Design of a Dual Propeller Micro-Pump in Conjunction With Flared TCPC for Cavopulmonary Assist in Fontan Patients

Abstract

A single ventricular physiology of the human heart caused by a dysfunctional right ventricle is usually treated with the three-stage Fontan operation. The outcome of this operation is an extra-cardiac total cavopulmonary connection (TCPC) which supplies the deoxygenated blood from the body to the lungs by directly connecting the inferior and superior vena cava (IVC and SVC) to the left and right pulmonary arteries (LPA and RPA). However, the situation is worsened due to non-physiologic flow conditions and pressure loss inside the cavopulmonary track, which ultimately calls for a heart transplantation. A modest pressure rise of 5–6 mm Hg will help to regain the normal physiology of the patient. In order to achieve this, a conceptual design of a dual propeller pump inside a flared TCPC is developed and studied. In order to provide a modest pressure rise, a blood pumping device was inserted inside the flared TCPC connection which consisted of two propellers, each placed in the SVC and the IVC and connected by a single shaft. The IVC and the SVC propellers were designed to rotate at the same rotational speed, having the same pressure rise but different blood inflow rate. The equal pressure rise across both the propellers was necessary at the design speed and flow rate to prevent any blood flow into the opposite vena cava. The TCPC-dual propeller conjunction was examined for the hydraulic performance and the flow pattern inside the TCPC using the 3D-CFD simulations on Ansys-CFX. The effect of axial distance between the two propellers on the blood flow interference and energy loss was also studied to select an optimal separation distance between them. The introduction of dual propeller pump inside the flared TCPC led to a pressure rise of 2–15 mm Hg at a total flow rate of 4.5 lpm (63% from IVC and 37% from SVC) with the rotational speed ranging from 6000–12000 rpm. It was seen that an axial separation of 70 mm between the two propellers provided the best performance in terms of flow interference and energy loss. A dual propeller pump assembled with an optimized TCPC could provide the required pressure rise for a particular age group of patients with univentricular Fontan physiology. The ability of dual micro-propeller pump to provide the required pressure rise will help to augment the cavopulmonary flow and hence help to regain the normal flow physiology as that witnessed by a human with biventricular circulation.