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Sino-atrial exit block: Difference between revisions
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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 destinguished from [[sinusarrest]] because the pause in SA exit block is a multiple of the P-P interval that preceded the pause. | 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 destinguished 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: | Three subtypes can be destinguished:<cite>Braunwald</cite> | ||
*Type I second degree (Wenkebach) SA exit block: the P-P interval progressively shortens prior to the pause | *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 | *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) | *Third degree SA exit block: absence of P waves (can only be diagnosed with an sinus node electrode, during electrophysiological evaluation) | ||
==References== | |||
<biblio> | |||
#Braunwald ISBN=0721605095 | |||
</biblio> | |||