Steven G. Chopski

Intravascular Mechanical Cavopulmonary Assistance for Patients With Failing Fontan Physiology

To provide a viable bridge-to-transplant, bridge-to-recovery, or bridge-to-surgical reconstruction for patients with failing Fontan physiology, we are developing a collapsible, percutaneously inserted, magnetically levitated axial flow blood pump to support the cavopulmonary circulation in adolescent and adult patients. This unique blood pump will augment pressure and thus flow in the inferior vena cava through the lungs and ameliorate the poor hemodynamics associated with the univentricular circulation. Computational fluid dynamics analyses were performed to create the design of the impeller, the protective cage of filaments, and the set of diffuser blades for our axial flow blood pump. These analyses included the generation of pressure-flow characteristics, scalar stress estimations, and blood damage indexes. A quasi-steady analysis of the diffuser rotation was also completed and indicated an optimal diffuser rotational orientation of approximately 12 degrees. The numerical predictions of the pump performance demonstrated a pressure generation of 2-25 mm Hg for 1-7 L/min over 3000-8000 rpm. Scalar stress values were less than 200 Pa, and fluid residence times were found to be within acceptable ranges being less than 0.25 s. The maximum blood damage index was calculated to be 0.068%. These results support the continued design and development of this cavopulmonary assist device, building upon previous numerical work and experimental prototype testing.

Pediatric Circulatory Support: Current Strategies and Future Directions. Biventricular and Univentricular Mechanical Assistance

Mechanical circulatory support is gaining increased recognition as a viable treatment option for pediatric patients who suffer from congenital or acquired heart disease. Historically, the treatment options have been very limited for pediatric patients, but recent technological advances, combined with new research into circulatory support devices, are seeking alternative therapeutics options for infants and children. We present a review of the technological advances of mechanical circulatory support in the pediatric population, including the recent emergence of a new class of circulatory support devices for pediatric patients with single ventricle physiology. The National Heart, Lung, and Blood Institute pediatric circulatory support program is discussed, in addition to the use of adult devices in pediatric applications, the Berlin Heart Excor, and several other blood pumps in development for bridge-to-transplant and bridge-to-recovery support. These devices have the potential to generate a paradigm shift in the treatment of the pediatric patients with heart failure—a shift is likely already be underway.

Laser Flow Measurements in an Idealized Total Cavopulmonary Connection With Mechanical Circulatory Assistance

This study examined the interactive fluid dynamics between a cavopulmonary assist device and univentricular Fontan circulation. We conducted two-dimensional particle image velocimetry measurements on an idealized total cavopulmonary connection (TCPC) with an axial pump prototype intravascularly inserted into the inferior vena cava (IVC) and then in the IVC and the superior vena cava (SVC) for a dual-pump support case. The glass model of the TCPC consisted of rigid vessels having a diameter of 13.4 mm and a one-diameter vessel offset at the TCPC junction. Fluid velocity profiles were examined at a cardiac output of 3 L/min and SVC and IVC flow ratios of 30/70%, 40/60%, and 50/50% and pump rotational speeds from 3000 to 9000 rpm. In addition, cardiac outputs of 5 and 7 L/min were also examined. As compared to the flow profile with the pump present, the measured velocity field demonstrated the presence of rotational (i.e., out of plane) motion, which forced the higher-velocity regions toward the periphery of the vessel. As a result, few flow vortices were captured in the image plane downstream of the pump in the TCPC junction. However, the velocity profiles for all cases demonstrated the expected shunting preference of IVC flow toward the right pulmonary artery. Furthermore, the inclusion of the pump provided a pressure rise of 3 to 9 mm Hg, which would be sufficient to relieve systemic hypertension in Fontan patients with circulatory dysfunction.

