In vivo validation of the coincidence of the peak and end of the T wave with full repolarization of the epicardium and endocardium in swine

A refined, minimally invasive, reproducible ovine ischaemia-reperfusion-infarction model using implantable defibrillators: Methodology and validation

Ischaemic heart disease remains a leading cause of premature mortality and morbidity. Understanding the associated pathophysiological mechanisms of cardiac dysfunction arising from ischaemic heart disease and the identification of sites for new therapeutic interventions requires a preclinical model that reproduces the key clinical characteristics of myocardial ischaemia, reperfusion and infarction. Here, we describe and validate a refined and minimally invasive translationally relevant approach to induce ischaemia, reperfusion and infarction in the sheep. The novelty and refinement in the procedure stems from utilization of implantable cardiac defibrillators prior to coronary engagement, balloon angioplasty to induce infarction, and intra-operative anti-arrhythmic drug protocols to reduce adverse arrhythmic events. The protocol is readily adoptable by researchers with access to standard fluoroscopic instrumentation, and it requires minimally invasive surgery. These refinements lead to a substantial reduction of intra-operative mortality to 6.7% from previously published values ranging between 13% and 43%. The model produces key characteristics associated with the fourth universal definition of myocardial infarction, including ECG changes, elevated cardiac biomarkers and cardiac wall motility defects. In conclusion, the model closely replicates the clinical paradigm of myocardial ischaemia, reperfusion and infarction in a translationally relevant large animal setting, and the applied refinements reduce the incidence of intra-operative mortality typically associated with preclinical myocardial infarction models.

Evaluation of Tpeak-end interval, Tpeak-end/QT, and Tpeak-end/Qtc ratio during acute migraine attack in the emergency department

INTRODUCTION

During an acute migraine attack, changes in ventricular repolarisation parameters may occur due to an imbalance in the autonomic nervous system. Tpeak-tend (Tp-e) interval, Tp-e/QT ratio, and Tp-e/corrected QT (QTc) ratio are novel parameters of arrhythmogenesis and can be easily calculated in electrocardiography (ECG). The objective of this study is to demonstrate that novel ventricular repolarisation parameters can anticipate the risk of ventricular dysrhythmia in the migraine attack period.

METHODS

This research was a prospective case-control study, which recruited a total of 144 participants, including 74 migraine patients and 70 healthy volunteers in the control group (CG) who met the criteria for migraine with or without aura. All participants underwent 12-lead ECG recordings, and the study compared the Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio with those of the CG.

RESULTS

The average age of patients experiencing migraine attacks was 38.14 ± 10.82, with 58 (76%) of these patients being female. The Tp-e interval mean was higher in the migraine attack group than the CG, with a statistically significant difference discovered (74.22 ± 20.20 ms [ms] compared to 65.39 ± 11.33 ms, p = 0.001). However, there were higher mean Tp-e/QT and Tp-e/QTc ratios in the migraine attack group compared to the CG, and this difference was found to be statistically significant (0.20 ± 0.05 vs. 0.17 ± 0.03, p = 0.001, 0.18 ± 0.52 vs 0.16 ± 0.29, p = 0.003, respectively).

CONCLUSION

Prolonged Tp-e interval and elevated Tp-e/QT and Tp-e/QTc ratios were observed in migraine patients who presented to the emergency department, indicating a potential risk of ventricular dysrhythmia.

Brugada Syndrome: From Molecular Mechanisms and Genetics to Risk Stratification

Brugada syndrome (BrS) is a rare hereditary arrhythmia disorder, with a distinctive ECG pattern, correlated with an increased risk of ventricular arrhythmias and sudden cardiac death (SCD) in young adults. BrS is a complex entity in terms of mechanisms, genetics, diagnosis, arrhythmia risk stratification, and management. The main electrophysiological mechanism of BrS requires further research, with prevailing theories centered on aberrant repolarization, depolarization, and current-load match. Computational modelling, pre-clinical, and clinical research show that BrS molecular anomalies result in excitation wavelength (k) modifications, which eventually increase the risk of arrhythmia. Although a mutation in the SCN5A (Sodium Voltage-Gated Channel Alpha Subunit 5) gene was first reported almost two decades ago, BrS is still currently regarded as a Mendelian condition inherited in an autosomal dominant manner with incomplete penetrance, despite the recent developments in the field of genetics and the latest hypothesis of additional inheritance pathways proposing a more complex mode of inheritance. In spite of the extensive use of the next-generation sequencing (NGS) technique with high coverage, genetics remains unexplained in a number of clinically confirmed cases. Except for the SCN5A which encodes the cardiac sodium channel NaV1.5, susceptibility genes remain mostly unidentified. The predominance of cardiac transcription factor loci suggests that transcriptional regulation is essential to the Brugada syndrome's pathogenesis. It appears that BrS is a multifactorial disease, which is influenced by several loci, each of which is affected by the environment. The primary challenge in individuals with a BrS type 1 ECG is to identify those who are at risk for sudden death, researchers propose the use of a multiparametric clinical and instrumental strategy for risk stratification. The aim of this review is to summarize the latest findings addressing the genetic architecture of BrS and to provide novel perspectives into its molecular underpinnings and novel models of risk stratification.

Prognostic value of the Tpeak-Tend interval for in-hospital subacute ventricular arrhythmias in tako-tsubo syndrome

INTRODUCTION AND OBJECTIVES

The clinical value of electrocardiogram (ECG) repolarization parameters associated with ventricular arrhythmias (VAs) in tako-tsubo syndrome is still under debate. We aimed to evaluate ECG predictors of subacute VAs, defined as those occurring after the first 48hours from admission.

METHODS

This single-center observational study enrolled patients admitted to the cardiology department between 2012 and 2018 with a confirmed diagnosis of tako-tsubo syndrome. Data collection included a 12-lead ECG on admission and at 48hours, continuous telemetry monitoring, blood testing, transthoracic echocardiography, and coronary angiography during hospitalization. VAs events were defined as: premature ventricular contractions ≥ 2000 within a 24-hour window of telemetry monitoring, ventricular fibrillation, sustained ventricular tachycardia (VT), polymorphic VT, and non-sustained VT.

RESULTS

A total of 87 patients (age 72±12 years) were enrolled. During a median of 8 days of hospitalization, subacute VAs were documented in 22 patients (25%) after a median of 91hours from admission. Subacute VAs were associated with an increase in mortality during hospitalization (P=.030). The corrected global (mean of the 12-lead ECG values) Tpeak-Tend interval at 48hours from admission was an independent predictor of subacute VAs and was statistically superior to the standard corrected QT interval (Z test, P=.040). A cut-off of 108 msec for the corrected global Tpeak-Tend yielded a 71% sensitivity and 72% specificity for subacute VAs.

CONCLUSIONS

In patients with tako-tsubo syndrome, subacute VAs are associated with repolarization alterations that can be identified on conventional ECG using the Tpeak-Tend interval.

The effects of methamphetamine on electrocardiographic parameters in male patients

OBJECTIVE

We aimed to compare the electrocardiographic parameters in patients with methamphetamine use to healthy controls.

METHODS

The study is a cross-sectional case-control study. Sixty-eight patients diagnosed with methamphetamine use disorder (MUD) according to DSM-5 criteria and 65 subjects in healthy control group who can match the patient group with demographic data were included in the study. Heart rate, P wave dispersion, QT dispersion, QTc and Tp-e/QTc ratios were calculated in the ECGs of all participants.

RESULTS

The mean age of the patients was 25.60 ± 5.70 and of the control group was 27.43 ± 6.10 (p = 0.076). There was no statistically significant difference between the blood pressure, body mass index, HDL-LDL-total cholesterol and triglyceride values of the participants (p > 0.05). Although QT dispersion was 13.68 ± 9.12 in patients with methamphetamine use disorder, it was calculated as 9.08 ± 7.85 in the control group (p = 0.002). Finally, the Tp-e/QTc ratio of the patients was higher than the healthy controls (p = 0.014).

CONCLUSION

In our study, we found a significant deterioration in QT dispersion and Tp-e/QTc ratio in the MUD group. Therefore, it should be kept in mind that there is a risk of malignant arrhythmia in this patient group and care should be taken in terms of arrhythmic events during follow-up in this patient group.Key pointsPatients with methamphetamine use showed significant deterioration in QTd and Tp-e/QTcMethamphetamine users have prolonged Tp-e/QTc ratio and QTdCaution should be exercised in terms of arrhythmic events in methamphetamine users.

