Combined assessment of T-wave alternans and late potentials used to predict arrhythmic events after myocardial infarction. A prospective study

Clinical Features of Brugada Syndrome Patients With SCN5A Variants

BACKGROUND

SCN5A is the most common susceptibility gene in patients with Brugada syndrome (BrS); however, the interpretation and management of benign or variants of unknown clinical significance (VUS) in SCN5A remains a challenge despite the availability of genetic testing.

OBJECTIVE

This study aimed to investigate the relationship between the SCN5A variants and clinical symptoms of BrS patients.

METHODS

We resequenced the SCN5A gene in 239 patients diagnosed with BrS at Hiroshima University Hospital and analyzed the association between the SCN5A variants and clinical features, 12-lead electrocardiography (ECG) parameters, and signal-averaged ECG.

RESULTS

Overall, 84 SCN5A variants were identified: 55 benign, 7 pathogenic, and 22 VUS. No significant difference in the incidence of previous cardiac events was observed between patients with and without SCA5A benign variants. The female proportion was higher in BrS patients with SCN5A VUS or pathogenic variants. Moreover, the symptomatic proportion was higher in BrS patients with SCN5A VUS or pathogenic variants than in those without SCN5A variants. Multivariate analyses revealed that the presence of SCN5A pathogenic variants, longer r-J intervals in lead V1, and the presence of fragmented QRS were independently associated with cardiac events in BrS patients, and that positive late potentials, longer LAS40, and lower RMS40 were significantly associated with symptomatic BrS in patients carrying SCN5A VUS.

CONCLUSIONS

SCN5A pathogenic variants were found to be independent risk factors for cardiac events in BrS patients. Although SCN5A VUS was not an independent risk factor for cardiac events, proportion of symptomatic patients was higher in BrS patients with SCN5A VUS than in those without SCN5A variants. In BrS patients with SCN5A VUS, the signal-averaged ECG was the key to the risk stratification for cardiac events.

Clinical phenotypes in acute and chronic infarction explained through human ventricular electromechanical modelling and simulations

Sudden death after myocardial infarction (MI) is associated with electrophysiological heterogeneities and ionic current remodelling. Low ejection fraction (EF) is used in risk stratification, but its mechanistic links with pro-arrhythmic heterogeneities are unknown. We aim to provide mechanistic explanations of clinical phenotypes in acute and chronic MI, from ionic current remodelling to ECG and EF, using human electromechanical modelling and simulation to augment experimental and clinical investigations. A human ventricular electromechanical modelling and simulation framework is constructed and validated with rich experimental and clinical datasets, incorporating varying degrees of ionic current remodelling as reported in literature. In acute MI, T-wave inversion and Brugada phenocopy were explained by conduction abnormality and local action potential prolongation in the border zone. In chronic MI, upright tall T-waves highlight large repolarisation dispersion between the border and remote zones, which promoted ectopic propagation at fast pacing. Post-MI EF at resting heart rate was not sensitive to the extent of repolarisation heterogeneity and the risk of repolarisation abnormalities at fast pacing. T-wave and QT abnormalities are better indicators of repolarisation heterogeneities than EF in post-MI.

Native mechano-regulative matrix properties stabilize alternans dynamics and reduce spiral wave stabilization in cardiac tissue

The stability of wave conduction in the heart is strongly related to the proper interplay between the electrophysiological activation and mechanical contraction of myocytes and extracellular matrix (ECM) properties. In this study, we statistically compare bioengineered cardiac tissues cultured on soft hydrogels ( E ≃ 12 kPa) and rigid glass substrates by focusing on the critical threshold of alternans, network-physiological tissue properties, and the formation of stable spiral waves that manifest after wave breakups. For the classification of wave dynamics, we use an improved signal oversampling technique and introduce simple probability maps to identify and visualize spatially concordant and discordant alternans as V- and X-shaped probability distributions. We found that cardiac tissues cultured on ECM-mimicking soft hydrogels show a lower variability of the calcium transient durations among cells in the tissue. This lowers the likelihood of forming stable spiral waves because of the larger dynamical range that tissues can be stably entrained with to form alternans and larger spatial spiral tip movement that increases the chance of self-termination on the tissue boundary. Conclusively, we show that a dysfunction in the excitation-contraction coupling dynamics facilitates life-threatening arrhythmic states such as spiral waves and, thus, highlights the importance of the network-physiological interplay between contractile myocytes and the ECM.

A Comprehensive Review on the Electrocardiographic Manifestations of Cardiac Sarcoidosis: Patterns and Prognosis

PURPOSE OF REVIEW

Cardiac sarcoidosis (CS) refers to cardiac involvement in sarcoidosis and is usually associated with worse outcomes. This comprehensive review aims to elucidate the electrocardiographic (ECG) signs and features associated with CS, as well as examine modern techniques and their importance in CS evaluation.

RECENT FINDINGS

The exact pathogenesis of CS is still unclear, but it stems from an abnormal immunological response triggered by environmental factors in individuals with genetic predisposition. CS presents with non-cardiac symptoms; however, conduction system abnormalities are common in patients with CS. The most common electrocardiographic (ECG) signs include atrioventricular blocks and ventricular tachyarrhythmia. Distinct patterns, such as fragmented QRS complexes, T-wave alternans, and bundle branch blocks, are critical indicators of myocardial involvement. The application of advanced ECG techniques such as signal-averaged ECG, Holter monitoring, wavelet-transformed ECG, microvolt T-wave alternans, and artificial intelligence-supported analysis holds promising outcomes for opportune detection and monitoring of CS. Timely utilisation of inexpensive and readily available ECG possesses the potential to allow early detection and intervention for CS. The integration of artificial intelligence models into ECG analysis is a promising approach for improving the ECG diagnostic accuracy and further risk stratification of patients with CS.

