No Influence of Asundexian on Cardiac Repolarization

Inhibition of activated factor XI reduces thrombogenesis while maintaining physiological hemostasis, with the expectation of reduced bleeding risk compared with standard of care in the clinical setting. Asundexian (BAY 2433334), an activated factor XI inhibitor, is in clinical development for the prevention of thromboembolic events. The effect of asundexian and its plasma metabolite M10 on cardiac repolarization and potential interactions with the hNav1.5 sodium, hCav1.2 calcium, and human ether-à-go-go-related gene (hERG) potassium channels was investigated in vitro. Additionally, asundexian effects on cardiac parameters and electrocardiogram were examined in telemetered beagle dogs. A randomized, placebo-controlled, 4-way crossover, thorough QT study in healthy adults evaluated the influence of 50 and 150 mg of asundexian on the corrected QT interval, including 400 mg of moxifloxacin as positive control. Across all studies, asundexian and M10 were not associated with any effects on cardiac repolarization. The largest in vitro effects of asundexian (approximately 20% inhibition) were seen for hCav1.2 and hERG. Throughout the thorough QT study, the upper limits of the one-sided 95% confidence interval of placebo-corrected mean changes from baseline in Fridericia corrected QT for 50 and 150 mg of asundexian were below Δ = 10 milliseconds. Asundexian demonstrated favorable safety and tolerability profiles.

A Randomized, Double-Blind, Parallel Design Thorough QT Study With a Nested Crossover to Compare the Cardiac Safety of Amiselimod With Placebo and Positive Control in Healthy Volunteers

This double-blind study evaluated the cardiac safety of amiselimod. Healthy adults (n = 190) were randomized (2:1:1) to receive (1) oral placebo (day -1), followed by oral amiselimod (days 1-26), which was upwardly titrated from 0.4 to 1.6 mg once daily to achieve steady-state concentrations comparable with 0.4 (therapeutic) and 0.8 mg (supratherapeutic) once daily, and placebo (day 27); (2) placebo (day -1), oral moxifloxacin 400 mg (day 1; positive control), followed by placebo (days 1-27); or (3) placebo (days -1 to 26), followed by moxifloxacin 400 mg (day 27). No participant had a corrected QT interval by Fredericia (QTcF) >500 milliseconds or a change from baseline (dQTcF) >60 milliseconds. The upper limits of the 90%CIs for the differences in least-squares mean difference in dQTcF between amiselimod and placebo on days 13 and 26 were <10 milliseconds. Area under the concentration-time curve from 0 to 23.5 hours after dosing and maximum plasma concentration of amiselimod and amiselimod-P (active metabolite) at steady-state concentrations for the 0.8-mg dose on day 26 were approximately double that observed with the 0.4-mg dose on day 13. All adverse events were mild to moderate in severity, and no deaths occurred. Amiselimod did not have any clinically relevant effect on the QTcF interval.

Genetic Biomarkers of Antipsychotic-Induced Prolongation of the QT Interval in Patients with Schizophrenia

Antipsychotics (AP) induced prolongation of the QT interval in patients with schizophrenia (Sch) is an actual interdisciplinary problem as it increases the risk of sudden death syndrome. Long QT syndrome (LQTS) as a cardiac adverse drug reaction is a multifactorial symptomatic disorder, the development of which is influenced by modifying factors (APs' dose, duration of APs therapy, APs polytherapy, and monotherapy, etc.) and non-modifying factors (genetic predisposition, gender, age, etc.). The genetic predisposition to AP-induced LQTS may be due to several causes, including causal mutations in the genes responsible for monoheme forms of LQTS, single nucleotide variants (SNVs) of the candidate genes encoding voltage-dependent ion channels expressed both in the brain and in the heart, and SNVs of candidate genes encoding key enzymes of APs metabolism. This narrative review summarizes the results of genetic studies on AP-induced LQTS and proposes a new personalized approach to assessing the risk of its development (low, moderate, high). We recommend implementation in protocols of primary diagnosis of AP-induced LQTS and medication dispensary additional observations of the risk category of patients receiving APs, deoxyribonucleic acid profiling, regular electrocardiogram monitoring, and regular therapeutic drug monitoring of the blood APs levels.

Declining Levels and Bioavailability of IGF-I in Cardiovascular Aging Associate With QT Prolongation-Results From the 1946 British Birth Cohort

Background

As people age, circulating levels of insulin-like growth factors (IGFs) and IGF binding protein 3 (IGFBP-3) decline. In rat cardiomyocytes, IGF-I has been shown to regulate sarcolemmal potassium channel activity and late sodium current thus impacting cardiac repolarization and the heart rate-corrected QT (QTc). However, the relationship between IGFs and IGFBP-3 with the QTc interval in humans, is unknown.

Objectives

To examine the association of IGFs and IGFBP-3 with QTc interval in an older age population-based cohort.

Methods

Participants were from the 1946 Medical Research Council (MRC) National Survey of Health and Development (NSHD) British birth cohort. Biomarkers from blood samples at age 53 and 60-64 years (y, exposures) included IGF-I/II, IGFBP-3, IGF-I/IGFBP-3 ratio and the change (Δ) in marker levels between the 60-64 and 53y sampled timepoints. QTc (outcome) was recorded from electrocardiograms at the 60-64y timepoint. Generalized linear multivariable models with adjustments for relevant demographic and clinical factors, were used for complete-cases and repeated after multiple imputation.

Results

One thousand four hundred forty-eight participants were included (48.3% men; QTc mean 414 ms interquartile range 26 ms). Univariate analysis revealed an association between low IGF-I and IGF-I/IGFBP-3 ratio at 60-64y with QTc prolongation [respectively: β -0.30 ms/nmol/L, (95% confidence intervals -0.44, -0.17), p < 0.001; β-28.9 ms/unit (-41.93, -15.50), p < 0.001], but not with IGF-II or IGFBP-3. No association with QTc was found for IGF biomarkers sampled at 53y, however both ΔIGF-I and ΔIGF-I/IGFBP-3 ratio were negatively associated with QTc [β -0.04 ms/nmol/L (-0.08, -0.008), p = 0.019; β -2.44 ms/unit (-4.17, -0.67), p = 0.007] while ΔIGF-II and ΔIGFBP-3 showed no association. In fully adjusted complete case and imputed models (reporting latter) low IGF-I and IGF-I/IGFBP-3 ratio at 60-64y [β -0.21 ms/nmol/L (-0.39, -0.04), p = 0.017; β -20.14 ms/unit (-36.28, -3.99), p = 0.015], steeper decline in ΔIGF-I [β -0.05 ms/nmol/L/10 years (-0.10, -0.002), p = 0.042] and shallower rise in ΔIGF-I/IGFBP-3 ratio over a decade [β -2.16 ms/unit/10 years (-4.23, -0.09), p = 0.041], were all independently associated with QTc prolongation. Independent associations with QTc were also confirmed for other previously known covariates: female sex [β 9.65 ms (6.65, 12.65), p < 0.001], increased left ventricular mass [β 0.04 ms/g (0.02, 0.06), p < 0.001] and blood potassium levels [β -5.70 ms/mmol/L (-10.23, -1.18) p = 0.014].

Conclusion

Over a decade, in an older age population-based cohort, declining levels and bioavailability of IGF-I associate with prolongation of the QTc interval. As QTc prolongation associates with increased risk for sudden death even in apparently healthy people, further research into the antiarrhythmic effects of IGF-I on cardiomyocytes is warranted.

Thorough QT/QTc Evaluation of the Cardiac Safety of Enarodustat (JTZ-951), an Oral Erythropoiesis-Stimulating Agent, in Healthy Adults

This study evaluated the effect of enarodustat on cardiac repolarization in healthy subjects. Enarodustat (20 and 150 mg [supratherapeutic dose]), placebo, and moxifloxacin (positive control, 400 mg) were administered orally to males and females (N = 54) in a crossover fashion. Continuous 12-lead Holter electrocardiogram (ECG) data were obtained before and after dosing, and blood samples were obtained for pharmacokinetic assessments of enarodustat, its circulating metabolite (R)-M2, and moxifloxacin. Central tendency analysis was performed for relevant ECG parameters, the relationship between individual-corrected interval from beginning of the QRS complex to end of the T wave in the frontal plane (QTcI, the primary end point) and plasma concentrations of enarodustat and (R)-M2 were assessed, and ECG waveforms were evaluated for morphological changes. The supratherapeutic dose resulted in 7- and 9-fold higher geometric mean maximum concentrations for enarodustat and (R)-M2, respectively, than the 20 mg dose. Based on time point analysis, the upper bound of the 2-sided 90% confidence interval (CI) for QTcI did not exceed 10 milliseconds at any of the time points for either dose. Based on QTcI-concentration analysis, the slopes for enarodustat and (R)-M2 were not statistically different than 0, and the upper bounds of the 2-sided 90% CI for QTcI at the geometric mean maximum concentrations for the supratherapeutic dose were 1.97 and 1.68 milliseconds for enarodustat and (R)-M2, respectively. The lower bound of the 2-sided 90% CI for moxifloxacin was ≥5 milliseconds, demonstrating assay sensitivity. The study demonstrated no clinically relevant effect of enarodustat and (R)-M2 on cardiac repolarization. There was no evidence of any clinically significant effect on the PR interval and QRS duration, and ECG waveforms showed no new clinically relevant morphological changes.

Omecamtiv mecarbil does not prolong QTc intervals at therapeutic concentrations

AIMS

Omecamtiv mecarbil (OM) is a novel selective cardiac myosin activator under investigation for the treatment of heart failure. This study aimed to evaluate the effect of therapeutic concentrations of OM on electrocardiogram (ECG) parameters and exclude a clinically concerning effect on the rate-corrected QT (QTc) interval.

