The initial ICH E14 guidance described the thorough QT/QTc (TQT) study with the purpose of evaluating whether a new drug has effects on the QTc interval. Following its adoption, concentration-QTc (C-QTc) modeling was applied to data from TQT studies, and results were comparable with those based on a "by time point" analysis. In 2014, the IQ-CSRC study demonstrated that a small study in healthy subjects using C-QTc as the primary analysis could detect mild drug-induced QTc prolongation. The study led to the revision of the E14 guidance in 2015, allowing the use of C-QTc modeling to exclude a QTc effect at the threshold of concern, 10 ms. The 2015 revision was the starting point for the use of C-QTc modeling applied to data from first-in-human (FIH) studies with the intent to waive requests for a designated TQT study. The 2022 revision (S7B/E14 Q&A) brought non-clinical studies into the decision process for a "definitive" QT evaluation. In this manuscript, the emergence of C-QTc analysis applied to FIH studies with the intent to waive the TQT study is described, and a survey of FDA labels and reviews of approved drugs since 2015 is shared. The uptake has been modest, with only 30% of approved drugs for which a TQT study would be expected using this approach, while a TQT study has been conducted in ∼70% of development programs. It can be expected that the 2022 S7B/E14 revision will increase the number of programs for which a TQT study can be replaced.

Concentration-QTc (C-QTc) analysis was accepted to serve as an alternative to the by-time point analysis with intersection-union test (IUT) as the primary basis for decisions to classify the arrhythmogenic risk of a drug by ICH E14 Q As (R3) in December 2015. Since then, this analysis method has been widely applied by industry as it significantly reduces the sample size to achieve the same power as with IUT. There are many model-based power calculation approaches available for C-QTc through simulation in the literature, however, there is still no standard method with a clear formula to determine the sample size for C-QTc analysis to exclude a small effect on the QTc interval. The current model-based simulation approaches are too complicated to prevent them from being widely used, which is not commensurate with the popular status. We have developed a systematic method based on t-tests to determine the sample size for different study designs using the C-QTc analysis method and applied it to many studies. The results of the sample sizes utilizing this method are consistent with simulation studies and validated by real analyses.

Pridopidine is a highly selective sigma-1 receptor (S1R) agonist in development for the treatment of Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). Pridopidine’s activation of S1R enhances cellular processes that are crucial for neuronal function and survival but are impaired in neurodegenerative diseases. Human brain positron emission tomography (PET) imaging studies show that at the therapeutic dose of 45 mg twice daily (bid), pridopidine selectively and robustly occupies the S1R. We conducted concentration-QTc (C-QTc) analyses to assess pridopidine’s effect on the QT interval and investigated its cardiac safety profile. C-QTc analysis was conducted using data from PRIDE-HD, a phase 2, placebo-controlled trial evaluating four pridopidine doses (45, 67.5, 90, 112.5 mg bid) or placebo over 52 weeks in HD patients. Triplicate electrocardiograms (ECGs) with simultaneous plasma drug concentrations were determined in 402 patients with HD. The effect of pridopidine on the Fridericia-corrected QT interval (QTcF) was evaluated. Cardiac-related adverse events (AEs) were analyzed from PRIDE-HD alone and from pooled safety data of three double-blind, placebo-controlled trials with pridopidine in HD (HART, MermaiHD, and PRIDE-HD). A concentration-dependent effect of pridopidine on the change from baseline in the Fridericia-corrected QT interval (ΔQTcF) was observed, with a slope of 0.012 ms (ms) per ng/mL (90