Diurnal Variation in and Optimal Time to Measure Holter-Based Late Potentials to Predict Lethal Arrhythmia after Myocardial Infarction

Background and Objectives: Holter-based late potentials (LPs) are useful for predicting lethal arrhythmias in organic cardiac diseases. Although Holter-based LPs exhibit diurnal variation, no studies have evaluated the optimal timing of LP measurement over 24 h for predicting lethal arrhythmia that leads to sudden cardiac death. Thus, this study aimed to validate the most effective timing for Holter-based LP testing and to explore factors influencing the diurnal variability in LP parameters. Materials and Methods: We retrospectively analyzed 126 patients with post-myocardial infarction (MI) status and 60 control participants who underwent high-resolution Holter electrocardiography. Among the 126 post-MI patients, 23 developed sustained ventricular tachycardia (VT) (the MI-VT group), while 103 did not (the MI-non-VT group) during the observation period. Holter-based LPs were measured at 0:00, 4:00, 8:00, 12:00, 16:00, and 20:00, and heart rate variability analysis was simultaneously performed to investigate factors influencing the diurnal variability in LP parameters. Results: Holter-based LP parameters showed diurnal variation with significant deterioration at night and improvement during the day. Assessment at the time with the longest duration of low-amplitude signals < 40 μV in the filtered QRS complex terminus (LAS40) gave the highest receiver operating characteristics curve (area under the curve, 0.659) and the highest odds ratio (3.75; 95% confidence interval, 1.45-9.71; p = 0.006) for predicting VT. In the multiple regression analysis, heart rate and noise were significant factors affecting the LP parameters in the MI-VT and control groups. In the non-VT group, the LP parameters were significantly influenced by noise and parasympathetic heart rate variability parameters, such as logpNN50. Conclusions: For Holter-based LP measurements, the test accuracy was higher when the LP was measured at the time of the highest or worst value of LAS40. Changes in autonomic nervous system activity, including heart rate, were factors influencing diurnal variability. Increased parasympathetic activity or bradycardia may exacerbate Holter-based LP parameters.

T-Wave Analysis on the 24 h Holter ECG Monitoring as a Predictive Assessment of Major Adverse Cardiovascular Events in Patients with Myocardial Infarction: A Literature Review and Future Perspectives

Myocardial ischemia is a pathophysiological state characterized by inadequate perfusion of the myocardium, resulting in an imbalance between myocardial oxygen demand and supply. It is most commonly caused by coronary artery disease, in which atherosclerotic plaques lead to luminal narrowing and reduced blood flow to the heart. Myocardial ischemia can manifest as angina pectoris or silent myocardial ischemia and can progress to myocardial infarction or heart failure if left untreated. Diagnosis of myocardial ischemia typically involves a combination of clinical evaluation, electrocardiography and imaging studies. Electrocardiographic parameters, as assessed by 24 h Holter ECG monitoring, can predict the occurrence of major adverse cardiovascular events in patients with myocardial ischemia, independent of other risk factors. The T-waves in patients with myocardial ischemia have prognostic value for predicting major adverse cardiovascular events, and their electrophysiological heterogeneity can be visualized using various techniques. Combining the electrocardiographic findings with the assessment of myocardial substrate may offer a better picture of the factors that can contribute to cardiovascular death.

Thyroid hormones regulate cardiac repolarization and QT-interval related gene expression in hiPSC cardiomyocytes

Prolongation of cardiac repolarization (QT interval) represents a dangerous and potentially life-threatening electrical event affecting the heart. Thyroid hormones (THs) are critical for cardiac development and heart function. However, little is known about THs influence on ventricular repolarization and controversial effects on QT prolongation are reported. Human iPSC-derived cardiomyocytes (hiPSC-CMs) and multielectrode array (MEA) systems were used to investigate the influence of 3,3',5-triiodo-L-Thyronine (T3) and 3,3',5,5'-tetraiodo-L-Thyronine (T4) on corrected Field Potential Duration (FPDc), the in vitro analog of QT interval, and on local extracellular Action Potential Duration (APD). Treatment with high THs doses induces a significant prolongation of both FPDc and APD, with the strongest increase reached after 24 h exposure. Preincubation with reverse T3 (rT3), a specific antagonist for nuclear TH receptor binding, significantly reduces T3 effects on FPDc, suggesting a TRs-mediated transcriptional mechanism. RNA-seq analysis showed significant deregulation in genes involved in cardiac repolarization pathways, including several QT-interval related genes. In conclusion, long-time administration of high THs doses induces FPDc prolongation in hiPSC-CMs probably through the modulation of genes linked to QT-interval regulation. These results open the way to investigate new potential diagnostic biomarkers and specific targeted therapies for cardiac repolarization dysfunctions.

Optical Ultrastructure of Large Mammalian Hearts Recovers Discordant Alternans by In Silico Data Assimilation

Understanding and predicting the mechanisms promoting the onset and sustainability of cardiac arrhythmias represent a primary concern in the scientific and medical communities still today. Despite the long-lasting effort in clinical and physico-mathematical research, a critical aspect to be fully characterized and unveiled is represented by spatiotemporal alternans patterns of cardiac excitation. The identification of discordant alternans and higher-order alternating rhythms by advanced data analyses as well as their prediction by reliable mathematical models represents a major avenue of research for a broad and multidisciplinary scientific community. Current limitations concern two primary aspects: 1) robust and general-purpose feature extraction techniques and 2) in silico data assimilation within reliable and predictive mathematical models. Here, we address both aspects. At first, we extend our previous works on Fourier transformation imaging (FFI), applying the technique to whole-ventricle fluorescence optical mapping. Overall, we identify complex spatial patterns of voltage alternans and characterize higher-order rhythms by a frequency-series analysis. Then, we integrate the optical ultrastructure obtained by FFI analysis within a fine-tuned electrophysiological mathematical model of the cardiac action potential. We build up a novel data assimilation procedure demonstrating its reliability in reproducing complex alternans patterns in two-dimensional computational domains. Finally, we prove that the FFI approach applied to both experimental and simulated signals recovers the same information, thus closing the loop between the experiment, data analysis, and numerical simulations.

Brugada syndrome genetics is associated with phenotype severity

Aims 

Brugada syndrome (BrS) is associated with an increased risk of sudden cardiac death due to ventricular tachycardia/fibrillation (VT/VF) in young, otherwise healthy individuals. Despite SCN5A being the most commonly known mutated gene to date, the genotype–phenotype relationship is poorly understood and remains uncertain. This study aimed to elucidate the genotype–phenotype correlation in BrS.

Methods and results

Brugada syndrome probands deemed at high risk of future arrhythmic events underwent genetic testing and phenotype characterization by the means of epicardial arrhythmogenic substrate (AS) mapping, and were divided into two groups according to the presence or absence of SCN5A mutation. Two-hundred probands (160 males, 80%; mean age 42.6 ± 12.2 years) were included in this study. Patients harbouring SCN5A mutations exhibited a spontaneous type 1 pattern and experienced aborted cardiac arrest or spontaneous VT/VF more frequently than the other subjects. SCN5A-positive patients exhibited a larger epicardial AS area, more prolonged electrograms and more frequently observed non-invasive late potentials. The presence of an SCN5A mutation explained >26% of the variation in the epicardial AS area and was the strongest predictor of a large epicardial area.