Electrocardiographic marker of the cardiac action potential triangulation induced by antiarrhythmic drugs in perfused guinea-pig heart

NEW FINDINGS

What is the central question of this study? Can triangular appearance of ventricular action potential, indicating proarrhythmic profile of antiarrhythmic agent, be approximated by specific changes on ECG? What is the main finding and its importance? The triangulation of the ventricular action potential seen when antiarrhythmic drugs induce a greater lengthening of the late repolarization compared to the initial repolarization in epicardium, is closely approximated by a greater prolongation of the T wave upslope relative to the interval between the J point and the start of the T wave (the JT_start interval) on ECG. These findings may improve the power of ECG assessments in predicting the drug-induced arrhythmia resulting from slowed phase 3 repolarization.

ABSTRACT

Antiarrhythmic drugs prescribed to treat atrial fibrillation can occasionally precipitate ventricular tachyarrhythmia through a prominent slowing of the phase 3 repolarization. The latter results in the triangular shape of ventricular action potential, indicating high arrhythmic risks. However, clinically, the utilility of triangulation assessments for predicting arrhythmia is limited owing to the invasive nature of the ventricular action potential recordings. This study examined whether the triangulation effect can be detected indirectly from ECG analysis. Epicardial monophasic action potentials and ECG were simultaneously recorded in perfused guinea-pig hearts. With antiarrhythmics (dofetilide, quinidine, procainamide and flecainide), a prolongation of the initial repolarization seen in the action potential recordings was closely approximated by lengthening of the interval bewteen the J point and the start of the T wave (the JT_start interval) on ECG, whereas a prolongation of the late repolarization was paralleled by widening of the T wave upslope. Dofetilide, quinidine and procainamide induced a prominent slowing of the phase 3 repolarization in epicardium, leading to triangulation of the action potential. These effects were accompanied by a greater prolongation of the T wave upslope compared to the JT_start interval. Flecainide elicited a proportional prolongation of the initial and the late ventricular repolarization, and therefore failed to induce triangulation, based on analysis of both epicardial action potential and ECG profiles. Collectively, these findings suggest that the ratio between the durations of the T wave upslope and the JT_start interval may represent ECG metric of the ventricular action potential triangulation induced by antiarrhythmic drugs. This article is protected by copyright. All rights reserved.

Examination of New Electrocardiographic Repolarization Markers in Diabetic Patients with Noncritical Coronary Artery Disease

Background

Diabetes mellitus (DM) is a multisystemic, chronic disease that affects many organs. Coronary artery disease (CAD) is the leading cause of death in patients with DM. The electrocardiogram's new ventricular repolarization parameters can predict mortality and morbidity. The ventricular repolarization indices were examined in diabetic patients with a CAD diagnosis in this study.

Methods

The study group consisted of 84 DM patients (51 males; mean age 58.8 ± 6.6) with noncritical CAD. The control group consisted of 84 DM patients (47 males; mean age 58.7 ± 8.8) with a normal coronary artery. The intervals of QT, QRS, JT, and Tp-e were all measured. Tp-e/QT, Tp-e/QTc, Tp-e/JT, and Tp-e/JTc ratios were determined with QTc, QTd, QTdc, and JTc intervals.

Results

Heart rate (74.4 ± 13.1 vs. 70.0 ± 13.6 bpm, p: 0.036), QT (381.0 ± 30.3 vs. 368.6 ± 29.1 ms, p: 0.008), QTc (407.5 (359-450) vs. 389 (339-430) ms, p < 0.001), QTd (25.1 ± 6.2 vs. 21.9 ± 9.9 ms, p: 0.013), QTdc (26.7 ± 6.1 vs. 23.1 ± 10.8 ms, p: 0.010), Tp-e (95.7 ± 12.2 vs. 73.6 ± 9.8 ms, p < 0.001), JT (293.8 ± 22.0 vs. 283.5 ± 30.9 ms, p: 0.014), and JTc (313.6 ± 12.3 vs. 302.4 ± 33.7 ms, p=0.005) intervals, and Tp-e/QT (0.25 ± 0.03 vs. 0.20 ± 0.03 ms, p < 0.001), Tp-e/QTc [0.23 (0.19-2.33) vs. 0.19 (0.14-0.25) ms, p=0.007], Tp-e/JT (0.33 ± 0.04 vs. 0.26 ± 0.04 ms, p < 0.001), and Tp-e/JTc (0.30 ± 0.03 vs. 0.24 ± 0.03 ms, p < 0.001) ratios were all found to be significantly higher in diabetic patients with noncritical CAD.

Conclusion

In this study, ventricular repolarization markers on the surface ECG were found to be elevated in diabetic CAD patients. These variables may be related to fatal arrhythmic events. To be sure, large-scale, randomized controlled trials are required.

Ventricular repolarization heterogeneity in patients with COVID-19: Original data, systematic review, and meta-analysis

BACKGROUND

Coronavirus disease-2019 (COVID-19) has been associated with an increased risk of acute cardiac events. However, the effect of COVID-19 on repolarization heterogeneity is not yet established. In this study, we evaluated electrocardiogram (ECG) markers of repolarization heterogeneity in patients hospitalized with COVID-19. In addition, we performed a systematic review and meta-analysis of the published studies.

METHODS

QT dispersion (QTd), the interval between T wave peak to T wave end (TpTe), TpTe/QT (with and without correction), QRS width, and the index of cardio-electrophysiological balance (iCEB) were calculated in 101 hospitalized COVID-19 patients and it was compared with 101 non-COVID-19 matched controls. A systematic review was performed in four databases and meta-analysis was conducted using Stata software.

RESULTS

Tp-Te, TpTe/QT, QRS width, and iCEB were significantly increased in COVID-19 patients compared with controls (TpTe = 82.89 vs. 75.33 ms (ms), p-value = .005; TpTe/QT = 0.217 vs. 0.203 ms, p-value = .026). After a meta-analysis of 679 COVID-19 cases and 526 controls from 9 studies, TpTe interval, TpTe/QT, and TpTe/QTc ratios were significantly increased in COVID-19 patients. Meta-regression analysis moderated by age, gender, diabetes mellitus, hypertension, and smoking reduced the heterogeneity. QTd showed no significant correlation with COVID-19.

CONCLUSION

COVID-19 adversely influences the ECG markers of transmural heterogeneity of repolarization. Studies evaluating the predictive value of these ECG markers are warranted to determine their clinical utility.

Effect of ranolazine on Tp-e interval, Tp-e/QTc, and P-wave dispersion in patients with stable coronary artery disease

INTRODUCTION

Ranolazine is an antianginal drug and also exhibits antiarrhythmic effect by affecting action potential time, refractory period, and repolarization reserve. We evaluated the effect of ranolazine therapy on myocardial repolarization parameters (Tp-e, QT, QTc intervals, Tp-e/QT, and Tp-e/QTc ratios), index of cardiac electrophysiological balance (iCEB) (QT/QRS, QTc/QRS) and P-wave dispersion (PWD) in patients with stable coronary artery disease (CAD).

METHODS

This study included 175 patients, aged between 35 and 90 years who were followed with stable CAD for at least 3 months. Ninety patients had been receiving ranolazine for at least 1 month, and 85 patients had never received ranolazine. All patients' basic demographic data, risk factors, medications, and echocardiographic parameters recorded. Myocardial repolarization parameters, P-wave times, and PWD were analyzed from 12 lead electrodes.

RESULTS

There was no variation between the groups in terms of basic demographic parameters and CAD risk factors. Tp-e interval (87.3 ± 14.4 vs. 90.8 ± 12.4 msn, P < .001), Tp-e/QT (0.22 ± 0.04 vs. 0.23 ± 0.03; P = .03), Tp-e/QTc (0.21 ± 0.04 vs. 0.22 ± 0.04 P = .001), and PWD (39.2 ± 13.7 vs. 43.5 ± 12.9 P = .028) were significantly lower in the ranolazine group. But iCEB was similar in both groups. In multivariate analysis after adjusted confounding factors such as age and BMI, Tp-e/QTc ratio, QTc, Pmax, and PWD were found significantly in ranolazine group again.

