Relation of QT interval measurements to evolving automated algorithms from different manufacturers of electrocardiographs

QT Interval Dynamics and Cardiovascular Outcomes: A Cohort Study in an Integrated Health Care Delivery System

Background

Long QT has been associated with ventricular dysrhythmias, cardiovascular disease (CVD) mortality, and sudden cardiac death. However, no studies to date have investigated the dynamics of within‐person QT change over time in relation to risk of incident CVD and all‐cause mortality in a real‐world setting.

Methods and Results

A cohort study among members of an integrated health care delivery system in Northern California including 61 455 people (mean age, 62 years; 60% women, 42% non‐White) with 3 or more ECGs (baseline in 2005–2009; mean±SD follow‐up time, 7.6±2.6 years). In fully adjusted models, tertile 3 versus tertile 1 of average QT corrected (using the Fridericia correction) was associated with cardiac arrest (hazard ratio [HR], 1.66), heart failure (HR, 1.62), ventricular dysrhythmias (HR, 1.56), all CVD (HR, 1.31), ischemic heart disease (HR, 1.28), total stroke (HR, 1.18), and all‐cause mortality (HR, 1.24). Tertile 3 versus tertile 2 of the QT corrected linear slope was associated with cardiac arrest (HR, 1.22), ventricular dysrhythmias (HR, 1.12), and all‐cause mortality (HR, 1.09). Tertile 3 versus tertile 1 of the QT corrected root mean squared error was associated with ventricular dysrhythmias (HR, 1.34), heart failure (HR, 1.28), all‐cause mortality (HR, 1.20), all CVD (HR, 1.14), total stroke (HR, 1.08), and ischemic heart disease (HR, 1.07).

Conclusions

Our results demonstrate improved predictive ability for CVD outcomes using longitudinal information from serial ECGs. Long‐term average QT corrected was more strongly associated with CVD outcomes than the linear slope or the root mean squared error. This new evidence is clinically relevant because ECGs are frequently used, noninvasive, and inexpensive.

Torsade de pointes: A nested case-control study in an integrated healthcare delivery system

Background

TdP is a form of polymorphic ventricular tachycardia which develops in the setting of a prolonged QT interval. There are limited data describing risk factors, treatment, and outcomes of this potentially fatal arrhythmia.

Objective

Our goals were as follows: (1) to validate cases presenting with Torsade de Pointes (TdP), (2) to identify modifiable risk factors, and (3) to describe the management strategies used for TdP and its prognosis in a real‐world healthcare setting.

Methods

Case–control study (with 2:1 matching on age, sex, and race/ethnicity) nested within the Genetic Epidemiology Research on Aging (GERA) cohort. Follow‐up of the cohort for case ascertainment was between January 01, 2005 and December 31, 2018.

Results

A total of 56 cases of TdP were confirmed (incidence rate = 3.6 per 100,000 persons/years). The average (SD) age of the TdP cases was 74 (13) years, 55 percent were female, and 16 percent were non‐white. The independent predictors of TdP were potassium concentration <3.6 mEq/L (OR = 10.6), prior history of atrial fibrillation/flutter (OR = 6.2), QTc >480 ms (OR = 4.4) and prior history of coronary artery disease (OR = 2.6). Exposure to furosemide and amiodarone was significantly greater in cases than in controls. The most common treatment for TdP was IV magnesium (78.6%) and IV potassium repletion (73.2%). The in‐hospital and 1‐year mortality rates for TdP cases were 10.7% and 25.0% percent, respectively.

Conclusions

These findings may inform quantitative multivariate risk indices for the prediction of TdP and could guide practitioners on which patients may qualify for continuous ECG monitoring and/or electrolyte replacement therapy.

Machine read frontal QRS-T angle and QTc is no substitute for manual measurement of QTc in pro-arrhythmic drug overdose

INTRODUCTION

To investigate whether there is an association between the blocking of cardiac potassium channels, which is characterised by a prolonged QTc interval and the frontal QRS-T angle after overdose by QT prolonging drugs.

METHODS

We obtained patient medical records associated with QT prolonging drugs from 3 different hospitals: the Calvary Mater Newcastle Hospital (CMNH), Royal Prince Alfred Hospital (RPAH) and Prince of Wales Hospital (POWH). RPAH and POWH admissions were taken between 4/01/2017 to 1/11/2019, and CMNH admissions were taken between 4/01/2013 to 24/06/2018. Demographic information and details of overdose were collected. All admission ECGs were manually measured. Linear regression was used to assess the relationship between various QTc formulas and the frontal QRS-T angle. A Bland-Altman plot was used to examine agreement between manual and machine QT intervals.