Conclusion 

In BrS, the genetic background is the main determinant for the extent of the electrophysiological abnormalities. SCN5A mutation carriers exhibit more pronounced epicardial electrical abnormalities and a more aggressive clinical presentation. These results contribute to the understanding of the genetic determinants of the BrS phenotypic expression and provide possible explanations for the varying degrees of disease expression.

Detection of cardiac involvement in pulmonary sarcoidosis using high-resolution Holter electrocardiogram

BACKGROUND

Early detection of cardiac involvement in patients with sarcoidosis is important but currently unresolved. The aim of this study was to elucidate the utility of frequency domain microvolt T-wave alternans (TWA), signal-averaged ECG (SAECG), and heart rate turbulence (HRT) using 24-hour Holter ECG for detecting cardiac involvement in patients with pulmonary sarcoidosis.

METHODS

This study consisted of consecutive 40 pulmonary sarcoidosis patients (11 males, 62 ± 13 years) who underwent 24-hour Holter monitoring with and without cardiac involvement. All patients underwent frequency domain TWA, SAECG, and HRT using 24-hour Holter monitoring. Patients with atrial fibrillation pacing or wide QRS electrocardiogram were excluded.

RESULTS

After 14 patients were excluded, a total of 26 patients (six males, 59 ± 14 years) were evaluated. Seven patients had cardiac involvement (cardiac sarcoidosis [CS] group). On the Holter SAECG, duration of low-amplitude signals <40 μV in the terminal filtered QRS complex (LAS40) was significantly higher, and root mean square voltage of the terminal 40 ms of the filtered QRS complex (RMS40) was significantly lower in the CS group compared with the non-CS group (LAS40: 61.4 ± 35.9 vs 37.6 ± 9.2 ms; P = .018, RMS40: 11.4 ± 10.3 vs 23.6 ± 13.2 ms; P = .023). Prevalence of positive late potential (LP) was also significantly higher in the CS group than that in the non-CS group (85.7% vs 31.5%; P = .026). The sensitivity, specificity, positive, and negative predictive values of LP for identifying patients with cardiac involvement were 85.7%, 68.4%, 50.0%, and 92.8%, respectively.

CONCLUSION

Holter SAECG may be useful for detecting cardiac involvement in patients with pulmonary sarcoidosis.

Non-invasive assessment of the arrhythmogenic substrate in Brugada syndrome using signal-averaged electrocardiogram: clinical implications from a prospective clinical trial

AIMS

Brugada syndrome (BrS) represents a major cause of sudden cardiac death in young individuals. The risk stratification to forecast future life-threatening events is still controversial. Non-invasive assessment of late potentials (LPs) has been proposed as a risk stratification tool. However, their nature in BrS is still undetermined. The purpose of this study is to assess the electrophysiological determinants of non-invasive LPs.

METHODS AND RESULTS

Two hundred and fifty consecutive patients with (Group 1, n = 96) and without (Group 2, n = 154) BrS-related symptoms were prospectively enrolled in the registry. Signal-averaged electrocardiogram (SAECG) was performed in all subjects before undergoing epicardial mapping. Group 1 patients exhibited larger arrhythmogenic substrates (AS; 5.8 ± 2.8 vs. 2.6 ± 2.1 cm2, P < 0.001) with more delayed potentials (220.4 ± 46.0 vs. 186.7 ± 42.3 ms, P < 0.001). Late potentials were present in 82/96 (85.4%) Group 1 and in 31/154 (20.1%) Group 2 individuals (P < 0.001). Patients exhibiting LPs had more frequently a spontaneous Type 1 pattern (30.1% vs. 10.9%, P < 0.001), SCN5A mutation (34.5% vs. 21.2%, P = 0.02), and exhibited a larger AS with longer potentials (5.8 ± 2.7 vs. 2.2 ± 1.7 cm2; 231.2 ± 37.3 vs. 213.8 ± 39.0 ms; P < 0.001, respectively). Arrhythmogenic substrate dimension was the strongest predictor of the presence of LPs (odds ratio 1.9; P < 0.001). An AS area of at least 3.5 cm2 identified patients with LPs (area under the curve 0.88, 95% confidence interval 0.843-0.931; P < 0.001) with a sensitivity of 86%, specificity 88%, positive predictive value 85%, and negative predictive value 89%.

CONCLUSION

The results of this study support the role of the epicardial AS as an electrophysiological determinant of non-invasive LPs, which may serve as a tool in the non-invasive assessment of the BrS substrate, as SAECG-LPs could be considered an expression of the abnormal epicardial electrical activity.

ClinicalTrials.gov number (NCT02641431; NCT03106701).

Combined evaluation of ambulatory-based late potentials and nonsustained ventricular tachycardia to predict arrhythmic events in patients with previous myocardial infarction: A Japanese noninvasive electrocardiographic risk stratification of sudden cardiac death (JANIES) substudy

Background

Noninvasive electrocardiographic (ECG) markers are promising arrhythmic risk stratification tools for identifying sudden cardiac death. However, little is known about the usefulness of noninvasive ECG markers derived from ambulatory ECGs (AECG) in patients with previous myocardial infarction (pMI). We aimed to determine whether the ECG markers derived from AECG can predict serious cardiac events in patients with pMI.

Methods

We prospectively analyzed 104 patients with pMI (88 males, age 66 ± 11 years), evaluating late potentials (LPs), heart rate turbulence, and nonsustained ventricular tachycardia (NSVT) derived from AECG. The primary endpoint was the documentation of ventricular fibrillation or sustained ventricular tachycardia.

Results

Eleven patients reached the primary endpoint during a follow‐up period of 25 ± 9.5 months. Of the 104 patients enrolled in this study, LP positive in worst values (w‐LPs) and NSVT were observed in 25 patients, respectively. In the arrhythmic event group, the worst LP values and/or NSVT were found in eight patients (7.6%). The positive predictive and negative predictive values of the combined assessment with w‐LPs and NSVT were 56% and 94%, respectively, for predicting ventricular lethal arrhythmia. Kaplan–Meier analysis demonstrated that the combination of w‐LPs and NSVT had a poorer event‐free period than negative LPs (p < .0001). In the multivariate analysis, the combined assessment of w‐LPs and NSVT was a significant predictor of arrhythmic events (hazard ratio = 14.1, 95% confidence intervals: 3.4–58.9, p < .0001).

