Day to day variation in 3 orthogonal lead electrocardiogram parameters after acute myocardial infarction.

Serial 3 orthogonal lead electrocardiograms were recorded on 67 patients with acute myocardial infarction. For each series of electrocardiograms, the day to day changes and the changes with respect to the initial computer measurements of selected ST-T segment amplitudes and vector orientations were investigated. The results indicated that the degree of rotation of ST-T vectors, which corresponded with a report of sequential change by a panel of cardiologists, was outside the upper limit of normal day to day variation. From the results, diagnostic criteria for use in the automated detection of sequential electrocardiographic changes after myocardial infarction were established.