The difference btwn INAPPROPRIATE SINUS TACHYCARDIA and SINUS TACHYCARDIA

HI,
I've just been reading up on Inappropriate Sinus Tachycardia.  I had been diagnosed with Sinus Tachycardia due to Panic Disorder after going through a bunch of tests at Cardiologist's (EKGs, echo, stress, 24 hour heart monitor) for my racing heart.  The cardiologist never mentioned IST but I've been reading that they can mix these up.  Is it possible I have this? What is it? Is it dangerous?
thank you...

[Brooke_38]

adviceseeker777,

Sinus Tach is a rhythm with an elevated rate of impulses originating from the SA node, defined as a rate greater than 100 beats/min in an average adult. The normal heart rate in the average adult ranges from 60–100 beats/min.

Sinus tachycardia is usually a response to normal physiological situations, such as exercise and an increased sympathetic tone with increased catecholamine release, stress, fright, flight, anger, anxiety, dehydration, fever etc.

When there is no known cause and all possible known causes of Sinus Tachycardia have been excluded, the heart rhythm is called 'Inappropriate' Sinus Tachycardia. patients have elevated resting heart rate and/or exaggerated heart rate in response to exercise. These patients have no apparent heart disease or other causes of sinus tachycardia. IST is thought to be due to abnormal autonomic control.

Your cardiologist may have diagnosed your sinus tach secondary to your panic disorder. What I mean is that your panic disorder is the cause to you ST. Did he mention that as a possible trigger? If you had all the above testing and everything came back normal, I would try not to worry.  Did the Dr prescribe any medication?

[adviceseeker777]

HI Brooke,
thank you so much for this explanation.  Actually, my cardiologist wanted to speak directly with my shrink who has me on anti-anxiety and antidepressant meds (we've gone through a ton of these).  The cardiologist is convinced that the racing heart is coming from the panic/anxiety but it's hard for me to tell which comes first and I am always terrified that I'm being dismissed as someone who has panic disorder when the panic may be coming from the heart not working properly.  According to him, it's all working fine...although I still have a difficult time understanding how my heart rate going up to 150-180 can be 'fine'.  
My shrink wants me to take a beta blocker (Inderal 10mg) along with the Klonopin and Prozac I'm on to try to ease the racing heart and hopefully keep me calmer about it, but the cardiologist actually told me I shouldn't even bother with the beta blocker at all because he didn't feel it would work since the problem wasn't my heart.  Thought that was strange since so many people with performance anxiety use beta blockers to control the racing heart when they are nervous and they don't necessarily have heart problems either.
Thank you again for this explanation. I know at some point I need to stop worrying about this and driving myself more crazy and just believe that I'm healthy.  Hard to do with panic attacks :-(
best to you!!
k

[shelly0721]

Like adviceseeker 777 said about sinus tachy and ist. I have ist due to autonomic dysfunction. This automonic dysfunction was just diagnose last week due to the fighting battle of severe gastroparesis. My heart rate and blood pressure is out of wack becsuse my body does not how to regulate it anymore. Once my gastroparesis stable then my ist and bp will be control also with meds. My cardio explained the difference to me and like adviceseeker 777 explained to you that's how he explained to me.