Question: how serious is a prolonged qt?
Answer: It can cause sudden, uncontrollable, dangerous arrhythmias (ah-RITH-me-ahs) in response to exercise or stress. Arrhythmias are problems with the rate or rhythm of the heartbeat. People who have LQTS also can have arrhythmias for no known reason. However, not everyone who has LQTS has dangerous heart rhythms.