The answer starts with something easy to forget: the heart isn’t just a pump; it’s also an electrical organ. Every heartbeat begins with a signal that ripples through the heart in a precise sequence, telling each chamber when to contract. In Sads, the fault often lies in that electrical system, not in the heart’s physical structure.
If the signal becomes unstable, an abnormal rhythm – an arrhythmia – can develop. Most are harmless. But some that start in the heart’s lower chambers, the ventricles, can be fatal. During ventricular fibrillation, electrical activity turns chaotic and the heart quivers instead of pumping. Blood stops reaching the brain, causing the person to lose consciousness.
Without CPR and a shock from a defibrillator, they can die within minutes. This is a cardiac arrest.
https://www.independent.co.uk/news/health/sudden-adult-death-syndrome-mark-hughes-b3034131.html