Commotio cordis – ventricular fibrillation (cardiac arrest) direct impact
Sudden death of a young athlete during a sports event often attracts a lot of media and public attention. Most often it is due to a previously undiagnosed cardiac disorder, either structural or electrical. But occasionally it is because the mechanical effect of the physical impact induces a life threatening electrical instability of the heart known as ventricular fibrillation. Technically this can occur only during a short period between two heart beats. So the hit has to be exactly timed to match the most vulnerable period in the cyclical electrical activity of the heart. This period is just before the heart starts relaxes after a contraction. If a ventricular fibrillation is triggered, then the person goes into cardiac arrest – heart goes into a standstill. Unless the person receives quick cardiopulmonary resuscitation (CPR), survival is unlikely.
Induction of ventricular fibrillation by a blunt chest trauma is called commotio cordis. In this there is no significant physical injury to the heart. If there is bruising of the heart by a blunt trauma, the technical term is contusio cordis.
The vulnerable period for commotio cordis is usually just 6% of time between two heart beats, just 30 milliseconds. The process can be initiated by hit by a hard ball like baseball, direct hit with the body of another player or with play device like hockey stick. In case of hit by a ball it has been shown that both very high velocity and very low velocity balls are less likely to cause it. Velocity in the range of about 65 Km/h is more likely to cause commotio cordis. Soft balls like football with air inside is less likely to cause it. Similarly, a hit on the chest which is not directly over the heart is also unlikely to cause it.
Survival rate depends on the promptness with which CPR is initiated. In the earlier years survival was very poor. But now with availability of trained personnel and AEDs in most competition venues, survival rates have improved very much. If CPR is delayed, even though a heart beat may be re-initiated, irreversible brain damage would have occurred.