RESULTS

144 patients met the inclusion criteria for analysis. None of the patients developed torsades de pointes (TdP). There was no linear association between the QRS-T angle and the various QTc formulas (For QRS-T angle: QTcRTH: p = 0.76, QTcB: p = 0.83, QTcFri: p = 0.90, QTcFra: p = 0.13, QTcH: p = 0.97; For square root transformation of the QRS-T angle: QTcRTH: p = 0.18, QTcB: p = 0.33, QTcFri: p = 0.95, QTcFra: p = 0.47, QTcH: p = 0.33). Agreement between machine and manual QT measurements was low.

CONCLUSIONS

The frontal QRS-T angle cannot substitute the QTc in assessing the blockage of cardiac potassium channels in drug induced long QT syndrome. We also support the consensus that despite the availability of machine measurements of the QT interval, manual measurements should also be performed.

Comparison of PR, QRS, and QT interval measurements by seven ECG interpretation programs

BACKGROUND

Electrocardiograph-generated measurements of PR, QRS, and QT intervals are generally thought to be more precise than manual measurements on paper records. However, the performance of different programs has not been well compared.

METHODS

Routinely obtained digital electrocardiograms (ECGs), including over 500 pediatric ECGs, were used to create over 2000 10 s analog ECGs that were replayed through seven commercially available electrocardiographs. The measurements for PR interval, QRS duration, and QT interval made by each program were extracted and compared against each other (using the median of the programs after correction for program bias) and the population mean values.

RESULTS

Small but significant systematic biases were seen between programs. The smallest and largest variation from the population mean differed by 4.7 ms for PR intervals, 5.8 ms for QRS duration, and 12.4 ms for QT intervals. In pairwise comparison programs showed similar accuracy for most ECGs, with the average absolute errors at the 75th percentile for PR intervals being 4-6 ms from the median, QRS duration 4-8 ms, and QT interval 6-10 ms. However, substantial differences were present in the numbers and extent of large, clinically significant errors (e.g at the 98th percentile), for which programs differed by a factor of two for absolute errors, as well as differences in the mix of overestimations and underestimations.

CONCLUSIONS

When reading digital ECGs, users should be aware that small systematic differences exist between programs and that there may be large clinically important errors in difficult cases.

Relationship of QTc Interval Prolongation with Acute Ischemic Stroke

Introduction:

Many electrocardiographic (ECG) changes have been observed after strokes. We analyzed the QTc interval prolongation following stroke.

Aim:

The study aimed to assess if the prolongation in QTc interval is related to the occurrence of acute ischemic stroke.

Methods:

This cross-sectional study was conducted from July to December 2018. We included 100 consecutive patients with first-ever ischemic stroke who were admitted to our emergency department, who were age-matched and gender-matched with a control group of 100 non-stroke patients that visited our outpatients department for diseases other than cerebrovascular or cardiovascular ones. A single 12-lead resting ECG examination was done in all patients at the time of their emergency department admission.

Results:

No significant difference between the two groups regarding the age distribution and mean age was found. 56.5% of the sample were males but the difference was not significant between both gender groups. The main presenting symptoms of stroke cases were right-sided weakness (47%), left-sided weakness (36%), and right-sided weakness and aphasia (10%). 34% of the cases had prolonged QTc interval while none of the controls had a prolonged interval (p-value<0.001). No significant difference was observed among stroke patients concerning gender (p-value=0.584).

Conclusion:

Our findings support many previous studies on the brain-heart interaction during acute ischemic strokes and reinforce previous conclusions that assessment of the QTc interval might aid to stratify morbidity and mortality risks in patients with acute ischemic stroke. To accomplish the acute stroke effects on QTc interval prolongation, we need further larger size analytic studies.

Comparison of automated interval measurements by widely used algorithms in digital electrocardiographs

BACKGROUND

Automated measurements of electrocardiographic (ECG) intervals by current-generation digital electrocardiographs are critical to computer-based ECG diagnostic statements, to serial comparison of ECGs, and to epidemiological studies of ECG findings in populations. A previous study demonstrated generally small but often significant systematic differences among 4 algorithms widely used for automated ECG in the United States and that measurement differences could be related to the degree of abnormality of the underlying tracing. Since that publication, some algorithms have been adjusted, whereas other large manufacturers of automated ECGs have asked to participate in an extension of this comparison.

METHODS

Seven widely used automated algorithms for computer-based interpretation participated in this blinded study of 800 digitized ECGs provided by the Cardiac Safety Research Consortium. All tracings were different from the study of 4 algorithms reported in 2014, and the selected population was heavily weighted toward groups with known effects on the QT interval: included were 200 normal subjects, 200 normal subjects receiving moxifloxacin as part of an active control arm of thorough QT studies, 200 subjects with genetically proved long QT syndrome type 1 (LQT1), and 200 subjects with genetically proved long QT syndrome Type 2 (LQT2).

