What can happen with qt prolongation?

Depends: Depends on severity of prolongation and underlying cause. Some causes of qt prolongation are reversible such as electrolyte abnormalities. Genetic qt prolongation may be associated with arrhythmias and risk of sudden death. Proper evaluation for possible causes should be done.

Sudden death: Long qt syndrome is a rare inherited disorder that can cause syncope (fainting) and cardiac arrest (heart attack). Prolonged qt is an arrhythmia that can also be caused by certain drugs.

Arrythmias: QT prolongation can cause cardiac arrythmias when there is a genetic defect in some cardiac channels.