Where results make sense

About us   |   Why use us?   |   Reviews   |   PR   |   Contact us

Repolarization - Wikipedia, the free encyclopedia In neuroscience, repolarization refers to the change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value. Repolarization results from the movement of positively charged potassium ions out of the cell. Typically the repolarization phase of an action potential results in hyperpolarization, attainment of a membrane potential that is more negative than the resting potential. en.wikipedia.org /wiki/Repolarization   (121 words)

Rochester Ventricular Repolarization Center   (Site not responding. Last check: 2007-11-02) Pre-clinical cardiac repolarization data and precise measurements of the QT interval and other repolarization-related phenomena on the surface ECG are being used to define whether an effect is present. The science of cardiac repolarization is evolving rapidly, and a thoughtful approach is required to tackle the scientific, medical, drug development and regulatory issues required to bring a safe and effective drug to market. This core Lab a large toolbox of customized-software has been designed for the analysis of the repolarization segment on the surface ECG for the analysis of repolarization segment based on electrocardiographic and vectocardiographic concepts equiped with various types of ECG devices (from the recorders to the software analysis). www.urmc.rochester.edu /heart/rvrc.htm   (862 words)

s000626c - Long QT Syndrome - Congenital & Acquired In the LQTS, prolonged repolarization is associated with increased spatial dispersion of repolarization. The peak of the negative T waves coincided with repolarization of the M region, whereas the end of the negative T wave coincided with the repolarization of epicardium. Under baseline and LQT conditions, repolarization of the epicardial action potential, the earliest to repolarize, coincided with the peak of the T wave; repolarization of the M cells, the last to repolarize, coincided with the end of the T wave. www.emory.edu /WHSCL/grady/amreport/litsrch99/s000626c.html   (6297 words)

Repolarization   (Site not responding. Last check: 2007-11-02) Upon completion of the electrical stimuli, the interior of the cells begin to return to their negatively charged state. Repolarization is the beginninig of relaxation for the myocardial cell. Repolarization causes the cells of the heart to return to the relaxed state thereby ending the completed cardiac cycle. www.utpb.edu /courses/jeldridge/repolarization.htm   (63 words)

Basic Electrocardiography Atrial repolarization occurs during ventricular depolarization and is obscured. These premature atrial depolarization waves may be conducted to ventricular tissue before complete repolarization has occurred, and in such cases, the subsequent ventricular depolarization may take place by an abnormal pathway, generating a wide, bizarre QRS complex. With early repolarization, however, the T wave is distinct from the elevated ST segment, whereas with myocardial infarction, it is incorporated into it. www.sh.lsuhsc.edu /fammed/OutpatientManual/BasicECG.htm   (4374 words)

eMedicine - Torsades de Pointes : Article Excerpt by: Syed Nazeer, MD Various studies support the concept that prolongation of the repolarization delays the inactivation of the ion channels responsible for the inward flow of positive depolarizing currents. Phase 3 of the repolarization is mediated by activation of delayed rectifier potassium current (IK) moving outward while the inward positive current decays. This heterogeneity of repolarization in the myocardial cells promotes the spread of triggered activity, which is initiated by EADs by a reentrant mechanism and currently is thought to be responsible for the maintenance of torsades de pointes. www.emedicine.com /med/byname/torsades-de-pointes.htm   (611 words)

QT Prolongation of repolarization (usually manifested as QT prolongation on the surface electrocardiogram) is sometimes benign or even antiarrhythmic (as with amiodarone, diltiazem, pentobarbital, ranolazine, and verapamil), but sometimes it is associated with arrhythmias, syncope, and death. To detect and characterize a drug-induced change in ventricular repolarization, several participants utilize 24-hour electrocardiograms, at least one at each subject's baseline and at least one during the subject's exposure to the suspect drug. Antzelevitch noted that the compounds that in wedge preparations induce harmless prolongation of repolarization can be distinguished from those that induce arrhythmias by experiments in which the basic cycle length is abruptly changed. www.fenichel.net /pages/Professional/subpages/QT/qt.htm   (2108 words)

