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: Medicine
Which of the following is a feature of first degree AV block? 
Select and explain. 
A. PR interval > 200 ms, B. Inversion of T wave, C. Progressive shoenting of PR interval, D. Presence of U wave
A: PR interval > 200 ms
Answer: A: PR interval > 200 ms 
Explanation: Answer- A. PR interval > 200 msFirst-degree AV block (PR interval >200 ms) is a slowing of conduction through the AV junction.The site of delay is typically in the AV node but maybe in the atria, bundle of His, or His-Purkinje system.In second degree AV block there is an intermittent failure of electrical impulse conduction from atrium to ventricle.Second-degree AV block is subclassified as Mobitz type I (Wenckebach) or Mobitz type II.