Tape recordings of the ECG of active men. Limitations and advantages of the Holter-Avionics instruments

The electronic and mechanical characteristics of the Holter-Avionics instruments for recording and analyzing the electrocardiogram of active men have been measured in the laboratory, and during carefully standardized 6-hour recordings of 385 active subjects. Although late model recorders have a cumulative timing error of less than 1%, the frequency response of the system is limited at both the upper and lower ends of the range, producing significant distortion of the complex. Scanning the taped data at 60 times real-time is a helpful screening procedure, but accurate analysis of records requires photographic write-out of R-R intervals with real-time scanning and analysis of all potential areas of abnormality. If records are made with subjects under constant observation and stop-watch timed, they can yield significant data on phenomena of rate, rhythm, and conduction, under a variety of circumstances and over long periods of time; but changes in the shape of the ST segment and T wave must be interpreted with great caution because of distortions produced by the recording system and by changes in position and activity.