Sino-atrial exit block
|This is part of: Sinus node rhythms and arrhythmias|
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:
- 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)