Reference values of electrocardiogram repolarization variables in a healthy population

A systematic review of electrocardiographic changes in populations temporarily ascending to high altitudes

High altitudes can cause hypobaric hypoxia, altering human physiology and the corresponding electrocardiogram (ECG). As part of the Altitude Nondifferentiated ECG Study (ANDES), this paper reviews ECG changes in subjects ascending to high altitudes. This review was conducted following PRISMA guidelines. PubMed, EMBASE, OVID Medline, and Web of Science were searched. 19 studies were ultimately included. Notable ECG changes at high altitudes include T wave inversion in the precordial leads and rightward QRS axis deviation in leads I, II and aVF. Less common findings were increases in P wave amplitude, QRS amplitude, and QTc interval. These ECG deviations typically self-resolved within 2-6 weeks following return to sea level. Consideration must be taken when interpreting ECG changes in individuals during ascent to, at, or upon return from high altitudes. Further large-scale studies are needed to elucidate temporal and altitude-dependent ECG patterns and establish reference standards for clinicians.

Optimizing ECG lead selection for detection of prolongation of ventricular repolarization as measured by the Tpeak-end interval

Background

The Tpeak‐end(Tp‐e) has not been compared in all 12 ECG leads in healthy adults to determine if the Tp‐e varies across leads. If there is variation, it remains uncertain, which lead(s) are preferred for recording in order to capture the maximal Tp‐e value.

Objective

The purpose of the current study was to determine the optimal leads, if any, to capture the maximal Tp‐e interval in healthy young adults.

Methods

In 88 healthy adults (ages 21–38 years), including derivation (n = 21), validation (n = 20), and smoker/vaper (n = 47) cohorts, the Tp‐e was measured using commercial computer software (LabChart Pro 8 with ECG module, ADInstruments) in all 12 leads at rest and following a provocative maneuver, abrupt standing. Tp‐e was compared to determine which lead(s) most frequently captured the maximal Tp‐e interval.

Results

In the rest and abrupt standing positions, the Tp‐e was not uniform among the 12 leads; the maximal Tp‐e was most frequently captured in the precordial leads. At rest, grouping leads V2–V4 resulted in detection of the maximum Tp‐e in 85.7% of participants (CI 70.7, 99.9%) versus all other leads (p < .001). Upon abrupt standing, grouping leads V2‐V6 together, resulted in detection of the maximum Tp‐e 85.0% of participants (CI 69.4, 99.9% versus all other leads; p < .001). These findings were confirmed in the validation cohort, and extended to the smoking/vaping cohort.

Conclusion

If only a subset of ECG leads will be recorded or analyzed for the Tp‐e interval, selection of the precordial leads is preferred since these leads are most likely to capture the maximal Tp‐e value.

Electrocardiographic markers of ventricular repolarization in the obese population: A descriptive review

Obesity is a global epidemiological problem that significantly contributes to the development of cardiovascular diseases. It is a proven factor for an increased risk of overall mortality and the occurrence of sudden cardiac death (SCD). The disease is accompanied by a structural and functional myocardium remodeling, which often results in ventricular repolarization abnormalities and contributes to the triggering of life-threatening arrhythmias. This heightened state of readiness for proarrhythmia is the cause of the sudden cardiac deaths which are recorded in this group of patients and which often constitute the first manifestation of ongoing cardiac pathology. One of the reasons for these arrhythmias may be abnormalities of ventricular muscle repolarization. In this descriptive review, we demonstrate electrocardiographic markers of ventricular repolarization (J point, QT/QTc/QTc-d, JT/JTc/JTc-d, ST segment, T wave and Tp-e/Tp-ed/Tp-e/QT), analyze their abnormalities in the obese population, and discuss their changes after weight loss.

Explaining deep neural networks for knowledge discovery in electrocardiogram analysis

Deep learning-based tools may annotate and interpret medical data more quickly, consistently, and accurately than medical doctors. However, as medical doctors are ultimately responsible for clinical decision-making, any deep learning-based prediction should be accompanied by an explanation that a human can understand. We present an approach called electrocardiogram gradient class activation map (ECGradCAM), which is used to generate attention maps and explain the reasoning behind deep learning-based decision-making in ECG analysis. Attention maps may be used in the clinic to aid diagnosis, discover new medical knowledge, and identify novel features and characteristics of medical tests. In this paper, we showcase how ECGradCAM attention maps can unmask how a novel deep learning model measures both amplitudes and intervals in 12-lead electrocardiograms, and we show an example of how attention maps may be used to develop novel ECG features.

Association of Mild Hyperbilirubinemia with Decreased ECG-Based Ventricular Repolarization Parameters in Young Men

OBJECTIVE

Hyperbilirubinemia is associated with protection against various oxidative stress-mediated diseases. We aimed to investigate the association between bilirubin and novel electrocardiography (ECG)-based ventricular repolarization parameters.

