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Background: Sudden cardiac death is the most frequent death mechanism in Chagas disease, responsible for 55% to 65% of the deaths of patients with chronic Chagas cardiomyopathy (CCC). The most often involved electrophysiological mechanisms are ventricular tachycardia and ventricular fibrillation. The implantable cardioverter defibrillator (ICD) has a beneficial role in preventing sudden death due to malignant ventricular arrhythmias, and, thus the correct identification of patients at risk is required. The association of microvolt T-wave alternans (MTWA) with the appearance of ventricular arrhythmias has been assessed in different heart diseases. The role of MTWA is mostly unknown in patients with CCC. Objectives: To evaluate the association between MTWA and the occurrence of malignant ventricular arrhythmias in patients with CCC. Method: This is a case-control study including patients with CCC and ICD, with history of malignant ventricular arrhythmias (case group), and patients with CCC and no history of those arrhythmias (control group). The MTWA test results were classified as negative and non-negative (positive and indeterminate). The significance level adopted was a = 0.05. Results: We recruited 96 patients, 45 cases (46.8%) and 51 controls (53.1%). The MTWA test was non-negative in 36/45 cases (80%) and 15/51 controls (29.4%) [OR = 9.60 (95%CI: 3.41 - 27.93)]. After adjustment for known confounding factors in a logistic regression model, the non-negative result continued to be associated with malignant ventricular arrhythmias [OR = 5.17 (95%CI: 1.05 - 25.51)]. Conclusion: Patients with CCC and history of malignant ventricular arrhythmias more often have a non-negative MTWA test as compared to patients with no history of arrhythmia. Resumo Fundamento: A morte súbita cardíaca é o mecanismo de morte mais comum na doença de Chagas, responsável pelo óbito de 55% a 65% dos pacientes com cardiomiopatia chagásica crônica (CCC). Os mecanismos mais frequentemente envolvidos são as taquiarritmias ventriculares. O cardioversor-desfibrilador implantável (CDI) apresenta impacto na redução da mortalidade por arritmias ventriculares e faz-se necessária a correta identificação de pacientes sob risco. A associação de microalternância de onda T (MTWA) com o aparecimento de arritmias ventriculares foi avaliada em diferentes cardiopatias através de um teste. O papel da MTWA na identificação de pacientes sob risco na CCC permanece incerto. Objetivo: Avaliar a associação entre MTWA e a ocorrência de arritmias ventriculares malignas na CCC. Método: Trata-se de um estudo caso-controle, que incluiu pacientes com CCC em uso de CDI, com história prévia de arritmias ventriculares malignas (casos) ou sem história prévia (controles). Os resultados do teste foram classificados em negativo e não negativo (positivo e indeterminado). O nível de significância foi a = 0,05. Resultado: Foram recrutados 96 pacientes, 45 no grupo caso (46,8%) e 51 no grupo controle (53,1%). O teste de MTWA apresentou resultado não negativo em 36/45 pacientes no grupo caso (80%) e 15/51 no grupo controle (29,4%), OR = 9,60 (IC95%: 3,41 - 27,93). Após ajuste para fatores de confusão num modelo de regressão logística, o resultado não negativo continuou associado à presença de arritmias ventriculares malignas, com OR = 5,17 (IC95%: 1,05 - 25,51). Conclusão: Na CCC, pacientes com história de arritmia ventricular maligna apresentam maior frequência de teste de MTWA não negativo quando comparados a pacientes sem ocorrência prévia de arritmias.

Prolonged exposure to weightlessness is known to induce cardiovascular deconditioning. The aim of this work was to assess changes in T-wave alternans (TWA) induced by 60 days exposure to simulated microgravity using the −6° head-down bed-rest model (HDBR) and the potential effectiveness of a jump training countermeasure. We hypothesized that TWA could be able to reflect these changes, if they exist. Twenty-four healthy men were recruited at the German Aerospace Center (12 in control group, 12 with applied countermeasure), from which ECG signals were acquired before (PRE), at day 21 of HDBR (HDT21), before the end of HDBR (HDT57), and the day after its conclusion (POST). The index of average alternans (IAA), quantifying the average TWA amplitude, was computed using a fully automated algorithm based on periodic component analysis and the Laplacian likelihood ratio method. A significant increase in HR was found at HDT57 and POST compared to PRE. The IAA showed an increasing trend at POST (median (25th;75th percentile): 0.467(0.381;0.574) μV) compared to PRE (0.337(0.204;0.437) μΥ p=0.18) only in the control group, although no significant differences along HDBR were found. In conclusion, long-term exposure to simulated microgravity did not induce significant alterations in electrical instability measured in terms of nocturnal TWA.

More than 80% of emergency patients succumb to cardiac related including Sudden Cardiac Deaths (SCD) in Pakistan whereas the global deaths due to SCD are 30–40% of total deaths. T-wave alternans refer to variation in amplitude, phase or wave shape in alternating T waves in ECG signals and has been linked with the SCD and ventricular arrhythmia. TWA detection is still a challenge as in many cases amplitude of TWA is well below indispensable process noises. Empirical mode decomposition (EMD) is a empirical signal processing technique employed as noise removal tool for nonlinear and non-stationary TWA signals. Recently very matured and developed least square techniques have been employed for the detection of TWA, which were previously not explored as considered limited practicability. Least square works in time domain and better for the non-stationary TWA signals that gives the technique an edge over the other techniques that assume stationary nature of the signals. Least square with higher order polynomial curve fitting has been recently explored as a promising TWA estimation technique for risk stratification of SCD. In this paper we are presenting a novel EMD based least square T-wave alternans estimation scheme which outperforms estimation in 10–40 dB Gaussian noise. The performance comparison of the technique with bench mark modified moving average method (MMAM) for TWA estimation confirms the enhanced performance for the various practical scenarios of TWA.

