Rate-dependent effects of lidocaine on cardiac dynamics: Development and analysis of a low-dimensional drug-channel interaction model.

State-dependent sodium channel blockers are often prescribed to treat cardiac arrhythmias, but many sodium channel blockers are known to have pro-arrhythmic side effects. While the anti and proarrhythmic potential of a sodium channel blocker is thought to depend on the characteristics of its rate-dependent block, the mechanisms linking these two attributes are unclear. Furthermore, how specific properties of rate-dependent block arise from the binding kinetics of a particular drug is poorly understood. Here, we examine the rate-dependent effects of the sodium channel blocker lidocaine by constructing and analyzing a novel drug-channel interaction model. First, we identify the predominant mode of lidocaine binding in a 24 variable Markov model for lidocaine-sodium channel interaction by Moreno et al. Specifically, we find that (1) the vast majority of lidocaine bound to sodium channels is in the neutral form, i.e., the binding of charged lidocaine to sodium channels is negligible, and (2) neutral lidocaine binds almost exclusively to inactivated channels and, upon binding, immobilizes channels in the inactivated state. We then develop a novel 3-variable lidocaine-sodium channel interaction model that incorporates only the predominant mode of drug binding. Our low-dimensional model replicates an extensive amount of the voltage-clamp data used to parameterize the Moreno et al. model. Furthermore, the effects of lidocaine on action potential upstroke velocity and conduction velocity in our model are similar to those predicted by the Moreno et al. model. By exploiting the low-dimensionality of our model, we derive an algebraic expression for level of rate-dependent block as a function of pacing frequency, restitution properties, diastolic and plateau potentials, and drug binding rate constants. Our model predicts that the level of rate-dependent block is sensitive to alterations in restitution properties and increases in diastolic potential, but it is insensitive to variations in the shape of the action potential waveform and lidocaine binding rates.

In Silico Assessment of Class I Antiarrhythmic Drug Effects on Pitx2-Induced Atrial Fibrillation: Insights from Populations of Electrophysiological Models of Human Atrial Cells and Tissues.

Electrical remodelling as a result of homeodomain transcription factor 2 (Pitx2)-dependent gene regulation was linked to atrial fibrillation (AF) and AF patients with single nucleotide polymorphisms at chromosome 4q25 responded favorably to class I antiarrhythmic drugs (AADs). The possible reasons behind this remain elusive. The purpose of this study was to assess the efficacy of the AADs disopyramide, quinidine, and propafenone on human atrial arrhythmias mediated by Pitx2-induced remodelling, from a single cell to the tissue level, using drug binding models with multi-channel pharmacology. Experimentally calibrated populations of human atrial action po-tential (AP) models in both sinus rhythm (SR) and Pitx2-induced AF conditions were constructed by using two distinct models to represent morphological subtypes of AP. Multi-channel pharmaco-logical effects of disopyramide, quinidine, and propafenone on ionic currents were considered. Simulated results showed that Pitx2-induced remodelling increased maximum upstroke velocity (dVdtmax), and decreased AP duration (APD), conduction velocity (CV), and wavelength (WL). At the concentrations tested in this study, these AADs decreased dVdtmax and CV and prolonged APD in the setting of Pitx2-induced AF. Our findings of alterations in WL indicated that disopyramide may be more effective against Pitx2-induced AF than propafenone and quinidine by prolonging WL.

Assessment of Drug Proarrhythmic Potential in Electrically Paced Human Induced Pluripotent Stem Cell-Derived Ventricular Cardiomyocytes Using Multielectrode Array.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been widely used for the assessment of drug proarrhythmic potential through multielectrode array (MEA). HiPSC-CM cultures beat spontaneously with a wide range of frequencies, however, which could affect drug-induced changes in repolarization. Pacing hiPSC-CMs at a physiological heart rate more closely resembles the state of in vivo ventricular myocytes and permits the standardization of test conditions to improve consistency. In this study, we systematically investigated the time window of stable ion currents in high-purity hiPSC-derived ventricular cardiomyocytes (hiPSC-vCMs) and confirmed that these cells could be used to correctly predict the proarrhythmic risk of Comprehensive In Vitro Proarrhythmia Assay (CiPA) reference compounds. To evaluate drug proarrhythmic potentials at a physiological beating rate, we used a MEA to electrically pace hiPSC-vCMs, and we recorded regular field potential waveforms in hiPSC-vCMs treated with DMSO and 10 CiPA reference drugs. Prolongation of field potential duration was detected in cells after exposure to high- and intermediate-risk drugs; in addition, drug-induced arrhythmia-like events were observed. The results of this study provide a simple and feasible method to investigate drug proarrhythmic potentials in hiPSC-CMs at a physiological beating rate.

