Is zyrtec (cetirizine) or allega safer for chronic use to treat chronic hives? Is it safe in patients with arrhythmia

Yes it is safe to us. Yes it is safe to use if it is effective for hives and safe in patients with arrythmia.
Yes. They are both rather safe drugs although zyrtec (cetirizine) may theoretically increase your heart rate when taken in large doses. However I am not aware of anyone having cardiac side effects even from 4 daily doses of zyrtec (cetirizine).