Final answer:
In a cardiac arrest situation, the next critical step for an AEMT after analyzing the patient's heart rhythm and receiving a deliver shock message from the AED is to clear the patient. This involves ensuring that no one is touching the patient or interfering with the shock.
Step-by-step explanation:
After analyzing a cardiac arrest patient's heart rhythm and receiving a deliver shock message from the AED, the next critical step for an AEMT involves clearing the patient. This means ensuring that no one is touching the patient or interfering with the shock. The AEMT should verbally announce 'Clear!' and make sure everyone steps away from the patient before delivering the shock. This step is crucial to avoid anyone getting injured from the electrical shock.