The electrical activity of the heart, characterised by the QT interval on an electrocardiogram (ECG), serves as a crucial parameter for evaluating cardiac health. Variations in the QT interval, particularly when corrected for heart rate using Fridericia's formula (QTcF), have long been of interest in cardiology and play a pivotal role in assessing cardiac safety in clinical trials. Understanding the influence of meals given at different times on QTcF intervals is essential for the accurate execution of Thorough QT (TQT) studies. Moreover, it has been proposed that this meal-related QT interval shortening could serve as a valuable indicator of assay sensitivity in TQT studies or even as a potential integration of TQT investigations into in Phase I/II studies. This study explores the impact of meals on QTcF intervals, specifically in the context of pharmacodynamic studies and TQT investigations. The primary goal is to gain insights into how different meals and baseline calculations affect QTcF changes and their potential implications for cardiac health and the risk of arrhythmias. Recent research has begun shedding light on the intricate relationship between meal composition, timing, and QTcF alterations. Several studies have investigated the effects of various nutrients, such as carbohydrates, fats, and proteins, on QTcF duration, as well as the implications of postprandial changes. These investigations have unveiled the complex interplay between dietary components and the cardiovascular system, raising essential questions about how our dietary choices may influence cardiac electrophysiology. In this comprehensive meta-analysis, we analyse data from nine studies, all conducted in accordance with Good Clinical Practice and ethical standards. These studies were approved by Ethics Committees and Regulatory authorities. Our analysis focuses on ECG assessments, involving the use of 12-lead ECGs recorded electronically and evaluated by certified cardiologists. We apply the Fridericia formula for QT correction (QTcF), as it has been shown to provide more accurate results across different heart rates compared to other correction methods. Our findings confirm existing literature into the impact of meals on QTcF intervals. We observe a consistent shortening of QTcF following breakfast, exceeding 5 milliseconds, which aligns with the positive control requirement defined by ICH E14, thus demonstrating the validity of our approach. In contrast, the effect of lunch is consistently less than 5 milliseconds across various timepoints and studies, indicating differences in the meal-related QTcF changes. Furthermore, our analysis incorporates gender-based assessments, showing that women exhibit a smaller effect than men, which is significant for breakfast and the fasted condition. These results suggest that the observed QTcF effect post-breakfast is a combination of the meal itself and factors unique to the initial day of a study. This insight holds potential for improving the design and interpretation of cardiac safety studies, particularly in Phase I investigations, and may offer the opportunity to explore the removal of positive control agents like Moxifloxacin, thereby reducing exposure to harmful challenge agents and contributing to the global effort to combat antimicrobial resistance (AMR). In conclusion, this meta-analysis advances our understanding of meal-induced QTcF changes and their significance in cardiac safety assessment, offering the prospect of more efficient and patient-focused drug development practices. This not only contributes to enhanced safety but also supports the reduction of antibiotic consumption, a key element in the global fight against AMR.

Aims Given the increasing emergence of drug resistance in Plasmodium, new antimalarials are urgently required. P218 is an aminopyridine that inhibits dihydrofolate reductase being developed as a malaria chemoprotective drug. Assessing the effect of new compounds on cardiac intervals is key during early drug development to determine their cardiac safety. Methods This double-blind, randomized, placebo-controlled, parallel group study evaluated the effect of P218 on electrocardiographic parameters following oral administration of seven single-ascending doses up to 1000 mg in 56 healthy volunteers. Participants were randomized to treatment or placebo at a 3:1 ratio. P218 was administered in the fasted state with standardized lunch served 4 hours after dosing. 12-lead ECGs were recorded in triplicate at regular intervals on the test day, and at 48, 72, 120, 168, 192 and 240 hours thereafter. Blood samples for pharmacokinetic evaluations were collected at similar time points. Concentration-effect modelling was used to assess the effect of P218 and its metabolites on cardiac intervals. Results Concentration-effect analysis showed that P218 does not prolong the QTcF, J-Tpeak or TpTe interval at all doses tested. No significant changes in QRS or PR intervals were observed. Two-sided 90% confidence intervals of subinterval effects of P218 and its metabolites were consistently below the regulatory concern threshold for all doses. Study sensitivity was confirmed by significant shortening of QTcF after a meal. Conclusion Oral administration of P218 up to 1000 mg does not prolong QTcF and does not significantly change QRS or PR intervals, suggesting low risk for drug-induced proarrhythmia.

