T-wave Amplitude Research Articles

Role of exercise electrocardiogram to screen for T-wave oversensing after implantation of subcutaneous implantable cardioverter-defibrillator

During early experience with subcutaneous implantable cardioverter-defibrillators (S-ICD), several patients had inappropriate shocks from T-wave oversensing (TWOS) during exercise. This prompted some operators to perform routine treadmill exercise tests after implantation of S-ICD to screen for TWOS. Meanwhile, improvements have been made in the detection algorithms by the manufacturer. To assess whether routine treadmill exercise post S-ICD implantation is warranted. Patients undergoing S-ICD implantation from October 2012 to December 2016 who were able to complete a treadmill exercise were included in the study. The amplitude of R and T waves as assessed by the device programmer at rest and peak exercise was calculated and incidence of TWOS recorded. Eighty-seven patients with complete treadmill exercise test data were included in the final analysis. The majority of the patients received S-ICD for primary prevention. Nine percent of the included patients had hypertrophic obstructive cardiomyopathy. During treadmill exercise, there was significant increase in the heart rate from rest (77 ± 14 beats per minute) to peak exercise (133 ± 14 beats per minute; P < .0001). There was no significant difference between R-wave amplitude at rest (2 ± 0.77 mV) and peak exercise (1.88 ± 0.94 mV; P = .36). Similarly, there was no significant difference between T-wave amplitude at rest (0.27 ± 0.19 mV) and peak exercise (0.33 ± 0.23 mV; P = .06). The incidence of TWOS during exercise was zero. With current screening and detection algorithms for S-ICD, routine treadmill exercise does not result in additional discrimination of patients susceptible to TWOS.

Effects of amiodarone on short QT syndrome variant 3 in human ventricles: a simulation study

BackgroundShort QT syndrome (SQTS) is a newly identified clinical disorder associated with atrial and/or ventricular arrhythmias and increased risk of sudden cardiac death (SCD). The SQTS variant 3 is linked to D172N mutation to the KCNJ2 gene that causes a gain-of-function to the inward rectifier potassium channel current (IK1), which shortens the ventricular action potential duration (APD) and effective refractory period (ERP). Pro-arrhythmogenic effects of SQTS have been characterized, but less is known about the possible pharmacological treatment of SQTS. Therefore, in this study, we used computational modeling to assess the effects of amiodarone, class III anti-arrhythmic agent, on human ventricular electrophysiology in SQT3.MethodsThe ten Tusscher et al. model for the human ventricular action potentials (APs) was modified to incorporate IK1 formulations based on experimental data of Kir2.1 channels (including WT, WT-D172N and D172N conditions). The modified cell model was then implemented to construct one-dimensional (1D) and 2D tissue models. The blocking effects of amiodarone on ionic currents were modeled using IC50 and Hill coefficient values from literatures. Effects of amiodarone on APD, ERP and pseudo-ECG traces were computed. Effects of the drug on the temporal and spatial vulnerability of ventricular tissue to genesis and maintenance of re-entry were measured, as well as on the dynamic behavior of re-entry.ResultsAmiodarone prolonged the ventricular cell APD and decreased the maximal voltage heterogeneity (δV) among three difference cells types across transmural ventricular wall, leading to a decreased transmural heterogeneity of APD along a 1D model of ventricular transmural strand. Amiodarone increased cellular ERP, prolonged QT interval and decreased the T-wave amplitude. It reduced tissue’s temporal susceptibility to the initiation of re-entry and increased the minimum substrate size necessary to sustain re-entry in the 2D tissue.ConclusionsAt the therapeutic-relevant concentration of amiodarone, the APD and ERP at the single cell level were increased significantly. The QT interval in pseudo-ECG was prolonged and the re-entry in tissue was prevented. This study provides further evidence that amiodarone may be a potential pharmacological agent for preventing arrhythmogenesis for SQT3 patients.