RESULTS

For the entire population of 800 subjects, pairwise differences between algorithms for each mean interval value were clinically small, even where statistically significant, ranging from 0.2 to 3.6milliseconds for the PR interval, 0.1 to 8.1milliseconds for QRS duration, and 0.1 to 9.3milliseconds for QT interval. The mean value of all paired differences among algorithms was higher in the long QT groups than in normals for both QRS duration and QT intervals. Differences in mean QRS duration ranged from 0.2 to 13.3milliseconds in the LQT1 subjects and from 0.2 to 11.0milliseconds in the LQT2 subjects. Differences in measured QT duration (not corrected for heart rate) ranged from 0.2 to 10.5milliseconds in the LQT1 subjects and from 0.9 to 12.8milliseconds in the LQT2 subjects.

CONCLUSIONS

Among current-generation computer-based electrocardiographs, clinically small but statistically significant differences exist between ECG interval measurements by individual algorithms. Measurement differences between algorithms for QRS duration and for QT interval are larger in long QT interval subjects than in normal subjects. Comparisons of population study norms should be aware of small systematic differences in interval measurements due to different algorithm methodologies, within-individual interval measurement comparisons should use comparable methods, and further attempts to harmonize interval measurement methodologies are warranted.

QTc Interval Prolongation and Hemorrhagic Stroke: Any Difference Between Acute Spontaneous Intracerebral Hemorrhage and Acute Non-traumatic Subarachnoid Hemorrhage?

BACKGROUND

A variety of ECG changes occur as an aftermath of stroke. Prolongation of the QTc interval is a well-documented change. We analyzed QTc interval prolongation among patients with acute hemorrhagic strokes.

METHODS

This observational study was conducted at the Emergency Department of Sulaymaniyah General Teaching Hospital and Shar Hospital from September 1^st, 2014 to August 31^st, 2015. Fifty patients who developed acute spontaneous hypertensive intracerebral hemorrhage (ICH) and 50 patients who developed acute non-traumatic subarachnoid hemorrhage (SAH) were included in the study. All patients underwent resting 12-lead ECG within half an hour of admission. The QTc interval was calculated and analyzed in those 100 patients.

RESULTS

Females (62%) outnumbered males (38%) with a female to male ratio of 1.6:1. Forty percent of the patients were between 60-69 years of age. Hypertension was seen in 82% of patients while left ventricular hypertrophy was documented in 40% of patients. The QTc was prolonged in 38 patients (17 patients in the ICH group and 21 patients in the SAH group). In both groups, males demonstrated QTc prolongation more than females. However, there were no statistically significant gender difference between both groups and within the same group. There was a statistically significant association between SAH and QTc prolongation (p-value<0.001); the ICH group did not demonstrate any significant relationship with QTc prolongation.

CONCLUSION

Prolongation in the QTc interval was "statistically" associated with acute SAH only. No gender difference was noted; whether this observation is clinically significant or not, it needs further analytic studies.

An evaluation of multiple algorithms for the measurement of the heart rate corrected JTpeak interval

Interest in the effects of drugs on the heart rate-corrected JTpeak (JTpc) interval from the body-surface ECG has spawned an increasing number of scientific investigations in the field of regulatory sciences, and more specifically in the context of the Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative. We conducted a novel initiative to evaluate the role of automatic JTpc measurement technologies by comparing their ability to distinguish multi- from single-channel blocking drugs. A set of 5232 ECGs was shared by the FDA (through the Telemetric and Holter ECG Warehouse) with 3 ECG device companies (AMPS, Mortara, and Philips). We evaluated the differences in drug-concentration effects on these measurements between the commercial and the FDA technologies. We provide a description of the drug-induced placebo-corrected changes from baseline for dofetilide, quinidine, ranolazine, and verapamil, and discuss the various differences across all technologies. The results revealed only small differences between measurement technologies evaluated in this study. It also confirms that, in this dataset, the JTpc interval distinguishes between multi- and single-channel (hERG) blocking drugs when evaluating the effects of dofetilide, quinidine, ranolazine, and verapamil. However, in the case of quinidine and dofetilide, we noticed a poor consistency across technologies because of the lack of standard definitions for the location of the peak of the T-wave (T-apex) when the T-wave morphology is abnormal.

Clinical ECG Assessment

With the adoption of the ICH E14 guidance, the thorough QT/QTc (TQT) study has become the focus of clinical assessment of an NCE's effects on ECG parameters. The TQT study is used as a guide to the liability of a drug to cause proarrhythmias on the basis of delayed cardiac repolarization. Around 300 TQT studies have been performed since 2005 and through interactions between sponsors and regulators, especially FDA's Interdisciplinary Review Team (IRT) for QT studies. These studies can today be performed more effectively and with great confidence in the generated data. This chapter will discuss technical features and the design and analysis of TQT studies, how assay sensitivity is demonstrated, and examples from recently conducted studies. ECG assessment for drugs that cannot be safely given to healthy volunteers is also addressed, and examples from studies in cancer patients and in healthy volunteers with tyrosine kinase inhibitors are discussed. The TQT study is resource intensive and designed to solely evaluate whether an NCE prolongs the QTc interval. If data with similar confidence can be generated from other studies that are routinely performed as part of the clinical development, this would represent a more optimal use of human resources. Methods and approaches to increase the confidence in ECG data derived from "early QT assessment" in single-ascending/multiple-ascending dose studies are therefore discussed, and a path toward replacing the TQT study using these approaches will be outlined.