The International Conference on Harmonization (ICH) E14 document was revised in 2015 to allow concentration–corrected QT interval (C–QTc) analysis to be applied to data from early clinical pharmacology studies to exclude a small drug‐induced effect on QTc. Provided sufficiently high concentrations of the drug are obtained in the first‐in‐human (FIH) study, this approach can be used to obviate the need for a designated thorough QT (TQT) study. The E14 revision has resulted in a steady reduction in the number of TQT studies and an increased use of FIH studies to evaluate electrocardiogram (ECG) effects of drugs in development. In this review, five examples from different sponsors are shared in which C–QTc analysis was performed on data from FIH studies. Case 1 illustrates a clearly negative C–QTc evaluation, despite observations of QTc prolongation at high concentrations in nonclinical studies. In case 2 C–QTc analysis of FIH data was performed prior to full pharmacokinetic characterization in patients, and the role of nonclinical assays in an integrated risk assessment is discussed. Case 3 illustrates a positive clinical C–QTc relationship, despite negative nonclinical assays. Case 4 demonstrates a strategy for characterizing the C–QTc relationship for a nonracemic therapy and formulation optimization, and case 5 highlights an approach to perform a preliminary C–QTc analysis early in development and postpone the definitive analysis until proof of efficacy is demonstrated. The strategy of collecting and storing ECG data from FIH studies to enable an informed decision on whether and when to apply C–QTc analysis to obviate the need for a TQT study is described.

Pridopidine is a highly selective Sigma-1 receptor (S1R) agonist, being evaluated in the PROOF-HD Ph3 trial. Pooled safety data from 22 trials assessing pridopidine at doses 10-112.5 mg bid was analyzed, encompassing safety data from 1300 patients (~1300 patient-years of exposure, including long-term data >5 years); 1100/1300 (85%) HD patients, and 981/1300 (75%) treated with 45 mg bid, the dose assessed in PROOF-HD. Due to different placebo and pridopidine exposures, AE rate analyses, corrected for patient-years of exposure, were performed. The rate of common AEs was similar for placebo vs. 45 mg bid (rate=2.35 vs.1.82 events/patient years). Serious adverse events (SAEs) were reported in placebo and 45 mg bid groups (rate=0.07 and 0.18, respectively). Most SAEs were common for HD; 1 case of subdural hematoma was considered drug-related. Concentration-QTc analysis was performed using PK sampling and ECG monitoring data from 402 PRIDE-HD Ph2 trial participants, for 52 weeks. Pridopidine shows a concentration dependent effect on QTcF interval (slope=0.012 ms/ng/mL; 90% CI: 0.0109-0.0127). The, predicted QTc effect at 45 mg bid is 6.6 ms, with a two-sided 90% CI below 8 ms, that is of no regulatory concern (FDA considers QTc <10 ms low risk for Torsade de Pointes, TdP). Across the integrated safety database, the rate of AEs for QT prolongation was higher in placebo vs 45 mg bid (rate=0.013 vs. 0.005). No cases of TdP, and no increased risk for pro-arrhythmic events reported at the clinical dose. As of June 16th, 2022, PROOF-HD has low dropout (23/499, 4.6%) and discontinuation (19/499, 3.8%) rates. In February 2022, an independent safety monitoring committee reported no safety signals of concern, and recommended PROOF-HD continue as planned.

Perhexiline has been used to treat hypertrophic cardiomyopathy. In addition to its effect on carnitine‐palmitoyltransferase‐1, it has mixed ion channel effects through inhibition of several cardiac ion currents. Effects on cardiac ion channels expressed in mammalian cells were assayed using a manual patch‐clamp technique, action potential duration (APD) was measured in ventricular trabeculae of human donor hearts, and electrocardiogram effects were evaluated in healthy subjects in a thorough QT (TQT) study. Perhexiline blocked several cardiac ion currents at concentrations within the therapeutic range (150‐600 ng/mL) with IC50 for hCav1.2 ∼ hERG < late hNav1.5. A significant APD shortening was observed in perhexiline‐treated cardiomyocytes. The TQT study was conducted with a pilot part in 9 subjects to evaluate a dosing schedule that would achieve therapeutic and supratherapeutic perhexiline plasma concentrations on days 4 and 6, respectively. Guided by the results from the pilot, 104 subjects were enrolled in a parallel‐designed part with a nested crossover comparison for the positive control. Perhexiline caused QTc prolongation, with the largest effect on ΔΔQTcF, 14.7 milliseconds at therapeutic concentrations and 25.6 milliseconds at supratherapeutic concentrations and a positive and statistically significant slope of the concentration‐ΔΔQTcF relationship (0.018 milliseconds per ng/mL; 90%CI, 0.0119‐0.0237 milliseconds per ng/mL). In contrast, the JTpeak interval was shortened with a negative concentration‐JTpeak relationship, a pattern consistent with multichannel block. Further studies are needed to evaluate whether this results in a low proarrhythmic risk.

