Hypertrophic cardiomyopathy: Subclassification by M mode echocardiography

Seventy-four patients with hypertrophic cardiomyopathy, hemodynamically classified into well defined subgroups (left ventricular outflow tract obstruction at rest [27 patients], labile obstruction [4 patients], latent obstruction [28 patients] and no obstruction [15 patients]) were studied with M mode echocardiography. Significant echocardiographic differences were found among these groups. The most important differentiating feature was the degree of systolic anterior motion of the anterior mitral leaflet. Combined with prolonged interventricular septal contact (that is, for more than 30 percent of echocardiographic systole), it occurred in all 27 patients with obstruction at rest but in no patient with latent or no obstruction. Another differentiating feature was aortic valve midsystolic notching, which occurred in all 25 patients with obstruction at rest (in whom adequate aortic valve echograms could be obtained) but in only 3 of 17 patients with latent obstruction and in no patients without obstruction. The third most useful differentiating feature was left atrial enlargement, which occurred in 25 of 27 in the group with obstruction at rest, but in only 4 of 28 in the group with latent obstruction and in 2 of 15 in the group without obstruction.Other M mode echocardiographic findings in patients with hypertrophic cardiomyopathy showed overlap among subgroups and therefore could not be relied on for noninvasive subclassification. These echocardiographic abnormalities included septal and posterior wall thickness, septum to posterior wall thickness ratio, septal and posterior wall systolic thickening, left ventricular internal diameter, left ventricular outflow tract size at the onset of systole, mitral leaflet position and percent diastolic anterior mitral leaflet-interventricular septal contact.It is concluded that a noninvasive classification of patients with hypertrophic cardiomyopathy into hemodynamic subgroups of obstruction at rest, latent obstruction and no obstruction can be made by assessing the degree of systolic anterior motion, the presence of aortic valve mid systolic notching, and left atrial size. This noninvasive M mode echocardiographic subclassification has important clinical implications.