Prevalence, management, and clinical consequences of QT interval prolongation during treatment with arsenic trioxide

PURPOSE

Arsenic trioxide (ATO) is a highly effective agent for the treatment of acute promyelocytic leukemia (APL). QT interval prolongation is common with ATO and can pose a barrier to effective administration. The objective of this study was to characterize the prevalence, management, and clinical consequences of QT prolongation in a large cohort of patients treated with ATO.

PATIENTS AND METHODS

We analyzed 3,011 electrocardiograms from 113 patients with non-APL acute myeloid leukemia and myelodysplastic syndrome who were treated on a previously reported clinical trial. QT intervals were assessed using four different correction formulas, and data were correlated with clinical parameters and treatment with ATO.

RESULTS

There were no clinically significant cardiac events in the study population. Of those receiving ATO therapy, 29 patients (26%) had rate-uncorrected QT values above 470 ms and 13 (12%) had values exceeding 500 ms. With the commonly used Bazett rate correction formula, 102 patients (90%) had QTc greater than 470 ms, including 74 (65%) above 500 ms. By using alternative rate correction formulas, only 24% to 32% of patients had rate-corrected QT intervals above 500 ms.

CONCLUSION

QT interval prolongation is common with ATO treatment, but clinically significant arrhythmias are rare and can be avoided with appropriate precautions. Use of the Bazett correction may result in unnecessary interruptions in ATO therapy, and alternative rate correction formulas should be considered for routine electrocardiographic monitoring.

Short QT in a cohort of 1.7 million persons: prevalence, correlates, and prognosis

BACKGROUND

Short QT syndrome (QTc ≤ 300 ms) is a novel hereditary channelopathy linked to syncope, paroxysmal atrial fibrillation, and sudden cardiac death. However, its epidemiological features remain unsettled.

OBJECTIVES

(1) To assess the prevalence of short QT in a large population-based sample; (2) to evaluate its demographic and clinical correlates and; (3) to determine its prognosis.

METHODS

A database of 6.4 million electrocardiograms (ECGs) obtained between 1995 and 2008 among 1.7 million persons was used. An internal, population-based method for heart rate correction (QTcreg ) was used and all ECGs with QTcreg ≤300 ms were manually validated. Linked health plan databases were used for covariate and survival ascertainment.

RESULTS

Of 6,387,070 ECGs, 1086 had an ECG with machine-read QTcreg ≤300 ms. Only 4% (45/1086) were validated yielding a prevalence of 0.7 per 100,000 or 1 of 141,935 ECGs. At the person level, the overall prevalence of QTcreg ≤300 ms was 2.7 per 100,000 or 1 of 37,335. The factors independently and significantly associated with validated QTcreg ≤300 ms were age over 65 years, Black race, prior history of ventricular dysrhythmias, chronic obstructive pulmonary disease, ST-T abnormalities, ischemia, bigeminy pattern, and digitalis effect. After 8.3 years of median follow-up and relative to normal QTcreg , validated QTcreg ≤300 ms was associated after multivariate adjustment with a 2.6-fold (95% confidence interval [CI] = 1.9-3.7) increased risk of death.

CONCLUSION

QTcreg ≤300 ms was extraordinarily rare and was associated with significant ECG abnormalities and reduced survival.

Comparison of automated measurements of electrocardiographic intervals and durations by computer-based algorithms of digital electrocardiographs

BACKGROUND AND PURPOSE

Automated measurements of electrocardiographic (ECG) intervals are widely used by clinicians for individual patient diagnosis and by investigators in population studies. We examined whether clinically significant systematic differences exist in ECG intervals measured by current generation digital electrocardiographs from different manufacturers and whether differences, if present, are dependent on the degree of abnormality of the selected ECGs.

METHODS

Measurements of RR interval, PR interval, QRS duration, and QT interval were made blindly by 4 major manufacturers of digital electrocardiographs used in the United States from 600 XML files of ECG tracings stored in the US FDA ECG warehouse and released for the purpose of this study by the Cardiac Safety Research Consortium. Included were 3 groups based on expected QT interval and degree of repolarization abnormality, comprising 200 ECGs each from (1) placebo or baseline study period in normal subjects during thorough QT studies, (2) peak moxifloxacin effect in otherwise normal subjects during thorough QT studies, and (3) patients with genotyped variants of congenital long QT syndrome (LQTS).