CONCLUSION

Tp-e/QTc ratio, QTc, Pmax, and PWD were significantly lower in stable CAD patients under ranolazine therapy. In stable CAD patients, the prognostic significance of ranolazine for arrhythmic events requires further evaluation of these parameters through long-term follow-up and large-scale prospective studies.

Electrocardiographic Evaluation of the Ventricular Arrhythmia Risk in Patients Diagnosed With Schizophrenia

OBJECTIVE

The purpose of this study was to examine electrocardiographic ventricular arrhythmia predictors in patients with schizophrenia by comparing with healthy controls.

METHODS

The study included 100 patients with schizophrenia and 100 healthy controls. Electrocardiography (ECG) was performed on all participants in resting position. T-wave peak to end (Tp-e), QT ranges, P-wave dispersion (Pd), and R-R range were measured. Then, the Schizophrenia Positive and Negative Syndrome Scale (PANSS) and the Calgary Depression Scale for Schizophrenia (CDSS) were applied to the schizophrenia group.

RESULTS

The PANSS positive symptom subscale was calculated as 10.41 (SD = 2.27), the negative symptom subscale was calculated as 14.44 (SD = 5.42), and the overall functionality level was calculated as 27.04 (SD = 5.43). The mean CDSS score was determined to be 3.74 (SD = 2.15). No differences were detected in the heart rate measurements of the patient and control groups in ECG results (P = .427). The minimum QT interval and minimum Tp-e wave times were found to be low in the patient group (P < .001 for both intervals). Corrected QTc dispersion, Pd, Tp-e dispersion, and QT dispersion were found to be higher in the patient group than in healthy controls (P < .001 for all intervals).

DISCUSSION

Based on our results, it is possible to speculate that patients with schizophrenia are at a risk of developing cardiac arrhythmia and cardiac dysfunction if they do not receive treatment. For this reason, clinicians should pay attention to cardiac transmission problems when organizing the treatment of patients. Further studies should be conducted to determine cardiac problems in patients with schizophrenia.

Diabetic microvascular complications associated with myocardial repolarization heterogeneity evaluated by Tp-e interval and Tp-e/QTc ratio

INTRODUCTION

The heterogeneity in myocardial repolarization increases the risk of ventricular arrhythmias and sudden death in patients with diabetes mellitus (DM). The Tp-e interval and Tp-e/QTc ratio are found to be useful in the prediction of ventricular arrhythmias. In this study, we aimed to investigate the Tp-e interval and Tp-e/QTc ratio in diabetic patients with and without microvascular complications.

MATERIALS AND METHODS

This cross-sectional observational study included patients with type 2 DM who presented to the endocrinology outpatient clinic. Diabetic microvascular complications were evaluated. The Tp-e interval, Tp-e/QT ratio, and Tp-e/QTc ratio were also calculated.

RESULTS

A total of 240 patients with type 2 DM (148 patients had microvascular complications) were included in the study. Diabetic neuropathy rate was 30.4%, diabetic nephropathy rate was 38.4%, and diabetic retinopathy rate was 21.7%. Upon comparing patients according to Tp-e/QTc ratio, the median Tp-e/QTc interval of the group of patients with complications was 0.21 (0.19-0.23) and the median Tp-e/QTc ratio of the group of patients without complications was 0.19 (0.18-0.20) (p < 0.001). When patients were grouped according to the presence and severity of retinopathy, the Tp-e/QTc ratio was more prolonged in the proliferative retinopathy group [0.27 (0.23-0.30)] than the non-proliferative retinopathy group [0.20 (0.19-0.22), p < 0.001]. When patients were grouped according to the presence and severity of nephropathy, the Tp-e/QTc ratio was more prolonged in the macroalbuminuria and microalbuminuria group than the normoalbuminuric group [0.25 (0.21-0.30), 0.23 (0.19-0.24), and 0.19 (0.20-0.22), respectively, p = 0.002].

CONCLUSIONS

Our study is the first to demonstrate the association of the Tp-e interval and Tp-e/QTc ratio with the presence and severity of microvascular complications in patients with type 2 DM.

ECG changes in patients with opioid use disorder; P-QT wave dispersion: a retrospective study

OBJECTIVE

We aimed to examine the electrocardiographic arrhythmia risk predictors in patients with opioid use disorder by P wave dispersion, QT dispersion, and by comparing Tp-e/QTc ratio with healthy controls.

METHODS

One hundred seventeen patients who were diagnosed with opioid use disorder according to DSM-5 criteria and who were hospitalized in 25 Aralık Gaziantep State Hospital AMATEM (Alcohol and substance addiction treatment center) service and a healthy control group consisting of 168 subjects were included in the study. Electrocardiography (ECG) scans of all participants were performed in the supine position and at rest. P wave dispersion, QT dispersion, and Tp-e/QTc ratio were calculated.

RESULTS

Of all the participants, 12 were women (4.21%), 273 (95.78%) were men. The mean age of all participants was 30.42 ± 9.36 years. No difference was found between the gender, mean age, marital status, educational level, and smoking status of the participants (p > 0.05). The entire patient group was using heroin. Heart rate of the patient group was calculated as 68.14 ± 13.26 beats per minute, being lower than healthy controls (p < 0.05). Although QT dispersion value was lower than healthy controls (p < 0.05); P wave dispersion did not differ between groups (p > 0.05).

CONCLUSION

It is thought that the patients with opioid use disorder are at risk for cardiac arrhythmia based on our findings. Therefore, physicians should be careful about cardiac rhythm and conduction problems while organizing any treatment of these patients.

Body Surface Mapping of Ventricular Repolarization Heterogeneity: An Ex-vivo Multiparameter Study

Background

Increased heterogeneity of ventricular repolarization is associated with life-threatening arrhythmia and sudden cardiac death (SCD). T-wave analysis through body surface potential mapping (BSPM) is a promising tool for risk stratification, but the clinical effectiveness of current electrocardiographic indices is still unclear, with limited experimental validation. This study aims to investigate performance of non-invasive state-of-the-art and novel T-wave markers for repolarization dispersion in an ex vivo model.

Methods

Langendorff-perfused pig hearts (N = 7) were suspended in a human-shaped 256-electrode torso tank. Tank potentials were recorded during sinus rhythm before and after introducing repolarization inhomogeneities through local perfusion with dofetilide and/or pinacidil. Drug-induced repolarization gradients were investigated from BSPMs at different experiment phases. Dispersion of electrical recovery was quantified by duration parameters, i.e., the time interval between the peak and the offset of T-wave (T_PEAK-T_END) and QT interval, and variability over time and electrodes was also assessed. The degree of T-wave symmetry to the peak was quantified by the ratio between the terminal and initial portions of T-wave area (Asy). Morphological variability between left and right BSPM electrodes was measured by dynamic time warping (DTW). Finally, T-wave organization was assessed by the complexity of repolarization index (CR), i.e., the amount of energy non-preserved by the dominant eigenvector computed by principal component analysis (PCA), and the error between each multilead T-wave and its 3D PCA approximation (NMSE). Body surface indices were compared with global measures of epicardial dispersion of repolarization, and with local gradients between adjacent ventricular sites.

Results

After drug intervention, both regional and global repolarization heterogeneity were significantly enhanced. On the body surface, T_PEAK-T_END was significantly prolonged and less stable in time in all experiments, while QT interval showed higher variability across the interventions in terms of duration and spatial dispersion. The rising slope of the repolarization profile was steeper, and T-waves were more asymmetric than at baseline. Interventricular shape dissimilarity was enhanced by repolarization gradients according to DTW. Organized T-wave patterns were associated with abnormal repolarization, and they were properly described by the first principal components.

Conclusion

Repolarization heterogeneity significantly affects T-wave properties, and can be non-invasively captured by BSPM-based metrics.

