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

Objective

In a univentricular Fontan circulation, modest augmentation of existing cavopulmonary pressure head (2–5 mm Hg) 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 nonrotating 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 increase and induced flow over 0 to 7K rpm in a laboratory mock loop.

Results

A nonrotating actuator disc stabilized cavopulmonary flow, reducing power loss by 88%. Disk rotation (from baseline dynamic flow of 4.4 L/min) resulted in a pressure increase of 0.03 mm Hg. A further increase in pressure of 5 to 20 mm Hg and 0 to 5 L/min flow was obtained with a vaned impeller at 0 to 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. A viscous impeller pump applies to the existing staged protocol as a temporary bridge-to-recovery or -transplant in established univentricular Fontan circulations and may enable compressed palliation of single ventricle without the need for intermediary surgical staging or use of a systemic-to-pulmonary arterial shunt.