What is a normal QTc interval (QT corrected interval) for females?

From the Guidelines

A normal QTcB for females is less than 450 ms, as indicated by recent guidelines. This value is crucial in assessing the risk of prolonged QT syndrome and associated dangerous arrhythmias like torsades de pointes 1. Women generally have slightly longer QTc intervals than men due to hormonal influences on cardiac repolarization. The QTc interval represents the time from the beginning of ventricular depolarization to the end of ventricular repolarization in the heart's electrical cycle. Key factors that can affect the QTc interval include:

• Electrolyte abnormalities, particularly low potassium, magnesium, or calcium
• Certain medications
• Congenital conditions It's essential to note that QTc values above 450 ms in women may indicate prolonged QT syndrome, increasing the risk of dangerous arrhythmias 1. If concerned about your QTc interval, it's advisable to consult with a healthcare provider who can interpret your ECG results in the context of your overall health status and any medications you may be taking.

From the Research

Normal QTc Interval for Females

• The normal QTc interval for females is typically considered to be less than 460 ms 2
• However, some studies suggest that the upper normal limit for QTc in females may vary by age, with proposed criteria including:
  • Age < 40 years: 440 ms 3
  • Age 40 to 69: 450 ms 3
  • Age ≥ 70 years: 460 ms 3
• It is also important to note that the QTc interval can be calculated using different formulas, which may produce slightly different results 4
• In general, a QTc interval of 470-500 ms or more in females may be considered prolonged and may increase the risk of torsades de pointes (TdP) 5

Factors Affecting QTc Interval

• The QTc interval can be affected by various factors, including:
  • Heart rate: the QTc interval is calculated to account for changes in heart rate 2
  • Sex: females tend to have longer QTc intervals than males 2, 3
  • Age: the QTc interval may vary by age, with shorter intervals in adolescent males and longer intervals in older adults 3
  • Electrolyte disturbances: hypokalemia and hypomagnesemia can prolong the QTc interval 5