Background We aimed to examine microvolt T wave alternans (MTWA) in 24-hour Holter electrocardiography (ECG) of children with repaired tetralogy of Fallot (TOF) to assess associations of MTWA with ventricular arrhythmias, ECG parameters, and echocardiographic findings. Methods Holter ECG records and archive files of 56 repaired TOF patients (62.5% male) who were analyzed retrospectively. Subjects’ ECG parameters and MTWA values were compared with age–sex-matched control group. T wave changes were analyzed by time-domain-modified moving average method from the three channels of 24-hour Holter ECG. Results Mean age was 123.4 ± 48.3 months. Median MTWA value was 55.5 μV in the control group, whereas 95.5 μV in patients group (P < 0.001). A significant weak positive correlation was found between the presence of ventricular extrasystoles and tricuspid regurgitation. There was no correlation between ECG parameters, echocardiographic findings, and MTWA. Conclusions MTWA was increased in children with repaired TOF as reported before. To our knowledge, this is the first study analyzing MTWA with 24-hour Holter ECG in repaired TOF patients.

Background Electrical alternans (EA) has not been fully studied in the current percutaneous coronary intervention (PCI) procedure. Objective The purpose of this study was to evaluate visible EA and the morphology of ST segment during PCI. Methods The incidence of visible EA and ST-segment morphology were studied while the coronary artery was occluded for 20 seconds. When data were available, the relationship between EA and blood pressure was analyzed. The clinical and electrocardiographic data were compared with those of the age- and sex-matched controls. Results During balloon inflation, visible EA was observed in 5 of 306 patients (1.6%) in the last 2 years. EA was limited to PCI in the proximal left anterior descending artery. The ST segment elevated to 10.1 ± 3.2 mm, followed by an alternating QRS complex with a lower ST segment (5.6 ± 1.9 mm; P = .0047) with characteristic ST-segment morphology, which is known as lambda pattern. The mean age of the 5 patients was 68 ± 20 years, and 4(80%). were men. After the release of inflation, the ST-segment level returned rapidly to baseline, followed by normalization of J point. Compared with controls, the maximal elevated ST segment was significantly higher in patients with EA (5.7 ± 2.7 mm; P = .0028). The occlusion of the proximal left anterior descending artery with more severe ischemia seemed to be a prerequisite for developing EA. A higher ST segment was associated with a lower blood pressure and vice versa. Conclusion A short period of ischemia during PCI may induce visible EA and alternating QRS complexes with a characteristic ST-segment morphology. A higher ST segment was associated with a lower blood pressure and vice versa.

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.

The purpose of the study was to improve the risk prediction of SCD in post-MI patients by comparing the informative value of new non-invasive SCD risk stratification factors (HRT, mTWA, DC) with the well-known factors (impaired HRV, low left ventricular ejection fraction (LVEF), ventricular arrhythmias) both alone and in combination. Holter monitoring (HM) with evaluation of the above factors and echocardiography with LVEF measurement were performed in 111 patients (84 males and 27 females) aged 64.1 10.5 years who had MI from 2 months to 36 years (mean 27 [9; 84] months) prior to admission. The follow-up period was 12 months. The endpoints included SCD and overall cardiovascular mortality. During follow-up 15 cases of SCD and 8 other cardiovascular deaths (5 repeated fatal MI and 3 lethal strokes) were registered. LVEF was the most significant predictor of overall mortality followed by DC, HRT, HRV, mTWA and QRS width. LVEF turned out to be the most significant risk factor for SCD followed by HRT, QRS width, DC, number of PVCs per day and mTWA. Noninvasive electrophysiological predictors showed the maximum SCD predictive value in patients with LVEF >40%, whereas at lower LVEF their predictive value was either decreased or completely lost. Combined risk assessment revealed that combination of HRT2 and increased mTWA caused a significantly increased risk of cardiovascular death (OR 30.7 (95% CI, 3.5-271.6), p 40%. The combination of HRT2 and mTWA 100 >53 mcV is associated with a maximum increased risk of cardiovascular death and SCD.

The presence of myocardial scar detected by late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) imaging has been described as a good independent predictor of mortality in patients with hypertrophic cardiomyopathy (HCM). Time-domain T-wave alternans (TWA) is also a potential predictor of cardiac mortality in patients with left ventricular dysfunction.The purpose of this study was to elucidate the relationship between LGE distribution and TWA in patients with HCM.CMR and TWA analyses using Holter monitoring were performed in 42 patients with HCM. The average transmural extent of LGE was scored as 1-4 in each segment, and the sum of the LGE scores (total LGE score) was calculated for each patient. The correlation between the maximal time-domain TWA voltage and LGE findings was analyzed, and the differences in time-domain TWA voltage, total LGE score, and cardiac function assessed by CMR imaging in the presence or absence of ventricular tachycardia (VT) were also compared.The total LGE score was significantly and positively correlated with the maximal time-domain TWA voltage (r = 0.59; P.001). Furthermore, the total LGE score and maximal time-domain TWA voltage were significantly greater in patients who had episodes of VT (n = 21) than in those without VT (23 ± 7 vs. 10 ± 8; P.001 and 87 ± 26 μV vs. 62 ± 12 μV; P.001, respectively). However, the left ventricular ejection fraction did not statistically differ between patients with VT and those without VT (56% ± 14% vs. 61% ± 7%; P = .102).The magnitude of the localized LGE was significantly correlated with abnormalities in ventricular repolarization as assessed by TWA and QT dispersion.

The aim of this study is to analyze different sources of noise in ECG recordings from stress tests in order to obtain reliable parameters and measurements for the analysis of T-wave and QRS-complex alternans (TWA & QRSA). Simple methods for eliminating common sources of noise like power-line interference, baseline drift and electromyographic noise were used. The pre-processing phase considered the detection of steep slope/spike, low amplitude signal, and flat line or missing lead artefacts. The detection of TWA and QRSA was based on Principal Component Analysis indices and wave amplitudes considering all the leads. A particular database of 106 ECG records during stress testing was considered. The signal quality analysis performed in this study has permitted to obtain reliable and noise-tolerant measurements of TWA and QRSA indices. The different diagnostic groups were used for the evaluation of the clinical significance of the alternans. Men have significantly higher values of QRSA than women. Smokers have significantly higher TWA values as compared with non-smokers. Significant negative correlation was obtained between age and both TWA and QRSA. Correlations between TWA and QRSA and the double product of arterial hypertension and the maximal heart rate during the stress test were statistically significant, positive and relatively strong.

