Based from the information, you are having a lump under your clavicle
and suffers from rheumatoid arthritis
, which results in pain in your back and pain sensation with numbness
in your hands and are worried about having heart attack
Here is the good news you are not having " HEART ATTACK", here is the explanation what might be going on. Their is nerve passing around the clavicle which goes to the arm and hands. It seems their is some kind on irritation to that nerve base due to injury or the inflammation around the clavicle , which appears as swelling and is very tender to touch.
Advice- consult near by physician and have it checked, you may need some addition care based on the condition.
Hope it helps.
Dr. JAY PATEL.