Uncomfortable heart rhythm for days

31 year old female:
For several years I have been experiencing episodes of extreme discomfort that seem to be centered around my heart (after numerous specialists, anxiety has been ruled out as a contributing factor to these episodes).  These episodes can last from about 24-72 hours straight.  Often times, these episodes seem to begin after feeling a palpitation.  It is as though the palpitation triggers my heart to start beating differently.  During these episodes, my heartbeat is very uncomfortable.  It beats more forcefully, making it noticable, and I experience more frequent palpitations during these attacks.  In between palpitations, I feel generally lousy...lightheaded, mild headache, sluggish and feel as though there is a "strain" in my chest area and have even mild exercise intolerance.  Sometimes, I even feel a horseness in my throat and esophagus.  I have had numerous echocardiograms, including at the Mayo clinc, as well as EKG's and heart monitors which have all reported that I have a perfectly structurally healthy heart with benign palpitations.  I have also undergone some autonmoic testing which yeilded a diagnosis of mild POTS.  In addition, I have been diagnosed with mast-cell activation disorder.  These episodes, however, do not seem to correlate to the symptoms of these disorders.  I have had EKG's done during these episodes, therefore, my symptoms have been recorded and observed while they were occuring.  My question is, could this still be an issue originating in my heart?  It is hard for me to believe that these episodes are not a problem with my heart since my heartbeat feels like the center of the discomfort during these episodes.  I have never had an EP study and wonder if this type of study would yield results or find something that did not show up on my EKG's.  Is it possible for my heart to be doing something abnormal, that would not be seen on an EKG, holter or event monitor, even while symptomatic...are EKG's capable of detecting all possible abnormalities if they are done while a patient is symptomatic.  I am concerned that these episodes may be too complex to show up on a regular EKG or monitor.  I am not sure if I should pursue seeing another doctor or specialist and wonder if there is some strange thing that my heart is doing, that only a more invasive approach could detect?  I just want relief of these symptoms.  Thank you for your time in answering my questions.

[Jenn0030]

What type of autonomic testing did you have to get the POTS dx as sometimes this is done within and EP lab?

Did you only have an EKG? EKG are capable of capturing abnormalities when you are having them, (I am sure that someone will correct me if I am wrong) but I have had holters that were unable of picking up abnormalities because that event just didn't happen when I wasn't wearing the until.  They can use a longer unit 30+ days (or even longer if needed) to capture events that don't occur on a daily basis

Are you on any cardiac meds (beta blockers or florinef) for the POTS?