Repolarization Changes Induced by Air Pollution in Ischemic Heart Disease Patients   (Site not responding. Last check: 2007-11-02) The purpose of this study was to assess associations between daily variations in particulate air pollution and repolarization ECG parameters representing abnormalities in the myocardial substrate and increased vulnerability of myocardium to arrhythmias. Novel measures of repolarization (e.g., T-wave complexity) were used to investigate the underlying pathophysiologic mechanisms leading to adverse reactions of the heart in response to air pollution. Abnormalities in repolarization morphology, described by the fairly novel measurement of T-wave complexity and T-wave amplitude, reflect the status of the myocardial substrate and were previously found to be associated with an increased risk of cardiac events in a cohort of healthy subjects (Kors et al. www.ehponline.org /members/2005/7579/7579.html   (4896 words)

Calcium-Activated Potassium Conductances Contribute to Action Potential Repolarization at the Soma But Not the ... Repolarization of action potentials in the distal dendrites is not affected by Ca channel blockade. In contrast, the repolarization of dendritic action potentials obtained >150 µm from the soma was not affected by the blockade In this case, the repolarization rate at both the soma and dendrites was computed as the slope of AP repolarization measured between 80 and 30% of action potential amplitude. www.jneurosci.org /cgi/content/full/19/13/5205   (4989 words)

Guidance for Industry: S7B Nonclinical Evaluation of the Potential for Delayed Ventricular Repolarization (QT Interval ... The assessment of the effects of pharmaceuticals on ventricular repolarization and proarrhythmic risk is the subject of active investigation. When ventricular repolarization is delayed and the QT interval is prolonged, there is an increased risk of ventricular tachyarrhythmia, including torsade de pointes, particularly when combined with other risk factors (e.g., hypokalemia, structural heart disease, bradycardia). Ventricular repolarization, determined by the duration of the cardiac action potential, is a complex physiological process. www.fda.gov /cder/guidance/6885fnl.htm   (3587 words)

Imaging Dispersion of Myocardial Repolarization, II: Noninvasive Reconstruction of Epicardial Measures -- Ghanem et al. ...   (Site not responding. Last check: 2007-11-02) Imaging Dispersion of Myocardial Repolarization, II: Noninvasive Reconstruction of Epicardial Measures -- Ghanem et al. of repolarization is faithfully reflected in epicardial electrophysiological Repolarization abnormalities, arrhythmia and sudden death in canine tachycardia-induced cardiomyopathy. circ.ahajournals.org /cgi/content/full/104/11/1306   (2798 words)

Electrophysiologic Characterization of the Antipsychotic Drug Sertindole in a Rabbit Heart Model of Torsade de Pointes: ... cardiac repolarization, i.e., induce prolongation of the QT interval of repolarization with sotalol was mainly a transmural phenomenon Eckardt L, Kirchhof P, Mönnig G, Breithardt G, Borggrefe M and Haverkamp W (2000) Modification of stretch-induced shortening of repolarization by streptomycin in the isolated rabbit heart. jpet.aspetjournals.org /cgi/content/full/300/1/64   (4503 words)

Errors in repolarization measurement using magnetocardiography   (Site not responding. Last check: 2007-11-02) In this study, errors in manual measurement of repolarization interval in the MCG were determined. In total, manual measurement of repolarization intervals in 2,048 (eight subjects X16 channels x eight presentations x two repeats) MCGs were made by each of four analysts. Measured repolarization intervals were reduced by 3 ms when noise was added and by a further 3 ms when this noise was doubled. www.rmpd.org.uk /abstracts/cardiovascular_physics/errors_in_repolarization_measurement.htm   (323 words)

CBER - Guidance for Industry: S7B Nonclinical Evaluation of the Potential for Delayed Ventricular Repolarization (QT ... The objectives of studies are to: (1) identify the potential of a test substance and its metabolites to delay ventricular repolarization, and (2) relate the extent of delayed ventricular repolarization to the concentrations of a test substance and its metabolites. Conduct of S7B nonclinical studies assessing the risk for delayed ventricular repolarization and QT interval prolongation prior to first administration in humans should be considered. Intact animal models allow investigation of ventricular repolarization or associated arrhythmias where integrated effects on the full complement of ion channel and cell types are assessed. www.fda.gov /cber/gdlns/ichqt.htm   (3587 words)

