Morphological findings of ‘cardiac concussion’ due to experimental blunt impact to the precordial region

The dog’s precordial region at the sternum was impacted with a mechanical elastic-cord propelled impactor at the velocity of 8.0 m/s. The left and right intraventricular pressures and electrocardiogram (ECG) were monitored continuously for 60 min after the impact. The micro- and ultra-structure of myocardium were examined. Localization of myocardial myoglobin (Mb), creatine kinase BB (CK-BB) and creatine kinase MM (CK-MM) as well as plasma membrane permeability were studied by immunohistochemical and lanthanum probe techniques. Upon the impact, abrupt over-pressures within both ventricles were recorded with transient depression of the left ventricular systolic pressure. In all the dogs, some rhythm- and conduction-disorders were noted, which lasted transiently and resumed to normal sinus rhythm. At autopsy, no gross injuries of the heart were detected, and microscopic examination showed no visible myocardial lesions. However, immunohistochemically, focal patchy loss of myocardial Mb, CK-BB and CK-MM was identified with scattered deposition of these substances between myocardial fibers elsewhere. Such changes as relaxed myofibrils with widened I band, contracted myofibrils and broken cristae of the mitochondria were observed in myocardial ultrastructure. Lanthanum particles deposited inside the mitochondria. These results indicate that increase in cardiac cell membrane permeability and ultrastructural damage in myocardium may be involved even in cardiac concussion.