PEDIATRICS Vol. 109 No. 5 May 2002, pp. 873-877
Reduced Risk of Sudden Death From Chest Wall Blows (Commotio Cordis) With Safety Baseballs
* Center for the Cardiovascular Evaluation of Athletes, the Cardiac Arrhythmia Center, New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts
Cardiovascular Research Division, Minneapolis Heart Institute Foundation, Minneapolis, Minnesota
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Objectives. In an experimental model of sudden death from baseball chest wall impact (commotio cordis), we sought to determine if sudden death by baseball impact could be reduced with safety baseballs.
Background. Sudden cardiac death can occur after chest wall impact with a baseball (commotio cordis). Whether softer-than-standard (safety) baseballs reduce the risk of sudden death is unresolved from the available human data. In a juvenile swine model, ventricular fibrillation (VF) has been shown to be induced reproducibly by precordial impact with a 30-mph baseball 10 to 30 ms before the T-wave peak, and this likelihood was reduced with the softest safety baseballs (T-balls). To further test whether safety baseballs would reduce the risk of sudden death at velocities more relevant to youth sports competition, we used our swine model of commotio cordis to test baseballs propelled at the 40-mph velocity commonly attained in that sport.
Methods. Forty animals received up to 3 chest wall impacts at 40 mph during the vulnerable period of repolarization for VF with 1 of 3 different safety baseballs of varying hardness, and also by a standard baseball.
Results. Safety baseballs propelled at 40 mph significantly reduced the risk for VF. The softest safety baseballs triggered VF in only 11% of impacts, compared with 19% and 22% with safety baseballs of intermediate hardness, and 69% with standard baseballs.
Conclusion. In this experimental model of low-energy chest wall impact, safety baseballs reduced (but did not abolish) the risk of sudden cardiac death. More universal use of these safety baseballs may decrease the risk of sudden death on the playing field for young athletes.
Key Words: sudden death • ventricular fibrillation • athletes • commotio cordis • baseball
Abbreviations: VF, ventricular fibrillation • RIF, Reduced Injury Factor • N/cm • newtons/centimeter • ECG, electrocardiogram
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INTRODUCTION |
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Sudden death from relatively innocent chest blows (commotio cordis) has been reported with increasing frequency in youth sports.1–4 Although once thought to be a rare event, it is now apparent that these tragedies are underreported and probably far more common than once considered; indeed, a significant proportion of sudden deaths on the athletic field are attributable to chest wall blows. The clinical spectrum of commotio cordis has now been well-documented in 128 cases by the Commotio Cordis Registry.4 Victims are usually young males who incur ventricular fibrillation (VF) when struck on the chest wall overlying the heart. It is thought that young individuals are uniquely susceptible to this phenomenon because of the compliance of their thoracic cage, which allows more energy to be transmitted by the impact object directly to the heart.5 The most common projectiles responsible for commotio cordis are baseballs (approximately 60% of the reported cases), but commotio cordis also occurs resulting from hockey pucks, lacrosse balls and softballs, fistfights, or virtually any circumstance involving precordial blows. Successful resuscitation is more difficult than expected given the youthful age and excellent health of the victims, and also the absence of structural heart disease. Autopsy examination is notable for the absence of significant cardiac or thoracic abnormalities.
Safety baseballs with rubber cores of different degrees of hardness, have been advocated to reduce the risk of traumatic injury to young athletes.5,6 Although there is agreement that safety baseballs reduce the risk for head and bodily injury,5–7 controversy persists regarding whether such balls will also reduce the risk of commotio cordis.8–10
We have developed an experimental model of commotio cordis in juvenile swine in which a chest blow from a baseball during the vulnerable time-window of repolarization triggers VF.11 This model has permitted definition of the variables responsible for commotio cordis, including the precise locations on the chest wall that are susceptible,12 the impact velocities most critical for these events, 13 and the importance of the activation of the autonomic nervous system in generating VF.14
Using our animal model, we sought to define the risk of commotio cordis-related sudden death with baseballs of varying degrees of hardness. In a previous experiment we reported that the softest safety baseballs, intended for 5- to 7-year-olds, delivered at the relatively low velocity of 30 mph decreased the risk of VF.11 However, for 11- to 12-year-olds, the average velocity of a pitched baseball is about 40 mph.15 Therefore, we sought to replicate such circumstances of youth baseball with our animal model of commotio cordis, and assess the consequences of chest blows from safety baseballs propelled at these velocities.