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

Objective The aim of this cross-sectional study was to evaluate microvolt T-wave alternans (MTWA) as a marker of myocardial electrical instability in normotensive and hypertensive individuals with either nondipper or dipper-type circadian rhythm of blood pressure. Materials and methods The study group included a total of 181 patients: 118 hypertensive patients and 63 normotensive healthy volunteers [mean age 46 ± 8; 34 men (54%)]. The patients with hypertension were divided into two groups on the basis of their results of 24-h ambulatory blood pressure monitoring: 61 patients with dipper hypertension [mean age 46 ± 6; 32 men (52.5%)] and 57 patients with nondipper hypertension [mean age 48 ± 10; 36 men (63.2%)]. The MTWAs of all patients were analyzed using the time-domain modified moving average method by means of a treadmill exercise stress test. Results MTWA positivity was statistically significantly different between all groups. Left ventricular mass index, E/E', interventricular septum, posterior wall, 24-h systolic blood pressure and diastolic blood pressure, and night-time systolic blood pressure and diastolic blood pressure were correlated positively with MTWA. Left ventricular mass index and the presence of nondipper hypertension were determined to be independent predictors of MTWA positivity. Conclusion The blunting of the nocturnal decrease in blood pressure was associated with MTWA positivity in hypertensive patients.

T-Wave alternans (TWA) testing using 12-lead electrocardiogram/Frank leads is emerging as an important non-invasive biomarker to identify patients at high risk of Sudden Cardiac Death (SCD). Cardiac scarring is very common among cardiomyopathy patients; however, its influence on the body surface distribution of TWA has not yet been defined. Our objective was to perform a simulation study in order to determine whether cardiac scarring affects the distribution of TWA on thorax such that the standard leads fail to detect TWA in some of cardiomyopathy patients; thereby producing a false-negative test. Developing such a novel lead configuration could improve TWA quantification and potentially optimize electrocardiogram (ECG) lead configuration and risk stratification of SCD in cardiomyopathy patients. The simulation was performed in a 1500-node heart model using ECGSIM. TWA was mimicked by simulating action potential duration alternans in the ventricles. Cardiac scarring with different sizes were simulated by manipulating the apparent velocity, transmembrane potential and transition zone at varied locations along the left ventricular posterior wall. Our simulation study showed that the location of maximum TWA depends on the location and size of the myocardium scarring in patients with cardiomyopathy, which can give rise to false-negative TWA signal detection using standard clinical leads. The TWA amplitude generally increased with the increment of scar size (P

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.

Several studies have demonstrated that oral intake of n-3 polyunsaturated fatty acids, specifically eicosapentaenoic acid (EPA), prevents ventricular tachyarrhythmias (VT) with ischemic heart disease, but the underlying mechanisms still remain unclear. Thus, we examined the relation between the serum EPA/arachidonic acid (AA) ratio and electrophysiological properties in patients with ischemic heart disease. The study subjects consisted of 57 patients (46 males, mean age, 66 ± 13 years) with ischemic heart disease. T-wave alternans (TWA) and heart rate variability were assessed by 24hour Holter ECG, and left ventricular ejection fraction (LVEF) was determined by echocardiography. Fasting blood samples were collected, and the serum EPA/AA ratio was determined. Based on a median value of the serum EPA/AA ratio, all subjects were divided into two groups: serum EPA/AA ratio below 0.33 (Group-L, n = 28) or not (Group-H, n = 29). We compared these parameters between the two groups. LVEF was not different between the two groups. The maximum value of TWA was significantly higher in Group-L than in Group-H (69.5 ± 22.8 μV versus 48.7 ± 12.0 μV, P = 0.007). In addition, VT defined as above 3 beats was observed in 7 cases (25%) in Group-L, but there were no cases of VT in Group-H (P = 0.004). However, low-frequency (LF) component, high-frequency (HF) component, LF to HF ratio, and standard deviation of all R-R intervals were not different between the two groups. These results suggest that a low EPA/AA ratio may induce cardiac electrical instability, but not autonomic nervous imbalance, associated with VT in patients with ischemic heart disease.

Background— Prophylactic defibrillator implantation is recommended in dilated, nonischemic heart disease and left ventricular ejection fraction of ≤0.30 to 0.35. Noninvasive testing should improve accuracy in decision making of prophylactic defibrillator implantation. Methods and Results— We enrolled 60 patients (median age, 57 years) with dilated cardiomyopathy and left ventricular ejection fraction ≤0.50, and 30 control subjects (median age, 59 years) with left ventricular ejection fraction >0.50. The protocol included an initial assessment, a second assessment after 3 years, and a final follow-up: pharmacological baroreflex testing (baroreceptor reflex sensitivity), short-term spectral analysis of heart rate variability (low frequency/high frequency), and long-term time domain analysis (SD of all normal-to-normal R–R intervals), exercise microvolt T wave alternans, and signal-averaged ECG, and corrected QT-time. The median follow-up was 7 years. End points were cardiac death, resuscitated cardiac arrest, and arrhythmic death. Cardiac death was observed in 21 patients. Resuscitated cardiac arrest and arrhythmic death caused by ventricular tachyarrhythmias ≥240 per minute was observed in 7 and 10 patients, respectively. In the single time point analysis, microvolt T wave alternans, baroreceptor reflex sensitivity, and SD of all normal-to-normal R–R intervals at initial testing added significant information regarding cardiac death. Microvolt T wave alternans added information on resuscitated cardiac arrest or arrhythmic death at multiple time points ( P Conclusions— Noninvasive testing and left ventricular ejection fraction could not reliably identify patients with dilated cardiomyopathy at risk of fatal ventricular tachyarrhythmias. Therefore, the strategy to confine prophylactic implantable cardioverter-defibrillator implantation to patients with dilated cardiomyopathy and severely reduced LV function should be reconsidered.

