Dynamic Beat-to-Beat Modeling of the QT-RR Interval Relationship: Analysis of QT Prolongation during Alterations of Autonomic State versus Human Ether a-go-go-Related Gene Inhibition

Concentration QTc analysis of giredestrant: Overcoming QT/heart rate confounding in the presence of drug-induced heart rate changes

Concentration-QTc (C-QTc) analysis has become a common approach for evaluating proarrhythmic risk and delayed cardiac repolarization of oncology drug candidates. Significant heart rate (HR) change has been associated with certain classes of oncology drugs and can result in over- or underestimation of the true QT prolongation risk. Because oncology early clinical trials typically lack a placebo control arm or time-matched, treatment-free baseline electrocardiogram collection, significant HR change brings additional challenges to C-QTc analysis in the oncology setting. In this work, a spline-based correction method (QTcSPL) was explored to mitigate the impact of HR changes in giredestrant C-QTc analysis. Giredestrant is a selective estrogen receptor degrader being developed for the treatment of patients with estrogen receptor-positive (ER+) breast cancer. A dose-related HR decrease has been observed in patients under giredestrant treatment, with significant reductions (>10 bpm) observed at supratherapeutic doses. The QTcSPL method demonstrated superior functionality to reduce the correlation between QTc and HR as compared with the Fridericia correction (QTcF). The effect of giredestrant exposure on QTc was evaluated at the clinical dose of 30 mg and supratherapeutic dose of 100 mg based on a prespecified linear mixed effect model. The upper 90% confidence interval of ΔQTcSPL and ΔQTcF were below the 10 ms at both clinical and supratherapeutic exposures, suggesting giredestrant has a low risk of QT prolongation at clinically relevant concentrations. This work demonstrated the use case of QTcSPL to address HR confounding challenges in the context of oncology drug development for the first time.

Risk assessment tools for QT prolonging pharmacotherapy in older adults: a systematic review

Purpose

Many drugs are associated with the risk of QT prolongation and torsades de pointes (TdP), and different risk assessment tools (RATs) are developed to help clinicians to manage related risk. The aim of this systematic review was to summarize the evidence of different RATs for QT prolonging pharmacotherapy.

Methods

A systematic review was conducted using PubMed and Scopus databases. Studies concerning risk assessment tools for QT prolonging pharmacotherapy, including older adults, were included. Screening and selection of the studies, data extraction, and risk of bias assessment were undertaken.

Results

A total of 21 studies were included, involving different risk assessment tools. Most commonly used tools were risk scores (n = 9), computerized physician order entry systems (n = 3), and clinical decision support systems (n = 6). The tools were developed mainly for physicians and pharmacists. Risk scores included a high number of risk factors, both pharmacological and non-pharmacological, for QT prolongation and TdP. The inclusion of patients’ risk factors in computerized physician order entry and clinical decision support systems varied.

Conclusion

Most of the risk assessment tools for QT prolonging pharmacotherapy give a comprehensive overview of patient-specific risks of QT prolongation and TdP and reduce modifiable risk factors and actual events. The risk assessment tools could be better adapted to different health information systems to help in clinical decision-making. Further studies on clinical validation of risk assessment tools with randomized controlled trials are needed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00228-022-03285-3.

OUP accepted manuscript

The content of this article derives from a Health and Environmental Sciences Institute (HESI) consortium with a focus to improve cardiac safety during drug development. A detailed literature review was conducted to evaluate the concordance between nonclinical repolarization assays and the clinical thorough QT (TQT) study. Food and Drug Administration and HESI developed a joint database of nonclinical and clinical data, and a retrospective analysis of 150 anonymized drug candidates was reviewed to compare the performance of 3 standard nonclinical assays with clinical TQT study findings as well as investigate mechanism(s) potentially responsible for apparent discrepancies identified. The nonclinical assays were functional (I_Kr) current block (Human ether-a-go-go related gene), action potential duration, and corrected QT interval in animals (in vivo corrected QT). Although these nonclinical assays demonstrated good specificity for predicting negative clinical QT prolongation, they had relatively poor sensitivity for predicting positive clinical QT prolongation. After review, 28 discordant TQT-positive drugs were identified. This article provides an overview of direct and indirect mechanisms responsible for QT prolongation and theoretical reasons for lack of concordance between clinical TQT studies and nonclinical assays. We examine 6 specific and discordant TQT-positive drugs as case examples. These were derived from the unique HESI/Food and Drug Administration database. We would like to emphasize some reasons for discordant data including, insufficient or inadequate nonclinical data, effects of the drug on other cardiac ion channels, and indirect and/or nonelectrophysiological effects of drugs, including altered heart rate. We also outline best practices that were developed based upon our evaluation.

Estimation of cardiac QTc intervals in people prescribed antipsychotics: a comparison of correction factors

BACKGROUND

A prolonged electrocardiogram (ECG) QT interval is associated with cardiac events and increased mortality. Antipsychotics can prolong the QT interval. The QT interval requires correction (QTc) for heart rate using a formula or QT-nomogram. The QT and QTc can be calculated automatically by the ECG machine or manually; however, machine-measured QT(c) intervals may be inaccurate.

OBJECTIVE

We aimed to investigate the mean QTc and proportion of prolonged QTc intervals in people taking antipsychotic medicines.

METHODS

We conducted an observational retrospective chart review and data analysis of all consecutive patients taking antipsychotics, with an ECG record, admitted to the psychiatric unit of a large tertiary hospital in Brisbane, Australia, between 1 January 2017 and 30 January 2019. We investigated the mean QTc of people taking antipsychotics to determine differences using (a) machine versus manual QT interval measurement and (b) QTc correction formulae (Bazett, Fridericia, Framingham, Hodges and Rautaharju) and the QT-nomogram. We also determined the number of people with a prolonged QTc using different methods and compared rates of prolonged QTc with antipsychotic monotherapy and polypharmacy.

RESULTS

Of 920 included people, the mean (±SD) machine-measured, Bazett-corrected QT interval (recorded from the ECG) was 435 ms (±27), significantly longer (p < 0.001) than the mean manually measured corrected QT intervals with Fridericia 394 ms (±24), Framingham 395 ms (±22), Hodges 398 ms (±22) and Rautaharju 400 ms (±24) formulae. There were significantly more people with a prolonged QTc using machine-measured QT and the Bazett formula (12.0%, 110/920) when compared with manually measured QT and the Fridericia formula (2.2%, 20/920) or QT-nomogram (0.7%, 6/920). Rates of QTc prolongation did not differ between people taking antipsychotic polypharmacy compared with monotherapy.