METHODS

In part A, 70 healthy subjects received a 25 mg oral dose of OM, and pharmacokinetics were assessed. Only subjects with maximum observed plasma concentration ≤ 350 ng/mL (n = 60) were randomized into part B, where they received a single oral dose of placebo, 50 mg OM and 400 mg moxifloxacin in a 3-period, 3-treatment, 6-sequence crossover study with continuous ECG collection.

RESULTS

After a 50-mg dose of OM, mean placebo-corrected change from baseline QTcF (∆∆QTcF; Fridericia correction) ranged from -6.7 ms at 1 hour postdose to -0.8 ms at 4 hours postdose. The highest upper bound of the 1-sided 95% confidence interval (CI) was 0.7 ms (4 h postdose). Moxifloxacin resulted in a clear increase in mean ∆∆QTcF, with a peak value of 13.1 ms (90% CI: 11.71-14.57) at 3 hours; lower bound of the 1-sided 95% CI was > 5 ms at all of the 3 prespecified time points. Based on a concentration-QTc analysis, an effect on ∆∆QTcF exceeding 10 ms can be excluded up to OM plasma concentrations of ~800 ng/mL. There were no serious or treatment-emergent adverse events leading to discontinuation from the study.

CONCLUSION

OM does not have a clinically relevant effect on the studied ECG parameters.

Exposure-response modeling of the effect of glasdegib on cardiac repolarization in patients with cancer

PURPOSE

To characterize the effect of glasdegib on cardiac repolarization (QTc) in patients with advanced cancer.

METHODS

A concentration-QTc model was developed using data from two glasdegib single-agent, dose-escalation trials. Triplicate electrocardiogram was performed at pre-specified timepoints paired with pharmacokinetic blood collections after a single dose and at steady-state. Changes in QTc from baseline were predicted by model-based simulations at the clinical dose (100 mg QD) and in a supratherapeutic setting.

RESULTS

Glasdegib did not affect the heart rate, but had a positive effect on the corrected QT interval, described by a linear mixed-effects model with ΔQTcF (QTc using Fridericia's formula) as the dependent variable with glasdegib plasma concentrations from doses of 5-640 mg QD. The predicted mean QTcF change (upper bound of the 95% CI) was 5.30 (6.24) msec for the therapeutic 100-mg QD dose; at supratherapeutic concentrations (40% and 100% increase over the therapeutic C_max), it was 7.42 (8.74) and 12.09 (14.25) msec, respectively.

CONCLUSIONS

The relationship of glasdegib exposure and QTc was well characterized by the model. The effect of glasdegib on the QTc interval did not cross the threshold of clinical concern for an oncology drug.

TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT01286467 and NCT00953758.

A Single Supratherapeutic Dose of Atogepant Does Not Affect Cardiac Repolarization in Healthy Adults: Results From a Randomized, Single-Dose, Phase 1 Crossover Trial

Atogepant is a selective, oral calcitonin gene–related peptide receptor antagonist in development for preventive treatment of migraine. This randomized, double‐blind, phase 1 crossover study evaluated the cardiac repolarization effect of a single supratherapeutic (300 mg) atogepant dose vs placebo in healthy adults. Moxifloxacin 400 mg was the open‐label active control. The primary end point was a change from baseline in Fridericia‐corrected QT intervals (ΔQTcF). Sixty participants were randomized to atogepant 300 mg, placebo, and moxifloxacin; 59 (98.3%) completed all interventions. Assay sensitivity was confirmed: lower 90% confidence interval limit for QTcF interval change from baseline (ΔΔQTcF) for moxifloxacin was >5 millisecond vs placebo at prespecified 2‐, 3‐, and 4‐hour time points. Following single‐dose atogepant 300 mg, mean atogepant ΔΔQTcF and upper 90% confidence interval limits were lower than the 10‐millisecond threshold at all time points. Atogepant mean peak plasma concentration was 3197 ng/mL, area under the concentration‐time curve from time 0 to time t was 16 640 ng • h/mL, area under the concentration‐time curve from time 0 to 24 hours was 16 607 ng • h/mL, and median time to peak plasma concentration was 2.1 hours. The incidence of adverse events was low; no serious adverse events or elevations of liver enzymes were reported. Overall, a single supratherapeutic dose of atogepant was safe and did not impact cardiac repolarization in healthy participants.

Thorough QT/QTc Study Evaluating the Effect of Macimorelin on Cardiac Safety Parameters in Healthy Participants

Macimorelin is an orally active growth hormone secretagogue indicated for the diagnosis of adult growth hormone deficiency. The primary objective of this study was to evaluate the effect of macimorelin on the baseline and placebo-corrected mean QT interval using Fridericia's formula (ΔΔQTcF). Secondary objectives were to determine QTcF for moxifloxacin; evaluate the effects of macimorelin on other cardiac intervals (PR, QRS, RR), heart rate, and electrocardiogram morphology parameters; characterize pharmacokinetics; and assess safety of macimorelin. The phase 1 thorough QT/QTc study, designed according to the International Council for Harmonisation E14 guideline, was a randomized, placebo-controlled, double-blind, 3-way complete crossover study comparing the effect of macimorelin 2.0 mg/kg with placebo and moxifloxacin 400 mg (positive control). Data were collected over a 3-month span from male (n=36) and female participants (n=24) aged 18 to 55 years with body mass index between 18.5 and 30.0 kg/m2 . Fifty-six participants received all 3 treatments. The ΔΔQTcF for macimorelin showed a prolongation with a maximum mean value of 9.61 milliseconds (2-sided 90% confidence interval, 7.81 milliseconds and 11.41 milliseconds) at 4 hours after dosing. The 2-sided 90% confidence interval of this value also exceeded the 10 millisecond threshold at 3 hours after dosing. Assay sensitivity was confirmed with moxifloxacin. Other electrocardiogram parameters evaluated were not influenced by macimorelin. Macimorelin did not raise other safety concerns and was well tolerated. In summary, a single supratherapeutic dose of macimorelin prolonged cardiac repolarization according to the regulatory guideline.

Absence of Rgs5 Influences the Spatial and Temporal Fluctuation of Cardiac Repolarization in Mice

Aims

This study investigated the contribution of the regulator of G-protein signaling 5 (Rgs5) knockout to the alteration of the action potential duration (APD) restitution and repolarizing dispersion in ventricle.

Methods and Results

The effects of Rgs5^–/– were investigated by QT variance (QTv) and heart rate variability analysis of Rgs5^–/– mice. Monophasic action potential analysis was investigated in isolated Rgs5^–/– heart. Rgs5^–/– did not promote ventricular remodeling. The 24-h QTv and QT variability index (QTVI) of the Rgs5^–/– mice were higher than those of wild-type (WT) mice (P < 0.01). In WT mice, a positive correlation was found between QTv and the standard deviation of all NN intervals (r = 0.62; P < 0.01), but not in Rgs5^–/– mice (R = 0.01; P > 0.05). The absence of Rgs5 resulted in a significant prolongation of effective refractory period and APD in isolated ventricle. In addition, compared with WT mice, the knockout of Rgs5 significantly deepened the slope of the APD recovery curve at all 10 sites of the heart (P < 0.01) and increased the spatial dispersions of S_max (COV-S_max) (WT: 0.28 ± 0.03, Rgs5^–/–: 0.53 ± 0.08, P < 0.01). Compared with WT heart, Rgs5^–/– increased the induced S1–S2 interval at all sites of heart and widened the window of vulnerability of ventricular tachyarrhythmia (P < 0.05).

Conclusion

Our findings indicate that Rgs5^–/– is an important regulator of ventricular tachyarrhythmia in mice by prolonging ventricular repolarization and increasing spatial dispersion in ventricle.

Probucol-induced hERG Channel Reduction can be Rescued by Matrine and Oxymatrine in vitro

Background

The human ether-a-go-go-related gene (hERG) potassium channel is the rapidly activating component of cardiac delayed rectifier potassium current (I_Kr), which is a crucial determinant of cardiac repolarization. The reduction of hERG current is commonly believed to cause Long QT Syndrome (LQTs). Probucol, a cholesterol-lowering drug, induces LQTs by inhibiting the expression of the hERG channel. Unfortunately, there is currently no effective therapeutic method to rescue probucol-induced LQTs.

Methods

Patch-clamp recording techniques were used to detect the action potential duration (APD) and current of hERG. Western blot was performed to measure the expression levels of proteins.

Results

In this study, we demonstrated that 1 μM matrine and oxymatrine could rescue the hERG current and hERG surface expression inhibited by probucol. In addition, matrine and oxymatrine significantly shortened the prolonged action potential duration induced by probucol in neonatal cardiac myocytes. We proposed a novel mechanism underlying the probucol induced decrease in the expression of transcription factor Specificity protein 1 (Sp1), which is an established transactivator of the hERG gene. We also demonstrated that matrine and oxymatrine were able to upregulate Sp1 expression which may be one of the possible mechanisms by which matrine and oxymatrine rescued probucol-induced hERG channel deficiency.

Conclusion

Our current results demonstrate that matrine and oxymatrine could rescue probucol-induced hERG deficiency in vitro, which may lead to potentially effective therapeutic drugs for treating acquired LQT2 by probucol in the future.

