Minimum Information about a Cardiac Electrophysiology Experiment (MICEE): standardised reporting for model reproducibility, interoperability, and data sharing.

Cardiac experimental electrophysiology is in need of a well-defined Minimum Information Standard for recording, annotating, and reporting experimental data. As a step towards establishing this, we present a draft standard, called Minimum Information about a Cardiac Electrophysiology Experiment (MICEE). The ultimate goal is to develop a useful tool for cardiac electrophysiologists which facilitates and improves dissemination of the minimum information necessary for reproduction of cardiac electrophysiology research, allowing for easier comparison and utilisation of findings by others. It is hoped that this will enhance the integration of individual results into experimental, computational, and conceptual models. In its present form, this draft is intended for assessment and development by the research community. We invite the reader to join this effort, and, if deemed productive, implement the Minimum Information about a Cardiac Electrophysiology Experiment standard in their own work.

Induced pluripotent stem cells as a model for accelerated patient- and disease-specific drug discovery.

Human induced pluripotent stem (iPS) cells hold great promise for therapy of a number of degenerative diseases such as ischemic heart failure, Parkinson's disease, Alzheimer's disease, diabetes mellitus, sickle cell anemia and Huntington disease. They also have the potential to accelerate drug discovery in 3 ways. The first involves the delineation of chemical components for efficient reprogramming of patient's blood cells or cells from biopsies, obviating the need for cellular delivery of reprogramming exogenous transgenes, thereby converting hope into reality for patients suffering from degenerative diseases. Patients worldwide stand to benefit from the clinical applicability of iPS cell-based cell replacement therapy for a number of degenerative diseases. The second is the potential for discovering novel drugs in a high throughput manner using patient-specific iPS cell-derived somatic cells possessing the etiology of the specific disease. The third is their suitability for toxicological testing of drugs and environmental factors. This review focuses on these potential applications of iPS cells with special emphasis on recent updates of iPS cell research contributing to the accelerated drug discovery.

Functionally distinct sodium channels in ventricular epicardial and endocardial cells contribute to a greater sensitivity of the epicardium to electrical depression.

A greater depression of the action potential (AP) of the ventricular epicardium (Epi) versus endocardium (Endo) is readily observed in experimental models of acute ischemia and Brugada syndrome. Endo and Epi differences in transient outward K(+) current and/or ATP-sensitive K(+) channel current are believed to contribute to the differential response. The present study tested the hypothesis that the greater sensitivity of Epi is due in part to its functionally distinct early fast Na(+) current (I(Na)). APs were recorded from isolated Epi and Endo tissue slices and coronary-perfused wedge preparations before and after exposures to elevated extracellular K(+) concentration ([K(+)](o); 6-12 mM). I(Na) was recorded from Epi and Endo myocytes using whole cell patch-clamp techniques. In tissue slices, increasing [K(+)](o) to 12 mM reduced V(max) to 51.1 +/- 5.3% and 26.8 +/- 9.6% of control in Endo (n = 9) and Epi (n = 14), respectively (P < 0.05). In wedge preparations (n = 12), the increase in [K(+)](o) caused selective depression of Epi APs and transmural conduction slowing and block. I(Na) density was not significantly different between Epi (n = 14) and Endo (n = 15) cells, but Epi cells displayed a more negative half-inactivation voltage [-83.6 +/- 0.1 and -75.5 +/- 0.3 mV for Epi (n = 16) and Endo (n = 16), respectively, P < 0.05]. Our data suggest that reduced I(Na) availability in ventricular Epi may contribute to its greater sensitivity to electrical depression and thus may contribute to the R-ST segment changes observed under a variety of clinical conditions including acute myocardial ischemia, severe hyperkalemia, and Brugada syndrome.

