Diagnosis of hypertrophic cardiomyopathy and screening for the phenotype suggestive of gene carriage in familial disease:: a simple echocardiographic procedure

Objectives-To design a new echocardiographic method of screening for hypertrophic cardiomyopathy applicable to children and adults, with a low false positive rate in athletes. Setting-Regional centre of cardiology, Oxford, UK. Methods-Forty one patients with hypertrophic cardiomyopathy, 66 first degree relatives from families with familial hypertrophic cardiomyopathy, 262 normal subjects, and 32 athletes were studied by long axis M mode and cross sectional echocardiography to determine the frequency distribution of diastolic and systolic ratios of cardiac wall thickness to cavity diameter. Results-The best screening measure for hypertrophic cardiomyopathy is diastolic septum to cavity ratio, where a value of > 0.26 yielded a 100% disease detection rate at all ages with 0% false positives in the ordinary population. In comparison, the conventional screening tool of diastolic septum to posterior left ventricular wall ratio of > 1.5 yielded a detection rate of only 75%, for a false positive rate of 2%. In first degree relatives, a septum to cavity ratio > 0.26 yielded a 100% detection rate for an abnormal phenotype suggestive of carriage of a mutation for hypertrophic cardiomyopathy with no obvious false positives. Conventional screening showed a detection rate of only 44%. Athletes with physiological cardiac hypertrophy showed only a 6% false positive rate with diastolic septum to cavity ratio, and could be differentiated from subjects with hypertrophic cardiomyopathy by the absence of hypercontractility shown by a normal systolic left ventricular wall to cavity ratio (cut off < 0.63; 0% false positives). Conclusions-M mode echocardiographic measurement of the septum to cavity ratio provides a good screening test for hypertrophic cardiomyopathy at all ages. Combining this measurement with systolic left ventricular wall to cavity ratio improves the accuracy further.