Timothy syndrome (TS) is a multisystemic disease that occurs because of a mutation in CACN1C gene and is characterized by prolonged QT interval. Mexiletine is a Class 1B antiarrhythmic drug that causes the disappearance of T-wave alternans by shortening QTc and peak-to-end of the T wave. It may block the development of torsades de pointes in a prolonged QT. This study presented the case of a patient diagnosed with TS and had a cardiac arrest history, prolonged QT, and T-wave alternans. After mexiletine treatment, the QTc interval shortened and T-wave alternans disappeared. Such a case has rarely been seen in the literature, and hence considered rare. This case presentation was of particular importance because it highlighted the use of mexiletine besides an initial beta-blocker treatment in the cases with TS.

BackgroundAcute myocardial ischemia is a common cause of ventricular arrhythmias, yet recent ECG methods predicting susceptibility to ventricular tachyarrhythmia have not been fully evaluated during spontaneous ischemia. We sought to evaluate the clinical utility of alternans and non-alternans components of repolarization variability from the standard 10-second 12-lead ECG signals to risk stratify patients with acute chest pain.MethodsWe enrolled consecutive, non-traumatic, chest pain patients transported through Emergency Medical Services (EMS) to three tertiary care hospitals with cardiac catheterization lab capabilities in Pittsburgh, PA. ECG signals were manually annotated by an electrophysiologist, then automatically processed using a custom-written software. Both T wave alternans (TWA) and non-alternans repolarization variability (NARV) were calculated using the absolute RMS differences over the repolarization window between odd/even averaged beats and between consecutive averaged pairs, respectively. The primary study outcome was the presence of acute myocardial infarction (AMI) documented by cardiac angiography.ResultsAfter excluding patients with secondary repolarization changes (n=123) and those with excessive noise (n=90), our final sample included 537 patients (age 57±16years, 56% males). Patients with AMI (n=47, 9%) had higher TWA and NARV values (p

Sleep apnea (SA) is linked to cardiovascular complications and to an increased risk of sudden cardiac death. Microvolt T-wave alternans (TWA) is a noninvasive electrocardiographic (ECG) index of cardiovascular risk; its rate of occurrence in SA patients remains unknown. Thus, this study investigated the occurrence of TWA in SA patients during night. To this aim, overnight ECG recordings of 16 SA patients were analyzed for TWA identification by means of our heart rate adaptive match filter. Results indicate that overnight TWA was characterized by a low mean amplitude (mean TWA: 6±3 μV). However, higher-amplitude transient TWA episodes (max TWA: 29±21 μV) occurred overnight, sometimes when patients were awake (max TWA: 33±18 μV; 56% of cases) and sometimes when patients were sleeping (max TWA: 24±23 μV; 44% of cases with 13%, 19%, 6% and 6% during sleep stage 1, 2, 3 and 4, respectively). In only 3 subjects (19%) TWA peaks occurred during an SA episode: during obstructive apnea with arousal in two cases (max TWA of 7 μV and 17 μV, during stages 1 and 2, respectively) and during hypoapnea with arousal in one case (max TWA of 6 μV while awake). Thus, SA patients show significant transient overnight TWA episodes, not necessarily occurring during a SA episode.

Hypertrophic cardiomyopathy (HCM) is a common cardiac genetic disorder. It is a leading cause of sudden cardiac death in young adults, yet most patients remain asymptomatic. T wave alternans (TWA) have been proposed as a potential tool for HCM risk stratification [1] [2] [3] but the mechanisms at stake remain unclear [4] [5]. HCM has been associated with a dysregulation of Ca2+ cycling and an elevation in intracellular calcium concentration [6] that may affect the cardiac action potential (AP). Our goal is to investigate whether these electrophysiological abnormalities may be a mechanism responsible for the presence of TWA in HCM. We use a population of 9,118 control and HCM models defined in [7] and measure alternans in AP and Ca2+ transient biomarkers for pacing cycle lengths from 250ms to 700ms. HCM cardiomyocytes show a distinct AP phenotype with longer AP and Ca2+ duration (486±84ms vs 286±52ms, 691±82ms vs 522±65ms p

Very little is known about the incidence and etiology of fetal T-wave alternans (TWA), an electrophysiologic phenomenon potentially associated to fetal suboptimal outcomes. Thus, availability of automatic methods for quantification of TWA from digital electrocardiograms (ECG) is desirable, since TWA occurrence might indicate the need of taking actions before or during delivery. The heart-rate adaptive match filter (HRAMF) is a well-established method to identify TWA in adult ECG. Aim of the present study was to investigate the possibility of using HRAMF to identify and quantify TWA also in direct fetal ECG (DFECG) recordings. To this aim, HRAMF was applied to 5 min-long DFECG acquired during delivery ("Abdominal and Direct Fetal Electrocardiogram Database" by Physionet) of five healthy fetuses. Significant levels of TWA were measured in all DFECG. Specifically, on average, TWA was quite high in amplitude (9±2 μV) and variable in time, as indicated by values of standard deviation (6±2 μV) and maximum (28±10 μV) of TWA amplitude. Eventually, a positive correlation (ρ=0.68) was observed between maximum TWA and fetal heart rate, even though the limited number of recordings makes this result preliminary. In conclusion, HRAMF proved to be a suitable tool to automatically identify TWA from DFECG.

Objective We analysed the prevalence of TWA during cardiopulmonary stress test (CPT) in athletes and in patients with suspected or proven coronary artery disease with stress electrocardiographic test. Materials and Methods Athlete's group comprised 414 subjects (24±8 years, 95.5% males), non-athlete's — 107 (63±10 years, 42% males). Stress testing lasted longer and heart rate (HR) increased more in athletes compared to non-athletes. A TWA cluster was defined in case of uninterrupted appearance of TWA > 30 seconds. Results Our initial analysis revealed higher prevalence and worse parameters of TWA in athletes compared to non-athletes: at least one TWA cluster in 389 athletes (94.0%) and in 56 (52.3%) non-athletes, p

We present the case of a 62-year-old woman with levofloxacin-induced Torsade de Pointes, in whom microvolt T-wave alternans was measured during acute hospitalization and when QT interval was dynamically changing, illustrating a means for monitoring proarrhythmia.