Clinical and Model-Based Evaluation of the Effect of Glasdegib on Cardiac Repolarization From a Randomized Thorough QT Study

Glasdegib is a potent, selective oral inhibitor of the Hedgehog signaling pathway. This phase 1 double‐blind thorough QT study (NCT03162900) evaluated the effects of glasdegib on QTc interval. The study enrolled 36 healthy volunteers to receive a single dose of 150 mg glasdegib (representing a therapeutic dose), 300 mg glasdegib (representing a supratherapeutic dose), 400 mg moxifloxacin (positive control), or placebo under fasted conditions. The study demonstrated that therapeutic and supratherapeutic doses of glasdegib had no significant effect on QTc interval; the upper bound of the 2‐sided 90% confidence intervals (CIs) for all time‐matched least‐squares mean differences in QT interval corrected using Fridericia's formula (QTcF) between glasdegib and placebo was below the prespecified criterion of 20 milliseconds (Food and Drug Administration correspondence reviewed and accepted). Based on an exposure–response analysis, glasdegib was determined not to have a meaningful effect on heart rate (change in RR interval). The mean (90%CI) model‐derived baseline and placebo‐adjusted QTcF at the average maximum observed concentration values corresponding to therapeutic and supratherapeutic glasdegib doses was 7.3 milliseconds (6.5‐8.2 milliseconds) and 13.7 milliseconds (12.0‐15.5 milliseconds), respectively. Together these results demonstrated that following therapeutic and supratherapeutic glasdegib dosing, the change in QTc from baseline was well below the 20‐millisecond threshold of clinical concern in oncology.

Low-Frequency Oscillations in Cardiac Sympathetic Neuronal Activity

Sudden cardiac death caused by ventricular arrhythmias is among the leading causes of mortality, with approximately half of all deaths attributed to heart disease worldwide. Periodic repolarization dynamics (PRD) is a novel marker of repolarization instability and strong predictor of death in patients post-myocardial infarction that is believed to occur in association with low-frequency oscillations in sympathetic nerve activity. However, this hypothesis is based on associations of PRD with indices of sympathetic activity that are not directly linked to cardiac function, such as muscle vasoconstrictor activity and the variability of cardiovascular autospectra. In this review article, we critically evaluate existing scientific evidence obtained primarily in experimental animal models, with the aim of identifying the neuronal networks responsible for the generation of low-frequency sympathetic rhythms along the neurocardiac axis. We discuss the functional significance of rhythmic sympathetic activity on neurotransmission efficacy and explore its role in the pathogenesis of ventricular repolarization instability. Most importantly, we discuss important gaps in our knowledge that require further investigation in order to confirm the hypothesis that low frequency cardiac sympathetic oscillations play a causative role in the generation of PRD.

Novel Methods for High-resolution Assessment of Cardiac Action Potential Repolarization

The profile of the action potential (AP) of cardiomyocytes contributes to the modality of ventricular repolarization of the heart. Experimentally, the examination of the AP in isolated cardiomyocytes provides information on their electrical properties, adaptations to physiological and pathological conditions, and putative ionic mechanisms involved in the process. Currently, there are no available platforms for automated assessment of AP properties and standard methodologies restrict the examination of the AP repolarization to discrete, user-defined ranges, neglecting significant intervals of the electrical recovery. This study proposes two automatic methods to assess AP profile throughout the entire repolarization phase. One method is based on AP data inversion and direct extraction of patterns describing beat-to-beat dynamics. The second method is based on evolutive singular value decomposition (ESVD), which identifies common patterns in a series of consecutive APs. The two methodologies were employed to analyze electrical signals collected from cardiomyocites obtained from healthy mice and animals with diabetes, a condition associated with alterations of AP properties in cardiac cells. Our methodologies revealed that the duration of the early repolarization phase of the AP tended to become progressively longer during a stimulation train, whereas the late repolarization progressively shortened. Although this behavior was comparable in the two groups of cells, alterations in AP dynamics occurred at distinct repolarization levels, a feature highlighted by the ESVD approach. In conclusion, the proposed methodologies allow detailed, automatic analysis of the AP repolarization and identification of critical alterations occurring in the electrical behavior of myocytes under pathological conditions.

Classification of drug-induced hERG potassium-channel block from electrocardiographic T-wave features using artificial neural networks

BACKGROUND

Human ether-à-go-go-related gene (hERG) potassium-channel block represents a harmful side effect of drug therapy that may cause torsade de pointes (TdP). Analysis of ventricular repolarization through electrocardiographic T-wave features represents a noninvasive way to accurately evaluate the TdP risk in drug-safety studies. This study proposes an artificial neural network (ANN) for noninvasive electrocardiography-based classification of the hERG potassium-channel block.

METHODS

The data were taken from the "ECG Effects of Ranolazine, Dofetilide, Verapamil, and Quinidine in Healthy Subjects" Physionet database; they consisted of median vector magnitude (VM) beats of 22 healthy subjects receiving a single 500 μg dose of dofetilide. Fourteen VM beats were considered for each subject, relative to time-points ranging from 0.5 hr before to 14.0 hr after dofetilide administration. For each VM, changes in two indexes accounting for the early and the late phases of repolarization, ΔERD_30% and ΔT_{S /A} , respectively, were computed as difference between values at each postdose time-point and the predose time-point. Thus, the dataset contained 286 ΔERD_30% -ΔT_{S /A} pairs, partitioned into training, validation, and test sets (114, 29, and 143 pairs, respectively) and used as inputs of a two-layer feedforward ANN with two target classes: high block (HB) and low block (LB). Optimal ANN (OANN) was identified using the training and validation sets and tested on the test set.

RESULTS

Test set area under the receiver operating characteristic was 0.91; sensitivity, specificity, accuracy, and precision were 0.93, 0.83, 0.92, and 0.96, respectively.

CONCLUSION

OANN represents a reliable tool for noninvasive assessment of the hERG potassium-channel block.

Different habitus but similar electrocardiogram: Cardiac repolarization parameters in children - Comparison of elite athletes to obese children

Introduction:

The standard 12-lead electrocardiogram (ECG) remains a widely used tool in the basic cardiac evaluation of children and adolescents. With the emergence of inherited arrhythmia syndromes, the period of cardiac repolarization has been the focus of attention. So far, data on cardiac repolarization and its normal variants in healthy children are scarce. This may cause uncertainties in the differentiation between pathologies and normal variants. As abnormal autonomic regulation seems to be a major influencing factor on cardiac repolarization, this study aimed to evaluate the parameters of cardiac repolarization of children in extremely good physical shape to obese children to improve knowledge about cardiac repolarization in these subgroups of pediatric patients that are vastly affected by the alterations of autonomic regulation.

Methods:

A total of 426 pediatric volunteers (84 lean, healthy controls; 130 obese healthy pediatric volunteers; and 212 elite athletes) were enrolled in the study, and the parameters of cardiac repolarization were determined in 12-lead ECG.

Results:

Most importantly, there were no pathological findings, neither in the healthy controls nor in the obese or athletes. Athletes showed overall shorter corrected QT intervals than children from the other groups. This is also true if a correction of the QT interval is performed using the Hodges formula to avoid bias due to a tendency to lower heart rates in athletes. Athletes showed the shortest Tpeak-to-end ratios between the groups. The comparison of athletes from primarily strength and power sports versus those from endurance sports showed endurance-trained athletes to have significantly longer QT intervals.

Conclusions:

This study suggests that neither obesity nor extensive sports seems to result in pathological cardiac repolarization parameters in healthy children. Therefore, pathology has to be assumed if abnormal repolarization parameters are seen and might not be simply attributed to the child's habitus or an excellent level of fitness.

Toll-like receptor 3 controls QT interval on the electrocardiogram by targeting the degradation of Kv4.2/4.3 channels in the endoplasmic reticulum

TLRs have been proven to be essential mediators for the early innate immune response. Overactivation of TLR-mediated immune signaling promotes deterioration of cardiovascular diseases; however, the role of TLRs in the heart under physiologic conditions remains neglected. Here, we show that Tlr3 deficiency induced the endoplasmic reticulum (ER) retention of Kv4.2/4.3 proteins and consequent degradation via the ubiquitin-proteasome pathway. Knockout of Tlr3 resulted in a prolonged QT interval (the space between the start of the Q wave and the end of the T wave) in mice with no significant signs of inflammation and tissue abnormality in cardiac muscles. Prolongation of action potential duration resulted from the depression of transient outward potassium channel (I_to) currents in Tlr3-deficient ventricular myocytes mirrored the change in QT interval. Mechanistically, we found that Tlr3 was exclusively localized in the ER of cardiomyocytes where it interacted with Kv4.2/4.3 subunits of I_to channel. Thus, our data indicated that TLR3 directly regulates I_to channel protein dynamics to maintain cardiac repolarization, which may implicate a new molecular surveillance system for cardiac electrophysiological homeostasis.-Gao, X., Gao, S., Guan, Y., Huang, L., Huang, J., Lin, L., Liu, Y., Zhao, H., Huang, B., Yuan, T., Liu, Y., Liang, D., Zhang, Y., Ma, X., Li, L., Li, J., Zhou, D., Shi, D., Xu, L., Chen, Y.-H. Toll-like receptor 3 controls QT interval on the electrocardiogram by targeting the degradation of Kv4.2/4.3 channels in the endoplasmic reticulum.

The Cardiovascular Effects of a Meal: J-Tpeak and Tpeak -Tend Assessment and Further Insights Into the Physiological Effects

Meal intake leads to a significant and prolonged increase in cardiac output to supply the splanchnic vasculature. A meal is associated with sympathetic activation of the cardiovascular system, and food ingestion is correlated with an increase in heart rate, an increase in cardiac stroke volume, and QTc interval shortening for up to 7 hours. Given the complexity of the system, one or several of many mechanisms could explain this observation. The shortening of the QTc interval was correlated with a rise of C‐peptide following food ingestion, but the mechanisms by which C‐peptide may be involved in the modulation of cardiac repolarization are still unknown. This shortening of the myocardial action potential caused by the ingestion of food was further investigated in the present study by measuring the QRS, J‐T_peak, and T_peak‐T_end intervals in search of further clues to better understand the underlying mechanisms. A retrospective analysis was conducted based on data collected in a formal thorough QT/QTc study in which 32 subjects received a carbohydrate‐rich “continental” breakfast, moxifloxacin without food, and moxifloxacin with food. We assessed the effect of food on T‐wave morphology using validated algorithms for measurement of J‐T_peak and T_peak‐T_end intervals. Our findings demonstrate that a standardized meal significantly shortened J‐T_peak for 4 hours after a meal and to a much lesser extent and shorter duration (up to 1 hour) prolonged the T_peak‐T_end and QRS intervals. This suggests that the QTc shortening occurs mainly during phase 2 of the cardiac action potential. As there was no corresponding effect on T_peak‐T_end beyond the first hour, we conclude that a meal does not interfere with the outward correcting potassium channels but possibly with Ca²⁺ currents. An effect on mainly Ca²⁺ aligns well with our understanding of physiology whereby an increase in stroke volume, as observed after a meal, is associated with changes in Ca²⁺ cycling in and out of the sarcoplasmic reticulum during cardiac myocyte contraction.

