1. “Why does so much Atrial Fibrillation come from the Pulmonary Vein openings?”
Perhaps A-Fib signals come from the PV openings because the embryonic origin of the Pulmonary Vein openings (Ostia) is the same as that of the Sinus and AV Nodes. They are similar in structure and have similar smooth muscle tissue.
The Pulmonary Vein openings are electrically active in the heart like the Sinus and AV Nodes but usually beat in sync with them. Disease, viral infections, stretching, fibrosis, or other factors may cause the Pulmonary Vein openings to start beating out of sync with the Sinus and AV Nodes thereby producing A-Fib signals.
Please be advised that the above statement is an observation, an attempt to explain, rather than a medical fact. Further research is necessary to confirm this observation.