T-Wave alternans (TWA) is a cardiac phenomenon regarded as an index of high risk of sudden cardiac death (SCD). Although a number of methods have been proposed for TWA detection, their final decision always fully depends on one single lead which is usually picked out for its strongest TWA detection result among all the other leads. That is to say that lots of useful information have been unused and wasted. To our best knowledge, no method that fuses TWA detection results independently obtained by each lead to do comprehensive decision has been introduced. In this paper, a novel multi-lead method for TWA fusion detection is proposed. This method combines Dezert-Smarandache theory (DSmT) with Laplacian likelihood ratio method (LLR) to gain higher detection rate. The proposed method was evaluated and compared with standard LLR method by means of a simulation study, in which extracted TWA waveform and clean background ECG from real records were used to synthetize simulated data with different types of simulated or physiological noises. These methods were also applied to real records from PTB Diagnostic ECG Database. The results are presented by constructing receiver-operator characteristic (ROC) curves. All test results show that the proposed method has a larger margin of separability and higher detection rate than traditional methods. A more accurate and robust TWA detection method has great value to predict the risk of sudden cardiac death(SCD).

Objectives: To evaluate predictive value of heart rate turbulence (HRT), deceleration capacity (DC) and microvolt T-wave alternans (mTWA) for risk stratification for sudden cardiac death (SCD) in patients after myocardial infarction (MI) during 60 months of follow-up.Methods: We studied 111 patients after MI occurred > 60 days (27 [9; 84] months) before enrollment (84 men; mean age 64.1±10.5 years). All subjects had 24-hour ambulatory ECG monitoring with HRT, DC and mTWA evaluation. Follow-up period was 60 months; primary endpoint was SCD, secondary endpoint included all non-sudden cardiovascular deaths.Results: During follow-up, we registered 19 cases of SCD and 11 cases of non-sudden cardiovascular deaths (including 7 fatal MI and 3 fatal strokes). DC had high negative predictive value (97.4% for all-cause mortality and 93.7% for SCD). DC values below 4.15 for all-cause mortality and 2.0 for SCD significantly increased risk of all-cause mortality (OR 8.5, 95% CI 2.9 to 24.6, р 53 mcV, which increased risk both of all-cause mortality (30.7-fold) and SCD (63.3-fold); however, at 60 months this predictive value for SCD decreased (OR = 20.8 (95% CI 2.8 to 114.0), p Conclusion: Evaluation of HRT, DC and mTWA during 24-hour ECG monitoring may define the high risk of cardiovascular mortality and SCD in post-MI patients especially during the first 12 months after the baseline examination.

A 26-year-old woman, 12 days in postpartum, developed recurrent syncope and cardiac arrest. Her ECG revealed QT-prolongation associated with LQT2-specific T-U wave patterns, T wave alternans, long QT-dependent torsade de pointes (TdP) and ventricular fibrillation (VF). She also had intermittent LBBB (80bpm) on alternate beats and RBBB at sinus tachycardia (113bpm). Family genotyping revealed a novel de novo missense mutation G604C of KCNH2. Propranolol slowed heart rate and further prolonged QT interval (610ms) that caused TdP recurrence. Mexiletine combined with magnesium and potassium supplements prevented TdP/VF recurrence. This patient has remained event-free after 9-month follow-up.

Background Patients with long QT syndrome (LQTS) are predisposed to polymorphic ventricular tachycardia (VT) during adrenergic stimulation. Microvolt T-wave alternans (MTWA) is linked to vulnerability to VT in structural heart disease. The prevalence of non-sustained MTWA (NS-MTWA) in LQTS is unknown. Methods 31 LQT1, 42 LQT2, and 80 controls underwent MTWA testing during exercise. MTWA tests were classified per standardized criteria, and re-analyzed according to the modified criteria to account for NS-MTWA. Results LQT1 and LQT2 patients had a significantly higher frequency of late NS-MTWA (26% and 12%) compared to controls (0%). There was no significant difference between the groups with respect to sustained and early NS-MTWA. Late NS-MTWA was significantly associated with QTc. Conclusion LQT1 and LQT2 patients had a higher prevalence of late NS-MTWA during exercise than matched controls. NS-MTWA likely reflects transient adrenergically mediated dispersion of repolarization, and could be a marker of arrhythmic risk in LQTS.

Sudden cardiac death (SCD) due primarily to ventricular fibrillation claims 1.5 million lives worldwide each year. In 45%–50% of cases, it is the first manifestation of underlying heart disease. Traditional risk factors including smoking, hypertension, age, sex, as well as depressed left ventricular ejection fraction lack sufficient sensitivity and specificity to forewarn of impending life-threatening arrhythmias. There has been a decades-long search for electrocardiographic (ECG) markers of SCD risk. Several interval-based indices such as QT dispersion and Tpeak-Tend interval held initial promise but ultimately yielded mixed results. Recently, the focus has been on interlead heterogeneity of R- and T-wave morphology. The new approaches have involved advanced analytical tools including vectorcardiographic techniques and second central moment analysis of QRS-aligned templates to quantify heterogeneity of depolarization and repolarization waveforms. The results of current studies appear to be robust and worthy of further exploration. This review examines the electrophysiological underpinnings of heterogeneity-based risk assessment and provides an update of clinical techniques. We also discuss future directions whereby tracking heterogeneity may help to disclose latent risk for SCD not only in ECG recordings made at rest but also during ambulatory ECG monitoring and exercise tolerance testing.

