Short-term effects of transcutaneous auricular vagus nerve stimulation on T-wave alternans in people with focal epilepsy - An exploratory pilot study

High levels of T-wave alternans (TWA) are linked to an increased risk of sudden cardiac death. People with epilepsy display elevated TWA levels that are decreased by chronic vagus nerve stimulation via implanted devices after 2-4 weeks or later. Our objective was to explore short-term effects of transcutaneous auricular vagus nerve stimulation (tVNS) on TWA. Five patients (3 female) with focal epilepsy undergoing video-EEG monitoring were included. TWA levels were determined using a one-channel modified lead I ECG via an open-source TWA-algorithm on two consecutive days, 1 h before, during and after tVNS via the left auricle. Data are given as mean ± SE. Mean TWA at baseline was 3.8 ± 0.4 µV and 3.0 ± 0.6 µV during stimulation on day 2. Stimulations on the second day were associated with TWA reductions by 22 ± 13 % that exceeded stimulation effects on the first day relative to baseline (p < 0.05). Linear mixed-models revealed effects of both stimulation (p < 0.05) and stimulation number (p < 0.005). Normalized TWA showed reproducible peak reductions at both days within 35 min after the initiation of tVNS (p < 0.05). Our observations suggest that tVNS has short-term effects on TWA, supporting the notion that vagus nerve stimulation has a beneficial impact on electrical cardiac properties.

Non-Invasive Risk Assessment and Prediction of Mortality in Patients Undergoing Coronary Artery Bypass Graft Surgery

Objectives: Heart rate turbulence (HRT) and T-wave alternans (TWA), non-invasive markers of cardiac autonomic dysfunction, and ventricular repolarization abnormality, reportedly, predict the risk of cardiovascular death after myocardial infarction. We investigated whether pre-operative assessment of HRT and/or TWA could predict long-term mortality following coronary artery bypass graft (CABG) surgery. Methods: From May 2010 to December 2017, patients undergoing elective CABG and receiving 24 h ambulatory electrocardiogram monitoring 1 to 5 days prior to CABG surgery were prospectively enrolled. Pre-operative HRT and TWA were measured using a 24 h ambulatory electrocardiogram. The relative risk of cardiac or overall death was assessed according to abnormalities of HRT, TWA, or left ventricular ejection fraction (LV EF). Results: During the mean follow-up period of 4.6 ± 3.9 years, 40 adjudicated overall (5.9%/yr) and 5 cardiac deaths (0.9%/yr) occurred in 146 enrolled patients (64.9 ± 9.3 years; 108 males). Patients with abnormal HRT exhibited significantly higher relative risks of cardiac death (adjusted hazard ratio [HR] 24.9, 95% confidence interval [CI] 1.46-427) and all-cause death (adjusted HR 5.77, 95% CI 2.34-14.2) compared to those with normal HRT. Moreover, abnormal HRT plus abnormal TWA and LV EF < 50% was associated with a greater elevation in cardiac and overall mortality risk. The predictive role of abnormal HRT with/without abnormal TWA for all-cause death was likely more prominent in patients with mildly reduced (35 to 50%) or preserved (≥50%) LV EF. Abnormal HRT plus abnormal TWA and LV EF < 50% showed high negative predictive value in cardiac and overall mortality risk. Conclusions: Assessment of pre-operative HRT and/or TWA predicted mortality risk in patients undergoing elective CABG. Combined analysis of HRT, TWA, and LVEF enhanced the prognostic power. In particular, the predictive value of HRT was enhanced in patients with preserved or mid-range LV EF.

Autonomic regulation therapy in chronic heart failure with preserved/mildly reduced ejection fraction: ANTHEM-HFpEF study results

BACKGROUND

Autonomic regulation therapy (ART) utilizing cervical vagus nerve stimulation (VNS) appeared to be safe and to improve autonomic tone, symptoms, and cardiac mechanical function in patients with symptomatic heart failure and reduced ejection fraction in the ANTHEM-HF Study. The ANTHEM-HFpEF Study is the first investigation to evaluate the safety and feasibility of ART in patients with symptomatic heart failure and preserved or mildly reduced ejection fraction (HFpEF, HFmrEF).

METHODS

This open-label interventional study enrolled 52 patients with HFpEF or HFmrEF, NYHA Class II-III, and LVEF ≥40%, who received stable guideline-directed medical therapy. All patients were successfully implanted with LivaNova VNS Therapy® system with an electrical lead surrounding the right cervical vagus nerve.

RESULTS

Adverse event incidence was low. At 12 months, NYHA class (p < 0.0001), 6-min walk distance (p < 0.05), and quality of life (p < 0.0001) were improved. Cardiac mechanical function measures were normal at baseline, except for left ventricular mass index in women and E/e' ratio in all patients, which were elevated at baseline, and were unchanged by ART. Autonomic tone and reflexes improved, indicated by 29% decrease in low-frequency/high-frequency heart rate variability to normal levels (p = 0.028) and by increased heart rate turbulence slope (p = 0.047). T-wave alternans (p = 0.001) and T-wave heterogeneity (p = 0.001) were reduced from abnormal to normal ranges. Nonsustained ventricular tachycardia incidence decreased (p = 0.027).

CONCLUSIONS

ART appeared well-tolerated and safe in patients with HFpEF or HFmrEF. Chronic ART did not alter mechanical function measures but was associated with improved heart failure symptoms, exercise tolerance, autonomic tone, and cardiac electrical stability.

CLINICAL TRIAL REGISTRY

Autonomic Neural Regulation Therapy to Enhance Myocardial Function in Heart Failure with Preserved Ejection Fraction [ClinicalTrials.gov #NCT03163030, registered 05/22/2017].

Mechanistic insights into spontaneous transition from cellular alternans to ventricular fibrillation

T-wave alternans (TWA) has been used for predicting the risk of malignant cardiac arrhythmias and sudden cardiac death (SCD) in multiple clinical settings; however, possible mechanism(s) underlying the spontaneous transition from cellular alternans reflected by TWA to arrhythmias in impaired repolarization remains unclear. The healthy guinea pig ventricular myocytes under E-4031 blocking IKr (0.1 μM, N = 12; 0.3 μM, N = 10; 1 μM, N = 10) were evaluated using whole-cell patch-clamp. The electrophysiological properties of isolated perfused guinea pig hearts under E-4031 (0.1 μM, N = 5; 0.3 μM, N = 5; 1 μM, N = 5) were evaluated using dual- optical mapping. The amplitude/threshold/restitution curves of action potential duration (APD) alternans and potential mechanism(s) underlying the spontaneous transition of cellular alternans to ventricular fibrillation (VF) were examined. There were longer APD80 and increased amplitude and threshold of APD alternans in E-4031 group compared with baseline group, which was reflected by more pronounced arrhythmogenesis at the tissue level, and were associated with steep restitution curves of the APD and the conduction velocity (CV). Conduction of AP alternans augmented tissue's functional spatiotemporal heterogeneity of regional AP/Ca alternans, as well as the AP/Ca dispersion, leading to localized uni-directional conduction block that spontaneous facilitated the formation of reentrant excitation waves without the need for additional premature stimulus. Our results provide a possible mechanism for the spontaneous transition from cardiac electrical alternans in cellular action potentials and intercellular conduction without the involvement of premature excitations, and explain the increased susceptibility to ventricular arrhythmias in impaired repolarization. In this study, we implemented voltage-clamp and dual-optical mapping approaches to investigate the underlying mechanism(s) for the arrhythmogenesis of cardiac alternans in the guinea pig heart at cellular and tissue levels. Our results demonstrated a spontaneous development of reentry from cellular alternans, arising from a combined actions of restitution properties of action potential duration, conduction velocity of excitation wave and interplay between alternants of action potential and the intracellular Ca handling. We believe this study provides new insights into underlying the mechanism, by which cellular cardiac alternans spontaneously evolves into cardiac arrhythmias.

Is T-Wave Alternans a Repolarization Abnormality Marker in COVID-19? An Investigation on the Potentialities of Portable Electrocardiogram Device

Background

Cardiac arrhythmias are significantly associated with poor outcomes in coronavirus disease 2019 (COVID-19) patients. Microvolt T-wave alternans (TWA) can be automatically quantified and has been recognized as a representation of repolarization heterogeneity and linked to arrhythmogenesis in various cardiovascular diseases. This study aimed to explore the correlation between microvolt TWA and COVID-19 pathology.

Methods

Patients suspected of COVID-19 in Mohammad Hoesin General Hospital were consecutively evaluated using Alivecor^® Kardiamobile 6L™ portable electrocardiogram (ECG) device. Severe COVID-19 patients or those who are unable to cooperate in active ECG self-recording were excluded from the study. TWA was detected and its amplitude was quantified using the novel enhanced adaptive match filter (EAMF) method.

