Since the pituitary gland secretes several hormones, and a tumor usually produces excess hormone, it’s very important that a pituitary hormone panel be done on blood to measure these levels. There are 2 in particular that could be related to the SVT- ACTH stimates the adrenal glands to produce cortisol and epinephrine (adrenaline). High levels can cause SVT. TSH stimulates the thyroid gland to produce thyroxin and high levels cause SVT. These are blood tests that your PCP, cardiologist or an endocrine specialist can check. Also, please research or ask your cardiologist about 3 mechanisms that may stop the SVT: Val Salva, ice water face plunge, and carotid massage. Don’t do carotid massage without permission from Dr. he may want carotid ultrasound first . Also a medication like a beta blocker may prevent the episodes until cause determined. I hope you get this resolved soon!