There's a lot of knee-jerk comments to this paper. The "100% accuracy" was NOT on the training set, but on a small sample of 33 real patients using a voting method from classifications over 5 minutes of their heart beats. Their classifier worked on individual heart beats, which were not 100% accurate. So yes the 100% accuracy is misleading but it's mainly because they have a small sample size to test against and potentially quite an easy problem - you have to start somewhere, the significance seems overblown.

My partner who is a doctor has commented that by the time you know they have CHF this detector is not terribly useful as by that stage they also have a large number of symptoms, what might be useful is detecting IF they're starting to develop CHF - which is probably a lot more subtle. The patients in this study were already known to have CHF which makes for a much easier classification.