Metoprolol

Metoprolol is a rate control drug, so it should have little effect on the arrhythmia, whatever it is, except to slow the beat rate down. This would also happen when in normal sinus rhythm. If you want to alter the rhythm because it is not NSR, then you'd take an anti-arrhythmic drug such as Flecainide, Sotalol, Multaq, propafenone, or amiodarone, just as a few examples (there are others). Naturally, this would all be done on the prescription by a qualified cardiologist or electrophysiologist.
Some people feel that their heart slows too much, and it is often demonstrated on an ECG. Some are simply getting too much metoprolol when their heart is in NSR and it slows it down into dangerous bradycardia territory, say below 40 BPM. Or, there will be long pauses evident on the ECG.
So, now is the point where I would ask you to define' gotten worse'. I'm unsure what has changed, changed from what was okay beforehand. Have any of your prescriptions changed?

Well, I have an arrhythmia.
I have taken propanolol for 30 years. I don't think it has helped, but I'm not sure without further investigation. Dr changed me to Metoprolol Extended Release. About 8 hours after taking the first Metoprolol, I had one of the worst episodes of arrhythmia ever. I went back to propanolol. None of my scripts has changed.

I take Metoprolol as needed for AFlutter. Takes about 45 mins to kick in fully and it does a wonderful job of putting things back into rhythm. No issues. Hopefully the upcoming ablation will take care of the situation and remove that need.

I am not sure what "getting worse" means, but I didn't not do well on metoprolol. Yes, it impacted my heart rate to the point that it was in the low 50s resting and only in the mid to upper 70s when I was involved in some activity. Since I am way past being an active athlete, that is too slow. I felt lethargic and I had pain and a kind of numbness in my legs below my knees. I went off of metoprolol about 2 months ago and the change/improvement was almost instantaneous. No more problems with my legs and I generally feel much better and have gone back to long walks in the morning. My heart rate is now in the mid 60s resting and in the mid 80s with activity.

It really worked for me in the ER. But as a daily thing not so much. Afib kept happening 1-2x month. I was on Diltalizan for a few years and I gained so much weight and my legs pigmented. My pcp over ruled the cardiologist who was wanting stronger drugs.
Now I’m just on Carvedilol and the weight is coming off and only 1 tiny bout with Afib 2 months ago when we did the change.