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Commotio cordis
  1. P McCrory
  1. Centre for Sports Medicine Research and Education and the Brain Research Institute, University of Melbourne, Melbourne, Australia
  1. Correspondence to:
 Dr McCrory, PO Box 93, Shoreham, Victoria 3916, Australia;
 pmccrory{at}compuserve.com

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Instantaneous cardiac arrest caused by a blow to the chest depends on the timing of the blow relative to the cardiac cycle

Sudden death following a sharp but seemingly inconsequential blow to the chest is a frightening occurrence known as “commotio cordis” or “concussion of the heart.” Although commotio cordis is considered rare by some authors, it represents one of the most common mechanisms of sudden death in sport seen in young athletes.1

Commotio cordis is generally understood to mean “instantaneous cardiac arrest produced by non-penetrating chest blows in the absence of heart disease or identifiable morphologic injury to the chest wall or heart”.2,3 Most cases report accidental death of otherwise healthy children or adolescents after chest impact during recreational or competitive sport or, less commonly, during road traffic accidents.4–9

Such fatalities receive extensive media coverage, provoke legal debate, and may stimulate research into the public health aspects of this condition—for example, the capacity of protective gear to prevent commotio cordis or the possibility of developing safer sporting equipment.10

HISTORY

The current concept of commotio cordis is often ascribed to a review of 70 cases by Maron et al.2 Their report portrays commotio cordis as a rare but dangerous condition in which there is usually a poor response to resuscitatory measures. Most of those affected were young (mean age 12 years), male (all but one), and, at the time of accident, engaged in sport (>90%). The event leading to sudden death was a precordial impact, most commonly by projectiles such as baseballs, softballs, or hockey pucks, probably occurring during an electrically vulnerable phase of the cardiac cycle.11

Interestingly, the term commotio cordis was in use as early as 1857.12,13 A review from 1896 shows that the term was applied to various forms (both lethal and non-lethal) of cardiovascular disorder caused by mechanical impact to the chest (both in the presence and absence of minor cardiac bruising).14

Commotio cordis underwent a conceptual modification at the turn of the century whereby a distinction between non-penetrating precordial impact in the presence (contusion) or absence (commotion) of cardiac bruising was established.15 In many ways, the concept of commotio cordis paralleled that of commotio cerebri (brain concussion) for which the issue of structural injury has been controversial since the early 1700s and terminological inexactitude has plagued the medical literature up to the present day.16

PATHOPHYSIOLOGY

The most comprehensive early experimental physiological studies of this condition were performed by Georg Schlomka at Bonn University in the early 1930s.17 On the basis of more than 800 experiments on anaesthetised animals, he identified three factors that determined the induction of arrhythmias by moderate precordial impact: type of impact, location of impact, and force of impact. Schlomka disproved the vagal reflex theory and proposed the “vascular crisis” concept of mechanically induced coronary vasospasms to explain commotio cordis.

The risk factors identified by Schlomka in the 1930s are still relevant, whereas the identification of a fourth factor (timing of impact) had to wait for technological advances. Contemporary experimental investigations into commotio cordis with anaesthetised pigs confirmed the existence of such a vulnerable period during early ventricular repolarisation and showed the involvement of ATP dependent potassium channels in the electrophysiological genesis of this condition.18–20

When the precordial impacts were delivered within a narrow temporal window between 30 and 15 milliseconds before the peak of the T wave, ventricular fibrillation was reproducibly induced. The vulnerable period of the cardiac cycle amounted to just over 1/100th of a second. Remarkably, ventricular fibrillation was immediate, occurring on the very next heart beat. The arrhythmia was not produced by impacts at any other time during the cardiac cycle, although transient complete heart block was sometimes observed with impacts during the QRS complex. Occasionally, with impacts delivered just outside the 15 millisecond period of vulnerability, unsustained polymorphic ventricular tachycardia was seen.18,19

The observation that transient rhythm disturbances may occur with chest impact raises the possibility that there may be “near miss” cases of commotio cordis. This may have happened in 1998 to St Louis Blues hockey captain Chris Pronger, when he collapsed briefly, then spontaneously regained consciousness, after being struck on the left side of his chest by a puck during a playoff game.21 It is possible that other near miss cases have gone undetected because the arrhythmias were too brief to cause loss of consciousness.

In another part of their study, Link et al18 examined whether the use of safety baseballs, which are softer than regulation balls, could reduce the risk of arrhythmia in the animal model. They found that the risk was proportional to the hardness of the ball. This finding may have implications for the prevention of commotio cordis in young baseball players, as properly designed safety baseballs are feasible for use in recreational baseball and Little League. Another approach to prevention is the use of chest protectors specifically designed to cushion the precordium. As not all cases will be preventable, it is important to emphasise that rapid cardiopulmonary resuscitation, including a precordial “thump” and immediate defibrillation when possible, may be lifesaving.

Both early and contemporary research into commotio cordis appears to have been motivated by case reports of sudden death. It is sobering that a seemingly minor chest impact at an instant when the heart is suspended in diastole can have such devastating consequences.

Instantaneous cardiac arrest caused by a blow to the chest depends on the timing of the blow relative to the cardiac cycle

REFERENCES

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