Sino-atrial exit block

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This is part of: Sinus node rhythms and arrhythmias
Sino-atrial exit block (more precisely: type II second degree SA exit block)
Sino-atrial exit block
Sino-atrial exit block

During sino-atrial exit block, the depolarizations that occur in the sinus node cannot leave the node towards the atria. They are blocked. On the ECG this is expressed as a pause. SA exit block can be distinguished from sinusarrest because the pause in SA exit block is a multiple of the P-P interval that preceded the pause.

Three subtypes can be destinguished:[1]

  • Type I second degree (Wenkebach) SA exit block: the P-P interval progressively shortens prior to the pause
  • Type II second degree SA exit block: the pause equals approximately 2-4 times the preceding PP interval
  • Third degree SA exit block: absence of P waves (can only be diagnosed with an sinus node electrode, during electrophysiological evaluation)


  1. Eugene Braunwald. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 2-Volume Set. Saunders. ISBN:0721605095 [Braunwald]