Previous studies from our laboratory have shown that the position of the ventricular septum relative to the two ventricles at end-diastole is determined by the instantaneous transseptal pressure gradient (TSG) defined as left ventricular minus simultaneous right ventricular pressure. Since patients with mitral stenosis often have exaggerated leftward (paradoxic) motion of the ventricular septum during early diastole, we studied seven patients with mitral stenosis undergoing cardiac

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... on to determine if position (and therefore motion) of the ventricular septum was determined by TSG throughout diastole. M Mode echocardiograms derived from a two-dimensional parasternal short-axis view were recorded with simultaneous micromanometer measurements of left ventricular and right ventricular pressures. Six of seven patients demonstrated abnormal early diastolic leftward motion of the ventricular septum in at least one cardiac cycle. TSG measured at intervals throughout diastole ranged from -2.5 to +20 mm Hg, with abnormal TSG observed in most of the 40 cardiac cycles selected for analysis. The intracardiac position of the ventricular septum, defined as the distance from the right ventricular epicardium (RVEpi) to the left surface of the ventricular septum normalized for total cardiac dimension (RVEpi-VS), was plotted against left ventricular pressure, right ventricular pressure, and TSG. Linear regression of pooled data from all patients (164 observations) demonstrated a highly significant correlation between the instantaneous TSG and the relative intracardiac position of the ventricular septum (RVEpi-VS = 1.-2 TSG + 42.7; r = .79, p < .0001). The position of the ventricular septum was significantly better coi'z:elated (p < .0001) with instantaneous TSG than with left ventricular intracavitary pressure (r -.51) or right ventricular intracavitary pressure (r = .28). We conclude that, in patients with mitr:! stenosis, septal position throughout diastole is determined by the instantaneous TSG. An abnormal TSG in early diastole, probably reflecting the increased impedance to left ventricular filling, results in the exaggerated leftward diastolic septal movement. These data further clarify the complex interplay between active and passive motion of the ventricular septum throughout the cardiac cycle. Circulation 76, No. 5, 974-980, 1987. THE PRESENCE of "paradoxic" or anterior (rightward) motion of the ventricular septum during systole has been recognized in a number of clinical conditions, including right ventricular volume -8 or pressure overload,3' 8-12 left bundle branch block,13' 14 Wolff-Parkinson-White syndrome, 15 and transposition of the