clinicians who diagnose and manage epilepsy frequently encounter diagnoses of a nonneurological nature, particularly when assessing patients with transient loss of consciousness (T-LOC). Among these, and perhaps the most important, is cardiac syncope. As a group, patients with cardiac syncope have the highest likelihood of subsequent sudden death, and yet, unlike sudden unexpected death in epilepsy (SUDEP) for example, it is the norm for these tragic occurrences to be both easily predictable and preventable. In the 12 months following initial presentation with cardiac syncope, sudden death has been found to be 6 times more common than in those with noncardiac syncope (N Engl J Med 309, 1983, 197). In short, for every patient seen with T-LOC, two fundamental aims of the consultation are to assess the likelihood of cardiac syncope as the cause, and to estimate the risk of future sudden death for the individual. This article aims to outline for the noncardiologist how to recognize cardiac syncope, how to tell it apart from more benign cardiovascular forms of syncope as well as from seizures and epilepsy, and what can be done to predict and prevent sudden death in these patients. This is achieved through the assessment triad of a clinical history and examination, risk stratification, and 12-lead electrocardiography (ECG).
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Affiliation(s)
- Joseph Anderson
- The Alan Richens Epilepsy Unit, University Hospital of Wales, Cardiff, United Kingdom
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Danielsson C, Brask J, Sköld AC, Genead R, Andersson A, Andersson U, Stockling K, Pehrson R, Grinnemo KH, Salari S, Hellmold H, Danielsson B, Sylvén C, Elinder F. Exploration of human, rat, and rabbit embryonic cardiomyocytes suggests K-channel block as a common teratogenic mechanism. Cardiovasc Res 2012; 97:23-32. [DOI: 10.1093/cvr/cvs296] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Lowe JS, Stroud DM, Yang T, Hall L, Atack TC, Roden DM. Increased late sodium current contributes to long QT-related arrhythmia susceptibility in female mice. Cardiovasc Res 2012; 95:300-7. [PMID: 22562703 DOI: 10.1093/cvr/cvs160] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
AIMS Female gender is a risk factor for long QT-related arrhythmias, but the underlying mechanisms remain uncertain. Here, we tested the hypothesis that gender-dependent function of the post-depolarization 'late' sodium current (I(Na-L)) contributes. METHODS AND RESULTS Studies were conducted in mice in which the canonical cardiac sodium channel Scn5a locus was disrupted, and expression of human wild-type SCN5A cDNA substituted. Baseline QT intervals were similar in male and female mice, but exposure to the sodium channel opener anemone toxin ATX-II elicited polymorphic ventricular tachycardia in 0/9 males vs. 6/9 females. Ventricular I(Na-L) and action potential durations were increased in myocytes isolated from female mice compared with those from males before and especially after treatment with ATX-II. Further, ATX-II elicited potentially arrhythmogenic early afterdepolarizations in myocytes from 0/5 male mice and 3/5 female mice. CONCLUSION These data identify variable late I(Na) as a modulator of gender-dependent arrhythmia susceptibility.
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Affiliation(s)
- John S Lowe
- Department of Medicine, Vanderbilt University School of Medicine, 2215B Garland Avenue, Nashville, TN 37232-0575, USA
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Zaklyazminskaya EV, Abriel H. Prevalence of Significant Genetic Variants in Congenital Long QT Syndrome is Largely Underestimated. Front Pharmacol 2012; 3:72. [PMID: 22557970 PMCID: PMC3338122 DOI: 10.3389/fphar.2012.00072] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Accepted: 04/06/2012] [Indexed: 11/17/2022] Open
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Windsor JS, Rodway G, Mukherjee R, Firth P, Shattock M, Montgomery H. Prolongation of the Corrected QT Complex - A Cause of Sudden Cardiac Death in the Mountain Environment? J ROY ARMY MED CORPS 2011; 157:63-7. [DOI: 10.1136/jramc-157-01-11] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Affiliation(s)
- Nam-Ho Kim
- Department of Interal Medicine, Wonkwang University College of Medicine, Korea.
| | - Kyeong Ho Yun
- Department of Interal Medicine, Wonkwang University College of Medicine, Korea.
| | - Seok Kyu Oh
- Department of Interal Medicine, Wonkwang University College of Medicine, Korea.
