The electrocardiogram during exercise. Its value in the diagnosis of angina pectoris.

THE DIAGNOSIS of angina pectoris, although fairly simple in the characteristic case, may not be made with certainty under a variety of conditions. In approximately 50 per cent of cases the diagnosis is made chiefly from the history, since objective evidence of myocardial abnormality may be lacking in the early stage. In the absence of a characteristic history, the difficulty in diagnosis may arise from atypical location of pain and simulation or association of angina with functional or extracardiac conditions. To make a definite diagnosis, we often need all the aids at our disposal. The purpose of this communication is to discuss critically the value of the electrocardiogram in diagnosis and particularly to evaluate the information obtained during as well as after exercise. We have performed exercise tests both during and after exercise in nearly 4,500 normal subjects and patients with various cardiac abnormalities in the past 4 years (table 1). Many improvements in the recording technics have been made during this period, e.g., in the type of electrodes, electrode placement, the transmitter, and the receiving apparatus. Variations in results have been reported because of differences in apparatus employed, in electrode placement, and in the criteria of positive findings. The use of patch electrodes has been extremely helpful in obtaining satisfactory tracings.1-6 One may use the standard electro-cardiograph with wire connections if the patient is located close to the recording apparatus .7 In our experience, however, varying degrees of interference are observed and the baseline is not as steady as with the telemetering apparatus. The Radio-electro-cardiograph employed by us (RKG 100) * has been continually improved during the past 4 years.1-5 It has the usual standardization of 1 millivolt per centimeter.t It seems to be superior to similar types of apparatus and has worked very well for us as well as for others.8 The results compare favorably with tThe Sanbom specifications state that the response of the Viso 100 recorder is from 0.1 to 80 cycles per sec. The response of the RKG 100 is from 0.15 to about 1,000 cycles per sec. At various degrees of sensitivity, the curve of the Sanborn electrocardiogram alone and the combined Sanborn plus the RKG system were almost identical.