Assessment of spatial heterogeneity of ventricular repolarization after multi-channel blocker drugs in healthy subjects.

BACKGROUND AND OBJECTIVES: In contrast to potassium channel blockers, drugs affecting multiple channels seem to reduce torsadogenic risks. However, their effect on spatial heterogeneity of ventricular repolarization (SHVR) is still matter of investigation. Aim of this work is to assess the effect of four drugs blocking the human ether-à-go-go-related gene (hERG) potassium channel, alone or in combination with other ionic channel blocks, on SHVR, as estimated by the V-index on short triplicate 10 s ECG. METHODS: The V-index is an estimate of the standard deviation of the repolarization times of the myocytes across the entire myocardium, obtained from multi-lead surface electrocardiograms. Twenty-two healthy subjects received a pure hERG potassium channel blocker (dofetilide) and 3 other drugs with additional varying degrees of sodium and calcium (L-type) channel block (quinidine, ranolazine, and verapamil), as well as placebo. A one-way repeated-measures Friedman test was performed to compare the V-index over time. RESULTS: Computer simulations and Bland-Altman analysis supported the reliability of the estimates of V-index on triplicate 10 s ECG. Ranolazine, verapamil and placebo did not affect the V-index. On the contrary, after quinidine and dofetilide administration, an increase of V-index from predose to its peak value was observed (ΔΔV-index values were 19 ms and 27 ms, respectively, p < 0.05). CONCLUSIONS: High torsadogenic drugs (dofetilide and quinidine) affected significantly the SHVR, as quantified by the V-index. The metric has therefore a potential in assessing drug arrhythmogenicity.

Cost-Effectiveness of Rate- and Rhythm-Control Drugs for Treating Atrial Fibrillation in Korea.

PURPOSE: Although the economic and mortality burden of atrial fibrillation (AF) is substantial, it remains unclear which treatment strategies for rate and rhythm control are most cost-effective. Consequently, economic factors can play an adjunctive role in guiding treatment selection. MATERIALS AND METHODS: We built a Markov chain Monte Carlo model using the Korean Health Insurance Review & Assessment Service database. Drugs for rate control and rhythm control in AF were analyzed. Cost-effective therapies were selected using a cost-effectiveness ratio, calculated by net cost and quality-adjusted life years (QALY). RESULTS: In the National Health Insurance Service data, 268149 patients with prevalent AF (age ≥18 years) were identified between January 1, 2013 and December 31, 2015. Among them, 212459 and 55690 patients were taking drugs for rate and rhythm control, respectively. Atenolol cost $714/QALY. Among the rate-control medications, the cost of propranolol was lowest at $487/QALY, while that of carvedilol was highest at $1363/QALY. Among the rhythm-control medications, the cost of pilsicainide was lowest at $638/QALY, while that of amiodarone was highest at $986/QALY. Flecainide and propafenone cost $834 and $830/QALY, respectively. The cost-effectiveness threshold of all drugs was lower than $30000/QALY. Compared with atenolol, the rate-control drugs propranolol, betaxolol, bevantolol, bisoprolol, diltiazem, and verapamil, as well as the rhythm-control drugs sotalol, pilsicainide, flecainide, propafenone, and dronedarone, showed better incremental cost-effectiveness ratios. CONCLUSION: Propranolol and pilsicainide appear to be cost-effective in patients with AF in Korea assuming that drug usage or compliance is the same.

Multi-dry-electrode plate sensor for non-invasive electrocardiogram and heart rate monitoring for the assessment of drug responses in freely behaving mice.

