Any ideas on Heart "Quivering" Sensation?

I hope someone can help. With a holter monitor test I have been diagnosed with PSV, PAC, and PSVT about 5 years ago. It got worse in the last year (I think because I have become very sick with chronic severe lyme disease it has affected my heart too). My cardiologist put me on Toprol 50 mg XL, which seemed to help the fluttering for a while. But now in the past month along with the chronic fatigue and pain from the lyme I have been having bad episodes of my heartbeat pounding fast, feeling faint, feeling pressure in chest and sweating, it will even wake me up at night and usually happens while laying down. These episodes can last from 10 minutes to hours with breaks in between. What really concerns me is that I also sometimes get that intense quivering feeling like my heart is spasming for a few seconds (very intense and scary!) this comes sometimes with the fast beat and sometimes just out of the blue with normal beating, I am getting this almost daily, sometimes a few times a day. A few times the quivering lasted longer than a few seconds and I almost passed out then it stopped, the worst one I felt that lasted possibly nearly a minute or so, a squeezing chest pain came with after a few seconds of the "quivering". I feel my heart is going to just give out one of these times! I also get episodes of very low blood pressure (89/45 or around that), especially during the "fast beating episodes" - Normal for me is 127/74. So I am worried the toprol will get it too low if I increase it. What I really worry about is the intense "quivering". I also sometimes feel a sensation in my chest just before it starts. We did not catch an intense "quivering" episode on the holter (I only had slight "flutters" while wearing that) Could a PVC feel that intense at times? It feels like erratic flopping or jerking, or quivering real fast. I am so scared of this, any ideas what this could be? Also, could alot of PVC's, PAC's or PSVT's be hard on my heart?(all of those did show up on the holter). My cardiologist only looks at what he found on the holter, which didn't catch the severe "quivering" or "spasming" so he just said it is PVCs and increase toprol, I don't think he undestands what I am experiencing, only relaying messages through his nurse - But I don't want to go to another cardiologist if they are not going to try to figure it out either. I need some advice on what might be going on. It is SCARY when it does that.
Hope someone can give me some advice. Thank you.

[arthur]

If the quivering you feel is unrelated to actual "skips", ie, PACs and PVCs, then you are not alone.  Otherwise that quivering sensation is a normal aftereffect of the "skip" due to the heart's chambers filling up with an extra volume of blood due to a preceding inefficient premature beat.

Back to the quivering independent of actual arrhythmia...it's been acknowledged by a number of EPs, most of whom have no good explanation for it.  The best explanation I have obtained (from an EP) is the quivering may be coming from a focus (or foci) located in a spot where they don't produce too many skips but whose signals get amplified for some reason to the point that you actually feel them.

I feel them.  Close to the middle of the chest, and behind the heart.  This would place their origin at or near typical locations for foci (at the PV ostia).  In my experience they are made worse when you are anxious or make sudden movements...or even when you get up at night you may feel them upon returning to bed.

They appear harmless...I've had them for about 7 years, and their intensity has dropped significantly as has my level of anxiety.  If you are experiencing the same symptoms, work on relaxation techniques...the one that worked best for me was to stop measuring my pulse.

-Arthur