My son just had a fainting spell or seizure (on the way to ER now). Diagnosed with WPW as an infant but no symptoms since. Might this be a factor?

Faniting. I am glad you are on the way to ER. WPW doesn't go away so it may be the cause- certainly be sure ER aware so they do the cardiac tests indicated as part of his work up- I hope he will be better soon.
Yes. The abnormal conduction may result in arrythmias! You are heading where you need to be! Good Luck! Dr Z.
Agree. Your thinking that this could be a faint, seizure, or cardiac is appropriate and you are doing the right thing.