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Short‐and Long‐Term Reproducibility of QT, QTc, and QT Dispersion Measurement in Healthy Subjects
Author(s) -
KAUTZNER JOSEF,
YI GANG,
CAMM A. JOHN,
MALIK MAREK
Publication year - 1994
Publication title -
pacing and clinical electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.686
H-Index - 101
eISSN - 1540-8159
pISSN - 0147-8389
DOI - 10.1111/j.1540-8159.1994.tb01435.x
Subject(s) - reproducibility , qt interval , medicine , standard deviation , electrocardiography , cardiology , heart rate , interval (graph theory) , dispersion (optics) , statistics , anesthesia , mathematics , combinatorics , physics , blood pressure , optics
The study investigated interobserver and intrasubject reproducibility of QT interval duration and dispersion measured in standard 12‐lead ECGs recorded at 25 mm/sec. Twenty‐eight healthy volunteers were studied. Each undenvent four ECG recordings, which were performed 1, 7, and 30 days apart. Two independent observers analyzed each ECG record. In each lead with a distinguishable T wave pattern, the RR interval, Q‐peak of T interval, and Q‐end of T interval were measured using a digitizing board with a 0.1‐mm resolution. From each recording the following measures were derived: the maximum, minimum, and mean QT interval; maximum, minimum, and mean heart rate corrected QT interval (QTc); QT and QTc dispersion (the difference between the maximum and minimum QT interval among the 12 leads); and adjusted QT and QTc dispersion (dispersion divided by the square root of the number of leads measured). The interobserver and short‐term (1 day) and long‐term (1 week and 1 month) reproducibility of individual indices was assessed by computing the relative errors and comparing them by a standard sign test. In addition, the distributions of maximum and minimum QTc values among electrocardiographicleads, and the differences between QT‐end and QT‐peak based measurements were investigated. The results showed that: (1) the measurement of the QT interval from standard ECG recordings is feasible and not operator dependent (interobserver relative error <4%); (2) the duration of the QT interval in healthy volunteers is stable and its short‐ and long‐term reproducibility is high (intrasubject relative error < 6%); (3) parameters that characterize dispersion of the QT interval in the 12‐lead ECG are highly nonreproducible, both between subsequent recording (relative error of 25%–35%) and between observers (relative errar 28%–33%), the reproducibility of QT dispersion is significantly lower than that of QT duration (P < 0.01); and (4) the duration of the entire QT interval correlates only weakly with the duration of the Q‐peak of T interval.