OUTFLOW OBSTRUCTION AFTER THE ARTERIAL SWITCH OPERATION - A MULTIINSTITUTIONAL STUDY

Objective: Our objectives were to discover whether outflow obstruction immutably accompanies the arterial switch operation and to identify f actors that may decrease its prevalence. Methods: Percutaneous or surg ical reintervention for obstruction after an arterial switch was selec ted as an end point for obstruction. Its risk factors were identified by time-related multivariable analyses of yearly follow-up data from 5 14 neonates,vith simple transposition or transposition with ventricula r septal defect entering 23 institutions before 15 days of age between January 1, 1985, and March 1, 1989. Results: Sixty-two patients under went 86 reinterventions for right-sided obstruction (83% free at 10 ye ars) and six for left-sided obstruction (98% free at 10 years). After 2 years, right-sided obstruction occurred at a rate of about 1% per ye ar and left-sided at a rate of about 0.1% per year. Right ventricular infundibular or valvular obstruction was associated with the aorta and pulmonary trunk positioned side-by-side, coexisting coarctation, use of prosthetic material in sinus reconstruction, one institution, and e arlier institutional experience. Pulmonary trunk or pulmonary artery o bstruction was associated with lower birth weight, left coronary arter y arising from sinus 2, coronary explantation away from the transectio n site, three institutions, and earlier institutional experience. Conc lusions: A risk-adjusted base incidence (0.5% per year) of reintervent ion for right-sided obstruction continues late after operation. It is due in part to congenital variability or abnormality of right ventricu lar outflow structures and to experience and surgeon variability resul ting in suboptimal pulmonary trunk reconstruction. The same sources of variability probably affect the aortic root, but its native character istics plus higher distending pressure make the base incidence conside rably less (0.1% per year).