Scientists have discovered any symptoms to cardic arrest before collappse?

Yes: Not always. For some, the first symptom is collapse. But for many, there are warning symptoms: bouts of chest tightness, pressure, or pain, especially with exertion. Bouts of rapid, pounding heart beat associated with faintness or nearly passing out (or even briefly passing out with injury, like a laceration or broken bone). Such symptoms should always be taken seriously.