A high-pass phaseless filter for eliminating low-frequency ECG noise during exercise and its clinical application to automatic analysis of the heart rate and ST segment level.

We developed a new technique to eliminate low-frequency ECG noise by the use of a specially designed high-pass phaseless filter. The phaseless filter was tested by computer-simulated ECG signals and it proved to be highly effective in eliminating ECG noise without any significant deformation of the ST segment level. The maximum distortion of ST segment level at 0.8 Hz cut off frequency of this filter is equivalent to the distortion of the usual ECG Amp having 0.1 Hz cut off frequency (JIS). Furthermore, studies of the stabilized ECG recordings during exercise, which became possible by using the phaseless filter, enabled us to develop a method of automatic analysis of the heart rate-ST segment level relationship during and after exercise. The submaximal exercise ECG test was done on 78 ostensibly healthy men. The heart rate (X axis) and three points on the ST segment levels (Y axis) were plotted automatically on an X-Y recorder. Although a great variety of patterns were drawn, we could discern clearly different patterns for normal subject and those with typical ischemic heart disease. Further analysis of this relationship will undoubtedly contribute to the detection of ischemic heart disease.