METHODS

We enrolled 201 healthy men with mild hyperbilirubinemia (group 1) and 219 healthy men with normal bilirubin levels (group 2). The Tpeak-Tend (Tp-e) interval (defined as the interval from the peak of the T wave to the end of the T wave), corrected (c) Tp-e interval, QT interval, cQT interval, and Tp-e interval/QT interval ratio were measured from leads V5 and V6 with 20 mm/mV amplitude and 50 mm/second rate.

RESULTS

The Tp-e interval, cTp-e interval, and Tp-e interval/QT interval ratio were significantly lower in group 1 compared with group 2. The cTp-e interval showed a significant negative correlation with total bilirubin, conjugated bilirubin, and unconjugated bilirubin. The cTp-e interval (odds ratio [OR], 0.900; P =.002) and Tp-e interval/QT interval ratio (OR, 0.922; P =.04) were significantly associated with mild hyperbilirubinemia.

CONCLUSION

We showed the association of mild hyperbilirubinemia with decreased novel ECG-based ventricular repolarization parameters.

Effects of Antipsychotics on Arrhythmogenic Parameters in Schizophrenia Patients: Beyond Corrected QT Interval

PURPOSE

Antipsychotic drugs have been implicated as risk factors for QT prolongation, which is a predictor of sudden cardiac death. However, the QT interval is considered an imperfect marker for proarrhythmic risk. Recently, improved methods, namely, QT dispersion (QTD), QTD ratio (QTDR), T wave peak-to-end interval (Tp-e), Tp-e/QT ratio and Tp-e/QTc ratio, have been regarded as proarrhythmic risk markers. We attempted to reevaluate the risk of sudden cardiac death due to antipsychotics use by measuring these improved evaluation methods.

PATIENTS AND METHODS

We retrospectively evaluated QTc, QTD, QTDR, Tp-e, Tp-e/QT ratio and Tp-e/QTc ratio from the medical records of 410 patients with schizophrenia diagnosed by the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision, or 5th Edition. Information on drugs administered was obtained from medical records. We investigated the correlation between each index on ECG and medication, such as antipsychotics, prescribed to participants with linear regression analysis. We also compared each index between 235 healthy controls and 235 patients matched for age and sex.

RESULTS

Positive correlations between QTc and levomepromazine and brexpiprazole were identified. Levomepromazine and lithium were positively correlated with QTD. Levomepromazine, quetiapine, asenapine, clozapine and carbamazepine were positively correlated with QTDR. Levomepromazine, olanzapine, brexpiprazole and lithium were positively correlated with Tp-e. Olanzapine, brexpiprazole and lithium were positively correlated with the Tp-e/QT ratio. Olanzapine, brexpiprazole and lithium were positively correlated with Tp-e/QTc ratio. Significant differences in all indexes were noted between the patients and healthy controls.

CONCLUSION

According to our results, the prediction of the risk of sudden cardiac death by each index was inconsistent. We should evaluate the predictive factor of ventricular arrhythmia according to various electrocardiogram indexes because QTc alone could not identify the risk of sudden cardiac death.

Wet Cupping Therapy Improves the Parameters of Ventricular Repolarization

BACKGROUND

Cupping therapy (CT) is an ancient medical treatment since antiquity and is used for the treatment of such various disease states as contagious diseases, chronic or acute inflammatory disease, and autoimmune disorders. Ventricular repolarization is represented by QT and corrected-QT (QTc) intervals from surface electrocardiography.

OBJECTIVES

As novel repolarization parameters, Tpeak-toTend (Tp-Te) interval, and Tp-Te/QT and Tp-Te/QTc ratios are suggested to correlate better with ventricular arrhythmia risk in various clinical conditions than sole QT and QTc intervals. In this study, we aimed to determine whether these parameters changed significantly after CT in healthy individuals.

METHODS

One hundred and twenty participants (57 women and 63 men; mean age: 49.0 ± 13.0 years) participated in this study. ECGs strips were recorded 1 hour before and 1 hour after CT from each participant, and relevant ECG parameters were compared.

RESULTS

Tp-Te interval [69.51 ± 11.54 msec vs 63.15 ± 10.89 msec, p = 0.001], Tp-Te/QT ratio [0.191 ± 0.030 vs 0.174 ± 0.031, p = 0.002] and Tp-Te/QTc ratio [0.175 ± 0.030 vs 0.159 ± 0.026, p = 0.001] were found to be significantly decreased 1 hour after the procedure compared with the pre-procedure values. However, no statistically significant change was observed in mean heart rate, QT and QTc intervals, QT/QRS and cQT/QRS, and frontal QRS/T angle after the procedure compared with the same parameters before the procedure (p > 0.05).

CONCLUSIONS

In accordance with the results of our study, it is plausible to conclude that CT may exert cardioprotective effect. However, larger scale prospective studies are needed to support our findings.

Variation of the T-wave peak-end interval and heart rate variability values in healthy males and females at various hours of the same day, and relationship of them

BACKGROUND

The prolongation of repolarization time between the myocardial epicardium and endocardial cells is closely related to malignant ventricular arrhythmias. The purpose of our study was to compare repolarization markers, namely, T-wave peak-end interval (Tp-e), QT, corrected QT (QTc), Tp-e/QT, Tp-e/corrected QT (QTc), and Heart Rate Variability (HRV) values in healthy men and women and to investigate their daily variations.