Background We tested the hypothesis that an alpha-glucosidase inhibitor (α-GI), miglitol, is effective in protecting the cardiovascular system in type 2 diabetes mellitus (T2DM). Methods We studied 19 hospitalized heart disease patients with T2DM in whom we performed continuous glucose monitoring, Holter electrocardiogram, and ambulatory blood pressure (BP) monitoring simultaneously for 48 h. The α-GI miglitol was administered for half of the study period by a cross-over fashion. T-wave alternans (TWA), a marker of future fatal arrhythmic events, was also analyzed by Holter ECG. Results Of the 19 patients, the measures of glucose variability were significantly lower during miglitol therapy than in control period. BP variability was similar with/without miglitol. However, TWA was significantly lower during the miglitol period compared to control period (63 ± 4.8 vs. 75.8 ± 5.1 μV, p = 0.032). Conclusion An α-GI, miglitol, can reduce TWA by reducing the fluctuation of glucose in heart disease patients with T2DM.

Background. Development of the methods for identification and assessment of early signs of heart disorders makes it possible to catch the sight of disease at its initial stage. The article considers the methods of early diagnosis of the cardiovascular system using electrocardiographic markers of cardiac electrical instability.Objective. The aim of the study is to identify low-amplitude components, which are inaccessible to standard procedures of electrocardiogram (ECG) evaluation by means of modern methods of registration, digital processing of electrocardiosignals and high resolution electrocardiography.Methods. For detection of diagnostic symptoms associated with cardiac electrical instability, changes in real and simulated electrocardiosignals have been studied using different types of analysis: in time and frequency domains, scattergrams, cluster analysis, wavelet analysis and principal component analysis.Results. The developed combined methods for analysis of low-amplitude components of electrocardiosignals allowed us to perform detection of late potentials, as well as T wave alternans, reflecting cardiac electrical instability.Conclusions. Identification and evaluation of subtle manifestations of cardiac electrical activity are carried out. The use of the proposed method made it possible to distinguish the bursts of late potentials from the noise and to determine the temporal area of their localization., Проблематика. Розробка методів ідентифікації та оцінювання ранніх ознак захворювань серця дає змогу виявити порушення в роботі серця на початковій стадії. У статті розглядаються методи ранньої діагностики серцево-судинної системи з використанням електрокардіографічних маркерів електричної нестабільності міокарда.Мета дослідження. Виявлення низькоамплітудних компонент електрокардіосигналів, які неможливо проаналізувати за допомогою стандартних процедур оцінювання електрокардіограми (ЕКГ), із використанням сучасних методів реєстрації, цифрової обробки електрокардіосигналів і електрокардіографії високого розділення.Методика реалізації. Для виявлення діагностичних ознак, пов’язаних з електричною нестабільністю міокарда, зміни в реальних і змодельованих електрокардіосигналах були вивчені з використанням різних видів аналізу: в часовій і частотній областях, скатерограм, кластерного аналізу, вейвлет-аналізу та аналізу головних компонент.Результати досліджень. Розроблені комбіновані методи аналізу низькоамплітудних компонент електрокардіосигналів дали змогу виконати виявлення пізніх потенціалів, а також альтернації Т-зубця на ЕКГ, які є маркерами електричної неста­біль­ності міокарда.Висновки. Проведено виявлення та оцінювання тонких проявів електричної активності серця. Використання запропонованого методу дало змогу виділити сплески пізніх потенціалів на фоні шуму і визначити часову область їх локалізації., Проблематика. Разработка методов идентификации и оценивания ранних признаков заболеваний сердца позволяет выявить нарушения в работе сердца на начальной стадии. В статье рассматриваются методы ранней диагностики сердечно-сосудистой системы с использованием электрокардиографических маркеров электрической нестабильности миокарда.Цель исследования. Выявление низкоамплитудных компонентов электрокардиосигналов, которые невозможно проанализировать при помощи стандартных процедур оценивания электрокардиограммы (ЭКГ), с использованием современных методов регистрации, цифровой обработки электрокардиосигналов и электрокардиографии высокого разрешения.Методика реализации. Для выявления диагностических признаков, связанных с электрической нестабильностью миокарда, изменения в реальных и смоделированных электрокардиосигналах были изучены с использованием различных видов анализа: во временной и частотной областях, скатерограмм, кластерного анализа, вейвлет-анализа и анализа главных компонент.Результаты исследований. Разработанные комбинированные методы анализа низкоамплитудных компонент электрокардиосигналов позволили выполнить обнаружение поздних потенциалов, а также альтернацию Т-зубца ЭКГ, которые являются маркерами электрической нестабильности миокарда.Выводы. Проведено выявление и оценивание тонких проявлений электрической активности сердца. Использование предложенного метода позволило выделить всплески поздних потенциалов на фоне шума и определить временную область их локализации.

Patients with hypertrophic cardiomyopathy (HCM) have elevated risk for sudden cardiac death (SCD). Our study aimed to quantitatively characterize microvolt T-wave alternans (TWA), a potential arrhythmia risk stratification tool, in this HCM patient population.TWA was analyzed with the quantitative modified moving average (MMA) in 132 HCM patients undergoing treadmill exercise testing, grouped according to Maron score risk factors as high-risk (H-Risk, n=67,), or low-risk (L-Risk, n=65, without these risk factors).TWA levels were much higher for the H-Risk than for the L-Risk group (101.40±75.61 vs. 54.35±46.26μV; p0.0001). A 53μV cut point, set by receiver operator characteristic (ROC), identified H-Risk patients (82% sensitivity, 69% specificity).High TWA levels were found for hypertrophic cardiomyopathy patients. Abnormal TWA associated with major risk factors for SCD: non-sustained ventricular tachycardia on Holter (p=0.001), family history of SCD (p=0.006), septal thickness ≥30mm (p0.001); and inadequate blood pressure response to effort (p=0.04).

