Idiopathic endocardial fibroelastosis in a foal with biventricular heart failure

Abstract

A six-month-old foal was initially presented with recurrent, progressive respiratory symptoms over a period of three months. During fixation for medical treatment of a suspected bacterial infection of the respiratory tract, the horse developed acute circulatory failure and was referred to an equine clinic. Cardiac auscultation revealed holosystolic murmur centered around the mitral valve, whilst thoracic auscultation and radiography revealed pulmonary edema and a highly enlarged cardiac silhouette. The foal collapsed during echocardiographic examination and was humanely euthanized. At necropsy, the heart was enlarged with severe dilation of all four chambers and the endocardium was markedly thickened and diffusely opacified. Histopathologically, the endocardium was also severely thickened to up to 601 µm by a significantly increased amount of collagen fibers and discontinuous and irregularly arranged elastic fibers, consistent with severe endocardial fibroelastosis (EFE). In contrast, five control horses with a median age of six months lacking cardiac alterations had a mean left ventricular endocardial thickness of 29.8 ±17.3 µm with few, regularly arranged collagen and elastic fibers. Further pathological findings included pulmonary edema and fibrosis, detection of hemosiderin-laden macrophages in the alveoli, vascular and perivascular fibrosis, as well as ascites and were consistent with biventricular heart failure. Idiopathic EFE has very rarely been described in young horses and other animals and its intravital diagnosis is very difficult. However, EFE should be considered as a differential diagnosis in foals with acute or chronic congestive heart failure. As in the present case, therapeutic approaches have to date always been unrewarding in animals and therefore, prognosis is generally considered poor.