Suggest Treatment For Still's Murmur

Question : My daughter has a still's murmar which is beinign. Last night she was in tachycardia with a resting heartbeat of 170. I rushed her to the hospital and the doctors monitored her and allowed her heart rate to come down on it's own after 6 hours. They did a cbc and an xray and found no anomalies except her phosphates was slightly low. After some monitoring we were sent home. She still feels like her heart is beating out of her chest, and her resting heart rate keeps fluctuating between 98 to 130 for no reason. When her rate goes back up, it feels like it's beating out of her chest. The ER doc's didn't seem to concerned but she is in great discomfort.
I just received her hospital report, she was diagnosed with Panic attack, Palpitations Sinus Tachycardia. Her sitting BP was 134/78. We are now 20 hours after the onset of this event. The event began as she was resting in her bed in her room. She said this has happened once or twice before, however she wasn't under stress or anxiety at the time, she stated that her heart just started beating out of her chest, then resolved after 45 seconds. She indicated that this episode, lasting this long has never happened. I Just looked at her blood work and thyroid is fine. She is complaining that her heart rate goes up, stays there for about 30 seconds then comes down. But it happens over and over again.

Her ECHO was unremarkable. However she still suffers from sinus tachycardia. Any exertion of energy causes her heart to become palpitate. It's not SVT, POTS or Vasovagal syncope. I believe given her symptoms she has IST (inappropriate sinus tachycardia), which is believed to be a Dysautonomic syndrome or a derangement of the sinus node, but sinus ablation is ineffectual in the long term. Because of it's relatively new discovery (1979) very few cardiologists are comfortable treating it. They want to throw beta blockers at the symptoms which have shown to be ineffectual. There is a medication that has had positive results called Ivabridine, but few doctors have experience prescribing this. It is unlikely that this is simple anxiety, since it has been ongoing on for more than 10 days now. If it is related to the ANS then hopefully SSRI's will help. I'm trying to find a cardiologist in the North East who are experienced in IST or specialize in autonomic dysfunction.