Conclusion

Combined evaluation of w‐LPs and NSVT was a powerful risk stratification strategy for predicting arrhythmia that can lead to sudden cardiac death in patients with pMI.

Qt Dispersion and Signal-Averaged Electrocardiogram in Hemodialysis and Capd Patients

Objective

The aim of this study was to compare QT dispersion (QTd) and signal-averaged electrocardiogram (SA-ECG) parameters that may predict risk of malignant arrhythmias in patients on hemodialysis (HD), on continuous ambulatory peritoneal dialysis (CAPD), and in controls.

Setting

Controlled cross-sectional study in a tertiary- care setting.

Patients

28 HD (M/F 18/10; mean age 32 ± 9 years), 29 CAPD (M/F 17/12; mean age 34 ± 10 years), and 29 healthy controls (M/F 17/12; mean age 32 ± 8 years) were included.

Interventions

On ECG, minimum (QTmin) and maximum (QTmax) QT duration and their difference (QTd) were measured. In SA-ECG, duration of filtered QRS, HFLA signals less than 40 μV, and RMS voltage (40 ms) were also measured.

Results

Higher serum Ca2+ and lower K+ levels were found in CAPD compared to HD. All QT parameters were increased in HD and CAPD compared to controls. QT dispersion was significantly prolonged in HD compared to CAPD. In HD, QTd was correlated with left ventricular (LV) mass index ( r = 0.53, p = 0.004), but not in CAPD ( r = -0.09, p = 0.63). QT dispersion was significantly prolonged in patients with LV hypertrophy compared to patients without hypertrophy on HD (68 ± 18 ms vs 49 ± 18 ms, p = 0.008). In the analysis of SA-ECG, 3 of the 28 (11%) HD and 2 of the 29 (7%) CAPD patients had abnormal late potentials. Patients on HD and CAPD had significantly higher filtered-QRS duration compared to controls (105 ± 15 ms and 104 ± 12 ms vs 95 ± 5 ms, respectively, p = 0.04). Patients with LV hypertrophy had higher filtered-QRS duration compared to patients without hypertrophy (109 ± 12 ms vs 95 ± 8 ms, p < 0.001).

Conclusion

Dialysis patients had prolonged QTd and increased filtered-QRS duration in SA-ECG compared to controls. Patients on HD had longer QTd than patients on CAPD. QTd has been correlated to LV mass index in HD, but not in CAPD. This difference might be due to the effect of different dialysis modalities on electrolytes, especially the higher serum Ca2+ levels.

The presence of late potentials after percutaneous coronary intervention for the treatment of acute coronary syndrome as a predictor for future significant cardiac events resulting in re-hospitalization

INTRODUCTION

We previously reported that LP positive patients after percutaneous coronary intervention (PCI) had higher rate of re-hospitalization in the small-scale study (135 patients). In this study, we evaluated correlation between LP and later cardiac events leading to re-hospitalization more extensively in greater population.

METHODS AND RESULTS

A 24-h high-resolution (HR) ambulatory electrocardiogram (ECG) was performed in 421 patients that received PCI for the treatment of acute coronary syndrome (ACS) within 30 days. Various baseline characteristics and post-PCI ECG parameters including LP were examined for correlation with later re-hospitalization. LP was evaluated based on 3 different conditions, i.e., the worst, mean and best values, from 24-h signal-averaged QRS wave data. During the post-PCI follow-up period (611 ± 489.0 days), 90 patients were re-hospitalized due to cardiac events. Multivariate analysis identified only positive LP based on the worst value as an independent predictor for re-hospitalization with OR 2.26. Most of re-hospitalization cases (>75%) were predominantly attributed to ischemic events. LP positive population had significantly higher incidences of ischemic events as well as overall re-hospitalization compared to LP negative population. The predictive power of LP was decreased when it was combined with other variables. The receiver operating characteristic analysis determined the LP cut-off values consistent with the LP positive criteria previously reported and standardized.

CONCLUSION

The presence of LP in the 24-h HR ambulatory ECG post-PCI was an independent predictor for a risk of re-hospitalization due to ischemic cardiac events in ACS patients.

Predictive Score for Identifying Survival and Recurrence Risk Profiles in Patients Undergoing Ventricular Tachycardia Ablation: The I-VT Score

BACKGROUND

Several distinct risk factors for arrhythmia recurrence and mortality following ventricular tachycardia (VT) ablation have been described. The effect of concurrent risk factors has not been assessed so far; thus, it is not yet possible to estimate these risks for a patient with several comorbidities. The aim of the study was to identify specific risk groups for mortality and VT recurrence using the Survival Tree (ST) analysis method.

METHODS

In 1251 patients 16 demographic, clinical and procedure-related variables were evaluated as potential prognostic factors using ST analysis using a recursive partitioning algorithm that searches for relationships among variables. Survival time and time to VT recurrence in groups derived from ST analysis were compared by a log-rank test. A random forest analysis was then run to extract a variable importance index and internally validate the ST models.

RESULTS

Left ventricular ejection fraction, implantable cardioverter defibrillator/cardiac resynchronization device, previous ablation were, in hierarchical order, identified by ST analysis as best predictors of VT recurrence, while left ventricular ejection fraction, previous ablation, Electrical storm were identified as best predictors of mortality. Three groups with significantly different survival rates were identified. Among the high-risk group, 65.0% patients were survived and 52.1% patients were free from VT recurrence; within the medium- and low-risk groups, 84.0% and 97.2% patients survived, 72.4% and 88.4% were free from VT recurrence, respectively.

CONCLUSIONS

Our study is the first to derive and validate a decisional model that provides estimates of VT recurrence and mortality with an effective classification tree. Preprocedure risk stratification could help optimize periprocedural and postprocedural care.

Diurnal variation of frequency domain T-wave alternans on 24-hour ambulatory electrocardiogram in subjects without heart disease: Significant effect of autonomic nervous activity of the heart

BACKGROUND

T-wave alternans (TWA) is a risk stratification predictor for sudden cardiac death. However, little is known about the diurnal variation of TWA. Whether TWA are affected by heart rate (HR) or cardiac autonomic nervous activity in the subjects without significant structural heart disease in daily life is not fully understood. Thus, this study was aimed to clarify these issues.

METHODS

Frequency domain (FD)-TWA analysis was conducted in 47 subjects without significant structural heart disease using 24-hr ambulatory electrocardiogram (AECG). Measurement of heart rate variability (HRV) was performed in order to evaluate the autonomic activity of the heart. The maximum FD-TWA value in each period was measured four times per day (A, 00:00-6:00 hr; B, 06:00-12:00 hr; C, 12:00-18:00 hr; D, 18:00-24:00 hr). Correlations between FD-TWA and either HR or HRV parameters (LF/HF, LFnu, HFnu, SDNN, CVNN, pNN50) were analyzed in each period (A-D).

