Application of beat-to-beat techniques.

The focus of this report is to describe a system for recording surface His-Purkinje and ventricular late potentials on a beat-by-beat basis outside of a shielded environment. An AC magnetic field monitoring device was designed for improved site selection, orientation, and quality control of the acquisition. His-Purkinje signals are detected utilizing spatial averaging and specific channel selection algorithms applied to discriminate random noise from signal. Beat-by-beat vectormagnitude complexes were generated from pairs of X, Y, and Z leads. Both infinite impulse response (IIR) filters, modified for beat-by-beat approaches, and finite impulse response (FIR) filters were utilized. Using the IIR filter, beat-by-beat recordings from test subjects were compared to the signal averaged electrocardiogram (SAECG). Measurement parameters from normal test subjects fell within the previously specified normal range for the SAECG. The IIR filter applied to beat-by-beat recordings exhibited sharp frequency response and a precisely defined cutoff frequency allowing maximal attenuation of the low frequency components in the ST segment. While filter ringing was eliminated, discontinuity and distortion of the filtered waveform resulted. The FIR filter with linear phase response retained the integrity and morphology of the complex but because of its flat frequency response, the ST segment was not as well attenuated and it was more difficult to isolate late potentials. A high order FIR filter should be used if the desire is to match the frequency response of the four-pole IIR filter, since the frequency response of the FIR filter is primarily determined by the order of the filter.(ABSTRACT TRUNCATED AT 250 WORDS)