Long QT syndrome is a congenital disease resulting from abnormalities in the ion channels of the heart. Long QT syndrome should be differentiated from secondary QT prolongation. There are multiple causes of secondary QT prolongation that are distinct from long QT syndrome such as drugs (anti-arrhythmic drugs, anti-psychotic drugs), electrolyte disturbances (hyperkalaemia, hypocalcaemia, hypoglycaemia, hypokalaemia, and hypomagnesemia), neurologic events such as subarachnoid hemorrhage, and anorexia nervosa.

Drug induced QT prolongation is usually a result of treatment by anti-arrhythmic drugs or a number of other drugs that have been reported to cause this problem (e.g. cisapride). Some anti-psychotic drugs, such as Haloperidol and Ziprasidone, have a prolonged QT interval as a rare side effect. Genetic mutations may make one more susceptible to drug induced QT prolongation.

Genetic abnormalities cause the Long QT Syndrome.

Electrolyte disturbances such as hyperkalaemia, hypocalcaemia, hypoglycaemia, hypokalaemia, and hypomagnesemia can cause QT prolongation.

Subarachnoid hemorrhage and other intracranial events can cause QT prolongation. Widely slayed cerebral T waves are often seen as well.

Anorexia nervosa and starvation can cause QT prolongation.