Obtain a standard 12-lead ECG
Identify the start of the QRS complex
Identify the end of the T wave
Measure the QT interval from QRS onset to T-wave end
Measure the RR interval between two consecutive R waves
Correct the QT interval for heart rate using a QT correction formula
Use Bazett’s formula: QTc = QT / √RR
Use Fridericia’s formula: QTc = QT / RR^(1/3)
Use Framingham’s formula: QTc = QT + 0.154 × (1 − RR)
Use Hodges’ formula: QTc = QT + 1.75 × (heart rate − 60)
Express QTc in milliseconds
Measure in a lead where the T wave end is clearest, often lead II or V5
Avoid including U waves in the QT measurement
Repeat the measurement if the T-wave end is unclear
Average measurements from multiple beats if needed