Vectorcardiography identifies patients with electrocardiographically concealed long QT syndrome

Long QT syndrome (LQTS) and genotypic subtypes are associated with distinctive T-wave patterns, arrhythmogenic triggers, and corrected QT (QTc) interval risk associations. Twenty percent of patients with LQTS have normal QTc values, defined as electrographically concealed LQTS (ecLQTS). Vectorcardiography (VCG) has value for sudden cardiac death risk assessment. The purpose of this study was to determine the use of VCG to identify patients with ecLQTS. We performed a retrospective analysis in patients with ecLQTS with resting QTc values <440 ms. Computerized derivation of the spatial mean and peak QRS-T angles, QTpeak, Tpeak-Tend (angle between QRS and T-wave peak amplitudes in 3-dimensional space), and T-wave eigenvalues (TwEVs; amplitudes [in microvolts] for each of the first 4 TwEVs were derived from the 12-lead electrocardiogram) was performed. The results were compared with those for healthy controls. Intergenotype differences were analyzed. Of 610 patients with LQTS, 169 patients (28%) had ecLQTS (86 (51%) men; mean age 22 ± 16 years; mean QTc interval 422 ± 14 ms). There were 519 healthy controls (44% men; mean age 19.8 ± 13.8 years) with a mean QTc interval of 426± 28 ms. Among VCG parameters, QTpeak and TwEVs significantly differentiated patients with ecLQTS from controls (P ≤ .01 for each) as well as differentiated KCNQ1-encoded type 1 LQTS (ecLQT1), KCNH2-encoded type 2 LQTS (ecLQT2), and SCN5A-encoded type 3 LQTS (ecLQT3) from controls (P < .01). ecLQT3 was differentiated from controls and ecLQT1 and ecLQT2 by the fourth TwEV (P < .01 for each). The fourth TwEV differentiated symptomatic patients with ecLQTS from asymptomatic patients with ecLQTS (P < .01). ecLQTS can be distinguished from controls using QTpeak. ecLQT3 was best differentiated by the fourth TwEV. VCG may facilitate familial diagnostic anticipation of LQTS status before the completion of mutation-specific genetic testing even with normal resting QTc values.

Noninvasive quantification of blood potassium concentration from ECG in hemodialysis patients

Blood potassium concentration ([K+]) influences the electrocardiogram (ECG), particularly T-wave morphology. We developed a new method to quantify [K+] from T-wave analysis and tested its clinical applicability on data from dialysis patients, in whom [K+] varies significantly during the therapy. To elucidate the mechanism linking [K+] and T-wave, we also analysed data from long QT syndrome type 2 (LQT2) patients, testing the hypothesis that our method would have underestimated [K+] in these patients. Moreover, a computational model was used to explore the physiological processes underlying our estimator at the cellular level. We analysed 12-lead ECGs from 45 haemodialysis and 12 LQT2 patients. T-wave amplitude and downslope were calculated from the first two eigenleads. The T-wave slope-to-amplitude ratio (TS/A) was used as starting point for an ECG-based [K+] estimate (KECG). Leave-one-out cross-validation was performed. Agreement between KECG and reference [K+] from blood samples was promising (error: −0.09 ± 0.59 mM, absolute error: 0.46 ± 0.39 mM). The analysis on LQT2 patients, also supported by the outcome of computational analysis, reinforces our interpretation that, at the cellular level, delayed-rectifier potassium current is a main contributor of KECG correlation to blood [K+]. Following a comprehensive validation, this method could be effectively applied to monitor patients at risk for hyper/hypokalemia.

Utility of T-wave amplitude as a non-invasive risk marker of sudden cardiac death in hypertrophic cardiomyopathy

ObjectiveSudden cardiac arrest (SCA) is the most devastating outcome in hypertrophic cardiomyopathy (HCM). We evaluated repolarisation features on the surface electrocardiogram (ECG) to identify the potential risk factors for SCA.MethodsData...

The effect of traditional Persian music on the cardiac functioning of young Iranian women

In the past few decades, several studies have reported the physiological effects of listening to music. The physiological effects of different music types on different people are not similar. Therefore, in the present study, we have sought to examine the effects of traditional Persian music on the cardiac function in young women. Twenty-two healthy females participated in this study. ECG signals were recorded in two conditions: rest and music. For each of the 21 ECG signals (15 morphological and six wavelet based feature) features were extracted. SVM classifier was used for the classification of ECG signals during and before the music. The results showed that the mean of heart rate, the mean amplitude of R-wave, T-wave, and P-wave decreased in response to music. Time-frequency analysis revealed that the mean of the absolute values of the detail coefficients at higher scales increased during rest. The overall accuracy of 91.6% was achieved using polynomial kernel and RBF kernel. Using linear kernel, the best result (with the accuracy rate of 100%) was attained.

A New Wavelet-Based ECG Delineator for the Evaluation of the Ventricular Innervation.

