Cavopulmonary assist for the univentricular Fontan circulation: von Kármán viscous impeller pump

Abstract

Objectives In a univentricular Fontan circulation, modest augmentation of existing cavopulmonary pressure head (2–5 mmHg) would reduce systemic venous pressure, increase ventricular filling, and thus, substantially improve circulatory status. An ideal means of providing mechanical cavopulmonary support does not exist. We hypothesized that a viscous impeller pump, based on the von Kármán viscous pump principle, is optimal for this role. Methods A 3-dimensional computational model of the total cavopulmonary connection was created. The impeller was represented as a smooth 2-sided conical actuator disk with rotation in the vena caval axis. Flow was modeled under 3 conditions: 1) passive flow with no disc; 2) passive flow with a non-rotating disk, and 3) induced flow with disc rotation (0–5K rpm). Flow patterns and hydraulic performance were examined for each case. Hydraulic performance for a vaned impeller was assessed by measuring pressure rise and induced flow over 0–7K rpm in a laboratory mock loop. Results A nonrotating actuator disc stabilizes cavopulmonary flow, reducing power loss by 88%. Disk rotation (from baseline dynamic flow of 4.4 L/min) resulted in a pressure rise of 0.03 mmHg. A further increase of pressure of 5–20 mmHg and 0–5 L/min flow were obtained with a vaned impeller at 0–7K rpm in a laboratory mock loop. Conclusions A single viscous impeller pump stabilizes and augments cavopulmonary flow in 4 directions, in the desired pressure range, without venous pathway obstruction. It applies to the existing staged protocol as a temporary bridge-to-recovery or –transplant in established univentricular Fontan circulations. It may also enable compressed palliation of single ventricle without need for intermediary surgical staging or use of a systemic-to-pulmonary arterial shunt.

Effect of mechanical assistance of the systemic ventricle in single ventricle circulation with cavopulmonary connection

“…Previous reports have focused on mechanical assistance of this failing circulation by use of subpulmonary blood pumps to drive blood forwards through the pulmonary circuit [4, 5, 10–14] or with a viscous impeller pump based on the Von Karman principle [3, 15]. Although there has been clinical success [10] with this approach of pushing blood through the pulmonary circuit, significant surgical modifications to the existing cavopulmonary circuit are required to implement this strategy.…”

“…Previous attempts to support the single ventricle circulation mechanically have suggested that a custom-built assist device is needed to push [ 3 –5] rather than pull through the pulmonary circulation. We hypothesized that using a conventional ventricular assist device, with or without conversion of a total cavopulmonary connection to a bidirectional Glenn cavopulmonary connection would allow assistance by pulling blood through the circuit and improve cardiac index (CI).…”

Ventricular Assist Devices in Children

“…[23][24][25][26] An ideal Fontan assist device/cavopulmonary assist device would provide equal continuous flow at a low-pressure head to avoid lung perfusion injury, would be resilient to afterload to overcome elevated and possibly fluctuating pulmonary vascular resistance, and would avoid inlet suction within the Fontan pathway in the absence of a venous reservoir. Rodefeld et al 27 have developed a pediatric transcatheter-expandable impellar pump that is positioned at the crux of the cavopulmonary junction and directs flow into both lungs. Although this device is still far from clinical application, significant strides have been made in understanding the unique anatomic and physiological constraints of total cavopulmonary connection circulation, with the hope of a durable assist device on the horizon.…”

Design Optimization and Performance Studies of an Adult Scale Viscous Impeller Pump for Powered Fontan in an Idealized Total Cavopulmonary Connection

“…15 In Fontan physiology, there is a relative increase in systemic venous pressure and decrease in pulmonary arterial pressure (Fontan paradox). 4 A partial assist device in the TCPC pathway which can provide 2-5 mmHg pressure augmentation will simultaneously reduce systemic venous pressure and increase pulmonary arterial pressure to restore conditions more closely resembling a more stable two ventricle circulation.…”

“…15 An expandable viscous impeller pump (VIP), based on the von Ka´rma´n viscous pump principle, appears to satisfactorily address these problems. The application of the VIP to the Fontan is defined here as Powered Fontan.…”