Young athletes seem to be dropping like the rain. Happily, Bolton Wanderers’ Fabrice Muamba is making a full recovery after his heart stopped during a match in March. The Italian footballer Piermario Morosini was not so lucky; he died on the pitch in Pescara last month. We don’t yet know for sure what killed him – nor the London Marathon runner Claire Squires. But it seems likely that the foibles of the human heart are to blame – in the UK alone, 12 people under the age of 35 succumb to “sudden cardiac death” every week.

The heart beats because of co-ordinated pulses of electricity that work their way through its cells in a wave, causing muscle to contract in a tightly synchronised dance that creates a highly efficient pumping mechanism. Under stress, this rhythm can break down. The organ falls into what physicists know as chaos.

In general, chaos has a strange beauty. Watching a chaotic pendulum swing is entrancing. Some of the movements look so tiny that you think the pendulum must be about to stop – and then it doesn’t. A chaotic system never repeats its movements, giving it unpredictable qualities. That is why a butterfly flapping its wings in Brazil really can cause a tornado in Texas.

A chaotic arrhythmia in the heart is equally disastrous. When the heart’s muscles contract in never-repeating patterns, the organ becomes a seething, pulsating mess of tissue rather than a pump. The defibrillators that stop this do not give a random jolt of electricity: the pulse is carefully designed to take the chaos into account and provide the electrical current patterns and pulses that will halt the quivering. Only then can the heart re-establish its proper beat.

As marvellous an invention as the defibrillator is, it would be much better to identify those whose hearts are prone to slipping into chaos. This has proved a surprisingly contentious task.

Two recent reviews of the scientific literature published in the same journal (Progress in Cardiovascular Disease) came to almost opposite conclusions. One suggests that an electrocardiogram is the only effective means of detecting a latent problem. The other says ECGs “have not been demonstrated to be effective in decreasing the inherent risk of athletic sudden death”.

Warning signs

A consensus is growing, however, that ECG screening does help. Fifa and Uefa both require that all professional footballers undergo ECG tests but Muamba’s case has provoked questions about whether the tests are being done often enough – or well enough. The FA’s medical committee will meet on 3 May to dissect the incident, and Premier League team doctors are getting together a week later to examine Muamba’s medical records to see whether any warning signs were missed.

For all the concern over professionals, it is amateur athletes who drop dead far too frequently. It is difficult to deal with the problem because many of these deaths are recorded as unexplained; post-mortem, many intricacies and weaknesses of a heart are undetectable. What is known is that one in 300 people has some kind of heart defect.

Those doing sport are at nearly three times greater risk of sudden cardiac death, which is why the European Society of Cardiology and the International Olympic Committee have recommended that any young person taking part in competitive sport should undergo precautionary screening. However, generally there is very limited access to such facilities. The charity Cardiac Risk in the Young has enlisted a few famous faces (David Walliams, Pixie Lott and James Cracknell) to help change that. But cardiac chaos will claim many more lives in the foreseeable future. 

For a list of ECG screening clinics for young people, visit c-r-y.org.uk