Abstract 17327: A New Correction Formula for the QT Interval
PURPOSE Estimation of the QT interval and its adjustment for heart rate (HR), represents a critical step in the analysis of every electrocardiogram (ECG). Of the many formulas proposed for the correction of the QT interval, the one developed by Bazett, remains the most used in practice. The popularity of the Bazett formula is based on its simplicity, not on its fit. Based upon theoretical considerations, we hypothesize that the very simple formula: QTc=QT/((1+RR)/2) would provide an accurate correction. Additionally, our new formula offers an easy eyeballing method to diagnose QT prolongation ( see figure). A normal QT, should end well before the half of (1+RR)/2.
METHODS We measured the QT interval in 390 normal ECGs, and then we calculate the QTc interval using five correction formulas (Bazett, Fridericia, Hodges, Framingham, and our new formula). To test the appropriateness of the corrections, we correlate the QTc values of each formula with HR. An ideal correction should lead to a lack of correlation between QTc and HR.
RESULTS Of the 5 formula evaluated, Bazett provides the worst correction (r = 0.300, p < 0.001), and our new formula the best ( r = 0.140, p = 0.005). The other three formulas have an intermediate score : Fridericia r = -0.278, p < 0.001, Framingham r = -0.233, p < 0.001, Hodgson r = -0.228, p < 0.001.
CONCLUSION: We propose a simpler, reliable formula for the correction of the QT interval.
- © 2012 by American Heart Association, Inc.