Natural Internal Banding in Adult Patients with a Large Ventricular Septal Defect and a Preserved Pulmonary Vascular System

Abstract

Hypertrophied anomalous muscle bands (AMBs) in the right ventricular outflow tract (RVOT) may develop in the context of ventricular septal defects (VSDs) and limit persistent pulmonary overflow. In adult patients with a large VSD, persistent AMBs in the RVOT therefore can simulate the role of an externally placed pulmonary artery band. We termed such alterations natural internal bands (NIBs). Our goal was to establish the morphologic nature of the obstructive muscular lesions of the RVOT in patients with a large VSD. Patients who underwent operations for a large VSD in our center, which has a high volume of adult patients with congenital defects, were retrospectively reviewed, and the nature of the NIBs in these patients was documented. All patients underwent transthoracic echocardiography and cardiac catheterization evaluations preoperatively and at postoperative month 3. Histopathologic examination of the AMBs was performed. Of 96 adult patients who underwent operations for a large isolated VSD (mean defect size, 16.9 ± 3.5 mm), 16 patients had a hemodynamically significant NIB. Two different patterns of obstruction were found. Ten of the 16 patients revealed an os infundibulum morphology, and 6 patients revealed systolic bulging of the conal septum. Four of the patients with os infundibulum also had classic tetralogy-type septal malalignment. The mean peak systolic gradient on the RVOT was 56.5 ± 17.2 mm Hg and 53.6 ± 12.3 mm Hg in the patients with os infundibulum and in the patients with systolic bulging of the conal septum, respectively. Surgical repair of the VSD was completed successfully in all patients. Resection of the os infundibulum was performed concomitantly in patients with os infundibulum. At the third postoperative month, the mean peak systolic gradient was 16.8 ± 3.5 mm Hg in patients with os infundibulum and 26 ± 5.9 mm Hg (range, 20-35 mm Hg) in patients with systolic septal bulging. Some mechanisms in adult type VSDs are essential for protecting the pulmonary vasculature. We tried to review these protective mechanisms: hypertrophied AMBs and NIBs.