Temporal variability of T‐wave morphology and risk of sudden cardiac death in patients with coronary artery disease

BackgroundThe possible relationship between temporal variability of electrocardiographic spatial heterogeneity of repolarization and the risk of sudden cardiac death (SCD) in patients with coronary artery disease (CAD) is not completely understood.MethodsThe standard deviation of T‐wave morphology dispersion (TMD‐SD), of QRST angle (QRSTA‐SD), and of T‐wave area dispersion (TW‐Ad‐SD) were analyzed on beat‐to‐beat basis from 10 min period of the baseline electrocardiographic recording in ARTEMIS study patients with angiographically verified CAD.ResultsAfter on average of 8.6 ± 2.3 years of follow‐up, a total of 66 of the 1,678 present study subjects (3.9%) had experienced SCD or were resuscitated from sudden cardiac arrest (SCA). TMD‐SD was most closely associated with the risk for SCD and was significantly higher in patients who had experienced SCD/SCA compared with those who remained alive (3.61 ± 2.83 vs. 2.64 ± 2.52, p = .008, respectively), but did not differ significantly between the patients who had experienced non‐SCD (n = 71, 4.2%) and those who remained alive (3.20 ± 2.73 vs. 2.65 ± 2.53, p = .077, respectively) or between the patients who succumbed to non‐cardiac death (n = 164, 9.8%) and those who stayed alive (2.64 ± 2.17 vs. 2.68 ± 2.58, p = .853). After adjustments with relevant clinical risk indicators of SCD/SCA, TMD‐SD still predicted SCD/SCA (HR 1.107, 95% CIs 1.035–1.185, p = .003).ConclusionsTemporal variability of electrocardiographic spatial heterogeneity of repolarization represented by TMD‐SD independently predicts long‐term risk of SCD/SCA in patients with CAD.     

T‐Wave Morphology in Short QT Syndrome

Background: Short QT syndrome (SQTS) is an inherited disorder characterized by a short QT interval and vulnerability to ventricular tachyarrhythmias. The diagnostic criteria for this syndrome are not well defined, since there is uncertainty about the lowest normal limits for the corrected QT (QTc) interval. Objective: The aim of this study was to determine whether T‐wave morphology parameters are abnormal in short QT subjects and whether those parameters can help in the diagnosis of SQTS. Methods and Results: We describe three families (10 patients) with short QT intervals (QTc 310 ± 32 ms). Seven subjects had suffered serious arrhythmic events and three were asymptomatic. T‐wave morphology was assessed using the principal component analysis (PCA). QTc was significantly shorter and T‐wave amplitude in lead V₂ higher in the short QT subjects compared to healthy controls (n = 149), (P < 0.001 for both). The total cosine of the angle between the main vectors of the QRS and T‐wave loops (TCRT) was markedly abnormal among the symptomatic patients with short QT syndrome (n = 7) (TCRT –0.14 ± 0.55 vs 0.36 ± 0.51, P = 0.019). None of the three asymptomatic patients with short QT but without a history of arrhythmic events had an abnormally low TCRT. Conclusion: Our observations suggest that patients with a short QT interval and a history of arrhythmic events have abnormal T‐wave loop parameters. These electrocardiogram (ECG) features may help in the diagnosis of SQTS in addition to the measurement of the duration of QT interval from the 12‐lead ECG.     

Comparison of Standard versus Orthogonal ECG Leads for T‐Wave Alternans Identification

T‐wave alternans (TWA), an electrophysiologic phenomenon associated with ventricular arrhythmias, is usually detected from selected ECG leads. TWA amplitude measured in the 12‐standard and the 3‐orthogonal (vectorcardiographic) leads were compared here to identify which lead system yields a more adequate detection of TWA as a noninvasive marker for cardiac vulnerability to ventricular arrhythmias. Our adaptive match filter (AMF) was applied to exercise ECG tracings from 58 patients with an implanted cardiac defibrillator, 29 of which had ventricular tachycardia or fibrillation during follow‐up (cases), while the remaining 29 were used as controls. Two kinds of TWA indexes were considered, the single‐lead indexes, defined as the mean TWA amplitude over each lead (MTWAA), and lead‐system indexes, defined as the mean and the maximum MTWAA values over the standard leads and over the orthogonal leads. Significantly (P < 0.05) higher TWA in the cases versus controls was identified only occasionally by the single‐lead indexes (odds ratio: 1.0–9.9, sensitivity: 24–76%, specificity: 76–86%), and consistently by the lead‐system indexes (odds ratio: 4.5–8.3, sensitivity: 57–72%, specificity: 76%). The latter indexes also showed a significant correlation (0.65–0.83) between standard and orthogonal leads. Hence, when using the AMF, TWA should be detected in all leads of a system to compute the lead‐system indexes, which provide a more reliable TWA identification than single‐lead indexes, and a better discrimination of patients at increased risk of cardiac instability. The standard and the orthogonal leads can be considered equivalent for TWA identification, so that TWA analysis can be limited to one‐lead system.     

