"The most common EKG abnormalities are non-specific ST-T wave changes, followed by RBBB. A normal EKG does not exclude the possibility of cardiac injury, although some investigators report a negative predictive value of up to 80-90%."
[El-Chami MF, Nicholson W, Helmy T. Blunt cardiac trauma. J Emerg Med 2008;35:127-133.]