Possible myocarditis -- or something else?

[tickintheticker]

For almost three years following a dog bite, I had an almost continuous crushing/squeezing sensation around my heart, was mostly bedbound, and could not be slightly upright without exacerbating the symptoms.  When my doctor began treating me with antibiotics for Lyme disease, we soon realized my heart responded to certain antibiotics known to target the coinfection bartonella: we tested and I came back positive.  

I had been treating both Lyme -- which became neurological -- and bartonella for a little over a year, with my cardiac symptoms improving substantially -- when I began to have new heart problems, such as shock-like sensations through my chest, fatigue, chest tightness and episodes where I would feel like I was blacking out.  After a blackout incident, I called 911 and spending time on a cardiac ward.  They found very little except for inconclusive abnormalities on ECG and hours of tachycardia.  There were no arrythmias and my ejection faction was normal.  Inflammation markers were also normal.  

Since I returned home, I have been devastatingly ill and my heart symptoms have gotten worse.  I am extremely weak, totally bedbound, and have severe chest tightness and shortness of breath from very minor exertions, as well as tachycardia that will start inexplicably and continue for long stretches of time (I am on a beta blocker now).  If I do much of any exertion, including talking, I will get very short of breath and, ultimately, feel like I'm going to black out -- with the chest tightness and sometimes chest pain.

I really think I have myocarditis and that the antibiotics are failing.  Is it possible to have myocarditis without positive inflammation markers or positive cardiac enzyme markers?  I did have a complete right bundle branch block on several different ECGs during the period of crushing chest pain.  If I do have Lyme myocarditis, what antibiotics are recommended?  If it isn't that, what else could it be?

[Cleveland Clinic]

Ceftriaxone and other cephalosporins are the antibiotics of choice for Lyme disease with heart involvement.  But it would be very unusual for you to have persistent myocarditis with normal cardiac markers.  Most of the time the problem with Lyme disease affecting the heart is heart block and feelings of lightheadedness or syncope.  The tachycardia is atypical, as is heart failure.  I think you should wear a Holter to document these heart rhythms.  If that doesn't reveal anything, consider having an EP study.