Myocardial Fibrosis and Ventricular Tachyarrhythmia in a Thoroughbred Filly

A 16-month-old Thoroughbred filly was evaluated for lethargy, tachycardia, tachypnea, and signs suggestive of colic. Rapid ventricular tachycardia with a heart rate of 210 beats/min was identified on initial physical examination. Multiple doses of lidocaine transiently restored sinus rhythm. Echocardiography revealed several foci of variably increased echogenicity within the left ventricular myocardium, including an area of marked transmural hyperechogenicity and endocardial depression suspected to be chronic scar tissue of the left ventricular free wall. Serum cardiac troponin I concentration was markedly elevated. Because of the recurrent ventricular tachyarrhythmia and echocardiographic findings, the filly was euthanized. Postmortem examination demonstrated multifocal, acute myocardial necrosis and an area of chronic myocardial fibrosis in the left ventricular free wall. The exact cause of the myocardial lesions remains undetermined; however, the chronic fibrosis is suspected to have resulted from myocardial injury or infarction associated with cardiopulmonary cerebral resuscitation when the filly was 5 days old.