The cause of artefactual ST segment distortions occurring in ambulatory ECG monitoring systems

The frequency characteristics of the ambulatory ECG monitoring systems equipped with direct-recorded magnetic tape recorder were found much worse than that of ordinary ECG equipment both in gain and phase responses. In order to investigate which of these two responses plays major role in generating false ST deviation, a computer program was run with several frequency response models. The actual ECG waveforms were fed into the fictitious frequency responses (mathmatical filters) through a digitizer. The artefactual distortions of ST segment in the reproduced ECG were clarified to be caused by the phase responses of the systems with direct-recorded magnetic tape recorder