Hodges et al developed a linear equation for correcting the QT interval for heart rate. The authors are from Hennepin County Medical Center and the University of Minnesota in Minneapolis.
estimate for QT based on heart rate in milliseconds =
= 496 - (1.75 * (heart rate))
corrected QT interval (QTm) =
= (QT interval) + (1.75 * ((heart rate) - 60))
(1) reduced variance in the correction
(2) absence of systematic error
(3) more accurate prediction of risk for ventricular arrhythmias
(1) prolongation of corrected QT interval during peak exercise
(2) overcorrects at high heart rates
Alternative representation (Luo et al):
corrected QT in milliseconds =
= (QT interval) + (105 * ((1/(RR interval in seconds)) - 1))
• R-R interval is the measurement between 2 consecutive R-R waves in seconds.
• RR = 60 / (heart rate) in a simplified world
• 105 = 1.75 * 60
As noted by Luo et al (in the abstract), QT shows a linear trend with heart rate but not with the RR-interval.
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