Quantification of flow through an interatrial communication. Application to the partial Fontan procedure.

The partial Fontan procedure has become an accepted alternative for the high-risk candidate. Creation of a small right-to-left shunt will lower the systemic venous pressure and improve systemic cardiac output while maintaining an acceptable systemic arterial saturation. However, because of variations in patient size and postoperative transpulmonary gradient, proper sizing of the residual defect is difficult. We have therefore conducted a series of experiments on a model that simulates the blood flow across interatrial defects of varying sizes at several pressure gradients. We used porcine blood to develop guidelines for the sizing of the residual defect. Our results demonstrate a linear relationship between flow and pressure gradient across all hole sizes tested. In addition, there was a linear relationship between atrial septal defect size and flow at each pressure gradient. Our data show that the Gorlin formula predictions overestimated flow by 10% to 40%. It is evident from these data that relatively small changes in the size of the atrial septal defect or in the pressure gradient result in significant changes in flow. Therefore we advocate the use of an adjustable interatrial communication such as the snare-controlled adjustable atrial septal defect for patients undergoing partial Fontan procedures.