Longterm ambulatory recording: Jeff Holter´s enduring contribution to medical diagnosis

In the 1950´s, Jeff Holter developed the idea that a meaningful assessment of an individual´s cardiovascular status could only be made by long-term continuous observation of that individual, ideally with the subject free to move around in their normal environment. With this in mind he set about developing a range of miniature portable recording instruments which would record physiological signals while allowing subjects significantly more freedom than had previously been possible. Initial work explored the use of radiotelemetry to transmit ECGs from exercising subjects to a remotely located display monitor. In spite of the fact that the transmitter weighed some 38 kg the technique served to establish the principle of monitoring physiological variables from freely moving active subjects. While Holter´s interest was the study of disturbances of heart rhythm, others quickly became interested in the use of the technique to study long-term ischaemic changes in the EGG, particularly when many of these were found to be asymptomatic. The technique has now been extended to include the analysis of a number of other electrocardiographic parameters which are known to contribute to risk assessment. With the development of various transducers the concept of long term recording of physiological variables has now been extended to most branches of medicine