How can you identify that a cardiac rhythm originates from the SA node?

Identifying that a cardiac rhythm originates from the SA node hinges on observing the characteristics of the P waves preceding the QRS complexes. When a rhythm is generated by the SA node, you will typically see upright P waves that precede each QRS complex consistently. This pattern indicates that the impulse is originating from the atrium, specifically from the SA node, which is the natural pacemaker of the heart.

The morphology of the P wave is crucial since it reflects the depolarization of the atria initiated by the SA node. If every QRS complex is preceded by an upright P wave, it suggests a normal conduction pathway through the atrioventricular (AV) node and into the ventricles, confirming the dominance of the SA node as the rhythm's origin.

In comparison, characteristics such as absent P waves, frequent premature ventricular contractions, or altered T wave morphology suggest different underlying issues or rhythms and do not imply that the rhythm is originating from the SA node.