T‐Wave Amplitude Is Related to Physical Fitness Status

Background: Abnormalities in repolarization may reflect underlying myocardial pathology and play a prominent role in arrhythmogenesis The T‐wave amplitude has been associated with cardiovascular outcome in patients with acute myocardial infarction (MI) Additionally, T‐wave amplitude is considered a predictor of arrhythmias, as well as being related to an individual's inflammatory status. The combined influence of different variables, such as inflammation, cardiovascular risk factors and physical fitness status, on the T‐wave amplitude has not been evaluated to date. The aim of this study was to identify factors that affect the T‐wave amplitude. Methods: Data from 255 consecutive apparently healthy individuals included in the Tel Aviv Medical Center Inflammation Survey (TAMCIS) were reviewed. All patients had undergone a physical examination and an exercise stress test, and different inflammatory and metabolic biomarkers (fibrinogen, potassium, and high‐sensitivity C‐reactive protein) were measured. Results: Multivariate stepwise analysis revealed that the body mass index and the resting heart rate were significantly associated with the T‐wave amplitude (β=?0.34, P < 0.001; β=?0.19, P = 0.03, respectively) in males, while the recovery rate and the usage of statins significantly affected the T‐wave amplitude in females (β= 0.36, P = 0.002; β= 0.35, P = 0.002, respectively). Inflammatory variables had no significant affect on the T‐wave amplitude of either gender. Conclusions: In conclusion, the T‐wave amplitude is linked to an individual's physical fitness and not to his/her inflammatory status.     

f‐Wave Suppression Method for Improvement of Locating T‐Wave Ends in Electrocardiograms during Atrial Fibrillation

This article is to propose an algorithm for improving T‐wave ends location during atrial fibrillation (AF). The traditional algorithms do not take the irregular baseline fibrillation of AF into consideration, so their location accuracy is relatively low. Based on simple assumptions that AF is a random signal while T waves and QRS complexes are deterministic signals, we suggest a novel method to suppress f wave for improving location of T‐wave ends during AF. We firstly define a new cardiac cycle and then match R peaks and T peaks in the three adjacent cardiac cycles. Finally, we suppress the interference of the f wave by averaging. When evaluating with the PhysioNet QT database and simulated AF signals in terms of the mean and the standard deviation of the T‐wave ends location errors, the proposed algorithm improves the performance of existing popular methods. Besides, the clinical significance of the proposed method is illustrated.     

巨大负性T波患者冠心病的预测影响因素

目的：探讨心电图巨大负性T波在冠心病诊断中的预测价值。方法：回顾性分析1998年1月至2001年12月64例心电图示巨大负性T波并在我院行冠状动脉造影检查的患者，对其心电图、超声心动图和临床资料进行统计分析。结果：心电图示无左心室肥厚或表现为对称性巨大负性T波则支持冠心病的诊断。巨大负性T波患者心电图缺乏左心室肥厚较对称性T波倒置对冠心病更有预测价值。结论：心电图巨大负性T波患者不伴左心室肥厚或对称性T波倒置是预测冠心病的重要因素。     

T‐Wave Abnormalities Are a Better Predictor of Cardiovascular Mortality than ST Depression on the Resting Electrocardiogram

