the functionally univentricular circulation in the norwood procedure: from analysis of fluid dynamics to surgical procedures

Abstract

the norwood procedure and its modifications have become the most commonly used surgical procedures for patients with hypoplastic left heart syndrome. many efforts have been made to understand the fluid dynamics of the norwood circulation, with the major impetus coming from the lumped-parameter model described by migliavacca et al. in this model, a large number of variables have been analysed to understand their effect on the norwood circulation. in the clinical setting, some of these parameters can be influenced by the surgeon during the operation. the shunt has been demonstrated to be the critical element in regulating the pulmonary and systemic flows, with the goal of the surgeon being to obtain balanced flows. in order to do this, it is possible to influence the flow through the shunt in three ways:

1. by augmenting the pressure of perfusion of the shunt, with a suboptimal aortic reconstruction that can leave some residual pressure gradient. this can work like an increment of systemic vascular resistance;

2. by varying the size of the shunt;

3. by varying the type of architecture of the shunt, since flow through the shunt is dependent on the site of anastomosis, the angle with the vessels, and so on.

in order to validate or verify the results obtained from the lumped-parameter model, we have reviewed our experience with the norwood procedure since 1992.