Tpeak-Tend and Tpeak-Tend Dispersion as Risk Factors for Ventricular Tachycardia/ Ventricular Fibrillation in Patients With the Brugada Syndrome

OBJECTIVES Our objective in this study was to evaluate Tpeak-Tend interval (Tp-e) and other electrocardiographic parameters as risk factors for recurrence of life-threatening cardiac events in patients with the Brugada syndrome (BS). BACKGROUND The Tp-e interval in the electrocardiogram (ECG) has been reported to predict life-threatening arrhythmias in the long QT syndrome. METHODS: Twenty-nine patients with the ECG pattern of BS and 29 healthy age- and gender-matched controls were studied. The follow-up period was 42.65 ± 24.42 months (range 11 to 108 months). RESULTS Upon presentation, five patients had suffered aborted sudden death, five syncope, and two presyncope. Eleven patients with the ECG pattern of BS had a prolonged (>460 ms) QTc in V2 but usually not in inferior or left leads. No patient had abnormally prolonged QT dispersion. Programmed electrical stimulation induced ventricular tachycardia/fibrillation in 5 out of 26 patients. Inducibility did not predict recurrence of events. Cardioverter-defibrillators were implanted in 14 patients (all symptomatic and two asymptomatic). During follow-up, nine symptomatic patients experienced recurrences. Previous cardiac events and a QTc >460 ms in V2 were significant risk factors (p = 0.00002 and p = 0.03, respectively). Tp-e and Tp-e dispersion were significantly prolonged in patients with recurrences versus patients without events (104.4 and 35.6 ms vs. 87.4 and 23.2 ms; p = 0.006 and p = 0.03, respectively) or controls (90.7 and 17.9 ms; p = 0.02 and p = 0.001, respectively).CONCLUSIONS Our study demonstrates significant correlation between previous events, QTc >460 ms in V2, Tp-e, and Tp-e dispersion and occurrence of life-threatening arrhythmic events, suggesting that these parameters may be useful in risk stratification of patients with the Brugada syndrome(AU)

OBJETIVOS Nuestro objetivo en este estudio fue evaluar Tpeak-Tienden intervalo (Tp-e) y otros parámetros electrocardiográficos como factores de riesgo para la recurrencia en peligro la vida de eventos cardíacos en pacientes con el síndrome de Brugada (BS). ANTECEDENTES El Tp-e intervalo en el electrocardiograma (ECG) se ha informado a predecir las arritmias que amenazan la vida en el síndrome del QT largo. MÉTODOS: Veintinueve pacientes con el patrón de ECG de BS y 29 sanos de edad y el sexo-los controles se estudiaron. El período de seguimiento fue de 42,65 ± 24,42 meses (rango 11 a 108 meses). RESULTADOS: Tras la presentación, cinco pacientes habían sufrido una muerte súbita abortada, cinco síncope, y dos presincope. Once pacientes con el patrón de ECG BS había un prolongado (> 460 ms) QTc en V2 pero generalmente no en la izquierda inferior o conduce. Ningún paciente había anormalmente dispersión QT prolongado. Inducida por la estimulación eléctrica programada taquicardia ventricular / fibrilación en 5 de 26 pacientes. Inducibility no predecir la recurrencia de eventos. Cardioverter-desfibriladores se implantaron en 14 pacientes (todos los sintomáticos y dos asintomáticos). Durante el seguimiento, nueve pacientes presentaron recidivas sintomáticas. Anteriores eventos cardíacos y un QTc> 460 ms en V2 fueron importantes factores de riesgo (p = 0,00002 yp = 0,03, respectivamente). Tp y Tp-e-e dispersión se prolongó significativamente en los pacientes con recidivas frente a los pacientes sin eventos (104,4 y 35,6 ms frente a 87,4 y el 23,2 ms, p = 0,006 y p = 0,03, respectivamente) o los controles (90,7 y 17,9 m, p = 0,02 yp = 0,001, respectivamente)..........

Therapy for the Brugada syndrome.