Association Between Depression, Anxiety, and Antidepressant Use With T-Wave Amplitude and QT-Interval

Objectives: Cardiac repolarization may be affected by psychiatric disorders and/or antidepressant use, but evidence for this is inconclusive. This study examined the relationship between depressive and anxiety disorder and use of antidepressants with T-wave amplitude (TWA) and QT-interval.

Methods: Data was obtained from the Netherlands Study of Depression and Anxiety (n = 1,383). Depression/anxiety was diagnosed with the DSM-IV based Composite International Diagnostic Interview. The use of tricyclic antidepressants (TCAs), selective serotonin and noradrenalin reuptake inhibitors (SNRIs), and selective serotonin reuptake inhibitors (SSRIs) was established. T-wave amplitude and QT-interval corrected for heart rate (QTc) were obtained from an ECG measured in a type II axis configuration.

Results: Compared to controls, persons with depression or anxiety disorders did not show a significantly different TWA (p = 0.58; Cohen's d = 0.046) or QTc (p = 0.48; Cohen's d = −0.057). In spite of known sympathomimetic effects, TCA use (p = 0.26; Cohen's d = −0.162) and SNRI use (p = 0.70; Cohen's d = −0.055) were not significantly associated with a lower TWA. TCA use (p = 0.12; Cohen's d = 0.225) and SNRI use (p = 0.11; Cohen's d = 0.227) were also not significantly associated with a prolonged QTc.

Conclusion: We did not find evidence that either depressive/anxiety disorder or antidepressant use is associated with abnormalities in TWA or QTc. Earlier found sympathomimetic effects of TCAs and SNRIs are not evident in these measures of cardiac repolarization.

Tramadol Hydrochloride at Steady State Lacks Clinically Relevant QTc Interval Increases in Healthy Adults

We evaluated the effects of therapeutic and supratherapeutic doses of tramadol hydrochloride on the corrected QT (QTc) interval in healthy adults (aged 18‐55 years) in a randomized, phase I, double‐blind, placebo‐ and positive‐controlled, multiple‐dose, 4‐way crossover study. Participants were randomized to receive 1 of 4 treatments (A‐D), 1 each in 4 treatment periods (1‐4), separated by a washout period (7‐15 days). Treatment A comprised tramadol 400 mg (therapeutic dose) on days 1 through 3, tramadol 100 mg and moxifloxacin‐matched placebo on day 4, and placebo on all 4 days. Treatment B comprised tramadol 600 mg (supratherapeutic dose) on days 1 through 3, and tramadol 150 mg and moxifloxacin‐matched placebo on day 4. Treatment C comprised placebo on days 1 through 4 and moxifloxacin‐matched placebo on day 4. Treatment D comprised placebo on days 1 through 4 and moxifloxacin 400 mg on day 4. Of 68 participants enrolled, 57 (83.8%) completed the study. Both therapeutic and supratherapeutic doses of tramadol were shown to be noninferior to placebo regarding their effect on QTc prolongation. Sixty‐one of 68 (89.7%) participants reported at least 1 treatment‐emergent adverse event (mild); nausea was the most frequently reported treatment‐emergent adverse event. Summarizing, tramadol at doses up to 600 mg/day did not cause clinically relevant QTc interval prolongation in healthy adults.

Cardiac Safety of Ozanimod, a Novel Sphingosine-1-Phosphate Receptor Modulator: Results of a Thorough QT/QTc Study

Ozanimod is a novel, selective, oral sphingosine-1-phosphate (1 and 5) receptor modulator in development for multiple sclerosis and inflammatory bowel disease. This randomized, double-blind, placebo-controlled, positive-controlled, parallel-group thorough QT study characterized the effects of ozanimod on cardiac repolarization in healthy subjects. Eligible subjects were randomized to 1 of 2 groups: ozanimod (escalated from 0.25 to 2 mg over 14 days) or placebo (for 14 days). A single dose of moxifloxacin 400 mg or placebo was administered on days 2 and 17. The primary end point was the time-matched, placebo-corrected, baseline-adjusted mean QTcF (ΔΔQTcF). A total of 113/124 (91.1%) subjects completed the study. The upper limits of the 2-sided 90% confidence intervals for ΔΔQTcF for both ozanimod 1 and 2 mg were below the 10-millisecond regulatory threshold. No QTcF >480 milliseconds or postdose change in QTcF of >60 milliseconds was observed. There was no evidence of a positive relationship between concentrations of ozanimod and its active metabolites and ΔΔQTcF. Although ozanimod blunted the observed diurnal increase in heart rate, excursions below predose heart rates were no greater than with placebo. Results demonstrate that ozanimod does not prolong the QTc interval or cause clinically significant bradycardia, supporting ozanimod's evolving favorable cardiac safety profile.

Cardiac repolarization during fingolimod treatment in patients with relapsing-remitting multiple sclerosis

Background

Fingolimod is a sphingosine-1-phosphate receptor modulator for the treatment of relapsing-remitting multiple sclerosis (RRMS). Despite an established effect on heart rate, the effect of fingolimod on cardiac repolarization is not completely known.

Methods

Twenty-seven patients with RRMS underwent 24-hr ambulatory ECG before fingolimod (baseline), at the day of fingolimod initiation (1D) and after three-month treatment (3M). The mean values of RR-interval as well as QT-interval corrected by Bazzet's (QTcBaz) and Fridericia's (QTcFri) formula were compared between baseline, 1D, and 3M over 24-hr period as well as at daytime and nighttime.

Results

QTcBaz over 24-hr was shorter at 1D (414 ± 20 ms, p < .001) and at 3M (414 ± 20 ms, p < .001) than at baseline (418 ± 20 ms). In contrast, QTcFri over 24-hr was longer at 1D (410 ± 19 ms, p < .001) but similar at 3M (406 ± 19 ms, p = .355) compared to baseline (407 ± 19 ms). Daytime QTcBaz was shorter at 1D (p < .001) and at 3M (p = .007), whereas daytime QTcFri was longer at 1D (p < .05) but similar at 3M (p = ns) compared to baseline. During the night, changes were observed neither in QTcBaz nor in QTcFri between baseline, 1D, and 3M.

Conclusions

Changes in cardiac repolarization after fingolimod initiation were mild and occurred at daytime. Ambiguously, QTcBaz demonstrated shortening, whereas QTcFri showed prolongation in cardiac repolarization after fingolimod initiation. The formula applied for QT-interval correction needs to be taken carefully into account as evaluating pharmacovigilance issues related to fingolimod.

Impact of the Norepinephrine Prodrug Droxidopa on the QTc Interval in Healthy Individuals

A double‐blind, 4‐period crossover study (NCT01327066) was conducted to assess the effect of the novel norepinephrine prodrug droxidopa on the QT interval in in healthy subjects. Subjects were randomized to receive a single dose of droxidopa 600 mg (maximal dose) and 2000 mg (supratherapeutic dose) compared with the positive control, moxifloxacin 400 mg, and placebo, each separated by a 3‐day washout period. Patients were monitored by continuous Holter monitoring, and electrocardiograms (ECGs) were extracted 0.5–23 hours after dosing. Blood samples for pharmacokinetic analysis were collected before dosing and after ECG data collection. The primary end point was the time‐matched placebo‐adjusted change from baseline in the individually corrected QT (QTcI). The time‐averaged QTcI mean placebo‐corrected changes from baseline for droxidopa 600 and 2000 mg were 0.1 milliseconds (90%CI, ‐0.9 to 1.0 milliseconds) and 0.3 milliseconds (90%CI, ‐0.6 to 1.3 milliseconds), respectively, and 9 milliseconds (90%CI, 8.4–10.3 milliseconds) for moxifloxacin. This study found no effect of either dose of droxidopa on cardiac repolarization using QTcI. Analysis of the pharmacokinetic/pharmacodynamic relationship and cardiac repolarization showed no association with droxidopa exposure. There were no clinically relevant effects of droxidopa on heart rate, atrioventricular conduction, or cardiac depolarization identified. No morphologic ECG changes were observed.

The impact of multiple sclerosis onset symptom on cardiac repolarization

INTRODUCTION

Multiple sclerosis is associated with prolonged cardiac repolarization but the underlying physiology has remained unknown. In this study, we compared cardiac repolarization during the relapsing-remitting multiple sclerosis (RRMS) disease course in patients with motor and sensory onset symptom.

METHODS

Twenty-five RRMS patients with motor and 33 RRMS patients with sensory onset symptom having 12-lead electrocardiogram (ECG) recorded at the time of the first demyelinating event (ECG1) as well as at the later disease course (ECG2) were identified from the patient records. The average time interval between ECG1 and ECG2 was 8.6 ± 5.9 y. Heart rate-corrected QT intervals reflecting cardiac repolarization were calculated by Bazett (QTcBaz), Fridericia (QTcFri), and Karjalainen (QTcKar) formulas.