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METHODS |
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Experimental Model
Juvenile domesticated swine, 6 to 8 weeks old and weighing 8 to 12 kg (mean 10.1 ± 1.5 kg), were used in this study. The research protocol was approved by the Animal Research Committee of the New England Medical Center in conformity with the regulations of the Association for Assessment and Accreditation of Laboratory Animal Care. Animals were sedated with 12 mg/kg intramuscular ketamine and then anesthetized with inhaled 1% to 2% isoflurane mixed with oxygen and nitrous oxide. Anesthesia was maintained with isoflurane. Animals were then placed prone in a sling to approximate physiologic blood flow and cardiac hemodynamics.11,16
Chest wall impact was produced by a baseball mounted on a lightweight (20-g) aluminum shaft. A chronograph (Oehler Research, Austin, TX), modified for low velocity, assessed the speed of the baseball. The impact object was propelled by a spring and directed, with echocardiographic guidance, to strike the animal perpendicular to the chest wall, directly over the center of the heart.12 At the time of impact the baseball and shaft were in free flight. The timing of the impact was accomplished using a commercially available cardiac stimulator (EP-2, EP Medical, Inc, Budd Lake, NJ) triggered from a surface electrocardiographic input from the swine. With a known and consistent 120-ms delay between the release of the object and the subsequent chest impact, precordial blows could be delivered during the vulnerable period for initiation of VF, 10 to 30 ms before the T-wave peak.11,16 Impacts occurring outside of this time window were excluded from the analysis.
Baseballs Tested
Baseballs used in this experiment represented 4 degrees of hardness but were of similar masses. The safety baseballs used (Reduced Injury Factor [RIF], Worth Inc, Tullahoma, TN) were composed of a rubber core varying in hardness and covered by a leather exterior; the standard baseball (Rawlings Little League, LLB-1, St. Louis, MO) had a rubber core covered by wound yarn and a leather exterior. The softest ball (RIF 1) marketed for use in T-ball for youths aged 5 to 7 years, has a stiffness of 213 ± 36 newtons/cm (N/cm) (1 newton = 0.225-lb force).17 Medium-soft balls (RIF 5), marketed for children 8 to 10 years old, have a stiffness of 353 ± 18 N/cm. Safety balls with hardness closest to the standard baseball (RIF 10, for youths 11–13 years old) have a stiffness of 1114 ± 36 N/cm. Standard baseballs had a hardness of 2533 ± 108 N/cm. The mass of the RIF 1 was 151 g, while the RIF 5, RIF 10, and standard baseballs weighed 149, 149, and 147 g, respectively.
Protocol
Animals were randomized to receive chest blows by 1 of the 4 baseballs delivered at 40 mph, with each receiving up to 3 impacts. When VF was triggered by chest impact from the baseball, the animal was defibrillated immediately. Blood pressure, left ventricular function, and electrocardiograms (ECGs) were assessed and observed over a period of 20 minutes. If blood pressure, left ventricular ejection fraction, and ECG pattern returned to normal, additional chest impacts were delivered. If these parameters did not return to normal, no additional chest impacts occurred and the animal was euthanized, and an autopsy performed.
Statistical Analysis
Data are given as mean ± standard deviation. The statistical significance of differences between groups was analyzed with a 2-sided Fisher exact test and 
2 test for trend. P values of <.05 were considered significant.
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RESULTS |
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VF
Forty animals underwent 83 chest impacts with baseballs propelled at 40 mph. Risk of VF (Fig 1) was linearly correlated with hardness of the baseball (Fig 2 and Table 1). With the softest ball (RIF 1), 10 animals received 26 impacts and VF was produced only 3 times (11%). With the medium-soft ball (RIF 5), 10 animals received 23 strikes and VF occurred 5 times (22%). With the hardest safety ball (RIF 10), 21 impacts in 10 animals resulted in 4 episodes of VF (19%).
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In contrast, with a standard baseball, 13 impacts in 10 animals resulted in 9 episodes of VF (69%). Differences in the incidence of VF between the standard baseball and each safety ball were statistically significant (P < .01 for comparison between each safety ball and the standard ball). No differences were evident among the safety baseballs of different hardness.
There was no significant difference between the probability of VF with respect to the number of the strike (35% of the first strike, 18% of the second, and 22% of the third), body weight of the animal or the baseline ECG pattern.
Other Electrophysiologic Changes
In the 62 40-mph chest impacts that did not produce VF, including all balls tested, ST segment elevation occurred in 65% but did not significantly differ relative to the hardness of the baseball (Table 1). Transient complete heart block was observed in 7 (11%) of 62 impacts, and occurrence did not differ significantly between the baseballs. Transient bundle branch block occurred in 44 (71%) of the 62 impacts and the occurrence did increase relative to the hardness of the baseball.
Pathologic Analysis
Postmortem study demonstrated only superficial bruises at the point of impact in all animals without evidence of rib fractures, hemothorax, or hemopericardium. Two animals showed small myocardial contusions caused by impact with a medium-soft baseball in one and by a standard baseball in the other (P = not significant). No animal showed significant structural damage involving the myocardium or valves.
Comparison Between 40- and 30-mph Impacts
At both 40 mph and 30 mph, chest wall blows by each of the 3 safety baseballs (RIF 1, 5, and 10) less frequently triggered VF than did standard baseballs (Table 1; Fig 2). These differences between the safety balls and the standard baseball were much more pronounced at 40 mph because of the marked difference in incidence of VF with standard baseballs at 40 mph (69%) compared with 30 mph (35%) (P = .046). There was no significant difference in the occurrence of VF between the 3 safety baseballs when propelled at 40 or 30 mph.
