[Silent myocardial ischemia in long-term ECG: is the standard of the American Heart Association for ST segment analysis adequate?].

Ambulatory ECG recording for ST-segment monitoring to detect episodes of silent ischemia has become of increasing clinical interest. Of the available Holter systems with different recording techniques, the direct recording (AM) systems are most commonly used. It still remains uncertain whether the recorded ECG signals are sufficient for the monitoring of transient ST-segment changes. A mathematical model was developed to allow a full description of a direct recording Holter system. As a representative, we used the Medilog I system which has been experimentally tested by Bragg-Remschel. Using the mathematical model, the ST-segment deformation was calculated at different heart rates for critical regions of the frequency response curve. Deviations of about +/- 30% occurred at different heart rates as compared to the original ST-segment signal. This is due to the half wavelength-to-head contact effect, inherent in direct recording systems. At present, ECG analysis for quantitation of ST-segment changes is already limited by upper and lower cutoff frequencies. In addition, system inherent amplitude and frequency of an induced sine wave need to be considered for correct measurements.