Where are you located? I have Inappropriate Sinus Tachycardia as well, and I really like my doctor in Md. They're associated with the University of Maryland Medical Center in Baltimore. I've had two catheter ablations so far, and unfortunately had to have a pacemaker implanted as a result of one. However, the docs are always on top of things with me..sometimes to the point where they're annoying! How long ago were you diagnosed?
A medical doctor who specializes in electrophysiology may be your best bet for a second opinion.