The Brugada syndrome is a congenital syndrome of sudden cardiac death first described as a new clinical entity in 1992. Electrocardiographically characterized by a distinct coved-type ST segment elevation in the right precordial leads, the syndrome is associated with a high risk for sudden cardiac death in young and otherwise healthy adults, and less frequently in infants and children. The ECG manifestations of the Brugada syndrome are often dynamic or concealed and may be revealed or modulated by sodium channel blockers. The syndrome may also be unmasked or precipitated by a febrile state, vagotonic agents, alpha-adrenergic agonists, beta-adrenergic blockers, tricyclic or tetracyclic antidepressants, a combination of glucose and insulin, and hypokalemia, as well as by alcohol and cocaine toxicity. An implantable cardioverter-defibrillator (ICD) is the most widely accepted approach to therapy. Pharmacological therapy aimed at rebalancing the currents active during phase 1 of the right ventricular action potential is used to abort electrical storms, as an adjunct to device therapy, and as an alternative to device therapy when use of an ICD is not possible. Isoproterenol and cilostazol boost calcium channel current, and drugs like quinidine inhibit the transient outward current, acting to diminish the action potential notch and thus suppress the substrate and trigger for ventricular tachycardia/fibrillation (VT/VF).

Amplification of spatial dispersion of repolarization underlies sudden cardiac death associated with catecholaminergic polymorphic VT, long QT, short QT and Brugada syndromes.

This review examines the hypothesis that amplification of spatial dispersion of repolarization in the form of transmural dispersion of repolarization (TDR) underlies the development of life-threatening ventricular arrhythmias associated with inherited ion channelopathies including the long QT, short QT and Brugada syndromes as well as catecholaminergic polymorphic ventricular tachycardia. In the long QT syndrome, amplification of TDR is often secondary to preferential prolongation of the action potential duration (APD) of M cells, whereas in the Brugada syndrome, it is thought to be because of selective abbreviation of the APD of right ventricular epicardium. Preferential abbreviation of APD of either endocardium or epicardium appears to be responsible for amplification of TDR in the short QT syndrome. In catecholaminergic polymorphic VT, the reversal of the direction of activation of the ventricular wall is responsible for the increase in TDR. In conclusion, the long QT, short QT, Brugada and catecholaminergic VT syndromes are pathologies with very different phenotypes and aetiologies, but which share a common final pathway in causing sudden death.

The Brugada Syndrome.

In 1992 a syndrome was described consisting of syncopal episodes and/or (resuscitated) sudden death in patients with a structurally normal heart and a characte ristic electrocardiogram (ECG) displaying a pattern resembling a right bundle branch block with ST segment elevation in leads V1 to V3. The disease is genetically determined with an autosomal dominant pattern of transmission in 50% of the familial cases. Several different mutations have been identified affecting the structure, function and trafficking of the sodium channel. The syndrome is ubiquitous. Its incidence and prevalence are difficult to estimate, but this disease may cause 4 to 10 sudden deaths per 10,000 inhabitants per year representing the most frequent cause of natural death in males younger than 50 in South Asia. The disease has been linked to the sudden infant death syndrome (SIDS) and to the sudden unexpected death syndrome (SUDS) by showing that the electrocardiogram and mutations are the same as in Brugada syndrome. The diagnosis is easily made by means of the ECG when it is typical. There exist, however, patients with concealed and intermittent electrocardiographic forms that make the diagnosis difficult. The ECG can be modulated by changes in autonomic balance, body temperature, glucose level and the administration of antiarrhythmic, neuroleptic and antimalaria drugs. Beta adrenergic stimulation normalizes the ECG. Loss of the action potential dome in right ventricular epicardium but not in endocardium underlies the ST segment elevation. Electrical heterogeneity within right ventricular epicardium leads to the development of closely coupled extrasystoles via phase 2 reentry that precipitate ventricular ,fibrillation. Antiarrhythmic drugs do not prevent sudden death in symptomatic or asymptomatic individuals. Implantation of an automatic cardioverter-defibrillator is the only currently proven effective therapy. Patients with frequent electrical storms may even need cardiac transplantation as last resort.

Coordinated down-regulation of KCNQ1 and KCNE1 expression contributes to reduction of I(Ks) in canine hypertrophied hearts.

