Medical Correspondent Dr Muiris Houstonlooks at the heart problems that can cause young people to die suddenly
While the first recorded case of sudden cardiac death (SCD) occurred during the running of the marathon in ancient Greece, public interest in the condition has been triggered by the deaths in recent years of young, high profile sportsmen.
Regardless of the underlying cause, a common feature of SCD is the sudden development of an abnormal rhythm in the heart. This chaotic beating of the heart means that blood is no longer pumped into the brain and the heart itself leading to sudden death. The rapid application of an external electric shock may jolt the heart's electrical system back to a regular beat.
In those under 25, the common reasons for the development of an arrhythmia are the presence of different forms of heart muscle disease and anomalies in the structure of the blood vessels supplying the heart (the coronary arteries).
In addition to these causes, older victims may die because they have prematurely developed a blockage in their coronary arteries (coronary heart disease). The commonest form of heart muscle disease is hypertrophic cardiomyopathy (HCM). It affects 1 in 500 people although only a small proportion, with the serious form of the disease, are at risk of sudden death. The term HCM describes a thickening (hypertrophy) of the heart muscle (myocardium).
Primarily affecting the main pumping chamber of the heart - the left ventricle - it also disrupts the dividing wall down the middle of the heart.
This wall carries the transmission system which both triggers and spreads a normal beat throughout the heart. So as the heart muscle thickens, both its pumping efficiency and its ability to maintain a smooth heart rate is impaired.
The other principal cardiac cause for sudden death in the young is a rhythm disturbance in the heart.
Since this is essentially an electrical malfunction, it cannot be found or tested for at postmortem.
Doctors believe most of these are due to a sudden catastrophic malfunctioning of the heart's electrical pacemaker.
For those at high risk of the condition, the treatment of choice is to place an implantable cardiac defibrillator in the chest.
This device automatically corrects the rhythm disturbance as soon as it starts.
The main risk factor for SCD is a family history of unexplained sudden death in a relative under the age of 40.
When SCD is suspected the person should be thoroughly investigated by a consultant cardiologist who will carry out a wide range of tests in an effort to find an underlying cause.