Athena and ER Policy

This article from the Saint Louis Post-Dispatch shows how insurance companies make policy that puts profits first and patients last:

In the past year, the health insurance company Anthem Blue Cross Blue Shield drew attention for stiffing patients in Missouri and other states for seeking emergency care that Anthem later decided wasn’t an emergency.

While making record profits, Anthem has begun retroactively refusing coverage for ER visits for patients with active insurance policies. They are telling patients they will not be covered because their condition did not end up being an emergency. How is a patient to know ahead of time that the chest pain was gastric and not cardiac?