Monitoring of electrocardiogram (ECG) and heart rate (HR) is essential in a wide range of experiments. For conscious animal studies, telemetry is the preferred approach; however, it requires 1-3 weeks of recovery after surgical device-implantation. The present paper describes a novel multi-dry-electrode plate (MDEP) sensor system to monitor ECG/HR in freely behaving mice without the need for surgery for device/electrode implantation. The MDEP sensor is a rectangular plate with 15 gold-plated stripe pattern electrodes, on which a mouse can walk around freely, and detects ECG whenever ≥2 paws (footpads) come in contact with the electrodes. Here we show that the MDEP sensor detected distinct QRS complexes which, were fragmented due to locomotion and insufficient perspiration on the footpads. Nonetheless, the HR calculated from the QRS complexes were similar to the HR calculated from R-R intervals simultaneously recorded from lead-II ECG (difference = 0.0 ±â€¯0.16 ms) as part of the validation exercise. Also, the archetypal responses to isoproterenol and metoprolol injections were successfully detected as a significantly elevation (+151 ±â€¯15 bpm) and reduction (-77 ±â€¯6 bpm) in HR, respectively, compared to vehicle at 20-60 min postdose. Conversely, the P wave was rarely identifiable unless signal averaging was undertaken. These results indicate a potential utility for the MDEP-sensor system for cardiac pharmacological studies. In addition, signal averaging appeared to be effective for detection of ECG intervals such as PR and QT, although the QT cannot be measured in the mouse heart as there is no T wave.

Effects of new antiarrhythmic agent SS-68 on excitation conduction, electrical activity in Purkinje fibers and pulmonary veins: Assessment of safety and side effects risk.

The compound SS-68 has been selected among numerous new derivatives of indole and demonstrated antiarrhythmic effects in animal models. The present study concerns several aspects of SS-68 safety and efficacy as a potential antiarrhythmic drug. The first estimation of atrioventricular conduction in mammalian heart under SS-68 has been carried out; effects of SS-68 in Purkinje fibers and myocardium of pulmonary veins have been investigated. The drug weakly affects cardiac atrioventricular conduction: only high concentrations of SS-68 (≥10 µmol/L) significantly decrease this parameter. Also, the drug weakly affects Purkinje fibers automaticity, but effectively alters action potential waveform in Purkinje fibers in a concentration-dependent manner. SS-68 (0.1-100 µmol/L) failed to induce any early or delayed afterdepolarizations in Purkinje fibers both in basal conditions and under provocation of proarrhythmic activity by norepinephrine (NE). Moreover, 10 µmol/L SS-68 suppressed NE-induced extra-beats and rapid firing in Purkinje fibers. In pulmonary veins only high concentrations of SS-68 significantly increased action potential duration, while lower concentrations (0.1-1 µmol/L) were ineffective. Also, 0.1-100 µmol/L SS-68 was unable to elicit arrhythmogenic alternations of action potential waveform in pulmonary veins. In conclusion, SS-68 has no proarrhythmic effects, such as afterdepolarizations or abnormal automaticity in used experimental models.

Evaluation of Batch Variations in Induced Pluripotent Stem Cell-Derived Human Cardiomyocytes from 2 Major Suppliers.

Drug-induced proarrhythmia is a major safety issue in drug development. Developing sensitive in vitro assays that can predict drug-induced cardiotoxicity in humans has been a challenge of toxicology research for decades. Recently, induced pluripotent stem cell-derived human cardiomyocytes (iPSC-hCMs) have become a promising model because they largely replicate the electrophysiological behavior of human ventricular cardiomyocytes. Patient-specific iPSC-hCMs have been proposed for personalized cardiac drug selection and adverse drug response prediction; however, many procedures are involved in cardiomyocytes differentiation and purification process, which may result in large line-to-line and batch-to-batch variations. Here, we examined the purity, cardiac ion channel gene expression profile, and electrophysiological response of 3 batches of iPSC-hCMs from each of 2 major cell suppliers. We found that iPSC-hCMs from both vendors had similar purities. Most of the cardiac ion channel genes were expressed uniformly among different batches of iCells, while larger variations were found in Cor.4U cells, particularly in the expression of CACNA1C, KCND2, and KCNA5 genes, which could underlie the differences in baseline beating rate (BR) and field potential duration (FPD) measurements. Although, in general, the electrophysiological responses of different batches of cells to Na+, Ca2+, Ikr, and Iks channel blockers were similar, with Ikr blocker-induced proarrhythmia, the sensitivities were depended on baseline BR and FPD values: cells that beat slower had longer FPD and greater sensitivity to drug-induced proarrhythmia. Careful evaluation of the performance of iPSC-hCMs and methods of data analysis is warranted for shaping regulatory standards in qualifying iPSC-hCMs for drug safety testing.

Minimal T-wave representation and its use in the assessment of drug arrhythmogenicity.