Drug development can be described as a series of experiments that span drug discovery, preclinical research, and clinical research. Statistics can be used to describe and explore data and thus generate hypotheses. However, the ultimate goal of many statistical analyses is to support or refute a hypothesis about the effect of a treatment. We first introduce the fundamentals of statistical modeling and some of the most common statistical models, followed by principles of experimental design and introduction of some designs that are particularly relevant to translational medicine. Multiplicity issues, biological modeling, and statistical models are discussed as well.

Cortexolone 17α-propionate, also known as clascoterone, is a potent androgen receptor inhibitor intended for the topical treatment of skin diseases associated with androgenic pathway alterations. In nonclinical studies, cortexolone 17α-propionate was found to have a weak inhibitory effect on human Ether-à-go-go-Related Gene (hERG) potassium channels, which are vital for normal electrical activity in the heart. When used in a cream formulation, little cortexolone 17α-propionate is absorbed. However, the solution formulation developed for the treatment of androgenetic alopecia leads to a measurable systemic concentration and accumulation of the antiandrogen. This phase 1 study assessed the effect of cortexolone 17α-propionate on the QTc interval using concentration-effect analysis and the effect of a meal on QTc to confirm assay sensitivity. Thirty-two volunteers were randomly assigned to receive the active drug or a matching vehicle as placebo. Participants were dosed twice daily on days 1 to 3 (225 mg applied topically as a 7.5% solution 12 hours apart) and once on day 4. Pharmacokinetic and electrocardiogram assessments were performed after supratherapeutic doses. Assay sensitivity was successfully confirmed by using the food effect on the QTc interval. The results of this concentration-QTc analysis demonstrate that cortexolone 17α-propionate and its metabolite/degradation product had no effect on the QTc interval in the concentration range tested.

Cortexolone 17α‐propionate, also known as clascoterone, is a potent androgen receptor inhibitor intended for the topical treatment of skin diseases associated with androgenic pathway alterations. In nonclinical studies, cortexolone 17α‐propionate was found to have a weak inhibitory effect on human Ether‐à‐go‐go‐Related Gene (hERG) potassium channels, which are vital for normal electrical activity in the heart. When used in a cream formulation, little cortexolone 17α‐propionate is absorbed. However, the solution formulation developed for the treatment of androgenetic alopecia leads to a measurable systemic concentration and accumulation of the antiandrogen. This phase 1 study assessed the effect of cortexolone 17α‐propionate on the QTc interval using concentration‐effect analysis and the effect of a meal on QTc to confirm assay sensitivity. Thirty‐two volunteers were randomly assigned to receive the active drug or a matching vehicle as placebo. Participants were dosed twice daily on days 1 to 3 (225 mg applied topically as a 7.5% solution 12 hours apart) and once on day 4. Pharmacokinetic and electrocardiogram assessments were performed after supratherapeutic doses. Assay sensitivity was successfully confirmed by using the food effect on the QTc interval. The results of this concentration‐QTc analysis demonstrate that cortexolone 17α‐propionate and its metabolite/degradation product had no effect on the QTc interval in the concentration range tested.

Nolasiban is an orally active oxytocin receptor antagonist being developed to increase the efficiency of assisted reproductive technologies. This study evaluated the pharmacokinetics, pharmacodynamics, and cardiac safety of nolasiban in 45 healthy women of child-bearing age. Nolasiban was administered in a fasted state with a standardised lunch served 4.5 h post-dose. Concentration-effect modelling was used to assess the effect of two dosages of nolasiban (900 mg and 1800 mg) on QTc following single-dose administration. We found no significant change in QTc at all tested dosages. Two-sided 90% confidence intervals of geometric mean C max for estimated QTc effects of nolasiban were below the threshold of regulatory concern. The sensitivity of the assay to detect small changes in QTc was confirmed by a significant shortening of QTc between 2 and 4 h after consumption of a meal, which served to validate the model. Independent of the nolasiban assessment, this study also explored the effects of sex hormones on ECG parameters, especially QT subintervals. We found a significant relationship between JTpc and oestradiol. Heart rate was negatively correlated with progesterone. This study confirms the cardiovascular safety of nolasiban and describes relationships of sex hormones and ECG parameters.

