I can only answer from my own experience, but I have had adenosine several times as well as taken metoprolol and a couple of other beta blockers and never had any memory problems or brain fog. Adenosine is very short acting with a half life of only seconds, so I really doubt it would have long standing side effects, but I am not a doctor.
Drugs can affect people differently. How much Metoprolol are you taking daily?