Characterization of T wave alternans with ambulatory electrocardiography.

T wave alternans (TWA) is a marker of ventricular electrical instability considered to be predictive for ventricular tachyarrhythmias. Techniques have been developed to detect TWA at the microv level as a method for arrhythmia risk stratification of persons at high risk for sudden cardiac death. Currently, TWA is typically calculated using spectral analysis, whereby TWA is presumed to assume characteristics of stationarity. In contrast, a nonspectral method known as modified moving average analysis is purported to detect transient TWA that would not be observed using a spectral approach. The purpose of this pilot study work was to establish the basic TWA signal properties obtained with a device developed by GE Medical Systems using a descriptive, correlational study design. Ambulatory electrocardiography (AECG) recordings (N = 24) were digitized and processed, and TWA was calculated via the modified moving average technique. Findings showed that noise was positively correlated with TWA in AECG channel 1 (r = .899, p < .01) and AECG channel 2 (r = .758, p < .01). However, no significant difference (p = .237) was observed in TWA values between the AECG channels. A weak positive correlation was found between TWA and heart rate, expressed as beats per min (r = .262). Heart rate mildly predicted TWA (R = 0.34). Nonstationarity was evaluated by testing for trend and randomness. TWA values measured from AECG recordings were found to be influenced moderately by noise and minimally by heart rate and lead placement.