General: Prolonged QT intervals may never cause any problems in some patients. However, physical or emotional stress may cause the heart to beat in a dangerous rhythm if an individual is susceptible to prolonged QT intervals.
Fainting (syncope): Fainting, or syncope, is a sudden loss of consciousness. It most often occurs when the blood pressure is too low (called hypotension) and the heart does not pump enough oxygen-containing blood to the brain. Typically, a faint lasts only a few seconds or minutes and then the individual regains consciousness. Fainting is a common problem that affects one million people in the United States every year. About one-third of individuals will faint at least once during a lifetime. A single fainting spell usually is not serious. It may be explained by factors such as stress, grief, overheating, dehydration, exhaustion, illness, or arrhythmias.
Sudden cardiac death: Sudden cardiac death is the sudden loss of heart function in an individual who may or may not have diagnosed heart disease. In long QT syndrome (LQTS), life-threatening arrhythmias are responsible for sudden death.
Torsade de pointes: A prolonged QT interval may trigger a particular arrhythmia (irregular heart rhythm) called torsade de pointes, or twist of the points. In this condition, the heart's ventricles beat fast, making the waves on an electrocardiogram (ECG) monitor look twisted. When this arrhythmia occurs, less blood is pumped out from the heart, which can cause fainting. If an episode of torsade de pointes is short (less than one minute), the heart can correct itself seconds later. If an episode of torsade de pointes persists, however, it can lead to a life-threatening arrhythmia called ventricular fibrillation.
Ventricular fibrillation: In ventricular fibrillation, the ventricles beat so fast that the heart quivers and stops pumping blood. Unless the heart is shocked back into a normal rhythm by a device called a defibrillator, ventricular fibrillation can lead to brain damage and death. LQTS may explain some cases of sudden death in young people who otherwise appear healthy.
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