Ambulatory monitoring of the ST segment, using direct-recording Holter systems.

Direct-recording ambulatory electrocardiographic monitoring systems may produce serious errors not only because of their restricted bandwidth, but even more because of the "half-wavelength-to-head-contact effect." This article describes an easy measurement procedure and a mathematic model of the storage medium. The frequency response is calculated by way of five data from a single measurement. Some errors of typical recorders are discussed with the help of synthesized electrocardiographs. Measurements by six different recorders are listed.