RESULTS

There was diurnal variation of FD-TWA (median, inter-quartile range [IQR]: A, 8.2 [6.5, 10.6] μV; B, 10.1 [8.4, 15.0] μV; C, 17.6 [12.3, 25.0] μV: D, 11.9 [9.1, 19.9] μV; p < 0.0001). Maximum FD-TWA had positive correlations with HR and LF/HF (HR, r = 0.496, p < 0.0001; LF/HF, r = 0.414, p = 0.004), while FD-TWA had a negative correlation with HFnu (r = -0.291, p = 0.048). On multiple linear regression analysis, HR had an independent effect on log FD-TWA amplitude (β = 0.461, p = 0.001).

CONCLUSIONS

FD-TWA has marked diurnal variation in the daily life of the subjects without significant structural heart disease. This variation could be more strongly affected by HR than the HRV indices.

Prevalence of late potentials on signal-averaged ECG in patients with psychiatric disorders

BACKGROUND

Sudden cardiac death (SCD) occurs three times more often in psychiatric patients than in the general population. QRS fragmentation (QRSfr) and signal-averaged electrocardiography (SAECG) are simple, inexpensive, readily available tools for detecting the presence of abnormal depolarization and late potentials (LPs) in these patients, a result of either the underlying disease or treatment.

METHODS

Frequency of LP detection by SAECG and QRSfr was studied in 52 psychiatric patients and compared with 30 healthy (without known structural heart disease or occurrence of ventricular arrhythmia) controls. Patients were then prospectively followed up and incidence of SCD was recorded.

RESULTS

LP prevalence was significantly higher in patients than in controls (16/52-31% vs 2/30-7%, p=0.012), while QRSfr was similar between these two groups (p=0.09). Of the LP presence criteria, the root mean square value at terminal 40msec of the QRS (RMS40) was significantly lower in patients (32μV, SD=19μV, vs 46μV, SD=32μV, p=0.015). Among patients, no differences were noted between the LP positive and negative groups regarding age, sex, number of medications, class of antipsychotics and defined daily doses. Mean follow-up was 46months (SD=11) and during it 3 patients suffered SCD. Although 2 SCD victims had both LPs and QRSfr concurrently present, neither of them, nor their simultaneous presence could definitely account for the events.

CONCLUSIONS

LP prevalence in psychiatric patients was significantly higher than in controls. SAECG performance was feasible in all cases and constitutes a readily available tool for assessing myocardial electrophysiological alterations in this patient group.

12-lead electrocardiogram features of arrhythmic risk: A focus on early repolarization

The 12-lead electrocardiogram (ECG) is still the most used tool in cardiology clinical practice. Considering its easy accessibility, low cost and the information that it provides, it remains the starting point for diagnosis and prognosis. More specifically, its ability to detect prognostic markers for sudden cardiac death due to arrhythmias by identifying specific patterns that express electrical disturbances of the heart muscle, which may predispose to malignant arrhythmias, is universally recognized. Alterations in the ventricular repolarization process, identifiable on a 12-lead ECG, play a role in the genesis of ventricular arrhythmias in different cardiac diseases. The aim of this paper is to focus the attention on a new marker of arrhythmic risk, the early repolarization pattern in order to highlight the prognostic role of the 12-lead ECG.

Microvolt T-wave alternans in young myocardial infarction patients with preserved cardiac function treated with single-vessel primary percutaneous coronary intervention

Introduction

Myocardial infarction continues to be the most important cause of morbidity and mortality, and recently this disease has begun to be seen commonly at young ages. In our study we aimed to assess microvolt T-wave alternans in young patients who had ST segment elevation myocardial infarction with preserved left ventricular function and who underwent single-vessel revascularization.

Material and methods

We enrolled 108 consecutive patients (age: 39.5 ±4.1) with ST segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention and 43 patients (age: 38.5 ±3.7) with normal coronary angiograms as a control group. The myocardial infarction patients were younger than 45 and had a preserved left ventricular ejection fraction. They were divided into three groups according to the culprit artery. The microvolt T-wave alternans (MTWA) values were calculated an average of 12 months after the primary percutaneous coronary intervention using the modified moving average method.

Results

The MTWA positivity was significantly higher in the STEMI group compared to the controls (p < 0.001). It was also significantly higher in STEMI patients with left anterior descending artery lesions compared to patients with circumflex artery and right coronary artery lesions (p = 0.013). Moreover, the culprit artery was independent predictor of MTWA positivity (p = 0.043).

Conclusions

In STEMI patients of a young age, MTWA positivity was higher than in healthy individuals, especially when the responsible vessel fed a wider region.

Arrhythmogenic Substrates in Sleep-Disordered Breathing with Arterial Hypertension

BACKGROUND

Sleep-disordered breathing (SDB) is highly associated with arterial hypertension (HT). Sympathetic hypertonia increases the risk of sudden cardiac death in patients with sleep apnea. This study aims to noninvasively investigate the electrophysiological features in SDB patients with and without arterial HT.

METHODS

Fifty-three patients with SDB were classified into two groups: SDB group and SDB + HT group. Twenty subjects with arterial HT were enrolled as controls (HT group). To assess arrhythmogenic vulnerability, high-resolution 24-hour ambulatory electrocardiograms were obtained for analyzing continuous late potential (LP), T-wave amplitude variability (TAV), and heart rate variability (HRV).

RESULTS

A higher incidence of positive LP was observed in the SDB + HT (85%) group than that observed in the SDB (50%) and HT (20%) groups (P < 0.01). TAV was highest in the SDB + HT group (78 μV) compared with the SDB (61 μV) and HT groups (42 μV; P < 0.01). Positive LP and TAV values were observed at night in the SDB + HT and SDB groups. The low-frequency/high-frequency of the HRV analysis was highest in the SDB + HT (4.7) group compared with that in the SDB (2.9) and HT (2.9) groups (P = 0.01).

CONCLUSION

Nocturnal LP, TAV, and HRV examinations were useful to investigate arrhythmogenesis. SDB patients with arterial HT showed a high prevalence of depolarization and repolarization abnormalities and relative sympathetic hyperactivity. This suggests that an electrophysiological instability is more prevalent in SDB patients with arterial HT.