METHODS

A total of 74 male and 78 female participants, being a government employee, and having no health problems, were included in the two study groups (males and females). A 24-hour, 12-lead Holter monitoring was performed on the volunteers. Then, the Tp-e interval and QT interval were measured on recordings. cTp-e and QTc were calculated by the use of Bazzet's formula.

RESULTS

There was no statistically significant difference between the groups in the cTp-e interval at 07.00 pm; however, it was significantly lower in the female group as compared with the male group at 07.00 am and 01.00 pm. It was significantly higher in the female group at 01.00 am compared with the male group. There were statistically significant moderate negative correlations between Tp-e intervals and a standard deviation of between two normal beats interval (SDNN) values at various hours of the same day.

CONCLUSION

There were statistically significant differences in terms of Tp-e and cTp-e intervals at various hours of the same day in both groups. In addition, there were statistically significant moderate negative correlations between Tp-e intervals and SDNN at various hours of the same day.

Handling of Ventricular Fibrillation in the Emergency Setting

Ventricular fibrillation (VF) and sudden cardiac death (SCD) are predominantly caused by channelopathies and cardiomyopathies in youngsters and coronary heart disease in the elderly. Temporary factors, e.g., electrolyte imbalance, drug interactions, and substance abuses may play an additive role in arrhythmogenesis. Ectopic automaticity, triggered activity, and reentry mechanisms are known as important electrophysiological substrates for VF determining the antiarrhythmic therapies at the same time. Emergency need for electrical cardioversion is supported by the fact that every minute without defibrillation decreases survival rates by approximately 7%–10%. Thus, early defibrillation is an essential part of antiarrhythmic emergency management. Drug therapy has its relevance rather in the prevention of sudden cardiac death, where early recognition and treatment of the underlying disease has significant importance. Cardioprotective and antiarrhythmic effects of beta blockers in patients predisposed to sudden cardiac death were highlighted in numerous studies, hence nowadays these drugs are considered to be the cornerstones of the prevention and treatment of life-threatening ventricular arrhythmias. Nevertheless, other medical therapies have not been proven to be useful in the prevention of VF. Although amiodarone has shown positive results occasionally, this was not demonstrated to be consistent. Furthermore, the potential proarrhythmic effects of drugs may also limit their applicability. Based on these unfavorable observations we highlight the importance of arrhythmia prevention, where echocardiography, electrocardiography and laboratory testing play a significant role even in the emergency setting. In the following we provide a summary on the latest developments on cardiopulmonary resuscitation, and the evaluation and preventive treatment possibilities of patients with increased susceptibility to VF and SCD.

Comparison of the Effects of Propofol and Sevoflurane on QT Interval in Pediatrics Undergoing Cochlear Implantation: A Randomized Clinical Trial Study

Background

Children with sensorineural hearing loss are at risk of cardiac electrophysiologic abnormalities. Inhalational Sevoflurane induction in these children can cause QT prolongation.

Objectives

In order to evaluate the safety of inhalational induction of anesthesia with sevoflurane in children with sensorineural hearing loss, who are candidates for cochlear implant, its electrophysiologic effects was compared with intravenous induction of anesthesia with propofol.

Methods

In this double-blind randomized clinical trial, 61 children aged between one and eighteen years old, who were candidates for cochlear implantation, were randomly allocated to groups receiving anesthesia with sevoflurane (n = 32) or propofol (n = 29) for induction of anesthesia. Two 12-leads ECG were taken from all of patients before and after induction and QTc, Tp-e interval, and JTc were measured and compared.

Results

Two cases, who had pre-induction QTc longer than 500 ms were excluded from the study. Patients had similar age (102.58 ± 87 versus 101.46 ± 67 months, P = 0.95) and gender (males: 48.3% versus 56.3%, P = 0.53) distribution. The researchers observed significant post induction difference in QTc values between these groups (propofol 422.5 ± 40, sevoflurane 445.0 ± 29, P = 0.016). There was no significant difference in the percent QTc and Tp-e changes in propofol and sevoflurane groups. Greater percentage of patients with increased Tp-e interval (> 100 ms) in the sevoflurane group than the propofol group was also seen. There was no significant long QTc difference (QTc > 500 ms or more than 60 ms increase from baseline) after induction of anesthesia in the sevoflurane group compared to the propofol group (15.6% versus 13.8%, P = 0.84).

Conclusions

After electrophysiological evaluations in children with sensorineural hearing loss, in patients whose pre-induction QTc is not longer than 500 ms, propofol seems safer than inhalational sevoflurane for induction of anesthesia.

Evaluation of index of cardiac-electrophysiological balance before and after hemodialysis in patients with end-stage renal disease

BACKGROUND

Ventricular arrhythmias and sudden cardiac deaths are the most common cause of mortality in patients with end-stage renal disease (ESRD). Index of cardiac-electrophysiological balance (iCEB) (QT/QRS) may predict malignant ventricular arrhythmias. In this study, we investigated whether iCEB value is increased in ESRD patients and whether it changes before and after hemodialysis.

