Atrioventricular (AV) Blocks



First Degree AV Block - "If your R is far from your P than you have a first degree"

 • 1:1 conduction with prolonged PR interval (>200 msec)

 • P wave preceding each QRS complex

 • Site of Block: Delayed conduction at the AV node



Second Degree AV Block - Mobitz Type 1 (Weinckebach) - "Longer, longer, longer DROP, now you have a Weinckebach"

 • Less than 1:1 AV conduction with progressively prolonged PR intervals until a P wave (ventricular complex) is dropped

 • Site of Block: Slowed conduction at the AV node

Second Degree AV Block - Mobitz Type 2 "If some P's don't get through, not you have a Mobitz Type 2"

 • Intermittently dropped QRS in a random fashion with progressive PR lengthening

 • Site of Block: Slowed conduction below AV node (His bundle or Purkinje Fibers)



Third Degree AV Block - "If your P's and Q's don't agree, then you have a Third Degree"

 • Complete Heart Block

 • AV conduction is completely absent, P waves fail to conduct to the ventricles

 • Ventricle beats independently of the atria leading to AV node dissociation and the rate is set at the site of conduction block

 • Site of Block: Any location in AV conducting system (AV node, His Bundle, trifasicular)



Ashley & Brooke Barlow PharmD @theABofPharmaC



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