Brugada syndrome: A comprehensive review of pathophysiological mechanisms and risk stratification strategies

Brugada syndrome (BrS) is an inherited ion channel channelopathy predisposing to ventricular arrhythmias and sudden cardiac death. Originally believed to be predominantly associated with mutations in SCN5A encoding for the cardiac sodium channel, mutations of 18 genes other than SCN5A have been implicated in the pathogenesis of BrS to date. Diagnosis is based on the presence of a spontaneous or drug-induced coved-type ST segment elevation. The predominant electrophysiological mechanism underlying BrS remains disputed, commonly revolving around the three main hypotheses based on abnormal repolarization, depolarization or current-load match. Evidence from computational modelling, pre-clinical and clinical studies illustrates that molecular abnormalities found in BrS lead to alterations in excitation wavelength (λ), which ultimately elevates arrhythmic risk. A major challenge for clinicians in managing this condition is the difficulty in predicting the subset of patients who will suffer from life-threatening ventricular arrhythmic events. Several repolarization risk markers have been used thus far, but these neglect the contributions of conduction abnormalities in the form of slowing and dispersion. Indices incorporating both repolarization and conduction based on the concept of λ have recently been proposed. These may have better predictive values than the existing markers. Current treatment options include pharmacological therapy to reduce the occurrence of arrhythmic events or to abort these episodes, and interventions such as implantable cardioverter-defibrillator insertion or radiofrequency ablation of abnormal arrhythmic substrate.

Changes in left ventricular repolarization after short-term testosterone replacement therapy in hypogonadal males

BACKGROUND AND AIM

Evidences suggest that androgen deficiency is associated with sudden cardiac death (SCD). Our purpose was to analyse some electrocardiographic (ECG) markers of repolarization phase in hypogonadal patients either at baseline or after testosterone replacement therapy (TRT).

PATIENTS AND METHODS

Baseline and after 6 months of testosterone replacement therapy, 14 hypogonadal patients and 10 age-matched controls underwent a short-term ECG recordings at rest and immediately after a maximal exercise test. The following ECG parameters have been collected: QTe (the interval between the q wave the end of T wave), QTp (the interval between the q wave and the peak of T wave), and Te (the interval between the peak and the end of T wave).

RESULTS

At baseline, in the hypogonadal patients, corrected QTe and QTp values were longer at rest than in the controls at rest (p < 0.05), whereas, during the recovery phase, only the QTp remained significantly longer (p < 0.05). After TRT, hypogonadal patients showed an improvement only in Te (p < 0.05). Conversely, any difference between hypogonadal patients and control subjects was found with respect to the markers of temporal dispersion of repolarization phases, except for a worse QTp → Te coherence (p = 0.001) obtained during the recovery phase.

CONCLUSIONS

In conclusion, at rest, hypogonadal patients suffer from a stable increase in the myocardial repolarization phase without an increase in its temporal dispersion and, hence, the SCD risk seems to be low.

Electrocardiographic measures of ventricular repolarization dispersion and arrhythmic outcomes among ST elevation myocardial infarction patients with pre-infarction angina undergoing primary percutaneous coronary intervention

BACKGROUND

Arrhythmias are considered one of the major causes of death in ST elevation myocardial infarction (STEMI), particularly in the early in-hospital phase. Pre-infarction angina (PIA) has been suggested to have a protective role.

OBJECTIVES

To study the difference in acute electrocardiographic findings between STEMI patients with and without PIA and to assess the in-hospital arrhythmias in both groups.

MATERIAL AND METHODS

We prospectively enrolled 238 consecutive patients with STEMI. Patients were divided into two groups: those with or without PIA. ECG data recorded and analyzed included ST-segment resolution (STR) at 90 min, corrected QT interval (QTc) and dispersion (QTD), T-peak-to-T-end interval (Tp-Te), and dispersion and Tp-Te/QT ratio. In-hospital ventricular arrhythmias encountered in both groups were recorded. Predictors of in-hospital arrhythmias were assessed among different clinical and electrocardiographic parameters.

RESULTS

Of the 238 patients included, 42 (17%) had PIA and 196 (83%) had no PIA. Patients with PIA had higher rates of STR (p < 0.0001), while patients with no PIA had higher values of QTc (p = 0.006), QTD (p = 0.001), Tp-Te interval (p = 0.001), Tp-Te dispersion (p < 0.0001), and Tp-Te/QT ratio (p = 0.01) compared to those with angina preceding their incident infarction (PIA). This was reflected into significantly higher rates of in-hospital arrhythmias among patients with no PIA (20% vs. 7%, p = 0.04). Furthermore, longer Tp-Te interval and higher Tp-Te/QT ratio independently predicted in-hospital ventricular arrhythmias.

CONCLUSION

Pre-infarction angina patients had better electrocardiographic measures of repolarization dispersion and encountered significantly less arrhythmic events compared to patients who did not experience PIA.

Electrocardiographic conduction and repolarization markers associated with sudden cardiac death: moving along the electrocardiography waveform

The QT interval along with its heart rate corrected form (QTc) are well-established ECG markers that have been found to be associated with malignant ventricular arrhythmogenesis. However, extensive preclinical and clinical investigations over the years have allowed for novel clinical ECG markers to be generated as predictors of arrhythmogenesis and sudden cardiac death. Repolarization markers include the older QTc, QT dispersion and newer Tpeak - Tend intervals, (Tpeak - Tend) / QT ratios, T-wave alternans (TWA), microvolt TWA and T-wave area dispersion. Meanwhile, conduction markers dissecting the QRS complex, such as QRS dispersion (QRSD) and fragmented QRS, were also found to correlate conduction velocity and unidirectional block with re-entrant substrates in various cardiac conditions. Both repolarization and conduction parameters can be combined into the excitation wavelength (λ). A surrogate marker for λ is the index of Cardiac Electrophysiological Balance (iCEB: QT / QRSd). Other markers based on conduction-repolarization are [QRSD x (Tpeak-Tend) / QRSd] and [QRSD x (Tpeak-Tend) / (QRSd x QT)]. Advancement in technology permitted sophisticated electrophysiological analyses such as principal component analysis and periodic repolarization dynamics to further improve risk stratification. This was closely followed by other novel indices including ventricular ectopic QRS interval, the f99 index and EntropyXQT, which integrates mathematical and physical calculations for determining the risk markers. Though proven to be effective in limited patient cohorts, more clinical studies across different cardiac pathologies are required to confirm their validity. As such, this review seeks to encapsulate the development of old and new ECG markers along with their associated utility and shortcomings in clinical practice.

Evaluation of myocardial dispersion of repolarization in patients with heart transplantation

Background/aim

The number of patients with heart transplantation has dramatically increased in the last decade. Considerable studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (Tp-e) may correspond to the transmural dispersion of repolarization and increased Tp-e interval and Tp-e/QT ratio are associated with malignant ventricular arrhythmias. We analyzed the dispersion of myocardial repolarization using electrocardiographic Tp-e interval and Tp-e/QTc ratio in patients with heart transplantation.

Materials and methods

This observational study included 38 patients (12 female and 26 male) with heart transplantation and 38 well-matched controls. From electrocardiograms, Tp-e interval and Tp-e/QTc ratio were calculated and compared between the 2 groups.

Results

Noninvasive arrhythmia indicators including Tp-e interval (84.63 ± 14.17 ms vs 71.82 ± 7.47 ms, P < 0.001), Tp-e/QTc ratio (0.19 ± 0.04 vs 0.16 ± 0.02, P < 0.001) and QTc interval except QT interval were significantly higher in transplanted hearts compared to normal hearts.

Conclusion

Patients with heart transplantation have increased myocardial dispersion of repolarization.

Evaluation of ventricular repolarization parameters during migraine attacks

AIMS

Migraine is a chronic neurovascular disorder characterized by intermittent episodes of severe headache. Abnormalities in the autonomic nervous system (sympathetic and parasympathetic nervous systems) have been detected during migraine-free periods in patients with migraine. In these patients, disrupted autonomic innervations of the heart and coronary arteries may lead to electrocardiographic changes during a migraine attack. T-wave peak-to-end interval (Tp-e interval) and Tp-e/QT ratio are relatively new markers of ventricular arrhythmogenesis and repolarization heterogeneity. In the present observational study, we investigated the changes in ventricular repolarization during migraine attacks and attack-free periods by performing 12‑lead electrocardiography (ECG).

METHODS

This study included 63 patients (54 [86%] women; mean age: 33.3 ± 9.9 years) with migraine. The QT and corrected QT (QTc) intervals, Tp-e interval, and Tp-e/QT ratio of the patients during migraine attacks and attack-free periods were measured by performing 12‑lead ECG.