RESULTS

Heart rate-corrected QT intervals as well as heart rate were similar in patients with motor and sensory onset symptom in ECG1. However, QTcBaz (p = .002), QTcFri (p = .019), and QTcKar (p = .026) were longer and heart rate was higher (p = .035) in patients with motor than sensory onset symptom in ECG2. Correspondingly, QTcBaz (p = .002), QTcFri (p = .033), and QTcKar (p = .043) prolonged and heart rate tended to increase (p = .060) during the disease course only in the patients with motor onset symptom.

CONCLUSIONS

Cardiac repolarization prolonged and heart rate increased during the disease course in RRMS patients with motor but not with sensory onset symptom. This suggests different traits in RRMS according to its initial manifestation and also association of motor onset symptom with more unfavorable cardiovascular prognostic determinants.

Contribution of two-pore K+ channels to cardiac ventricular action potential revealed using human iPSC-derived cardiomyocytes

Two-pore K⁺ (K_2p) channels have been described in modulating background conductance as leak channels in different physiological systems. In the heart, the expression of K_2p channels is heterogeneous with equivocation regarding their functional role. Our objective was to determine the K_2p expression profile and their physiological and pathophysiological contribution to cardiac electrophysiology. Induced pluripotent stem cells (iPSCs) generated from humans were differentiated into cardiomyocytes (iPSC-CMs). mRNA was isolated from these cells, commercial iPSC-CM (iCells), control human heart ventricular tissue (cHVT), and ischemic (iHF) and nonischemic heart failure tissues (niHF). We detected 10 K_2p channels in the heart. Comparing quantitative PCR expression of K_2p channels between human heart tissue and iPSC-CMs revealed K_2p1.1, K_2p2.1, K_2p5.1, and K_2p17.1 to be higher expressed in cHVT, whereas K_2p3.1 and K_2p13.1 were higher in iPSC-CMs. Notably, K_2p17.1 was significantly lower in niHF tissues compared with cHVT. Action potential recordings in iCells after K_2p small interfering RNA knockdown revealed prolongations in action potential depolarization at 90% repolarization for K_2p2.1, K_2p3.1, K_2p6.1, and K_2p17.1. Here, we report the expression level of 10 human K_2p channels in iPSC-CMs and how they compared with cHVT. Importantly, our functional electrophysiological data in human iPSC-CMs revealed a prominent role in cardiac ventricular repolarization for four of these channels. Finally, we also identified K_2p17.1 as significantly reduced in niHF tissues and K_2p4.1 as reduced in niHF compared with iHF. Thus, we advance the notion that K_2p channels are emerging as novel players in cardiac ventricular electrophysiology that could also be remodeled in cardiac pathology and therefore contribute to arrhythmias.NEW & NOTEWORTHY Two-pore K⁺ (K_2p) channels are traditionally regarded as merely background leak channels in myriad physiological systems. Here, we describe the expression profile of K_2p channels in human-induced pluripotent stem cell-derived cardiomyocytes and outline a salient role in cardiac repolarization and pathology for multiple K_2p channels.

Potassium currents in the heart: functional roles in repolarization, arrhythmia and therapeutics

This is the second of the two White Papers from the fourth UC Davis Cardiovascular Symposium Systems Approach to Understanding Cardiac Excitation-Contraction Coupling and Arrhythmias (3-4 March 2016), a biennial event that brings together leading experts in different fields of cardiovascular research. The theme of the 2016 symposium was 'K⁺ channels and regulation', and the objectives of the conference were severalfold: (1) to identify current knowledge gaps; (2) to understand what may go wrong in the diseased heart and why; (3) to identify possible novel therapeutic targets; and (4) to further the development of systems biology approaches to decipher the molecular mechanisms and treatment of cardiac arrhythmias. The sessions of the Symposium focusing on the functional roles of the cardiac K⁺ channel in health and disease, as well as K⁺ channels as therapeutic targets, were contributed by Ye Chen-Izu, Gideon Koren, James Weiss, David Paterson, David Christini, Dobromir Dobrev, Jordi Heijman, Thomas O'Hara, Crystal Ripplinger, Zhilin Qu, Jamie Vandenberg, Colleen Clancy, Isabelle Deschenes, Leighton Izu, Tamas Banyasz, Andras Varro, Heike Wulff, Eleonora Grandi, Michael Sanguinetti, Donald Bers, Jeanne Nerbonne and Nipavan Chiamvimonvat as speakers and panel discussants. This article summarizes state-of-the-art knowledge and controversies on the functional roles of cardiac K⁺ channels in normal and diseased heart. We endeavour to integrate current knowledge at multiple scales, from the single cell to the whole organ levels, and from both experimental and computational studies.

Intravenous Dosing as an Alternate Approach to Safely Achieve Supratherapeutic Exposure for Assessments of Cardiac Repolarization: A Randomized Clinical Trial with Mavoglurant (AFQ056)

PURPOSE

The conduct of thorough QTc (TQT) studies is often challenging with compounds that are characterized by limited tolerability in healthy individuals. This is applicable to several central nervous system drugs, including mavoglurant acting as a selective allosteric modulator of metabotropic glutamate receptor 5. This TQT study describes the use of a single intravenous dosing regimen as an alternate approach allowing for sufficiently high C_max values while controlling tolerability.

METHODS

This study was a randomized, placebo- and active-controlled, 4-period, crossover, TQT study composed of 2 sequential phases. In the pilot phase, the safety and tolerability profile of 10-minute infusions of 25, 37.5, and 50 mg of mavoglurant was assessed in 36 healthy individuals. In the TQT phase, individuals received in random sequence single intravenous doses of mavoglurant (25 and 50 mg) and placebo and an oral dose of moxifloxacin (400 mg).

FINDINGS

Mavoglurant was well tolerated up to a single intravenous dose of 50 mg, and supratherapeutic C_max values were achieved that were approximately 2-fold higher than at the multiple maximum tolerated dose and more than 3-fold higher relative to therapeutic plasma concentrations. The upper bound of the 2-sided 90% CI of Fridericia-corrected placebo- and baseline-adjusted QTc intervals (QTcFs) did not exceed 10 milliseconds at any postdose time point for both mavoglurant doses. The pharmacokinetic and pharmacodynamic analysis confirmed the lack of an association between mavoglurant plasma concentrations and ΔΔQTcF data over the entire range of plasma concentration data at 25 and 50 mg of mavoglurant. An outlier analysis revealed no individuals with newly identified QTcF intervals >480 milliseconds or any QTcF prolongations >60 milliseconds compared with baseline in any of the treatment groups. Hence, the lack of any clinically relevant QTc prolongation was found for therapeutic and supratherapeutic single intravenous doses of 25 and 50 mg of mavoglurant.

IMPLICATIONS

This TQT study describes the use of single intravenous dosing as an alternate approach to achieve supratherapeutic plasma concentrations as required per the International Council for Harmonisation E14 guideline with compounds characterized by exposure related tolerability limitations. The increased C_max/AUC ratio compared with conventional oral dosing may contribute to a reduced incidence of adverse events that appear more related to overall exposure.

Executive Cognitive Functioning and Cardiovascular Autonomic Regulation in a Population-Based Sample of Working Adults

Objective: Executive cognitive functioning is essential in private and working life and is sensitive to stress and aging. Cardiovascular (CV) health factors are related to cognitive decline and dementia, but there is relatively few studies of the role of CV autonomic regulation, a key component in stress responses and risk factor for cardiovascular disease (CVD), and executive processes. An emerging pattern of results from previous studies suggest that different executive processes may be differentially associated with CV autonomic regulation. The aim was thus to study the associations between multiple measures of CV autonomic regulation and measures of different executive cognitive processes. Method: Participants were 119 healthy working adults (79% women), from the Swedish Longitudinal Occupational Survey of Health. Electrocardiogram was sampled for analysis of heart rate variability (HRV) measures, including the Standard Deviation of NN, here heart beats (SDNN), root of the mean squares of successive differences (RMSSD), high frequency (HF) power band from spectral analyses, and QT variability index (QTVI), a measure of myocardial repolarization patterns. Executive cognitive functioning was measured by seven neuropsychological tests. The relationships between CV autonomic regulation measures and executive cognitive measures were tested with bivariate and partial correlational analyses, controlling for demographic variables, and mental health symptoms. Results: Higher SDNN and RMSSD and lower QTVI were significantly associated with better performance on cognitive tests tapping inhibition, updating, shifting, and psychomotor speed. After adjustments for demographic factors however (age being the greatest confounder), only QTVI was clearly associated with these executive tests. No such associations were seen for working memory capacity. Conclusion: Poorer CV autonomic regulation in terms of lower SDNN and RMSSD and higher QTVI was associated with poorer executive cognitive functioning in terms of inhibition, shifting, updating, and speed in healthy working adults. Age could largely explain the associations between the executive measures and SDNN and RMSSD, while associations with QTVI remained. QTVI may be a useful measure of autonomic regulation and promising as an early indicator of risk among otherwise healthy adults, compared to traditional HRV measures, as associations between QTVI and executive functioning was not affected by age.

Patients with Obstructive Sleep Apnea Have Cardiac Repolarization Disturbances when Travelling to Altitude: Randomized, Placebo-Controlled Trial of Acetazolamide

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) promotes myocardial electrical instability and may predispose to nocturnal sudden cardiac death. We evaluated whether hypobaric hypoxia during altitude travel further impairs cardiac repolarization in patients with OSA, and whether this is prevented by acetazolamide, a drug known to improve oxygenation and central sleep apnea at altitude.