Sudden cardiac death (SCD) is the leading cause of cardiovascular mortality, accounting for more than 50% or greater than 300,000 deaths in the United States annually. As such, this is a major health care problem. Identifying high risk patients that may benefit from preventative strategies has been studied for decades. The implantable cardiac defibrillator (ICDs) has had a major impact on the treatment of SCD. However, this therapy has been largely used in patients with left ventricular dysfunction. A changing epidemiology of SCD with fewer patients having marked reductions in left ventricular ejection fraction (LVEF) has renewed the focus on identifying other high risk populations. This chapter summarizes the current understanding of the diverse clinical, genetic, electrocardiographic and imaging techniques available to detect patients most at risk. Despite many identified risk factors, no single predictor has been shown to have sufficient predictive value to be used to guide preventative therapy and reduce mortality. More recent effort has been directed towards combining markers to increase the sensitivity of identifying high risk cohorts.

Objective Indications for sudden cardiac death (SCD) primary prevention are unknown in patients with repaired tetralogy of Fallot (ToF). The role of microvolt T-wave alternans (MTWA) in SCD risk stratification was documented. However, the prevalence of spectral MTWA and its association with ventricular arrhythmia (VA) in adults after ToF repair were not elucidated. Design Microvolt T-wave alternans, electrocardiogram (ECG), ambulatory ECG monitoring, echocardiography, and spiroergometry were evaluated in 102 adults after ToF repair. Microvolt T-wave alternans results were classified as normal: negative(−), abnormal: positive(+), and indeterminate(ind). Owing to similar prognostic significance, MTWA(+) and MTWA(ind) due to patient factors were combined into nonnegative group: MTWA(abnormal). Results Microvolt T-wave alternans(abnormal) was more frequent in the studied group as compared with controls (P = .0005). The MTWA(abnormal) group had greater right ventricular end-diastolic diameter (P = .005), higher incidence of pulmonary regurgitation (P = .015), lower peak oxygen consumption (P = .01), and higher VE/VCO2 slope (P = .04) in comparison with MTWA(normal). Univariate logistic regression proved pulmonary regurgitation (OR = 3.57, 95% CI 1.27–10.04), VA (OR = 3.26, 95% CI 1.06–10.05), right ventricular end-diastolic enlargement (OR = 1.11, 95% CI 1.03–1.2), increase in VE/VCO2 slope (OR = 1.08, 95% CI 1.01–1.17), and decrease in peak oxygen uptake (OR = .91, 95% CI 0.83–0.99) to increase MTWA(abnormal) prevalence. Conclusions In adults after ToF repair, abnormal MTWA occurred more often than in controls. Probability of abnormal MTWA did not rise with prevalence of malignant VA; however, presence of abnormal MTWA was associated with VA risk factors: pulmonary regurgitation, right ventricular enlargement, and consequent heart failure. The role of MTWA in selecting patients late after ToF repair at risk of SCD needs further observation.

Aims T-wave alternans (TWA) represents myocardial instability. The present study was to determine the impact of cardiac resynchronization therapy (CRT) on TWA and left ventricular ejection fraction (LVEF) in heart failure patients. Methods and results T-wave alternans was analysed using a spectral method in 27 CRT-ICD patients. Ambulatory device electrograms were collected and LVEF and New York Heart Association (NYHA) classification were assessed at baseline prior to CRT and 3 months following CRT. Patients were followed for 6 months to monitor cardiac events. Spectral TWA of device electrograms was measured during AAI and CRT pacing tests. Each pacing mode had the up-titration pacing rate from 90 to 105 b.p.m. with 90 s for each pacing rate. At baseline, 20 (76.9%) patients had TWA during AAI pacing tests and 13 (50%) during CRT pacing tests ( P = 0.044 between two pacing modes). Following 3-month CRT, TWA was identified in 11 patients (45.8%) during AAI pacing tests (a 31.1% reduction from the baseline value, P = 0.023) and 7 patients (28%) during CRT pacing tests (a 22% reduction, P = 0.108). Six of seven patients who had cardiac events had TWA (three patients had arrhythmic events, two died of heart failure, one received heart transplant). Overall, LVEF improved from 27.3 ± 5.8 to 35.9 ± 10.5% ( P < 0.001) and NYHA classification improved from 2.8 ± 0.6 to 1.6 ± 0.6 after 3-month CRT ( P < 0.001). Conclusion In heart failure patients who receive a CRT-ICD, CRT reduces TWA that is associated to cardiac events, suggesting that CRT promotes clinically significant reverse electrical and mechanical remodelling.

T-wave alternans (TWA) is a noninvasive index of risk for the occurrence of ventricular arrhythmias. It is known that TWA amplitude (TWAA) increases with heart rate (HR) but how the TWA predictive power varies with HR remains unknown. Thus, the aim of this study was to evaluate the dependency of exercise-induced TWA predictive power for the occurrence of ventricular arrhythmias from HR.TWA was identified using our HR adaptive match filter in exercise ECGs from 248 patients with implanted cardiac defibrillator (ICD), of which 72 developed ventricular tachycardia and/or fibrillation during the 4 year follow-up (ICD_Cases) and 176 did not (ICD_Controls). TWA predictive power was evaluated at HRs from 80 to 120 bpm by computing the area under the receiver operating characteristic curve (AUC) obtained using the maximum TWAA (maxTWAA) and the TWAA ratio (TWAAratio; i.e., the ratio between TWAA at a specific HR and at 80 bpm).TWAA increased with HR. At 80 bpm maxTWAA was lower than at 120 bpm in both ICD_Cases (22 μV vs 41 μV; P < 10(-2) ) and ICD_ Controls (16 μV vs 36 μV; P < 10(-4) ). However, only at 80 bpm ICD_Cases showed significantly higher maxTWAA than ICD_Controls (AUC = 0.6486; P = 0.0080). TWAAratio was higher in ICD_Controls than ICD_Cases for all HR but 120 bpm, and its predictive power was maximum at 115 bpm (AUC = 0.6914; P < 0.05).Exercise-induced TWA predictive power for the occurrence of ventricular arrhythmias, quantified using both maxTWAA and TWAAratio, was higher at low rather than at high HR.