Results

A total of 175 patients, 114 COVID-19 patients (polymerase chain reaction (PCR)-positive group), and 61 non-COVID-19 patients (PCR-negative group) were enrolled in the study. PCR-positive group was subdivided according to the severity of COVID-19 pathology into mild and moderate severity subgroups. Baseline TWA levels were similar between both groups during admission (42.47 ± 26.52 µV vs. 44.72 ± 38.21 µV), but higher TWA levels were observed during discharge in the PCR-positive compared to the PCR-negative group (53.45 ± 34.42 µV vs. 25.15 ± 17.64 µV, P = 0.03). The correlation between PCR-positive result in COVID-19 and TWA value was significant, after adjustment of other confounding variables (R² = 0.081, P = 0.030). There was no significant difference in TWA levels between mild and moderate severity subgroups in patients with COVID-19, both during admission (44.29 ± 27.14 µV vs. 36.75 ± 24.46 µV, P = 0.34) and discharge (49.47 ± 33.62 µV vs. 61.09 ± 35.99 µV, P = 0.33).

Conclusions

Higher TWA values can be observed on follow-up ECG obtained during discharge in the PCR-positive COVID-19 patients.

Continuous multi-day tracking of post-myocardial infarction recovery of cardiac electrical stability and autonomic tone using electrocardiogram patch monitors

BACKGROUND

Sudden cardiac death (SCD) risk is elevated following acute myocardial infarction (MI). The time course of SCD susceptibility post-MI requires further investigation.

METHODS

In this observational cohort study, we employed state-of-the-art noninvasive ECG techniques to track the daily time course of cardiac electrical instability and autonomic function following ST-segment elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI). Preventice BodyGuardian MINI-EL Holters continuously recorded ECGs for 7 days at hospital discharge and at 40 days for STEMI (N = 5) or at 90 days for NSTEMI patients (N = 5). Cardiac electrical instability was assessed by T-wave alternans (TWA) and T-wave heterogeneity (TWH); autonomic tone was determined by rMSSD-heart rate variability (HRV).

RESULTS

TWA was severely elevated (≥60 μV) in STEMI patients (80 ± 10.3 μV) at discharge and throughout the first recording period but declined by 50% to 40 ± 2.3 μV (p = .03) by Day 40 and remained in the normal range (<47 μV). TWH, a related phenomenon analyzed from 12-lead ECGs, was reduced by 63% in the five STEMI patients from discharge to normal (<80 μV) at follow-up (105 ± 27.3 to 39 ± 3.3 μV, p < .04) but increased by 65% in a STEMI case (89 to 147 μV), who received a wearable defibrillator vest and later implantable cardioverter defibrillator. In NSTEMI patients, TWA was borderline abnormal (47 ± 3.3 μV) at discharge and declined by 19% to normal (38 ± 1.2 μV) by Day 90 (p = .05). An overall reciprocal increase in rMSSD-HRV suggested recovery of vagal tone.

CONCLUSIONS

This study provides proof-of-principle for tracking post-MI SCD risk in individual patients with implications for personalized therapy.

Epileptic seizures and Epilepsy Monitoring Unit admission disclose latent cardiac electrical instability

BACKGROUND

Sudden cardiac arrest results from cardiac electrical instability and is 3-fold more frequent in patients with chronic epilepsy than in the general population. We hypothesized that focal to bilateral tonic-clonic seizures (FTBTCS) would acutely impact T-wave alternans (TWA), a marker of cardiac electrical instability linked to an elevated risk for sudden cardiac death, more than focal seizures (FS) [focal aware seizures (FAS) and focal with impaired awareness seizures (FIAS)], due to their greater sympathetic stimulation of the heart. Since stress has been shown to cause significant TWA elevations in patients with heart disease, we also hypothesized that the early days of an inpatient admission to an epilepsy monitoring unit (EMU) would be associated with higher TWA levels compared to later hospital days in patients with chronic epilepsy, presumably due to stress.

DESIGN/METHODS

We analyzed the acute effects of seizures [FAS, FIAS, FTBTCS, and nonepileptic seizures (NES)] and day of hospital stay on TWA in 18 patients admitted to the EMU using high-resolution wireless electrocardiographic (ECG) patch monitors.

RESULTS

A total of 5 patients had FTBTCS, 7 patients had FS (2 FAS, 5 FIAS), and 3 patients had NES only during the index hospital stay. Four patients did not have any electroclinical seizures or NES. FTBTCS resulted in marked acute increases in ictal TWA from baseline (2 ± 0.3 µV) to ictal maximum (70 ± 6.1 µV, p < 0.0001), the latter exceeding the 60 µV cut point defined as severely abnormal. By comparison, while FAS and FIAS also provoked significant increases in TWA (from 2 ± 0.5 µV to 30 ± 3.3 µV, p < 0.0001), maximum ictal TWA levels did not reach the 47 µV cut point defined as abnormal. Heart rate increases during FTBTCS from baseline (62 ± 5.8 beats/min) to ictal maximum (134 ± 8.6 beats/min, an increase of 72 ± 7.2 beats/min, p < 0.02) were also greater (p = 0.014) than heart rate increases during FS (from 70 ± 5.2 beats/min to 118 ± 6.2 beats/min, an increase of 48 ± 2.6 beats/min, p < 0.03). In 3 patients with NES, TWA rose mildly during the patients' typical episodes (from 2 ± 0.6 µV to 14 ± 2.6 µV, p < 0.0004), well below the cut point of abnormality, while heart rate increases were observed (from 75 ± 1.3 to 112 ± 8.7 beats/min, an increase of 37 ± 8.9 beats/min, p = 0.03). Patients with EEG-confirmed electroclinical seizures recorded while in the EMU exhibited significantly elevated interictal TWA maxima (61 ± 3.4 µV) on EMU admission day which were similar in magnitude to ictal maxima seen during FTBTCS (70 ± 6.1 µV, p = 0.21). During subsequent days of hospitalization, daily interictal TWA maxima showed gradual habituation in patients with both FS and FTBTCS but not in patients with NES only.

CONCLUSIONS

This is the first study to our knowledge demonstrating that FTBTCS acutely provoke highly significant increases in TWA to levels that have been associated with heightened risk for sudden cardiac death in other patient populations. We speculate that mortality temporally associated with FTBTCS may, in some cases, be due to sudden cardiac death rather than respiratory failure. In patients with EEG-confirmed epilepsy, hospital admission is associated with interictal TWA maxima that approach those seen during FTBTCS, presumably related to stress during the early phase of hospitalization compared to later in the hospitalization, indicating cardiac electrical instability and potential vulnerability to sudden cardiac death related to stress independent of temporal relationships to seizures. The elevated heart rates observed acutely with seizures and on hospital Day 1 are consistent with a hyperadrenergic state and the effect of elevated sympathetic output on a vulnerable cardiac substrate, a phenomenon termed "the Epileptic Heart."

Microvolt T-wave alternans in early repolarization syndrome associated with ventricular arrhythmias: A case report

Despite early repolarization (ER) syndrome being usually considered benign, its association with severe/malignant ventricular arrhythmias (VA) was also reported. Microvolt T-wave alternans (MTWA) is an electrocardiographic marker for the development of VA, but its role in ER syndrome remains unknown. A 90-second 6-lead electrocardiogram from an ER syndrome patient, acquired with the Kardia recorder, was analyzed by the enhanced adaptive matched filter for MTWA quantification. On average, MTWA was 50 μV, higher than what was previously observed on healthy subjects using the same method. In our ER syndrome patient, MTWA plays a potential role in VA development in ER syndrome.

Prolonged ST segment and T-wave alternans with torsade de pointes secondary to hypocalcemia due to hypoparathyroidism: A case report

Hypoparathyroidism predisposes patients to hypocalcemia. Patients with hypoparathyroidism are thus at risk of electrocardiographic abnormalities, including T-wave alternans. T-wave alternans is poorly understood and lacks uniform diagnostic criteria. Its presence suggests myocardial electrical instability, and it has become an important sign for identifying patients at high risk of malignant arrhythmias and sudden cardiac death. We report a rare case of T-wave alternans with torsade de pointes due to hypocalcemia. The etiology of T-wave alternans may easily be overlooked. It should thus be thoroughly investigated to avoid misdiagnosis and poor outcomes.

Spectrum of clinical applications of interlead ECG heterogeneity assessment: From myocardial ischemia detection to sudden cardiac death risk stratification

Heterogeneity in depolarization and repolarization among regions of cardiac cells has long been recognized as a major factor in cardiac arrhythmogenesis. This fundamental principle has motivated development of noninvasive techniques for quantification of heterogeneity using the surface electrocardiogram (ECG). The initial approaches focused on interval analysis such as interlead QT dispersion and T_peak -T_end difference. However, because of inherent difficulties in measuring the termination point of the T wave and commonly encountered irregularities in the apex of the T wave, additional techniques have been pursued. The newer methods incorporate assessment of the entire morphology of the T wave and in some cases of the R wave as well. This goal has been accomplished using a number of promising vectorial approaches with the resting 12-lead ECG. An important limitation of vectorcardiographic analyses is that they require exquisite stability of the recordings and are not inherently suitable for use in exercise tolerance testing (ETT) and/or ambulatory ECG monitoring for provocative stress testing or evaluation of the influence of daily activities on cardiac electrical instability. The objectives of the present review are to describe a technique that has been under clinical evaluation for nearly a decade, termed "interlead ECG heterogeneity." Preclinical testing data will be briefly reviewed. We will discuss the main clinical findings with regard to sudden cardiac death risk stratification, heart failure evaluation, and myocardial ischemia detection using standard recording platforms including resting 12-lead ECG, ambulatory ECG monitoring, ETT, and pharmacologic stress testing in conjunction with single-photon emission computed tomography myocardial perfusion imaging.

