“Inappropriate Sinus Tachycardia” with Symptoms

Good Evening,

I was diagnosed with “inappropriate sinus tachycardia” by my EP in June 2023 and have been dealing with worsening symptomatic DOE and tachycardia (consistently 120 bpm, up to 150 bpm) that occurs with minimal exertion, then returns to “normal resting heart rate” with upon sitting and/or < 1 minute of standing still. No changes in HR with sit-to-stand and no orthostatic symptoms, only with minimal exertion (walking). To date, I have failed multiple AV nodal agents due to drug intolerance (which actually create new POTS symptoms).

Currently, ivabradine isn’t an option because of insurance and economic barriers.

Based on a literature study (I happen to be a PhD candidate in cardiac engineering and electrophysiology) I have ‘class II’, non-typical IST, defined as “normal resting heart rate (< 85 bpm) with an exaggerated increase in HR in response to minimal exertion”.

All secondary causes (including environmental and dietary) for my tachycardia and symptoms have been ruled out.

Has anyone else had a similar IST experience?

Thanks in advance for any insight, suggestions, and/or feedback.