Modeling of systemic-to-pulmonary shunts in newborns with a univentricular circulation: State of the art and future directions Giancarlo Pennati a, ⁎, Francesco Migliavacca a , Gabriele Dubini a , Edward L. Bove b a Laboratory of Biological Structure Mechanics, Department of Structural Engineering, Politecnico di Milano, Milan, Italy b Section of Cardiac Surgery, The University of Michigan School of Medicine, Ann Arbor, MI, USA abstract article info Keywords: Mathematical model In vitro test Fluid dynamics Congenital heart diseases A systemic-to-pulmonary artery shunt is a surgically created connection inserted between the systemic and pulmonary circulations to control pulmonary blood flow during surgical reconstruction of the univentricular heart. The hemodynamic effect of these shunts in the postoperative setting has not been well characterized because of the difficulties in making accurate measurements. In vitro investigations as well as computer flow modeling have been increasingly utilized to study the cardiovascular system and, specifically, to examine the hemodynamic effects of a number of surgical operations. The present review discusses the available literature on systemic to pulmonary artery shunt modeling. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction 1.1. Systemic-to-pulmonary arterial shunts In critically ill neonates with cyanotic congenital heart disease, a systemic-to-pulmonary arterial shunt (shunt) has been shown to provide an excellent form of palliation. A wide variety of congenital heart defects, ranging from tetralogy of Fallot (TOF) to complex univentricular hearts with major associated malformations, may be treated with a shunt. A shunt is a surgically-created connection between the systemic arterial circulation and the pulmonary arteries. After the introduction of the first shunt in 1945 in patients with TOF by Blalock and Taussig [1], in which the divided end of the subclavian artery was anastomosed to the pulmonary artery, various modifications of this original operation have been described and applied to other cardiac defects. The various techniques that have been used to create a palliative shunt [2] include classic and modified (Gore-Tex) Blalock–Taussig shunts (BT), direct aortopulmonary anastomoses (Waterston and Potts shunts), interposition prosthetic conduits, and right ventricle-to- pulmonary artery conduits (Fig. 1). More recently, a new palliative strategy has been introduced to treat patients with hypoplastic left heart syndrome (HLHS) as an alternative to the classic Norwood procedure. This hybrid approach, combining interventional catheter- ization with surgery, consists of inserting a stent to maintain patency of the ductus arteriosus, enlarging the atrial septal defect, and banding the branch pulmonary arteries, avoids the need for cardiopulmonary bypass and circulatory arrest [3]. The stented ductus arteriosus functions as a shunt, maintaining unobstructed systemic blood flow as in the fetal circulation. The common idea behind all these operations is to create a connection to increase pulmonary blood flow and alleviate cyanosis in patients with insufficient pulmonary blood flow or to maintain systemic blood flow in patients with an inadequate systemic ventricle such as those with HLHS. For those babies born with HLHS, subsequent surgical palliation utilizing direct cavopulmonary con- nections is then performed after neonatal pulmonary vascular resistance falls to normal levels. However, a shunt also results in an increased volume load to the systemic ventricular chamber, a potentially deleterious effect in those patients with a univentricular heart, such as HLHS. In the normal heart, the circulation consists of an in-series circuit in which the left and right ventricles pump blood to the systemic and pulmonary circulations, respectively (Fig. 2a). However, in the presence of a univentricular heart, a parallel circuit is created after the shunt connection (Fig. 2b) with the single ventricular chamber pumping for both chambers. Patient survival at this stage is strongly dependent on the balance between systemic and pulmonary flows, which in turn is related to the construction of the shunt. The optimal shunt should possess the following features: a) Be rapid and technically simple to construct. b) Be easily excluded from the circulation when definitive repair is performed. c) Avoid pulmonary artery distortion or stenosis. Progress in Pediatric Cardiology 30 (2010) 23–29 ⁎ Corresponding author. Laboratory of Biological Structure Mechanics, Structural Engineering Department, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy. Tel.: +39 02 2399 4223; fax: +39 02 2399 4286. E-mail address: giancarlo.pennati@polimi.it (G. Pennati). 1058-9813/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ppedcard.2010.09.004 Contents lists available at ScienceDirect Progress in Pediatric Cardiology journal homepage: www.elsevier.com/locate/ppedcard