# sinus arrest,pause,block?



## smalizia (Sep 7, 2013)

how do i tell the difference between a sinus arrest, block, and pause on a strip?


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## Dwindlin (Sep 7, 2013)

smalizia said:


> how do i tell the difference between a sinus arrest, block, and pause on a strip?



Arrest and Pause are essentially the same thing. A block will have some sort of alteration in the PR segment and/or P:QRS ratio.


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## Christopher (Oct 10, 2013)

smalizia said:


> how do i tell the difference between a sinus arrest, block, and pause on a strip?



*Sinus pause* is any unexpected missed P-wave during a sinus rhythm which is not an even multiple of the P-P.

*Sinus arrest* is arbitrarily defined as >3s without an expected P-wave. The two terms are somewhat interchangeable and I vary which one I use based on the length of the gap.

Sinoatrial block (also sinoatrial exit block / SA Block) is akin to AV block and thus requires more detail. Basically this is a block between the SA node and the atrial tissue. As with any site you can have entrance or exit blocks. When discussing SA blocks, we almost exclusively mean SA _exit_ blocks due to the extreme difficulty in identifying entrance blocks to the SA node on the surface ECG.

SA Blocks take a bit of mental wrestling to identify readily on the ECG, and are probably best an extracurricular activity during interpretation 

A *1st degree SA Block* is not detectable on the surface ECG, as we do not visualize the SA-A time with any interval. EP studies are required to determine its existence.

A *2nd degree Type I SA Block (SA Wenckebach)* has the same characteristics as an AV Wenckebach (just substitute R-R with P-P):

First P-P interval is the longest
Subsequent P-P intervals shorten
Missing P-wave at the end
P-P interval around the gap is less than the prior two P-P's

A *2nd degree Type II SA Block* has the same characteristics as your Type II AVB:

Constant P-P
Gap for dropped P-P even multiple of base P-P interval
In 2nd degree Type II SA Block the sinus rate is typically slower.

A *3rd degree SA block* has the same characteristics as your 3AVB but is no different looking than SA Pause/Arrest on the surface ECG. This one also requires an EP study to determine.

The last one, which was not mentioned, is a *sinoventricular rhythm*. This is seen nearly exclusively in hyperkalemia and results in intact SA-AV conduction without atrial activation (hence no P-waves). The atrial myocardium is very sensitive to hyperkalemia while the SA node and intranodal pathways are not. It would be difficult to authoritatively state it is present from the surface ECG alone, but EP studies have confirmed it is an actual rhythm.

I hope this helps!


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