RESULTS

Differences of means between manufacturers were generally small in the normal and moxifloxacin subjects, but in the LQTS patients, differences of means ranged from 2.0 to 14.0 ms for QRS duration and from 0.8 to 18.1 ms for the QT interval. Mean absolute differences between algorithms were similar for QRS duration and QT intervals in the normal and in the moxifloxacin subjects (mean ≤6 ms) but were significantly larger in patients with LQTS.

CONCLUSIONS

Small but statistically significant group differences in mean interval and duration measurements and means of individual absolute differences exist among automated algorithms of widely used, current generation digital electrocardiographs. Measurement differences, including QRS duration and the QT interval, are greatest for the most abnormal ECGs.

Validation of a population-based method to assess drug-induced alterations in the QT interval: a self-controlled crossover study

PURPOSE

The purpose of this study was to ascertain, in the context of an integrated health care delivery system, the association between a comprehensive list of drugs known to have potential QT liability and QT prolongation or shortening.

METHODS

By using a self-controlled crossover study with 59 467 subjects, we ascertained intra-individual change in log-linear regression-corrected QT (QTcreg ) during the period between 1995 and mid-2008 for 90 drugs while adjusting for age, gender, race/ethnicity, comorbid conditions, number of electrocardiograms (ECGs), and time between pre-ECG and post-ECG. The proportion of users of each drug-developing incident long QT was also estimated.

RESULTS

Two drugs (nicardipine and levalbuterol) had no statistically significant intra-individual QTcreg shortening effects, 10 drugs had no statistically significant prolonging effect, and 78 (87%) of the drugs had statistically significant intra-individual mean QTcreg lengthening effects, ranging from 7.6 ms for aripiprazole to 25.2 ms for amiodarone. Three drugs were associated with mean QTcreg prolongation of 20 ms or greater: amiodarone (antiarrhythmic), terfenadine (antihistaminic), and quinidine (antiarrhythmic); whereas 11 drugs were associated with mean QTcreg prolongation of 15 ms or greater but less than 20 ms: trimipramine (tricyclic antidepressant), clomipramine (tricyclic antidepressant), disopyramide (antiarrhythmic), chlorpromazine (antipsychotic), sotalol (beta blocker), itraconazole (antifungal), phenylpropanolamine (decongestant/anorectic), fenfluramine (appetite suppressant), midodrine (antihypotensive), digoxin (cardiac glycoside/antiarrhythmic), and procainamide (antiarrhythmic).

CONCLUSIONS

QT prolonging effects were common and varied in strength. Our results lend support to past Food and Drug Administration regulatory actions and support the role for ongoing surveillance of drug-induced QT prolongation.

Normal standards for computer-ECG programs for prognostically and diagnostically important ECG variables derived from a large ethnically diverse female cohort: the Women's Health Initiative (WHI)

BACKGROUND

Substantial new information has emerged recently about the prognostic value for a variety of new ECG variables. The objective of the present study was to establish reference standards for these novel risk predictors in a large, ethnically diverse cohort of healthy women from the Women's Health Initiative (WHI) study.

METHODS AND RESULTS

The study population consisted of 36,299 healthy women. Racial differences in rate-adjusted QT end (QT(ea)) and QT peak (QT(pa)) intervals as linear functions of RR were small, leading to the conclusion that 450 and 390 ms are applicable as thresholds for prolonged and shortened QT(ea) and similarly, 365 and 295 ms for prolonged and shortened QT(pa), respectively. As a threshold for increased dispersion of global repolarization (T(peak)T(end) interval), 110 ms was established for white and Hispanic women and 120 ms for African-American and Asian women. ST elevation and depression values for the monitoring leads of each person with limb electrodes at Mason-Likar positions and chest leads at level of V1 and V2 were first computed from standard leads using lead transformation coefficients derived from 892 body surface maps, and subsequently normal standards were determined for the monitoring leads, including vessel-specific bipolar left anterior descending, left circumflex artery and right coronary artery leads. The results support the choice 150 μV as a tentative threshold for abnormal ST-onset elevation for all monitoring leads. Body mass index (BMI) had a profound effect on Cornell voltage and Sokolow-Lyon voltage in all racial groups and their utility for left ventricular hypertrophy classification remains open.

CONCLUSIONS

Common thresholds for all racial groups are applicable for QT(ea), and QT(pa) intervals and ST elevation. Race-specific normal standards are required for many other ECG parameters.

Oral contraceptive use and the ECG: evidence of an adverse QT effect on corrected QT interval

BACKGROUND

A prolonged corrected QT (QTc) interval is a marker for an increased risk of sudden cardiac death. We evaluated the relationship between oral contraceptive (OC) use, type of OC, and QTc interval.

