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This study investigated interobserver (two observers) and intrasubject (two measurements) reproducibility of QT dispersion from abnormal electrocardiograms in patients with previous myocardial infarction, and compared a user-interactive with an automatic measurement system. Standard 12-lead electrocardiograms, recorded at 25 mm.s-1, were randomly chosen from 70 patients following myocardial infarction. These were scanned into a personal computer, and specially designed software skeletonized and joined each image. The images were then available for user-interactive (mouse and computer screen), or automatic measurements using a specially designed algorithm. For all methods reproducibility of the RR interval was excellent (mean absolute errors 3-4 ms, relative errors 0.3-0.5%). Reproducibility of the mean QT interval was good; intrasubject error was 6 ms (relative error 1.4%), interobserver error was 7 ms (1.8%), and observers' vs automatic measurement errors were 10 and 11 ms (2.5, 2.8%). However QTc dispersion measurements had large errors for all methods; intrasubject error was 12 ms (17.3%), interobserver error was 15 ms (22.1%), and observers' vs automatic measurement were errors 30 and 28 ms (35.4, 31.9%). QT dispersion measurements rely on the most difficult to measure QT intervals, resulting in a problem of reproducibility. Any automatic system must not only recognize common T wave morphologies, but also these more difficult T waves, if it is to be useful for measuring QT dispersion. The poor reproducibility of QT dispersion limits its role as a useful clinical tool, particularly as a predictor of events.

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1 To examine the influence of age on beta‐adrenergic receptor mechanisms, we have observed the cardiovascular, bronchial and metabolic effects of an intravenous infusion of the beta‐adrenoceptor agonist terbutaline in healthy young and elderly female subjects (mean ages 20.9 and 72.1 years respectively). 2 There was a highly significant fall in systolic blood pressure in the elderly, in contrast to the rise in systolic pressure seen in the young subjects. A similar fall in diastolic pressure occurred in both groups, indicating comparable beta‐adrenoceptor‐mediated vasodilatation. The fall in mean arterial pressure was significantly greater in the old than in the young subjects. The increase in heart rate was significantly less in the elderly. 3 Changes in plasma glucose and potassium during the infusion were similar in the two groups. 4 The observed abnormality of myocardial sensitivity to beta‐adrenergic receptor stimulation, which is not associated with a generalized blunting of beta‐adrenoceptor mediated effects, may significantly impair autonomic cardiovascular regulation in the elderly.