Microvolt T-Wave Alternans Is Modulated by Acute Low-Level Tragus Stimulation in Patients With Ischemic Cardiomyopathy and Heart Failure

Aims: Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular tachy-arrhythmias, while vagus nerve stimulation has shown promising anti-arrhythmic effects in in vivo and ex vivo animal studies. We aimed to examine the effect of non-invasive, acute low-level tragus stimulation (LLTS) on TWA in patients with ischemic cardiomyopathy and heart failure.

Methods: 26 patients with ischemic cardiomyopathy (left ventricular ejection fraction <35%) and chronic stable heart failure, previously implanted with an automatic implantable cardioverter defibrillator (ICD) device with an atrial lead (dual chamber ICD or cardiac resynchronization therapy defibrillator), were enrolled in the study. Each patient sequentially received, (1) Sham LLTS (electrode on tragus, but no stimulation delivered) for 5 min; (2) Active LLTS at two different frequencies (5 and 20 Hz, 15 min each); and (3) Active LLTS, during concomitant atrial pacing at 100 bpm at two different frequencies (5 and 20 Hz, 15 min each). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 5/20 Hz, amplitude 1 mA lower than the discomfort threshold). TWA burden was assessed using continuous ECG monitoring during sham and active LLTS in sinus rhythm, as well as during atrial pacing.

Results: Right atrial pacing at 100 bpm led to significantly heightened TWA burden compared to sinus rhythm, with or without LLTS. Acute LLTS at both 5 and 20 Hz, during sinus rhythm led to a significant rise in TWA burden in the precordial leads (p < 0.05).

Conclusion: Acute LLTS results in a heart-rate dependent increase in TWA burden.

Epileptic heart: A clinical syndromic approach

Prevention of premature death in patients with chronic epilepsy remains a major challenge. Multiple pathophysiologic factors have been implicated, with intense investigation of cardiorespiratory mechanisms. Up to four in five patients with chronic epilepsy exhibit cardiovascular comorbidities. These findings led us to propose the concept of an "epileptic heart," defined as "a heart and coronary vasculature damaged by chronic epilepsy as a result of repeated surges in catecholamines and hypoxemia leading to electrical and mechanical dysfunction." Among the most prominent changes documented in the literature are high incidence of myocardial infarction and arrhythmia, altered autonomic tone, diastolic dysfunction, hyperlipidemia, and accelerated atherosclerosis. This suite of pathologic changes prompted us to propose for the first time in this review a syndromic approach for improved clinical detection of the epileptic heart condition. In this review, we discuss the key pathophysiologic mechanisms underlying the candidate criteria along with standard and novel techniques that permit evaluation of each of these factors. Specifically, we present evidence of the utility of standard 12-lead, ambulatory, and multiday patch-based electrocardiograms, along with measures of cardiac electrical instability, including T-wave alternans, heart rate variability to detect altered autonomic tone, echocardiography to detect diastolic dysfunction, and plasma biomarkers for assessing hyperlipidemia and accelerated atherosclerosis. Ultimately, the proposed clinical syndromic approach is intended to improve monitoring and evaluation of cardiac risk in patients with chronic epilepsy to foster improved therapeutic strategies to reduce premature cardiac death.

Electrophysiological Mechanisms Underlying T-Wave Alternans and Their Role in Arrhythmogenesis

T-wave alternans (TWA) reflects every-other-beat alterations in the morphology of the electrocardiogram ST segment or T wave in the setting of a constant heart rate, hence, in the absence of heart rate variability. It is believed to be associated with the dispersion of repolarization and has been used as a non-invasive marker for predicting the risk of malignant cardiac arrhythmias and sudden cardiac death as numerous studies have shown. This review aims to provide up-to-date review on both experimental and simulation studies in elucidating possible mechanisms underlying the genesis of TWA at the cellular level, as well as the genesis of spatially concordant/discordant alternans at the tissue level, and their transition to cardiac arrhythmia. Recent progress and future perspectives in antiarrhythmic therapies associated with TWA are also discussed.

Vagus Nerve Stimulation Provides Multiyear Improvements in Autonomic Function and Cardiac Electrical Stability in the ANTHEM-HF Study

BACKGROUND

Patients with heart failure with reduced left ventricular ejection fraction (LVEF) (HFrEF) experience long-term deterioration of autonomic function and cardiac electrical stability linked to increased mortality risk. The Autonomic Neural Regulation Therapy to Enhance Myocardial Function in Heart Failure (ANTHEM-HF) trial reported improved heart rate variability (HRV) and heart rate turbulence (HRT) and reduced T-wave alternans (TWA) after 12 months of vagus nerve stimulation (VNS). We investigated whether the benefits of chronic VNS persist in the long term.

METHODS AND RESULTS

Effects of chronic VNS on heart rate, HRV, HRT, TWA, R-wave and T-wave heterogeneity (RWH, TWH), and nonsustained ventricular tachycardia (NSVT) incidence were evaluated in all ANTHEM-HF patients with ambulatory ECG data at 24 and 36 months (n = 25). Autonomic markers improved significantly at 24 and 36 months compared to baseline [heart rate, square root of the mean squared differences of successive normal-to-normal intervals (rMSSD), standard deviation of the normal-to-normal intervals (SDNN), HF-HRV, HRT slope, P < 0.05]. Peak TWA levels remained reduced at 24 and 36 months (P < 0.0001). Reductions in RWH and TWH at 6 and 12 months persisted at 24 and 36 months (P < 0.01). NSVT decreased at 12, 24, and 36 months (P < 0.025). No sudden cardiac deaths, ventricular fibrillation, or sustained ventricular tachycardia occurred.

CONCLUSION

In symptomatic patients with HFrEF, chronic VNS appears to confer wide-ranging, persistent improvements in autonomic tone (HRV), baroreceptor sensitivity (HRT), and cardiac electrical stability (TWA, RWH, TWH).

Fatal arrhythmias: Another reason why doctors remain cautious about chloroquine/hydroxychloroquine for treating COVID-19

Background

Early during the current coronavirus disease 19 (COVID-19) pandemic, hydroxychloroquine (HCQ) received a significant amount of attention as a potential antiviral treatment, such that it became one of the most commonly prescribed medications for COVID-19 patients. However, not only has the effectiveness of HCQ remained questionable, but mainly based on preclinical and a few small clinical studies, HCQ is known to be potentially arrhythmogenic, especially as a result of QT prolongation.

Objective

The purpose of this study was to investigate the arrhythmic effects of HCQ, as the heightened risk is especially relevant to COVID-19 patients, who are at higher risk for cardiac complications and arrhythmias at baseline.

Methods

An optical mapping technique utilizing voltage-sensitive fluorescent dyes was used to determine the arrhythmic effects of HCQ in ex vivo guinea pig and rabbit hearts perfused with the upper therapeutic serum dose of HCQ (1000 ng/mL).

Results

HCQ markedly increased action potential dispersion, resulted in development of repolarization alternans, and initiated polymorphic ventricular tachycardia.

Conclusion

The study results further highlight the proarrhythmic effects of HCQ.

Spatial-Temporal Signals and Clinical Indices in Electrocardiographic Imaging (II): Electrogram Clustering and T-wave Alternans

During the last years, attention and controversy have been present for the first commercially available equipment being used in Electrocardiographic Imaging (ECGI), a new cardiac diagnostic tool which opens up a new field of diagnostic possibilities. Previous knowledge and criteria of cardiologists using intracardiac Electrograms (EGM) should be revisited from the newly available spatial-temporal potentials, and digital signal processing should be readapted to this new data structure. Aiming to contribute to the usefulness of ECGI recordings in the current knowledge and methods of cardiac electrophysiology, we previously presented two results: First, spatial consistency can be observed even for very basic cardiac signal processing stages (such as baseline wander and low-pass filtering); second, useful bipolar EGMs can be obtained by a digital processing operator searching for the maximum amplitude and including a time delay. In addition, this work aims to demonstrate the functionality of ECGI for cardiac electrophysiology from a twofold view, namely, through the analysis of the EGM waveforms, and by studying the ventricular repolarization properties. The former is scrutinized in terms of the clustering properties of the unipolar an bipolar EGM waveforms, in control and myocardial infarction subjects, and the latter is analyzed using the properties of T-wave alternans (TWA) in control and in Long-QT syndrome (LQTS) example subjects. Clustered regions of the EGMs were spatially consistent and congruent with the presence of infarcted tissue in unipolar EGMs, and bipolar EGMs with adequate signal processing operators hold this consistency and yielded a larger, yet moderate, number of spatial-temporal regions. TWA was not present in control compared with an LQTS subject in terms of the estimated alternans amplitude from the unipolar EGMs, however, higher spatial-temporal variation was present in LQTS torso and epicardium measurements, which was consistent through three different methods of alternans estimation. We conclude that spatial-temporal analysis of EGMs in ECGI will pave the way towards enhanced usefulness in the clinical practice, so that atomic signal processing approach should be conveniently revisited to be able to deal with the great amount of information that ECGI conveys for the clinician.

