Vector spectral analysis of ventricular late potentials using the Hartley transform

Frequency-domain analysis of ventricular late potentials in the three orthogonal leadsXYZ, signal-averaged ECG can reveal features of these bio-signals that can be of clinical importance. However, a consistent and simple method of spectral analysis has not been agreed. Consistency and simplicity of the method may be enhanced by optimising the windowing technique and by combining the spectral information of the three orthogonal leads. A convenient windowing technique and a novel method of vector spectral analysis of ventricular late potentials is presented in this paper. The method exploits the property of zero-phase normalisation in the N amplitude coefficients (real-valued) of the Discrete Hartley Transform. This property of the DHT allows an advantageous way of combining the three orthogonal spectra, SX, SY, and SZ, into a vector magnitude spectrum, (SX^2 + SY^2 + SZ^2)^1/2. Summation of amplitude coefficients in the -300 to -60 Hz and 60 to 300 Hz frequency ranges in the DHT vector spectrum provided a simple clinical parameter, S. A clinical evaluation of S indicated that S is of significantly greater value (38.3 ± 12.6 μV) in patients at risk than in healthy subjects (27 ± 10.3 μV), p <0.01.