METHODS

The study included 52 ESRD patients and 53 control subjects matched for age and comorbidities. Biochemical, electrocardiographic and echocardiographic values of all participants were recorded. QRS, QT, Tp-e were measured manually. QTC was calculated using Bazett's formula. Then, Tp-e/QT, Tp-e/QTc, QT/QRS, and QTc/QRS ratios were calculated. The changes in ECG parameters of the ESRD patients before and after HD were compared using paired t-test.

RESULTS

Mean age and male sex ratio was comparable in both groups (p = 0.448 and p = 0.777, respectively). Comorbidity incidences, and biochemical parameters except eGFR (p < 0.001), albumin (p < 0.001), HDL cholesterol (p = 0.03) and platelet counts (p < 0.001) were comparable in both groups. Compared to the control group, QT, QTc, Tp-e, Tp-e/QT, Tp-e/QTc, QT/QRS, and QTc/QRS ratios were higher in the ESRD group (p < 0.05 for each). While QT and QTc intervals did not change after HD in ESRD patients, Tp-e, Tp-e/QT, Tp-e/QTc, QT/QRS, and QTc/QRS parameters increased significantly.

CONCLUSION

In addition to ventricular repolarization dispersion indices in ESRD patients, iCEB elevation and increasing values after HD session indicate the increased risk of TdP-mediated ventricular arrhythmia after HD. Larger studies are needed to confirm our results.

Investigation of the Proarrhythmic Effects of Antidepressants according to QT Interval, QT Dispersion and T Wave Peak-to-End Interval in the Clinical Setting

OBJECTIVE

Some antidepressants have been implicated as risk factors for QT prolongation, which is a predictor of sudden cardiac death. However, the QT interval is considered an imperfect biomarker for proarrhythmic risk. Therefore, we reevaluated the risk of sudden cardiac death due to antidepressants using improved.

METHODS

, namely, QT dispersion (QTD), T wave peak-to-end interval (Tp-e), and Tp-e/QT ratio.

METHODS

We compared the effects of antidepressants on QTc (QT/RR1/3), QTD, Tp-e, and Tp-e/QT ratio in 378 patients with mood disorder. We also compared each index between 165 healthy controls and 215 randomly selected age-matched patients.

RESULTS

Age (p<0.01), sex (p<0.05), tricyclic antidepressant (TCA) use (p<0.05), and clomipramine (p<0.01) and mianserin (p<0.05) use in particular, significantly associated with a prolonged QTc. We also found that age (p<0.01), TCA use (p<0.05), and clomipramine (p<0.01) and mianserin (p<0.05) use in particular, significantly prolonged QTD. However, there was no correlation between each variable and Tp-e or Tp-e/QT ratio. Significant differences in QTc and QTD were found between the patients and healthy controls.

CONCLUSION

From our results, prediction of risk of sudden cardiac death by QTD, Tp-e, or Tp-e/QT ratio was inconsistent. Increased QTD may be more suitable for predicting sudden cardiac death due to antidepressants.

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

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

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

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

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

Is myocardial repolarization duration associated with repolarization heterogeneity?

BACKGROUND

Dispersion of repolarization is theorized as one mechanism by which myocardial repolarization prolongation causes lethal torsades de pointes, (TdP). Our primary purpose was to determine whether prolongation of myocardial repolarization as measured by the heart rate-corrected J-to-T peak interval (JTpkc), is associated with repolarization heterogeneity as measured by transmural dispersion, defined as the median duration from the peak to the end of the T wave (TpTe).

METHODS

A retrospective cohort study was performed at a single urban tertiary ED from July 2011-September 2012. Inclusion criteria included all consecutive ED patients with ECG based on QTc and QRS intervals. Automated measurements of all intervals were performed. The association of JTpkc with the dependent variable TpTe was assessed after adjustment for QRS and RR interval durations with a multiple linear regression model. A secondary analysis included a similar adjusted assessment of the association of JTpkc with QT dispersion, QTd. Finally, we constructed two multiple regression models to assess the association of clinical causative factors of TdP with TpTe and JTpkc.

RESULTS

Eight hundred seventy-four cases were included: 186 with QTc <500 ms, 118 with QTc ≥500 and QRS ≥120 ms, and 570 with QTc ≥500 and QRS <120 ms. The coefficient for association of JTpkc with TpTe was -0.10 (95%CI -0.15 to -0.05), and for JTpkc with QTd was 0.03 (95% CI -0.01 to 0.06). Clinical causative TdP factors were associated more with JTpkc than TpTe.

CONCLUSION

Repolarization duration as measured by JTpkc is not positively associated with dispersion of repolarization as measured by TpTe or QTd. Dispersion of repolarization may not be a critical mechanistic link between QTc prolongation and TdP.

