Final answer:
In an idioventricular rhythm, the atrial rate is not related to the ventricular rhythm and is considered 'Not measurable' because the atria and ventricles beat independently of each other. The ventricular rate, which originates from the Purkinje fibers, typically ranges from 20 to 40 impulses per minute.
Step-by-step explanation:
An idioventricular rhythm occurs when the impulse starts in the conduction system below the AV node, primarily within the ventricles. This can happen when higher pacemaker sites in the heart (SA and AV nodes) fail to initiate the impulse, or when their impulses are not conducted to the ventricles. The expected atrial rate in such a rhythm would not typically correlate with the ventricular rhythm because the atria and ventricles are beating independently of each other. The ventricular rate in idioventricular rhythm (originating from the Purkinje fibers) is typically slow, ranging from 20 to 40 impulses per minute. This rate is indicative of the inherent pacing capability of the Purkinje fibers.
Atrial rates may still be governed by the SA node and can be normal or fast; however, they do not correlate to the idioventricular rhythm because the ventricles are not being stimulated by the atrial impulses. In a complete AV block, the atria may be contracting at a normal SA node rate (60-100 beats per minute), but these contractions are not linked to the ventricular beats initiated below the block. The correct answer to the nurse's expectation of atrial rates in an idioventricular rhythm would be 'Not measurable', as the atrial rate is not influencing the ventricular rhythm and is therefore not relevant to the question about ventricular rates in idioventricular rhythm.