The distribution of cardiac muscle cell disorganization in different regions of the left ventric-ular wall was studied quantitatively in 52 patients with hypertrophic cardiomyopathy. Cellular disorganiza-tion in the ventricular septum was both common and extensive (mean area ofseptal tissue section disorganized, 35 i 4%). Disorganization was also substantial (24±3%) in theleft ventricular free wall of these patients, although less marked than inthe ventricular septum (p< 0.05). Anterior left ventricular free wall dis-organization was particularly extensive (32±4%) and did not differ significantly from that present in the ven-tricular septum. Marked cardiac muscle cell disorganization (> 5% of the tissue section) was diffusely distributed in the ventricular septum and left ventricular free wall in 33 of the 52 patients (63%). Particularly marked left ventricular free wall andcombined free wall and septal disorganization was present in 14 patients without functional limitation in whom sudden death occurred early in life (< 25 years of age) and was the initial manifestation of cardiac disease. In contrast, although abnormally arranged cardiac muscle cells were identified in the left ventricular free wall in 47% of patients with other congenital or acquired heart diseases or normal hearts, this disorganization was usually limited in extent (mean area of section disorganized, 2 0.5%).

Hence, in a large population of patients with hypertrophic cardiomyopathy, cellular disorganization was widely distributed throughout both the ventricular septum and left ventricularfree wall. No definitive con-clusions can be made regarding the significance of this distribution of cellular disorganization; however, our data suggest that this pattern may represent a diffuse cardiomyopathic process and be a determinant of clinical outcome in certain patients with hypertrophic cardiomyopathy.