BACKGROUND: Recently, numerous models and techniques have been developed for analyzing and extracting features from the T wave which could be used as biomarkers for drug-induced abnormalities. The majority of these techniques and algorithms use features that determine readily apparent characteristics of the T wave, such as duration, area, amplitude, and slopes. METHODS: In the present work the T wave was down-sampled to a minimal rate, such that a good reconstruction was still possible. The entire T wave was then used as a feature vector to assess drug-induced repolarization effects. The ability of the samples or combinations of samples obtained from the minimal T-wave representation to correctly classify a group of subjects before and after receiving d,l-sotalol 160 mg and 320 mg was evaluated using a linear discriminant analysis (LDA). RESULTS: The results showed that a combination of eight samples from the minimal T-wave representation can be used to identify normal from abnormal repolarization significantly better compared to the heart rate-corrected QT interval (QTc). It was further indicated that the interval from the peak of the T wave to the end of the T wave (Tpe) becomes relatively shorter after IKr inhibition by d,l-sotalol and that the most pronounced repolarization changes were present in the ascending segment of the minimal T-wave representation. CONCLUSIONS: The minimal T-wave representation can potentially be used as a new tool to identify normal from abnormal repolarization in drug safety studies.

Assessment of the clinical cardiac drug-drug interaction associated with the combination of hepatitis C virus nucleotide inhibitors and amiodarone in guinea pigs and rhesus monkeys.

In 2015, European and U.S. health agencies issued warning letters in response to 9 reported clinical cases of severe bradycardia/bradyarrhythmia in hepatitis C virus (HCV)-infected patients treated with sofosbuvir (SOF) in combination with other direct acting antivirals (DAAs) and the antiarrhythmic drug, amiodarone (AMIO). We utilized preclinical in vivo models to better understand this cardiac effect, the potential pharmacological mechanism(s), and to identify a clinically translatable model to assess the drug-drug interaction (DDI) cardiac risk of current and future HCV inhibitors. An anesthetized guinea pig model was used to elicit a SOF+AMIO-dependent bradycardia. Detailed cardiac electrophysiological studies in this species revealed SOF+AMIO-dependent selective nodal dysfunction, with initial, larger effects on the sinoatrial node. Further studies in conscious, rhesus monkeys revealed an emergent bradycardia and bradyarrhythmia in 3 of 4 monkeys administered SOF+AMIO, effects not observed with either agent alone. Morever, bradycardia and bradyarrhythmia were not observed in rhesus monkeys when intravenous infusion of MK-3682 was completed after AMIO pretreatment. CONCLUSIONS: These are the first preclinical in vivo experiments reported to replicate the severe clinical SOF+AMIO cardiac DDI and provide potential in vivo mechanism of action. As such, these data provide a preclinical risk assessment paradigm, including a clinically relevant nonhuman primate model, with which to better understand cardiovascular DDI risk for this therapeutic class. Furthermore, these studies suggest that not all HCV DAAs and, in particular, not all HCV nonstructural protein 5B inhibitors may exhibit this cardiac DDI with amiodarone. Given the selective in vivo cardiac electrophysiological effect, these data enable targeted cellular/molecular mechanistic studies to more precisely identify cell types, receptors, and/or ion channels responsible for the clinical DDI. (Hepatology 2016;64:1430-1441).

The cross-bridge dynamics is determined by two length-independent kinetics: Implications on muscle economy and Frank-Starling Law.

The cellular mechanisms underlying the Frank-Starling Law of the heart and the skeletal muscle force-length relationship are not clear. This study tested the effects of sarcomere length (SL) on the average force per cross-bridge and on the rate of cross-bridge cycling in intact rat cardiac trabeculae (n=9). SL was measured by laser diffraction and controlled with a fast servomotor to produce varying initial SLs. Tetanic contractions were induced by addition of cyclopiazonic acid, to maintain a constant activation. Stress decline and redevelopment in response to identical ramp shortenings, starting at various initial SLs, was analyzed. Both stress decline and redevelopment responses revealed two distinct kinetics: a fast and a slower phase. The duration of the rapid phases (4.2 ± 0.1 msec) was SL-independent. The second slower phase depicted a linear dependence of the rate of stress change on the instantaneous stress level. Identical slopes (70.5 ± 1.6 [1/s], p=0.33) were obtained during ramp shortening at all initial SLs, indicating that the force per cross-bridge and cross-bridge cycling kinetics are length-independent. A decrease in the slope at longer SLs was obtained during stress redevelopment, due to internal shortening. The first phase is attributed to rapid changes in the average force per cross-bridge. The second phase is ascribed to both cross-bridge cycling between its strong and weak conformations and to changes in the number of strong cross-bridges. Cross-bridge cycling kinetics and muscle economy are length-independent and the Frank-Starling Law cannot be attributed to changes in the force per cross-bridge or in the single cross-bridge cycling rates.

