A genetic heart rhythm condition called long QT syndrome may be behind sudden fainting and cardiac death.
A normal QT interval generally ranges between 340-460 milliseconds.
People with long QT syndrome (QT interval ≥ 500 milliseconds) have potentially dangerous QT prolongation.
Stress to the heart of a person with long QT syndrome may cause a chaotic heartbeat. Triggers may include the following:
When the heart is beating erratically, the brain does not get sufficient blood flow, which can lead to a sudden faint (also called syncope).
If the heart continues to beat out of rhythm, known as arrhythmia, serious complications may occur.
Mayo Clinic is a nonprofit organization and proceeds from Web advertising help support our mission. Mayo Clinic does not endorse any of the third party products and services advertised.
A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.org," "Mayo Clinic Healthy Living," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.