Abnormalities of these channels can be acquired or inherited. The acquired form is caused by certain medications. The inherited form occurs when a mutation develops in one of the genes which makes a channel. The mutations cause the electrical recovery of the heart to be slow. Sudden loss of consciousness, or syncope, usually occurs during physical exertion or emotional excitement like anger or fear.
Sudden death can often occur when the victim is asleep, or when they are waking up.
In patients with syncope the heart rhythm reverts spontaneously to normal. When this occurs, the patient regains consciousness within a minute or two When the abnormal rhythm persists, however, the outcome is death. It is not common for the syncope or sudden death to occur when the person is awake and at rest. In the other two-thirds, some have just one or two syncopal spells as children. Others have many episodes over a number of years.