Atrial flutter is almost never life threatening and you don't describes any high risk factors for yourself.
Metoprolol (Toprol) is a very safe medication. There are very few drug interactions.
The interpretation of heart rhythms on these monitors is very accurate for easy rhythms and not very accurate for some arrhythmia's. Atrial flutter is sometimes hard to make a diagnosis because the notches that you need to see on the EKG to make a diagnosis are hidden at 150 beats per minute. From your history, sinus tachycardia is the most likely diagnosis. I haven't' seen the strips so I can't really comment on what your doctor saw but I can tell you that I have seen atrial flutter called sinus tachycardia on monitors before.
I hope this helps.
I am just a layperson but as someone with anxiety and eight years of heart arrhythmias I wanted to express my sympathy and offer a few ideas.
If it turns out that you have atrial flutter, and it looks to me like they don't know whether that is true or not, and meds don;' control it, there is an ablation for it that has been done for a long time and which is well understood. Also, as the doc said, aflutter is not normally something that kills people. In fact, I had no idea that it even had the remote possibility of doing that until he mentioned it. So I think you can put your mind at ease about that possibility.
But, as a been there done that anxiety person myself, it sounds like you are driving yourself nuts worrying about this. If you can manage to lower the amount of that, I suspect things will improve.
I used to check my pulse a lot. Don't do it unless your doctor tells you to. I am so much happier since I stopped doing that.
Also, I suspect you would have been better off with the type of monitor that records continuously, not one that has you being constantly vigilant and having to decide what to record and so getting worried about stuff and bringing on a high heart rate.
Do you know about relaxation breathing? You can google for that on the web. Try doing that several times a day, and doing it when you start to panic. I automatically snap into it now in stressful situations. If your breathing is controlled, it is harder for your body to go nuts.
You mentioned benzos. You probably know those can be addictive, and a symptom of withdrawal is a high heart rate. So you might want to look at what's been going on with how you are using those.
It sounds like you are just starting the Toprol. I ran the drug interaction checker at drugstore.com for the three meds and it said Lexapro can increase the effect of Toprol. I was actually on both Lexapro and Toprol for awhile and noticed no effect.
It may be that the Toprol is all you need to set this problem at rest, or at least reduce it a lot, as it both keeps the heart rate lower and has anti-anxiety effect. It does take about a week to build up in the blood.
Lastly, is there anyone you can vent to when this stuff i going on? A sibling, maybe?
Hang in there. I really do think a lot of this is anxiety. The fact that you had a normal stress test and echo is good news.