<prompt> Which of the following is a feature of first degree AV block?PR interval 200 msInversion of T waveProgressive shoenting of PR intervalPresence of U wave  <response>: 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. 