Numerical Simulation and Optimization of Blalock-Taussig Shunt

The goal of this study is to create an optimized Blalock-Taussig shunt used to temporarily repair pulmonary vascular blockages allowing a child time to grow so a more permanent surgical repair of the heart and vasculature can be performed. Blalock-Taussig or BT shunts are a surgical procedure performed on infants suffering from cyanosis or “Blue Baby Syndrome.” A BT shunt is an artificial vessel placed between the right ventricle and the pulmonary artery to increase blood flow in the lung and blood oxygen saturation levels. In a study of 96 patients with currently in use modified BT shunts, 32 patients (21%) had greater than 50% stenosis caused by myofibroblastic proliferation at the shunt lumen due to shunt geometry [1]. A 2007 study by the cardiac surgery division of Johns Hopkins Medical Institutions found an operative mortality rate of 14% (227 of 1,574) with patients undergoing BT surgery [2]. In this paper, the flow of blood through several different BT shunt configurations from actual patient data was analyzed using the commercial CFD software ANSYS Fluent. Results from each shunt’s analysis were then compared to determine the shunt parameters with optimal flow dynamics for use in infants suffering from pulmonary vascular blockage. It was found that the entrance boundary of current BT shunts caused blood flow hindrances due to high wall shear values and flow separation. A newly designed shunt was proven to partially fix this problem; however, a superior model could be optimized by using characteristics from currently used shunts and CFD results. Many iterations and designs of BT shunts were made using Solidworks, a solid modeling computer-aided design program, and were tested using Fluent to create a shunt optimized by smoothening the transition between areas of high and low wall shear stress, lowering the overall maximum wall shear stress, reducing flow separation, and equalizing the flow to the left and right lung. All these factors contribute to the chance of thrombosis and morbidity within patients. The resultant model shunt showed drastic improvement in lowering the average wall shear stress by more than 85% at the initial boundary with over 20% drop in overall average wall shear. It also achieved a decline of the maximum wall shear stress by over 25% while negating the possibility of any flow separation and improving the equality in flow to the left and right lung by more than 60%.