METHODS

We identified 410,782 ECGs performed at Northern California Kaiser Permanente on female patients between 15 and 53 years from January, 1995 to June, 2008. QT was corrected for heart rate using log-linear regression. OC generation (first, second and third) was classified by increasing progestin androgenic potency, while the fourth generation was classified as antiandrogenic.

RESULTS

Among 410,782 women, 8.4% were on OC. In multivariate analysis after correction for comorbidities, there was an independent shortening effect of OCs overall (slope = -0.5 ms; SE = 0.12, P < 0.0002). Users of first and second generation progestins had a significantly shorter QTc than nonusers (P < 0.0001), while users of fourth generation had a significantly longer QTc than nonusers (slope = 3.6 ms, SE = 0.35, P < 0.0001).

CONCLUSION

Overall, OC use has a shortening effect on the QTc. Shorter QTc is seen with first and second generation OC while fourth generation OC use has a lengthening effect on the QTc. Careful examination of adverse event rates in fourth generation OC users is needed.

Improvement and limitation of the reliability of automated QT measurement by recent algorithms

BACKGROUND

Newer algorithms for automated QT interval measurements may be more reliable than previous algorithms.

OBJECTIVE

This study compares Bazett-corrected QTc obtained by an older algorithm (Old12SL) and by 2 newer ones (New12SL and v3.19) to semiautomated measurement performed by experienced cardiologists.

METHODS

A total of 6105 randomly selected electrocardiograms were classified by the cardiologists as normal (4227), borderline (1254), abnormal (575), or not analyzable (49). Errors of automated measurement were defined by more than 30 milliseconds of absolute difference between Bazett-corrected QTc obtained by automated algorithms and semiautomated measurement.

RESULTS

The Old12SL had approximately twice as many errors (5.25%) as the New12SL (2.33%) and v3.19 (2.30%), P < .0001. Abnormal tracings resulted in more errors than did normal ones (Old12SL: 16.52% vs 3.45%, New12SL: 7.30% vs 1.51%, and v3.19: 10.61% vs 1.21%).

CONCLUSION

Newer automated algorithms for QT measurements are highly reliable in normal tracings. However, electrocardiogram abnormalities increase the risk of QT measurement errors.

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.

Current challenges in the evaluation of cardiac safety during drug development: translational medicine meets the Critical Path Initiative

In October 2008, in a public forum organized by the Cardiac Safety Research Consortium and the Health and Environmental Sciences Institute, leaders from government, the pharmaceutical industry, and academia convened in Bethesda, MD, to discuss current challenges in evaluation of short- and long-term cardiovascular safety during drug development. The current paradigm for premarket evaluation of cardiac safety begins with preclinical animal modeling and progresses to clinical biomarker or biosignature assays. Preclinical evaluations have clear limitations but provide an important opportunity to identify safety hazards before administration of potential new drugs to human subjects. Discussants highlighted the need to identify, develop, and validate serum and electrocardiogram biomarkers indicative of early drug-induced myocardial toxicity and proarrhythmia. Specifically, experts identified a need to build consensus regarding the use and interpretation of troponin assays in preclinical evaluation of myocardial toxicity. With respect to proarrhythmia, the panel emphasized a need for better qualitative and quantitative biomarkers for arrhythmogenicity, including more streamlined human thorough QT study designs and a universal definition of the end of the T wave. Toward many of these ends, large shared data repositories and a more seamless integration of preclinical and clinical testing could facilitate the development of novel approaches to both cardiac safety biosignatures. In addition, more thorough and efficient early clinical studies could enable better estimates of cardiovascular risk and better inform phase II and phase III trial design. Participants also emphasized the importance of establishing formal guidelines for data standards and transparency in postmarketing surveillance. Priority pursuit of these consensus-based directions should facilitate both safer drugs and accelerated access to new drugs, as concomitant public health benefits.

The measurement of the QT and QTc on the neonatal and infant electrocardiogram: a comprehensive reliability assessment

BACKGROUND

An electrocardiogram has been proposed to screen for prolonged QT interval that may predispose infants to sudden death in the first year of life. Understanding the reliability of QT interval measurement will inform the design of a screening program.

METHODS

Three pediatric cardiologists measured the QT/RR intervals on 60 infant electrocardiograms (median age 46 days), from leads II, V5 and V6 on three separate occasions, 7 days apart, according to a standard protocol. The QTc was corrected by Bazett's (QTcB), Fridericia's (QT(CFrid)), and Hodges' (QTcH) formulae. Intraobserver and interobserver reliability were assessed by intraclass correlation coefficients (ICC), limits of agreement and repeatability coefficients for single, average of two and average of three measures. Agreement for QTc prolongation (> 440 msec) was assessed by kappa coefficients.