METHODS

Thirty-nine OSA patients living < 600 m, discontinued continuous positive airway pressure therapy during studies at 490 m and during two sojourns of 3 days at altitude (2 days at 1860 m, 1 day at 2590 m). During one altitude sojourn, patients took acetazolamide, during the other placebo, or vice versa, according to a randomized, double-blind crossover design. Twelve-lead electrocardiography and pulse oximetry (SpO2) were recorded during nocturnal polysomnography. Heart rate corrected mean QT intervals during the entire night (meanQTc) and during 1 min of the night with the longest meanQTc (maxQTc) were determined.

RESULTS

At 490 m the median nocturnal SpO2 was 93%, medians of meanQTc and maxQTc were 420 ms and 478 ms. At 2590 m, on placebo, SpO2 was lower (85%), and meanQTc and maxQTc were prolonged to 430 ms and 510 ms (P < 0.02 vs. 490 m, all corresponding comparisons). At 2590 m on acetazolamide, median SpO2 was increased to 88% (P < 0.05 vs. placebo), meanQTc was reduced to 427 ms (P < 0.05 vs. placebo), whereas maxQTc remained increased at 502 ms (P = ns vs. placebo).

CONCLUSIONS

At 2590 m OSA patients experienced cardiac repolarization disturbances in association with hypoxemia. Prolongation of meanQTc at altitude was prevented and hypoxemia was improved by acetazolamide, whereas maxQTc remained increased suggesting imperfect protection from repolarization disturbances.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov ID: NTC-00714740. URL: www.clinicaltrials.gov.

Aspects of Hyperglycemia Contribution to Arterial Stiffness and Cardiovascular Complications in Patients With Type 1 Diabetes

Controlling the blood glucose level is of outmost importance for the prevention of the micro- and macrovascular diabetic complications observed in patients with type 1 diabetes (T1D). Although the pathogenesis behind the complex cascade of complications is far from solved, one possible mechanism could be a negative effect of glucose on the arteries resulting in a stiffening of the arteries and ultimately in vascular complications. Intriguingly, patients with T1D have been shown to suffer from premature arterial aging compared to nondiabetic subjects-an association that is even more evident in the presence of diabetic complications such as diabetic nephropathy. Arterial stiffness has in several patient populations been shown to independently predict cardiovascular disease. However, interventional studies aimed at attenuating arterial stiffness to reduce cardiovascular disease in T1D are yet to come. Moreover, most of the data on pharmacological treatments of arterial stiffening are directed toward pathophysiological pathways other than hyperglycemia. Interestingly, the sodium-glucose transport-2 (SGLT2) inhibitor empagliflozin was recently shown to reduce both blood pressure and arterial stiffness in patients with type 2 diabetes. Whether, these effects can also be replicated in patients with T1D is an intriguing question. Tight metabolic and antihypertensive control are still of central importance for the prevention and the treatment of diabetic complications. However, the need for a noninvasive intermediate marker to identify at risk patients for aggressive treatment is evident. One such tool might be arterial stiffness linking diabetes to increased cardiovascular risk. Future research efforts exploring large-scale databases will play a key role in the identification of other clinically useful markers.

Analysis of ECG Measures of Cardiac Repolarization in Relation to Arrhythmic Events in an Implantable Cardioverter Defibrillator Population

BACKGROUND

ECG-derived measures of cardiac repolarization may have utility in risk prediction of future ventricular arrhythmia, and a range of different measures have been proposed. We compared time-based, vectorcardiographic, and singular value decomposition (SVD) derived measures of repolarization to determine which was most predictive of appropriate therapy in an ICD population.

METHODS

We examined the independent prognostic value of a range of repolarization measures derived from 60 second 12-lead ECG recordings in 150 patients receiving new ICD implants in relation to the occurrence of appropriate therapy during follow-up.

RESULTS

Over an average follow-up of 2.15 ± 0.87 years, male gender, presence of premature ventricular complex (PVC), relative T wave residuum (TWR-rel, measures regional repolarization heterogeneity), and TCRT (the total cosine R-to-T, describes the global angle between repolarization and depolarization wavefronts) were the only independent predictors of appropriate therapy. With every 0.01% increase in TWR-rel, there was 2% increased risk of appropriate therapy (HR = 1.02, 95% CI 1.006-1.034, P < 0.001). With every 1° decrease in TCRT, there was an increase in arrhythmic risk of 0.9% (HR 1.009, 95% CI 1.003-1.015, P = 0.003).

CONCLUSIONS

The use of advanced analytic ECG techniques to derive measures of repolarization abnormality might shave utility in risk stratification in an ICD population.

The influence of regional anaesthesia and local anaesthetics on cardiac repolarization

The normal function of the heart muscle is the result of electro-mechanic and hemodynamic coupling. Modification of the structure and activity of ion channels within the cardiomyocytes may induce cardiac arrhythmias. Electrophysiological mechanisms of arrhythmia, generated by a prolonged period of repolarization, result either from conduction disturbances (reentry mechanism) and/or the induction of beats (early after-depolarizations). Local anaesthetic drug deposition does not affect the repolarization period, as long as the concentration of the free drug in the plasma does not reach the critical value to cause toxic effects in the cardiomyocytes. When analyzing the effect of regional anaesthesia on the repolarization period it is essential to acknowledge the activity or blockade of adrenergic fibres. Blocking the sympathetic fibres', including level T1 to T4, leads to a shortening of the QT interval and a reduction of QT dispersion. Adrenergic blockade as a result of spinal anaesthesia causes severe adrenergic activity above the level of the block and therefore prolongs repolarization. Stellate ganglion block on the right side causes a significant prolongation of the QT interval and QT dispersion. Regardless of the reasons for prolongation of the repolarization period (congenital or acquired), vigilance is required within the perioperative anaesthetic management of a patient, so as not to lead to the occurrence of ventricular arrhythmias. Regional anaesthesia techniques and properly used local anaesthetic drugs are regarded as being safe in these patients.

Effect of Retosiban on Cardiac Repolarization in a Randomized, Placebo- and Positive-controlled, Crossover Thorough QT/QTc Study in Healthy Men and Women

PURPOSE

Retosiban is a small molecule oxytocin receptor antagonist that is under evaluation in clinical studies for treatment of spontaneous preterm labor. A Thorough QT/QTc study was conducted to evaluate the effect of retosiban on cardiac repolarization according to International Conference on Harmonization E14 guidance. This was a randomized, placebo- and positive-controlled, single-dose, crossover study of healthy men and women.

METHODS

All study participants received a 100 mg dose of retosiban (therapeutic target exposure), a 800 mg dose of retosiban (supratherapeutic target exposure), a 400 mg dose of moxifloxacin (positive control), and placebo with an appropriate washout. Holter monitoring data at baseline (predose) and at 13 subsequent time points during the next 24 hours were extracted and manually read by a central ECG reader who was blinded to the treatment assignment and corrected for heart rate by using the Fridericia formula (QTcF). A linear exposure-QTc response model was developed: ΔΔQTcF=RI+Cp,R⋅RS+MI+Cp,M⋅MS, where RI and MI are intercept terms for retosiban and moxifloxacin, respectively, RS and MS are slope terms for retosiban and moxifloxacin, respectively, and Cp,R and Cp,M are plasma concentrations for retosiban and moxifloxacin, respectively.

FINDINGS

A total of 52 healthy men (n = 27) and women (n = 25), with a mean age of 32 years, were enrolled in the study, and 43 (83%) completed all treatment periods and assessments. Mean placebo-corrected change from baseline QT (ΔΔQTcF) for the 2 retosiban dose groups revealed statistically significant decreases in ΔΔQTcF between 2 and 3 hours after administration, reaching a value of -2.5 msec for both retosiban dose groups. The 400 mg moxifloxacin group had a statistically significant increase in the ΔΔQTcF value at 0.75 hours after administration, reaching a maximal increase of 11.10 msec at 4 hours after administration. Results of the exposure-QTc response modeling revealed that there was no significant effect of retosiban on the ΔΔQTcF at therapeutic exposures. For the supratherapeutic exposure of retosiban, there was a slight negative effect, with a mean decrease of -3.05 msec. The moxifloxacin arm had a mean increase in ΔΔQTcF of 10.7 msec.

IMPLICATIONS

At therapeutic and supratherapeutic exposures, retosiban had no significant effect on cardiac repolarization, as estimated by the ΔΔQTcF. However, both doses of retosiban had a minor shortening effect. This is not considered to be clinically significant. CLINICALTRIALS.

GOV IDENTIFIER

NCT01702376.

Evaluation of opicapone on cardiac repolarization in a thorough QT/QTc study

Opicapone, a novel third-generation catechol-O-methyltransferase inhibitor for use as adjunctive therapy in levodopa-treated Parkinson's disease patients, was investigated on cardiac repolarization in healthy adult volunteers. This was a single-center, randomized, double-blind, placebo-controlled, open-label active-controlled, 4-period crossover study conducted in 64 subjects. In each period, subjects received a single oral dose of 50 mg opicapone, 800 mg opicapone, placebo, or 400 mg moxifloxacin and 24-hour 12-lead Holter monitoring was performed on day -1 (baseline) and after each single dose. After a single oral administrations of 50 and 800 mg opicapone, opicapone was the major entity in the circulation, with a median tmax of 1.5-2.0 hours. Opicapone was rapidly eliminated, with an elimination half-life of 1-2 hours. There was no clinically relevant effect of 50 and 800 mg opicapone versus placebo on cardiac depolarization or repolarization. All upper bounds of the 1-sided 95% confidence interval (CI) were below 10 milliseconds, confirming that opicapone has no QT-prolonging effect. Moxifloxacin caused an increase in the QTcI, with a lower bound of the 2-sided 95% CI always higher than 5 milliseconds, around the tmax of peak concentration, demonstrating assay sensitivity. In conclusion, administration of opicapone at therapeutic (50 mg) and supratherapeutic (800 mg) doses did not induce a clinically significant prolongation of the QTc interval.

