Familial hypertrophic cardiomyopathy - Cardiac ultrasonic abnormalities in genetically affected subjects without echocardiographic evidence of left ventricular hypertrophy

Aims It is not known whether the apparent normality of echocardiographic examination results, in subjects bearing a mutation for hypertrophic cardiomyopathy but without ultrasonic left ventricular hypertrophy, is due to incomplete phenotypic expression, or inaccurate echocardiographic criteria. The aim of this study was to search for echocardiographic abnormalities in these patients. Methods and Results Echocardiography was performed in 100 subjects from two families with a mutation in the beta-MHC (720) or My-BPC (714) genes. We compared genetically affected subjects with an apparently normal left ventricle (thickness <13 mm) (20 patients), and nonaffected first-degree relatives (61 normal subjects). (1) Patients had a thicker left ventricular wall (9.7+/-1.4 vs 8.9+/-1.4 mm, P=0.03), a greater indexed mass (107+/-18 vs 97+/-17 g.m(-2), P=0.03), a larger left atrium (27+/-9 vs 23+/-10 mm(3), P=0.09) and lower wall stress (78+/-11 vs 89+/-15 10(3) dynes.cm(-2), P=0.002); these differences were highly significant after adjustment for height, age and systolic blood pressure either for wall thickness (P=0.000003), mass (P=0.005) or atrial volume (P=0.001), and the ventricular systolic dimension appeared smaller (P=0.01); (2) results remained significant (P<0.01) when a lower cut-off value (less than or equal to 11 mm) or only adults (greater than or equal to 18 years) were considered; (3) a subanalysis of Family 714 (13 patients, 25 normals matched for sex, age and height) showed the same trends. Conclusion In familial hypertrophic cardiomyopathy, genetically affected subjects with an apparently normal heart by echocardiography show slight ultrasonic structural and functional left ventricular modifications, suggesting that the phenotype of the disease is a continuous spectrum from normal structure to typical hypertrophy.