Masked Infundibular Pulmonary Obstruction in Ventricular Septal Defect with Pulmonary Hypertension

Abstract

Recent observations have suggested that infundibular pulmonary obstruction may exist in association with a ventricular septal defect and pulmonary hypertension but not be apparent because of greater obstruction in the pulmonary arterial bed which "masks" the more proximal infundibular obstruction. Following the administration of the pulmonary vasodilator tolazoline to patients with a ventricular septal defect and pulmonary hypertension, pullback tracings have revealed infundibular obstruction where none was apparent in control studies. An analysis of the catheterization findings in those patients with a ventricular septal defect and pulmonary hypertension revealed 32 subjects who had received and responded to tolazoline. Twenty-seven of these patients had gradients after tolazoline ranging from 8 to 73 mm. Hg. The findings suggest that in the presence of pulmonary hypertension, infundibular obstruction is present from birth and continues to develop, becoming apparent or "unmasked" by virtue of a reduction (acutely with drugs or slowly by delayed maturation) in pulmonary vascular resistance.