In contrast to 40-mph impacts in which the hardness of the ball did not alter the incidence of ST segment elevation and transient heart block, in 30-mph impacts, safety baseballs produced significantly less of these abnormalities (P = .0004 and 0.008, respectively). Safety baseballs thrown at both 40 and 30 mph produced less bundle branch block (Table 1).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Sudden death attributable to chest wall impact has been reported with increasingly frequency in youth sports, and consequently there is considerable interest in strategies to prevent these tragic events.10 Baseball chest impact is the most common cause of commotio cordis; thus, prevention in this sport would have the largest impact on saving lives in sporting activities. Several approaches have been considered for prevention of commotio cordis, including the use of softer-than-normal baseballs, development of effective chest wall barriers, and improved coaching techniques.10 Softer baseballs and chest wall barriers have been proposed to potentially decrease the transmission of energy to the heart from the chest impact and thereby prevent VF. Better coaching techniques would include preventing chest wall blows from occurring by instructing children to turn away from the ball while batting or fielding. These alternative strategies may well prove to be effective in reducing the risk for commotio cordis, although the present investigation focuses on the benefits of altering the composition of the baseball.
In our experimental model of commotio cordis, safety baseballs reduced the incidence of VF with chest impact at 40 mph, a velocity commonly responsible for fatal commotio cordis events in youth baseball. Of note, with 40-mph impacts, the incidence of VF decreased sixfold with the softest safety ball and 3.5 times with balls of intermediate hardness when compared with a standard baseball.
Our data seemingly contrast with the findings reported with testing of safety baseballs in a 3-rib dummy model and in swine struck with baseballs at a particularly high velocity of 95 mph.18 Safety-baseball chest impacts in these animals were associated with reduction in fatal arrhythmias; however, with 95-mph Hybrid III dummy impacts, some safety baseballs failed to show reduced values for force and momentum transfer. In a later study, using a 3-rib dummy model impacted at velocities of 40 to 60 mph, investigators found that values for force and momentum transfer with baseball impact were not surprisingly directly related to the velocity of impact.19 For baseballs of the same weight (similar to those assessed in our current study) thrown at the same velocity, the values for force and momentum transfer were lower with softer baseballs, supporting our conclusions that reducing the hardness of the baseball will reduce the risk of injury.19 Furthermore, theoretic computations by another investigator have confirmed that both the weight and hardness of the baseball are significant factors in the risk of injury with head and chest wall impacts.20 In our current study, we chose projectiles of equivalent weight to test only the variable of hardness of the impact object.
There is a large measure of consensus among researchers, coaches, and parents that softer baseballs reduce the risk of serious blunt head and bodily injury.5–7, 21 Recommendations for reduction of risk of sudden death from chest wall blows have been limited by the absence of a credible biological model for commotio cordis. However, with our experimental swine model, which replicates the clinical syndrome of commotio cordis,11,12,16 we have been able to convincingly show that safety baseballs reduce the risk of VF and sudden death attributable to chest wall blows. The results of the present study also support the view that more widespread use of safety baseballs will significantly decrease (although probably not abolish) the occurrence of commotio cordis-related sudden death in youth baseball. Indeed, rare cases of sudden death associated with chest blows by safety baseballs have been reported,3 underlining the need for complementary strategies for reducing the risk of sudden death from chest wall blows such as improved coaching techniques and protective chest wall barriers.
Obstacles to more widespread introduction of safety baseballs into organized youth sports include negative attitudes of coaches, administrators, and even some parents, who note that the nontraditional safety baseball alters the fundamental nature of the game because of unpredictable and exaggerated bounce, and insufficient velocity when struck by the bat.8,9,22,23 For these reasons, the softest baseballs, marketed for T-ball use in children under age 7, may be inappropriate for older players. However, safety baseballs of intermediate grades of hardness are largely indistinguishable from the standard baseball while in play, and would appear to be reasonable and safer options for play in older age groups.
Others have raised the theoretical possibility that safety balls might paradoxically enhance risk for sudden cardiac death.10,18,19 However, evidence for this hypothesis is lacking. In fact, the results of the present experimental study show that projectiles of this design may significantly reduce risk (relative to standard baseballs) and are therefore potentially life-saving. Our observations regarding commotio cordis and safety balls, in combination with the universal agreement that these projectiles cause less traumatic injury to the head and other body parts,5–7,21 support more universal use of such baseballs in organized youth baseball as well as informal play around the home.
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ACKNOWLEDGMENTS |
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This work was supported by a grant from the National Operating Committee on Standards for Athletic Equipment, Overland Park, Kansas, and the Paul G. Allen Foundations, Seattle, Washington (to Dr Maron).
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FOOTNOTES |
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Received for publication Oct 22, 2001; Accepted Feb 8, 2002.
Reprint requests to (M.S.L.) New England Medical Center, Box 197, 750 Washington St, Boston, MA 02111. E-mail: mlink{at}lifespan.org
The opinions expressed in this article are those of the authors and do not necessarily reflect the opinions of the National Operating Committee on Standards for Athletic Equipment or the Paul G. Allen Foundations.
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PEDIATRICS (ISSN 1098-4275). ©2002 by the American Academy of Pediatrics
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