RESULTS

The QT and QTc intervals, Tp-e interval, and Tp-e/QT ratio were higher during migraine attacks than during attack-free periods (P < 0.001 for all).

CONCLUSION

These results indicate that migraine attacks are associated with an increase in ventricular repolarization parameters compared with attack-free periods possibly because of the dysregulation of the autonomic nervous system.

T-Wave Indices and Atherosclerosis

Tpeak-Tend interval, the time difference between the peak and the end of the T-wave, reflects the degree of dispersion of repolarization. Its prolongation has been associated with higher risks of developing ventricular arrhythmias and sudden cardiac death in different pro-arrhythmic conditions such as Brugada and long QT syndromes. In this review, we will provide a comprehensive overview on how Tpeak-Tend is altered in different atherosclerotic conditions such as hypertension, stable coronary artery disease, acute coronary obstruction, and coronary slow flow as well as inflammatory diseases affecting the arterial tree. We will explore its relationship with arterial function and dysfunction, ventricular remodeling, and arrhythmic and mortality outcomes. The published literature shows that patients with coronary atherosclerosis, whether in the form of stable coronary artery disease, chronic total occlusion, slow flow, or acute coronary obstruction, have prolonged Tpeak-Tend intervals and Tpeak-Tend/QT ratios. These can be used to predict the occurrence of ventricular arrhythmias and sudden cardiac death. They also correlate with the extent and severity of arterial stenosis and structural remodeling of the ventricles as well as arterial function and dysfunction. Finally, they can be normalized following revascularization and may therefore be used as a surrogate measure of treatment success.

Meta-analysis of Tpeak-Tend and Tpeak-Tend/QT ratio for risk stratification in congenital long QT syndrome

BACKGROUND AND OBJECTIVES

Congenital long QT syndrome (LQTS) predisposes affected individuals to ventricular tachycardia/fibrillation (VF/VF), potentially resulting in sudden cardiac death. The Tpeak-Tend interval and the Tpeak-Tend/QT ratio, electrocardiographic markers of dispersion of ventricular repolarization, were proposed for risk stratification but their predictive values in LQTS have been controversial. A systematic review and meta-analysis was conducted to examine the value of Tpeak-Tend intervals and Tpeak-Tend/QT ratios in predicting arrhythmic and mortality outcomes in congenital LQTS.

METHOD

PubMed and Embase databases were searched until 9th May 2017, identifying 199 studies.

RESULTS

Five studies on long QT syndrome were included in the final meta-analysis. Tpeak-Tend intervals were longer (mean difference [MD]: 13ms, standard error [SE]: 4ms, P=0.002; I2=34%) in congenital LQTS patients with adverse events [syncope, ventricular arrhythmias or sudden cardiac death] compared to LQTS patients without such events. By contrast, Tpeak-Tend/QT ratios were not significantly different between the two groups (MD: 0.02, SE: 0.02, P=0.26; I2=0%).

CONCLUSION

This meta-analysis showed that Tpeak-Tend interval is significant higher in individuals who are at elevated risk of adverse events in congenital LQTS, offering incremental value for risk stratification.

Traditional and novel electrocardiographic conduction and repolarization markers of sudden cardiac death

Sudden cardiac death, frequently due to ventricular arrhythmias, is a significant problem globally. Most affected individuals do not arrive at hospital in time for medical treatment. Therefore, there is an urgent need to identify the most-at-risk patients for insertion of prophylactic implantable cardioverter defibrillators. Clinical risk markers derived from electrocardiography are important for this purpose. They can be based on repolarization, including corrected QT (QTc) interval, QT dispersion (QTD), interval from the peak to the end of the T-wave (Tpeak - Tend), (Tpeak - Tend)/QT, T-wave alternans (TWA), and microvolt TWA. Abnormal repolarization properties can increase the risk of triggered activity and re-entrant arrhythmias. Other risk markers are based solely on conduction, such as QRS duration (QRSd), which is a surrogate marker of conduction velocity (CV) and QRS dispersion (QRSD) reflecting CV dispersion. Conduction abnormalities in the form of reduced CV, unidirectional block, together with a functional or a structural obstacle, are conditions required for circus-type or spiral wave re-entry. Conduction and repolarization can be represented by a single parameter, excitation wavelength (λ = CV × effective refractory period). λ is an important determinant of arrhythmogenesis in different settings. Novel conduction-repolarization markers incorporating λ include Lu et al.' index of cardiac electrophysiological balance (iCEB: QT/QRSd), [QRSD× (Tpeak - Tend)/QRSd] and [QRSD × (Tpeak - Tend)/(QRSd × QT)] recently proposed by Tse and Yan. The aim of this review is to provide up to date information on traditional and novel markers and discuss their utility and downfalls for risk stratification.

High risk electrocardiographic markers in Brugada syndrome

Several clinical, electrocardiographic (ECG) and electrophysiological markers have been proposed to provide optimal risk stratification in patients with Brugada syndrome (BrS). Of the different markers, only a spontaneous type 1 ECG pattern has clearly shown a sufficiently high predictive value. This review article highlights specific ECG markers based on depolarization and/or repolarization that have been associated with an increased risk of arrhythmic events in patients with BrS.

Arrhythmogenic drugs can amplify spatial heterogeneities in the electrical restitution in perfused guinea-pig heart: An evidence from assessments of monophasic action potential durations and JT intervals

Non-uniform shortening of the action potential duration (APD90) in different myocardial regions upon heart rate acceleration can set abnormal repolarization gradients and promote arrhythmia. This study examined whether spatial heterogeneities in APD90 restitution can be amplified by drugs with clinically proved proarrhythmic potential (dofetilide, quinidine, procainamide, and flecainide) and, if so, whether these effects can translate to the appropriate changes of the ECG metrics of ventricular repolarization, such as JT intervals. In isolated, perfused guinea-pig heart preparations, monophasic action potentials and volume-conducted ECG were recorded at progressively increased pacing rates. The APD90 measured at distinct ventricular sites, as well as the JTpeak and JTend values were plotted as a function of preceding diastolic interval, and the maximum slopes of the restitution curves were determined at baseline and upon drug administration. Dofetilide, quinidine, and procainamide reverse rate-dependently prolonged APD90 and steepened the restitution curve, with effects being greater at the endocardium than epicardium, and in the right ventricular (RV) vs. the left ventricular (LV) chamber. The restitution slope was increased to a greater extent for the JTend vs. the JTpeak interval. In contrast, flecainide reduced the APD90 restitution slope at LV epicardium without producing effect at LV endocardium and RV epicardium, and reduced the JTpeak restitution slope without changing the JTend restitution. Nevertheless, with all agents, these effects translated to the amplified epicardial-to-endocardial and the LV-to-RV non-uniformities in APD90 restitution, paralleled by the increased JTend vs. JTpeak difference in the restitution slope. In summary, these findings suggest that arrhythmic drug profiles are partly attributable to the accentuated regional heterogeneities in APD90 restitution, which can be indirectly determined through ECG assessments of the JTend vs. JTpeak dynamics at variable pacing rates.

