People who have cardiac problems (and may be unaware of them) carry a slightly higher risk of sudden death during periods of fairly intensive activity than at other times. This is why as a precaution if someone is diagnosed with a cardiac disorder they will often be advised to avoid competitive sport or endurance training as this can bring on heart failure.
The risk of someone who has no symptoms of heart disease and no history of heart disease or sudden death in their family dying during sporting activity is very small (perhaps 1 in 100,000). Some countries (certain states of the USA and Italy) do screen everybody but this can cause unforeseen problems as there is sometimes a grey area between normal and abnormal tests, and having possible abnormalities detected may influence career choices, ability to take out insurance, mortgages etc. There is no right answer to this question, but concentrating efforts initially on those with symptoms or possible heart disease in the family would probably be most useful.
Is there a difference? Defibrillators are machines that can deliver an electrical shock to the heart to knock it out of a potentially fatal rhythm disorder. Most people are familiar with the machine with paddles in hospitals, as seen on TV programmes such as ‘ER’. There is a move to have user-friendly clever versions of these machines available in public places (airports, sports stadium, shopping centre etc). These devices with a built-in computer which will recognise the rhythm and deliver the treatment are called Automated External Defibrillators. It is intended that there are easy to follow instructions on them so that if someone collapses staff members or possibly even passers by can attach the machines and possibly save a life.
An ICD is an Implantable Cardioverter Defibrillator. This is a miniature version of the defibrillator which is placed under the skin in someone who is considered to be at high risk of having a fatal rhythm problem. Wires are passed down a vein under the collarbone to the heart, and the battery box with built-in computer chip is placed under the skin on the front of the chest. This is a like a pacemaker(can treat slow heart beats), but can also recognise when the heart rhythm has changed to a life threatening one and deliver a shock internally within seconds.
If ICDs save lives shouldn’t everyone have one? ICDs do save lives but are expensive and require changing of the battery and possibly the wires every 5 to 8 years. There are also risks of complications when the device is being fitted or changed, and this can sometimes also be fatal. Therefore they are best used in people where the risk of dying suddenly is high enough that it is greater than the risk of complications of the device. This is more important than the cost of the device.