commotio cordis

Commotio Cordis is Latin for 'chaotic heart'. Sometimes known as cardiac concussion.

In rare cases, a thump to the chest directly over the heart can cause the heart to misfire (arrhythmia), leading to a cardiac arrest. This is most common in baseball, but has been reported in other sports (hockey, softball, lacrosse, soccer, and even karate), and outside of sports, it can be caused by anything that gives you a descent whack in the chest.

It's hard to be certain that heart stoppage was caused by Commotio Cordis, but the United States Commotio Cordis Registry has collected a list of 120 suspected cases since it's founding in 1998. In order to cause Commotio Cordis a blow has to be timed exactly right -- perhaps to the exact millisecond. If you are hit at just the right time, it can cause a ventricular fibrillation, and will cause death in 86% of cases*. Death can be avoided by defibrillation or, possibly, cardiopulmonary resuscitation (CPR).

The surprising thing about Commotio Cordis is that it is more likely to happen to younger, healthier people (especially athletes), due to the greater pliability of their chest walls. Protective padding helps, but doesn't eliminate the risk. Using a softer, lighter ball also helps, but it's possible that RIF (Reduction In Force) baseballs increase risk, due to their heavier weight.

*108 out of 125, Science News Dec 1, 2001. Vol. 160, No. 22.