Blunt chest trauma: an experimental model for heart and lung contusion.

BACKGROUND: Blunt chest trauma is an important clinical problem leading to injury of the heart and lungs that may be fatal. Experimental models in large animals have been developed previously. This study was aimed at developing a small-animal (rat) model for the purpose of evaluating blunt chest trauma.
METHODS: Blunt trauma was delivered to the left side of the chest in rats by a captive bolt handgun. The gun was modified so that the amount of energy delivered to the chest wall could be adjusted. The injury energy varied from 1.7 to 6.8 J. Thirty-eight experiments in adult rats were performed. Electrocardiographic monitoring was performed continuously to determine cardiac rhythm. Gross and histologic examination of lungs and heart was performed at the time of death resulting from injury or euthanasia up to 13 days after injury.
RESULTS: Some form of cardiac arrhythmia accompanied blunt chest trauma in every case. Serious ventricular arrhythmia (tachycardia or fibrillation) was nearly always fatal (15 of 16 cases), but gross or histologic evidence of cardiac injury was present in only 31% of fatal cases. Lung injury (often bilateral) as shown by atelectasis and hemorrhage into the parenchyma or airway was found in 93% of the experiments when medium range energy force was applied.
CONCLUSION: This study has established a useful model for the study of blunt chest trauma in a small animal (rat). Blunt chest trauma is associated with cardiac arrhythmia, which may be fatal. Injury to the heart may not correlate with serious cardiac arrhythmia resulting in death, lending credence to the concept of cardiac concussion or commotio cordis. Lung contusion is always more obvious than morphologic injury to the heart.