Commotio cordis

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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

Commotio cordis (from Latin commotion of the heart - a functional effect of mechanical stimulation in the absence of structural damage, as opposed to myocardial contusion which involves tissue damage) is a sudden disturbance of heart rhythm observed nowadays mostly in young people during participation in sports. It occurs as the result of a blunt, non-penetrating impact to the precordial region, often caused by impact of a ball, a bat or other projectile. The impact is transmitted to the heart muscle, and depending on the precise timing in relation to the cardiac cycle, it may affect the heart's electrical activity, causing an arrhythmia, such as an ectopic beat, ventricular tachycardia or ventricular fibrillation. Pre-existing conditions, such as undetected electrical or structural abnormalities in the heart of these individuals, have been speculated to render individuals more vulnerable, but this view is not currently corroborated by hard evidence. The phenomenon was confirmed experimentally in the 1930s, with research in anaesthetized rabbits, cats and dogs (Schlomka, 1934).

1 Incidence
2 Other situations
3 Mechanism of injury
4 Outcome and treatment
5 Prevention
6 Legal issues
7 References
8 External links

[edit] Incidence

Commotio cordis is a very rare event, but nonetheless it is the second leading cause of sudden death in young athletes, predominantly male. 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 due to their more fragile thoracic skeleton. The USA Commotio Cordis Registry had more than 130 cases recorded by September 2001, with most of the cases occurring in Little League baseball, lacrosse and softball. The real number of cases may be much larger.

[edit] Other situations

Commotio cordis may occur also 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 (Cannon, 2001), 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 (Hiss et al., 1997).

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 to 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 (Kohl, 2005).

[edit] Mechanism of injury

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

The following factors increase 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., speed of the projectile multiplied by its mass)
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 explains also why the heart becomes more vulnerable when it is physically strained by sports activities:

The increase in heart frequency (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 windows of vulnerability 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 an incredible 1028 joules in boxer Rocky Marciano's punch [1]. The 50 joules threshold, however, can be considerably lowered when the victim's heart is under ischemic conditions, such as in coronary artery insufficiency (Kohl, 2005).

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 (Cooper PJ et al, 2005). 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.

[edit] 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 first cause of fatalities in youth baseball in the US, with 2 to 3 deaths per year, Abrunzo, 1991), 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." (Salib et al., 2005).

[edit] 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, 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 weights 450 grams, may reach speeds of 30 meters per second [2], and barrier defenses actually encourage the reception of the ball against the 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.

[edit] 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 (Maron et al., 2002), 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.

[edit] References

Abrunzo TJ. Commotio cordis. The single, most common cause of traumatic death in youth baseball. Am J Dis Child. 1991 Nov;145(11):1279-82. Review. PMID 1951221
Cannon L. Behind armour blunt trauma--an emerging problem. J R Army Med Corps. 2001 Feb;147(1):87-96. Review. PMID 11307682
Cooper PJ, Epstein A, Macleod IA, Schaaf ST, Sheldon J, Boulin C, Kohl P. Soft tissue impact characterisation kit (STICK) for ex situ investigation of heart rhythm responses to acute mechanical stimulation. Prog Biophys Mol Biol. 2006 Jan-Apr;90(1-3):444-68. Review. PMID 16125216
Geddes LA, Roeder RA. Evolution of our knowledge of sudden death due to commotio cordis. Am J Emerg Med. 2005 Jan;23(1):67-75. Review. PMID 15672341
Hiss J, Hellman FN, Kahana T. Rubber and plastic ammunition lethal injuries: the Israeli experience. Med Sci Law. 1997 Apr;37(2):139-44. PMID 9149508
Kohl P, Sachs F & Franz M (eds): Cardiac Mechano-Electric Feedback and Arrhythmias: from Pipette to Patient. Elsevier (Saunders), Philadelphia 2005.
Kohl P, Nesbitt AD, Cooper PJ, Lei M. Sudden cardiac death by Commotio cordis: role of mechano-electric feedback. Cardiovasc Res. 2001 May;50(2):280-9. Review. PMID 11334832
Maron BJ, Mitten MJ, Greene Burnett C. Criminal consequences of commotio cordis. Am J Cardiol. 2002 Jan 15;89(2):210-3. Review. PMID 11792344
Salib EA, Cyran SE, Cilley RE, Maron BJ, Thomas NJ. Efficacy of bystander cardiopulmonary resuscitation and out-of-hospital automated external defibrillation as life-saving therapy in commotio cordis. J Pediatr. 2005 Dec;147(6):863-6. Review. PMID 16356450
Schlomka G. Commotio cordis und ihre Folgen. Die Einwirkung stumpfer Brustwandtraumen auf das Herz. Ergebnisse der inneren Medizin und Kinderheilkunde. 1934;47: 1-91.