MORPHOLOGY OF LEFT-VENTRICULAR OUTFLOW TRACT STRUCTURES IN PATIENTS WITH SUBAORTIC STENOSIS AND A VENTRICULAR SEPTAL-DEFECT

Objective-To compare the incidence and prognosis of subaortic stenosis associated with a ventricular septal defect and to define the morphol ogical basis of subaortic stenosis. Design-Presentation and follow up data on 202 patients with subaortic stenosis seen at the Royal Liverpo ol Children's Hospital between 1 January 1960 and 31 December 1991 wer e reviewed. Survivors were traced to assess their current clinical sta te. Necropsy specimens of 291 patients with lesions associated with su baortic stenosis were also examined. Results-In the clinical study; 65 (32.1%) of the 202 patients with subaortic stenosis had a ventricular septal defect (excluding an atrioventricular septal defect). 32 of th ese patients had a short segment (fibromuscular) subaortic stenosis. 3 3 had subaortic stenosis produced by deviation of muscular components of the outflow tracts. In 17 patients (51.5%) this was caused by poste rior deviation or extension of structures into the left ventricular ou tflow tract, resulting in obstruction above the ventricular septal def ect. In the other 16 patients (48.5%) there was overriding of the aort a with concordant ventriculoarterial connections, (without compromise to right ventricular outflow) producing subaortic stenosis below the v entricular septal defect. Additional fibrous obstruction occurred in 3 9% of the patients with deviated structures. The age at presentation w as lower (P < 0.01) in patients with deviated structures (median (rang e) 0.4 (0 to 9.2) months) than in those with short segment obstruction (median (range) 4.2 (0 to 84.9) months). The incidence of aortic arch obstruction was higher (P < 0.002) in patients with deviated structur es than in those with short segment obstruction (38%). In the morpholo gical study 35 Liverpool pathological specimens showed obstructive mus cular structures in the left ventricular outflow tract either above or below the ventricular septal defect. 16 had either posterior deviatio n of the outlet septum or extension of the right ventriculoinfundibula r fold, or both of these together into the left ventricle. 19 had ante rior deviation of the outlet septum into the right ventricle with over riding of the aorta (without compromise to right ventricular outflow). The earliest age at which additional fibrous obstruction was seen was 9 months. The aortic valve circumference was small in 18% of specimen s. Follow up-The median (range) duration of follow up in survivors fro m the clinical study was 6.6 (1 to 25.7) years. 16 patients with devia ted musculature (49%) and 16 with short segment fibromuscular stenosis (50%) underwent operation for subaortic stenosis. Patients with devia ted structures were younger at operation than those with short segment stenosis (P < 0.005). Patients with posterior deviation or extension of structures into the left ventricular outflow tract underwent operat ion for subaortic stenosis more frequently (P < 0.05) than those with anterior deviation of the outlet septum and aortic override. The ventr icular-septal defect required surgical closure more frequently (P < 0. 005) in patients with deviation (93.9%) than in those with short segme nt obstruction (21.9%). There was no significant difference in the mor tality between patients with deviation (27%) and those with short segm ent obstruction (12%). Conclusions-32% of patients in the clinical stu dy with subaortic stenosis had a ventricular septal defect. Only 51% o f these had obstructive and deviated muscular structures in the left v entricular outflow tract. These patients had a significantly higher in cidence of aortic arch obstruction and required surgery for subaortic stenosis at a younger age than those with short segment obstruction. T he ventricular septal defect also required surgical closure more frequ ently in those patients with deviation. The morphological study define d the two sites of obstruction. The presence or absence and type of de viation should be clearly defined in all patients with a ventricular s eptal defects, because of the potential for the development of subaort ic stenosis.