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Abstract
PURPOSE OF REVIEW Advances in understanding the biophysical underpinnings of long QT syndrome have provided growing insight into the risk of this syndrome in the pediatric population. This review focuses on developments in this area as reflected in the recent literature. RECENT FINDINGS QT interval prolongation on the surface ECG is the hallmark of long QT syndrome. This prolongation reflects protracted ventricular repolarization, primarily due to mutations in genes coding for cardiac ion channels. To date, 12 different genes have been implicated, and current genetic testing methods can provide a specific diagnosis in approximately 70% of patients. Clinical indicators, including age, sex, corrected QT duration, and prior syncope are the most powerful predictors of future life-threatening cardiac events. However, diagnosis, risk assessment, and therapeutic strategies are being guided by genetic analysis to an increasing degree. SUMMARY Impressive advancements have been made in understanding the genetic and clinical determinants of this heterogeneous syndrome. As genetic testing techniques become more robust, the ability to assess risk in affected individuals and tailor therapy will improve.
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Ziv O, Morales E, Song YK, Peng X, Odening KE, Buxton AE, Karma A, Koren G, Choi BR. Origin of complex behaviour of spatially discordant alternans in a transgenic rabbit model of type 2 long QT syndrome. J Physiol 2009; 587:4661-80. [PMID: 19675070 DOI: 10.1113/jphysiol.2009.175018] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Enhanced dispersion of repolarization has been proposed as an important mechanism in long QT related arrhythmias. Dispersion can be dynamic and can be augmented with the occurrence of spatially out-of-phase action potential duration (APD) alternans (discordant alternans; DA). We investigated the role of tissue heterogeneity in generating DA using a novel transgenic rabbit model of type 2 long QT syndrome (LQT2). Littermate control (LMC) and LQT2 rabbit hearts (n = 5 for each) were retrogradely perfused and action potentials were mapped from the epicardial surface using di-4-ANEPPS and a high speed CMOS camera. Spatial dispersion (Delta APD and Delta slope of APD restitution) were both increased in LQT2 compared to LMC (Delta APD: 34 +/- 7 ms vs. 23 +/- 6 ms; Delta slope: 1.14 +/- 0.23 vs. 0.59 +/- 0.19). Onset of DA under a ramp stimulation protocol was seen at longer pacing cycle length (CL) in LQT2 compared to LMC hearts (206 +/- 24 ms vs. 156 +/- 5 ms). Nodal lines between regions with APD alternans out of phase from each other were correlated with conduction velocity (CV) alternation in LMC but not in LQT2 hearts. In LQT2 hearts, larger APD dispersion was associated with onset of DA at longer pacing CL. At shorter CLs, closer to ventricular fibrillation induction (VF), nodal lines in LQT2 (n = 2 out of 5) showed persistent complex beat-to-beat changes in nodal line formation of DA associated with competing contribution from CV restitution and tissue spatial heterogeneity, increasing vulnerability to conduction block. In conclusion, tissue heterogeneity plays a significant role in providing substrate for ventricular arrhythmia in LQT2 rabbits by facilitating DA onset and contributing to unstable nodal lines prone to reentry formation.
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Affiliation(s)
- Ohad Ziv
- Cardiovascular Research Center, Division of Cardiology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI 02903, USA
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Gu DF, Li XL, Qi ZP, Shi SS, Hu MQ, Liu DM, She CB, Lv YJ, Li BX, Yang BF. Blockade of HERG K+ channel by isoquinoline alkaloid neferine in the stable transfected HEK293 cells. Naunyn Schmiedebergs Arch Pharmacol 2009; 380:143-51. [PMID: 19424681 DOI: 10.1007/s00210-009-0419-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Accepted: 04/07/2009] [Indexed: 11/24/2022]
Abstract
We studied the effects of isoquinoline alkaloid neferine (Nef) extracted from the seed embryo of Nelumbo nucifera Gaertn on Human ether-à-go-go-related gene (HERG) channels stably expressed in human embryonic kidney (HEK293) cells using whole-cell patch clamp technique, western blot analysis and immunofluorescence experiment. Nef induced a concentration-dependent decrease in current amplitude according to the voltage steps and tail currents of HERG with an IC(50) of 7.419 microM (n(H) -0.5563). Nef shifted the activation curve in a significantly negative direction and accelerated recovery from inactivation and onset of inactivation, however, slowed deactivation. In addition, it had no significant influence on steady-state inactivation curve. Western blot and immunofluorescence results suggested Nef had no significant effect on the expression of HERG protein. In summary, Nef can block HERG K(+) channels that functions by changing the channel activation and inactivation kinetics. Nef has no effect on the generation and trafficking of HERG protein. A blocked-off HERG channel was one mechanism of the anti-arrhythmic effects by Nef.
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Affiliation(s)
- Dong-fang Gu
- Department of Pharmacology, Harbin Medical University, Harbin, People's Republic of China
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