Important cardiac manifestations in the idiopathic hypereosinophilic syndrome include mitral regurgitation and peripheral embolization. To determine the anatomic basis of these abnormalities, real-time, wide-angle, two-dimensional echocardiography (2-D echo) was performed in 21 patients with the hypereosinophilic syndrome. Nine patients (43%) had clinical evidence of mitral regurgitation, and each had localized thickening of the posterobasal left ventricular wall behind the posterior mitral

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... let and absent (seven patients) or diminished (two patients) motion of the posterior leaflet. Anatomic observations at operation or necropsy in four patients with mitral regurgitation demonstrated that the echocardiographic abnormalities resulted from posterior mitral leaflet thickening and adherence of the leaflet to the underlying mural endocardium of the posterobasal wall. On 2-D echo, each of the six patients with peripheral emboli had either apical left ventricular echo-dense targets consistent with thrombus or thickening of the posterobasal wall of the left ventricle, and these findings were validated at autopsy or operation in three patients. Hence, in patients with the hypereosinophilic syndrome, 2-D echo is useful in identifying the probable etiology of two important cardiac manifestations. Thickening of the posterobasal wall is usually associated with impairment of posterior mitral leaflet function, resulting in mitral regurgitation. Because the hypereosinophilic syndrome is associated with peripheral embolization, thrombus formation and subsequent endocardial scarring, the noninvasive identification of intracavitary ventricular thrombi may be important. CARDIAC INVOLVEMENT is a major cause of death in the idiopathic hypereosinophilic syndrome, a systemic illness characterized by a persistently elevated blood eosinophil count without an identifiable etiology for the eosinophilia. l 2 Although almost any organ may be affected, cardiovascular abnormalities have been identified in most patients.3 Roberts et al.4 suggested that intracavitary thrombi and extensive endocardial fibrosis are causally related to the occurrence of restrictive cardiomyopathy, atrioventricular valve abnormalities (particularly mitral regurgitation) and peripheral embolism. To determine the morphologic cause of the mitral regurgitation and peripheral embolization, wide-angle two-dimensional echocardiography (2-D echo) was performed in 21 patients with the hypereosinophilic syndrome, and the findings were compared with other clinical features. Methods Patients Twenty-one consecutive patients with the idiopathic hypereosinophilic syndrome who had been identified prospectively at the National Institutes of Health constitute the study group (table 1). All patients had been