Final answer:
The finding of a HR of 60 bpm and regular should be immediately reported since it is lower than the pacemaker's set rate of 70 bpm, potentially indicating a pacemaker malfunction or underlying bradycardia.
Step-by-step explanation:
A client diagnosed with atrial fibrillation and with a pacemaker set at a ventricular rate of 70 bpm should have a heart rate close to that setting. Among the provided options, the finding that should be most immediately reported to the provider is a heart rate (HR) of 60 bpm and regular. This is because the rate is lower than the pacemaker's set rate, which could indicate that the pacemaker is not functioning properly or that there is another underlying issue leading to bradycardia, where the resting rate drops below 60 bpm.