The Epileptic Heart: Concept and clinical evidence

Sudden unexpected death in epilepsy (SUDEP) is generally considered to result from a seizure, typically convulsive and usually but not always occurring during sleep, followed by a sequence of events in the postictal period starting with respiratory distress and progressing to eventual cardiac asystole and death. Yet, recent community-based studies indicate a 3-fold greater incidence of sudden cardiac death in patients with chronic epilepsy than in the general population, and that in 66% of cases, the cardiac arrest occurred during routine daily activity and without a temporal relationship with a typical seizure. To distinguish a primarily cardiac cause of death in patients with epilepsy from the above description of SUDEP, we propose the concept of the "Epileptic Heart" as "a heart and coronary vasculature damaged by chronic epilepsy as a result of repeated surges in catecholamines and hypoxemia leading to electrical and mechanical dysfunction." This review starts with an overview of the pathophysiological and other lines of evidence supporting the biological plausibility of the Epileptic Heart, followed by a description of tools that have been used to generate new electrocardiogram (EKG)-derived data in patients with epilepsy that strongly support the Epileptic Heart concept and its propensity to cause sudden cardiac death in patients with epilepsy independent of an immediately preceding seizure.

T-Wave Alternans in Nonpathological Preterm Infants

BACKGROUND

Sudden infant death syndrome is more frequent in preterm infants (PTI) than term infants and may be due to cardiac repolarization instability, which may manifest as T-wave alternans (TWA) on the electrocardiogram (ECG). Therefore, the aim of the present work was to analyze TWA in nonpathological PTI and to open an issue on its physiological interpretation.

METHODS

Clinical population consisted of ten nonpathological PTI (gestational age ranging from 29 3 7 to 34 2 7  weeks; birth weight ranging from 0.84 to 2.10 kg) from whom ECG recordings were obtained ("Preterm infant cardio-respiratory signals database" by Physionet). TWA was identified through the heart-rate adapting match filter method and characterized in terms of mean amplitude values (TWAA). TWA correlation with several other clinical and ECG features, among which gestational age-birth weight ratio, RR interval, heart-rate variability, and QT interval, was also performed.

RESULTS

TWA was variable among infants (TWAA = 26 ± 11 µV). Significant correlations were found between TWAA versus birth weight (ρ = -0.72, p = .02), TWAA versus gestational age-birth weight ratio (ρ = 0.76, p = .02) and TWAA versus heart-rate variability (ρ = -0.71, p = .02).

CONCLUSIONS

Our preliminary retrospective study suggests that nonpathological PTI show TWA of few tens of µV, the interpretation of which is still an open issue but could indicate a condition of cardiac risk possibly related to the low development status of the infant. Further investigations are needed to solve this issue.

Arrhythmias due to Inherited and Acquired Abnormalities of Ventricular Repolarization

Several acquired and congenital disease conditions and many cardiac and noncardiac drugs affect ventricular repolarization and increase susceptibility to ventricular arrhythmias. Abnormal ventricular repolarization can be reflected on the surface ECG by prolonged or shortened QT interval, early repolarization, and abnormal T-wave configuration. Reduced outward K+ currents and abnormal or increased sodium or calcium currents increase the vulnerability to ventricular arrhythmias. Multiple mechanisms give rise to ventricular arrhythmias in conditions of congenital or acquired abnormal ventricular repolarization. Ventricular arrhythmias associated with abnormalities of ventricular repolarization typically are rapid, usually polymorphic, ventricular tachycardia or torsades de pointes, often degenerating into ventricular fibrillation.

Evaluation of T-wave alternans in pediatric patients with chronic renal failure

INTRODUCTION

Microvolt T-wave alternans (TWA) is known to be useful in prediction of ischemia and sudden death in high-risk populations and there are no studies in children with chronic renal failure (CRF). Cardiac problems seem to be responsible for an important part of death in children and young adults with CRF. The aim of this study is to evaluate Holter microvolts TWA measurements in children with CRF comparing to the control group.

METHODS

This prospective study included 40 patients with CRF and 48 healthy controls. The history, echocardiography and microvolt TWA values based on 24-hour ECG recordings of the patients were evaluated. Analysis of microvolt TWA was considered on the basis of three leads (V5, V1 and AVF).

RESULTS

Compared with the controls, the mean systolic and diastolic blood pressure values and average heart rates were significantly higher in the children with CRF (p = 0.001 and p = 0.026, respectively). Also, the values of left ventricular internal dimensions at end diastole and end-diastolic volume were significantly higher in CRF group (p = 0.01 and p = 0.049, respectively) and couplet ventricular extrasystole was detected in 2 patients with CRF. Consequently, all TWA values in three leads were increased in CRF group than the control group but the only increase in V5 lead was statistically significant (p = 0.028).

CONCLUSIONS

This study has demonstrated that microvolt TWA values increased in pediatric patients with CRF. TWA might be used for early risk assessment in pediatric patients with CRF in the future.

T-wave alternans in a case with systemic lupus erythematosus-related myocarditis

A 42-year-old woman presented with fever, dyspnea, lower-leg edema, significant pulmonary congestion, pleural effusion, and severely reduced left ventricular contractions. She was resistant to treatment for heart failure, including catecholamines, furosemide, phosphodiesterase III inhibitors, and human atrial natriuretic peptide, and antibiotics failed to reduce her inflammation. She had renal dysfunction and hypocomplementemia and was positive for anti-nuclear and anti-ds-DNA antibodies. The patient was diagnosed with myocarditis and pleurisy associated with systemic lupus erythematosus (SLE). Prednisolone administration improved her general condition, reducing inflammation and improving left ventricular function. On day 1, an electrocardiography (ECG) revealed a T-wave inversion similar to a T-U complex configuration in leads II, aVF, and V3-6. By day 8, however, ECG showed prolonged corrected QT (QTc) and T-wave alternans (alternating beat-to-beat T-wave patterns) in lead V3-6. Careful ECG monitoring should be used to identify potentially fatal ventricular arrhythmias during the recovery phase of SLE-related myocarditis. <Learning objective: This was a case of significant T-wave alternans (TWA) during recovery from systemic lupus erythematosus (SLE)-related myocarditis. Fatal ventricular arrhythmia appears to be a risk during recovery from myocardial damage caused by SLE. Up to now, there have been no published case reports of TWA during this period. Patients with myocarditis should be carefully monitored for arrhythmia, even after ventricular function and inflammation have improved with prednisolone therapy.>.

Utility of heart rate turbulence and T-wave alternans to assess risk for readmission and cardiac death in hospitalized heart failure patients

BACKGROUND

Heart failure (HF) patients have a higher risk of recurrent HF and cardiac death, and electrical remodeling is considered to be an important factor for HF progression. The present study aimed to validate the utility of electrocardiogram and Holter monitoring for the risk stratification of HF patients.

METHODS

Our study comprised 215 patients (144 males, mean age 62 years) who had been hospitalized due to acute decompensated HF. Electrocardiogram (QRS duration and QTc interval) and 24-hour Holter monitoring (heart rate variability, heart rate turbulence, and T-wave alternans [TWA]) were performed in stable condition before discharge. The clinical characteristics and outcomes were then investigated.

RESULTS

During a median follow-up period of 2.7 years, there were 83 (38.6%) cardiac events (rehospitalization due to worsening HF [n = 51] or cardiac death [n = 32]). The patients with cardiac events had a lower turbulence slope (TS) and higher TWA compared to those without cardiac events (TS, 3.0 ± 5.5 ms/RR vs. 5.3 ± 5.6 ms/RR, P = 0.001; TWA, 66.1 ± 19.6 μV vs. 54.7 ± 15.1 μV, P < 0.001). Univariable analysis showed that TS, TWA, QRS duration, and QTc interval were associated with cardiac events (P = 0.004, P < 0.001, P = 0.037, and P = 0.024, respectively), while the multivariable analysis after the adjustment of multiple confounders showed that TS and TWA were independent predictive factors of cardiac events with a hazard ratio of 0.936 and 1.015 (95% confidence interval [CI]: 0.860-0.974, P = 0.006; and 95% CI: 1.003-1.027, P = 0.016), respectively.

CONCLUSION

The measurement of TS and TWA is useful for assessing risk for rehospitalization and cardiac death in HF patients.