RESULTS

QT interval intraobserver ICC was 0.86 and repeatability coefficient was 25.9 msec; interobserver ICC increased from 0.88 for single observations to 0.94 for the average of 3 measurements and repeatability coefficients decreased from 22.5 to 16.7 msec. For QTcB, intraobserver ICC was 0.67, and repeatability was 39.6 msec. Best interobserver reliability for QTcB was for the average of three measurements (ICC 0.83, reproducibility coefficient 25.8 msec), with further improvement for QTcH (ICC 0.92, reproducibility coefficient 16.69 msec). Maximum interobserver kappa for prolonged QTc was 0.77. Misclassification around specific cut points occurs because of the repeatability coefficients.

CONCLUSIONS

Uncorrected QT measures are more reliable than QTcB and QT(CFrid). An average of three independent measures provides the most reliable QT and QTc measurements, with QTcH better than QTcB.

Philips QT interval measurement algorithms for diagnostic, ambulatory, and patient monitoring ECG applications

BACKGROUND

Commonly used techniques for QT measurement that identify T wave end using amplitude thresholds or the tangent method are sensitive to baseline drift and to variations of terminal T wave shape. Such QT measurement techniques commonly underestimate or overestimate the "true" QT interval.

METHODS

To find the end of the T wave, the new Philips QT interval measurement algorithms use the distance from an ancillary line drawn from the peak of the T wave to a point beyond the expected inflection point at the end of the T wave. We have adapted and optimized modifications of this basic approach for use in three different ECG application areas: resting diagnostic, ambulatory Holter, and in-hospital patient monitoring. The Philips DXL resting diagnostic algorithm uses an alpha-trimming technique and a measure of central tendency to determine the median QT value of eight most reliable leads. In ambulatory Holter ECG analysis, generally only two or three channels are available. QT is measured on a root-mean-square vector magnitude signal. Finally, QT measurement in the real time in-hospital application is among the most challenging areas of QT measurement. The Philips real time QT interval measurement algorithm employs features from both Philips DXL 12-lead and ambulatory Holter QT algorithms with further enhancements.

RESULTS

The diagnostic 12-lead algorithm has been tested against the gold standard measurement database established by the CSE group with results surpassing the industrial ECG measurement accuracy standards. Holter and monitoring algorithm performance data on the PhysioNet QT database were shown to be similar to the manual measurements by two cardiologists.

CONCLUSION

The three variations of the QT measurement algorithm we developed are suitable for diagnostic 12-lead, Holter, and patient monitoring applications.

Comparison of QTinno, a fully automated electrocardiographic analysis program, to semiautomated electrocardiographic analysis methods in a drug safety study in healthy subjects

BACKGROUND

Improved automated methods for electrocardiographic (ECG) analysis are needed, particularly for drug development purposes.

OBJECTIVES

This study compared a novel fully automated method for ECG analysis (QTinno; NewCardio, Santa Clara, CA) to 2 semiautomated digital methods: global measurement from the earliest QRS onset to the latest T-wave offset on representative superimposed beats (global) and tangent measurement on 3 consecutive beats in one lead (tangent).

METHODS

All 3 methods were used to determine uncorrected and rate-corrected QT interval duration (QT and QTcF) and related metrics in 1422 digital 12-lead ECGs from a phase 1 drug study. Global and tangent annotations were manually adjusted by the same 3 cardiologists wherever necessary. No adjustments were made in QTinno determinations.

RESULTS

QTinno returned QTcF change from time-matched baseline (DeltaQTcF) that differed minimally from both global and tangent methods (mean pairwise difference: 0.1 millisecond between QTinno and global, 1.1 milliseconds between QTinno and tangent). The average absolute QT and QTcF intervals by QTinno were approximately 5 milliseconds longer than global and 25 milliseconds longer than by tangent. QTinno had lower intrinsic variability for DeltaQTcF than either global or tangent (between-subject SD: QTinno 4.0 milliseconds, global 5.6 milliseconds, tangent 6.4 milliseconds; within-subject SD: QTinno 4.8 milliseconds, global 7.4 milliseconds, tangent 10.6 milliseconds). All methods were robust in detecting the largest placebo-adjusted mean time-matched DeltaQTcF (15-25 milliseconds) induced by study drug.

CONCLUSIONS

The methods show good agreement for drug-induced QTc prolongation. Lower intrinsic variability of DeltaQTcF by QTinno could facilitate smaller sample sizes or increase study power in thorough QTc studies.

Comparison of manual and automated measurements of the QT interval in healthy volunteers: an analysis of five thorough QT studies

We analyzed five crossover, thorough QT (TQT) studies to compare automated, manual, and computer-assisted (CA) measurement methods. All the methods detected moxifloxacin-induced, baseline-adjusted, placebo-subtracted mean changes in Fridericia-corrected QT interval (QTcF), with peak effect ranging from 10 to 21 ms. The variability associated with manual and CA measurements was generally 5-28% greater than that associated with automated methods. The performances of automated, manual, and CA measurements were comparable for the purpose of demonstrating assay sensitivity in TQT studies with healthy volunteers.