Background: ST depression and T‐wave amplitude abnormalities are known to be independent predictors of cardiovascular (CV) death, but a direct comparison between them has not been described. Methods: Analyses were performed on the first electrocardiogram (ECG) digitally recorded on 46,950 consecutive patients at the Palo Alto Veterans Affairs Medical Center since 1987. Females and patients with electrocardiograms exhibiting bundle branch block, left ventricular hypertrophy, electronic pacing, diagnostic Q waves, or Wolff–Parkinson–White syndrome were excluded, leaving 31,074 male patients for analysis (mean age 55 ± 14). There were 1878 (6.0%) cardiovascular deaths (mean follow‐up of 6 ± 4 years). Electrocardiograms were classified using Minnesota code according to the degree of ST depression and T‐wave abnormality, and the nine possible combinations of ST segment and T‐wave abnormalities were recoded for analysis. Results: The combination of major abnormalities in ST segments and T‐waves carried the greatest hazard [3.2 (CI 2.7–3.8)]. Minor ST depression combined with more severe T‐wave abnormalities carried a hazard of 3.1 (CI 2.5–3.7), whereas minor T‐wave abnormalities combined with more severe ST depression carried a hazard of only 1.9 (CI 1.6–2.3). Conclusion: While both ST segment depression and abnormal T‐wave amplitude are clinically important, T‐wave abnormalities appear to be greater predictors of cardiovascular mortality.     

Relation between Beat‐to‐Beat QT Interval Variability and T‐Wave Amplitude in Healthy Subjects

Objectives: Elevated beat‐to‐beat QT interval variability (QTV) has been associated with increased cardiovascular morbidity and mortality.The aim of this study was to investigate interlead differences in beat‐to‐beat QTV of 12‐lead ECG and its relationship with the T wave amplitude. Methods: Short‐term 12‐lead ECGs of 72 healthy subjects (17 f, 38 ± 14 years; 55 m, 39 ± 13 years) were studied. Beat‐to‐beat QT intervals were extracted separately for each lead using a template matching algorithm. We calculated the standard deviation of beat‐to‐beat QT intervals as a marker of QTV as well as interlead correlation coefficients. In addition, we measured the median T‐wave amplitude in each lead. Results: There was a significant difference in the standard deviation of beat‐to‐beat QT intervals between leads (minimum: lead V₃ (2.58 ± 1.36 ms), maximum: lead III (7.2 ± 6.4 ms), ANOVA: P < 0.0001). Single measure intraclass correlation coefficients of beat‐to‐beat QT intervals were 0.27 ± 0.18. Interlead correlation coefficients varied between 0.08 ± 0.33 for lead III and lead V₁ and 0.88 ± 0.09 for lead II and lead aVR. QTV was negatively correlated with the T‐wave amplitude (r =–0.62, P < 0.0001). There was no significant affect of mean heart rate, age or gender on QT variability (ANOVA: P > 0.05). Conclusions: QTV varies considerably between leads in magnitude as well as temporal patterns. QTV is increased when the T wave is small.     

Practical use of T wave morphology assessment

QT dispersion (QTd) has not proven to be a useful marker derived from the 12-leadelectrocardiogram (ECG) for stratification of patients at risk for sudden cardiac death. To overcomeits methodological shortcomings, novel ECG variables of T wave morphology have been proposed. The total cosineR-to-T (TCRT), T wave morphology dispersion, T wave loop dispersion, normalized T wave loop area, aswell as absolute and relative T wave residuum evaluating non-dipolar ECG signal contents were evaluated in twoclinical studies involving post myocardial infarction (MI) patients and US veterans with cardiovasculardisease.In 280 post MI patients with 27 events over a mean follow-up of 32 months, TCRT and T wave loop dispersionwere independent predictors of mortality. In 813 male US veterans with cardiovascular disease the absolute andrelative T wave residua were independent predictors of patient risk during a long-term follow-up of more than 10years. On Cox regression analysis, age, presence of left ventricular hypertrophy (LVH) and leftventricular ejection fraction (LVEF) were also predictors of survival. The latter study in US veteranstherefore was the first to demonstrate that a novel parameter characterizing heterogeneity of ventricularrepolarization within the 12-lead surface ECG permits risk stratification in patients with cardiovasculardisease.All of the ECG variables are easily accessible from digital 12-lead surface ECG recordings using customcomputer programs. They may prove useful to identify risk patients that benefit from the implantablecardioverter-defibrillator (ICD).     

J wave patterns—morphology,prevalence and nomenclature

The recent resurgence of interest in early repolarization has demonstrated a variation in the definition of the term and a consequent variation in the prevalence of the pattern in different studies. This can vary from 35% in males and 21.5% in females if ST elevation is not considered part of the definition, to 3.3% and 0.5% in females with the inclusion of ST elevation. In contrast, the prevalence of the Brugada Syndrome is in the order of 0.1%–0.2% in Japan for example and has been found to be significantly lower in Denmark. Standardisation of measurement definitions, particularly for early repolarisation, is required.