In August 2020, the International Council on Harmonisation (ICH) released a new draft document, which for the first time combined nonclinical (S7B) and clinical (E14) Questions and Answers (Q&As) into 1 document. FDA describes the revision as a “value proposition”: if the human ether‐à‐go‐go assay and the in vivo study are performed in a standardized way, the number of dedicated thorough QT (TQT) studies can be reduced. In this article, we describe and discuss the Q&As that relate to clinical ECG evaluation. If supported by negative standardized nonclinical assays, Q&A 5.1 will obviate the need for a TQT study in the case that a >2‐fold exposure margin vs high clinical scenario cannot be obtained. Q&A 6.1 addresses drugs that are poorly tolerated in healthy subjects and cannot be studied at high doses or in placebo‐controlled studies; it therefore mainly applies to oncology drugs. It will enable sponsors to claim that a new drug has a “low likelihood of proarrhythmic effects” in the case that the mean corrected QT effect is <10 milliseconds at the time of market application. The E14 2015 revision allowed application of concentration–corrected QT analysis on data from routinely performed clinical pharmacology studies, for example, the first‐in‐human study and the proportion of dedicated TQT studies has since steadily decreased. It can be foreseen that the proposed new revision will further reduce the number of TQT studies. To achieve harmonization across regulatory regions, it seems important to reach consensus within the International Council on Harmonisation group on the new threshold proposed in 6.1. For this purpose, the Implementation Working Group has asked for public comments.

The JTpeak interval has been proposed as a new biomarker to demonstrate mixed ion channel effects, potentially leading to reduced late-stage electrocardiogram (ECG) monitoring for mildly QT-prolonging drugs. ECG waveforms from the IQ-CSRC study were used. Twenty healthy subjects were enrolled with 6 subjects on placebo and 9 subjects on each of 5 mildly QT-prolonging drugs-moxifloxacin, dofetilide, ondansetron, dolasetron, and quinine - and 1 negative drug, levocetirizine. A vector magnitude lead was derived from 12-lead ECGs, and measurements were made on a median beat from three 10-second replicates. Data were analyzed using a linear concentration-response model with QTcF and heart rate corrected JTpeak (JTpeak_c) as dependent variables. For moxifloxacin, dofetilide, and ondansetron, all pure hERG blockers, slopes of the concentration (C)-QTcF and C-JTpeak_c relationships were positive and statistically significant. With the prespecified linear model, the predicted effects on Delta Delta QTcF and Delta Delta JTpeak_c were 11.4 and 9.4 milliseconds for moxifloxacin at the geometric mean C-max on day 1, 9.0 and 11.7 milliseconds for dofetilide and 11.5, and 7.9 milliseconds for ondansetron, respectively. In contrast, dolasetron and quinine, both with additional ion channel effects, prolonged QTcF with a positive C-Delta QTcF slope and predicted Delta Delta QTcF effect on day 1 of 6.2 and 11.4 milliseconds, whereas the C-Delta JTpeak_c slope and the predicted Delta Delta JTpeak on day 1 were negative (-0.3 and -7.5 milliseconds per ng/mL). Pure hERG-blocking drugs prolonged both the QTc and the JTpeak_c intervals, whereas drugs with mixed ion channel effects, including peak sodium inhibition, prolonged QTcF but not the JTpeak_c interval.

