This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Digitalic toxicity produce the following changes in ECG except - 
Select and explain. 
A. Inveed T wave, B. Prolonged QT interval, C. ST depression, D. Prolonged PR interval
B: Prolonged QT interval
Answer: B: Prolonged QT interval 
Explanation: Ans. is 'b' i.e., Prolongation of QT interval ECG changes produced by digitalis o First see the relation of ECG and cardiac cycle. P wave represents atrial depolarization. QRS complex represents ventricular depolarization. PR interval represents conduction through AV node. QT interval corrosponds with ventricular depolarization +- ventricular repolarization. ST interval and T wave represent ventricular repolarization. o Digitalis causes PR interval --> due to delayed conduction in AV node. QT interval --> Due to increased contractility and better emptying of ventricle --> L systole. Decrease amplitute or inversion of T wave and ST depression --> Due to interference with repolarization.