Bidirectional Glenn shunt as an adjunct to surgical repair of congenital heart disease associated with pulmonary outflow obstruction: relevance of the fluid pressure drop-flow relationship.

A bidirectional Glenn shunt (BGS) was successfully incorporated into a two-ventricle repair for 10 patients (age, 3-17 years) who had congenital heart disease associated with severe pulmonary outflow obstruction. The BGS was used to volume-unload the pulmonary ventricle faced with residual outflow obstruction, thereby avoiding the need for insertion of a ventricle-to-pulmonary artery conduit. Transthoracic Doppler flow velocity analysis was used to determine transpulmonary peak systolic pressure drops as a measure of obstruction. Preoperative values ranged from 70 to 100 mmHg, and postoperative values ranged from less than 10 to 16 mmHg. At this writing, all patients are doing well 15 to 52 months after surgery. To gain further insight into the reduced pressure drop that may be achieved by decreasing flow rate across obstruction, a computer-based description of fluid flow was used to simulate blood traversing circumferentially narrowed passages. Overall pressure drops and associated flow energy losses were determined from numeric solutions (using finite-element analysis) to the Navier-Stokes equations for the proposed fluid reactions. Pressure drops and flow energy losses were found to decrease dramatically as flow rate was progressively reduced. For selected patients, a BGS can be an effective adjunct to the surgical treatment of pulmonary outflow obstruction. This approach avoids the use of a ventricle-to-pulmonary artery conduit, and thus the inevitable need in most patients for reoperations because of somatic growth, conduit failure, or both.