Corrected QT Interval (QTc)

Usage

Corrected QT interval (QTc)

• The corrected QT interval (QTc) estimates the QT interval at a standard heart rate of 60 bpm
• This allows comparison of QT values over time at different heart rates and improves detection of patients at increased risk of arrhythmias

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Summary

The Life in the Fastlane website provides a concise overview with examples in an article called QT Interval (Burns & Buttner, 2022). Here are a few key points.

 

There are multiple formulas used to estimate QTc. It is not clear which formula is the most useful:

• Bazett formula: QTC = QT / √ RR
• Fridericia formula: QTC = QT / RR 1/3
• Framingham formula: QTC = QT + 0.154 (1 – RR)
• Hodges formula: QTC = QT + 1.75 (heart rate – 60)

 

Note: The RR interval is given in seconds (RR interval = 60 / heart rate).

 

Prolonged QT (≥440 msec): 

• QTc is prolonged if ≥ 440ms in men or ≥ 460ms in women
• QTc > 500 is associated with an increased risk of torsade de pointes

 

Short QT (<350ms)

• Congenital short QT syndrome has been found to be associated with an increased risk of paroxysmal atrial and ventricular fibrillation and sudden cardiac death

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