The Electrocardiogram During Exercise

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Abstract
Nonstandard ecg leads and recording procedures are being applied in monitoring the ecg response during performance tests. Detailed systematic studies in well-defined populations with adequate control of the numerous variables of electrode position, body posture, the type, amount, and duration of work, recording intervals, and instrumentation are required before the dynamic ecg response may be interpreted with confidence. This study reports the distribution of ecg findings during moderate treadmill exercise in a group of 1449 working men in the railroad industry of ages 45 to 64. Two bipolar chest leads commonly used in work monitoring were compared, each with the exploring electrode at chest position C5, 1 with the reference opposite at C5R (CC5) and the other on the manubrium (CM5). Of the examined men, 96%, excluding those with manifest cardiac or other disabilities, were subjected to a 3-min. treadmill walk at 3 mph on a 5% grade, and the maximal codable S-T or other findings was used in the analysis. About 90% of all men had standing control records free of any codable ecg finding. Less than 1% of these developed ischemic type of S-T depression during work. About 2% developed J (junctlonal) type of S-T depression of 0.2 mv (2 mm) or greater. Less than 1% developed significant ventricular blocks or arrhythmias, and about 3% developed frequent extrasystoles. Any of these findings during moderate exercise may then, on a statistical basis, be considered an abnormal response. The discriminative diagnostic power of the ecg responses during exercise is poor, however, and evidence about its predictive import for future disease risk requires careful quantitation and follow-up studies. Standardization of methods for exercise ecg is not yet possible because of rapid developments in theory and instrumentation. When it is not feasible to obtain good data from conventional limb and pre-cordial leads, information from simple bipolar chest leads may be profitably utilized in screening and monitoring programs. This should be a temporary expedient, until a practical and acceptable quantitative approach is available for exercise ecg.