Assessment of total cardiac repolarization's spatial distribution among patients with aortic sclerosis

OBJECTIVE

To measure the Tp-e value, which shows the spatial distribution of cardiac repolarization and is defined as a possible predictor for ventricular arrhythmia among patients with aortic sclerosis (AS), and to compare this parameter's length to QTc length within the same population.

METHOD

60 patients that have been diagnosed with AS have been prospectively included in this study.

RESULTS

60 AS and 64 control patients were evaluated as part of the study. The median age, prevalence for hypertension and diabetes, baseline medications and laboratory results of the groups were similar. The Electrocardiographic QT length of both groups were found similar. In the AS group Tp-e tangent and Tp-e tail values were more longer than control group (P < 0.001). Tp-e tangent index and Tp-e tail index values were also statistically higher among AS patients when compared to the control group. (P < 0.001).

CONCLUSION

Our study showed that Tp-e durations had increased in AS patients with no structural coronary heart disease. AS causes local degeneration on the aortic root and also has a negative effect on the total cardiac spatial repolarization.

QT correction methods in infants and children: effects of age and gender

BACKGROUND

Accurate determination of the QTc interval in children is important especially when using drugs which can prolong cardiac repolarization. Previous work suggests the most appropriate correction formula to be QTc = QT/RR(0.38) . We set out to compute the best population-derived age and gender-related QT correction formula factor in normal children.

METHODS

We evaluated a cohort of 1400 healthy children. From a resting 12-lead electrocardiogram, QT and RR intervals were measured. Subjects were divided into four age and gender groups: 0-1 years (n = 540); 1-5 years (n = 281); 5-10 years (n = 277), and > 10 years (n = 302). QT/RR intervals were plotted and fitted with two regression analyses, linear regression obtaining constant α (QTc = QT + α x (1-RR)), and log-linear analysis deriving constant β (QTc = QT/RR(β) ). Furthermore, regression analysis of QTc/RR for the two formulas was performed obtaining slope and R(2) .

RESULTS

Correction constant α decreased steadily with increasing age, genders remained on par until 10 years of age followed by more pronounced decrease in females (range 0.24-0.18). The β constant showed a similar trend however with more pronounced decline (range 0.45-0.31). Regression slopes of QTc/RR plots (all ages and both genders) were close to zero (both formulas).

CONCLUSION

For the full range of pediatric subjects, the optimum population-based correction factors α and β decreased with increasing age and gender, digressing more so in adolescent girls. More specific correction factors, based on age and gender, are necessary in QT correction.

Detection of QTc interval prolongation using jacket telemetry in conscious non-human primates: comparison with implanted telemetry

BACKGROUND AND PURPOSE

During repeat-dose toxicity studies, ECGs are collected from chemically or physically-restrained animals over a short timeframe. This is problematic due to cardiovascular changes caused by manual restraint stress and anesthesia, and limited ECG sampling. These factors confound data interpretation, but may be overcome by using a non-invasive jacket-based ECG collection (JET). The current study investigated whether a jacketed external telemetry system could detect changes in cardiac intervals and heart rate in non-human primates (NHPs), previously implanted with a PCT transmitter.

EXPERIMENTAL APPROACH

Twelve male cynomolgus monkeys were treated weekly with vehicle or sotalol (8, 16, 32 mg kg⁻¹) p.o. ECGs were collected continuously for 24 hours, following treatment, over 4 weeks. A satellite group of six NHPs was used for sotalol toxicokinetics.

KEY RESULTS

Sotalol attained Cmax values 1-3 hours after dosing, and exhibited dose-proportional exposure. In jacketed NHPs, sotalol dose-dependently increased QT/QTc intervals, prolonged PR interval, and reduced heart rate. Significant QTc prolongation of 27, 54 and 76 msec was detected by JET after 8, 16, and 32 mg kg⁻¹ sotalol, respectively, compared with time-matched vehicle-treated animals. Overall, JET-derived PR, QT, QTc intervals, QRS duration, and heart rate correlated well with those derived from PCT.

CONCLUSIONS AND IMPLICATIONS

The current findings clearly support the use of JET to quantify cardiac interval and rhythm changes, capable of detecting QTc prolongation caused by sotalol. JET may be a preferred method compared to restraint-based ECG because high-density ECG sampling can be collected in unstressed conscious monkeys, over several weeks.

Assessment of the effect of ofatumumab on cardiac repolarization

Ofatumumab is a human monoclonal antibody that binds to a unique CD20 epitope on the surface of B lymphocytes, resulting in efficient lysis of CD20-expressing cells via complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity. The potential effect of ofatumumab on cardiac repolarization and the relationship between ofatumumab concentration and change in corrected QT interval (ΔQTcF) were evaluated in data from three clinical trials in 82 patients with chronic lymphocytic leukemia receiving ofatumumab alone (n = 14), ofatumumab with chemotherapy (n = 33), and chemotherapy alone (n = 35). Because of ofatumumab accumulation, baseline QTcF interval was recorded prior to the first infusion for each patient. No patient had a post-baseline QTcF interval >480 milliseconds or a ΔQTcF >60 milliseconds; five patients (four on ofatumumab) had a ΔQTcF between 30 and 60 milliseconds. At cycle 6 (week 21; 308 μg/mL), there was an increase in QTcF in patients on ofatumumab treatment, with an estimated between-treatment difference (90% CI) of 12.5 (4.5, 20.5) milliseconds. However, at the visit with the highest median concentration (week 8; 1386 μg/mL), median ΔQTcF was 4.8 milliseconds. There was no significant relationship between ofatumumab plasma concentration and ΔQTcF. Ofatumumab did not have a clinically significant effect on cardiac repolarization.

QT interval prolongation in end-stage liver disease cannot be explained by nonhepatic factors

INTRODUCTION

QT interval prolongation in patients with end-stage liver disease (ESLD) is common. However, electrolyte abnormalities, renal insufficiency, treatment with QT-prolonging drugs, and other factors known to prolong QT interval independently of liver disease occur frequently in ESLD. Moreover, elevated heart rate may be present in ESLD and result in spurious QTc prolongation if the Bazett formula is used for rate correction. It thus remains unclear whether QT prolongation in ESLD is directly caused by liver failure, or indirectly by these confounding factors.

METHODS

Medical records of all patients (n = 437) who received orthotopic liver transplantation (OLTx) at our institution between 2008 and 2011 were reviewed. Data from 51 patients with available pre-OLTx dobutamine stress echo (DSE), post-OLTx ECG and without nonhepatic factors affecting QT interval duration were analyzed. For each patient, QT versus RR regression line was calculated from ECG tracings obtained during DSE. The QT interval on post-OLTx ECG was compared with the pre-OLTx QT predicted by the regression line for the same RR interval.

RESULTS

QT interval shortened significantly post-OLTx (from 394 ± 47 to 364 ± 45 ms at RR interval 750 ± 144 ms; P < 0.002) when compared using the regression method. Corrected QT intervals calculated by Bazett and Fridericia formulas also shortened. Patients with prolonged QT pre-OLTx had significantly higher INR and lower serum albumin.

CONCLUSION

ESLD impairs ventricular repolarization even in the absence of other known factors affecting repolarization. QT prolongation in ESLD is associated with impaired synthetic liver function.

Evaluation of the effect of Naloxegol on cardiac repolarization: a randomized, placebo- and positive-controlled crossover thorough QT/QTc study in healthy volunteers

BACKGROUND

Opioid-induced constipation (OIC) is a common adverse effect associated with opioid use. Naloxegol is a PEGylated derivative of naloxone in clinical development as a once-daily oral treatment of OIC.

OBJECTIVES

A thorough QT/QTc study was conducted, according to International Conference on Harmonisation E14 guidelines, to characterize the effect of naloxegol on cardiac repolarization.

METHODS

In this randomized, positive- and placebo-controlled crossover study, healthy men received a single dose of naloxegol 25 mg (therapeutic dose), naloxegol 150 mg (supratherapeutic dose), moxifloxacin 400 mg (positive control), or placebo in 1 of 4 sequences (Williams Latin square design). The washout time between treatment periods was at least 5 days. Digital 12-lead ECGs were recorded at baseline and at 10 time points over 24 hours after dosing in each treatment period. QT intervals were corrected for heart rate using the Fridericia formula (QTcF) and the Bazett formula (QTcB).

RESULTS

A total of 52 subjects were enrolled (mean age, 28 years), and 45 received all 4 treatments. The placebo-corrected, baseline-adjusted, mean increases in QTcF with naloxegol 25 and 150 mg were both <5 msec at each time point, and all upper limits of the 2-sided 90% CI were <10 msec. Similar findings were observed using QTcB; the upper limits of the 2-sided 90% CI were <10 msec at all time points after dosing with naloxegol 25 or 150 mg. With moxifloxacin 400 mg, mean QTcF was increased by a maximum of 11.1 msec (90% CI, 9.3-12.9 msec), supporting assay sensitivity.

CONCLUSION

Naloxegol at 25 and 150 mg was not associated with QT/QTc interval prolongation in these healthy men, and at the proposed therapeutic dose of 25 mg/d, naloxegol is not expected to have a clinically relevant effect on cardiac repolarization in patients with OIC. ClinicalTrials.gov identifier: NCT01325415.

Field and action potential recordings in heart slices: correlation with established in vitro and in vivo models

BACKGROUND AND PURPOSE

Action potential (AP) recordings in ex vivo heart preparations constitute an important component of the preclinical cardiac safety assessment according to the ICH S7B guideline. Most AP measurement models are sensitive, predictive and informative but suffer from a low throughput. Here, effects of selected anti-arrhythmics (flecainide, quinidine, atenolol, sotalol, dofetilide, nifedipine, verapamil) on field/action potentials (FP/AP) of guinea pig and rabbit ventricular slices are presented and compared with data from established in vitro and in vivo models.