Effect of age and gender on the QTc-interval in healthy individuals and patients with long-QT syndrome

Age- and gender-related differences in QTc-interval are most likely the result of changes in sex-specific hormones. Although the exact mechanisms and pathophysiology of sex hormones on the QTc-interval are not known, testosterone appears to shorten the QTc-interval. In females, however, there is a more complex interaction between progesterone and estrogen. In patients with an impaired repolarization, such as long-QT syndrome (LQTS), the effect of these sex hormones on the QTc-interval is more pronounced with a differing sensitivity between the LQTS genotypes.

Effect of action potential duration on Tpeak-Tend interval, T-wave area and T-wave amplitude as indices of dispersion of repolarization: Theoretical and simulation study in the rabbit heart

BACKGROUND

The aim of the study was to differentiate the effect of dispersion of repolarization (DOR) and action potential duration (APD) on T-wave parameters being considered as indices of DOR, namely, Tpeak-Tend interval, T-wave amplitude and T-wave area.

METHODS

T-wave was simulated in a wide physiological range of DOR and APD using a realistic rabbit model based on experimental data. A simplified mathematical formulation of T-wave formation was conducted.

RESULTS

Both the simulations and the mathematical formulation showed that Tpeak-Tend interval and T-wave area are linearly proportional to DOR irrespectively of APD range, while T-wave amplitude is non-linearly proportional to DOR and inversely proportional to the minimal repolarization time, or minimal APD value.

CONCLUSION

Tpeak-Tend interval and T-wave area are the most accurate DOR indices independent of APD. T-wave amplitude can be considered as an index of DOR when the level of APD is taken into account.

Age- and sex-based reference ranges for non-invasive ventricular repolarisation parameters

BACKGROUND

Some electrocardiographic parameters are able to assess indirectly ventricular repolarisation homogeneity. It is consequently essential to discriminate between normal and abnormal values in clinical decision-making. Considering there is still not a consensus about normal cut-off values, the aim of this study was to document reference intervals in all age groups of a healthy population, providing for age- and sex-percentile tables, which can be used easily and quickly in clinical practice.

METHODS

We evaluated repolarisation markers in 606 sex-matched participants aged 1 day-94 years. Each subject underwent a 12-lead electrocardiogram at rest, and the following parameters were measured: QT, corrected QT, QTpeak, Tpeak-Tend, Tpeak-Tend dispersion, Tpeak-Tend/QT and QTpeak/QT ratio.

RESULTS

A relationship was demonstrated between age and QTpeak, Tpeak-Tend, QT and QTc. In children, QTpeak, Tpeak-Tend and QT intervals increased linearly with age. In adolescents, all the three parameters remained stable. In adults, QTpeak and QT showed a further significant increase. On the contrary, Tpeak-Tend interval was longer in adults aged between 20 and 64 years than in participants aged 65 years or over, but the difference was not statistically significant. Male vs female participants showed longer Tpeak-Tend intervals; this sex difference was not statistically significant at birth and during childhood, whereas it was in adolescents and in adults.

CONCLUSIONS

Repolarisation parameters showed age- and sex-based variations, which are important to know to differentiate normal from pathological values.

Glucose ingestion causes cardiac repolarization disturbances in type 1 long QT syndrome patients and healthy subjects

BACKGROUND

Both hypoglycemia and severe hyperglycemia constitute known risk factors for cardiac repolarization changes potentially leading to malignant arrhythmias. Patients with loss of function mutations in KCNQ1 are characterized by long QT syndrome (LQTS) and may be at increased risk for glucose-induced repolarization disturbances.

OBJECTIVE

The purpose of this study was to test the hypothesis that KCNQ1 LQTS patients are at particular risk for cardiac repolarization changes during the relative hyperglycemia that occurs after an oral glucose load.

METHODS

Fourteen KCNQ1 LQTS patients and 28 control participants matched for gender, body mass index, and age underwent a 3-hour oral 75-g glucose tolerance test with ECGs obtained at 7 time points. Fridericia corrected QT interval (QTcF), Bazett corrected QT interval (QTcB), and the Morphology Combination Score (MCS) were calculated.

RESULTS

QTc and MCS increased in both groups. MCS remained elevated until 150 minutes after glucose ingestion, and the maximal change from baseline was larger among KCNQ1 LQTS patients compared with control subjects (0.28 ± 0.27 vs 0.15 ± 0.13; P <.05).

CONCLUSION

Relative hyperglycemia induced by ingestion of 75-g glucose caused cardiac repolarization disturbances that were more severe in KCNQ1 LQTS patients compared with control subjects.

Computer-assisted image processing 12 lead ECG model to diagnose hyperkalemia

BACKGROUND

We sought to develop an improved 12 lead ECG model to diagnose hyperkalemia by use of traditional and novel parameters.

METHODS

We retrospectively analyzed ECGs in consecutive hyperkalemic patients (serum potassium (K)>5.3mEq/L) by blinded investigators with normokalemic ECGs as internal controls. Potassium levels were modeled using general linear mixed models followed by refit with standardized variables. Optimum sensitivity and specificity were determined using cut point analysis of ROC-AUC.

