Effect of cannula position in the thoracic aorta with continuous left ventricular support: four-dimensional flow-sensitive magnetic resonance imaging in an in vitro model

Objectives: Left ventricular assist devices (LVADs) have become an important treatment option for heart failure patients. However, altered blood flow patterns are suspected to affect perfusion in the aorta or cause structural changes to the aortic root, leading to regurgitation and valve dysfunction or thrombus formation. The purpose of this study was to evaluate flow patterns in a realistic in vitro model system using four-dimensional flow-sensitive magnetic resonance imaging.

Methods: A magnetic resonance compatible model system was developed consisting of an aorta connected to a VAD simulating the pulsatile flow of the native heart. An LVAD was connected to the aorta model via three different cannula positions. Flow patterns in the entire system as well as flow rates in predefined positions for reduced and zero cardiac output were evaluated.

Results: Cannula position influences flow patterns and flow rates in the entire thoracic aorta. For a residual cardiac output, a larger anastomosis and a decreased flow rate of the LAVD result in a higher flow rate and smaller retrograde flow in the ascending aorta when compared with a smaller anastomosis or a cannula position in the descending aorta. Pronounced flow turbulences in the aorta were observed for the cannula position in the descending aorta.

Conclusions: In the setting of reduced cardiac output, as commonly observed in patients on LVAD therapy, a large anastomosis to the ascending aorta for the outflow cannula induces the least-adverse flow patterns in the aortic root. Our approach may aid in a better understanding of LVAD-induced flow-pattern changes. Optimization of the cannula position and anastomosis may help to prevent the progression of aortic valve-regurgitation and thrombus formation.