Pearls of Knowledge: Sinus Block and Sinus Arrest
Wednesday, December 03, 2025
Rhythm Interpretation: Sinus Block and Sinus Arrest
Pearls of Knowledge © BrainyNurses.com
Sinus block and sinus arrest both originate in the SA node and are characterized by a sudden pause. In sinus block, the impulse cannot get out of the SA node. In sinus arrest, the SA node does not fire correctly and is evidence of SA nodal dysfunction and a precursor to sick sinus syndrome and the need for a pacemaker.
The pause in sinus block will be for an interval related to the established heart rate. In sinus block, when the rhythm resumes, it resumes on time.
The pause in sinus arrest may be for any length of time and is not related to the rate established prior to the pause. Typically, when the rhythm resumes in sinus arrest, it resumes at a slower rate.
Sinus Block
(Rhythm resumes on time and the rate remains essentially unchanged.)
Sinus Arrest
(SA node is unable to recover after the pause and resumes at a slower rate.)
Calculating a Pause
• Each block is 0.04 seconds. Count the blocks and multiply by 0.04.
• This is sinus rhythm with sinus block. The pause is related to the established heart rate and the rhythm resumes on time. The pause is 2.52 seconds.
Summary
There are several rhythms that can result in a pause. The most common is a blocked PAC. Once it has been eliminated as a potential “cause of the pause”, the next investigation should focus on the possibility of a sinus block or sinus arrest. Of the two, sinus arrest is more concerning because it signifies damage to the SA node.
To enhance care provided for cardiac patients, check out Comprehensive Rhythm Review and Clinical Application. It is on-line, on-demand, with voice-over-power-point. The extensive handout is easy to follow and includes our “In My Pocket” cards as a ready reference tool.
