Ventricular septal defect associated with left ventricular outlfow tract obstruction below the defect.

Muscular subaortic stenosis associated with ventricular septal defect (VSD) is a rare but important anomaly. Two types of left ventricular outflow tract (LVOT) obstruction should be distinguished on the basis of morphologic as well as hemodynamic differences, depending on whether the stenosis is localized above (Type I) or below (Type II) the defect. The five cases presented are all in the latter category. In the first two cases the correct diagnosis was not made until after repair of the VSD. Two patients had previously undergone banding of the pulmonary artery (PAB). Marked carotid shudder and a vertical QRS axis in the frontal plane were presented in all cases. For the diagnosis to be established by catheterization, the catheter tip must be maneuvered into the apical part of the left ventricular cavity in order to detect the stenosis on the withdrawal curve. It is difficult to visualize the stenosis by angiography. The surgical approach through the VSD via a right atriotomy is highly recommended for Type II subaortic stenosis.