Magnitude, mechanism, and reproducibility of QT interval differences between superimposed global and individual lead ECG complexes

BACKGROUND

The global QT interval, emerging as a standard measurement provided by digital electrocardiographs, is defined by the earliest QRS onset and latest T-wave offset that occur in any of the standard leads. Differences between global ECG measurements and those from individual ECG leads have implications for the redefinition of normal values, for recognition of disease, and for drug safety. This study sought to quantify the differences between global QT intervals measured from 12 superimposed ECG leads with QT intervals and from single lead complexes, to examine the separate effects of QRS onset and T-wave offset on these differences, and to examine the reproducibility of these measurements.

METHODS

QTo intervals (Q onset to T offset) from 50 digitized ECGs sampled at 500 Hz were examined by computer assisted derivation of representative complexes from standard leads II, V(2), and V(3), by both baseline and tangent methods. Global QTo intervals were measured from superimposition of the representative complexes of all 12 leads. A time-coherent matrix of waveform onset and offset points allowed direct comparison of the components of the differences.

RESULTS

Global QTo and Bazett-adjusted global QTc were greater than each of the baseline and tangent measurements in representative leads II, V(2), and V(3), with mean differences ranging from 8 to 18 ms. QRS onset was earlier in the global complex than in each of the representative leads, with mean differences of 3-5 ms, whereas T-wave offset was significantly later in the global complex than in each of the representative leads, with mean differences of 5-11 ms. Remeasurement of all ECGs after an interval of 6 months confirmed the relative magnitudes of the global and individual lead QTo durations and small mean differences between pairs (-0.9 to 2.7 ms). Although global QTo had the largest mean difference (only 2.7 ms), it had the smallest standard deviation of the mean difference and lowest coefficient of variability (1.58%) of all measurements.

CONCLUSION

Global QT measurements are systematically larger than measurements from representative complexes of individual leads. These differences result from the combined effects of earlier QRS onset and later T-wave offset in the global complex, with T-wave offset the more dominant component of the difference.

Electrocardiographic reference ranges derived from 79,743 ambulatory subjects

BACKGROUND

Reference ranges for electrocardiogram (ECG) intervals, heart rate, and QRS axis in general use by medical personnel and ECG readers are unrepresentative of true age- and sex-related values in large populations and are not based on modern electrocardiographic and ECG reading technology.

METHODS AND RESULTS

The results of ECG interpretation by cardiologists using digital technology for viewing and interpreting ECGs were compiled from single, baseline ECGs of 79,743 individuals included in pharmaceutical company-sponsored clinical trials. Women comprised 48% of the total population. Ages ranged from 3 months to 99 years, and the bulk of the population (56%) was aged 40 to 70 years. Striking differences in numerical ECG values based on age and sex were observed. A subgroup of 46,129 individuals with a very low probability of cardiovascular disease was identified. The following were the reference ranges for this subgroup, determined using the 2nd and 98th percentiles: heart rate, 48 to 98 beats/min; PR interval, 113 to 212 milliseconds; QRS interval, 69 to 109 milliseconds; frontal plane QRS axis, -40 degrees to 91 degrees ; QT interval, 325 to 452 milliseconds; QTc-Bazett, 361 to 457 milliseconds; and QTc-Fridericia, 359 to 445 milliseconds. There were marked age- and sex-related variations in the reference ranges of this subgroup, and they differ substantially from previously reported norms. Small differences were observed in ECG values obtained using our digital methods as compared with readings done using paper tracings and values computed by 2 commercial computer algorithms.

CONCLUSIONS

We observed large differences in electrocardiographic heart rate, interval, and axis reference ranges in this study compared with those reported previously and with reference ranges in general use. We also observed a large influence of age and sex upon normal values. Very large cohorts are required to fully assess age- and sex-related variation of reference ranges. Electrocardiographic reference ranges should be modernized.

The effects of noise on computerized electrocardiogram measurements

Computerized measurements provide objective and reproducible assessments of the electrocardiogram (ECG). These measurements may be affected by noise or other lead quality issues. The effects of noise on the repeatability of computer-measured PR interval, QRS duration, QT interval, P/QRS/T axes, and ST levels were examined.

METHODS

The 125 ECGs of the Common Standards for Quantitative Electrocardiography (CSE) measurement database (MO1 series) were merged with records from the MIT Noise Stress Test database. For each CSE ECG, 720 unique noise ECGs were created, for a total of 90,000 noisy ECGs. Computerized measurements from the noisy ECGs were compared to the original ECG measurements. The repeatability of the measurements was assessed as a function of a lead quality score.

RESULTS

The repeatability of the measurements was found to be in excellent agreement with the original ECG measurements when the noise level was no worse than that of the original ECGs. Noise did not introduce any bias to the measurements, although not surprisingly, the variation of the errors increased as the lead quality degraded.