Muscular subaortic stenosis: the quantitative relationship between systolic anterior motion and the pressure gradient.

We performed simultaneous echocardiographic and hemodynamic studies in 11 patients with muscular subaortic stenosis to determine whether systolic anterior motion (SAM) of the anterior mitral leaflet and the pressure gradient are related quantitatively. SAM without septal contact was associated with either no gradient or a small impulse gradient of less than 10 mm Hg. SAM with septal contact was always associated with a pressure gradient of more than 10 mm Hg. The size of the pressure gradient correlated inversely with the time periods: (1) onset of SAM-septal contact (r = .79, p less than .001) and (2) onset of aortic ejection to onset of SAM-septal contact (r = -.89, p less than .001). Size also correlated directly with the time period: (3) duration of SAM-septal contact (r = .80, p less than .001). Thus when the time from the onset of SAM to the onset of SAM-septal contact was long, SAM-septal contact developed late in systole, the duration of SAM-septal contact was brief and the pressure gradient was low. When SAM-septal contact developed in early systole, the duration of SAM-septal contact was long and the pressure gradient was high. With the index of time period (3) divided by time period (1), a regression equation was devised to predict the size of the pressure gradient (pressure gradient mm Hg = 25 ratio + 25; r = .90, p less than .001; SE +/- 15 mm Hg). The echocardiographic time period index was validated prospectively in nine other patients and the significant correlation with the hemodynamically determined gradient persisted (r = .89, p less than .01). We conclude that SAM and the pressure gradient are related quantitatively in muscular subaortic stenosis. These observations have implications regarding the mechanism and significance of the pressure gradient in muscular subaortic stenosis.