T-wave alternans, a beat-to-beat re-polarization pattern variation phenomenon, plays an important role in sudden cardiac death prediction. The proposed method modifies the currently available Modified Moving Average Method (MMAM) by a multi-lead principal component analysis (PCA) approach. Application of PCA will concentrate the alternans effect, which is supposed to be distributed on multiple leads in a single derived lead. MMAM is applied to the derived lead and alternans magnitude is measured. Results are compared with MMAM, implemented by the authors and by an open source tool, TWAnalyser. The TWA Physionet/CinC 2008 Challenge Database is used for testing. Performances are measured in terms of root mean square error (rmse) and correlation coefficients. The rmse is highest for TWAnalyser results and lowest for the proposed method. While the correlation coefficient is highest for the proposed method, 0.88, that for normal MMAM is 0.73 and for TWAnalyser is 0.75. The proposed multi-lead PCA approach provides improved performance of current MMAM.

The aim of the Endocardial T-Wave Alternans Study was to prospectively assess the presence of T-wave alternans (TWA) or beat-to-beat repolarization changes on implantable cardioverter-defibrillator (ICD)-stored electrograms (EGMs) immediately preceding the onset of spontaneous ventricular tachycardia (VT) or fibrillation (VF).

OBJECTIVE Microvolt T-wave Alternans (TWA) is associated with abnormal repolarization and predicts arrhythmic mortality in patients with previous myocardial infarction (MI). Infarct tissue size and heterogeneity characterized by cardiac magnetic resonance (CMR) has been shown to be associated with arrhythmogenic substrates and sudden cardiac death. Although both delayed enhancement-CMR (de-CMR) and TWA are useful in risk stratification of post-MI patients with preserved left ventricular function, the relationship between scar size and TWA has not studied yet. In this study, we aimed to study the relation between TWA and scar size and characteristics assessed with CMR in post-MI patients (pts) with relatively preserved systolic function presented with nonsustained VT. METHODS This observational cross-sectional study was enrolled 36 post-MI patients with mild-systolic dysfunction and non-sustained ventricular tachycardia. Eight pts were excluded. Both TWA and contrast enhanced CMR were performed. Left ventricular ejection fraction (LVEF), dense scar, peri-infarct zone and total scar masses were assessed and these values to left ventricular (LV) mass ratios were calculated. Infarct ratios and characteristics were determined and compared among patients with negative TWA and those with positive TWA. RESULTS For the positive (n=12) vs. negative (n=16) TWA patients there were no significant difference between LVEF (44.9 ± 5.4% vs. 44.0 ± 3.2%, p=NS) and LV masses (121.89 ± 26.56 g vs. 106.14 ± 21.16 g, p=NS). The ratio of scar core to LV mass (3.37 ± 0.68% vs. 3.31 ± 1.01%, p=NS), peri-infarct zone to LV mass (23.61 ± 7.93% vs. 21.64 ± 9.08%, p=NS), total scar to LV mass (26.98 ± 7.86% vs. 24.96 ± 9.62%, p=NS) were all similar. CONCLUSION There were no association between scar size and infarct heterogeneity and prevelance of TWA in post-MI patients with relatively preserved LVEF with non-sustained VT. Our data suggest that these two modalities may reflect different arrhythmogenic mechanisms in this cohort.

We explored the utility of T-wave alternans (TWA) in predicting mortality in patients with non-ST-segment elevation acute coronary syndrome (NSTEACS). Maximum TWA was calculated using Modified Moving Average method from continuous electrocardiographic recordings in patients with left ventricular ejection fraction40% and ventricular tachycardia (VT) ≥4 beats during index hospitalization or sudden cardiac death during the follow-up year and age- and sex-matched controls in the Metabolic Efficiency with Ranolazine for Less Ischemia in Non-ST Elevation Acute Coronary Syndrome-Thrombolysis In Myocardial Infarction (MERLIN-TIMI) 36 trial. All patients received standard therapy for NSTEACS plus ranolazine (n = 109) or placebo (n = 101). Median follow-up was 1 year. Baseline clinical characteristics did not differ between patients with elevated TWA (≥47 μV) compared with lower levels. Patients with TWA ≥47 μV at admission had increased risk of total mortality (adjusted odds ratio [ORadj] 2.35, p = 0.04) during follow-up and VT ≥4 beats (ORadj 2.70, p = 0.01) during hospitalization with a trend toward increased cardiovascular death risk (ORadj 2.18, p = 0.07) during follow-up. In patients receiving placebo, TWA ≥47 μV on day 6 was associated with increased risk of total mortality (OR 4.12, 95% confidence interval 1.25 to 13.64, p = 0.02) and cardiovascular death (OR 4.73, p = 0.01) during follow-up. No deaths occurred among patients with TWA ≥47 μV assigned to ranolazine. In conclusion, in patients with NSTEACS and left ventricular ejection fraction40%, TWA ≥47 μV early after admission is associated with increased risk of mortality at 1 year and with nonsustained VT during hospitalization. TWA may be useful in risk estimation in patients with NSTEACS. The possibility that TWA may serve as a therapeutic target deserves further exploration.

INTRODUCTION Recent studies point to analysis of T-wave alternans as a promising indicator of an increased risk of life-threatening ventricular arrhythmias. In this study the occurrence of T-wave alternans in the high-resolution ECGs recorded during the exercise stress test and scintigraphic tests (SPECT) in patients with ischemic heart disease was examined. MATERIAL AND METHODS The study group consisted of 33 patients after myocardial infarction. In the group of patients after myocardial infarction and with low left ventricular ejection fraction correlations of 70% between the test results of T-wave alternans and SPECT and 60% between the test results of T-wave alternans and stress test were found. RESULTS In the group of patients after myocardial infarction but with high left ventricular ejection fraction correlations were respectively 39% and 48%. The analysis of the electrocardiographic maps showed a strong dependence of this correlation on the T-wave alternans amplitude and location of the ECG measuring electrode on the chest. The results might suggest that in patients after myocardial infarction and at increased risk for sudden cardiac death T-wave alternans may also provide information about cardiac electrical instability associated with ischemia. CONCLUSIONS It can also be assumed that the position of the electrode where the highest level of the T-wave alternans was detected can indicate the location of the ischemic region of the heart.