Commotio cordis

Commotio cordis
Classification and external resources
File:Heart-thorax-gray.gif Human adult thorax, showing the outline of the heart (in red). The sensitive zone for mechanical induction of heart rhythm disturbances lies between the 2nd and the 4th ribs, to the left of the sternum
ICD-10	S26.
eMedicine	ped/3019

Commotio cordis (Latin, "agitation of the heart") is a disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart (the precordial region), at a critical time during the cycle of a heart beat. It is a form of ventricular fibrillation, not mechanical damage to the heart muscle or surrounding organs, and not the result of heart disease. The fatality rate is about 65%. It can sometimes, but not always, be reversed by defibrillation.

Commotio cordis occurs mostly in boys and young men (average age 15), usually during sports, most often baseball, often despite a chest protector. It is most often caused by a projectile, but can also be caused by the blow of an elbow or other body part. Being less developed, the thorax of an adolescent is likely more prone this injury given the circumstances.

The phenomenon was confirmed experimentally in the 1930s, with research in anaesthetized rabbits, cats and dogs.

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, association football, ice hockey, polo, rugby football, cricket, softball, pelota, fencing, lacrosse, boxing, karate, kung fu and other martial arts. Children are especially vulnerable, possibly 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).

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

File:Commotio-cordis-ecg.jpg

Electrocardiogram schematic tracing, showing the period of vulnerability to stretch-induced ventricular fibrillation which occurs in commotio cordis

The 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:

1. 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);
2. 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

Most cases are fatal. Survival is now about 35%, with the more common use of automatic external defibrillators. Defibrillation must be started within 3 minutes, and can only sometimes restore heart activity. 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

The risk would "probably" be reduced by improved coaching techniques, such as teaching young batters to turn away from the ball to avoid errant pitches, according to doctors. Defensive players in lacrosse and hockey are now taught to avoid using their chest to block the ball or puck. Automated external defibrillators have helped increase the survival rate to 35%.

Chest protectors and vests are designed to reduce trauma from blunt bodily injury, but this does not offer protection from commotio cordis and may offer a false sense of security. Almost 20% of the victims in competitive football, baseball, lacrosse and hockey were wearing protectors. This ineffectiveness has been confirmed by animal studies. Development of adequate chest protectors may prove difficult.

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.

See also

• Pulmonary contusion

Further reading

• Kohl P, Nesbitt AD, Cooper PJ, Lei M (2001). "Sudden cardiac death by Commotio cordis: role of mechano-electric feedback". Cardiovasc. Res. 50 (2): 280–9. doi:10.1016/S0008-6363(01)00194-8. PMID 11334832. CS1 maint: Multiple names: authors list (link)

• Geddes LA, Roeder RA (2005). "Evolution of our knowledge of sudden death due to commotio cordis". Am J Emerg Med. 23 (1): 67–75. doi:10.1016/j.ajem.2003.12.023. PMID 15672341. 

• Maron BJ, Estes NA 3rd (11 Mar 2010). "Medical Progress: Commotio cordis". N Engl J Med. 362 (10): 917–27. doi:10.1056/NEJMra0910111. PMID 20220186. 

External links

• Induction of Ventricular Arrhythmias Following A Mechanical Impact: A Simulation Study in 3D.
• Yabek, S.M. Commotio cordis. eMedicine, September 2005.
• Sports Sciences Feature: Commotio Cordis: Sudden death following chest wall trauma. ACC.
• Mechanical effects on heart rhythm: from commotio cordis to pre-cordial thump. PowerPoint slides, by P. Kohl. Sept. 2005 (n PDF).
• International Liaison Committee on Resuscitation (ILCOR)
• American Heart Association guidelines on resuscitation
• Resuscitation Council (UK) guidelines on resuscitation

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