Make wordpress listen to server events AKA push notification in front end

Make wordpress listen to server events AKA push notification in front end

I'm planning to build a web app with wordpress.
This app is multiuser so I need the front end of one user to know when another user change something.
Usually this should be made with shortly intervalled ajax calls, but since an ajax call load the whole wordpress stack each time I was wondering how efficient this system could be.
Any idea about this system?
Thanks!