This whole situation reminds me of somebody I knew once. She was 18 when she died of SAD's (Sudden Arrhythmic Death syndrome). If you're lucky, and you get the correct medical attention quickly, you've got a chance of surviving. She, I'm sorry to say, was not so lucky. Her Brother, a few years later, would suffer the same heart problems. He was lucky, he got medical care in the nick of time.
There is virtually no way of diagnosing it. Often, by the time a person or their relatives realises they've got it, it's too late. In this case, I would suggest that the reactions of the medical team have given Muamba a chance. And, where this kind of syndrome or condition is concerned, any chance has to be more hopeful than having no chance. The tragedy is that so many people have this condition, and can know nothing about it. It's a scary thing, because it can happen at any time, in the blink of an eye. Here's hoping that he can pull through. At 23, he's still got so much to do with his career and his life.