Integrated Switchable Ventricular Assist Devices for Pediatric Patients
Authors:   , Sarkisyan Harutyun , Balasubramanian Sriram 
Published: July 2021

Thousands of children are born each year with significant cardiac defects that result in the development of heart disease and ultimately premature congestive heart failure (CHF). In addition, hundreds of children are exposed to viruses and bacteria that attack the heart muscle, causing myocarditis or cardiomyopathy that leads to CHF. The current treatment paradigm involves pharmacologic agents to mitigate symptoms and slow the progression to failure. Most severe cases require heart transplantation or the use of short or long-term mechanical circulatory support (MCS) systems, such as ventricular assist devices (VADs). Due to the shortage of donor hearts, waiting periods, and the difficulty of finding a donor heart, the implementation of MCS devices is on the rise as an alternative treatment strategy for pediatric patients with CHF. VADs specifically for children, continue to lag behind those developed for adults. In addition, there is no heart pump with the design innovation to support the dysfunctional states of heart failure and the range of the anatomic and physiological heterogeneity in pediatric patients from one stage of development to another. To address this unmet clinical need, I am developing two dual-configured mechanical VADs that only have two moving parts and the versatility to provide full or partial cardiovascular support to either the right or left ventricle of pediatric patients. These devices will not only support pediatric patients (body surface area [greater than or equal to] 0.7 m²), but they will also support their growth and development. he two VADs were designed to deliver flows of 1 - 5 L/min and pressure rises of 50 - 120 mmHg at 2,000 - 15,000 RPM. Both VADs underwent 2 design phases in order for the overall pump housing to be small enough to fit within the thoracic cavity of children. Having the VADs be completely implantable within the thoracic cavity eliminates the need for percutaneous driveline that protrudes from the abdomen. The research was focused on advancing the development of 4 centrifugal blood pumps and 3 axial blood pumps, which are incorporated in the VADs being developed, also referred to as the Parallel Concept and Series Concept Pediatric VADs. The generation 1 centrifugal pumps that were incorporated for both the Parallel and Series Concept VADs were designed using the Taguchi Optimization Method to produce 80 to 120 mmHg in the 3 to 5 LPM range. The diameter of both of the centrifugal impellers were 35.6 mm. Both Gen 1 centrifugal pumps were evaluated computationally and experimentally. The design of generation 1 axial pump was iteratively improved to maintain an overall length less than 50 mm while generating 50 to 80 mmHg. Generation 1 axial and centrifugal pumps were able to satisfy physiological pressure requirements while maintaining the blood damage index to less than 2%. The axial and centrifugal pumps were experimentally evaluated using a water-glycerin mixture in order to verify pressure generation predictions. The Gen 1 axial and centrifugal pumps experimentally outperformed computational predictions. Both of the centrifugal pumps experimentally outperformed computational predictions by 10-15%. The generation 1 pumps were decreased in size by 30 to 40% in order to establish the generation 2 axial and centrifugal pumps for both the Parallel and Series Concept VADs. The Gen 2 centrifugal pumps for both the Series and Parallel Concept VADs had an overall diameter of 30 mm. The impeller diameter for the Series Concept pump was 24 mm and the impeller diameter for the Parallel Concept was 22 mm. The axial pump length for both concepts was less than 35mm. Generation 2 pumps were able to satisfy the physiological pressure requirements at their new scaled size while maintaining the blood damage index to less than 2%. The experimental results for the Series Concept axial and centrifugal pumps demonstrated that the designs outperform computational predictions. The research performed for both the Series and Parallel Concept VADs demonstrates significant progress in the design of 2 Pediatric VADs. The Gen 2 impeller and the volute combination for both concepts is already less than 30 mm in diameter which satisfies the design requirement for the VADs to be implanted within the thoracic cavity of pediatric patients. These innovative pump design will support a wide range of patient ages and dysfunctional states of heart failure.