A trial to detect high frequency low amplitude ECG signal in time sequence

High-frequency, low-amplitude signals (HFLA) in the ECG, such as the late potential after QRS or P waves, have been shown to contain important information. So far, it has been difficult to detect these signals in time sequence, since digital filters “ring” after the QRS or the P waves so as to hide the following HFLA signals. This study is a trial to eliminate the influence of filter ringing and to detect the signal in time sequence. The method is based on the understanding that the effect of filter ringing depends on the amplitude of the high-frequency components contained in the signal, instead of the signal´s absolute value. In detecting the late potential after the QRS wave, the averaged signal is filtered in the forward direction. As a characteristic point (which is identified based on the high-frequency components of the signal) is encountered, the filter is reset by feeding back zeros to the filter as the previous filter outputs, so as to restart the filtering process. The effectiveness of this method is evaluated by comparing it with a “bidirectional filter”. The results suggest that this method can eliminate the influence of filter ringing and therefore it can be used in detecting HFLA signals in time sequence