Improved Biocompatibility of Heparin Surface-Coated Ventricular Assist Devices

Abstract

Heparin surface coated ventricular assist devices (VADs) and cannulas were evaluated in comparison to uncoated VADs in 10 bovine experiments (body weight 77 ± 6 kg). All systems were primed with cristalloid solution. No systemic heparin was given. Left ventricular assist was started with a blood flow of 4.2 ± 0.4 l/min and maintained over 6 hours. Besides hemodynamic monitoring, blood samples were taken at regular intervals for blood gas, hematological, biochemical and coagulation studies. All animals in the study group (coated) were assisted for the scheduled 6 hours without device failure. In the control group, however, total occlusion occurred in 1 VAD after 1 hour of left ventricular assist whereas the other 4 VADs remained functional throughout the protocol. Mixed venous oxygens saturation was preassist 56 ± 12% for coated versus 63 ± 11% for uncoated and the final value at 60 minutes after weaning was 58 ± 16% versus 59 ± 5% (NS). Mean hematocrit dropped from a baseline value of 33 ± 4% for coated versus 29 ± 8% for uncoated to 29 ± 7% versus 30 ± 5% (NS) after 6 hours of assist. There was no significant difference between the baseline values (5.7 ± 3.0/jmol/l for coated versus 4.6 ± 3.1/umol/l for uncoated) and the 6-hour values (3.8 ± 3.7/umol/l versus 7.6 ± 6.4/jmol/l) for mean plasma hemoglobine. The normalized platelet levels dropped after 10 minutes of assist to 91 ± 21% for coated versus 94 ± 49% for uncoated (NS) and 89 ± 29% versus 65 ± 44 at 6 hours (NS). The activated clotting time evolved from a baseline value of 127 ± 12 s for coated versus 131 ± 5 s for uncoated (NS) to 122 ± 17 s versus 139 ± 18 s at 60 minutes after assist (NS). Renal embolus score showed a mean level of 11 ± 8 for coated versus 15 ± 12 for uncoated. The VAD clot score showed a mean level of 0.2 ± 0.4 for coated versus 2.2 ± 1.6 for uncoated (p < 0.5). We conclude, that heparin coating of blood exposed surfaces provides significant improvement of VAD biocompatibility.