AV blocks

Types

First degree AV block

Types of second degree AV block

Rhythm strip showing third degree AV block. Note that the P waves are not related to the QRS complexes (PP interval and QRS interval both constant), demonstrating that the atria are electrically disconnected from the ventricles.

• First Degree AV Block
  • Prolonged PR interval (>200msec) but constant and always conducts
• Second Degree
  • Second Degree AV Block Type I (Wenckeback)
    • Progressive prolongation with intermittent dropped QRS complexes
    • Progressively shortening RR intervals
  • Second Degree AV Block Type II
    • PR interval is constant with intermittent P waves not conducting QRS complexes
    • Surrounding RR intervals are constant
• Third Degree AV Block
  • Complete Heart Block - no AV conduction
  • Dissociation between P waves and QRS complexes

Evaluation

• March out P waves
• March out QRS complex
• Look at PR interval to determine relation

AV blocks

• First degree AV block
• Second degree
  • Second degree AV block type I (Wenkebach)
  • Second degree AV block type II
• Third degree AV block
• AV dissociation without complete heart block

See Also

• ECG rhythms