How often does this sensation occur?
Is it associated with difficulty in breathing?
During evaluation for Afib, did you get a chest x-ray?
The only organs that might cause sensation in the chest are the lungs, liver and the breast on the outside (right side)
the left side excludes the liver, but includes the spleen and the heart.
the lungs and heart would have caused associative symptoms like cough, shortness of breath or palpitations
Midline has the big vessels Aorta and vena cava which may cause symptoms leaning to the right.
The description you are giving sounds like turbulence within the large vessels (Aorta/vena cava) OR a turbulence in the liver (hepatic arteries)
One would want to rule out Aneurysms of the Aorta.
Which is the most life-threatening
therefore you need a Chest X-ray, as well as a CT scan of the chest.