CONCLUSION

Machine-measured QTc using the Bazett formula overestimates the QTc interval length and number of people with a prolonged QTc, compared with other formulae and the QT-nomogram. We recommend manually measuring the QT and correcting with the Fridericia formula or QT-nomogram prior to modifying antipsychotic therapies.

An explainable algorithm for detecting drug-induced QT-prolongation at risk of torsades de pointes (TdP) regardless of heart rate and T-wave morphology

Torsade de points (TdP), a life-threatening arrhythmia that can increase the risk of sudden cardiac death, is associated with drug-induced QT-interval prolongation on the electrocardiogram (ECG). While many modern ECG machines provide automated measurements of the QT-interval, these automated QT values are usually correct only for a noise-free normal sinus rhythm, in which the T-wave morphology is well defined. As QT-prolonging drugs often affect the morphology of the T-wave, automated QT measurements taken under these circumstances are easily invalidated. An additional challenge is that the QT-value at risk of TdP varies with heart rate, with the slower the heart rate, the greater the risk of TdP. This paper presents an explainable algorithm that uses an understanding of human visual perception and expert ECG interpretation to automate the detection of QT-prolongation at risk of TdP regardless of heart rate and T-wave morphology. It was tested on a large number of ECGs (n=5050) with variable QT-intervals at varying heart rates, acquired from a clinical trial that assessed the effect of four known QT-prolonging drugs versus placebo on healthy subjects. The algorithm yielded a balanced accuracy of 0.97, sensitivity of 0.94, specificity of 0.99, F1-score of 0.88, ROC (AUC) of 0.98, precision-recall (AUC) of 0.88, and Matthews correlation coefficient (MCC) of 0.88. The results indicate that a prolonged ventricular repolarisation area can be a significant risk predictor of TdP, and detection of this is potentially easier and more reliable to automate than measuring the QT-interval distance directly. The proposed algorithm can be visualised using pseudo-colour on the ECG trace, thus intuitively 'explaining' how its decision was made, which results of a focus group show may help people to self-monitor QT-prolongation, as well as ensuring clinicians can validate its results.

Translational Models and Tools to Reduce Clinical Trials and Improve Regulatory Decision Making for QTc and Proarrhythmia Risk (ICH E14/S7B Updates)

After multiple drugs were removed from the market secondary to drug-induced torsade de pointes (TdP) risk, the International Council for Harmonisation (ICH) released guidelines in 2005 that focused on the nonclinical (S7B) and clinical (E14) assessment of surrogate biomarkers for TdP. Recently, Vargas et al. published a pharmaceutical-industry perspective making the case that "double-negative" nonclinical data (negative in vitro hERG and in vivo heart-rate corrected QT (QTc) assays) are associated with such low probability of clinical QTc prolongation and TdP that potentially all double-negative drugs would not need detailed clinical QTc evaluation. Subsequently, the ICH released a new E14/S7B Draft Guideline containing Questions and Answers (Q&As) that defined ways that double-negative nonclinical data could be used to reduce the number of "Thorough QT" (TQT) studies and reach a low-risk determination when a TQT or equivalent could not be performed. We review the Vargas et al. proposal in the context of what was contained in the ICH E14/S7B Draft Guideline and what was proposed by the ICH E14/S7B working group for a "stage 2" of updates (potential expanded roles for nonclinical data and details for assessing TdP risk of QTc-prolonging drugs). Although we do not agree with the exact probability statistics in the Vargas et al. paper because of limitations in the underlying datasets, we show how more modest predictive value of individual assays could still result in low probability for TdP with double-negative findings. Furthermore, we expect that the predictive value of the nonclinical assays will improve with implementation of the new ICH E14/S7B Draft Guideline.

Management of pharmaceutical and recreational drug poisoning

BACKGROUND

Poisoning is one of the leading causes of admission to the emergency department and intensive care unit. A large number of epidemiological changes have occurred over the last years such as the exponential growth of new synthetic psychoactive substances. Major progress has also been made in analytical screening and assays, enabling the clinicians to rapidly obtain a definite diagnosis.

METHODS

A committee composed of 30 experts from five scientific societies, the Société de Réanimation de Langue Française (SRLF), the Société Française de Médecine d'Urgence (SFMU), the Société de Toxicologie Clinique (STC), the Société Française de Toxicologie Analytique (SFTA) and the Groupe Francophone de Réanimation et d'Urgences Pédiatriques (GFRUP) evaluated eight fields: (1) severity assessment and initial triage; (2) diagnostic approach and role of toxicological analyses; (3) supportive care; (4) decontamination; (5) elimination enhancement; (6) place of antidotes; (7) specificities related to recreational drug poisoning; and (8) characteristics of cardiotoxicant poisoning. Population, Intervention, Comparison, and Outcome (PICO) questions were reviewed and updated as needed, and evidence profiles were generated. Analysis of the literature and formulation of recommendations were then conducted according to the GRADE® methodology.

RESULTS

The SRLF-SFMU guideline panel provided 41 statements concerning the management of pharmaceutical and recreational drug poisoning. Ethanol and chemical poisoning were excluded from the scope of these recommendations. After two rounds of discussion and various amendments, a strong consensus was reached for all recommendations. Six of these recommendations had a high level of evidence (GRADE 1±) and six had a low level of evidence (GRADE 2±). Twenty-nine recommendations were in the form of expert opinion recommendations due to the low evidences in the literature.

CONCLUSIONS

The experts reached a substantial consensus for several strong recommendations for optimal management of pharmaceutical and recreational drug poisoning, mainly regarding the conditions and effectiveness of naloxone and N-acetylcystein as antidotes to treat opioid and acetaminophen poisoning, respectively.