T-wave amplitude (TWA) has been proposed as a marker of the innervation of the myocardium. Until now, TWA has been calculated manually or with poor algorithms, thus making its use not efficient in a clinical environment. We introduce a new wavelet-based algorithm for the delineation QRS complexes and T-waves, and the automatic calculation of TWA. When validated in the MIT/BIH Arrhythmia database, the QRS detector achieved sensitivity and positive predictive value of 99.84% and 99.87%, respectively. The algorithm was validated also on the QT database and it achieved sensitivity of 99.50% for T-peak detection. In addition, the algorithm achieved delineation accuracy that is similar to the differences in delineation between expert cardiologists. We applied the algorithm for the evaluation of the influence in TWA of anticholinergic and antiadrenergic drugs (i.e., atropine and metoprolol) for healthy subjects. We found that the TWA decreased significantly with atropine and that metoprolol caused a significant increase in TWA, thus confirming the clinical hypothesis that the TWA is a marker of the innervation of the myocardium. The results of this paper show that the proposed algorithm can be used as a useful and efficient tool in clinical practice for the automatic calculation of TWA and its interpretation as a non-invasive marker of the autonomic ventricular innervation.

Effects of bosentan, sildenafil and their combination on T-wave amplitude and QT interval in a rat model of pulmonary hypertension

Effects of bosentan, sildenafil and their combination on T-wave amplitude and QT interval in a rat model of pulmonary hypertension

Differential Analysis of Nitroglycerin Influence on Myocardium in Coronary Artery Disease Patients

Objective: The mechanism of nitrates action and its positive influence on the myocardium is unclear and cause sharp debates. In current study we made an attempt to open new sides of nitrates and myocardium interaction. Methods: We examined 14 patients with G-criterion during an episode of chest pain. In 10 cases, the angina pectoris was cut off using nitroglycerin 0.8 mg sublingually. The recordings were made during the angina pectoris and nearly 16 minutes after NTG administration. This gives us the dynamic of changes in myocardium during drug administration. In 11 cases the CAD was proved by coronary angiography, but another 3 patient had non-cardiac cause of chest pain. The G-criterion is calculated by mathematical division of standard deviation by average value of T-wave amplitude values from 60 seconds in each electrocardiographic channel. Then the G-criteria from all channels were compared by relation the maximum value in ischemic zone to minimum value non-ischemic to get the second order G-criteria (SOG-criteria). Results: It was shown that the arrest of angina in 10 cases occurred in the 2-4th minutes after NTG administration, but, according to the G-criterion and SOG-criterion, the decrease of myocardium ischemia (-51%) was basically in the 4-8th minutes, and the duration of ischemia reduction lasted from between 2 and 8 minutes. We registered the opposite reaction on NTG administration in all 11 CAD patients: in ischemic zone of the myocardium the G-criterion decreased on average -28.4% and in normal zone the G-criterion increased +54.5%. Conclusion: This study indicates the different response of ischemic and normal myocardium on the same dosage of NTG, which can be used as diagnostic criterion for ischemic zones. The assessment of NTG effect should be based not only on the subjective patient’s sensations, but also on the positive or negative evolution of objective criteria for myocardial ischemia.

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.

Variability of Ventricular Repolarization Dispersion Quantified by Time-Warping the Morphology of the T-Waves.

We propose two electrocardiogram (ECG)-derived markers of T-wave morphological variability in the temporal, dw, and amplitude, da, domains. Two additional markers, dwNL and daNL, restricted to measure the nonlinear information present within dw and da are also proposed. We evaluated the accuracy of the proposed markers in capturing T-wave time and amplitude variations in 3 situations: 1) In a simulated set up with presence of additive Laplacian noise, 2) when modifying the spatio-temporal distribution of electrical repolarization with an electro-physiological cardiac model, and 3) in ECG records from healthy subjects undergoing a tilt table test. The metrics dw, da , dwNL , and daNL followed T-wave time- and amplitude-induced variations under different levels of noise, were strongly associated with changes in the spatio-temporal dispersion of repolarization, and showed to provide additional information to differences in the heart rate, QT and Tpe intervals, and in the T-wave width and amplitude. The proposed ECG-derived markers robustly quantify T-wave morphological variability, being strongly associated with changes in the dispersion of repolarization. The proposed ECG-derived markers can help to quantify the variability in the dispersion of ventricular repolarization, showing a great potential to be used as arrhythmic risk predictors in clinical situations.

Application of a new robust ECG T-wave delineation algorithm for the evaluation of the autonomic innervation of the myocardium.