RESULTS

The training set included 236 ECGs (84 patients) and validation set 97 ECGs (23 patients). Predicted K=(5.2354)+(0.03434*descending T slope)+(-0.2329*T width)+(-0.9652*reciprocal of new QRS width>100msec). ROC-AUC in the validation set was 0.78 (95% CI 0.69-0.88). Maximum specificity of the model was 84% for K>5.91 with sensitivity of 63%.

CONCLUSION

ECG model incorporating T-wave width, descending T-wave slope and new QRS prolongation improved hyperkalemia diagnosis over traditional ECG analysis.

Effects of Gender on Electrocardiography in Subjects with Shortened Ventricular Depolarization (QRS)

BACKGROUND

Distinctions between electrocardiograms of female and male subjects have been recognized for many years. Due to these differences, arrhythmias in each gender have a tendency to differ. In our study, we aimed to compare electrocardiography intervals between men and women with short QRS durations.

METHODS

Subjects with a QRS interval of ≤80 ms were included in the study. Patients were grouped by gender and the parameters were compared. Patients with diseases that might affect QRS interval and/or who were on medications were excluded. The electrocardiogram intervals of the subjects were measured, Holter monitors were placed, and parameters of time-based heart rate variation were analyzed.

RESULTS

A total of 100 patients (55% female) were included in the study. According to statistical analysis, no significant difference between the genders was observed in the heart rate or in the parameters, such as QT, JT, JTp, and TpTe intervals or heart rate-corrected QTc, JTc, JTpc, and TpTec intervals, which affect repolarization and are known to be arrhythmia precursors by shortening or elongation. No statistically significant difference was found between the two groups for the parameters of heart rate variability time measures (SDNN, SDANN, rMSSD, and pNN50).

CONCLUSION

We observed that when the QRS interval gets shorter, repolarization differences between the genders disappear. New studies are required on this subject.

Ventricular repolarization markers for predicting malignant arrhythmias in clinical practice

Malignant cardiac arrhythmias which result in sudden cardiac death may be present in individuals apparently healthy or be associated with other medical conditions. The way to predict their appearance represents a challenge for the medical community due to the tragic outcomes in most cases. In the last two decades some ventricular repolarization (VR) markers have been found to be useful to predict malignant cardiac arrhythmias in several clinical conditions. The corrected QT, QT dispersion, Tpeak-Tend, Tpeak-Tend dispersion and Tp-e/QT have been studied and implemented in clinical practice for this purpose. These markers are obtained from 12 lead surface electrocardiogram. In this review we discuss how these markers have demonstrated to be effective to predict malignant arrhythmias in medical conditions such as long and short QT syndromes, Brugada syndrome, early repolarization syndrome, acute myocardial ischemia, heart failure, hypertension, diabetes mellitus, obesity and highly trained athletes. Also the main pathophysiological mechanisms that explain the arrhythmogenic predisposition in these diseases and the basis for the VR markers are discussed. However, the same results have not been found in all conditions. Further studies are needed to reach a global consensus in order to incorporate these VR parameters in risk stratification of these patients.

Multiscale cardiac modelling reveals the origins of notched T waves in long QT syndrome type 2

The heart rhythm disorder long QT syndrome (LQTS) can result in sudden death in the young or remain asymptomatic into adulthood. The features of the surface electrocardiogram (ECG), a measure of the electrical activity of the heart, can be equally variable in LQTS patients, posing well-described diagnostic dilemmas. Here we report a correlation between QT interval prolongation and T-wave notching in LQTS2 patients and use a novel computational framework to investigate how individual ionic currents, as well as cellular and tissue level factors, contribute to notched T waves. Furthermore, we show that variable expressivity of ECG features observed in LQTS2 patients can be explained by as little as 20% variation in the levels of ionic conductances that contribute to repolarization reserve. This has significant implications for interpretation of whole-genome sequencing data and underlies the importance of interpreting the entire molecular signature of disease in any given individual.

Ambulatory measurement of the ECG T-wave amplitude

Ambulatory recording of the preejection period (PEP) can be used to measure changes in cardiac sympathetic nervous system (SNS) activity under naturalistic conditions. Here, we test the ECG T-wave amplitude (TWA) as an alternative measure, using 24-h ambulatory monitoring of PEP and TWA in a sample of 564 healthy adults. The TWA showed a decrease in response to mental stress and a monotonic decrease from nighttime sleep to daytime sitting and more physically active behaviors. Within-participant changes in TWA were correlated with changes in the PEP across the standardized stressors (r = .42) and the unstandardized naturalistic conditions (mean r = .35). Partialling out changes in heart rate and vagal effects attenuated these correlations, but they remained significant. Ambulatory TWA cannot replace PEP, but simultaneous recording of TWA and PEP provides a more comprehensive picture of changes in cardiac SNS activity in real-life settings.

Diurnal modulation and sources of variation affecting ventricular repolarization in Warmblood horses

OBJECTIVES

Irregularities in cardiac repolarization are known to predispose for arrhythmias and sudden cardiac death in humans. The QT interval is a quantitative measurement of repolarization, and clinically, the QTc (QT interval corrected for heart rate) and Tpeak to Tend intervals (TpTe) are used as repolarization markers. To support the use of these markers in horses, we sought to describe the possible influence of the environment, time of day, day-to-day effects, T wave conformation, age, body weight (BW), and horse-to-horse variation on repolarization measurements.

