What causes Long QT syndrome?
Most cases, especially those in young people, are caused by viruses, such as the coxsackievirus, type B. Other causes include bacteria, rickettsiae, parasites, an adverse drug reaction, arsenic or other toxic substances, or other diseases.
The cause of the long QT syndrome is a mutation in a gene that regulates the heart's electrical system. The mutation causes a defect in heart muscle structures called ion channels that predisposes the heart to lapse into a very rapid, ineffectual rhythm called fibrillation. The mutation responsible for the long QT syndrome is inherited as an autosomal dominant, which means that the mutant gene is on a non-sex chromosome and that each child of an affected parent has a 1 in 2 (50%) chance of inheriting it.
Doctors can record the electrical signal produced by the ions on an electrocardiogram (EKG or ECG) machine. The machine makes a tracing of the signal, called a waveform. The different parts of the waveform are represented by the letters P, Q, R, S, and T.
By looking at the waveform, doctors can see the time it takes for the electrical signal to activate and inactivate your heart's lower chambers (the ventricles). This is called the Q-T interval. A problem in one of the ion channels can prolong the Q-T interval. A prolonged Q-T interval can increase your risk for a type of arrhythmia called torsade de pointes. When torsade de pointes occurs, your heart cannot pump enough oxygen-rich blood to the rest of your body, especially your brain. Torsade de pointes can also lead to ventricular fibrillation, a dangerous form of arrhythmia that causes rapid, uncoordinated contractions in the muscle fibers of the ventricles. With ventricular fibrillation, the heart cannot pump oxygen-rich blood to the rest of the body, which can lead to death.