The roles of mid-myocardial and epicardial cells in T-wave alternans development: a simulation study

Background

The occurrence of T-wave alternans in electrocardiographic signals was recently linked to susceptibility to ventricular arrhythmias and sudden cardiac death. Thus, by detecting and comprehending the origins of T-wave alternans, it might be possible to prevent such events.

Results

Here, we simulated T-wave alternans in a computer-generated human heart model by modulating the action potential duration and amplitude during the first part of the repolarization phase. We hypothesized that changes in the intracardiac alternans patterns of action potential properties would differentially influence T-wave alternans measurements at the body surface. Specifically, changes were simulated globally in the whole left and right ventricles to simulate concordant T-wave alternans, and locally in selected regions to simulate discordant and regional discordant, hereinafter referred to as “regional”, T-wave alternans. Body surface potential maps and 12-lead electrocardiographic signals were then computed. In depth discrimination, the influence of epicardial layers on T-wave alternans development was significantly higher than that of mid-myocardial cells. Meanwhile, spatial discrimination revealed that discordant and regional action potential property changes had a higher influence on T-wave alternans amplitude than concordant changes. Notably, varying T-wave alternans sources yielded distinct body surface potential map patterns for T-wave alternans amplitude, which can be used for location of regions within hearts exhibiting impaired repolarization. The highest ability for T-wave alternans detection was achieved in lead V1. Ultimately, we proposed new parameters Vector Magnitude Alternans and Vector Angle Alternans, with higher ability for T-wave alternans detection when using multi-lead electrocardiographic signals processing than for single leads. Finally, QT alternans was found to be associated with the process of T-wave alternans generation.

Conclusions

The distributions of the body surface T-wave alternans amplitude have been shown to have unique patterns depending on the type of alternans (concordant, discordant or regional) and the location of the disturbance in the heart. The influence of epicardial cells on T-wave alternans development is significantly higher than that of mid-myocardial cells, among which the sub-endocardial layer exerted the highest influence. QT interval alternans is identified as a phenomenon that correlate with T-wave alternans.

Increased beat-to-beat T-wave variability in myocardial infarction patients

The purpose of this study was to investigate the beat-to-beat variability of T-waves (TWV) and to assess the diagnostic capabilities of T-wave-based features for myocardial infarction (MI). A total of 148 recordings of standard 12-lead electrocardiograms (ECGs) from 79 MI patients (22 females, mean age 63±12 years; 57 males, mean age 57±10 years) and 69 recordings from healthy subjects (HS) (17 females, 42±18 years; 52 males, 40±13 years) were studied. For the quantification of beat-to-beat QT intervals in ECG signal, a template-matching algorithm was applied. To study the T-waves beat-to-beat, we measured the angle between T-wave max and T-wave end with respect to Q-wave (∠α) and T-wave amplitudes. We computed the standard deviation (SD) of beat-to-beat T-wave features and QT intervals as markers of variability in T-waves and QT intervals, respectively, for both patients and HS. Moreover, we investigated the differences in the studied features based on gender and age for both groups. Significantly increased TWV and QT interval variability (QTV) were found in MI patients compared to HS (p<0.05). No significant differences were observed based on gender or age. TWV may have some diagnostic attributes that may facilitate identifying patients with MI. In addition, the proposed beat-to-beat angle variability was found to be independent of heart rate variations. Moreover, the proposed feature seems to have higher sensitivity than previously reported feature (QT interval and T-wave amplitude) variability for identifying patients with MI.

Mechanisms linking T-wave alternans to spontaneous initiation of ventricular arrhythmias in rabbit models of long QT syndrome

KEY POINTS

T-wave alternans (TWA) and T-wave lability (TWL) are precursors of ventricular arrhythmias in long QT syndrome; however, the mechanistic link remains to be clarified. Computer simulations show that action potential duration (APD) prolongation and slowed heart rates promote APD alternans and chaos, manifesting as TWA and TWL, respectively. Regional APD alternans and chaos can exacerbate pre-existing or induce de novo APD dispersion, which combines with enhanced I_Ca,L to result in premature ventricular complexes (PVCs) originating from the APD gradient region. These PVCs can directly degenerate into re-entrant arrhythmias without the need for an additional tissue substrate or further exacerbate the APD dispersion to cause spontaneous initiation of ventricular arrhythmias. Experiments conducted in transgenic long QT rabbits show that PVC alternans occurs at slow heart rates, preceding spontaneous intuition of ventricular arrhythmias.

ABSTRACT

T-wave alternans (TWA) and irregular beat-to-beat T-wave variability or T-wave lability (TWL), the ECG manifestations of action potential duration (APD) alternans and variability, are precursors of ventricular arrhythmias in long QT syndromes. TWA and TWL in patients tend to occur at normal heart rates and are usually potentiated by bradycardia. Whether or how TWA and TWL at normal or slow heart rates are causally linked to arrhythmogenesis remains unknown. In the present study, we used computer simulations and experiments of a transgenic rabbit model of long QT syndrome to investigate the underlying mechanisms. Computer simulations showed that APD prolongation and slowed heart rates caused early afterdepolarization-mediated APD alternans and chaos, manifesting as TWA and TWL, respectively. Regional APD alternans and chaos exacerbated pre-existing APD dispersion and, in addition, APD chaos could also induce APD dispersion de novo via chaos desynchronization. Increased APD dispersion, combined with substantially enhanced I_Ca,L , resulted in a tissue-scale dynamical instability that gave rise to the spontaneous occurrence of unidirectionally propagating premature ventricular complexes (PVCs) originating from the APD gradient region. These PVCs could directly degenerate into re-entrant arrhythmias without the need for an additional tissue substrate or could block the following sinus beat to result in a longer RR interval, which further exacerbated the APD dispersion giving rise to the spontaneous occurrence of ventricular arrhythmias. Slow heart rate-induced PVC alternans was observed in experiments of transgenic LQT2 rabbits under isoproterenol, which was associated with increased APD dispersion and spontaneous occurrence of ventricular arrhythmias, in agreement with the theoretical predictions.

An α-glucosidase inhibitor could reduce T-wave alternans in type 2 diabetes patients

BACKGROUND

We tested the hypothesis that an alpha-glucosidase inhibitor (α-GI), miglitol, is effective in protecting the cardiovascular system in type 2 diabetes mellitus (T2DM).

METHODS

We studied 19 hospitalized heart disease patients with T2DM in whom we performed continuous glucose monitoring, Holter electrocardiogram, and ambulatory blood pressure (BP) monitoring simultaneously for 48h. The α-GI miglitol was administered for half of the study period by a cross-over fashion. T-wave alternans (TWA), a marker of future fatal arrhythmic events, was also analyzed by Holter ECG.

RESULTS

Of the 19 patients, the measures of glucose variability were significantly lower during miglitol therapy than in control period. BP variability was similar with/without miglitol. However, TWA was significantly lower during the miglitol period compared to control period (63±4.8 vs. 75.8±5.1μV, p=0.032).

CONCLUSION

An α-GI, miglitol, can reduce TWA by reducing the fluctuation of glucose in heart disease patients with T2DM.

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.

Exercise-induced quantitative microvolt T-wave alternans in hypertrophic cardiomyopathy

BACKGROUND/PURPOSE

Patients with hypertrophic cardiomyopathy (HCM) have elevated risk for sudden cardiac death (SCD). Our study aimed to quantitatively characterize microvolt T-wave alternans (TWA), a potential arrhythmia risk stratification tool, in this HCM patient population.

METHODS

TWA was analyzed with the quantitative modified moving average (MMA) in 132 HCM patients undergoing treadmill exercise testing, grouped according to Maron score risk factors as high-risk (H-Risk, n=67,), or low-risk (L-Risk, n=65, without these risk factors).

RESULTS

TWA levels were much higher for the H-Risk than for the L-Risk group (101.40±75.61 vs. 54.35±46.26μV; p<0.0001). A 53μV cut point, set by receiver operator characteristic (ROC), identified H-Risk patients (82% sensitivity, 69% specificity).

CONCLUSIONS

High TWA levels were found for hypertrophic cardiomyopathy patients. Abnormal TWA associated with major risk factors for SCD: non-sustained ventricular tachycardia on Holter (p=0.001), family history of SCD (p=0.006), septal thickness ≥30mm (p<0.001); and inadequate blood pressure response to effort (p=0.04).

T-Wave Alternans, Heart Rate Turbulence, and Ventricular Ectopy in Standard versus Daily Hemodialysis: Results from the FHN Daily Trial

BACKGROUND

Hemodialysis (HD) patients are at high risk of sudden cardiac death (SCD). HD 6-times/week (6x/wk) may reduce SCD risk compared to usual 3-times/week HD (3x/wk) by mechanisms unknown. T-wave alternans (TWA), heart rate turbulence (HRT), and ventricular ectopy (VE) are elevated in HD patients, but their response to 6x/wk HD has not been assessed.

