Effects of signaled and unsignaled stressor on ECG T-wave amplitude

Thirty-six human subjects were exposed to noise (noxious US) under one of the following signal (CS) conditions: signaled stressor (SS), unsignaled stressor (NS) and a truly random control group (RS). Changes in ECG T-wave amplitude were used to index the stress response and the greatest change in amplitude occurred in the SS group. T-wave amplitude change was compared to HR change as an index of sympathetic stimulation and the former proved the more sensitive. The increased sympathetic responding in the SS condition suggests that a reliable signal may serve a physiologically adaptive purpose.     

Effects of Beta-Adrenergic Activity on T-Wave Amplitude

This study addresses the hypothesis that electrocardiographic T-wave amplitude is influenced by beta-adrenergic stimulation of the heart. Beta-adrenergic activity was manipulated both pharmacologically and through behavioral challenge. Under resting conditions, 12 healthy men underwent infusion of placebo and then the beta-agonist, isoproterenol, and the beta-blocker, propranolol, in a counterbalanced, crossover design. During infusion of placebo, subjects also underwent two behavioral challenges, a structured interview and mental arithmetic. Analysis of the resting data indicated that propranolol produced a significant increase in T-wave amplitude, and isoproterenol produced significant T-wave amplitude attenuation. As previously reported, drug effects were also in evidence for heart rate. Behaviorally-induced reduction of T-wave amplitude was observed for mental arithmetic but not structured interview, which again paralleled heart rate data. Both pharmacological and behavioral data reported in this study support the hypothesis that the T-wave is significantly affected by beta-sympathetic influence on the heart. However, a nonspecific effect of heart rate change on T-wave amplitude would also account for these results. The findings are discussed in terms of their implications for the utility of T-wave amplitude in psychophysiological research.     

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

BackgroundSudden cardiac death (SCD) risk is elevated following acute myocardial infarction (MI). The time course of SCD susceptibility post‐MI requires further investigation.MethodsIn 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).ResultsTWA 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.ConclusionsThis study provides proof‐of‐principle for tracking post‐MI SCD risk in individual patients with implications for personalized therapy.     

一种新的T波终点定义方法及其在QT间期检测中的应用

T波终点识别是ECG信号QT间期检测中的关键技术。由于T波末端呈对数衰减及易受杂音叠加的影响,使得高精度的T波终点识别显得困难。定义T波末端衰减率至某一阈值δ的时刻为T波终点,并将此法应用于QT间期的自动检测。以T波顶点为标识,将其后的0.2 s数据叠加成一个平均信号φ(t),以函数φ^(t)=Aeαt拟合φ的末端,并利用最小二乘法确定其参数。将此φ函数作为模板去匹配心电图的T波可获得相应的A和α值,并通过微分运算得出T波终点的位置。利用此方法进行QT间期检测,显示出良好的准确性和鲁棒性。     

Utility of implantable cardioverter defibrillator electrograms to estimate repolarization alternans preceding a tachyarrhythmic event

Electrical alternans is a pattern of variation in the shape of the ECG waveform that appears on an every-other-beat basis. In humans, alternation in ventricular repolarization, namely, repolarization alternans, has been associated with increased vulnerability to ventricular tachycardia/ventricular fibrillation and sudden cardiac death. This study investigates the utility of implantable cardioverter defibrillator electrograms to estimate repolarization alternans preceding a tachyarrhythmic event. It is demonstrated that microvolt-level repolarization alternans is present prior to an arrhythmic event, and one can record low-amplitude-noise signals that can be used to obtain reliable estimates of repolarization alternans. This study eventually may lead to new methods that would prevent the onset of malignant tachyarrhythmias.     

Early electrocardiographic indices for predicting chronic doxorubicin-induced cardiotoxicity

BackgroundDealing with chemotherapy-related cardiac dysfunction (CTRCD) remains a significant problem complicated by the difficulty in early detection of cardiotoxicity. Electrocardiogram (ECG) is expected to be the most realistic methodology due to lower cost-performance and non-invasiveness. We investigated the long-term visual fluctuations in the ECG waveforms in patients with chronic doxorubicin (DOX)-induced cardiotoxicity to identify ECG indices for the early detection of cardiotoxicity.MethodsWe conducted a retrospective case series study by reviewing the medical records of 470 consecutive patients with malignant lymphoma who were treated with DOX at our institute between January 2010 and December 2017. Of them, 23 (4.9%) patients developed left ventricular dysfunction and were diagnosed with CTRCD using echocardiography. We assessed the ECG indices on 12-lead ECG recordings before and after treatment in 15 patients; eight patients were excluded due to conduction disturbances or atrial fibrillation.ResultsCTRCD was detected at a median of 475 (interquartile range, IQR: 341–1333) days after initiating chemotherapy. The evaluation of ECG indices preceding CTRCD development was performed 93 (IQR: 52–232) days before the detection of CTRCD. In the stage of CTRCD, the most significant ECG change was T-wave flattening in leads V3–V6 (12 patients, 80%). Additionally, QTa prolongation was observed in leads I and aVL (n = 10, 66%), leads II, III, and aVF (n = 9, 60%), and leads V3–V6 (n = 10, 73%). These ECG changes were not observed before the treatment but were detected mildly in the pre-CTRCD stage, which subsequently worsened in the CTRCD stage.ConclusionsThis study indicated that T-wave changes and QTa prolongation may be useful as an early indicator before the onset of CTRCD in patients with DOX-induced cardiotoxicity.