T-wave Alternans Analysis Research Articles

T-wave alternans for risk stratification and prevention of sudden cardiac death.

Despite considerable progress in the management of ischemic heart disease, a substantial proportion of patients continue to experience life-threatening arrhythmic events. The Multicenter Automatic Defibrillator Implantation Trial 2 has recently shown the superiority of implantable cardioverter defibrillators (ICDs) over conventional strategies to prevent sudden death in patients with reduced ejection fraction, but at the expense of potentially unnecessary ICD implantation in a large percentage of patients. T-wave alternans (TWA), which reflects alternation of cellular repolarization, results in a substantial increase in dispersion of repolarization, a prerequisite for reentrant arrhythmias. Recent trials, cumulating close to 3000 patients, have established TWA analysis as a powerful tool for arrhythmia prevention. Based on the most recent estimates, at least one third of post-myocardial infarction patients are expected to be tested negative. With a negative predictive value greater than 90%, TWA might allow for targeting of patients most likely to benefit from ICD therapy. Accurate identification of high-risk patients by noninvasive TWA may allow for improved widespread screening for sudden death prevention in the general population.

Short‐Term Reproducibility of T Wave Alternans Measurement

Microvolt T wave alternans (TWA) has been proposed as a strong independent predictor of malignant ventricular tachyarrhythmias and sudden cardiac death. TWA reproducibility during bicycle stress test has not been previously investigated. We sought to assess the short-term reproducibility of TWA, as well as heart rate (HR) threshold for TWA, and its spatial distribution and magnitude. The study enrolled 42 patients who were able to complete two bicycle stress tests with HR at peak exercise >110 beats/min within 4 hours of each other and who had technically adequate recordings for TWA analysis during both tests. Concordant results for TWA determination were obtained in 39 (93%) of 42 cases. TWA was present during both tests in 23 patients and was absent during both tests in 16 patients. In the 23 patients with two positive tests, HR at the onset of TWA was not significantly different during the two tests. Further, the number of leads showing TWA and the magnitude of TWA were not significantly different between the two tests. TWA is characterized by satisfactory short-term reproducibility and, when present, by high temporal and spatial stability.

Modified moving average analysis of T-wave alternans to predict ventricular fibrillation with high accuracy.

T-wave alternans is a marker of cardiac electrical instability with the potential for arrhythmia risk stratification. The modified moving average method was developed to measure alternans in settings with artifacts, noise, and nonstationary data. Algorithms were developed and performance characteristics were validated with simulated electrocardiograms (ECGs). Experimental laboratory ECGs with dynamically changing alternans values were analyzed. Alternans values estimated by modified moving average analysis correlated strongly with input alternans values (r(2) = 0.9999). Rapidly changing alternans levels and phase reversals did not perturb the measurement. When heart rate was increased from 60 to 180 beats/min, with T-wave alternans apex moving from 237 to 103 ms after the R wave, the measured alternans peak varied <5% from input value. Simulated 50- to 1,000-microV motion artifact spikes typical of treadmill ECGs produced inaccuracies <2%. Alternans values in experimental laboratory study using standard electrodes tracked vulnerability to myocardial ischemia-induced ventricular fibrillation with 100% sensitivity and specificity at a cut point of 0.75 mV. Modified moving average analysis is a robust method that precisely measures T-wave alternans in settings with artifacts, noise, and nonstationary data typical of clinical ECGs and yields an accurate estimate of risk for ventricular fibrillation.

Optimizing ambulatory ECG monitoring of T-wave alternans for arrhythmia risk assessment.

Considerable scientific data support the potential value of T-wave alternans (TWA) as an index of vulnerability to ventricular fibrillation. This chapter summarizes our state of knowledge regarding the use of routine ambulatory ECGs to evaluate TWA and discusses recent methodologic approaches designed to optimize AECG-based TWA analysis for arrhythmia risk stratification. Newer methods, including the nonspectral technique of Modified Moving Average analysis, appear promising in detecting TWA during the changing conditions associated with daily activities. The Modified Moving Average approach does not require specialized electrodes and is not encumbered by the need to achieve target heart rates, as is the case for conventional spectral-based methods. Guidelines are provided for evaluating latent cardiac electrical instability using AECG-based TWA testing. These recent developments make possible the TWA analysis of ambulatory ECGs not only in prospective trials but also in vast stores of archival data.

T wave alternans and ventricular arrhythmias in arterial hypertension.

Patients with a positive microvolt-level T wave alternans (TWA) are characterized by an increased risk of ventricular tachyarrhythmias. Arterial hypertension leads to an increase of sudden cardiac death risk, particularly if left ventricular hypertrophy is present. The aim of this study was to investigate the value of TWA in patients with arterial hypertension. Fifty-one consecutive patients were included in the study. TWA analysis was performed with patients sitting on a bicycle ergometer and exercising with a gradual increase of workload to maintain a heart rate of at least 105/min. After recording 254 consecutive low-noise-level heartbeats, the exercise test was stopped. The ECG signals were digitally processed by a spectral analysis method. The magnitude of TWA was measured at a frequency of 0.5 cycle per beat. A TWA was defined as positive if the ratio between TWA and noise level was >3.0 and the amplitude of the TWA was >1.8 microV. Eight of the 51 patients (16%) showed a positive TWA. If left ventricular hypertrophy was present, the prevalence of TWA was higher (33.3% versus 8.3%; P:<0.05). Sensitivity concerning a previous arrhythmic event was 73%, and specificity was 100%. The alternans ratio was significantly higher in patients with a previous event (39.3+/-62.3 versus 2.4+/-4.6; P:<0.001), as was the cumulative alternans voltage (4.7+/-4.1 versus 1.6+/-1.9 microV; P:<0.001). In 16 patients invasively investigated by an electrophysiological study, a significant correlation between inducibility of tachyarrhythmias and a positive TWA result was found (Spearman R:=0.36, P:=0.01). We conclude that the arrhythmic risk of patients with arterial hypertension is markedly increased if microvolt-level TWA is present. The prevalence of TWA is higher in patients with left ventricular hypertrophy.