METHODS

Baseline and 1-year Holter recordings were analyzed from enrollees in the Frequent Hemodialysis Network Daily Trial, a randomized trial comparing 3x/wk to 6x/wk in 245 chronic HD patients. TWA, HRT, and VE were assessed using MARS software.

RESULTS

Sixty-eight patients (34 with 6x/wk) had complete baseline and 1-year Holter recordings. Mean age was 50 ± 13 years and 38% were female. Maximum TWA in the 3x/wk and 6x/wk groups were 52.4 μV at baseline and 51.2 μV at 1-year versus 54.0 and 49.9 μV, respectively (P = 0.28). The proportion of abnormal HRT (scores of 1 or 2) in the 3x/wk group decreased from 65% to 56% at 1-year versus 53% to 53% in the 6x/wk group (P = 0.58). Mean %VE changed from 1.6% to 2.9% in the 3x/wk group from baseline to 1-year and from 2.1% to 3.7% in the 6x/wk group (P = 0.85).

CONCLUSIONS

There were no significant differences in HRT or VE at 1-year in chronic HD patients randomized to 6x/wk versus 3x/wk and a trend in TWA reduction. Additional studies are needed to evaluate the impact and mechanisms of SCD in HD.

Eleclazine, an inhibitor of the cardiac late sodium current, is superior to flecainide in suppressing catecholamine-induced ventricular tachycardia and T-wave alternans in an intact porcine model

BACKGROUND

The capacity of catecholamines to induce ventricular tachycardia (VT) is well documented.

OBJECTIVE

The effectiveness of the novel cardiac late sodium inhibitor eleclazine in suppressing catecholamine-induced VT in a large animal model was compared with that of flecainide.

METHODS

In 13 closed-chest anesthetized Yorkshire pigs, spontaneous VT and surges in T-wave alternans (TWA) level measured using the Modified Moving Average method were induced by epinephrine (2.0 µg/kg, i.v., bolus over 1 minute). Effects of eleclazine (0.3 mg/kg, i.v., infused over 15 minutes; n = 6) or flecainide (1 mg/kg, i.v., bolus over 2 minutes followed by 1 mg/kg/hr, i.v., for 1 hour; n = 7) on VT incidence and TWA level were measured from right intraventricular electrogram recordings.

RESULTS

Epinephrine reproducibly elicited hemodynamically significant spontaneous VT in all 13 pigs and increased TWA level by 33-fold compared to baseline (P < .001). Eleclazine reduced the incidence of epinephrine-induced ventricular premature beats and couplets by 51% (from 31.3 ± 1.91 to 15.2 ± 5.08 episodes; P = .038) and the incidence of 3- to 7-beat VT by 56% (from 10.8 ± 3.45 to 4.7 ± 3.12 episodes; P = .004). Concurrently, the drug reduced the peak epinephrine-induced TWA level by 64% (from 217 ± 22.2 to 78 ± 15.3 µV; P < .001). Flecainide also reduced the incidence of epinephrine-induced ventricular premature beats and couplets by 53% (from 40.4 ± 6.37 to 19.0 ± 2.73 episodes; P = .024) but did not affect the incidence of VT (from 15.0 ± 3.08 to 11.6 ± 2.93 episodes; P = .29) or the peak TWA level (from 207 ± 30.6 to 172 ± 26.2 µV; P = .34).

CONCLUSION

Selective inhibition of cardiac late sodium current with eleclazine is more effective than flecainide in reducing catecholamine-induced VT and TWA in an intact porcine model.

Does manual T-wave window adjustment affect microvolt T-wave alternans results in patients with structural heart disease?

INTRODUCTION

Microvolt T-wave alternans (MTWA) analysis can identify patients at low risk of sudden cardiac death who might not benefit from an implantable cardioverter-defibrillator (ICD). Current spectral methodology for performing MTWA analysis may "miss" part of the T-wave in patients with QT prolongation. The value of T-wave window adjustment in patients with structural heart disease has not been studied.

METHODS

We assembled MTWA data from 5 prior prospective studies including 170 patients with reduced left ventricular ejection fraction, adjusted the T-wave window to include the entire T-wave, and reanalyzed MTWA.

RESULTS

Of 170 patients, 43% required T-wave window adjustment. Only 3 of 170 patients (1.8%) had a clinically significant change in MTWA results.

CONCLUSIONS

In 98.2% of patients, T-wave window adjustment did not improve the accuracy of MTWA analysis. Spectral MTWA as currently implemented remains effective for identifying patients with structural heart disease unlikely to benefit from ICD therapy.

Baseline elevation and reduction in cardiac electrical instability assessed by quantitative T-wave alternans in patients with drug-resistant epilepsy treated with vagus nerve stimulation in the AspireSR E-36 trial

OBJECTIVE

Reports of cardiac arrhythmias and cardiac pathology at postmortem examination of patients with epilepsy suggest a possible cardiac component of risk for sudden unexpected death in epilepsy (SUDEP). T-wave alternans (TWA) is an established marker of cardiac electrical instability and risk for sudden death in patients with cardiovascular disease. We determined the TWA level before vagus nerve stimulation (VNS) system implantation and subsequently the effect of VNS on TWA in patients with drug-resistant epilepsy.

METHODS

Patients (n=28) from the Seizure Detection and Automatic Magnet Mode Performance Study (E-36), a clinical trial of the AspireSR® VNS Therapy System® (NCT01325623), were monitored with ambulatory electrocardiograms (ECGs) ~2weeks before de novo VNS system implantation and following 2- to 4-week VNS titration during a protocol-specified 3- to 5-day epilepsy monitoring unit stay with concurrent EEG/ECG recordings. The TWA level was assessed interictally by the Modified Moving Average (MMA) method.

RESULTS

At preimplantation baseline, TWA was elevated above the 47-μV abnormality cutpoint in 23 (82%) patients with drug-resistant epilepsy. In 16 (70%) patients, TWA level was reduced during VNS treatment to <47μV, thereby converting positive TWA test results to negative. Peak TWA level in all 28 patients improved (group mean, 43%, from 72±4.3 to 41±2.3μV; p<0.0001). Vagus nerve stimulation was not associated with reduced heart rate (77±1.4 to 75±1.4beats/min; p=0.18). Heart rate variability was unchanged.

SIGNIFICANCE

These findings suggest significant interictal cardiac electrical instability in this population of patients with drug-resistant epilepsy and suggest that VNS may be a novel approach to reducing risk.

The utility of T-wave alternans during the morning in the summer for the risk stratification of patients with Brugada syndrome

The prognostic value of the seasonal variations of T-wave alternans (TWA) and heart rate variability (HRV), and the seasonal distribution of ventricular fibrillation (VF) in Brugada syndrome (Br-S) is unknown. We assessed the utility of seasonal variations in TWA and HRV for risk stratification in Br-S using a 24-h multichannel Holter electrocardiogram (24-M-ECG). We enrolled 81 patients with Br-S (grouped according to their history of VF, n = 12; syncope, n = 8; no symptoms, n = 61) who underwent 24-M-ECG in all four seasons. Precordial electrodes were attached to the third (3L-V2) and fourth (4L-V2, 4L-V5) intercostal spaces. We determined the maximum TWA (max-TWA) values and calculated HRV during night and morning time periods for all seasons. During a follow-up period of 5.8 ± 2.8 years, 11 patients experienced new VF episodes and there was a peak in new VF episodes in the summer. The VF group had the greatest 3L-V2 max-TWA value during morning time in the summer among the three groups and showed higher 3L-V2 max-TWA value than in the other seasons. The cutoff value for the 3L-V2 max-TWA during morning time in the summer was determined to be 42 µV using ROC analysis (82 % sensitivity, 74 % specificity; p = 0.0006). Multivariate analysis revealed that a 3L-V2 max-TWA value ≥42 µV during morning time in the summer and previous VF episodes were predictors of future VF episodes. The 3L-V2 max-TWA value during morning time in the summer may be a useful predictor of future VF episodes in Br-S.

Screening for Cardiac Magnetic Resonance Scar Features by 12-Lead ECG, in Patients with Preserved Ejection Fraction

BACKGROUND

Increased QRS score and wide spatial QRS-T angle are independent predictors of cardiovascular mortality in the general population. Our main objective was to assess whether a QRS score ≥ 5 and/or QRS-T angle ≥ 105° enable screening of patients for myocardial scar features.

METHODS

Seventy-seven patients of age ≤ 70 years with QRS score ≥ 5 and/or spatial QRS-T angle ≥ 105° as well as left ventricular ejection fraction (LVEF) >35% were enrolled in the study. All participants underwent complete clinical examination, signal-averaged ECG (SAECG), 30-minute ambulatory ECG recording for T-wave alternans (TWA), and late gadolinium enhancement cardiac magnetic resonance (LGE-CMR). Relationship between QRS score, QRS-T angle with scar presence and pattern, as well as gray zone, core, and total scar size by LGE-CMR were assessed.