Electrocardiographic Markers of Appropriate Implantable Cardioverter-Defibrillator Therapy in Young People with Congenital Heart Diseases

Implantable cardioverter-defibrillators (ICDs) are increasingly utilized in patients with congenital heart disease (CHD). Prediction of the occurrence of shocks is important if improved patient selection is desired. The electrocardiogram (ECG) has been the first-line tool predicting the risk of sudden death, but data in CHD patients are lacking. We aim to evaluate the predictive value of electrocardiographic markers of appropriate therapy of ICD in young people with CHD. We conducted a prospective, longitudinal study, in twenty-six CHD patients (mean age 24.7 ± 5.3 years) who underwent first ICD implantation. Forty-two age- and diagnosis-matched controls were recruited. Twelve-lead ECG and 24 h Holter analysis were performed during a mean follow-up of 38.9 months. Data included heart rate, heart rate variability, QRS duration (QRSd), QTc interval and its dispersion, Tpeak-Tend (Tp-Te) interval and its dispersion, presence of fragmented QRS (fQRS), T wave alternans, atrial arrhythmias, and non-sustained ventricular tachycardia. Implant indication was primary prevention in ten cases (38.5%) and secondary prevention in 16 (61.5%). Overall, 17 subjects (65.3%) received at least one appropriate and effective ICD discharge. fQRS was present in 64.7% of cases with ICD therapy compared with patients without events or controls (p < 0.0001). Tp-e and Tp-e dispersion were significantly prolonged in patients with recurrences (113.5 and 37.2 ms) versus patients without ICD discharge (89.6 and 24.1 ms) or controls (72.4 and 19.3 ms) (p < 0.0001 and p < 0.0001, respectively). On univariate Cox regression analysis QRSd (hazard ratio: 1.19 per ms, p = 0.003), QTc dispersion (hazard ratio: 1.57 per ms, p = 0.002), fQRS (hazard ratio: 3.58 p < 0.0001), Tp-e (hazard ratio: 2.27 per ms, p < 0.0001), and Tp-e dispersion (hazard ratio: 4.15 per ms, p < 0.0001), emerged as strong predictors of outcome. On multivariate Cox analysis fQRS, Tp-e and Tp-e dispersion remained in the model. The presence of fQRS, and both Tp-e and Tp-e dispersion are useful ECG tools in daily clinical practice to identify CHD patients at risk for appropriate ICD therapy.

Tracking interlead heterogeneity of R- and T-wave morphology to disclose latent risk for sudden cardiac death

Sudden cardiac death (SCD) due primarily to ventricular fibrillation claims 1.5 million lives worldwide each year. In 45%-50% of cases, it is the first manifestation of underlying heart disease. Traditional risk factors including smoking, hypertension, age, sex, as well as depressed left ventricular ejection fraction lack sufficient sensitivity and specificity to forewarn of impending life-threatening arrhythmias. There has been a decades-long search for electrocardiographic (ECG) markers of SCD risk. Several interval-based indices such as QT dispersion and T_peak-T_end interval held initial promise but ultimately yielded mixed results. Recently, the focus has been on interlead heterogeneity of R- and T-wave morphology. The new approaches have involved advanced analytical tools including vectorcardiographic techniques and second central moment analysis of QRS-aligned templates to quantify heterogeneity of depolarization and repolarization waveforms. The results of current studies appear to be robust and worthy of further exploration. This review examines the electrophysiological underpinnings of heterogeneity-based risk assessment and provides an update of clinical techniques. We also discuss future directions whereby tracking heterogeneity may help to disclose latent risk for SCD not only in ECG recordings made at rest but also during ambulatory ECG monitoring and exercise tolerance testing.

Psychotropic drugs and ventricular repolarisation: The effects on QT interval, T-peak to T-end interval and QT dispersion

OBJECTIVE

We aimed to investigate in a clinical setting, the effects of different classes of psychotropic drugs on cardiac electrophysiological measures linked with an increased risk of sudden cardiac death.

METHODS

We conducted a cross-sectional study in a population of 1059 psychiatric inpatients studying the effects of various psychotropic drugs on the T-peak to T-end (TpTe) interval, QT dispersion and QT interval.

RESULTS

Methadone use showed a strong association with TpTe prolongation (odds ratio (OR)=12.66 (95% confidence interval (CI), 3.9-41.1), p<0.001), an effect independent from action on QT interval. Mood stabilisers showed significant effects on ventricular repolarisation: lithium was associated with a TpTe prolongation (OR=2.12 (95% CI, 1.12-4), p=0.02), while valproic acid with a TpTe reduction (OR=0.6 (95% CI, 0.37-0.98), p=0.04). Among antipsychotics, clozapine increased TpTe (OR=9.5 (95% CI, 2.24-40.39), p=0.002) and piperazine phenothiazines increased QT dispersion (OR=2.73 (95% CI, 1.06-7.02), p=0.037).

CONCLUSIONS

Treatment with psychotropic drugs influences TpTe and QT dispersion. These parameters might be considered to better estimate the sudden cardiac death risk related to specific medications. Beyond antipsychotics and antidepressants, mood stabilisers determine significant effects on ventricular repolarisation.

Among patients with left bundle branch block, T-wave peak to T-wave end time is prolonged in the presence of acute coronary occlusion

BACKGROUND

Assessing the effect of myocardial ischemia on ventricular repolarization in the setting of left bundle branch block (LBBB) poses a challenge due to secondary prolongation of the QT interval inherent in LBBB. The T-wave peak to T-wave end (TpTe) interval has been noted to prolong during myocardial ischemia and correct after reperfusion in patients with normal conduction. Here we compare the TpTe intervals of patients with LBBB both with and without complete acute coronary occlusion (ACO).

METHODS

Retrospectively, emergency department patients with LBBB and symptoms of myocardial ischemia were identified both with angiographically-proven ACO and with No-ACO. The longest QT, JT, and TpTe intervals were analyzed.

RESULTS

The ACO and No-ACO groups consisted of 33 and 129 patients, respectively. The mean TpTe was longer in ACO (103.6ms [95%CI 98.5-108.7]) compared to No-ACO patients (88.6ms [95%CI 85.3-91.9]) (P<0.0001) and this held true after correction for heart rate. In ACO versus No-ACO, the TpTe also more frequently exceeded prolongation cutoffs of 85ms (30 [90%] versus 69 [54%]) and 100ms (25 [76%] versus 42 [33%]) (P<0.0001 for all). The mean QT, JT, QTc, and JTc intervals were not significantly different between the groups for either the Bazett's or Rautaharju's correction formulas.

CONCLUSIONS

In patients with LBBB on the ECG, the TpTe is longer and more frequently prolonged in patients with ACO compared to patients without ACO. Future studies of ventricular repolarization in patients with LBBB should include analyses of the TpTe interval.

Tpeak-to-Tend interval corrected for heart rate: A more precise measure of increased sudden death risk?

BACKGROUND

The Tpeak to Tend (Tpe) interval on the 12-lead electrocardiogram predicts an increased risk of sudden cardiac arrest (SCA). There is controversy over whether Tpe would be more useful if corrected for heart rate (Tpec).

OBJECTIVES

We evaluated whether the predictive value of Tpe for SCA improves with heart rate correction and sought to determine an optimal cutoff value for Tpec in the context of SCA risk.

METHODS

Cases of SCA (n = 628; mean age 66.4 ± 14.5 years; n = 416, 66.2% men) from the Oregon Sudden Unexpected Death Study with an archived electrocardiogram available prior and unrelated to the SCA event were analyzed. Comparisons were made with control subjects (n = 819; mean age 66.7 ± 11.5 years; n = 559, 68.2% men). The Tpe interval was corrected for heart rate using Bazett (TpecBa) and Fridericia (TpecFd) formulas, and the predictive value of Tpec for SCA was evaluated using logistic regression models.

RESULTS

The area under the curve for Tpec predicting SCA improved with both correction formulas. TpecBa and TpecFd were shown to have an area under the curve of 0.695 and 0.672, respectively, as compared with a baseline of 0.601 with an uncorrected Tpe. A TpecBa value of >90 ms was predictive of SCA, independent of age, sex, comorbidities, QRS duration, corrected QT interval, and severely reduced left ventricular ejection fraction (≤35%; odds ratio 2.8; 95% confidence interval 1.92-4.17; P < .0001).

CONCLUSION

Correcting Tpe for heart rate, using either the Bazett or the Fridericia formula, improved the independent predictive value of this marker for the assessment of SCA risk. Prolongation of TpecBa beyond 90 ms was associated with a nearly 3-fold increased risk of SCA.

Microvolt T-wave alternans amplifies spatial dispersion of repolarization in human subjects with ischemic cardiomyopathy

INTRODUCTION

In experimental models, spatial dispersion of repolarization (DOR) due to discordant cellular alternans predisposes to ventricular fibrillation. To test the hypothesis that microvolt T-wave alternans (MTWA) in humans causes spatial DOR, we measured Tpeak-Tend interval (Tpe) and Tpe/QT ratio, electrocardiographic indices of spatial DOR.

METHODS

Mean Tpe and Tpe/QT were compared in ischemic cardiomyopathy patients with positive and negative MTWA studies.

RESULTS

MTWA was positive in 12 and negative in 24 patients. Tpe and Tpe/QT were higher in MTWA+ subjects compared to MTWA- subjects during exercise (64.5±6.8 vs. 54.9±8.7ms, p=0.001 and 0.218±0.03 vs. 0.177±0.02, p=0.001) but not at rest.