ECG Restitution Analysis and Machine Learning to Detect Paroxysmal Atrial Fibrillation: Insight from the Equine Athlete as a Model for Human Athletes

Atrial fibrillation is the most frequent arrhythmia in both equine and human athletes. Currently, this condition is diagnosed via electrocardiogram (ECG) monitoring which lacks sensitivity in about half of cases when it presents in paroxysmal form. We investigated whether the arrhythmogenic substrate present between the episodes of paroxysmal atrial fibrillation (PAF) can be detected using restitution analysis of normal sinus-rhythm ECGs. In this work, ECG recordings were obtained during routine clinical work from control and horses with PAF. The extracted QT, TQ, and RR intervals were used for ECG restitution analysis. The restitution data were trained and tested using k-nearest neighbor (k-NN) algorithm with various values of neighbors k to derive a discrimination tool. A combination of QT, RR, and TQ intervals was used to analyze the relationship between these intervals and their effects on PAF. A simple majority vote on individual record (one beat) classifications was used to determine the final classification. The k-NN classifiers using two-interval measures were able to predict the diagnosis of PAF with area under the receiving operating characteristic curve close to 0.8 (RR, TQ with k ≥ 9) and 0.9 (RR, QT with k ≥ 21 or TQ, QT with k ≥ 25). By simultaneously using all three intervals for each beat and a majority vote, mean area under the curves of 0.9 were obtained for all tested k-values (3-41). We concluded that 3D ECG restitution analysis can potentially be used as a metric of an automated method for screening of PAF.

Pseudo-colouring an ECG enables lay people to detect QT-interval prolongation regardless of heart rate

Drug-induced long QT syndrome (diLQTS), characterized by a prolongation of the QT-interval on the electrocardiogram (ECG), is a serious adverse drug reaction that can cause the life-threatening arrhythmia Torsade de Points (TdP). Self-monitoring for diLQTS could therefore save lives, but detecting it on the ECG is difficult, particularly at high and low heart rates. In this paper, we evaluate whether using a pseudo-colouring visualisation technique and changing the coordinate system (Cartesian vs. Polar) can support lay people in identifying QT-prolongation at varying heart rates. Four visualisation techniques were evaluated using a counterbalanced repeated measures design including Cartesian no-colouring, Cartesian pseudo-colouring, Polar no-colouring and Polar pseudo-colouring. We used a multi-reader, multi-case (MRMC) receiver operating characteristic (ROC) study design within a psychophysical paradigm, along with eye-tracking technology. Forty-three lay participants read forty ECGs (TdP risk n = 20, no risk n = 20), classifying each QT-interval as normal/abnormal, and rating their confidence on a 6-point scale. The results show that introducing pseudo-colouring to the ECG significantly increased accurate detection of QT-interval prolongation regardless of heart rate, T-wave morphology and coordinate system. Pseudo-colour also helped to reduce reaction times and increased satisfaction when reading the ECGs. Eye movement analysis indicated that pseudo-colour helped to focus visual attention on the areas of the ECG crucial to detecting QT-prolongation. The study indicates that pseudo-colouring enables lay people to visually identify drug-induced QT-prolongation regardless of heart rate, with implications for the more rapid identification and management of diLQTS.

The Incidence of QT Prolongation and Torsades des Pointes in Patients Receiving Droperidol in an Urban Emergency Department

INTRODUCTION

Droperidol carries a boxed warning from the United States Food and Drug Administration for QT prolongation and torsades des pointes (TdP). After a six-year hiatus, droperidol again became widely available in the US in early 2019. With its return, clinicians must again make decisions regarding the boxed warning. Thus, the objective of this study was to report the incidence of QT prolongation or TdP in patients receiving droperidol in the ED.

METHODS

Patients receiving droperidol at an urban Level I trauma center from 1997-2001 were identified via electronic health record query. All patients were reviewed for cardiac arrest. We reviewed electrocardiogram (ECG) data for both critically-ill and noncritical patients and recorded Bazett's corrected QT intervals (QTc). ECGs from critically-ill patients undergoing resuscitation were further risk-stratified using the QT nomogram.

RESULTS

Of noncritical patients, 15,374 received 18,020 doses of droperidol; 2,431 had an ECG. In patients with ECGs before and after droperidol, the mean QTc was 424.3 milliseconds (ms) (95% confidence interval [CI], 419.7-428.9) before and 427.6 ms (95% CI, 424.3-430.9), after droperidol (n = 170). Regarding critically-ill patients, 1,172 received droperidol and 396 had an ECG. In the critically-ill group with ECGs before and after droperidol mean QTc was 435.7 ms (95% CI, 426.7-444.7) before and 435.8 ms (95% CI, 427.5-444.1) after droperidol (n = 114). Of 337 ECGs suitable for plotting on the QT nomogram, 13 (3.8%) were above the "at-risk" line; 3/136 (2.2%; 95% CI, 0.05-6.3%) in the before group, and 10/202 (4.9%; 95% CI, 2.4%-8.9%) in the after group. A single case of TdP occurred in a patient with multiple risk factors that did not reoccur after a droperidol rechallenge. Thus, the incidence of TdP was 1/16,546 (0.006%; 95% CI, 0.00015 - 0.03367%).

CONCLUSION

We found the incidence of QTc prolongation and TdP in ED patients receiving droperidol to be extremely rare. Our data suggest the FDA "black box warning" is overstated, and that close ECG monitoring is useful only in high-risk patients.

Information transfer in QT-RR dynamics: Application to QT-correction

The relation between the electrical properties of the heart and the beating rate is essential for the heart functioning. This relation is central when calculating the “corrected QT interval” — an important measure of the risk of potentially lethal arrhythmias. We use the transfer entropy method from information theory to quantitatively study the mutual dynamics of the ventricular action potential duration (the QT interval) and the length of the beat-to-beat (RR) interval. We show that for healthy individuals there is a strong asymmetry in the information transfer: the information flow from RR to QT dominates over the opposite flow (from QT to RR), i.e. QT depends on RR to a larger extent than RR on QT. Moreover, the history of the intervals has a strong effect on the information transfer: at sufficiently long QT history length the information flow asymmetry inverts and the RR influence on QT dynamics weakens. Finally, we demonstrate that the widely used QT correction methods cannot properly capture the changes in the information flows between QT and RR. We conclude that our results obtained through a model-free informational perspective can be utilised to improve and test the QT correction schemes in clinics.

QT interval prolongation in opioid agonist treatment: analysis of continuous 12-lead electrocardiogram recordings

AIMS

Methadone is a widely used opioid agonist treatment associated with QT prolongation and torsades de pointes. We investigated the QT interval in patients treated with methadone or buprenorphine using continuous 12-lead Holter recordings.

METHODS

We prospectively made 24-h Holter recordings in patients prescribed methadone or buprenorphine, compared to controls. After their normal dose a continuous 12-lead Holter recorder was attached for 24 h. Digital electrocardiograms were extracted hourly from the Holter recordings. The QT interval was measured automatically (H-scribe software, Mortara Pty Ltd) and checked manually. The QT interval was plotted against heart rate (HR) on the QT nomogram to determine abnormality. Demographics, dosing, medical history and laboratory investigations were recorded.