RESULTS

Myocardial scar was present in 41 (53%) patients, of whom 19 (46%) exhibited a typical ischemic pattern. QRS score but not QRS-T angle was related to total scar size and gray zone size (R(2) = 0.12, P = 0.002; R(2) = 0.17; P ≤ 0.0001, respectively). Patients with QRS scores ≥ 6 had significantly greater myocardial scar and gray zone size, increased QRS duration and QRS-T angle, a higher prevalence of late potentials (LPs) presence, increased LV end-diastolic volume and decreased LVEF. There was a significant independent and positive association between TWA value and total scar (P = 0.001) and gray zone size (P = 0.01).

CONCLUSION

Patients with preserved LVEF and myocardial scar by CMR also have electrocardiographic features that could be involved in ventricular arrhythmogenesis.

Heart Rate-Dependent Hysteresis of T-Wave Alternans in Primary Prevention ICD Patients

BACKGROUND

T-wave alternans (TWA) is usually performed at accelerated heart rates (HR) during exercise, while recovery TWA is typically not analyzed. Consequently, it is still unknown if TWA shows a HR-dependent hysteresis or not. Thus, the aim of the present study was to investigate TWA dependency on HR during both the exercise and recovery phases of an ergometer test, and to evaluate if recovery TWA may contribute to identify subjects at increased risk of arrhythmic events.

METHODS

Our HR adaptive match filter was used to identify TWA from electrocardiographic recordings acquired during a bicycle ergometer test in 266 patients with implanted cardio-defibrillator. During the 4-year follow-up, 76 patients developed tachycardia or ventricular fibrillation (ICD_Cases) and 190 did not (ICD_Controls).

RESULTS

TWA was statistically lower during exercise than recovery for HRs between 75 and 110 bpm (16-21 μV vs 20-27 μV; P < 0.05), and reverse for HRs between 120 and 130 bpm (41-51 μV vs 28 μV; P < 0.05). ICD_Cases and ICD_Controls showed significantly different TWA at 80 bpm (20 μV vs 15 μV; P < 0.05) and 140 bpm (15 μV vs 22 μV; P < 0.05) during exercise, and at 90 bpm (38 μV vs 21 μV; P < 0.05) and 95 bpm (33-24 μV vs 28 μV; P < 0.05) during recovery.

CONCLUSIONS

TWA shows a HR-dependent hysteresis and there is a different behavior of TWA in ICD_Cases and ICD_Controls groups. Consequently, beside exercise TWA also recovery TWA may contribute to identify subjects at increased risk of arrhythmic events.

Risk Stratification for Ventricular Tachyarrhythmias by Ambulatory Electrocardiogram-Based Frequency Domain T-Wave Alternans

BACKGROUND

Ambulatory electrocardiogram (ECG)-based T-wave alternans (TWA) quantified by the modified moving average method (MMA) can be used to identify patients at risk for sudden cardiac death. However, there is no information available on ambulatory ECG-based TWA as quantified by the frequency domain (FD) method to identify patients with an implantable cardioverter defibrillator (ICD) who are at high risk for ventricular tachyarrhythmias. Further, there are few data regarding the comparison of clinical utility of FD-TWA with MMA-TWA, heart rate variability (HRV), and heart rate turbulence (HRT).

METHODS AND RESULTS

In 41 patients with ICD, of whom 14 patients had a past history of at least one appropriate ICD discharge, FD-TWA, MMA-TWA, HRV, and HRT were analyzed from 24-hour Holter ECG monitoring recordings. Only positive results of FD-TWA and abnormal HRV (standard deviation of all normal-to-normal intervals ≤111 ms) were significantly more frequently observed in patients with than without appropriate ICD discharge. Patients with FD-TWA positive had a significantly higher risk of appropriate ICD discharge than those with FD-TWA negative (50% vs 16%; odds ratio, 5.3 [95% confidence interval, 1.2-23.7], P = 0.02). When FD-TWA and HRV were combined, the specificity (93% vs 59%, P = 0.003) and predictive accuracy (83% vs 66%, P = 0.07) for the identification of patients with appropriate ICD discharge were greater than those for FD-TWA only.

CONCLUSION

The ambulatory ECG-based FD-TWA might be useful to detect patients with ICD who are at high risk for ventricular tachyarrhythmias, and the combination of FD-TWA and HRV might improve the ability to detect such high-risk patients.

Prominent J-wave and T-wave alternans associated with mechanical alternans in a patient with takotsubo cardiomyopathy

A 74-year-old woman with takotsubo cardiomyopathy developed polymorphic ventricular tachycardia during the acute phase. She exhibited prominent J-wave and T-wave alternans preceding ventricular tachycardia. These abnormalities disappeared after recovery from myocardial stunning.

Utility of T-wave alternans during night time as a predictor for ventricular fibrillation in patients with Brugada syndrome

The prognostic value of T-wave alternans (TWA) during the night time in patients with Brugada syndrome (Br-S) remains unknown. We assessed TWA for risk stratification using 24-h multichannel Holter electrocardiogram (24-M-ECG) in Br-S. We enrolled 129 patients with Br-S [grouped according to histories of ventricular fibrillation (VF), n = 16; syncope, n = 10; or no symptoms (asymptomatic), n = 103] and 11 controls. Precordial electrodes were attached to the third (3L-V1, 3L-V2) and fourth (4L-V1, 4L-V2 and 4L-V5) intercostal spaces. We measured the values of maximum TWA (max-TWA) during the night time (12 a.m.-6 a.m.) and the day time (12 p.m.-6 p.m.) and calculated parameters of heart rate variability. Compared to the asymptomatic and control groups, the VF and syncope groups showed significantly greater 3L-V2 max-TWA during the night time. The cutoff value for the 3L-V2 max-TWA during the night time was determined as 20 µV (sensitivity 94 % and specificity 48 %; p = 0.01). Multivariate analysis revealed that 3L-V2 max-TWA during the night time ≥20 µV and previous VF episodes were independent predictors of future VF episodes. During a mean follow-up period of 68 ± 37 months, 16 patients experienced VF episodes. The incidence of VF episodes was the highest during the night time (p < 0.001). The 3L-V2 max-TWA during the night time may be a useful predictor for VF episodes in patients with Br-S.

Automatic SVM classification of sudden cardiac death and pump failure death from autonomic and repolarization ECG markers

BACKGROUND

Considering the rates of sudden cardiac death (SCD) and pump failure death (PFD) in chronic heart failure (CHF) patients and the cost-effectiveness of their preventing treatments, identification of CHF patients at risk is an important challenge. In this work, we studied the prognostic performance of the combination of an index potentially related to dispersion of repolarization restitution (Δα), an index quantifying T-wave alternans (IAA) and the slope of heart rate turbulence (TS) for classification of SCD and PFD.

METHODS

Holter ECG recordings of 597 CHF patients with sinus rhythm enrolled in the MUSIC study were analyzed and Δα, IAA and TS were obtained. A strategy was implemented using support vector machines (SVM) to classify patients in three groups: SCD victims, PFD victims and other patients (the latter including survivors and victims of non-cardiac causes). Cross-validation was used to evaluate the performance of the implemented classifier.

RESULTS

Δα and IAA, dichotomized at 0.035 (dimensionless) and 3.73 μV, respectively, were the ECG markers most strongly associated with SCD, while TS, dichotomized at 2.5 ms/RR, was the index most strongly related to PFD. When separating SCD victims from the rest of patients, the individual marker with best performance was Δα≥0.035, which, for a fixed specificity (Sp) of 90%, showed a sensitivity (Se) value of 10%, while the combination of Δα and IAA increased Se to 18%. For separation of PFD victims from the rest of patients, the best individual marker was TS ≤ 2.5 ms/RR, which, for Sp=90%, showed a Se of 26%, this value being lower than Se=34%, produced by the combination of Δα and TS. Furthermore, when performing SVM classification into the three reported groups, the optimal combination of risk markers led to a maximum Sp of 79% (Se=18%) for SCD and Sp of 81% (Se=14%) for PFD.

CONCLUSIONS

The results shown in this work suggest that it is possible to efficiently discriminate SCD and PFD in a population of CHF patients using ECG-derived risk markers like Δα, TS and IAA.

Evaluation of T-wave alternans in high-resolution ECG maps recorded during the stress test in patients after myocardial infarction

INTRODUCTION

Recent studies point to analysis of T-wave alternans as a promising indicator of an increased risk of life-threatening ventricular arrhythmias. In this study the occurrence of T-wave alternans in the high-resolution ECGs recorded during the exercise stress test and scintigraphic tests (SPECT) in patients with ischemic heart disease was examined.

MATERIAL AND METHODS

The study group consisted of 33 patients after myocardial infarction. In the group of patients after myocardial infarction and with low left ventricular ejection fraction correlations of 70% between the test results of T-wave alternans and SPECT and 60% between the test results of T-wave alternans and stress test were found.

