On-Line Analysis of Exercise Electrocardiograms Maarten L. Simoons, Ed Smallenburg, Cees Zeelenberg, Wim Engelse Thoraxcenter, Medical Faculty and University Hospital Rotterdam and Department of Physiology, University of Utrecht, The Netherlands Introduction Computer assisted interpretation of exercise electro- cardiograms (XECGs) is generally expected to improve the value of exercise testing for detection of ischemic heart disease (IHD) in patients with normal resting ECGs. There are several reasons for this: 1. The noise content of the XECG may be reduced by averaging a number of heartbeats." 3 Prior to the averaging, premature beats and other beats with an aberrant shape should be eliminated. This can hardly be done automatically without a digital computer system. 2. The measurement accuracy with a digital computer system (0.005 mv or even smaller) is better than that obtained with visual reading (0.05 mv). 42 3. When ECGs are read visually the observer variation is large,4 whereas the reproducibility is almost complete when a computer system is used. 4. Measurements such as slopes, time-integrals, and the instantaneous changes of the ECG during exercise can only be made with computer techniques. 5. Finally, the diagnostic accuracy can be improved by sophisticated logic, such as multivariate analysis.5 In addition, a computer system for XECG analysis in an on-line environment can reduce the tasks of the physician and technician who conduct the test by 1) automatic adjustment of the workload according to a predetermined protocol, 2) automatic recording of the ECG, 3) automatic recording of associated other signals such as blood pressure (either by cuff or intravascular catheter), and respiratory parameters like oxygen uptake, and 4) automatic COMPUTER