RESULTS

There were 58 patients (19 methadone, 20 buprenorphine and 19 control); median age 35 years (20-56 years); 33 males. Baseline characteristics were similar. Median dose of methadone was 110 mg day-1 (70-170 mg day-1 ) and buprenorphine was 16 mg day-1 (12-32 mg day-1 ). Seven participants had abnormal QT intervals. There was a significant difference in the proportion of prescribed methadone with abnormal QT intervals, 7/19 (37%; 95% confidence interval: 17-61%), compared to controls 0/19 (0%; 95% confidence interval: 0-21%; P = 0.008), but no difference between buprenorphine and controls (0/20). QT vs. HR plots showed patients prescribed methadone had higher QT-HR pairs over 24 h compared to controls. There was no difference in dose for patients prescribed methadone with abnormal QT intervals and those without.

CONCLUSIONS

Methadone is associated with prolonged QT intervals, but there was no association with dose. Buprenorphine did not prolong the QT interval. Twenty four-hour Holter recordings using the QT nomogram is a feasible method to assess the QT interval in patients prescribed methadone.

Optimizing QT Interval Measurement for the Preparticipation Screening of Young Athletes

PURPOSE

Sudden cardiac death is the leading cause of death in athletes. Long QT syndrome (LQTS) is one of the most common cardiogenetic diseases that can lead to sudden cardiac death and is identified by QT interval prolongation on an ECG. Recommendations for QT monitoring in athletes are adopted from nonathlete populations. To improve screening, ECG data of athletes are assessed to determine a more appropriate method for QT interval estimation.

METHODS

ECG (CardeaScreen) data were collected from June 2010 to March 2015. ECG data with HR greater than 100 bpm were excluded. Fiducial points of outliers were manually corrected if the QRS onset or the T wave offset was misidentified. A model of best fit was determined and compared across four QT correction factors. Classification analysis was used to compare the Bazett's corrected QT interval to the 99th percentile of uncorrected QT interval.

RESULTS

High school (n = 597), college (n = 1207), and professional athletes (n = 273) (N = 2077) were analyzed. Mean age was 19 ± 3.5 yr. QT interval varied by cohort (HS = 388 ± 30, Col = 410 ± 33, Pro = 407 ± 27, p < 0.0001). A nonlinear power function with a cubic exponent of -0.349 fit the data the best (R = 0.64). Of the four common correction factors, Fridericia had the lowest residual dependence to HR (m = -0.10). With standard screening, 75% of athletes within the top 1% for QT interval were not identified for further investigation for LQTS.

CONCLUSION

Up to 75% of athletes possessing an uncorrected QT interval greater than 99% of the population are not identified for investigation for LQTS using the recommended criteria. We propose a new method of risk stratification that replaces QT interval correction. Further study is needed to establish QT interval distributions and risk thresholds in athletes.

Beat-to-beat ECG restitution: A review and proposal for a new biomarker to assess cardiac stress and ventricular tachyarrhythmia vulnerability

BACKGROUND

Cardiac restitution is the ability of the heart to recover from one beat to the next. Ventricular arrhythmia vulnerability can occur when the heart does not properly adjust to sudden changes in rate or in hemodynamics leading to excessive temporal and/or spatial heterogeneity in conduction or repolarization. Restitution has historically been used to study, by invasive means, the dynamics of the relationship between action potential duration (APD) and diastolic interval (DI) in sedated subjects using various pacing protocols. Even though the analogous measures of APD and DI can be obtained using the surface ECG to acquire the respective QT and TQ intervals for ECG restitution, this methodology has not been widely adopted for a number of reasons.

METHODS

Recent development of more advanced software algorithms enables ECG intervals to be measured accurately, on a continuous beat-to-beat basis, in an automated manner, and under highly dynamic conditions (i.e., ambulatory or exercise) providing information beyond that available in the typical resting state.

RESULTS

Current breakthroughs in ECG technology will allow ECG restitution measures to become a practical approach for providing quantitative measures of the risks for ventricular arrhythmias as well as cardiac stress in general.

CONCLUSIONS

In addition to a review of the underlying principles and caveats of ECG restitution, a new approach toward an advancement of more integrated restitution biomarkers is proposed.

Utility of hERG Assays as Surrogate Markers of Delayed Cardiac Repolarization and QT Safety

HERG (human-ether-a-go-go-related gene) encodes for a cardiac potassium channel that plays a critical role in defining ventricular repolarization. Noncardiovascular drugs associated with a rare but potentially lethal ventricular arrhythmia (Torsades de Pointes) have been linked to delayed cardiac repolarization and block of hERG current. This brief overview will discuss the role of hERG current in cardiac electrophysiology, its involvement in drug-induced delayed repolarization, and approaches used to define drug effects on hERG current. In addition, examples of hERG blocking drugs acting differently (i.e., overt and covert hERG blockade due to multichannel block) together with the utility and limitations of hERG assays as tools to predict the risk of delayed repolarization and proarrhythmia are discussed.

Evaluation of cardiac function in unrestrained dogs and monkeys using left ventricular dP/dt

INTRODUCTION

Preclinical assessment for alterations in cardiac ventricular function for drug candidates has not been a focus of ICH S7b guidelines for cardiovascular safety studies, but there is growing interest given that the cardiovascular risk is associated with positive and negative inotropes.

METHODS

From 2003 through 2013, 163 telemetry studies with left-ventricular function analyses were conducted in dogs and monkeys at Bristol Myers Squibb (BMS) in support for drug development programs. The ability of the telemetry system to detect changes in cardiac contractility was verified with positive control agents pimobendan and atenolol. Control data from a subset of studies were analyzed to determine dP/dt reference range values, and minimum detectable mean differences (control vs. treated) for statistical significance.

RESULTS

Median minimum detectable differences for dogs ranged from 14 to 21% for positive dP/dt and 11 to 21% for negative dP/dt. For monkeys, median minimum detectable differences were 25 and 14% for positive and negative dP/dt, respectively. For BMS programs, 15 drug candidates were identified that produced primary effects on contractility. Changes in contractility that were associated with, and potentially secondary to, drug-related effects on heart rate or systemic blood pressure were observed with an additional 29 drug candidates.