Early-phase studies quantifying the QTc prolongation potential for a new drug often use linear concentration-QTc (C-QTc) models, assuming no delay between plasma concentrations and QTc changes. However, that assumption is not always correct. The term “hysteresis” has been utilized to describe a time lag present between a measurable concentration and a measurable effect. To detect and quantify hysteresis and its impact on study interpretation, studies with hysteresis of 0.25–4 h were simulated with different doses, half-lives, and sampling schedules in a crossover design. Hysteresis was quantified using a novel method termed exposure-normalized GRI (enGRI), a proposed modification of the Glomb-Ring Index (GRI), to account for delay and magnitude of QTc effects. With realistic sampling, the rate of false negative studies (FN) increased proportionally to the delay, even for delays shorter than 1 h. Using an enGRI threshold (γ) of 2 ms resulted in FN with undetected delay and FN without hysteresis at approximately the same rate. For γ = 2 ms, the specificity of enGRI was > 90% throughout the investigated scenarios. We therefore propose the incorporation of enGRI when interpreting results from C-QTc analysis with the intent of characterizing QTc effects.

Background: Lofexidine is a non-opioid treatment for opioid withdrawal syndrome. Its sympatholytic actions counteract the nor-adrenergic hyperactivity that occurs during abrupt opioid withdrawal. Methods: The effect of lofexidine 2.16 and 2.88 mg/day on QTcF (QT interval, heart-rate corrected, Fridericia formula) was studied as part of a large, double-blind, placebo-controlled trial (ClinicalTrials.gov identifier. NCT01863186). ECGs were time-matched to blood sampling for lofexidine concentration and were collected at prespecified timepoints over a 7-day inpatient period. Analyses included mean change-from-baseline QTcF and exposure-response modeling to predict QTcF at relevant lofexidine concentrations. Results: A total of 681 adult men and women received at least 1 dose of study drug; 566 qualified for inclusion in the concentration-QTcF analysis. Most subjects were withdrawing from heroin. During the first 24 h (Days 1-2) post-baseline, small increases in QTcF were observed in all groups: 4.7 ms for lofexidine 2.16 mg, 7.4 ms for lofexidine 2.88 mg and 1.4 ms for placebo. These increases were transient; by Day 4, when lofexidine levels had reached steady-state, QTcF increases were not present. By Day 7, QTcF was decreased from baseline in all groups. Exposure-response modeling predicted < 10 ms increases in QTcF at lofexidine concentrations 3 times those obtained at maximal recommended dose. Conclusions: Lofexidine was associated with small, transient QTcF increases. Decreases in QTcF that occurred with higher lofexidine concentrations argue for an indirect QTcF effect, potentially from changes in autonomic tone. Both opioid withdrawal and lofexidine's sympatholytic actions would be expected to alter sympathetic outflow over the 7-day withdrawal.

Women are associated with longer electrocardiographic QT intervals and increased proarrhythmic risks of QT-prolonging drugs. The purpose of this study was to characterize the differences in cardiac electrophysiology between moxifloxacin and levofloxacin in men and women and to assess the balance of inward and outward currents through the analysis of QT subintervals. Data from 2 TQT studies were used to investigate the impact of moxifloxacin (400 mg) and levofloxacin (1000 and 1500 mg) on QT subintervals using algorithms for measurement of J-Tpeak and Tpeak -Tend intervals. Concentration-effect analyses were performed to establish potential relationships between the ECG effects and the concentrations of the 2 fluoroquinolones. Moxifloxacin was shown to be a more potent prolonger of QT interval corrected by Fredericia (QTcF) and had a pronounced effect on J-Tpeak c. Levofloxacin had little effect on J-Tpeak c. For moxifloxacin, the concentration-effect modeling showed a greater effect for women on QTcF and J-Tpeak c, whereas for levofloxacin the inverse was true: women had smaller QTcF and J-Tpeak c effects. The different patterns in repolarization after administration of both drugs suggested a sex difference, which may be related to the combined IKs and IKr inhibitory properties of moxifloxacin versus IKr suppression only of levofloxacin. The equipotent inhibition of IKs and IKr appears to affect women more than men. Sex hormones are known to influence cardiac ion channel expression and differences in QT duration. Differences in IKr and IKs balances, influenced by sex hormones, may explain the results. These results support the impact of sex differences on the cardiac safety assessment of drugs.

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-Tpeak , and Tpeak -Tend 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-Tpeak and Tpeak -Tend intervals. Our findings demonstrate that a standardized meal significantly shortened J-Tpeak for 4 hours after a meal and to a much lesser extent and shorter duration (up to 1 hour) prolonged the Tpeak -Tend 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 Tpeak -Tend 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.