RESULTS

In the group of patients after myocardial infarction but with high left ventricular ejection fraction correlations were respectively 39% and 48%. The analysis of the electrocardiographic maps showed a strong dependence of this correlation on the T-wave alternans amplitude and location of the ECG measuring electrode on the chest. The results might suggest that in patients after myocardial infarction and at increased risk for sudden cardiac death T-wave alternans may also provide information about cardiac electrical instability associated with ischemia.

CONCLUSIONS

It can also be assumed that the position of the electrode where the highest level of the T-wave alternans was detected can indicate the location of the ischemic region of the heart.

Heart Rate Turbulence and T-Wave Alternans in Patients with Coronary Artery Disease: The Influence of Diabetes

BACKGROUND

Patients with diabetes mellitus (DM) have a higher risk of sudden cardiac death. Factors associated with the risk profiles of coronary artery disease (CAD) patients with DM are not well established. Heart rate turbulence (HRT) and T-wave alternans (TWA) are often used to predict arrhythmia events.

METHODS AND RESULTS

HRT and TWA were measured in two independent groups: the ARTEMIS cohort study and the REFINE-ICD randomized trial. ARTEMIS assesses risk 3-12 months after coronary angiography in patients with CAD. The initial 1001 patients in ARTEMIS, 526 with and 475 without DM, are included in this analysis. REFINE-ICD compares usual care versus usual care plus ICD therapy in patients with left ventricular (LV) ejection fraction (EF) values of 36-50% assessed 2-15 months after myocardial infarction. The initial 275 patients screened in REFINE ICD are included in this analysis. Abnormal HRT plus TWA was more common in patients with versus without DM in ARTEMIS (125/526, 24% vs 63/475, 13%; P < 0.001) and REFINE-ICD (43/55, 78% vs 55/220, 25%; P < 0.001), respectively. Abnormal HRT plus TWA was also more common in patients with LVEF values < 50% (28%) vs ≥ 50% (18%; P < 0.001) in ARTEMIS and LVEF values below the population median of 42% (60/138, 43%) versus above the median (38/137, 28%; P < 0.01) in REFINE-ICD.

CONCLUSIONS

Abnormal HRT plus TWA is more common in CAD patients with DM compared with the patients without DM and is related to the severity of LV dysfunction.

CLINICAL TRIAL REGISTRATION INFORMATION

http://www.clinicaltrials.gov, NCT01426685; http://www.clinicaltrials.gov, NCT00673842.

Vagus nerve stimulation reduces cardiac electrical instability assessed by quantitative T-wave alternans analysis in patients with drug-resistant focal epilepsy

OBJECTIVE

The cardiac component of risk for sudden unexpected death in epilepsy (SUDEP) and alterations in cardiac risk by vagus nerve stimulation (VNS) are not well understood. We determined changes in T-wave alternans (TWA), a proven noninvasive marker of risk for sudden cardiac death in patients with cardiovascular disease, and heart rate variability (HRV), an indicator of autonomic function, in association with VNS in patients with drug-resistant focal epilepsy.

METHODS

Ambulatory 24-h electrocardiograms (N = 9: ages 29-63, six males) were analyzed.

RESULTS

Mean TWA during the interictal period was 37 ± 3.1 μV (mean ± SEM) in lead V1 for nine patients monitored following implantation of the VNS system (n = 7) or battery change (n = 2). Of these, six patients also monitored prior to implantation (n = 5) or battery change (n = 1) showed abnormally high TWA levels pre-VNS (60.0 ± 4.3 μV), which were significantly reduced by 24.3 μV (to 35.7 ± 4.8 μV, p = 0.02) after VNS settings were adjusted for desired clinical response. TWA in four (67%) of the six patients was reduced in association with VNS to levels below the 47-μV cut point of abnormality. The decrease in TWA was correlated with VNS intensity (r = 0.88, p < 0.02). In addition, low-frequency HRV was reduced by 60% (805.61 ± 253.96 to 323.49 ± 102.74 msec(2) , p = 0.05) and low-to high-frequency HRV ratio by 32% (3.34 ± 0.57 to 2.26 ± 0.31, p = 0.025), indicating a change in autonomic balance in favor of parasympathetic dominance.

SIGNIFICANCE

This is the first report that elevated levels of TWA in patients with drug-refractory partial-onset seizures were reduced in association with VNS, potentially by improving sympathetic/parasympathetic balance. VNS may have a cardioprotective role at stimulation settings typically used for seizure control. These findings indicate the utility of TWA for tracking improvement in cardiac status in this population.

Dependency of exercise-induced T-wave alternans predictive power for the occurrence of ventricular arrhythmias from heart rate

BACKGROUND

T-wave alternans (TWA) is a noninvasive index of risk for the occurrence of ventricular arrhythmias. It is known that TWA amplitude (TWAA) increases with heart rate (HR) but how the TWA predictive power varies with HR remains unknown. Thus, the aim of this study was to evaluate the dependency of exercise-induced TWA predictive power for the occurrence of ventricular arrhythmias from HR.

METHODS

TWA was identified using our HR adaptive match filter in exercise ECGs from 248 patients with implanted cardiac defibrillator (ICD), of which 72 developed ventricular tachycardia and/or fibrillation during the 4 year follow-up (ICD_Cases) and 176 did not (ICD_Controls). TWA predictive power was evaluated at HRs from 80 to 120 bpm by computing the area under the receiver operating characteristic curve (AUC) obtained using the maximum TWAA (maxTWAA) and the TWAA ratio (TWAAratio; i.e., the ratio between TWAA at a specific HR and at 80 bpm).

RESULTS

TWAA increased with HR. At 80 bpm maxTWAA was lower than at 120 bpm in both ICD_Cases (22 μV vs 41 μV; P < 10(-2) ) and ICD_ Controls (16 μV vs 36 μV; P < 10(-4) ). However, only at 80 bpm ICD_Cases showed significantly higher maxTWAA than ICD_Controls (AUC = 0.6486; P = 0.0080). TWAAratio was higher in ICD_Controls than ICD_Cases for all HR but 120 bpm, and its predictive power was maximum at 115 bpm (AUC = 0.6914; P < 0.05).

CONCLUSIONS

Exercise-induced TWA predictive power for the occurrence of ventricular arrhythmias, quantified using both maxTWAA and TWAAratio, was higher at low rather than at high HR.

Sudden paradoxical QT-interval prolongation exacerbating T-wave alternans in a patient with type 3 long QT syndrome

We report a case with type 3 congenital long QT syndrome, who exhibited a sudden paradoxical QT-interval prolongation during a progressive increase in heart rate, which exacerbated T-wave alternans.

Time-domain T-wave alternans is strongly associated with a history of ventricular fibrillation in patients with Brugada syndrome

AIMS

T-wave alternans (TWA) is an indicator of vulnerability to ventricular arrhythmias and is useful for predicting sudden cardiac death (SCD) in patients with various structural heart diseases. We evaluated whether high levels of time-domain TWA on ambulatory ECG (AECG) are associated with a history of ventricular fibrillation (VF) in Brugada syndrome (BrS) patients.

METHODS AND RESULTS

We examined the associations among VF history, family history of SCD, spontaneous type 1 electrocardiogram (ECG), late potentials, VF induction by programmed electrical stimulation, and TWA in 45 BrS patients (44 males; mean age, 45 ± 15 years). TWA analyzed from 24-h AECG recordings using the modified moving average method was positive in 13 of 43 patients (30%). Patients with a history of VF had a significantly higher incidence of a positive TWA test (82% vs. 13%; P < 0.001) and spontaneous type 1 ECG (92% vs. 38%; P = 0.007) than those without VF history. Multivariate analysis indicated that positive TWA (OR 7.217; 95% CI 2.503-35.504; P = 0.002) and spontaneous type 1 ECG (OR 5.530; 95% CI 1.651-34.337; P = 0.020) were closely associated with VF history. Spontaneous type 1 ECG had high sensitivity (92%) but low specificity (63%). Positive TWA was a reliable marker with high sensitivity and specificity (82% and 88%, respectively).

CONCLUSION

Elevated time-domain TWA on AECG confirms arrhythmia risk in symptomatic BrS patients without the need for provocative stimuli.

A simulation of T-wave alternans vectocardiographic representation performed by changing the ventricular heart cells action potential duration

The presence of T wave alternans (TWA) in the surface ECG signals has been recognized as a marker of electrical instability, and is hypothesized to be related to patients at increased risk for ventricular arrhythmias. In this paper we present a TWA simulation study. The TWA phenomenon was simulated by changing the duration of the ventricular heart cells action potential. The magnitude was calculated in the surface ECG with the use of the time domain method. The spatially concordant TWA, where during one heart beat all ventricular cells display a short-duration action potential and during the next beat they exhibit a long-duration action potential, as well as the discordant TWA, where at least one region is out of phase, was simulated. The vectocardiographic representation was employed. The obtained results showed a high level of T-loop pattern and location disturbances connected to the discordant TWA simulation in contrast to the concordant one. This result may be explained by the spatial heterogeneity of the ventricular repolarization process, which could be higher for the discordant TWA than for the concordant TWA.