DISCUSSION

Changes in contractility have been observed in large animals during drug development studies at BMS over the past 10years. Model sensitivity has been demonstrated and a dP/dt beat-to-beat cloud analysis tool has been developed to help distinguish primary effects from those potentially secondary to systemic hemodynamic changes.

The Half RR Rule: A Poor Rule of Thumb and Not a Risk Assessment Tool for QT Interval Prolongation

OBJECTIVES

Measuring the QT interval on an electrocardiogram (ECG) is integral to risk assessment of Torsade de Pointes (TdP). This study aimed to investigate the accuracy of the 1/2 RR rule as a risk assessment tool for drug-induced TdP, comparing it to the QT nomogram, Bazett's corrected QT (QTcB), and Fridericia's corrected QT (QTcF).

METHODS

The authors calculated sensitivity and specificity of the 1/2 RR rule using a published data set of 129 cases of drug-induced TdP and 316 controls (noncardiotoxic overdoses), compared to the QT nomogram, QTcB > 500 msec and QTcF > 500 msec. To further determine the value of the 1/2 RR rule, its observed positive, and negative agreement were calculated when compared to the QT nomogram for determining an abnormal QT in eight samples of different drugs in overdose.

RESULTS

The sensitivity and specificity of the 1/2 RR rule were 88% (95% confidence interval [CI] = 80% to 93%) and 53% (95% CI = 47% to 58%), respectively, compared to the QT nomogram (sensitivity = 97%, 95% CI = 92% to 99%; specificity = 99%, 95% CI = 97% to 100%). It was also less sensitive than QTcB > 500 msec and had a lower specificity than QTcB > 500 msec and QTcF > 500 msec. In drug overdose patients, the 1/2 RR rule had poor observed agreement averaging 41%, which was mainly due to poor positive agreement, except for amisulpride where there was good agreement.

CONCLUSIONS

The 1/2 RR rule was not as sensitive as the QT nomogram or QTcB > 500 msec for drug-induced TdP. It had poor positive agreement in almost all overdose patients, resulting in over half of patients receiving unnecessary cardiac monitoring and repeat ECGs.

Risk assessment of drug-induced QT prolongation

Drugs can cause prolongation of the QT interval, alone or in combination, potentially leading to fatal arrhythmias such as torsades de pointes. When prescribing drugs that prolong the QT interval, the balance of benefit versus harm should always be considered. Readouts from automated ECG machines are unreliable. The QT interval should be measured manually. Changes in heart rate influence the absolute QT interval. Heart rate correction formulae are inaccurate, particularly for fast and slow heart rates. The QT nomogram, a plot of QT interval versus heart rate, can be used as a risk assessment tool to detect an abnormal QT interval.

Risk factors for QT prolongation associated with acute psychotropic drug overdose

BACKGROUND

Antipsychotic/Antidepressant use is a risk factor for QT interval (QT) prolongation and sudden cardiac death. However, it is unclear which drugs are risk factors for QT prolongation and torsades de pointes in cases of psychotropic drug overdose.

METHODS

After correction of QT data by Bazett formula (QTc), QTc was classified into 3 categories (QTc<440 milliseconds, 440 milliseconds≤QTc<500 milliseconds, and QTc≥500 milliseconds), and the blood concentration of each drug was classified as not detected, therapeutic range, or toxic range. The association of the blood concentration of each drug with QTc was analyzed using the ordinal logistic regression model. Drugs that induced QT-heart rate pairs higher than the at-risk line of Isbister's QT-heart rate nomogram (QT nomogram) were further analyzed using the binomial logistic regression model.

RESULTS

A total of 649 patients were enrolled in the study. The independent risk factors for QTc prolongation were therapeutic and toxic range of phenotiazine antipsychotic drug (therapeutic range: odds ratio [OR], 1.56 [P=.039]; toxic range: OR, 3.85 [P<.001]), and toxic range of cyclic antidepressants (OR, 2.39; P=.018). In addition, toxic range of phenotiazine antipsychotic drug (OR, 3.87; P=.012) and tricyclic antidepressants (OR, 4.94; P<.001) were risk factors for QT higher than the at-risk line of the QT nomogram.

CONCLUSIONS

The possibility of QT prolongation and torsades de pointes due to overdose of phenotiazine antipsychotic drug or tricyclic antidepressants requires particular consideration.

Use of ECG restitution (beat-to-beat QT-TQ interval analysis) to assess arrhythmogenic risk of QTc prolongation with guanfacine

BACKGROUND

Guanfacine (Intuniv) is a centrally active alpha-2A adrenergic agonist for the new indication of attention-deficit/hyperactivity disorder. QTc (QTcF and QTcNi) was prolonged at both therapeutic (4 mg) and supratherapeutic (8 mg) doses of a thorough QT study even though guanfacine has had a safe clinical history of over 3 million prescriptions for the treatment of hypertension. In an attempt to understand this disparity, retrospective evaluation of the continuous ECG data utilized dynamic beat-to-beat and ECG restitution analyses was performed.

METHODS

Sixty healthy subjects using 24-hour Holters were examined in a 3-arm, placebo- and positive-controlled, double-blind crossover study for effects on beat-to-beat QT, TQ, and RR intervals.

RESULTS

ECG restitution analyses indicated that, at all time points, a disproportionate effect to increase the TQ interval (rest) occurred more in relationship to each QT interval lengthening resulting in a placebo-adjusted reduced QT/TQ ratio of 21% after 4 mg and 31% after 8 mg (both antiarrhythmic responses). Additionally, the percentage of time and magnitude of stress on the heart, as measured by the upper limits of the QT/TQ ratio, were reduced with guanfacine by 22% to 24%. In contrast to guanfacine, moxifloxacin did not show a significant improvement in any restitution parameters but reflected a trend toward proarrhythmia with an increase in the QT/TQ ratio of up to 11%.

CONCLUSION

These results indicate that guanfacine causes a stabilizing effect on cardiac restitution that helps reconcile the clinical evidence for a lack of arrhythmia liability despite apparent increases in typical QT/QTc prolongation measures.

Drug-induced QT interval prolongation: mechanisms and clinical management

The prolonged QT interval is both widely seen and associated with the potentially deadly rhythm, Torsades de Pointes (TdP). While it can occur spontaneously in the congenital form, there is a wide array of drugs that have been implicated in the prolongation of the QT interval. Some of these drugs have either been restricted or withdrawn from the market due to the increased incidence of fatal polymorphic ventricular tachycardia. The list of drugs that cause QT prolongation continues to grow, and an updated list of specific drugs that prolong the QT interval can be found at www.qtdrugs.org. This review focuses on the mechanism of drug-induced QT prolongation, risk factors for TdP, culprit drugs, prevention and monitoring of prolonged drug-induced QT prolongation and treatment strategies.

