Novel Integrated Pediatric Total Artificial Heart
Authors:   , Hirschhorn Matthew D. , Throckmorton Amy , Han Lin 
Published: February 2023

Four million live births occur in the US each year, and 25% of those babies are born with a congenital heart defect requiring treatment. Of that cohort, approximately 40,000 are born with significant heart malformations necessitating surgical intervention within the first days to years of life. Patients receiving early surgical intervention frequently require multiple open-heart surgeries and develop premature heart failure (HF). A growing number of patients with complex congenital heart disease are also developing cardiomyopathies (ventricular dysfunction), due to inherited muscle disorders, metabolic and mitochondrial defects, exposure to bacteria and viruses that attack the myocardium, and arrhythmias. The gold standard treatment for end-stage HF is heart transplantation, and there are a limited number of donor organs, especially for children. More than 15% of transplant eligible patients will die before a heart becomes available. Thus, there continues to be a significant clinical need for alternative solutions for pediatric HF, such as the use of mechanical circulatory assist devices. Ventricular assist device (VAD), or blood pump technology for adults, has achieved significant milestones in recent years by a demonstrated improvement in clinical outcomes due to design innovation. These devices leverage contact, surface free magnetic levitation and eliminate thrombosis-inducing mechanical or polymeric valves. However, VAD technologies for children significantly lag behind those for adults. While adult devices have been used in children, the operation of these pumps at off-design conditions increases the risk for irregular blood flow, contributing to blood cell damage (hemolysis) and dangerous clotting (thrombosis). High-risk pediatric patients also have limited options due to their size and require devices for a range of physiological heterogeneity due to childhood heart disease and the changing cardiovascular demands of physical growth. Thus, there was a substantial unmet clinical need, and the purpose of this dissertation research was to advance a breakthrough innovation of a high-impact, hybrid-design, magnetically levitated, medical device that uniquely integrated two blood pumps for supporting pediatric patients. This new device (Dragon Heart) had only 2 moving parts - an axial pump impeller for the pulmonary circulation and a centrifugal pump impeller for the systemic circulation. As a hybrid dual design, the centrifugal pump rotated around the separate axial pump domain. This device utilized the latest generation of bearings to levitate the rotating impellers in a magnetic field, thus facilitating a long operational lifespan and wider clearances between the rotating and stationary surfaces. Wider clearances lowered fluid stresses, hence reducing the risk of thrombosis and hemolysis. This design avoided the use of mechanical or biologic valves, thus further minimizing the thrombosis risk. It maintained pulse pressure by producing continuous flow. The Dragon Heart was also compact and delivers physiologic pressures and blood flows for high-risk pediatric with various degrees of heart failure, anatomic defects, and sizes/ages. Prior to the work presented in this dissertation, the Dragon Heart went through three design phases for the axial pump and four design phases for centrifugal pump. These design phases focused on the development of the blood-contacting pump regions using computational modeling and experimental testing. In these design phases, each of the two pumps were developed and tested independently using shaft-driven prototypes. The research presented in this dissertation integrated the two pumps into a single device and added magnetic levitation and drive components, removing the need for shafts to induce impeller rotation. To support the development of the Dragon Heart, this dissertation achieved three specific aims. In Aim 1, I established two fully integrated, combined pump prototypes with magnetic components. These prototypes leveraged an existing validated magnetically levitated axial flow pump and focused on development of the centrifugal pump. In Aim 2, I demonstrated the capabilities of the magnetically levitated prototypes through in vitro hydraulic and hemolytic experiments. In these experiments, pressure-flow performance curves were created and the measured hemolysis was assessed. Additionally, the two pumps of the Dragon Heart were operated and tested in tandem under a single housing for the first time. Finally, in Aim 3, I characterized the improved device designs using computational studies of transient flow phenomena and flow path modifications. These studies leveraged steady state, quasi steady state, and transient computational studies. Transient studies included both transient rotating sliding interface studies and time varying boundary condition studies. Pressure generation capabilities, calculated axial and radial fluid forces on the impeller and predicted blood damage were all assessed.