[ST-segment analysis in long-term ECG: amplitude and phase response of various systems in comparison with standard ECG and their effect on true original reproduction of ST segment depression].

Ambulatory ECG monitoring has been suggested as a method for the detection of transient myocardial ischemia. But it is still unclear how accurately ST-segment alterations can be detected with the different systems. Measurement of amplitude and phase response is a valid method to estimate the fidelity of reproduction of an ECG-signal. We investigated the direct-recording long-term ECG systems CardioData Mk4 with recorder PR3, CardioData Mk4 with Spacelabs recorder, DMI Eclipse with DMI Recorder, Reynolds Pathfinder II with Oxford replay PB2 and recorder MR-10 and Reynolds Pathfinder III with tracker in comparison to a standard ECG recorder Picker Schwarzer C6800. Amplitude vs frequency response curves were derived from input sinus waves ranging from 0.01 to 500 Hz. The phase response was measured with a phase-sensitive waveform at a frequency range from 0.05 to 10 Hz. To determine the distortion of the ST-segment on the actual ECG, we produced a standard PQRST-signal that was modified to provide flat ST-segment depressions from 0 to 0.5 mV at 0.05 mV increments. The low and high frequency cut-off of the amplitude response was found at 0.09 and 220 Hz with the standard ECG recorder. A phase shift of -30 degrees was detected at 0.07 Hz. ST-segment depressions of the test-ECG were reflected to the same extent. For the CardioData-System, both cassette recorders yielded lower and upper cut-off frequencies of 0.06 and 0.07, and 20 and 16 Hz, respectively. A phase shift of -30 degrees was found at 0.35 and 0.31 Hz, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)