Use of the Hartley transform for vector spectral combination of orthogonal leads in late potential analysis

Frequency-domain analysis of ventricular late potentials in the three orthogonal leads XYZ can reveal features of clinical significance. However, a consistent and simple method of spectral analysis has not been agreed. For a more easy interpretation of the spectral information in the 3 orthogonal leads a novel method of vector spectral analysis of ventricular late potentials is proposed here. The method exploits the property of zero-phase normalisation in the N amplitude coefficients (real-valued) of the Discrete Hartley Transform (DHT). This property of the DHT allows an advantageous way of combining the three orthogonal spectra, SX, SY and SZ, into a vector magnitude spectrum, (SX²+SY²+SZ³)^½. 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 (10.4±5.8 μV) in post-MI patients which are VT inducibles (at risk) than in healthy subjects (3.2±2.4 μV), p<0.001