Incidence:

Commotio cordis is a very rare event, but nonetheless is often considered when an athlete presents with sudden cardiac death. Some of the sports which have a risk for this cause of trauma are baseball, soccer, ice hockey, polo, rugby, cricket, softball, pelota, fencing, lacrosse, boxing, karate, kung fu and other martial arts. Children are especially vulnerable, possibly[citation needed] due to the mechanical properties of their thoracic skeleton. From 1996 to spring 2007, the USA National Commotio Cordis Registry had 188 cases recorded, with about half occurring during organized sports Almost all (96%) of the victims were male, the mean age of the victims during that period was 14.7 years, and fewer than 1 in 5 survived the incident.

Other situations:

Commotio cordis may also occur in other situations, such as in children who are punished with blows over the precordium, cases of torture, frontal collisions of motor vehicles (the impact of the steering wheel against the thorax, although this has decreased substantially with the use of safety belts and air bags).

Cases of commotio cordis have been recorded in people who were shot by firearms over the precordium and were using body armour, thus stopping the bullet but causing a mechanical impact to the thorax (the so-called Behind Armour Blunt Trauma or BABT); or after being hit by less-lethal crowd control firearm shots using rubber bullets or plastic bullets.

In contrast, the precordial thump (hard blows given over the precordium with a closed fist in order to revert cardiac arrest) is a sanctioned procedure for emergency resuscitation by trained health professionals witnessing a monitored arrest when no equipment is at hand, endorsed by the latest guidelines of the International Liaison Committee on Resuscitation.

It has been discussed controversially, as - in particular in severe hypoxia - it may cause the opposite effect (i.e., a worsening of rhythm - commotio cordis). In a normal adult, the energy range involved in the precordial thump is 5-10 times below that associated with commotio cordis.

Mechanism of injury:

Electrocardiogram schematic tracing, showing the period of vulnerability to stretch-induced ventricular fibrillation which occurs in commotio cordisThe following factors influence the chance of commotio cordis:
Direction of impact over the precordium (precise area, angle of impact) Total applied energy (area of impact versus energy, i.e., the mass of the projectile multiplied half the square of its velocity) Impact occurring within a specific 10-30 millisecond portion of the cardiac cycle. This period occurs in the ascending phase of the T wave, when the ventricular myocardium is repolarizing, moving from systole to diastole (relaxation).

The small window of vulnerability explains why it is a rare event. Considering that the total cardiac cycle has a duration of 1000 milliseconds (for a base cardiac frequency of 60 beats per minute), the probability of a mechanical trauma within the window of vulnerability is 1 to 3% only. That also explains why the heart becomes more vulnerable when it is physically strained by sports activities:
The increase in heart rate (exercise tachycardia) may double the probability above (e.g., with 120 beats per minute the cardiac cycle shortens to 500 milliseconds without fundamentally altering the window-of-vulnerability's size); Relative exercise-induced hypoxia and acceleration of the excito-conductive system of the heart make it more susceptible to stretch-induced ventricular fibrillation. The cellular mechanisms of commotio cordis are still poorly understood, but probably related to the activation of mechano-sensitive proteins, ion channels.

It is estimated that impact energies of at least 50 joules are required to cause cardiac arrest, when applied in the right time and spot of the precordium of an adult. Impacts of up to 130 joules have already been measured with hockey pucks and lacrosse balls, 450 joules in karate punches and 1028 joules in boxer Rocky Marciano's punch. The 50 joules threshold, however, can be considerably lowered when the victim's heart is under ischemic conditions, such as in coronary artery insufficiency.

There is also an upper limit of impact energy applied to the heart; too much energy will create structural damage to the heart muscle as well as causing electrical upset. This condition is referred to as contusio cordis (from Latin for bruising of the heart). On isolated guinea pig hearts, as little as 5 mJ was needed to induce release of creatine kinase, a marker for muscle cell damage. Obviously one should take into account that this figure does not include the dissipation of energy through the chest wall, and is not scaled up for humans, but it is indicative that relatively small amounts of energy are required to reach the heart before physical damage is done.

Outcome and treatment:

Fulminant death is the most common outcome, because cardiopulmonary resuscitation requires quick action by a specialized medical team, using a defibrillator and cardioactive drugs, and these are rarely on hand in sports arenas. Due to the significant danger to children (death by commotio cordis is the leading cause of fatalities in youth baseball in the US, with 2 to 3 deaths per year), it has been recommended that "communities and school districts reexamine the need for accessible automatic defibrillators and cardiopulmonary resuscitation-trained coaches at organized sporting events for children.

Prevention:

Equipment and dress used in several sports. clearly demonstrating the lack of protection against chest concussion. From left to right, top to bottom: boxing, field hockey, baseball, karate, cricket, woman's lacrosse and soccer.The mandatory use of heavily padded special vests in front of the thorax is generally sufficient to prevent high energy impacts to the precordium. The problem with many sports such as soccer, baseball and karate is that, despite the danger posed by a multitude of punches, kicks, pads, mallets, bats, pucks and balls moving at high speeds, etc., their dress codes represent an obstacle to the use of mechanical protection to the precordium for all players, or at least for goalkeepers, batters, ball catchers, etc. For example, boxing traditionally requires a naked chest, cricket gear protects the legs but not the chest, and soccer has practically no protection gear at all; although the ball weighs only 450 grams, it can reach speeds of 30 meters per second, and barrier defenses actually encourage the player to block the ball with his chest.

Parents of children active in these sports are advised to adopt simple protective measures, particularly in informal "backyard" games, which are often much more dangerous than formal ones, which require some protection.

Legal issues:

Several people have been convicted of involuntary manslaughter in cases involving insufficient and slow medical help to athletes who underwent commotio cordis during sports events, as well as in cases of intentional delivery of contusive blows. In one such case, a man was sentenced to 18 years of prison for killing his own son with a blow to the chest.