SINOATRIAL (SA) EXIT BLOCKS:

A disorder of the sinus node in which there is intermittent complete failure of sinus impulses to conduct to from the sinus node to the atria.

•First Degree SA Exit Block:

•Delay from the time the SA node creates an action potential to the time the atrium actually depolarizes.

•Not recognizable on the ECG (may simply look like a sinus rhythm or sinus bradycardia).

•Second Degree SA Exit Block:

•Mobitz 1: A disorder of the sinus node in which there is progressive shortening of the P to P interval until a P wave is blocked in the SA node (shortening of the PP interval then a dropped P wave).

•Mobitz 2: A disorder of the sinus node in which there is consistent P to P interval until a P wave is blocked in the SA node (Constant PP interval then a dropped P wave).

•Third Degree SA Exit Block:

•A disorder of the sinus node in which no SA nodal action potentials are able to leave the SA node (no P waves seen). Appears as sinus arrest and can actually only be diagnosed with a sinus node electrode during an electrophysiology study.