AGREEMENT AND REPRODUCIBILITY OF AUTOMATIC VERSUS MANUAL MEASUREMENT OF QT INTERVAL AND QT DISPERSION

To determine whether the automatic measurement of the QT interval is c onsistent with the manual measurement, this study evaluated the reprod ucibility and agreement of both methods in 70 normal subjects and 54 p atients with hypertrophic cardiomyopathy. The mean, minimum, and maxim um QT interval and QT dispersion were computed in a set of 6 consecuti ve electrocardiograms (3 in the supine and 3 in the standing position) obtained from each subject. The automatic method determined the T-wav e end as the intersect of the least-squares-fit line around the tangen t to the T-wave downslope with the isoelectric baseline. Manual measur ements were obtained using a high-resolution digitizing board. QT disp ersion was defined as the difference between the maximum and minimum Q T interval and as standard deviations of the QT interval duration in a ll and precordial leads. In patients with hypertrophic cardiomyopathy, the absolute values of the QT interval and QT dispersion were signifi cantly higher than those in normal subjects (p <0.0001). In both group s, the intrasubject variability of the QT interval was significantly l ower with automatic than with manual measurement (p <0.05). The agreem ent between automatic and manual QT interval measurements was surprisi ngly poor, but it was better in patients with, hypertrophic cardiomyop athy (r(2) = 0.46 to 0.67) than in normal subjects (r(2) = 0.10 to 0.2 5), In both groups, the reproducibility and agreement of both methods for QT dispersion were significantly poorer than for QT interval. Henc e, the automatic QT interval measurements are more stable and reproduc ible than manual measurement, but the lack of agreement between manual and automatic measurement suggests that clinical experience gained wi th manual assessment cannot be applied blindly to data obtained from t he automatic systems. (C) 1998 by Excerpta Medica, Inc.