Hey Geraniumgirl,
I am 45F and had some similar experience as you - anemic AND heart palpitations but I had an event that brought all that on - I also, couldn't handle atenelol - gave me a fierce headache but anyways, I started noticing the palpitations too and had one night where I wouldn't go to sleep because I was afraid I wouldn't wake up - when I spoke to my cardio about these he assured me that they are common and are nothing to worry about (I wore several types of monitors just for my own reassurance and they indulged me without question because they're "good" doctors). I'm sure your holter test will probably confirm this but bug'em again - it's too stressful not knowing what the heck is going on! They should have had the results in about a week. Make sure you push on this just for your own peace of mind.
By the way - I get the palpitations when near my cycle. I take iron when my cycle nears and they seem to help lesson the severity and since I know they're nothing to worry about I have them even less - maybe a couple here and there every month or so. Are you also aware of what not to have before and after taking the iron pills? It helps knowing this so you can be assured you're absorbing it properly. No coffee, milk or dairy at all for that matter 2 hours before or 1 hour after ingestion. Just in case you weren't aware of it - there's more too - just ****** it to find out the best way for absorption. I've read on this board that magnesium works too but I haven't tried that.
Hang in there - and hope you're feeling better
Linda1962