ABSTRACT
BACKGROUND: Prolonged cardiac repolarization is associated with ventricular tachycardia and sudden cardiac death. Repolarization, represented by the QT interval, is usually measured on a 12-lead ECG recording. Measurements of the interval on bedside monitor ECG recordings have not been compared quantitatively with measurements on 12-lead ECG recordings. OBJECTIVE: To determine if QT intervals and QTc values obtained by using monitor recordings are as accurate as those obtained by using 12-lead ECG recordings. METHODS: For each of 50 subjects, 2 ECG recordings were obtained, 1 with a 12-lead ECG and 1 with the bedside monitor, and QT intervals were measured manually. The QT intervals on each type of recording were compared on a lead-by-lead basis, the maximum QT interval and the QTc maximum determined with each method were compared, and the "best single leads" for determining the QTc were ascertained for each method. RESULTS: QT intervals, on a lead-by-lead basis; maximum QT intervals; and QTc maximum values measured on the monitor recordings were consistently longer than those measured on the 12-lead ECG recordings. When the monitor ECG leads I or II and the 12-lead ECG QTc maximum were examined for simple agreement by using 460 milliseconds as a cutoff, agreement was found in 82% to 84% of the sample, and false negatives were 12% and 8%, respectively. CONCLUSION: Recordings from leads I or II on the bedside ECG monitor should be used to measure the QT interval. Once prolonged QT values are detected, recordings obtained with a 12-lead ECG can be used to confirm the analysis.
Subject(s)
Electrocardiography/methods , Long QT Syndrome/diagnosis , Point-of-Care Systems/standards , Adolescent , Adult , Aged , Aged, 80 and over , Death, Sudden, Cardiac/etiology , Electrocardiography/instrumentation , Female , Humans , Long QT Syndrome/complications , Male , Middle Aged , Monitoring, Physiologic , Reproducibility of Results , Sensitivity and Specificity , Tachycardia, Ventricular/etiologyABSTRACT
Cardiac repolarization, represented on the ECG by the QT interval, is of particular clinical interest in critical care. Once it is measured and corrected for changes in heart rate, the QT interval is known as the QTc. Measurement of the QT interval is important because a prolonged QT interval is associated with ventricular tachycardia and sudden cardiac death. Despite the serious complications associated with a prolonged QT interval, the interval is not routinely measured because a standardized method for measuring it has not been established and the length of QT interval critical to the development of ventricular tachycardia has not been determined. Much has been written about the conditions associated with prolonged QT intervals and specific actions to take when complications appear. Guidelines to be used for QT analysis in the clinical area, based on currently available information, include (1) procedures for measuring QT interval and calculating QTc, (2) procedures for QT analysis, (3) warning signs that indicate increased risk of ventricular tachycardia associated with a prolonged QT interval, and (4) actions to consider once increased risk is determined.
