Quantitative analysis of cardiac muscle cell disorganization in the ventricular septum of patients with hypertrophic cardiomyopathy.

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 quantitative 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 section 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 important, when present in these 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.