Markedly abnormal mitral valve motion without simultaneous intraventricular pressure gradient due to uneven mitral-septal contact in idiopathic hypertrophic subaortic stenosis

Although echocardiographic analysis reliably diagnoses idiopathic hypertrophic subaortic stenosis by detection of systolic forward anterior mitral valve motion and estimates severity of obstruction by the timed mitral encroachment of the interventricular septum, echographic stenosis may occur without hemodynamic obstruction or pressure gradient across the left ventricular outflow tract. Demonstration and mechanism of this apparent inconsistency are described in three patients with a previously unrecognized state of Idiopathic hypertrophic subaortic stenosis characterized by marked systolic forward movement of the anterior mitral valve without a simultaneous intraventricular pressure gradient, resulting from uneven septal apposition by the anterior leaflet. Echographic obstruction indexes (40, 34 and 31) during cardiac catheterization in the three patients were predictive of respective peak gradients of 37, 25 and 20 mm Hg. The horizontal nonparallel mitralseptal contact consistent with severe systolic forward movement of the anterior mitral valve in the absence of hemodynamic stenosis is believed to be caused by markedly forward displacement of the anterior papillary muscle, so that its chordae tendineae produce greater tension on the posteromedial aspect of the anterior mitral valve. Thereby the posterior portion of the leaflet is pulled forward more than its anterior side, allowing marked systolic forward anterior mitral valve motion without a pressure gradient in idiopathic hypertrophic subaortic stenosis.