Ventricular repolarization measures for arrhythmic risk stratification

Ventricular repolarization is a complex electrical phenomenon which represents a crucial stage in electrical cardiac activity. It is expressed on the surface electrocardiogram by the interval between the start of the QRS complex and the end of the T wave or U wave (QT). Several physiological, pathological and iatrogenic factors can influence ventricular repolarization. It has been demonstrated that small perturbations in this process can be a potential trigger of malignant arrhythmias, therefore the analysis of ventricular repolarization represents an interesting tool to implement risk stratification of arrhythmic events in different clinical settings. The aim of this review is to critically revise the traditional methods of static analysis of ventricular repolarization as well as those for dynamic evaluation, their prognostic significance and the possible application in daily clinical practice.

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.

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.

Quantitative T-wave alternans analysis for guiding medical therapy: an underexploited opportunity

Reducing the toll of sudden cardiac death (SCD) remains a major challenge in cardiology, as it is the leading cause of adult mortality in the industrially developed world, claiming 310,000 lives annually in the United States alone. The main contemporary noninvasive index of cardiovascular risk, left ventricular ejection fraction (LVEF), has not proved adequately reliable, as the majority of individuals who die suddenly have relatively preserved cardiac mechanical function. Monitoring of T-wave alternans (TWA), a beat-to-beat fluctuation in ST-segment or T-wave morphology, is an attractive approach to risk stratification on both scientific and clinical grounds, as this ECG phenomenon has been shown using the FDA-cleared Spectral and Modified Moving Average methods to assess risk for cardiovascular mortality including SCD in studies enrolling >12,000 individuals with depressed or preserved LVEF. The evidence supporting TWA as a therapeutic target is reviewed.

Improved modified moving average analysis of T-wave alternans using least squares-based curve fitting method

T-wave alternans (TWA) in surface electrocardiograph (ECG) signal is considered a marker of abnormal ventricular function which may be associated with ventricular tachycardia. Several methods have been developed in recent years to evaluate the important feature. One such method is known as modified moving average (MMA) analysis, which performs well for different levels of TWA, but it is sensitive to the noise in T-waves. In this paper we propose an improved MMA algorithm, which adds a stage of T-wave curve fitting for the MMA method before intermediate averaging. The curve fitting is performed by means of least square method technique. Our assessment study demonstrates the improved performance.

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.

Microvolt T-wave alternans predicts cardiac events after acute myocardial infarction in patients treated with primary percutaneous coronary intervention

BACKGROUND

Current risk stratification after acute myocardial infarction (MI) depends on left ventricular ejection fraction. Microvolt T-wave alternans (MTWA) is one of promising markers to predict cardiac events in patients after acute MI treated according to current guidelines.

METHODS

In this single center study, 112 consecutive patients with the first anterior ST-elevation MI undergoing PCI <12 hours from symptom onset, were enrolled prospectively. Demographics, established risk factors, myocardial contrast echocardiography (MCE) perfusion, index event data and MTWA were assessed. Composite cardiac events (CCE) defined as: death, recurrent MI, sustained ventricular tachycardia (sVT) or readmission for acute heart failure (HF) were recorded during follow-up.

RESULTS

MTWA test was negative in 76, positive in 18 and undetermined in 7 patients. MTWA negative patients had significantly higher LVEF at 30 days. At 4 years, 26 patients experienced CCE (10 died, 2 reinfarcted and 14 HF events). In multivariate Cox proportional hazard model maximum CKMB, non-negative MTWA and reduced LVEF made the best model to predict CCE. Four year CCE free survival was 77% and was significantly lower for non-negative MTWA (94% vs 50%, p<0.003).

CONCLUSIONS

Non-negative MTWA with infarct size index and reduced LVEF could predict cardiac events in patients with anterior STEMI treated with primary PCI. MTWA non-negative patients have significantly worse outcome.

Comparison of late potentials for 24 hours between Brugada syndrome and arrhythmogenic right ventricular cardiomyopathy using a novel signal-averaging system based on Holter ECG

BACKGROUND

Late potentials (LP) detected with signal-averaged ECGs are known to be useful in identifying patients at risk of Brugada syndrome (BS) and arrhythmogenic right ventricular cardiomyopathy (ARVC). Because the pathophysiology is clearly different between these disorders, we clarified the LP characteristics of these disorders.

METHODS AND RESULTS

This study included 15 BS and 12 ARVC patients and 20 healthy controls. All BS patients had characteristic ECG changes and symptomatic episodes. All ARVC patients had findings that were consistent with recent criteria. Three LP parameters (filtered QRS duration, root mean square voltage of the terminal 40 ms of the filtered QRS complex, and duration of low-amplitude signals [<40 µV] in the terminal, filtered QRS complex) were continuously measured for 24 hours using a novel Holter-based signal-averaged ECG system. The incidences of LP determination in BS (80%) and ARVC (91%) patients were higher than in healthy controls (5%; P<0.0001 in both) but did not differ between BS and ARVC patients. In BS patients, the dynamic changes of all LP parameters were observed, and they were pronounced at nighttime. On the contrary, these findings were not observed in ARVC patients. When the SD values of the 3 LP parameters (filtered QRS duration, root mean square voltage of the terminal 40 ms of the filtered QRS complex, and duration of low-amplitude signals [<40 µV] in the terminal, filtered QRS complex) over 24 hours were compared for the 2 patient groups, those values in BS patients were significantly greater than those in ARVC patients (P<0.0001 in all).

CONCLUSIONS

LP characteristics detected by the Holter-based signal-averaged ECG system over 24 hours differ between BS and ARVC patients. Dynamic daily variations of LPs were seen only in BS patients. This may imply that mechanisms of lethal ventricular arrhythmia in BS may be more correlated with autonomic abnormality than that of ARVC.

Relationship between late ventricular potentials and myocardial 123I-metaiodobenzylguanidine scintigraphy in patients with dilated cardiomyopathy with mild to moderate heart failure: results of a prospective study of sudden death events

PURPOSE

Late ventricular potentials (LPs) are considered to be useful for identifying patients with heart failure at risk of developing ventricular arrhythmias. (123)I-metaiodobenzylguanidine (MIBG) scintigraphy, which is used to evaluate cardiac sympathetic activity, has demonstrated cardiac sympathetic denervation in patients with malignant ventricular tachyarrhythmias. This study was undertaken to clarify the relationship between LPs and (123)I-MIBG scintigraphy findings in patients with dilated cardiomyopathy (DCM).

