Of baseballs and hockey pucks: Projectile shape may affect chest-blow-induced VF risk

June 16, 2011

Washington, DC - If a play goes wrong, a baseball infielder may want to put it down to bad luck. But in sports there's no luck worse than when a player is struck by sudden cardiac death after a blow to the chest directly over the heart.

Whether such an impact actually causes ventricular fibrillation or sudden death—commotio cordis can happen in athletics or in other situations off the playing field— seems to depend partly on the shape of the striking object, according to a study using an experimental model in pigs [1].

"Spherical objects were much more likely to cause VF compared with a flat object of equal weight," according to the authors, led Dr John Kalin (Tufts Medical Center, Boston, MA), in a report published online May 18, 2011 in Heart Rhythm.

Earlier research, the group notes, has suggested that vulnerability to VF with a chest blow can depend on the magnitude of the resulting peak LV pressure increase.

It has also defined the critical moment of vulnerability during repolarization as 10 to 40 ms prior to the T-wave peak and found that the impact's location, direction, and energy also affect the risk, they write.

Those variables were kept constant in the experimental model, in which the chests of 16 pigs were struck by wooden objects of different sizes and shapes but equal weight. They consisted of a larger sphere the size of a baseball, a smaller one the size of a golf ball, and a flat, round object 72 mm in diameter. The chest impacts were timed to the vulnerable period of repolarization; they occurred, on average, at 21.1 ms prior to the T-wave peak.

Of the 144 impacts, the group writes, 14 (9.7%) induced VF and 21 (14.6%) induced either VF or nonsustained VF (NSVF). The smaller and larger spheres induced VF 19% and 10% of the time, respectively.

Among subjects without VF, the smaller sphere was significantly more likely than the larger sphere to cause ST-segment elevation or bundle branch block (BBB).

Electrophysiologic and hemodynamic outcomes of chest wall impacts in a pig model of commotio-cordis induction

End point
Flat object
Large sphere
Small sphere
p
VF
0
10
19
0.25 small vs large
VF/ nonsustained VF (%)
0
15
29
0.08 small vs large
ST-segment elevation, no VF (%)
0
40
59
<0.0001 small vs large
BBB, no VF (%)
0
7
18
0.004 small vs large
Peak LV pressure from impact (mm Hg)
292
387
473
0.001 small vs large; <0.0001 small vs flat

"In this study, it is remarkable that impacts with the flat object not only failed to induce VF but also never resulted in nonsustained VF, ST-segment elevation, or bundle branch block," the group writes. "It is likely that the spheres had greater penetration into the chest wall of the animals, focusing the energy of impact directly over the LV myocardium, resulting in the increased LV pressure generated by the chest blow and the resultant increased risk for VF."

The pressure increase was most pronounced with the smaller sphere. "A smaller diameter object might have greater penetration into the chest wall, resulting in a greater degree of force transmitted to the heart, and thus create an increased LV pressure."

In a multivariate analysis, the only significant predictor of VF induction was peak LV pressure caused by the impact and the only significant predictors of VF/nonsustained VF were peak LV pressure and smaller-sized sphere.

In a related editorial published June 8 in the same journal [2], Drs Jose Osorio and Raymond Ideker (University of Alabama, Birmingham) note that the study is limited in that, of course, pigs aren't humans and have differences in thoracic and cardiac anatomy, but also in that "the smaller-diameter golf-ball-sized sphere is not as germane to sudden death during sports as are larger-diameter spheres such as lacrosse balls and softballs."

Although the VF-induction rate wasn't significantly different for the sphere sizes, note Osorio and Ideker, the LV pressure increase was significantly greater for the smaller sphere. "If the likelihood of VF is related to the increase in left ventricular pressure, then it is reasonable to think that the smaller-diameter sphere is more likely to induce VF."

Kalin et al note that their findings "have practical implications with regard not only to the shape and size of projectiles causing commotio cordis, but also with regards to the design of chest protectors that are intended to decrease the risk of chest-blow-induced VF." (One of the coauthors holds a patent on such a chest protector.)

"The data in the current study suggest that spreading impact force over a greater surface area reduces the risk of VF with chest wall blows."

The report says coauthor Dr Mark S Link (Rush University Medical Center, Chicago, IL ) holds a patent on a chest protector, licensed to Cascade Sports, that is " designed to reduce the risk of sudden death with chest wall impact." The other coauthors do not list any conflicts of interest. The editorialists list no conflicts of interest.

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