The QT Interval and Medication Safety
Why some medicines affect your heart rhythm and how QTc is measured.
QT basics
The QT interval on an ECG reflects how long the heart’s lower chambers take to reset. It shortens as heart rate rises, so it is corrected to give QTc.
When it is too long
A QTc above about 450 ms in men or 460 ms in women is prolonged. Very long values increase the risk of a dangerous rhythm called torsades de pointes.
What to do
Some antibiotics, antipsychotics and antidepressants prolong QT. Tell clinicians about all medicines and any family history of fainting or sudden death.
Try it: Corrected QT (QTc) Calculator
Example with sample values. Open the full calculator →
QTc is within the normal range. Fridericia is more reliable at fast or slow heart rates.
Educational content only. This article does not replace advice from a qualified health professional. Medical disclaimer.