Table 2.

Methods for Correction of the QT Interval

Formula	Equation	Strengths	Limitations	When to use
Bazett	$Q{T}_c=\frac{\mathit{QT}}{\sqrt{\mathit{RR}}}$	• Simplest formula • Widely accepted and used	• Tendency to over-diagnose long QT as it overcorrects at high heart rates and undercorrects at low heart rates	• Best used when HR is between 50 and 70 bpm55
Fridericia	$Q{T}_c=\frac{\mathit{QT}}{\sqrt[3]{\mathit{RR}}}$	• More accurate than Bazett formula at abnormal heart rates	• Tendency to overcorrect at high heart rates (i.e. over-diagnosis of long QT)	• Useful in bradycardic patients (HR < 50 bpm)
Framingham	QTc = QT + 0.154 (1 − RR)	• Less affected by abnormal heart rate	• Complex formula	• In any patient, especially if heart rate is < 50 bpm or > 70 bpm
Hodges	$Q{T}_c=\mathit{QT}+105\left(\frac{1}{\mathit{RR}-1}\right)$	• Least affected by abnormal heart rate56	• Complex formula	• In any patient, especially if heart rate is < 50 bpm or > 70 bpm
Nomogram	Not applicable (see Fig. 3)	• Designed for use with abnormal heart rates	• Needs to be physically or digitally available at point of care • Difficult to apply to serial testing	• Patients with abnormal heart rates • Well described in toxicology and overdose
The “Half R-R” method	If QT is less than half the RR interval, it is normal	• No calculation required	• Non-quantitative • If the QT is greater than half the RR interval, it may still be normal • Cannot be used at HR < 60 bpm	• Useful as a “screening” test, especially in AF but not as a true diagnostic test.

RR, the R-R interval, measured in seconds; HR, heart rate; AF, atrial fibrillation