ANIMALS

12 Warmblood geldings, age 10.8 ± 4.8 years.

METHODS

Holter ECGs were performed on days 0, 7 and 14. Measures of RR, QT, QTp, QTc and TpTe intervals and T wave conformation were obtained each hour during the recordings. An ANCOVA analysis was performed to estimate diurnal variation and the sources of variation affecting these intervals.

RESULTS

Differences between individual horses were the largest source of repolarization variability although the environment had a significant effect on repolarization as well. Diurnal variation affected both the RR interval and the repolarization markers. The QT, QTc and TpTe intervals were prolonged on day 0. Biphasic T waves shortened the TpTe interval approximately 10 ms. Age and BW did not appear to affect repolarization.

CONCLUSIONS

Equine repolarization markers exhibit significant variation. Factors affecting repolarization measurements include horse-to-horse variation, diurnal variation, the environment, and T wave conformation. These factors must be considered if markers of equine repolarization are used diagnostically.

Short-term repeatability of electrocardiographic Tpeak-Tend and QT intervals

BACKGROUND

The electrocardiographic (ECG) Tpeak-Tend interval (TpTe) is associated with arrhythmias and sudden cardiac death. TpTe offers a supplementary measure for the QT interval (QT), yet its repeatability has not been established.

PURPOSE

Evaluate short-term repeatability of TpTe and QT.

METHODS

Four ECGs were obtained on sixty participants. The sources of variation, intra-class correlation coefficient (ICC) - an index of reproducibility - and minimal detectable change (MDC) were estimated for TpTe and QT. The impact of repeated measurements on repeatability was estimated for a hypothetical clinical trial designed to detect drug-induced prolongation of TpTe and QT.

RESULTS

We used heart rate-adjusted QT [(QT)a] but TpTe in the study group was rate-invariant. The ICC [95% confidence interval (CI)] was 0.77 (0.69, 0.85) for TpTe, 0.75 (0.65, 0.85) for QT and 0.60 (0.47, 0.73) for (QT)a. The MDC (ms) was 21, 32 and 26 for TpTe, QT and (QT)a respectively.

CONCLUSION

TpTe has excellent repeatability supporting its use as a supplement to QT in observational and clinical studies.

Normal electrocardiographic QT interval in race-fit Standardbred horses at rest and its rate dependence during exercise

OBJECTIVES

Cardiac repolarization, measured as QT and Tpeak to Tend (TpTe) intervals on the ECG, is important, as irregularities caused by diseases, ventricular hypertrophy, drugs and genetic defects can trigger arrhythmias which predispose human patients to syncope and sudden cardiac death. In horses, repolarization is not well described and therefore QT analysis cannot yet be used diagnostically. Therefore, we sought to describe reference values for the normal QT and TpTe intervals in Standardbreds and to determine the best method for heart rate (HR) correction.

ANIMALS

30 Standardbreds.

METHODS

QT and TpTe intervals were measured during rest and exercise and plotted against HR converted to Rpeak to Rpeak interval (RR). Data were fitted with relevant regression models. Intra- and inter-observer agreement was assessed using Bland-Altman analyses.

RESULTS

Data were best described by a piecewise linear model (r(2) > 0.97). Average prediction error of this model was smaller than for both Bazett and Fridericia corrections. Coefficient of repeatability of intra- and inter-observer variability was 8.76 ms and 5.64 ms respectively and coefficient of variation was 1.77% and 2.76% respectively. TpTe increased with RR in stallions.

CONCLUSIONS

The QT interval in Standardbred horses shortens with decreasing RR interval (increasing HR) as in humans, but in a markedly different order as it clearly follows a piecewise linear model. The equine QT interval can be measured easily and there is small intra- and inter-observer variability. This model of the equine QT interval provides clinicians with a method that could support a diagnosis of repolarization disturbances in horses.

[The QT interval: standardization, limits and interpretation]

Despite clinical importance of ventricular repolarisation, it remains difficult to analyse. Conventionally, quantification of the electrocardiographic ventricular repolarization is usually performed with reference to axis of the T wave and QT interval duration. A variety of factors can prolong the QT interval, such as drug effects, electrolyte imbalances, and myocardial ischemia. The biggest risk with prolongation of the QT interval is the development of torsades de pointes. Commonly accepted reference ranges for the electrocardiogram (ECG) have been in use, with little change, for many years. Populations throughout the world present several differences: age, ethnic compositions, and are exposed to different environmental factors. Recent studies have reported reference data for QT interval in healthy population and have evaluated the influence of age, gender, QRS duration and heart rate on this interval. In this review, we address several issues relative to the measurement, and interpretation of QT interval and its adjustment for rate, age, gender and QRS duration.

