Surgical pathology of subaortic septal myectomy associated with hypertrophic cardiomyopathy: A study of 204 cases (1996-2000)

Background: No large surgical series have qualitatively examined all histopathologic features of hypertrophic cardiomyopathy (HCM). Methods: Medical records and microscopic slides were reviewed from 204 patients undergoing septal myectomy for HCM at Mayo Clinic Rochester. Results: The 108 females and 96 males (1-86 years old; mean, 48) included 133 patients <60 years old (Group 1) and 71 patients ≥60 years (Group 2). Clinical features more prevalent in Group 2 than in Group 1 included female gender (68% vs. 45%; P=.003), aortic valve disease (31% vs. 12%; P=.01) and severe coronary atherosclerosis (43% vs. 9%; P=.001). Overall, microscopic abnormalities included myocyte hypertrophy (100%), endocardial (96%) and myocardial (93%) fibrosis, myocyte disarray (79%) and vacuolization (60%), endocardial inflammation (48%), arterial thickening (46%), dilated venules (28%), arterial dysplasia (16%), left bundle branch tissue (12%), infarction (2%), endocardial (1%) and myocardial (<1%) calcium, and amyloid (1%; senile type in all three). Lesions more prevalent in Group 1 than Group 2 were vacuolization (68% vs. 45%; P=.002), disarray (87% vs. 65%; P=.0003) and dilated venules (33% vs. 18%; P=.02). In contrast, lesions more frequent in Group 2 than in Group 1 included left bundle branch (20% vs. 8%; P=.02) and amyloid and endocardial calcium (4% vs. 0%; P=.04, each). Conclusions: Among patients undergoing septal myectomy for HCM, 53% were women and 35% were ≥60 years old. The most common microscopic features were hypertrophy, disarray, fibrosis, inflammation and vascular alterations. Disarray cannot be used as a morphologic hallmark for HCM in small surgical myectomy specimens because it was absent in 21% of the patients. Because amyloid unexpectedly affected three elderly patients, routine amyloid staining is recommended for patients ≥65 years old.