Time frequency distributions (Wavelet Transform, WT) and Short-Time Fourier Transform (STFT) of the XYZ vector magnitude of the body-surface electrocardiogram of a patient with and a patient without ventricular tachycardia (VT).
 

Post-MI patient with VT and late potentials Wavelet transform (scalogram) Prolonged high-frequency activity may be distinguished in the terminal portion of the QRS complex. This coinsides with findings in the standard high-resolution signal averaged electrocardiogram.	Post-MI patient with VT and late potentials STFT (spectrogram) Late high-frequency activity may be recognized here as well. However, frequency resolution in the range 30-80 Hz is poorer as compared to the WT. The QRS appears to set off earlier, which is due to poorer time resolution and is wrong.
Post-MI patient with no VT and no late potentials in time domain Wavelet transform (scalogram) No prolonged high-frequency activity in the terminal portion of the QRS complex is observed.	Post-MI patient with no VT and no late potentials in time domain (same as to the left) STFT (spectrogram) No long-lasting QRS decay may be identified here.