T-wave amplitude (TWA) is a well know index of the autonomic innervation of the myocardium. However, until now it has been evaluated only manually or with simple and inefficient algorithms. In this paper, we developed a new robust single-lead electrocardiogram (ECG) T-wave delineation algorithm that is able to detect the T-wave with a wavelet based method and automatically calculate the TWA. We evaluated the algorithm on the QT database, achieving a sensitivity of 99.92% for the T wave peak and 99.38% for the T wave end. In addition, the percentage of records automatically delineated with high precision was higher than previous published works. Finally, the algorithm was applied to study the influence of anticholinergic and antiadrenergic drugs (i.e. atropine and metoprolol) on the TWA. It was observed that atropine significantly decreased the TWA when compared to baseline level, that head-up tilt caused a decrease of TWA and that metoprolol blunted this decrease. Through the development of a robust algorithm, this study opens the way for further research on the T-wave analysis for the assessment of the autonomic innervation of the ventricular myocardium.

Posterior reperfusion T-waves: Wellens' syndrome of the posterior wall

BackgroundReperfusion after coronary occlusion (myocardial infarction, MI), as in Wellens' syndrome, is often represented on ECG as T-wave inversion in the leads overlying the affected myocardial wall(s). As an extension...

Improved Clinical Risk Stratification in Patients with Long QT Syndrome? Novel Insights from Multi-Channel ECGs

BackgroundWe investigated whether multichannel ECG-recordings are useful to risk-stratify patients with congenital long-QT syndrome (LQTS) for risk of sudden cardiac death under optimized medical treatment.MethodsIn 34 LQTS-patients (11 male; age 31±13 years, QTc 478±51ms; LQT1 n = 8, LQT2 n = 15) we performed a standard 12-channel ECG and a 120-channel body surface potential mapping. The occurrence of clinical events (CE; syncope, torsade de pointes (TdP), sudden cardiac arrest (SCA)) was documented and correlated with different ECG-parameters in all lead positions.ResultsSeven patients developed TdP, four survived SCA and 12 experienced syncope. 12/34 had at least one CE. CE was associated with a longer QTc-interval (519±43ms vs. 458±42ms; p = 0.001), a lower T-wave integral (TWI) on the left upper chest (-1.2±74.4mV*ms vs. 63.0±29.7mV*ms; p = 0.001), a lower range of T-wave amplitude (TWA) in the region of chest lead V8 (0.10±0.08mV vs. 0.18±0.07mV; p = 0.008) and a longer T-peak-T-end time (TpTe) in lead V1 (98±23ms vs. 78±26ms; p = 0.04). Receiver-operating-characteristic (ROC) analyses revealed a sensitivity of 96% and a specificity of 75% (area under curve (AUC) 0.89±0.06, p = 0.001) at a cut-off value of 26.8mV*ms for prediction of CE by TWI, a sensitivity of 86% and a specificity of 83% at a cut-off value of 0.11mV (AUC 0.83±0.09, p = 0.002) for prediction of CE by TWA and a sensitivity of 83% and a specificity of 73% at a cut-off value of 87ms (AUC 0.80±0.07, p = 0.005) for prediction of CE by TpTe.ConclusionsOccurrence of CE in LQTS-patients seems to be associated with a prolonged, low-amplitude T-wave.

Changes in P-wave, T-wave, and ST segment amplitude in 12 lead electrocardiogram in children with breath holding spell

To explore the change of the amplitude of P wave, T wave and ST segment of 12 lead electrocardiogram (ECG) in children with breath holding spell. A total of 29 children (24 males and 5 females) with breath holding spell in Second Xiangya Hospital, Central South University were enrolled for this study from October, 2009 to September, 2015. Their ages ranged from 3 months to 6 years, with an average of 1.82±1.27 years old. The control group consisted of 30 age-matched and gender-matched healthy children. All subjects were underwent electrocardiography by the SR-1000A comprehensive automatic electrocardiograph analyzer, and the changes of the ECG parameters were compared between the two groups. Compared with the control group, the amplitude of P-wave of V5 lead was decreased [(44.10±23.98) vs (58.30±21.19) μV, P<0.05], the amplitude of T-wave of V6 lead was increased [(423.80±122.6) vs (350.00±105.73) μV, P<0.05], the amplitude of ST segment of II lead was increased [(84.80±39.97) vs (57.30±38.77) μV, P<0.05], the amplitude of ST segment of aVR lead was increased [(-77.60±37.41) vs (-51.00±33.46) μV, P<0.05], the amplitude of ST segment of aVL lead was increased [(35.20±28.24) vs (17.70±33.90) μV, P<0.05], the amplitude of ST segment of V5 lead was increased [(111.00±59.36) vs (69.00±36.33) μV, P<0.05], the amplitude of ST segment of V6 lead was increased [(79.30±45.51) vs (51.30±33.19) μV, P<0.05]. The children with breath holding spell have autonomic nerve dysfunction. The amplitude of ST segment changes is sensitive.