Mechanical Circulatory Support Devices for Pediatric Patients With Congenital Heart Disease

The use of mechanical circulatory support (MCS) devices is a viable therapeutic treatment option for patients with congestive heart failure. Ventricular assist devices, cavopulmonary assist devices, and total artificial heart pumps continue to gain acceptance as viable treatment strategies for both adults and pediatric patients as bridge-to-transplant, bridge-to-recovery, and longer-term circulatory support alternatives. We present a review of the current and future MCS devices for patients having congenital heart disease (CHD) with biventricular or univentricular circulations. Several devices that are specifically designed for patients with complex CHD are in the development pipeline undergoing rigorous animal testing as readiness experiments in preparation for future clinical trials. These advances in the development of new blood pumps for patients with CHD will address a significant unmet clinical need, as well as generally improve innovation of the current state of the art in MCS technology.

Design of axial blood pumps for patients with dysfunctional fontan physiology: computational studies and performance testing.

Limited treatment options for patients having dysfunctional single ventricle physiology motivate the necessity for alternative therapeutic options. To address this unmet need, we are developing a collapsible axial flow blood pump. This study investigated the impact of geometric simplicity to facilitate percutaneous placement and maintain optimal performance. Three new pump designs were numerically evaluated. A transient simulation explored the impact of respiration on blood flow conditions over the entire respiratory cycle. Prototype testing of the top performing pump design was completed. The top performing Rec design generated the highest pressure rise range of 2-38 mm Hg for flow rates of 1-4 L/min at 4000-7000 RPM, exceeding the performance of the other two configurations by more than 26%. The blood damage indices for the new pump designs were determined to be below 0.5% and predicted hemolysis levels remained low at less than 7 × 10(-5)  g/100 L. Prototype testing of the Rec design confirmed numerical predictions to within an average of approximately 22%. These findings demonstrate that the pumps are reasonably versatile in operational ability, meet pressure-flow requirements to support Fontan patients, and are expected to have low levels of blood trauma.

Experimental Measurements of Energy Augmentation for Mechanical Circulatory Assistance in a Patient-Specific Fontan Model

A mechanical blood pump specifically designed to increase pressure in the great veins would improve hemodynamic stability in adolescent and adult Fontan patients having dysfunctional cavopulmonary circulation. This study investigates the impact of axial-flow blood pumps on pressure, flow rate, and energy augmentation in the total cavopulmonary circulation (TCPC) using a patient-specific Fontan model. The experiments were conducted for three mechanical support configurations, which included an axial-flow impeller alone in the inferior vena cava (IVC) and an impeller with one of two different protective stent designs. All of the pump configurations led to an increase in pressure generation and flow in the Fontan circuit. The increase in IVC flow was found to augment pulmonary arterial flow, having only a small impact on the pressure and flow in the superior vena cava (SVC). Retrograde flow was neither observed nor measured from the TCPC junction into the SVC. All of the pump configurations enhanced the rate of power gain of the cavopulmonary circulation by adding energy and rotational force to the fluid flow. We measured an enhancement of forward flow into the TCPC junction, reduction in IVC pressure, and only minimally increased pulmonary arterial pressure under conditions of pump support.

Three-dimensional laser flow measurements of a patient-specific fontan physiology with mechanical circulatory assistance.

Mechanical assistance of the Fontan circulation is hypothesized to enhance ventricular preload and improve cardiac output; however, little is known about the fluid dynamics. This study is the first to investigate the three-dimensional flow conditions of a blood pump in an anatomic Fontan. Laser measurements were conducted having an axial flow impeller in the inferior vena cava. Experiments were performed for a physiologic cardiac output, pulmonary arterial flows, and pump speeds of 1000-4000 rpm. The impeller had a modest effect on the flow conditions entering the total cavopulmonary connection at low pump speeds, but a substantial impact on the velocity at higher speeds. The higher speeds of the pump disrupted the recirculation region in the center of the anastomosis, which could be advantageous for washout purposes. No retrograde velocities in the superior vena cava were measured. These findings indicate that mechanical assistance is a viable therapeutic option for patients having dysfunctional single ventricle physiology.