Long-term stability, reproducibility, and statistical sensitivity of a telemetry-instrumented dog model: A 27-month longitudinal assessment.

INTRODUCTION: ICH guidelines, as well as best-practice and ethical considerations, provide strong rationale for use of telemetry-instrumented dog colonies for cardiovascular safety assessment. However, few studies have investigated the long-term stability of cardiovascular function at baseline, reproducibility in response to pharmacologic challenge, and maintenance of statistical sensitivity to define the usable life of the colony. These questions were addressed in 3 identical studies spanning 27months and were performed in the same colony of dogs. METHODS: Telemetry-instrumented dogs (n=4) received a single dose of dl-sotalol (10mg/kg, p.o.), a ß1 adrenergic and IKr blocker, or vehicle, in 3 separate studies spanning 27months. Systemic hemodynamics, cardiovascular function, and ECG parameters were monitored for 18h post-dose; plasma drug concentrations (Cp) were measured at 1, 3, 5, and 24h post-dose. RESULTS: Baseline hemodynamic/ECG values were consistent across the 27-month study with the exception of modest age-dependent decreases in heart rate and the corresponding QT-interval. dl-Sotalol elicited highly reproducible effects in each study. Reductions in heart rate after dl-sotalol treatment ranged between -22 and -32 beats/min, and slight differences in magnitude could be ascribed to variability in dl-sotalol Cp (range=3230-5087ng/mL); dl-sotalol also reduced LV-dP/dtmax 13-22%. dl-Sotalol increased the slope of the PR-RR relationship suggesting inhibition of AV-conduction. Increases in the heart-rate corrected QT-interval were not significantly different across the 3 studies and results of a power analysis demonstrated that the detection limit for QTc values was not diminished throughout the 27month period and across a range of power assumptions despite modest, age-dependent changes in heart rate. DISCUSSION: These results demonstrate the long-term stability of a telemetry dog colony as evidenced by a stability of baseline values, consistently reproducible response to pharmacologic challenge and no diminished statistical sensitivity over time.

Characterization of an anesthetized dog model of transient cardiac ischemia and rapid pacing: a pilot study for preclinical assessment of the potential for proarrhythmic risk of novel drug candidates.

INTRODUCTION: Preclinical proarrhythmic risk assessment of drug candidates is focused predominantly on arrhythmias arising from repolarization abnormalities. However, drug-induced cardiac conduction slowing is associated with significant risk of life-threatening ventricular arrhythmias, particularly in a setting of cardiac ischemia. Therefore, we optimized and characterized an anesthetized dog model to evaluate the potential proarrhythmic risk of drug candidates in ischemic heart disease patients. METHODS: Anesthetized dogs were instrumented with atrial and ventricular epicardial electrodes for pacing and measurement of conduction times, and a balloon occluder and flow probe placed around the left anterior descending coronary artery (LAD) distal to the first branch. Conduction times, ECG intervals and incidence of arrhythmias were assessed serially at the end of each dose infusion (flecainide: 0.32, 0.63, 1.25, 2.5 and 5mg/kg, i.v.; dofetilide:1.25, 2.5, 5, 10 and 20 µg/kg, i.v.; or vehicle; n=6/group) both during normal flow (with and without rapid pacing) and during 5-min LAD occlusion (with and without rapid pacing). Compound X, a development candidate with mild conduction slowing activity, was also evaluated. RESULTS: Flecainide produced pronounced, dose-dependent slowing of conduction that was exacerbated during ischemia and rapid pacing. In addition, ventricular tachycardia (VT) and fibrillation (VF) occurred in 4 of 6 dogs (3 VF @ 0.63 mg/kg; 1VT @ 2.5mg/kg). In contrast, no animals in the vehicle group developed arrhythmias. Dofetilide, a potent IKr blocker that does not slow conduction, prolonged QT interval but did not cause further conduction slowing during ischemia with or without pacing and there were no arrhythmias. Compound X, like flecainide, produced marked conduction slowing and arrhythmias (VT, VF) during ischemia and pacing. DISCUSSION: This model may be useful to more accurately define shifts in safety margins in a setting of ischemia and increased cardiac demand for drugs that slow conduction.

Assessment of anti-arrhythmic activity of antipsychotic drugs in an animal model: influence of non-cardiac α1-adrenergic receptors.