OBJECTIVE: In animal models of hypertrophy, electrical remodeling giving rise to QT prolongation occurs rapidly and is associated with the development of torsade de pointes (TdP) arrhythmias and sudden death. Chronic AV block (CAVB)-induced hypertrophy in dogs has been associated with a reduction in the slow component (I(Ks)) of the delayed rectifier potassium current (I(K)), which contributes to a prolongation of ventricular repolarization, the development of an acquired form of long QT, and the substrate for triggered activity and TdP. The present study was designed to probe the molecular basis for the decrease in I(Ks) by studying the characteristics of KCNE1 and KCNQ1, the putative genes responsible for formation of the channel. METHODS AND RESULTS: Using a combination of Northern blot, competitive multiplex PCR and immunoblot assays, we found that CAVB reduces KCNE1 and KCNQ1 RNA in the canine ventricles by 70 and 80%, respectively. Protein levels of KCNE1 and KCNQ1 were reduced by 60 and 50%, respectively. We also demonstrate at the molecular level the basis for inter-ventricular difference in I(Ks) density previously reported in hearts of normal dogs and show the basis for reduction of this difference in the CAVB dog. CONCLUSIONS: Our results indicate that the CAVB-induced reduction in I(Ks) is due to a down-regulation of KCNE1 and KCNQ1 transcription. The data suggest that electrical remodeling of the cardiac ventricle during hypertrophy involves regulation of the gene expression through modulation of transcriptional and translational regulatory pathways. The reduction in KCNE1 and KCNQ1 expression increases the dependence of ventricular repolarization on the rapid component of I(K) and may potentiate the action of Class III antiarrhythmic agents.

Brugada syndrome: a decade of progress.

The Brugada syndrome has gained wide recognition throughout the world and today is believed to be responsible for 4% to 12% of all sudden deaths and approximately 20% of deaths in patients with structurally normal hearts. The incidence of the disease is on the order of 5 per 10 000 inhabitants and, apart from accidents, is the leading cause of death of men under the age of 50 in regions of the world where the inherited syndrome is endemic. This minireview briefly summarizes the progress made over the past decade in our understanding of the clinical, genetic, cellular, ionic, and molecular aspects of this disease.

Divergent expression of delayed rectifier K(+) channel subunits during mouse heart development.

The repolarization phase of the cardiac action potential is dependent on transmembrane K(+) currents. The slow (I(Ks)) and fast (I(Kr)) components of the delayed-rectifier cardiac K(+) current are generated by pore-forming alpha subunits KCNQ1 and KCNH2, respectively, in association with regulatory beta-subunit KCNE1, KCNE2 and perphaps KCNE3. In the present study we have investigated the distribution of transcripts encoding these five potassium channel-forming subunits during mouse heart development as well as the protein distribution of KCNQ1 and KCNH2. KCNQ1 and KCNH2 mRNAs (and protein) are first expressed at embryonic day (E) 9.5, showing comparable levels of expression within the atrial and ventricular myocardium during the embryonic and fetal stages. In contrast, the beta-subunits display a more dynamic pattern of expression during development. KCNE1 expression is first observed at E9.5 throughout the entire myocardium and progressively is confined to the ventricular myocardium. With further development (E16.5), KCNE1 expression is mainly confined to the compact ventricular myocardium. KCNE2 is first expressed at E9.5 and it is restricted already to the atrial myocardium. KCNE3 is first expressed at E8.5 throughout the myocardium and with further development, it becomes restricted to the atrial myocardium. The fact that alpha subunits are homogeneously distributed within the myocardium, whereas the beta subunits display a regionalized expression profile during cardiac development, suggest that differences in the slow and fast component of the delayed-rectifier cardiac K(+) currents between the atrial and the ventricular cardiomyocytes are mainly determined by differential beta-subunit distribution.

Larger late sodium conductance in M cells contributes to electrical heterogeneity in canine ventricle.

