Published definitions of the normal QT interval vary. A prolonged QT interval is defined as a heart rate-corrected QT interval (QTc) of >450 ms in males and >460 ms in females. The European Society of Cardiology suggests using a QTc of ≥480 ms for diagnosing LQTS and using a QTc of 460-479 as a borderline range where a diagnosis may be considered along with other criteria 🏳️