Drug induced QT prolongation: the measurement and assessment of the QT interval in clinical practice

There has been an increasing focus on drug induced QT prolongation including research on drug development and QT prolongation, following the removal of drugs due to torsades de pointes (TdP). Although this has improved our understanding of drug-induced QT prolongation there has been much less research aimed at helping clinicians assess risk in individual patients with drug induced QT prolongation. This review will focus on assessment of drug-induced QT prolongation in clinical practice using a simple risk assessment approach. Accurate measurement of the QT interval is best done manually, and not using the measurement of standard ECG machines. Correction for heart rate (HR) using correction formulae such as Bazett's is often inaccurate. These formulae underestimate and overestimate the duration of cardiac repolarization at low and high heart rates, respectively. Numerous cut-offs have been suggested as an indicator of an abnormal QT, but are problematic in clinical practice. An alternative approach is the QT nomogram which is a plot of QT vs. HR. The nomogram has an 'at risk' line and QT-HR pairs above this line have been shown in a systematic study to be associated with TdP and the line is more sensitive and specific than Bazett's QTc of 440 ms or 500 ms. Plotting the QT-HR pair for patients on drugs suspected or known to cause QT prolongation allows assessment of the QT interval based on normal population QT variability. This risk assessment then allows the safer commencement of drugs therapeutically or management of drug induced effects in overdose.

Predicting drug-induced QT prolongation and torsades de pointes: a review of preclinical endpoint measures

Compound-induced prolongation of the cardiac QT interval is a major concern in drug development and this unit discusses approaches that can predict QT effects prior to undertaking clinical trials. The majority of compounds that prolong the QT interval block the cardiac rapid delayed rectifier potassium current, IKr (hERG). Described in this overview are different ways to measure hERG, from recent advances in automated electrophysiology to the quantification of channel protein trafficking and binding. The contribution of other cardiac ion channels to hERG data interpretation is also discussed. In addition, endpoint measures of the integrated activity of cardiac ion channels at the single-cell, tissue, and whole-animal level, including for example the well-established action potential to the more recent beat-to-beat variability, transmural dispersion of repolarization, and field potential duration, are described in the context of their ability to predict QT prolongation and torsadogenicity in humans.

Use of continuous ECG for improvements in assessing the standing response as a positive control for QT prolongation

BACKGROUND

Standing invoked change in QT interval has been identified as a promising autonomic maneuver for the assessment of QT/QTc prolongation in patients with underlying heart abnormalities or as a positive control in healthy volunteers for drug studies. Criticism for its more widespread use is the high variability in reported results and the need for a more standardized methodology with defined normal ranges.

METHODS

Forty healthy male subjects underwent continuous ECG collection on the day before dosing in a double-blind, placebo-controlled, randomized, single ascending dose trial. A brisk supine to standing (3 minutes) response was conducted at three time points. Results were grouped by treatment cohort or assessed as a pooled group at each time point. Maximum time and median change from baseline (ΔTmax QTcF, ΔQTcF) were calculated for each individual over sequential 30-second periods staggered by 5 seconds.

RESULTS

Maximum ΔQTcF at all time points and in all groups was significant (i.e., the lower bound of 90% CI was > 5 milliseconds) which is the ICH E14 regulatory requirement for a positive control. Variability of the time to maximum response was also reduced 9-fold by the third time period.

CONCLUSIONS

Standing invoked ΔQTcF can be utilized to validate the sensitivity of a study for assessment of the QT interval effect of drugs in early development. The methodology may be used to further improve its diagnostic use of long QT syndromes by reducing the variability and allowing adequate definition of normal limits.

Validation of QT Interval Correction Methods When a Drug Changes Heart Rate

The QT interval is correlated with heart rate; therefore, the QT interval is usually corrected by heart rate when drug-induced QT effect is studied. Currently, there are many correction methods that use either fixed or data-driven approaches. The effectiveness of correction methods depends on many factors and varies from study to study. Statistical validation and comparisons need to be performed to determine the most appropriate correction method for each study. We examined different validation methods and explored a new approach to use when the testing drug changes heart rate.

Population pharmacokinetics and pharmacodynamics of escitalopram in overdose and the effect of activated charcoal

AIMS

To describe the pharmacokinetics and pharmacodynamics (PKPD) of escitalopram in overdose and its effect on QT prolongation, including the effectiveness of single dose activated charcoal (SDAC).

METHODS

The data set included 78 escitalopram overdose events (median dose, 140mg [10-560mg]). SDAC was administered 1.0 to 2.6 h after 12 overdoses (15%). A fully Bayesian analysis was undertaken in WinBUGS 1.4.3, first for a population pharmacokinetic (PK) analysis followed by a PKPD analysis. The developed PKPD model was used to predict the probability of having an abnormal QT as a surrogate for torsade de pointes.

RESULTS

A one compartment model with first order input and first-order elimination described the PK data, including uncertainty in dose and a baseline concentration for patients taking escitalopram therapeutically. SDAC reduced the fraction absorbed by 31% and reduced the individual predicted area under the curve adjusted for dose (AUC(i) /dose). The absolute QT interval was related to the observed heart rate with an estimated individual heart rate correction factor (α= 0.35). The heart rate corrected QT interval (QT(c) ) was linearly dependent on predicted escitalopram concentration [slope = 87ms/(mgl(-1) )], using a hypothetical effect-compartment (half-life of effect-delay, 1.0h). Administration of SDAC significantly reduced QT prolongation and was shown to reduce the risk of having an abnormal QT by approximately 35% for escitalopram doses above 200mg.

CONCLUSIONS

There was a dose-related lengthening of the QT interval that lagged the increase in drug concentration. SDAC resulted in a moderate reduction in fraction of escitalopram absorbed and reduced the risk of the QT interval being abnormal.