Indoxconsulting.com - Medical Expert Witnesses for Medical Malpractice & Negligence Cases The 12-lead ECG is the most frequently used technique for obtaining the surface electrocardiographic signal for evaluation of ventricular repolarization. If a second low-amplitude repolarization wave interrupts the terminal portion of the T wave, it is difficult to determine whether the second deflection is a biphasic T wave or an early-occurring U wave. This method reflects accurately the real duration of ventricular repolarization, but it introduces a large degree of subjectivity, particularly when biphasic T waves are present or when large U waves interrupt the return of the T wave to the baseline. www.indoxconsulting.com /UnderstandingQTIntervals.html   (826 words)

Divergent Proarrhythmic Potential of Macrolide Antibiotics Despite Similar QT Prolongation: Fast Phase 3 Repolarization ... The macrolide antibiotics erythromycin, clarithromycin, and azithromycin prolong myocardial repolarization. Daleau P, Lessard E, Groleau MF and Turgeon J (1995) Erythromycin blocks the rapid component of the delayed rectifier potassium current and lengthens repolarization of guinea pig ventricular myocytes. Verduyn SC, Vos MA, van-der ZJ, Van-der HF and Wellens HJ (1997) Role of interventricular dispersion of repolarization in acquired Torsade-de-Pointes arrhythmias: reversal by magnesium. jpet.aspetjournals.org /cgi/content/full/303/1/218   (3601 words)

IngentaConnect Coronary Artery Disease Alters Ventricular Repolarization Dynamic...   (Site not responding. Last check: 2007-11-02) Ventricular repolarization dynamics (VRD) is an important predictor of outcome in diabetes.We examined the potential impact of coronary artery disease (CAD) on VRD in type 2 diabetic patients. Ventricular repolarization dynamics in diabetic patients with negative angiograms did not differ from VRD in controls (SDNN(QT): 8.94 ± 6.04 ms versus 7.44 ± 5.72 ms; P = 0.67, rMSSD(QT): 11.18 ± 7.45 ms versus 10.22 ± 5.35 ms; P = 0.82). Therefore, changes in ventricular repolarization in diabetic patients may be due to silent CAD rather than due to diabetes per se. www.ingentaconnect.com /content/bsc/pace/2005/00000028/A00101s1/art00044   (277 words)

Non-pacemaker action potentials Calcium-channel blockers such as verapamil and diltiazem affect the plateau phase (phase 2) of the action potential. Potassium-channel blockers delay repolarization (phase 3) by blocking the potassium channels that are responsible for this phase. For example, drugs that block potassium channels (e.g., amiodarone, a Class III antiarrhythmic) retards phase 3 repolarization and increase the ERP. www.cvphysiology.com /Arrhythmias/A006.htm   (594 words)

Clean Air Initiative: Asia - Repolarization Changes Induced by Air Pollution in Ischemic Heart Disease Patients We tested the hypothesis that patients with preexisting coronary heart disease experience changes in the repolarization parameters in association with rising concentrations of air pollution. A prospective panel study was conducted in Erfurt, East Germany, with 12 repeated electrocardiogram (ECG) recordings in 56 males with ischemic heart disease. This study provides evidence suggesting an immediate effect of air pollution on repolarization duration, morphology, and variability representing myocardial substrate and vulnerability, key factors in the mechanisms of cardiac death. www.cleanairnet.org /caiasia/1412/article-69603.html   (227 words)

Correlation of repolarization of ventricular monophasic action potential with ECG in the murine heart -- Danik et al. ... Correlation of repolarization of ventricular monophasic action potential with ECG in the murine heart -- Danik et al. Correlation of repolarization of ventricular monophasic action potential with ECG in the murine heart the upstroke to 90% repolarization from the crest of the plateau ajpheart.physiology.org /cgi/content/full/283/1/H372   (5299 words)

