Feline hypertrophic cardiomyopathy: gross anatomic and quantitative histologic features.

Gross anatomic features and the pattern and extent of cardiac muscle cell disorganization were studied in the hearts of 51 with spontaneously occurring hypertrophic cardiomyopathy. Each cat had a hypertrophied, but nondilated, left ventricle. Ventricular septal disorganization was extensive, involving 5% or more of the relevant areas of the tissue section, in 14 (27%) of the 51 cats. Marked septal disorganization occurred only in those cats with asymmetric septal hypertrophy (ventricular septal to left ventricular free wall thickness ratio of greater than or equal to 1.1) Disorganization of cardiac muscle cells was uncommon and less extensive in the left ventricular free wall of the cats with hypertrophic cardiomyopathy. Disorganization involved the free wall of only 7 cats, each with asymmetric septal hypertrophy, and occupied greater than 5% of the free wall tissue sections in just 3. Hence, about one fourth of this population of cats had hypertrophic cardiomyopathy resembling the human form of this disease, with asymmetric left ventricular hypertrophy and marked disorganization of cardiac muscle cells in the ventricular septum. The majority of cats (about 75%), however, demonstrated a form of hypertrophic cardiomyopathy characterized by symmetric ventricular hypertrophy and normal arrangement of cardiac muscle cells.