Marked variability in susceptibility to ventricular fibrillation in an experimental commotio cordis model

Background- Precordial blows in sports and daily activities can trigger ventricular fibrillation (VF) (commotio cordis). Whereas chest wall blows are common, commotio cordis is rare. Although factors such as timing, location, orientation, and energy of impact are critically important, we also hypothesize that there is individual susceptibility to commotio cordis. Using our model of commotio cordis, we evaluated individual animal susceptibility to VF induction and assessed animal characteristics that might be involved. Methods and Results- This retrospective analysis included 139 juvenile swine (weight, 8 to 54 kg) that were anesthetized and placed prone in a sling to receive chest wall strikes with a ball propelled at 30 to 40 mph. Each animal received a minimum of 4 impacts directly over the cardiac silhouette, all timed to a narrow vulnerable window during cardiac repolarization. Of 1274 total impacts, 360 impacts (28%) resulted in VF. There was wide variability in individual animal susceptibility to VF. In 38 animals, none of the impacts resulted in VF (range, 4 to 18 impacts per animal). The majority of animals (91; 65%) were induced into VF with <30% of the strikes. In fact, only 19 animals (14%) had >50% occurrence of VF with chest wall impacts, and only 7 (5%) had >80% occurrence of chest impacts that induced VF. In the animal-based analysis, individual correlates of VF included animal weight, mean impact velocity, mean left ventricular pressure generated by the blow, mean QRS duration, mean QTc, and QTc variability. In multivariable analysis, mean left ventricular pressure generated by the blow, mean QRS duration, and QTc variability remained significant correlates of risk, and number of impacts gained statistical significance such that animals with more impacts were less susceptible to VF. Conclusions- Swine display a wide range of individual vulnerability to VF triggered by chest wall impact, with a distinct minority being uniquely susceptible. Mild abnormalities in cardiac depolarization and repolarization might underlie this susceptibility. Such individual susceptibility may also be present in humans and contribute to the rarity of commotio cordis.