Multiscale analysis of surface thrombosis in vivo in a left ventricular assist system

Thrombosis limits the success of ventricular assist devices as the demand for alternatives to heart transplants is increasing. This study mapped the occurrence of thrombosis in a left ventricular assist system (LVAS) to better understand the biologic response to these devices. Nine calves divided into two groups were implanted with LVAS for 28 to 30 days. One group was anticoagulated, whereas the second group received no long-term anticoagulation. The blood-contacting poly(urethane urea) surfaces of blood sacs in the LVAS were examined for macroscopic thrombi upon retrieval. The sac was partitioned into eight sections and imaged for thrombi by scanning electron microscopy. No difference in thrombosis was observed macroscopically between the groups. Anticoagulation appeared to result in reduction of platelet-like structures, but the presence of fibrin-like structures remained similar between groups. Regional differences correlating with high and low shear stress regions were observed. At the macroscale, fewer thrombi were recorded in the high shear stress ports. At the microscale, features resembling fibrin were observed primarily in the ports and platelet-like features were common in lower shear stress regions. These variations in thrombosis with anticoagulation and location are likely due to varied fluid dynamics within the LVAS blood sac.