Serial Electrocardiographic Findings in a Prospective Epidemiological Study

The prevalence of classified electrocardiographic items among the adult population of Tecumseh, Michigan, during two examinations approximately 4 years apart is reported. Changes in the prevalence rates of certain items are probably due to reader differences, the effect of prior ingestion of glucose in the first series of examinations, and possibly the treatment of abnormalities detected during the first examinations. Among the cohort of 3,745 persons who had classified electrocardiograms on both examinations, the Q and QS items were relatively stable, the more marked ST and T items were less stable, and the minor ST or T classifications were extremely variable. Still, 31% of persons whose second electrocardiogram revealed codable Q or QS items for the first time had classified ST-segment or T-wave items in their previous electrocardiogram and another 9% had nonspecific QRS abnormalities, either high amplitude R waves or left axis deviation. The Minnesota code is a useful system for the classification of large numbers of electrocardiograms, but for accurate identification of new events, tracings exhibiting category I, IV, or V items must be examined serially.