corrected Q-T interval in ms^(0.5) =
= (measured Q-T interval) / SQRT(R-R interval)
corrected Q-T interval in ms^(0.5) =
= (measured Q-T interval) * SQRT((heart rate) / 60)
where:
• R-R interval is the measurement between 2 consecutive R-R waves in seconds.
Interpretation:
• A QTc above a certain cutoff (varies between 420 to 440 milliseconds) indicates a prolonged QTc (Luo et al).
The R-R interval depends on the heart rate. The following equation approximates the R-R interval if the heart rate is known, based on the data from Friedman (1985; see documentation).
R-R interval =
= (0.1349829 * ((HR / 60)^4)) - (1.131181* ((HR / 60)^3)) + (3.5907994 * ((HR / 60)^2)) - (5.373251 * ((HR / 60))) + 3.7807829
where:
• HR is the heart rate in beats per minute.
Limitations of Bazett's correction (Strevel et al):
(1) The formula is nonlinear.
(2) It tends to overcorrect the QT at fast heart rates.
(3) It tends to undercorrect the QT at slow heart rates. This may result in underestimating a patient's risk of torsade de pointes.