Effect of nalmefene 20 and 80 mg on the corrected QT interval and T-wave morphology: a randomized, double-blind, parallel-group, placebo- and moxifloxacin-controlled, single-centre study

BACKGROUND

Nalmefene is an orally administered competitive opioid receptor antagonist targeted at reducing alcohol consumption in alcohol-dependent patients. As part of the regulatory requirements for drug approval, the potential of novel compounds for causing unwanted proarrhythmia should be studied in a thoroughly designed clinical QT/corrected QT (QTc) study (International Conference on Harmonisation [ICH] E14 guideline).

OBJECTIVE

This study was designed to evaluate whether nalmefene 20 and 80 mg/day induced changes in cardiac repolarization biomarkers indicative of proarrhythmia (the QTc interval and T-wave morphology).

METHODS

This was a prospective, randomized, double-blind, parallel-group, placebo- and moxifloxacin-controlled, single-centre study carried out in a clinical pharmacology unit. The study included 270 healthy male and female subjects (age 18-45 years). The subjects were randomized to a 7-day treatment period of placebo, nalmefene 20 mg/day or nalmefene 80 mg/day, or placebo for 6 days followed by a single dose of moxifloxacin 400 mg on day 7. Serial triplicate ECGs were obtained over a 24-hour period at protocol-defined time-points. The primary protocol-defined endpoint was the largest time-matched baseline- and placebo-adjusted mean difference in the individually heart rate-corrected QT interval (QTcNi) recorded at any of the 12 ECG time-points distributed over a 24-hour period on day 7 of treatment. Secondary endpoints included a similar analysis using the Fridericia- (QTcF) and Bazett-corrected (QTcB) intervals. An explorative analysis included quantitative assessment of T-wave morphology using the T-wave morphology composite score (MCS) to assess for differences between treatment groups and placebo on day 7 of treatment. The frequency of outliers in the QTc intervals, the pharmacokinetics of nalmefene and the tolerability of nalmefene were also assessed.

RESULTS

Nalmefene was rapidly absorbed with a time to reach maximum plasma concentration of 2.2 hours and a dose-proportionate relationship between dose administered and exposure. The largest baseline- and placebo-adjusted mean changes from baseline in the individualized QTcNi (primary endpoint) were 5.45 ms (90% CI 1.52, 9.37) and 5.57 ms (90% CI 1.62, 9.52) for nalmefene 20 and 80 mg/day, respectively, with study sensitivity confirmed by the expected largest increase in mean QTcNi of 10.15 ms (90% CI 5.67, 14.63) for moxifloxacin. Quantitative assessment using the T-wave MCS demonstrated the largest baseline- and placebo-adjusted increase in MCS to be non-significantly different from the intra-subject variability of triplicate recordings in the placebo group. No deaths or serious adverse events occurred in the study.

CONCLUSION

This thorough QT/QTc study was a negative study in accordance with the ICH E14 guideline, meaning that nalmefene has no clinically relevant effect on the QTc interval and T-wave morphology. The study predicts no concern over proarrhythmia or need for intensive QTc monitoring with the use of nalmefene in clinical practice.

Heritability of Tpeak-Tend interval and T-wave amplitude: a twin study

BACKGROUND

Tpeak-Tend interval (TpTe) and T-wave amplitude (Tamp) carry diagnostic and prognostic information regarding cardiac morbidity and mortality. Heart rate and QT interval are known to be heritable traits. The heritability of T-wave morphology parameters such as TpTe and Tamp is unknown. TpTe and Tamp were evaluated in a large sample of twins.

METHODS AND RESULTS

Twins from the GEMINAKAR study (611 pairs, 246 monozygotic, 365 dizygotic; mean age, 38±11 years; 49% men) who had an ECG performed during 1997 to 2000 were included. Tamp was measured in leads V1 and V5. Duration variables (RR interval, QTpeak and QTend interval) were measured and averaged over 3 consecutive beats in lead V5. TpTe was calculated as the QTend- and QTpeak-interval difference. Heritability was assessed using structural equation models adjusting for age, sex, and body mass index. All models were reducible to a model of additive genetics and unique environment. All variables had considerable genetic components. Adjusted heritability estimates were as follows: TpTe, 46%; Tamp lead V1, 34%; Tamp lead V5, 47%; RR interval, 55%; QT interval, 67%; and Bazett-corrected QT interval, 42%.

CONCLUSIONS

RR interval, QT interval, Tamp, and TpTe interval are heritable ECG parameters.

Postanesthetic torsade de pointes in a patient with unrecognized long QT syndrome -A case report-

Torsade de pointes (TdP) is a devastating form of polymorphic ventricular arrhythmia associated with corrected QT (QTc) interval prolongation. TdP usually terminates spontaneously but frequently recurs and may degenerate to ventricular fibrillation. The present report describes a case of TdP in a patient being transferred to the postanesthetic care unit following an emergency laparoscopic appendectomy. The patient had undergone open heart surgery 1 week before. Retrospective electrocardiogram analysis revealed the patient had QTc and Tpeak-Tend interval prolongation that had gone unrecognized. We believe TdP may have been induced by accentuation of sympathetic nervous system during emergence from general anesthesia.