QT-interval parameters are potentially proposed as available non-invasive markers for assessing the ventricular homogeneity as well as for predicting electrical instability ,QT interval (QTI) is defined as the longest interval from the beginning of the QRS complex to the end of the T-wave; QT dispersion (QTd) is defined as the difference between the longest and shortest QTI, and reflects electrical activity of the ventricles . .