This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Stimulation of the sympathetic nerves to the normal heart: 
Select and explain. 
A. Increases duration of the TP interval, B. Increases the duration of the PR interval, C. Decreases the duration of the QT interval, D. Leads to fewer P waves than QRS complexes
C: Decreases the duration of the QT interval
Answer: C: Decreases the duration of the QT interval 
Explanation: Ans. C. Decreases the duration of the QT intervalStimulation of the sympathetic nerves to the normal heart decreases the duration of the ventricular action potential and, therefore, decreases the QT interval. As heart rate increases, the duration of diastole and, therefore, the TP interval decreases. Increased conduction velocity in the AV node decreases the duration of the PR interval. Fewer P waves than QRS complexes are indicative of AV block. On the contrary, sympathetic stimulation may reverse AV block. The frequency of QRS complexes increases with the heart rate.