What does progonlation of the qi interval of the heart mean ?

QT: I think you mean qt since there is no qi. This is a measurement (in milliseconds) obtained on ekg of the time it takes for the ventricles to electrically prepare for their next contraction. Sodium, potassium, and calcium ions move through channels during this period. Some drugs and some families have abnormalities of this movement which can lead to characteristic rhythm problems.