Action potentials and whole cell sodium current were recorded in canine epicardial, midmyocardial, and endocardial myocytes in normal sodium at 37 degrees C. Tetrodotoxin (TTX) reduced the action potential duration of midmyocardial cells to a greater degree than either epicardial or endocardial cells. Whole cell recordings in potassium-free and very-low-chloride solutions revealed a slowly decaying current that was completely inhibited by 5 microM TTX or replacement of external and internal sodium with the impermeant cation N-methyl-D-glucamine. Late sodium current density at 0 mV was 47% greater in midmyocardial cells and averaged -0.532 +/- 0.058 pA/pF in endocardial, -0.463 +/- 0.068 pA/pF in epicardial, and -0.785 +/- 0.070 pA/pF in midmyocardial cells. Neither the frequency dependence of late sodium current nor its recovery from inactivation exhibited transmural differences. After a 4.5-s pulse to -30 mV, late sodium current recovered with a single time constant of 140 ms. We conclude that a larger late sodium conductance in midmyocardial cells will favor longer action potentials in these cells. More importantly, drugs that slow inactivation of sodium channels will produce a nonuniform response across the ventricular wall that is proarrhythmic.

The Brugada syndrome: clinical, genetic, cellular, and molecular abnormalities.

The Brugada syndrome is an arrhythmic syndrome characterized by a right bundle branch block pattern and ST segment elevation in the right precordial leads of the electrocardiogram in conjunction with a high incidence of sudden death secondary to ventricular tachyarrhythmias. No evidence of structural heart disease is noted during diagnostic evaluation of these patients. In 25% of families, there appears to be an autosomal dominant mode of transmission with variable expression of the abnormal gene. Mutations have been identified in the gene that encodes the alpha subunit of the sodium channel (SCN5A) on chromosome 3. This genetic defect causes a reduction in the density of the sodium current and explains the worsening of the above electrocardiographic abnormalities when patients are treated with sodium channel blocking antiarrhythmic agents, which further diminish the already reduced sodium current. The prognosis is poor with up to a 10% per year mortality. Antiarrhythmic drugs including beta-blockers and amiodarone have no benefit in prolonging survival. The treatment of choice is the insertion of an implantable cardioverter-defibrillator.

Molecular basis for the transmural distribution of the transient outward current.

Regional differences in electrical properties of cardiac cells contribute to the normal function of the heart as well as to the inscription of the J wave and T wave of the ECG. Amplification of these electrical heterogeneities can lead to the development of life-threatening cardiac arrhythmias and sudden death. A number of ionic distinctions have been shown to contribute to the different action potential morphologies of epicardial, M and endocardial ventricular cells as well as to the distinctive responses of these three cell types to pharmacological agents and pathophysiological states (for reviews see Antzelevitch et al. 1999; Antzelevitch & Dumaine, 2000).

Chromanol 293B inhibits slowly activating delayed rectifier and transient outward currents in canine left ventricular myocytes.

INTRODUCTION: Drugs that selectively inhibit the slowly activating component of the delayed rectifier potassium current (I(Ks)) are being considered as possible antiarrhythmic agents, because they produce more prolongation of action potential duration at fast rates with less transmural dispersion of repolarization compared with blockers of the rapidly activating component (I(Kr)). Although the chromanol derivative chromanol 293B has been shown to be relatively selective in blocking I(Ks) in some species, its selectivity is far from established. METHODS AND RESULTS: The present study uses whole-cell, patch-clamp technique to examine the selectivity of this compound for inhibition of I(Ks) in comparison with other repolarizing ionic currents, such as I(Kr), inward rectifier potassium current (I(Kl)), transient outward current (I(to)), and L-type calcium current (I(Ca-L)) in canine left ventricular mid-myocardial and endocardial cells. Chromanol 293B blocked I(Ks) with an IC50 of 1.8 microM and I(to) with an IC50 of 38 microM. Concentrations as high as 30 microM did not affect I(Kl), I(Kr), or I(Ca-L). Higher concentrations of chromanol 293B (100 microM) caused a slight, but statistically insignificant, inhibition of I(Kr). CONCLUSION: Our results indicate that chromanol 293B is a relatively selective blocker of I(Ks) in canine left ventricular myocytes.