Commotio Cordis

Commotio cordis is cardiac arrest caused by a blunt, non-penetrating blow to the chest over a structurally normal heart, which triggers ventricular fibrillation.

It strikes young, healthy people in ordinary play, most often a child or young adult hit in the chest by a cricket ball, a hockey ball or puck, or an opponent's knee or elbow. A collapse after a chest blow is cardiac arrest until proven otherwise and must never be dismissed as winding. Because the heart is normal, early CPR and defibrillation give a good chance of survival, so the outcome rests largely with whoever is there.

The heart is structurally normal, which separates commotio cordis from cardiac contusion, where a harder impact bruises the myocardium. The injury is electrical: the blow delivers a mechanical stimulus that, at the wrong instant, triggers ventricular fibrillation (VF), a chaotic rhythm in which the heart quivers rather than pumps.

Timing is decisive. The vulnerable moment is a narrow window on the upstroke of the T wave, while the ventricles repolarise; in animal models it is about 1% of the cardiac cycle. The same blow a fraction of a second earlier or later does nothing. Other factors:

• •Site: the impact falls over the centre of the chest, directly over the heart
• •Energy: a light contact does nothing, and a very heavy one tends to cause structural injury instead
• •Age and sex: the thinner, more pliable chest wall of children and adolescents is thought to transmit the impact more readily; in the US registry 95% were male, with a mean age of 15