METHODS

A total of 56 patients with DCM were divided into an LP-positive group (n = 24) and an LP-negative group (n = 32). During the compensated period, the delayed heart/mediastinum count (H/M) ratio, delayed total defect score (TDS), and washout rate (WR) were determined from (123)I-MIBG images and plasma brain natriuretic peptide (BNP) concentrations were measured. Left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), and left ventricular ejection fraction (LVEF) were simultaneously determined by echocardiography.

RESULTS

LVEDV, LVESV, LVEF and plasma BNP concentrations were similar in the two groups. However, TDS was significantly higher (35 ± 8 vs. 28 ± 6, p < 0.005), the H/M ratio was significantly lower (1.57 ± 0.23 vs. 1.78 ± 0.20, p < 0.005), and the WR was significantly higher (60 ± 14% vs. 46 ± 12%, p < 0.001) in the LP-positive than in the LP-negative group. The average follow-up time was 4.5 years, and there were nine sudden deaths among the 56 patients (16.1%). In logistic regression analysis, the incidences of sudden death events were similar in those LP-negative with WR <50%, LP-negative with WR ≥ 50% and LP-positive with WR <50% (0%, 10.0% and 14.3%, respectively), but was significantly higher (41.2%) in those LP-positive with WR ≥ 50% (p < 0.01, p < 0.05, and p < 0.05, respectively).

CONCLUSION

The present study demonstrated that the values of cardiac (123)I-MIBG scintigraphic parameters were worse in LP-positive DCM patients than in LP-negative DCM patients. Furthermore, in LP-positive DCM patients with a high WR, the incidence of sudden death events was higher than that in other subgroups of DCM patients.

Crescendo in depolarization and repolarization heterogeneity heralds development of ventricular tachycardia in hospitalized patients with decompensated heart failure

BACKGROUND

A critical need exists for reliable warning markers of in-hospital life-threatening arrhythmias. We used a new quantitative method to track interlead heterogeneity of depolarization and repolarization to detect premonitory changes before ventricular tachycardia (VT) in hospitalized patients with acute decompensated heart failure.

METHODS AND RESULTS

Ambulatory ECGs (leads V(1), V(5), and aVF) recorded before initiation of drug therapy from patients enrolled in the PRECEDENT (Prospective Randomized Evaluation of Cardiac Ectopy with Dobutamine or Nesiritide Therapy) trial were analyzed. R-wave heterogeneity (RWH) and T-wave heterogeneity (TWH) were assessed by second central moment analysis and T-wave alternans (TWA) by modified moving average analysis. Of 44 patients studied, 22 had experienced episodes of VT (≥4 beats at heart rates >100 beats/min) following ≥120 minutes of stable sinus rhythm, and 22 were age- and sex-matched patients without VT. TWA increased from 18.6±2.1 μV (baseline, mean±SEM) to 27.9±4.6 μV in lead V(5) at 15 to 30 minutes before VT (P<0.05) and remained elevated until the arrhythmia occurred. TWA results in leads V(1) and aVF were similar. RWH and TWH were elevated from 164.1±33.1 and 134.5±20.6 μV (baseline) to 299.8±54.5 and 239.2±37.0 μV at 30 to 45 minutes before VT (P<0.05), respectively, preceding the crescendo in TWA by 15 minutes. Matched patients without VT did not display elevated RWH (185.5±29.4 μV) or TWH (157.1±27.2 μV) during the 24-hour period.

CONCLUSIONS

This investigation is the first clinical demonstration of the potential utility of tracking depolarization and repolarization heterogeneity to detect crescendos in electrical instability that could forewarn of impending nonsustained VT. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00270400.

T-wave alternans and heart rate variability: a comparison in patients with myocardial infarction with or without diabetes mellitus

BACKGROUND

The aim of this study was to investigate the differences in T-wave alternans (TWA) and heart rate variability (HRV) among patients with myocardial infarction with or without diabetes mellitus and the relationship between TWA and HRV.

METHODS

The study population included 133 patients: 59 patients with myocardial infarction (MI) (group post-MI without diabetes); 40 myocardial infarction with diabetes (group post-MI with diabetes); and 34 controls (group control). Cardiac autonomic neuropathy assessment was made using frequency domain (low-frequency [LF] power, high-frequency [HF] power, LF/HF) and time domain (SDNN, standard deviation of the averaged normal sinus RR intervals for all 5-minute segments [SDANN]) of HRV indexes. Both TWA and HRV were measured on the Holter monitor, and TWA was calculated automatically using the time-domain modified moving average method.

RESULTS

TWA values differed significantly between controls (40 ± 16 μV) and group post-MI with (62 ± 17 μV, P < 0.05) or without (60 ± 15 μV, P < 0.05) diabetes. In addition, group post-MI with diabetes had lower standard deviation of all normal sinus RR intervals (SDNN), standard deviation of the averaged normal sinus RR intervals for all 5-minute segments (SDANN), and HF, indicating depressed vagus nerve activity, and higher LF/HF ratio, indicating elevated sympathetic nerve activity, than controls and group post-MI without diabetes (P < 0.05). TWA correlated with SDNN and SDANN (r = 0.29, 0.31; P < 0.001).

CONCLUSIONS

TWA was elevated in patients following myocardial infarction, both in those with or without diabetes. Myocardial infarction patients had a lower time domain, HF, and a higher LF/HF ratio HRV, especially in those with diabetes. The analysis of modified moving agerage (MMA)-based TWA and HRV can be a useful tool for identifying post-myocardial infarction patients at high risk of arrhythmic events.

Microvolt T-wave alternans physiological basis, methods of measurement, and clinical utility--consensus guideline by International Society for Holter and Noninvasive Electrocardiology

This consensus guideline was prepared on behalf of the International Society for Holter and Noninvasive Electrocardiology and is cosponsored by the Japanese Circulation Society, the Computers in Cardiology Working Group on e-Cardiology of the European Society of Cardiology, and the European Cardiac Arrhythmia Society. It discusses the electrocardiographic phenomenon of T-wave alternans (TWA) (i.e., a beat-to-beat alternation in the morphology and amplitude of the ST-segment or T-wave). This statement focuses on its physiological basis and measurement technologies and its clinical utility in stratifying risk for life-threatening ventricular arrhythmias. Signal processing techniques including the frequency-domain Spectral Method and the time-domain Modified Moving Average method have demonstrated the utility of TWA in arrhythmia risk stratification in prospective studies in >12,000 patients. The majority of exercise-based studies using both methods have reported high relative risks for cardiovascular mortality and for sudden cardiac death in patients with preserved as well as depressed left ventricular ejection fraction. Studies with ambulatory electrocardiogram-based TWA analysis with Modified Moving Average method have yielded significant predictive capacity. However, negative studies with the Spectral Method have also appeared, including 2 interventional studies in patients with implantable defibrillators. Meta-analyses have been performed to gain insights into this issue. Frontiers of TWA research include use in arrhythmia risk stratification of individuals with preserved ejection fraction, improvements in predictivity with quantitative analysis, and utility in guiding medical as well as device-based therapy. Overall, although TWA appears to be a useful marker of risk for arrhythmic and cardiovascular death, there is as yet no definitive evidence that it can guide therapy.

