Heterogeneous Morphologic Expression of Genetically Transmitted Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is a disease of cardiac muscle that is often genetically transmitted as. an autosomal dominant trait and is characterized by a wide variety of patterns of left ventricular hypertrophy that may be identified with wide-angle, two-dimensional echocardiography. To determine the degree to which left ventricular morphology is similar in related patients with hypertrophic cardiomyopathy, 40 index cases with this disease and 66 of their affected first-degree relatives were studied by twodimensional echocardiography. A diverse variety of patterns of distribution of left ventricular hypertrophy were identified in the study group. In 48% of the patients, hypertrophy involved both the ventricular septum and anterolateral left ventricular free wall. Twenty percent of the patients showed hypertrophy involving regions of the left ventricle other than the basal anterior ventricular septum; hence, hypertrophic cardiomyopathy could not be diagnosed from M-mode echocardiograms, and two-dimensional echocardiography was required. In the remaining patients, hypertrophy either was confined to the anterior portion of the ventricular septum or involved the entire septum but not the free wall. Left ventricular morphology was compared in pairs of first-degree relatives. Only 41 of 105 pairs of firstdegree relatives (39%) showed phenotypically similarhearts with the same pattern of left ventricular hypertrophy. Morphologic similarity was most common in patients who had diffuse distribution of hypertrophy involving the septum and free wall. Further analysis of left ventricular morphology was performed by assessing whether hypertrophy was present in each of 10 segments of left ventricular wall. Using this method, only 32 of 105 pairs of relatives (30%) were found to have a similar or identical morphologic appearance of the left ventricle. Hence, almost all patterns of distribution of left ventricular hypertrophy may represent expressions of genetically transmitted hypertrophic cardiomyopathy. Furthermore, the morphologic appearance of the left ventricle is particularly variable and markedly dissimilar in most closely related individuals with the genetically transmitted form of hypertrophic cardiomyopathy. This marked morphologic variability in closely related patients suggests that in screening families for hypertrophic cardiomyopathy, both M-mode and two-dimensional echocardiography should be used.