Sino-atrial exit block

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)

References

1. ISBN:0721605095