Twisted cardiovascular cages for intravascular axial flow blood pumps to support the Fontan physiology.

Failing single ventricle physiology represents an ongoing challenge in mechanical assist device development, requiring pressure augmentation in the cavopulmonary circuit, reduction of systemic venous pressure, and increased cardiac output to achieve hemodynamic stabilization. To meet these requirements, we are developing a percutaneously-placed, axial flow blood pump to support ailing single ventricle physiology in adolescents and adults. We have modified the outer cage of the device to serve as both a protective and functional design component. This study examined the performance of 3 cage geometries with varying directions of filament twist using numerical simulations and hydraulic experiments. All 3 cage and pump models performed in acceptable ranges to support Fontan patients. The cage design employing filaments that are twisted in the opposite direction to the impeller blades and in the direction of the diffuser blades (against-with) demonstrated superior performance by generating a pressure rise range of 5–38 mm Hg of flow rates of 0.5–6 l/min at rotational speeds of 5000–7000 rpm. The blood damage indices for all of the cages were found to be well below 2%, and the scalar stress levels were below 200 Pa. This study represents ongoing progress in the development of the impeller and cage assembly. Validation of the results will continue in experiments with blood bag evaluation as well as by particle image velocimetry measurements.

Pressure-Flow Experimental Performance of New Intravascular Blood Pump Designs for Fontan Patients.

An intravascular axial flow pump is being developed as a mechanical cavopulmonary assist device for adolescent and adult patients with dysfunctional Fontan physiology. Coupling computational modeling with experimental evaluation of prototypic designs, this study examined the hydraulic performance of 11 impeller prototypes with blade stagger or twist angles varying from 100 to 600 degrees. A refined range of twisted blade angles between 300 and 400 degrees with 20-degree increments was then selected, and four additional geometries were constructed and hydraulically evaluated. The prototypes met performance expectations and produced 3-31 mm Hg for flow rates of 1-5 L/min for 6000-8000 rpm. A regression analysis was completed with all characteristic coefficients contributing significantly (P < 0.0001). This analysis revealed that the impeller with 400 degrees of blade twist outperformed the other designs. The findings of the numerical model for 300-degree twisted case and the experimental results deviated within approximately 20%. In an effort to simplify the impeller geometry, this work advanced the design of this intravascular cavopulmonary assist device closer to preclinical animal testing.

Stereo-Particle Image Velocimetry Measurements of a Patient-Specific Fontan Physiology Utilizing Novel Pressure Augmentation Stents

Single ventricle anomalies are a challenging set of congenital heart defects that require lifelong clinical management due to progressive decline of cardiovascular function. Few therapeutic devices are available for these patients, and conventional blood pumps are not designed for the unique anatomy of the single ventricle physiology. To address this unmet need, we are developing an axial flow blood pump with a protective cage or stent for Fontan patients. This study investigates the 3-D particle image velocimetry measurements of two cage designs being deployed in a patient-specific Fontan anatomy. We considered a control case without a pump, impeller placed in the inferior vena cava, and two cases where the impeller has two protective stents with unique geometric characteristics. The experiments were evaluated at a cardiac output of 3 L/min, a fixed vena caval flow split of 40%/60%, a fixed pulmonary arterial flow split of 50%/50%, and for operating speeds of 1000-4000 rpm. The introduction of the cardiovascular stents had a substantial impact on the flow conditions leaving the pump and entering the cavopulmonary circulation. The findings indicated that rotational speeds above 4000 rpm for this pump could result in irregular flows in this specific circulatory condition. Although retrograde flow into the superior vena cava was not measured, the risk of this occurrence increases with higher pump speeds. The against-with stent geometry outperformed the other configurations by generating higher pressures and more energetic flows. These results provide further support for the viability of mechanical cavopulmonary assistance as a therapeutic treatment strategy for Fontan patients.