A new robust T wave alternans detector and its threshold optimization

The conventional spectral method is indeed a typical confidence interval computation that use normalized Fourier transform frequencies F{f} at f = 0.5. In order to get a robust detector with respect to spikes due to single-frequency tone interference and to exploit the entire frequency band to reduce the variance we proposed new parameter called SMM (F{0.5}/median(F{]0.5, 0[})). The second stage of this work was to optimize the threshold selection by using a full Monte-Carlo simulation where alternans/no-alternans episodes of length 16 with magnitude of 2 were corrupted by a gaussian noise with different powers and a sines with different frequencies. All the combinations of noise and frequency, repeated 500 times, were selected in order to compute a mean probability of detection (Pd) and mean false alarm probability (Pfa) for different thresholds. Imposing Pfa=0.05, we get the Pd for the t-test, matched pair t-test, GLRT, SM, SMM equal to 0.65, 0.68, 0.63, 0.75, 0.8, respectively. The optimized threshold is 2.05 for SMM and 3.6 for SM. Study group consisted of 50 patients with ICD stimulated (ventricular) at 100bpm (age: 55.3 σ16.4; LVEF: 42.8 σ15.5). Two minutes recordings were analyzed. XYZ orthogonal lead system was used. The best performance was detected with use of SMM method in comparison with conventional spectral method. Positive TWA was detected when median of duration of all episodes above threshold was greater than 4.