SA Node Abnormalities
Sinus Arrhythmia
| Parameter | Definitions |
|---|---|
| HR | Average heart rate greater than 60 |
| Regularity | Irregular pattern of bradycardia and tachycardia |
| P | Upright, regular P waves |
| QRS | Narrow QRS complexes |
| P:QRS Ratio | 1:1 |
The P-QRS waves of Sinus Arrhythmia do not appear unusual, but there is a rhythmic pattern of bradycardia and tachycardia that usually follows the change in intrathoracic pressure from breathing: getting faster with inspiration, and slower with expiration. It's a common finding in young individuals and is otherwise benign.
Very rarely, Sinus Arrhythmia may be unrelated to respirations and is often linked to the elderly and with cardiac disease through an unknown mechanism. Sinus Arrhythmia is not treated directly.
SA Nodal Blocks
An SA nodal block is a delay or interruption to the SA node's ability to generate an impulse. In a sinus rhythm, P waves are generated at regular intervals, and so an SA nodal block is apparent when there's a delay or missed P wave.
There are characterically three "degrees" of SA nodal blocks (like the AV nodal blocks), but for the purposes of cardiac monitoring, we will consider them all similarly.
Sinus Arrest
A sinus arrest is a complete interruption to the generation of a sinus impulse for 3 seconds or longer. During this time, the rhythm may change to a junctional (or ventricular) escape rhythm in the absence of the SA node impulse. In these cases, we would monitor or treat the resulting bradycardia of the escape rhythm.