My daughter is 16 years old and always has a resting heart rate of over 90 beats per minute.  Today at a clinic, it was 109 beats per minute and is VERY often over 100.  She is not that stressed out or anything.  We have googled where thyroid can cause this, among other things.  She is very worried.  Should she be???
Hi, Increased heart rate & palpitations can have a lot of causes. It can be normal sinus tachycardia due to anxiety or stress, or it could be abnormal supra ventricular tachycardia. For the diagnosis, you need to do ECG at the time of palpitation and tachycardia. If the duration of palpitations are short enough to reach a nearby hospital, we put a 24hr ECG monitoring (Holder Monitor). You also need to do a 2D Echo and thyroid function test to see for any associated abnormality if any. Hope I have answered your query. Let me know if I can assist you further.