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To Study the Effect of Different Phases of Menstrual Cycle on ECG &amp; Blood Pressure in Healthy Young Adult Females

Menstruation coupled periodic bleeding from the blood vessels, at the time of shedding of the uterine mucosa has directed interest, more especially in the ECG changes & Blood Pressure changes during different phases of menstrual cycle. The aim of the present study was to compare and evaluate the changes in the ECG & BP measured during different phases of menstrual cycle. Variation in BP during different phases of menstrual cycle can also be attributed to the effect of ovarian hormones on cardiovascular function. Since the hormonal changes follow a non-linear trend throughout the menstrual cycle, it may have unpredicted effect on BP regulation. The present study was carried out on 50 healthy female students aged 17-22 years who had regular menstrual cycle of 30 ± 3 days. The electrocardiogram (ECG) recordings were taken on lead II for convenience during the different phases of the menstrual cycle (Phase I –days 1-5, Phase-II-days 9-12, Phase-III-days 1921) in female subjects & Blood Pressure was analyzed by means of Indirect method during three phases in females. Statistical analysis was done by ONEWAY-ANOVA test. The P wave amplitude, T-wave amplitude, QRS complex amplitude, QRS complex duration, PR interval, ST interval did not show any significant change during different phases of menstrual cycle, although some mild changes were observed which were statistically not significant. QT interval, RR interval has shown significant changes as longer QT interval observed in Phase-II(follicular Phase )& shorter during Phase-III (Luteal phase).The longer RR interval observed during Phase-III (luteal phase) & shorter during Phase-I (Menstrual Phase). HR was found higher in Phase-I (menstrual phase) & lower in Phase-III (luteal phase)in females. They did not show any significant changes in BP measurement taken during three phases. This study was a moderate attempt to determine regular variation in ECG & BP during the different phases of menstrual cycle in normal healthy females.

Aroused at Home: Basic Autonomic Regulation during Orthostatic and Physical Activation is Altered in Children with Social Anxiety Disorder.

Previous research has documented altered autonomic nervous system (ANS) reactivity to laboratory-based social stress tasks in children with social anxiety disorder (SAD). It is unclear, however, whether these alterations are caused by the unfamiliar and possibly threatening lab environment or whether they generalize to other, more representative contexts. Sympathetic and parasympathetic autonomic functioning was assessed in the home (minimizing environmental threat) during a supine baseline phase and two physical activation phases (orthostatic stress, stair stepping) in children (9-13years) with SAD (n = 27) and healthy control children (n = 27). Relative to controls, children with SAD showed tonic autonomic hyperarousal as indicated by higher heart rate and electrodermal activity during the supine baseline phase. Further, there was evidence for stronger cardiac and vascular sympathetic reactivity (T-wave amplitude, pulse wave transit time) to moderate physical activation in children with SAD. Higher autonomic arousal during rest was related to measures of trait social anxiety and general psychopathology. Groups did not differ on parasympathetic parameters. Our results extend previous laboratory findings and provide the first evidence for alterations in children with SAD during basal autonomic regulation and in the absence of explicit social evaluative threat. They may further help to clarify conflicting study results from previous laboratory studies. The findings underline the importance of psychophysiological assessment using different environments and tasks to elucidate the physiological bases of SAD.

MACROSCOPIC T-WAVE ALTERNANS: AN UNUSUAL COMPANION OF QT PROLONGATION

Macroscopic T-wave alternans (MTWA) is beat to beat variability in the vector or amplitude of T-waves on surface ECG. Often linked with acquired long-QT syndrome, MTWA is a sign of electrical instability and impending reentrant arrhythmias. This is a case of medication related QT-prolongation with

NON-SUSTAINED MICROVOLT LEVEL T-WAVE ALTERNANS IN CONGENITAL LONG QT SYNDROME TYPES 1 AND 2

Congenital long QT syndrome (LQTS) is a group of inherited disorders with predisposition to torsades de pointes ventricular tachycardia during adrenergic stimulation, with subtypes LQT1 and LQT2 being most common. Microvolt T-wave alternans (MTWA), a beat-to-beat fluctuation in T-wave amplitude and