The Effect of Exercise on Postural Changes in the Electrocardiogram

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Abstract
The electrocardiogram before, during, and after a double two-step exercise test was studied in the upright position in 1,026 subjects with no apparent heart disease and in 70 patients with angina. Postural changes were found much more frequently in subjects with angina (18.5 per cent) and in apparently normal subjects with positive exercise tests (10.7 per cent) than in normal subjects with negative exercise tests, in which postural changes were found in only 3.4 per cent. Probable causes for these findings are discussed. The criterion for positivity in over 80 per cent of exercise tests, namely, an ischemic ST depression, is rarely seen as a postural change in normal subjects. On the other hand, isolated T-wave changes, which represent approximately 90 per cent of the postural changes of the repolarization period, are very rarely the sole criteria for a positive exercise test. Therefore, only a small area of possible confusion exists between postural changes and positive exercise tests. However, even in such cases, careful examination of the tracings can resolve these difficulties.