Anyone find root cause for IST(inappropriate sinus tachycardia)?

[helplessinoklahoma]

I’ve been told I have IST(inappropriate sinus tachycardia).  I see a lot of post about it, but haven’t been able to find any from anyone that after searching for a long time had actually found the root cause instead of it being still “inappropriate”.   So if anyone out there has actually found the cause after maybe years of looking, PLEASE post what you found.   I have had a sudden onset of this 6 months ago and I am tiring of going to doctors for test after test for nothing.  Is there any hope?   Am I doomed to beta blockers and their side effects forever?  I feel hopeless…

[juliejujube]

I have the same condition.  It was classified as not inappropriate but idiopathic sinus tachycardia.  I was hospitalized recently for back surgery and my potassium was found to be low (possible cause).  I was taking hydrochlorothiazide HCTZ which is a diuretic and even though I was on 20 meq of potassium daily I still had low potassium.  At present I have been taken off HCTZ yet I'm still taking potassium.  I will go for a blood level as too much potassium can cause cardiac arrest as can a low level.  Good luck to you.

[updownleftright]

I actually have a similar story. I was put on atenolol initially which works beautifully for me, but 6 months later I went to a new cardiologist and they insisted I switch to bisoprolol and claimed it works much better. Went on brisoprolol and my heart would shoot up to 150-160 about ten minutes after taking and it would stay there the rest of the day. Switched back to atenolol and everything went back to normal. Keep trying you may find one that works.

[helplessinoklahoma]

Well that is not encouraging.   I am on my second type of beta blocker because the first would lower my BP too much.   The 1 day I had to stop them to allow my BP get back up, my heart rate shot up and stayed up all day long.  It was horrible, like I am having a heart attack all day long.  I just don't understand how this just suddenly happened.   I am hoping the new beta blocker will work, but it still has side affects that are bothersome too.   I am fairly sure I don't have POTS, I've not have a problem with dizziness getting up and down.   I know they keep saying it is not life threatening, but it feels that way, and I have a very young child that I really need to be able to stick around for.  Sigh..

[updownleftright]

I've had IST for 3-4 years now. At first it was terrible, and well it still is, but with time you get used to it, and you find a new normal. The fast heart rate will stop bothering you as much or all together. I've been told by doctors that it can in some circumstances go away with age. If beta blockers work for you than consider yourself very lucky as a lot of people with IST do not respond to beta blockers. A tilt table test might be useful, but if you had POTS your symptoms would be much worse, and you'd feel extremely light headed or pass out upon standing. It's very unlikely. A normal persons blood pressure rises when they stand. Someone with POTS drops by more than 30 points.

[Red_Star]

I had to diagnose my two autoimmune diseases from online research and one of those diseases is 100% fatal without treatment.  Lost a bit of your spark eh?  Crank up Christina Aguilera's song Fighter! The diagnosis might be a click away. :P

Diagnosing Dysautonomia:
http://www.medhelp.org/tags/health_page/39830/neurological-disorders/Diagnosing-Dysautonomia?hp_id=827

[helplessinoklahoma]

Guess what I am looking for is missed diagnosis then that is finally moved from IST to something else.   Like for me, they have done significant blood and urine work and heart u/s, event monitors..etc.   But I've never had a "tilt" table test or an EP study.  But they are already ready to go with IST.  I still have an appt with an endocrinologist next month but that is because I pushed the issue with my internal doctor and she finally referred me.   But I am getting tired of fighting to keep trying to find a cause and wondering if it is worth it or just take the IST diagnosis keep sucking down the beta blockers.   I have very young children, and I am really worried that maybe something is being missed and 5 years from now, it won't be fixable.  

[Red_Star]

"IST is a diagnosis of exclusion. Almost always, sinus tachycardia is appropriate. Therefore causes of appropriate sinus tachycardia must first be excluded:

Anemia
Pheochromocytoma
Hyperthyroidism
Volume Depletion
Fever
Anxiety Disorder
Medications
Cardiomyopathy"

"Patients who are being considered for IST must have blood or urine tests to exclude anemia, hyperthyroidism, and pheochromocytoma. Medications can also cause heart racing (hydralazine or other vasodilators, too much thyroid hormone replacement, sympathomimetics for asthma or COPD, anticholinergic medications for irritable bowel syndrome, stimulants prescribed for ADD).

A tilt table test is then required to exclude autonomic disorders that can mimic IST: postural orthostatic tachycardia syndrome (POTS) or orthostatic hypotension. This disorder involves abnormal control of blood pressure, and the fast heart rhythm is necessary because of the hypotension that occurs when the patient stands and blood pools in the veins of the legs. Eventually, an EP study may be required to exclude tachycardias arising from near the sinus node, but not from the sinus node itself (5)."

Excerpts from Heart Racing - Inappropriate Sinus Tachycardia.