On the estimation of T-wave alternans using the spectral fast fourier transform method

BACKGROUND

T-wave alternans (TWA) has been associated with increased vulnerability to ventricular tachyarrhythmias and sudden cardiac death. However, both random (white) noise and (patho)physiologic processes (ie, premature ventricular contractions and heart and respiration rates) may hamper TWA estimation and therefore lessen its clinical utility for risk stratification.

OBJECTIVE

To investigate the effect of random noise and certain (patho)physiologic processes on the estimation of TWA by using the fast Fourier transform method and to develop methods to overcome these potential sources of error.

METHODS

We used a combination of human electrocardiogram data and computer simulations to assess the effects of a premature ventricular contraction and random and colored noise on the accuracy of TWA estimation.

RESULTS

We quantitatively demonstrate that replacing a "bad" beat with an odd/even median beat is a more accurate approach than replacing it with the overall average or the overall median beat. We also show that phase resetting may have a significant effect on alternans estimation and that estimation of alternans by using frequencies >0.4922 cycles/beat in a 128-point fast Fourier transform provides the most accurate approach for estimating the alternans when phase resetting is likely to occur. In addition, our data demonstrate that the number of indeterminate TWA tests due to high levels of noise can be reduced when the alternans voltage exceeds a new higher threshold. Furthermore, the amplitude of random noise has a significant effect on alternans estimation and the alternans voltage threshold should be adjusted for noise levels >1.8 μV. Finally, we quantitatively demonstrate that colored noise may lead to a false-positive or a false-negative result. We propose methods to estimate the effect of these (patho)physiologic processes on the alternans estimation in order to determine whether a TWA test is likely to be a true positive or a true negative.

CONCLUSION

This study introduces novel methods to overcome potential sources of error in the estimation of TWA. These methods may improve the utility of TWA either for ambulatory monitoring or for clinical risk stratification for ventricular arrhythmias and sudden cardiac death.

Repolarization alternans heterogeneity in healthy subjects and acute myocardial infarction patients

An association between heterogeneity of repolarization alternans (RA) and cardiac electrical instability has been reported. Characterization of RA in health and identification of physiological RA heterogeneity may help discrimination of abnormal RA cases more likely associated to arrhythmic events. Thus, aim of the present study was the identification of a physiological RA region in terms of mean temporal location (MRAD) with respect to the T apex, and mean amplitude (MRAA), by application of our heart-rate adaptive match filter method to clinical ECG recordings from 51 control healthy (CH) subjects and 43 acute myocardial infarction (AMI) patients. Results indicate that RA occurring within the first half of the T wave is dominant in both CH and AMI populations (74.5% and 53.5% of cases, respectively; P<0.05). Definition of physiological RA region in the MRAD vs. MRAA plane (-83 ms ≤ MRAD ≤ 23 ms, 0≤ MRAA ≤ 30 μV) provided 0% and 32.6% abnormal RA cases among the CH subjects and AMI patients, respectively. We conclude that myocardial infarction may associate with an RA occurring early (MRAD<-83 ms) or late (MRAD >23 ms) along the JT segment, in addition or in alternative to an abnormally high RA amplitude (MRAA >30 μV).

Risk stratification for sudden cardiac death

Sudden cardiac death (SCD) is a leading cause of mortality in industrialized countries, and ventricular fibrillation and sustained ventricular tachycardia are the major causes of SCD. Although there are now effective devices and medications that can prevent such serious arrhythmias, it is crucial to have methods of identifying patients at risk. Numerous studies suggest that most patients dying of SCD have coronary artery disease or cardiomyopathy. Functional or electrophysiological measurements are effective in risk stratification. Left ventricular ejection fraction measured by echocardiography or cardiac imaging techniques is the gold standard to detect high-risk patients. Electrophysiological studies have also been used for risk stratification. Noninvasive techniques and measurements, such as T-wave alternans, signal-averaged electrocardiography, nonsustained ventricular tachycardia, heart rate variability, and heart rate turbulence, have been proposed as useful tools in identifying patients at risk for SCD. This article reviews the epidemiology, mechanisms, substrates, and current status of risk stratification of SCD.

Increased intraatrial conduction abnormality assessed by P-wave signal-averaged electrocardiogram in patients with Brugada syndrome

BACKGROUND

Atrial fibrillation (AF) is observed in patients with Brugada syndrome (BS), especially those showing coved-type electrocardiogram (ECG) pattern. Using P-wave signal-averaged ECG (P-SAE), we investigated whether increased intraatrial conduction abnormality contributed to AF generation in BS patients.

METHODS

Twenty BS patients and 20 age- and gender-matched healthy controls were enrolled. At the P-SAE recording, 12 of the 20 BS patients showed coved-type (C-BS) and eight showed saddleback-type (S-BS). The total duration (Ad) and root mean square voltage for the terminal 20 ms (LP(20) ) of the filtered P wave were measured. P-wave dispersion (P-disp) was defined as the difference between the maximum and minimum, measured from 16 precordial recording sites.

RESULTS

BS patients had a significantly longer Ad (128.2 ± 7.6 vs 116.3 ± 8.2 ms, P < 0.0001), lower LP(20) (2.6 ± 0.9 vs 3.4 ± 0.8 μV, P < 0.01), and greater P-disp (15.5 ± 7.0 vs 7.4 ± 3.2 ms, P < 0.0001) than the controls. C-BS patients had significantly longer Ad (131.0 ± 7.2 vs 124.1 ± 6.8 ms, P < 0.05) and lower LP(20) (2.2 ± 0.6 vs 3.2 ± 1.0 μV, P < 0.05) than S-BS patients. All C-BS patients and only three S-BS patients had atrial late potential (100% vs 38%, P < 0.01).

CONCLUSION

Intraatrial conduction delay and its heterogeneity may exist in BS patients, especially those showing coved-type ECG patterns. These atrial electrical abnormalities could be a substrate for atrial reentrant tachycardia such as AF.