meaning the sternal pressure and the SVT. Did they rule out a Pulmonary Embolism when dxing the svt?
Also, any form of arthritis can have and effect on the sternum and rib cage making the rib cage swell, and making it more difficult to breathe and more prone to want to cough. Which in turn can cause anxiety and make the heart race.
Throwing out some shots in the dark for you since nobody replied yet.