Third degree AV block

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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.
  • Also known as complete heart block
  • No conduction through the AV node, causing the atria and ventricles beat completely independently from each other
  • The ventricular beat is an escape rhythm anywhere from the AV node to the bundle-branches (normally slow, varying from 35 to 45 beats per minute)


Clinical Features

Differential Diagnosis

AV blocks


Rhythm 3rdAVblock.jpg
  • No atrial impulses are conducted
    • P waves normal and regular P-P intervals unrelated to slower regular R-R intervals
    • QRS narrow if block above bundle of His
    • QRS wide if block below bundle of His
    • PR variable
  • Differentiate from AV dissociation without complete heart block
AVD without CHB, courtesy of public access Amal Mattu EKG videos



See Also


  1. Sovari AA et al. Second-Degree Atrioventricular Block Treatment & Management. eMedicine. Apr 28, 2014.