<prompt> PR interval corresponds to ECG changes asVentricular depolarizationVentricular depolarization and atrial rcpolarizationAtrial depolarization and conduction through AV nodeVentricular repolarization  <response>: C. i.e. Atrial - depolarization and conduction through AV node 551 - Ganong 22nd 494- Ganong 23rdECG IntervalsIntervalNormal Durations SEvents in the heart during intervalAverageRangePR interval0.180.12-0.20Atrial depolarization and conduction through AV nodeQRS duration0.08to 0.10Ventricular depolarization and atrial repolarizationQT interval0.40to 0.43Ventricular depolarization plus ventricular repolarizationST interval QT minus QRS0.32 Ventricular repolarization QRS complex denotes - ventricular depolarization The normal direction of mean QRS vector is generally said to be - 30 to 110 on the coordinate system U wave - It is due to slow repolarization of papillary muscle TP segment - It represents polarized state of whole heart J-point - point between S wave and ST segment. It is a point of no electrical activity 305-A.K Jain 3rd 