CONCLUSION

Ischemic cardiomyopathy patients have increased Tpe and Tpe/QT when MTWA is induced during exercise, suggesting that MTWA causes increased spatial DOR in humans. Future studies are needed to determine if Tpe and Tpe/QT during exercise might predict increased risk of SCD alone or in combination with measurement of MTWA.

Spatial QT Dispersion Predicts Nonsustained Ventricular Tachycardia and Correlates with Confined Systodiastolic Dysfunction in Hypertrophic Cardiomyopathy

Objectives: An increased dispersion of myocardial repolarization represents one of the mechanisms underlying the arrhythmic risk in hypertrophic cardiomyopathy (HCM). We investigated spatial myocardial repolarization dispersion indices in HCM patients with nonsustained ventricular tachycardia (NSVT) and, contextually, their main clinical determinants. Methods: Fifty-two well-matched HCM outpatients were categorized into two groups according to the presence or the absence of NSVT at 24-hour Holter electrocardiogram (ECG) monitoring. Each patient underwent a clinical examination, including Doppler echocardiogram integrated with tissue Doppler imaging, cardiac magnetic resonance, and 12-lead surface ECG to calculate the dispersion for the following intervals: QRS, Q-Tend (QTe), Q-Tpeak, Tpeak-Tend (TpTe), J-Tpeak, and J-Tend. Results: The NSVT group showed only QTe dispersion and TpTe dispersion values to be significantly higher than their counterparts. NSVT occurrence was independently predicted by late gadolinium enhancement presence (p = 0.021) and QTe Bazett dispersion (p = 0.030), the latter strongly associated with the myocardial performance index (MPI) obtained at the basal segment of the interventricular septum (p = 0.0004). Conclusion: Our data support QTe dispersion as an easy and noninvasive tool for identifying HCM patients with NSVT propensity. The strong relationship between QTe dispersion and MPI allows us to hypothesize an intriguing link between electrical instability and confined myocardial areas of systodiastolic dysfunction.

Sympathetic nerve stimulation, not circulating norepinephrine, modulates T-peak to T-end interval by increasing global dispersion of repolarization

BACKGROUND

T-peak to T-end interval (Tp-e) is an independent marker of sudden cardiac death. Modulation of Tp-e by sympathetic nerve activation and circulating norepinephrine is not well understood. The purpose of this study was to characterize endocardial and epicardial dispersion of repolarization (DOR) and its effects on Tp-e with sympathetic activation.

METHODS AND RESULTS

In Yorkshire pigs (n=13), a sternotomy was performed and the heart and bilateral stellate ganglia were exposed. A 56-electrode sock and 64-electrode basket catheter were placed around the epicardium and in the left ventricle (LV), respectively. Activation recovery interval, DOR, defined as variance in repolarization time, and Tp-e were assessed before and after left, right, and bilateral stellate ganglia stimulation and norepinephrine infusion. LV endocardial and epicardial activation recovery intervals significantly decreased, and LV endocardial and epicardial DOR increased during sympathetic nerve stimulation. There were no LV epicardial versus endocardial differences in activation recovery interval during sympathetic stimulation, and regional endocardial activation recovery interval patterns were similar to the epicardium. Tp-e prolonged during left (from 40.4±2.2 ms to 92.4±12.4 ms; P<0.01), right (from 47.7±2.6 ms to 80.7±11.5 ms; P<0.01), and bilateral (from 47.5±2.8 ms to 78.1±9.8 ms; P<0.01) stellate stimulation and strongly correlated with whole heart DOR during stimulation (P<0.001, R=0.86). Of note, norepinephrine infusion did not increase DOR or Tp-e.

CONCLUSIONS

Regional patterns of LV endocardial sympathetic innervation are similar to that of LV epicardium. Tp-e correlated with whole heart DOR during sympathetic nerve activation. Circulating norepinephrine did not affect DOR or Tp-e.

Intravenous amiodarone homogeneously prolongs ventricular repolarization in patients with life-threatening ventricular tachyarrhythmia

BACKGROUND

The most critical adverse effects of class III drugs are marked QT prolongation and torsade de pointes. Even though intravenous amiodarone (iv-Amio) is a representative class III drug, it peculiarly inhibits both clinical ventricular tachycardia/fibrillation (VT/VF) and proarrhythmic effects. To test the hypothesis that iv-Amio homogeneously prolongs repolarization, we evaluated electrocardiographic changes before and during short-term amiodarone therapy, focusing closely on the ventricular dispersion of repolarization.

METHODS

Twenty-seven consecutive patients treated with iv-Amio for VT/VF as a first-line antiarrhythmic therapy were enrolled in this study. Twelve-lead electrocardiography was recorded before and during amiodarone therapy to evaluate the following electrocardiographic intervals: R-R, QRS, QT, QRS to T-peak (QTp), and T-peak to T-end (Tp-e; as an index of dispersion of repolarization). Repolarization indices were corrected to the heart rate by Bazett's method (QTc, c-QTp, c-Tp-e).

RESULTS

Amiodarone suppressed VT/VF in 19/27 (70%) patients without conferring any proarrhythmic effect. The QTc, c-QTp, and R-R interval were significantly prolonged during amiodarone (476±45ms vs 511±45ms, p<0.05; 338±40ms vs 364±35ms, p<0.05; 762±272ms vs 870±189ms, p<0.05; respectively), whereas the c-Tp-e and QRS durations did not change significantly (139±33ms vs 145±41ms, p=0.25; 96±20ms vs 97±21ms, p=0.33; respectively).

CONCLUSIONS

Iv-Amio homogeneously prolongs repolarization and properly inhibits original VT/VF recurrence without inducing torsade de pointes.

Intra-QT spectral coherence as a possible noninvasive marker of sustained ventricular tachycardia

Sudden cardiac death is the main cause of mortality in patients affected by chronic heart failure (CHF) and with history of myocardial infarction. No study yet investigated the intra-QT phase spectral coherence as a possible tool in stratifying the arrhythmic susceptibility in patients at risk of sudden cardiac death (SCD). We, therefore, assessed possible difference in spectral coherence between the ECG segment extending from the q wave to the T wave peak (QTp) and the one from T wave peak to the T wave end (Te) between patients with and without Holter ECG-documented sustained ventricular tachycardia (VT). None of the QT variability indexes as well as most of the coherences and RR power spectral variables significantly differed between the two groups except for the QTp-Te spectral coherence. The latter was significantly lower in patients with sustained VT than in those without (0.508 ± 0.150 versus 0.607 ± 0.150, P < 0.05). Although the responsible mechanism remains conjectural, the QTp-Te spectral coherence holds promise as a noninvasive marker predicting malignant ventricular arrhythmias.

A novel ECG-index for prediction of ventricular arrhythmias in patients after myocardial infarction

BACKGROUND

Risk prediction of ventricular arrhythmias after myocardial infarction (MI) is still insufficient. Prolonged QTc is a known risk marker of mortality and ventricular arrhythmias. QTc has not achieved clinical importance in predicting arrhythmic events in patients after MI. Recent studies have displayed that the terminal part of the QT-interval, Tpeak to Tend (TpTe), may be a more promising predictor of adverse outcome. Herein, we assessed whether TpTe may serve as a predictor of ventricular arrhythmias in patients with previous MI fulfilling current implantable cardioverter-defibrillator (ICD) indications.

METHODS

Seventy-six patients with previous MI eligible for ICD therapy were prospectively enrolled. ECG measurements at baseline were recorded using a 12-lead ECG with 50 mm/s paper speed. TpTe was measured from peak of the T wave to end of T wave. Events during follow up were defined as ventricular arrhythmias requiring appropriate ICD therapy, including antitachycardia pacing and shock.

RESULTS

During 23 ± 19 months, arrhythmic events occurred in 36 (47%) patients. TpTe was longer in ICD patients with recorded ventricular arrhythmias compared with those without (116 ± 26 ms vs. 102 ± 20 ms; P = 0.01), whereas ejection fraction (EF) at baseline did not differ (35 ± 9% vs. 35 ± 11%; P = 0.87). TpTe was an independent predictor of ventricular arrhythmias when adjusted for age, EF and QRS duration (HR 1.16; 95% CI 1.03-1.31; P = 0.02).