Unique Topographical Distribution of M Cells Underlies Reentrant Mechanism of Torsade de Pointes in the Long-QT ...   (Site not responding. Last check: 2007-11-02) The subpopulation of M cells exhibiting disproportionate APD prolongation in response to bradycardia and d-sotalol forms the substrate for reentrant excitation in TdP (as shown from separate experiment in Figure 7). S2 was applied on the epicardial surface in the wake of the refractory barrier (R) produced by the island of M cells extending from the midwall to the epicardial surface. Role of interventricular dispersion of repolarization in acquired torsade-de-pointes arrhythmias: reversal by magnesium. ahavj.ahajournals.org /cgi/content/full/circulationaha;hc1002.105231   (3716 words)

eMedicine - Torsade de Pointes : Article Excerpt by: Jatin Dave, MD, MPH Phase 1: During initial upstroke of action potential in a normal cardiac cell, a rapid net influx of positive ions (Na and Ca) occurs, which results in the depolarization of the cell membrane. The deep endocardial region and midmyocardial layer (composed of M cells) of the ventricle are more prone to prolongation of repolarization and EADs because they have a less rapid delayed rectifier potassium current (IKr), while other regions might have short or normal cycles. This heterogeneity of repolarization in the myocardial cells promotes the spread of triggered activity, which is initiated by EADs by a reentrant mechanism and currently is thought to be responsible for the maintenance of torsade. www.emedicine.com /med/byname/torsade-de-pointes.htm   (705 words)

CiteULike: Alterations in early action potential repolarization causes localized failure of sarcoplasmic reticulum Ca2+ ...   (Site not responding. Last check: 2007-11-02) Alterations in early action potential repolarization causes localized failure of sarcoplasmic reticulum Ca2+ release. SR Ca2+ release becomes dyssynchronized in failing feline ventricular myocytes because of reductions in Ca2+ influx induced in part by alterations in early repolarization of the AP. Therefore, therapies that restore normal early repolarization should improve the contractility of the failing heart. www.citeulike.org /user/cherrie/article/807817   (554 words)

Influence of IV haloperidol on ventricular repolarization and monophasic action potential duration in anesthetized dogs ...   (Site not responding. Last check: 2007-11-02) Effective refractory period (ERP), action potential duration at 90% repolarization (AP[D.sub.90]), and QTc interval measurements were performed at baseline and after each of four doses of haloperidol (0.15, 0.5, 2.0, and 3.0 mg/kg) or placebo at three different pacing cycle lengths (450, 300, and 250 ms). Torsades de pointes is a potentially life-threatening polymorphic ventricular tachycardia that is characterized on a surface ECC by a twisting QRS morphology that is associated with prolongation of the QTc interval. Drugs that produce early afterdepolarizations are those associated with the prolongation of monophasic action potential duration (APD) primarily through the prolongation of phase 3 membrane repolarization via blockade of delayed rectifier potassium channels. www.findarticles.com /p/articles/mi_m0984/is_5_125/ai_n6094563   (894 words)

IngentaConnect Repolarization Abnormality for Prediction of All-Cause and Cardio... IngentaConnect Repolarization Abnormality for Prediction of All-Cause and Cardio... Repolarization Abnormality for Prediction of All-Cause and Cardiovascular Mortality in American Indians: The Strong Heart Study Background: Analysis of electrocardiographic (ECG) repolarization abnormality using QTc interval and principal component analysis (PCA) of the T-wave vector predict all-cause and cardiovascular (CV) mortality. www.ingentaconnect.com /content/bsc/jce/2005/00000016/00000009/art00004   (404 words)

Modulation of Ca2+ Release in Cardiac Myocytes by Changes in Repolarization Rate: Role of Phase-1 Action Potential ... Repolarization rate modulates the synchrony and amplitude of Ca spikes. Effect of slowed phase-1 repolarization and ISO on Ca release in rabbit ventricular myocytes. Molecular dissection of cardiac repolarization by in vivo Kv4.3 gene transfer. circres.ahajournals.org /cgi/content/full/90/2/165   (4791 words)

Mechanisms of Abnormal Cardiac Repolarization During Insulin-Induced Hypoglycemia -- Robinson et al. 52 (6): 1469 -- ... Mechanisms of Abnormal Cardiac Repolarization During Insulin-Induced Hypoglycemia -- Robinson et al. to abnormal cardiac repolarization with an increase of QTc and Jervell A, Lange-Neilson F: Congenital deaf-mutism; funtional heart disease with prolongation of the QT interval and sudden death. diabetes.diabetesjournals.org /cgi/content/full/52/6/1469   (3605 words)

Try your search on: Qwika (all wikis)

About us   |   Why use us?   |   Reviews   |   Press   |   Contact us   Copyright © 2005-2007 www.factbites.com Usage implies agreement with terms.