The presence of numerous abnormally arranged cardiac muscle cells in the ventricular septum has been considered a characteristic anatomic feature of patients with hypertrophic cardiomyopathy. To determine the specificity of this histologic marker for patients with hypertrophic cardiomyopathy, we used a quan-titative method to determine the area of myocardium occupied by disorganized cells. In hypertrophic cardiomyopathy, septal disorganization was present in 94% of the 54 patients studied at necropsy. Furthermore, disorganization was extensive in most of these patients, involving 5% or more of the transverse plane tissue sec-tion in 89% of the patients and 25% or more of the section in 56% of the patients. Septal disorganization was best identified in tissue sections cut perpendicular to the long axis of the left ventricle. Septal disorganization was present in only 26% of the 144 control patients with other heart diseases or normal hearts. Most impor-tant, when present inthese patients, disorganization was usually limited in extent. In only 7% of the controls studied did abnormally arranged cells occupy 5% or more of the tissue section. The average area of septum disorganized was 31±3%(mean i SEM) in patients with hypertrophic cardiomyopathy and only 1.5±0.6% in the controls (p< 0.001). Hence, while the presence of ventricular septal disorganization is not pathognomonic of hypertrophic cardiomyopathy, widespread distribution of this abnormality is a very sensitive and specific histologic marker for this disease.

IN THE INITIAL PATHOLOGIC REPORT of hypertrophic cardiomyopathy published in 1958, Teare described a bizarre and unique arrangement of cardiac muscle cells in the asymmetrically hypertrophied ventricular septum.'Several otherin-vestigators2-11 have madesimilar observations regarding the histologic appearance of ventricular septal myocardium in this disease. However, the presence of disorganized septal architecture per se is not pathognomonic of hypertrophic cardiomyopathy, ie, areas of disorganization, although usually small, may be present in the ventricular septum of some patients with various acquired or congenital heart diseases, 12-15 as well as in normal embryos and fetuses,'6 normal in-fants'6'1'and infants who die suddenly without evidence of structural cardiac disease. 17