A New QT Interval Correction Formulae to Adjust for Increases in Heart Rate

Abstract

Objectives: This study sought to develop a formula from a large population-based study that best fit the QT-heart rate (HR) relationship independent of the standard mathematical relationships.

Background: Attempts to adjust or correct for the impact of HR on the QT interval (QTc) have applied various mathematical equations to electrocardiographic (ECG) data rather than allowing the data to determine the form of the relationship.

Methods: A spline correction function was developed using the ECG data from NHANES (National Health and Nutrition Examination Surveys) II and III. The magnitude of linear, quadratic, and cubic trends in the relationship between HR and each QTc was quantified using an F-statistic with differences between QTcs compared using a permutation procedure.

Results: The effect of HR on QT was obliterated by the spline QT for both men and women. The cross-validated spline QTc was superior (i.e., flatter) to 6 other formulae, including ones proposed previously. In ECGs from the clinic with HRs faster than 70 beats/min, the QTcs from different formulae were significantly (p < 0.0001) different from one another. Individual values suggest the use of the longest and shortest QTc intervals as developed originally. The new QTc and its population percentile ranking can be provided for clinical ECGs.

Conclusions: A new QTc formula was developed which eliminates the relationship between QT and HR. At faster HRs, the 2 most commonly used QTcs provide numerical values at the extremes of QTc. Compared to existing formulae, the new formula had the best performance.

Keywords: QT interval; QTc formulae; heart rate.