EXPERIMENTAL APPROACH

Data from measurements of membrane currents (hERG, I(Na) ), AP/FP (guinea pig and rabbit ventricular slices), AP (rabbit Purkinje fibre), haemodynamic/ECG parameters (conscious, telemetered dog) were collected, compared and correlated to complementary published data (focused literature search).

KEY RESULTS

The selected anti-arrhythmics, flecainide, quinidine, atenolol, sotalol, dofetilide, nifedipine and verapamil, influenced the shape of AP/FP of guinea pig and rabbit ventricular slices in a manner similar to that observed for rabbit PF. The findings obtained from slice preparations are in line with measurements of membrane currents in vitro, papillary muscle AP in vitro and haemodynamic/ECG parameters from conscious dogs in vivo, and were also corroborated by published data.

CONCLUSION AND IMPLICATIONS

FP and AP recordings from heart slices correlated well with established in vitro and in vivo models in terms of pharmacology and predictability. Heart slice preparations yield similar results as papillary muscle but offer enhanced throughput for mechanistic investigations and may substantially reduce the use of laboratory animals.

Chronic arsenic exposure and cardiac repolarization abnormalities with QT interval prolongation in a population-based study

BACKGROUND

Chronic arsenic exposure is associated with cardiovascular abnormalities. Prolongation of the QT (time between initial deflection of QRS complex to the end of T wave) interval and profound repolarization changes on electrocardiogram (ECG) have been reported in patients with acute promyelocytic leukemia treated with arsenic trioxide. This acquired form of long QT syndrome can result in life-threatening arrhythmias.

OBJECTIVE

The objective of this study was to assess the cardiac effects of arsenic by investigating QT interval alterations in a human population chronically exposed to arsenic.

METHODS

Residents in Ba Men, Inner Mongolia, have been chronically exposed to arsenic via consumption of water from artesian wells. A total of 313 Ba Men residents with the mean arsenic exposure of 15 years were divided into three arsenic exposure groups: low (< or = 21 microg/L), medium (100-300 microg/L), and high (430-690 microg/L). ECGs were obtained on all study subjects. The normal range for QTc (corrected QT) interval is 0.33-0.44 sec, and QTc > or = 0.45 sec was considered to be prolonged.

RESULTS

The prevalence rates of QT prolongation and water arsenic concentrations showed a dose-dependent relationship (p = 0.001). The prevalence rates of QTc prolongation were 3.9, 11.1, 20.6% for low, medium, and high arsenic exposure, respectively. QTc prolongation was also associated with sex (p < 0.0001) but not age (p = 0.486) or smoking (p = 0.1018). Females were more susceptible to QT prolongation than males.

CONCLUSIONS

We found significant association between chronic arsenic exposure and QT interval prolongation in a human population. QT interval may potentially be useful in the detection of early cardiac arsenic toxicity.

Effects of sex on the pharmacokinetic and pharmacodynamic properties of quinidine

AIMS

To investigate the source of the apparent increased susceptibility of women to develop QT interval prolongation and torsade de pointes after the administration of drugs that delay cardiac repolarization.

METHODS

Plasma quinidine concentrations and electrocardiographic changes (QRS and QT intervals) were measured over 24 h following the administration of single oral doses of the QT prolonging drug quinidine (3 mg kg(-1)) and compared between 27 male and 21 female healthy volunteers.

RESULTS

There were no significant differences between males and females in plasma quinidine concentrations or in calculated pharmacokinetic variables. Maximum quinidine concentrations in males and females were 997 +/- 56 and 871 +/- 57 ng ml(-1), respectively (mean difference (-125, 95% confidence intervals (CI) -239, 11 ng ml(-1), P = NS). Quinidine lengthened actual (QTa) and corrected (QTc) QT intervals and the QRS interval to a greater extent in females than males (P < 0.001 for each), but there were no significant sex differences detected in the effects of quinidine on the heart rate corrected JT interval. Maximum prolongation of QTc interval was observed 2 h after quinidine and was significantly greater in women (33 +/- 16 vs 24 +/- 17 ms, mean difference 9 +/- 20 ms, 95% CI 3, 15, P = 0.037). At this time mean differences (95% CI) were 1.0 min(-1) (-2.5, 4.4, P = NS) for heart rate, 5.5 ms (3.5, 7.6, P = 0.05) for the QRS and 3.4 ms (-2.5, 9.3, P = NS) for the JTc intervals.

CONCLUSIONS

Quinidine-induced increases in QTc were larger in females, but no sex differences in quinidine pharmacokinetics were found. The disparity in prolongation of cardiac repolarization is thus due to a pharmacodynamic difference which appears more complex than simply an increase in repolarization delay in females.

Designing and interpreting the results of first-time-to-man studies

First human administration of a new chemical entity (NCE) constitutes a critical step in drug development. The primary objective of such a study is the assessment of the shortterm safety and tolerability of single and multiple doses of the NCE in healthy volunteers. Secondary objectives are to obtain preliminary data on the pharmacokinetics and pharmacodynamics using surrogate or biornarkers of the beneficial as well as the adverse effects of the drug. Interpretation of safety data should be cautious and mainly based on comparisons with placebo. A special focus should be made on the assessment of adverse events, liver enzymes, and cardiac repolarization. Well-designed, first-time-to-man studies should determine the safety of the NCE in humans and predict the dose range that may be used to safely and accurately conduct further clinical trials in the target patient population based on safety data (maximum tolerated dose), pharmacodynamics (minimum active dose, duration of action, and dosage regimen), and pharmacokinetics (dosage regimen).

Study of cardiac repolarization in healthy volunteers performed with mizolastine, a new H1-receptor antagonist

AIMS

The occurrence of serious dysrhythmias, such as torsades de pointes, with terfenadine and astemizole had led to a reexamination of the potential effect of H1 antihistamines on cardiac repolarization. Mizolastine is a potent, selective, nonsedating peripherally acting H1-receptor antagonist which is registered for rhinitis and urticaria at a recommended dose of 10 mg once daily. The present study was carried out to investigate the effects of therapeutic and supratherapeutic doses of mizolastine, on ventricular repolarization in healthy volunteers.

METHODS

Twenty-four healthy young volunteers participated in a double-blind, placebo-controlled, randomised study with three parallel groups. Each group consisted of 2 way cross-over 7 day treatment periods where mizolastine (10, 20 or 40 mg) and placebo were randomly administered. On day 1 and day 7, 12-lead ECG recordings were performed prior and 0.5, 1, 2, 3, 4, 6, 8, 12, 16, and 20 h after dosing and from day 2 to day 6, before dosing and 1, 2, 3, and 4 h after.

RESULTS

Whatever the analysis used (raw data, changes from baseline, incidence of individual out-of-range values) no significant differences were observed at any dose level vs placebo, on any of ECG parameters (HR, PR, QRS, QT, and QTc). In particular, no effect of mizolastine vs placebo was shown on QT and QTc although 95% CIs were wide. The only subject who exhibited a QTc>/=450 ms received placebo for 7 days.

CONCLUSIONS

This study found no evidence of an effect of mizolastine up to 40 mg (four times the therapeutic dose) on ventricular repolarization in healthy volunteers.

Distinct transient outward potassium current (Ito) phenotypes and distribution of fast-inactivating potassium channel alpha subunits in ferret left ventricular myocytes

The biophysical characteristics and alpha subunits underlying calcium-independent transient outward potassium current (Ito) phenotypes expressed in ferret left ventricular epicardial (LV epi) and endocardial (LV endo) myocytes were analyzed using patch clamp, fluorescent in situ hybridization (FISH), and immunofluorescent (IF) techniques. Two distinct Ito phenotypes were measured (21-22 degrees C) in the majority of LV epi and LV endo myocytes studied. The two Ito phenotypes displayed marked differences in peak current densities, activation thresholds, inactivation characteristics, and recovery kinetics. Ito,epi recovered rapidly [taurec, -70 mV = 51 +/- 3 ms] with minimal cumulative inactivation, while Ito,endo recovered slowly [taurec, -70 mV = 3,002 +/- 447 ms] with marked cumulative inactivation. Heteropoda toxin 2 (150 nM) blocked Ito,epi in a voltage-dependent manner, but had no effect on Ito,endo. Parallel FISH and IF measurements conducted on isolated LV epi and LV endo myocytes demonstrated that Kv1.4, Kv4.2, and Kv4.3 alpha subunit expression in LV myocyte types was quite heterogenous: (a) Kv4.2 and Kv4.3 were more predominantly expressed in LV epi than LV endo myocytes, and (b) Kv1.4 was expressed in the majority of LV endo myocytes but was essentially absent in LV epi myocytes. In combination with previous measurements on recovery kinetics (Kv1.4, slow; Kv4.2/4.3, relatively rapid) and Heteropoda toxin block (Kv1.4, insensitive; Kv4.2, sensitive), our results strongly support the hypothesis that, in ferret heart, Kv4.2/Kv4.3 and Kv1.4 alpha subunits, respectively, are the molecular substrates underlying the Ito,epi and Ito,endo phenotypes. FISH and IF measurements were also conducted on ferret ventricular tissue sections. The three Ito alpha subunits again showed distinct patterns of distribution: (a) Kv1.4 was localized primarily to the apical portion of the LV septum, LV endocardium, and approximate inner 75% of the LV free wall; (b) Kv4. 2 was localized primarily to the right ventricular free wall, epicardial layers of the LV, and base of the heart; and (c) Kv4.3 was localized primarily to epicardial layers of the LV apex and diffusely distributed in the LV free wall and septum. Therefore, in intact ventricular tissue, a heterogeneous distribution of candidate Ito alpha subunits not only exists from LV epicardium to endocardium but also from apex to base.