Methodologies to characterize the QT/corrected QT interval in the presence of drug-induced heart rate changes or other autonomic effects

This White Paper, written collaboratively by members of the Cardiac Safety Research Consortium from academia, industry, and regulatory agencies, discusses different methods to characterize the QT effects for drugs that have a substantial direct or indirect effect on heart rate. Descriptions and applications are provided for individualized QT-R-R correction, Holter bin, dynamic QT beat-to-beat, pharmacokinetic-pharmacodynamic modeling, and QT assessment at constant heart rate. Most of these techniques are optimally performed using continuous electrocardiogram data obtained in clinical studies designed to characterize a drug's effect on the QT interval. An important study design element is the collection of drug-free data over a range of heart rates seen on treatment. The range of heart rates is increased at baseline by using ambulatory electrocardiogram recordings in addition to those collected under semisupine, resting conditions. Discussions in this study summarize areas of emerging consensus and other areas in which consensus remains elusive and provide suggestions for additional research to further increase our knowledge and understanding of this topic.

A NOVEL FRAMEWORK FOR SIGNAL REPRESENTATION AND SOURCE SEPARATION: APPLICATIONS TO FILTERING AND SEGMENTATION OF BIOSIGNALS

A general technique for representing quasi-periodic oscillations, typical of biomedical signals, is described. Using energy thresholding and Gaussian kernels, in conjunction with a nonlinear gradient descent optimization, it is shown that significant noise reduction, compression and turning point location is possible. As such, the signal representation model can be considered a form of correlated source separation. Applications to filtering, modelling and robust ECG QT-analysis are described.

Cardiac abnormalities in severe acute dichlorvos poisoning

OBJECTIVE

Patients with organophosphorus poisoning sometimes die suddenly during rigorous treatment, possibly from myocardial injury. This study sought to elucidate the mechanisms underlying organophosphorus poisoning-induced cardiotoxicity.

DESIGN

Prospective observational study.

SETTING

Urban, tertiary teaching hospital emergency intensive care unit with 10 beds.

PATIENTS

Forty-one patients with severe acute dichlorvos poisoning were consecutively enrolled (n = 92) at emergency intensive care unit and followed for 3 months.

MEASUREMENTS AND MAIN RESULTS

Levels of serum creatine kinase isoenzyme myocardium, cardiac troponin I, acetylcholinesterase, acetylcholine, epinephrine, and norepinephrine were tested on hospital days 1, 3, and 5 and on discharge day. Electrocardiography was recorded on admission and then every other day. Transthoracic echocardiography was performed at admission, in the acute phase, before discharge, and during follow-up. Technetium 99m-sestamibi myocardial single photon emission computed tomography was conducted in four patients. Thirty-seven (90.2%) patients survived and four (9.8%) patients died during treatment. We observed sinus tachycardia in 37 (90.2%) patients and ST-T changes in 33 (80.4%) patients. Creatine kinase isoenzyme myocardium and cardiac troponin I levels peaked at day 3 postadmission and then decreased to normal levels. Serum acetylcholine, epinephrine, and norepinephrine peaked at day 1 after admission and then decreased. Echocardiography revealed marked decreases in wall motion of the interventricular septum and left ventricle in the acute phase but returned to normal in the recovery phase. The left ventricular ejection fraction improved significantly from 42 ± 5% to 59 ± 4% (p = .001). Single photon emission computed tomography showed abnormal left ventricle perfusion.

CONCLUSION

Severe acute dichlorvos poisoning is associated with reversible myocardial dysfunction, possibly through an increase in catecholamine levels.

Evaluation of a QT nomogram for risk assessment after antidepressant overdose

AIMS

A QT-heart rate nomogram has recently been proposed as a means of identifying patients at risk of torsades de pointes after antidepressant overdose, based on published cases of drug-induced torsades de pointes. The present study sought to examine the performance of the nomogram in patients who ingest an antidepressant overdose but do not develop arrhythmia.

METHODS

A retrospective case control study of patients presenting to hospital after overdose of citalopram, mirtazapine and venlafaxine was carried out. The primary outcome variable was QT higher than the nomogram, and was compared with occurrence of QT(c) (QT corrected by Bazett's formula) greater than ≥440 ms and QT(c) ≥500 ms, with comparison between drugs. Data are expressed as proportions in each group with 95% confidence intervals.

RESULTS

There were 858 electrocardiograms from 541 patients. QT was higher than the nomogram in 2.4% (1.4, 4.1%), whereas QT(c) was ≥440 ms in 23.1% (95% CI 19.8, 26.8%), and QT(c) was ≥500 ms in 1.1% (0.5, 2.5%). Citalopram overdose was more likely to be associated with QT higher than the nomogram compared with the other agents (difference 7.0%, 95% CI 2.9, 11.9%, P = 0.001) and more likely to be associated with QT(c) ≥440 ms (difference = 11.0%, 95% CI 2.6, 19.0%, P = 0.013).

CONCLUSIONS

The QT nomogram was associated with a lower false positive rate than widely accepted QT(c) criteria, and allowed detection of different effects of individual drugs. The nomogram offers potential advantages over QT(c) criteria and merits further investigation in a clinical setting.

Amisulpride overdose is frequently associated with QT prolongation and torsades de pointes

This study aimed to describe the effects of the antipsychotic amisulpride in overdose, including the frequency of QT prolongation and torsades de pointes. Cases of amisulpride overdose (>1 g) were recruited from 2 state poison centers and a tertiary toxicology unit over 5 years. A 1-page clinical research form was used to collect clinical information. Copies of all electrocardiograms were obtained. Electrocardiogram parameters (QRS and QT intervals) were manually measured as previously described, and plots of QT-heart rate (HR) pairs were compared with the QT nomogram. There were 83 patients with amisulpride overdoses with a median age of 29 years (interquartile range [IQR], 23-40 years), and 42 (51%) were female. The median dose ingested was 6 g (IQR, 3-13 g, range, 1.2-120 g). The median HR was 66 beats/min (IQR, 60-81 beats/min). Bradycardia occurred in 20 cases (24%), and hypotension in 19 (23%). From 440 electrocardiograms (average of 5 per case; range, 1-15), an abnormal QT-HR pair occurred in 61 cases (73%). Torsades de pointes developed in 6 cases (7%), with doses of 4, 4.6, 18, 24, 32, and 80 g. The patient taking 32 g died after a cardiac arrest. Widened QRS did not occur except transient rate-dependent bundle-branch block in 3 cases. There were significant associations of bradycardia, hypokalemia, and hypocalcaemia, with QT prolongation and torsades de pointes. Central nervous system effects were uncommon with coma in 7 cases, seizures in 2, and dystonic reactions in 2. Amisulpride overdose commonly causes QT prolongation, bradycardia, and hypotension. Torsades de pointes occurred commonly enough to suggest that amisulpride is highly cardiotoxic in overdose.

