Final answer:
The nursing action that should be prioritized in the subsequent diagnostic workup of a patient presenting with syncope of unknown origin is preparing to assist with a head-up tilt test.
Step-by-step explanation:
In a patient presenting with syncope of unknown origin, the nursing action that should be prioritized in the subsequent diagnostic workup is preparing to assist with a head-up tilt test.
A head-up tilt test is a diagnostic procedure that helps to evaluate a patient's response to changes in body position. It can be used to assess for conditions such as orthostatic hypotension or vasovagal syncope, which can cause syncope (fainting) episodes.
Assessing the patient's knowledge of pacemakers, preparing an intravenous dose of a β-adrenergic blocker, and teaching the patient about the role of antiplatelet aggregators may be relevant in specific cases, but they are not the priority in this patient's diagnostic workup.