QT interval is the length between the beginning of the QRS complex (ventricular depolarization) and end of the T wave (ventricular re-polarization).
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QTc is prolonged if > 440ms in men or > 460ms in women
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QTc >500ms is associated with increased risk of torsades de pointes
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QTc is abnormally short if < 350ms
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A useful rule of thumb is that a normal QT is less than half the preceding RR interval
QTc prolongation can be caused by the following:
REFERENCES
- Goldstein, J. N., Dudzinski, D. M., Erickson, T. B., & Linder, G. (2018). Case 12-2018: A 30-Year-Old Woman with Cardiac Arrest. New England Journal of Medicine, 378(16), 1538-1549. doi:10.1056/nejmcpc1800322
- QT Interval. Edward Burns, Last updated November 21, 2017.https://lifeinthefastlane.com/ecg-library/basics/qt_interval/
- http://www.rxfiles.ca/rxfiles/uploads/documents/qa%20torsadesdepoint.pdf