Dear Trudy,
As you describe the most likely cause of these symptoms is the atria beating against a closed ventricular valve. The blood subsequently goes backwards and may be causing these sensations. I suppose the only way to deal with it would be medication to control the sinus tachycardia. I would discuss this option with your doctor.
I am sorry about your new symptoms, it sounds very unpleasant. I have IST, too, so I was wondering if you would mind answering a few questions for me. Was it a sinus node ablation or modification that they were trying? Why did you decide to try it? In reading your post I was thinking maybe you did it to get away from taking medicine and here they are telling you you'll probably need to take medicine for SINUS TACHYCARDIA! What would you tell someone, like myself, concerning treatment options for IST? Thanks and good luck.
You are quite right, I decided to try sinus node ablation because the drugs either did not work or caused undesirable symptoms for me. I don't want to try them again. To answer your questions, they first tried sinus node modification and, when that failed, complete ablation, which also failed. I couldn't recommend any specific course of action as they all have their drawbacks which you don't find out about until they happen to you! I would say that, if drugs work for you, don't rush into anything as drug therapy is always reversible but what I've had done isn't.
All the best to you,
Trudy