CONCLUSIONS

TpTe predicted malignant arrhythmias in patients after MI independently of EF. TpTe may contribute in the risk stratification of patients to identify post-MI patients disposed to malignant arrhythmias and their need of ICD therapy.

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.

Myocardial repolarization dispersion and autonomic nerve activity in a canine experimental acute myocardial infarction model

BACKGROUND

Evidence from a canine experimental acute myocardial infarction (MI) model shows that until the seventh week after MI, the relationship between stellate ganglion nerve activity (SGNA) and vagal nerve activity (VNA) progressively increases.

OBJECTIVE

The purpose of this study was to evaluate how autonomic nervous system activity influences temporal myocardial repolarization dispersion at this period.

METHODS

We analyzed autonomic nerve activity as well as QT and RR variability from recordings previously obtained in nine dogs. From a total of 48 short-term ECG segments, 24 recorded before and 24 recorded 7 weeks after experimentally-induced MI, we obtained three indices of temporal myocardial repolarization dispersion: QTe (from Q-wave to T-wave end), QTp (from Q-wave to T-wave peak), and Te (from T-wave peak to T-wave end) variability index (QTeVI, QTpVI, TeVI). We also performed heart rate variability power spectral analysis on the same segments.

RESULTS

After MI, all the QT variables increased QTeVI (median [interquartile range]) (from -1.76[0.82] to -1.32[0.68]), QTeVI (from -1.90[1.01] to -1.45[0.78]), and TeVI (from -0.72[0.67] to -0.22[1.00]), whereas all RR spectral indices decreased (P <.001 for all). Distinct circadian rhythms in QTeVI (P <.05,) QTpVI (P <.001) and TeVI (P <.05) appeared after MI with circadian variations resembling that of SGNA/VNA. The morning QTpVI and TeVI acrophases approached the SGNA/VNA acrophase. Conversely, the evening QTeVI acrophase coincided with another SGNA/VNA peak. After MI, regression analysis detected a positive relationship between SGNA/VNA and TeVI (R(2): 0.077; β: 0.278; p< 0.001).

CONCLUSION

Temporal myocardial repolarization dispersion shows a circadian variation after MI reaching its peak at a time when sympathetic is highest and vagal activity lowest.

Electrocardiographic predictors of incident heart failure in men and women free from manifest cardiovascular disease (from the Atherosclerosis Risk in Communities [ARIC] study)

The risk of incident hospitalized heart failure (HF) was evaluated for 23 electrocardiographic (ECG) variables in men and women free from cardiovascular disease. The hazard ratios with 95% confidence intervals were determined from Cox regression analysis for 13,428 participants 45 to 65 years old in the Atherosclerosis Risk in Communities (ARIC) study. New-onset HF during a 14-year follow-up period occurred in 695 men (11.9%) and 721 women (9.5%). Several ECG variables were significant predictors of incident HF when evaluated as single ECG variables. Predominant among them were spatial angles, reflecting deviations of the direction of the repolarization sequence from the normal reference direction. After controlling for collinearity among the ECG variables, the spatial angle between T peak and normal T reference vectors, Ө(Tp|Tref), was a significant independent predictor in men (HF risk increased 31%) and women (HF risk increased 46%). Other independent predictors in men included epicardial repolarization time (62% increased risk) and T wave peak to T wave end (TpTe) interval, reflecting global dispersion of repolarization (27% increased risk). The independent predictors in women, in addition to Ө(Tp|Tref), were Ө(R|STT) the spatial angle between the mean QRS and STT vectors (54% increased risk) and QRS nondipolar voltage (46% increased risk). In conclusion, wide Ө(Tp|Tref), wide Ө(R|STT), and increased QRS nondipolar voltage in women and wide Ө(Tp|Tref), increased epicardial repolarization time, prolonged TpTe interval and T wave complexity in men were independent predictors of incident HF, and the presence of these abnormal findings could warrant additional diagnostic evaluation for possible preventive action for HF.

Predictive value of electrocardiographic T-wave morphology parameters and T-wave peak to T-wave end interval for sudden cardiac death in the general population

BACKGROUND

Previous population studies have found an association between electrocardiographic T-wave morphology parameters and cardiovascular mortality, but their relationship to sudden cardiac death (SCD) is not clear. To our knowledge, there are no follow-up studies assessing the association between electrocardiographic T-wave peak to T-wave end interval (TPE) and SCD. We assessed the predictive value of electrocardiographic T-wave morphology parameters and TPE for SCD in an adult general population sample.

METHODS AND RESULTS

A total of 4 T-wave morphology parameters (principal component analysis ratio, T-wave morphology dispersion, total cosine R-to-T, T-wave residuum) as well as TPE were measured from digital standard 12-lead ECGs in 5618 adults (46% men; mean age 50.9±12.5 years) participating in the Finnish population-based Health 2000 Study. After a mean follow-up time of 7.7±1.4 years, 72 SCDs had occurred. In univariable analyses, all T-wave morphology parameters were associated with an increased SCD risk. In multivariable Cox models, T-wave morphology dispersion and total cosine R-to-T remained as predictors of SCD, with T-wave morphology dispersion showing the highest SCD risk (hazard ratio of 1.4 [95% confidence interval 1.1-1.7, P=0.001] per 1 SD increase in the loge T-wave morphology dispersion). In contrast, TPE was not associated with SCD in univariable or multivariable analyses.

CONCLUSIONS

Electrocardiographic T-wave morphology parameters describing the 3-dimensional shape of the T-wave stratify SCD risk in the general population, but we did not find an association between TPE and SCD.

Influence of aging and chronic heart failure on temporal dispersion of myocardial repolarization

Background and purpose:

QT and T_peak-T_end (Te) intervals are associated with sudden cardiac death in patients with chronic heart failure (CHF). We studied age-dependent influence on short-term temporal dispersion of these two variables in patients with postischemic CHF.

Method:

We grouped 75 CHF and 53 healthy control subjects into three age subsets: ≤50 years, >50 years and ≤65 years, and >65 years. We then calculated the following indices: QT and Te variability index (QTVI and TeVI), the ratio between the short-term variability (STV) of QT or Te, and the STV of resting rate (RR) (QT/RR STV and Te/RR STV).

Results:

In all different age subgroups, patients with CHF showed a higher level of QTVI than age-matched control subjects (≤50 years: P < 0.0001; >50 years and ≤65 years: P < 0.05; >65 years: P < 0.05). Patients with CHF < 50 years old also had all repolarization variability indices higher than normal age-matched controls (TeVI, P < 0.05; QT/RR STV, P < 0.05; Te/RR STV, P < 0.05), whereas we did not find any difference between the two older classes of subjects. Both QTVI (r²: 0.178, P < 0.05) and TeVI (r²: 0.433, P < 0.001) were positively related to age in normal subjects, even if the first correlation was weaker than the second one.

Conclusion:

Our data showed that QTVI could be used in all ages to evaluate repolarization temporal liability, whereas the other indices are deeply influenced by age. Probably, the age-dependent increase in QTVI was more influenced by a reduction of RR variability reported in older normal subjects.

Sex differences in cardiac autonomic regulation and in repolarisation electrocardiography

The review summarises the present knowledge on the sex differences in cardiac autonomic regulations and in related aspects of electrocardiography with particular attention to myocardial repolarisation. Although some of the sex differences are far from fully established, multitude of observations show consistent differences between women and men. Despite more pronounced parasympathetic cardiac regulation, women have higher resting heart rate and lower baroreflex sensitivity. Of the electrocardiographic phenomena, women have longer QT interval duration, repolarisation sequence more synchronised with the inverse of the depolarisation sequence, and likely increased regional heterogeneity of myocardial repolarisation. Studies investigating the relationship of these sex disparities to hormonal differences led frequently to conflicting results. Although sex hormones seem to play a key role by influencing both autonomic tone and electrophysiological properties at the cellular level, neither the truly relevant hormones nor their detailed actions are known. Physiologic usefulness of the described sex differences is also unknown. The review suggests that new studies are needed to advance the understanding of the physiologic mechanisms responsible for these inequalities between women and men and provides key methodological suggestions that need to be followed in future research.