Torsades de Pointes (TdP) is a potentially lethal cardiac arrhythmia and a known adverse effect of many drugs secondary to block of the rapidly activating delayed rectifier potassium current (IKr). In animal models antipsychotic drugs have shown reduced pro-arrhythmic potential compared to drugs with comparable IKr-blocking characteristics. The reduced pro-arrhythmic properties of antipsychotic drugs has been attributed to a variety of different causes e.g., effects on α1-adrenergic receptors, ß-adrenergic receptors, muscarinic receptors or cardiac ion channels like Ca(2+)- and Na(+)-channels. Since only limited experimental information exists about the effects of α1-adrenergic receptor activity of antipsychotic drugs in pro-arrhythmic models, we have decided to investigate this. In this study we show that four antipsychotic drugs all have high affinity for α1-adrenergic receptor (sertindole>risperidone>haloperidol>olanzapine) and all block IKr (sertindole>haloperidol>risperidone>olanzapine). In canine Purkinje fibres, α1-adrenergic stimulation prolonged action potential duration; however, the stimulation does not cause afterdepolarizations, even in the presence of dofetilide-induced delayed repolarization. We showed for the first time in an in vivo pro-arrhythmic rabbit model that several antipsychotic drugs in accordance with their known α1-adrenergic receptor blocking properties reduced the incidence of drug-induced TdP and that the overall ability of the antipsychotic drugs to prevent TdP was associated with prevention of methoxamine induced increase in blood pressure. Further investigations are required to clarify the relative importance of α1-adrenergic receptor antagonism in conjunction with the additional effects of antipsychotic drugs on various receptors and ion channels.

Antiarrhythmic drug therapy for atrial fibrillation.

Atrial fibrillation (AF) is the most frequently encountered arrhythmia. Prevalence increases with advancing age and so as its associated comorbidities, like heart failure. Choice of pharmacologic therapy depends on whether the goal of treatment is maintaining sinus rhythm or tolerating AF with adequate control of ventricular rates. Antiarrhythmic therapy and conversion of AF into sinus rhythm comes with the side effect profile, and we should select best antiarrhythmic therapy, individualized to the patient. New antiarrhythmic drugs are being tested in clinical trials. Drugs that target remodeling and inflammation are being tested for their use as prevention of AF or as upstream therapy.

Cardiac Safety Research Consortium: can the thorough QT/QTc study be replaced by early QT assessment in routine clinical pharmacology studies? Scientific update and a research proposal for a path forward.

The International Conference on Harmonization E14 guidance for the clinical evaluation of QT/QTc interval prolongation requires almost all new drugs to undergo a dedicated clinical study, primarily in healthy volunteers, the so-called TQT study. Since 2005, when the E14 guidance was implemented in United States and Europe, close to 400 TQT studies have been conducted. In February 2012, the Cardiac Safety Research Consortium held a think tank meeting at Food and Drug Administration's White Oak campus to discuss whether "QT assessment" can be performed as part of routine phase 1 studies. Based on these discussions, a group of experts convened to discuss how to improve the confidence in QT data from early clinical studies, for example, the First-Time-in-Human trial, through collection of serial electrocardiograms and pharmacokinetic samples and the use of exposure response analysis. Recommendations are given on how to design such "early electrocardiogram assessment," and the limitation of not having a pharmacologic-positive control in these studies is discussed. A research path is identified toward collecting evidence to replace or provide an alternative to the dedicated TQT study.

Assessment of testing methods for drug-induced repolarization delay and arrhythmias in an iPS cell-derived cardiomyocyte sheet: multi-site validation study.

A prospective comparison study across 3 independent research laboratories of a pure IKr blocker E-4031 was conducted by using the same batch of human iPS cell-derived cardiomyocytes in order to verify the utility and reliability of our original standard protocol. Field potential waveforms were recorded with a multi-electrode array system to measure the inter-spike interval and field potential duration. The effects of E-4031 at concentrations of 1 to 100 nM were sequentially examined every 10 min. In each facility, E-4031 significantly prolonged the field potential duration corrected by Fridericia's formula and caused early afterdepolarizations occasionally resulting in triggered activities, whereas it tended to decrease the rate of spontaneous contraction. These results were qualitatively and quantitatively consistent with previous non-clinical in vitro and in vivo studies as well as clinical reports. There were inter-facility differences in some absolute values of the results, which were not observed when the values were normalized as percentage change. Information described in this paper may serve as a guide when predicting the drug-induced repolarization delay and arrhythmias with this new technology of stem cells.