(CNN) -- Chris Brooks, just 22, was out for a night of bowling with friends. Exhausted, on the way home, he texted his girlfriend, "I'm dead." Fifteen minutes later, he was -- clinically dead -- suffering an unexplained cardiac arrest on the couch at home, right in front of his parents. But it wasn't the end.

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The same night Chris Brooks died, he came back to life. Doctors say that for every minute without a heartbeat, your odds of survival go down 10 percent. Chris Brooks was out for more than 20 minutes -- and yet he survived, without even a hint of brain damage.

Doctors at the University of Pennsylvania's Center for Resuscitation Science, where Brooks was treated, call him a medical miracle -- but cases like his are increasingly common, thanks to advances in basic emergency techniques including improved CPR and cooling patients to a lower body temperature. Here's the catch: Many hospitals and doctors don't know or want to use the latest techniques -- and so survival rates for cardiac arrest vary tenfold among major cities.