Reference regions for beat-to-beat ECG data

The QT interval is regarded as an important biomarker for the assessment of arrhythmia liability, and evidence of QT prolongation has led to the withdrawal and relabeling of numerous compounds. Traditional methods of assessing QT prolongation correct the QT interval for the length of the RR interval (which varies inversely with heart-rate) in a variety of ways. These methods often disagree with each other and do not take into account changes in autonomic state. Correcting the QT interval for RR reduces a bivariate observation (RR, QT) to a univariate observation (QTc). The development of automatic electrocardiogram (ECG) signal acquisition systems has made it possible to collect continuous (so called 'beat-to-beat') ECG data. ECG data collected prior to administration of a compound allow us to define a region for (RR, QT) values that encompasses typical activity. Such reference regions are used in clinical applications to define the 'normal' region of clinical or laboratory measurements. This paper motivates the need for reference regions of (RR, QT) values from beat-to-beat ECG data, and describes a way of constructing these. We introduce a measure of agreement between two reference regions that points to the reliability of 12-lead digital Holter data. We discuss the use of reference regions in establishing baselines for ECG parameters to assist in the evaluation of cardiac risk and illustrate using data from two methodological studies.

Covariate analysis of QTc and T-wave morphology: new possibilities in the evaluation of drugs that affect cardiac repolarization

This study adds the dimension of a T-wave morphology composite score (MCS) to the QTc interval-based evaluation of drugs that affect cardiac repolarization. Electrocardiographic recordings from 62 subjects on placebo and 400 mg moxifloxacin were compared with those from 21 subjects on 160 and 320 mg D,L-sotalol. T-wave morphology changes, as assessed by DeltaMCS, are larger after 320 mg D,L-sotalol than after 160 mg D,L-sotalol; and the changes associated with 160 mg D,L-sotalol are, in turn, larger than those associated with moxifloxacin and placebo. Covariate analyses of DeltaQTc and DeltaMCS showed that changes in T-wave morphology are a significant effect of D,L-sotalol. By contrast, moxifloxacin was found to have no significant effect on T-wave morphology (DeltaMCS) at any given change in QTc. This study offers new insights into the repolarization behavior of a drug associated with low cardiac risk vs. one associated with a high risk and describes the added benefits of a T-wave MCS as a covariate to the assessment of the QTc interval.

Interferences of the autonomic nervous system with drug induced QT prolongation: a point to consider in non-clinical safety studies

INTRODUCTION

QT interval assessment by telemetry has become one of the most useful models in testing strategies adopted for detection of drug induced QT prolongation in non-clinical safety pharmacology studies. This study reports experimental data showing that the autonomic nervous system might influence drug induced QT prolongation.

METHODS

Animals were instrumented with telemetric transmitters and epicardial ECG leads. Effects on QT interval of reference drugs such as thioridazine and terfenadine were analysed with different approaches, the Holzgrefe's probabilistic method, the QT shift method and an individual analysis of beat-to-beat QT/RR pair distribution visualised as points-cloud.

RESULTS

Two cases of unexpected absence of QT interval prolongation are reported with thioridazine and terfenadine in conscious beagle dogs under conditions of concomitant tachycardia. The pro-arrhythmic properties of these two molecules were unmasked by co-treatment with sympatholytic agents, atenolol and clonidine respectively suggesting that sympathetic activation and/or parasympathetic withdrawal might impair a drug induced QT prolongation.

DISCUSSION

The apparent absence of changes in the QT interval due to novel drug candidates should be interpreted cautiously under conditions of concomitant tachycardia or elevated heart rate levels in non-clinical safety studies.

The thorough QT/QTc study 4 years after the implementation of the ICH E14 guidance

The ICH E14 guidance on how to clinically assess a new drug's liability to prolong the QT interval was adopted in May 2005. A centre-piece of the guidance was the establishment of one single trial, the 'thorough QT/QTc study', intended to confidently identify drugs that may cause QT prolongation. Initially perceived as a great challenge, this study has rapidly become a standard component of all clinical development programs for new molecular entities. The study is normally conducted in healthy volunteers, includes both a positive and a negative (placebo) control and is stringently powered to exclude an effect on the QTc interval exceeding 10 ms. The E14 guidance was intentionally not very prescriptive and allowed sponsors and service providers to explore new methodologies. This has allowed for a rapid development of new methods during the first years after the guidance's implementation, such as computer-assisted algorithms for QT measurements. Regulators have worked in close collaboration with pharmaceutical industry to set standards for the design and conduct of the 'thorough QT/QTc study', which therefore has evolved as a key component of cardiac safety assessment of new drugs. This paper summarizes the requirements on the 'thorough QT/QTc study' with emphasis on the standard that has evolved based on interactions between regulators and sponsors and the experience from a large number of completed studies.

Lengthening of corrected QT during epileptic seizures

PURPOSE

To measure the corrected QT cardiac repolarization time before and during epileptic seizures.

METHODS

Thirty-nine video-EEG/ECG/SAO(2) (electroencephalography/electrocardiography/oxygen saturation) telemetry patients were included in this prospective study. Epileptic seizures were identified both clinically and electrographically. RR intervals and associated QT intervals were measured 5 min prior to the onset of the identified seizure. Consecutive RR and associated QT intervals were then measured from the seizure onset until the seizure had ended and the EEG had resumed its preseizure trace. Averaged RR and QT intervals over nine consecutive beats were applied to Bazett's, Hodge's, Fridericia's, and Framingham's formulas to compare the corrected QT values before and during the seizures.

RESULTS

A total of 156 seizures had corrected QT analysis performed. Nine generalized tonic-clonic seizures (5 patients), 34 absences (6 patients), 12 tonic seizures (6 patients), 27 temporal lobe seizures (14 patients), 58 frontal lobe seizures (4 patients), and 16 subclinical seizures (4 patients). All formulae reported a statistically significant difference in corrected QT (p < 0.001) during total seizure data compared to total preseizure values. According to Bazett's formula, 21 seizures (nine patients) transiently increased their corrected QT beyond normal limits, with a maximum corrected QT of 512 ms during a right temporal lobe seizure.

CONCLUSION

Significant lengthening of corrected QT cardiac repolarization time occurred during some epileptic seizures in this study. Prolonged corrected QT may have a role in sudden unexplained death in epilepsy (SUDEP).