Leskosek B

Evaluation of phospholipidic surface coatings ex-vivo.

To evaluate the thromboresistant properties of phospholipidic surface coatings mimicking the lipid surface of blood cells, we studied four different types of phospholipids bound onto PVC tubings in comparison to uncoated as well as heparin bonded controls. The samples analyzed included diacetylenic phospholipid coated as a monomeric treatment (A), diacetylenic phospholipid polymerised prior to being coated (B), and two types of polymeric phospholipids made using methacrylate containing monomers (C and D). A bovine (bodyweight 67 ± 3 kg) left heart bypass model (pump flow 3.2 ±0.1 l/min) was selected and the surfaces were exposed to the blood stream up to 360 min without systemic heparinization. Thereafter another set of samples was exposed to stagnant blood over 20 min. Besides hemodynamic, hematologic and biochemical analyses, the macroscopic appearance of 119 blood exposed surface samples was graded semiquantitatively on a scale of 0 to 10: no macroscopic deposits = grade 0, 1 spot (1 mm diameter) = grade 1, 2 spots = grade 2, 5 or more spots = grade 5, up to 10% of the surface covered with clots = grade 6, 100% covered = grade 10 (p<0.05=∗): mean grade of deposits was 0.0 ± 0.0 for segments perfused and 0.0 ± 0.0 for segments exposed to stagnant blood with surfaces exposing to the blood either heparin, phopholipid A, or phospholipid B (NS). Phospholipids C and D were graded 0.0 ± 0.0 if perfused and 0.7 ± 1.2 if exposed to stagnant blood. Uncoated PVC control tubings however were graded 0.2 ± 0.8 for segments perfused and 2.7 ± 3.0 for segments exposed to stagnat blood (p<0.05 in comparison to all surfaces coated with phospholipids or heparin if perfused and if exposed to stagnant blood). Hence phospholipidic surface coatings expose significant antithrombotic properties which out perform todays standard for tubings in clinical perfusion (uncoated PVC).

Improved biocompatibility of heparin surface-coated ventricular assist devices.

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.

Biomembrane mimicry provides improved thromboresistance for total artificial hearts.

Thromboembolic events remain a significant issue in mechanical circulatory support. The aim of this study was to evaluate the potential benefit of surface modification in total artificial hearts (TAHs) using polymeric phospholipids (biomembrane mimicry). For this purpose, pneumatic TAHs (vacuum formed pellethane housing, hard double flap hinged inflow valves, soft trileaflet polyurethane outflow valves) had their blood-exposed surfaces either modified with polymeric phospholipids or unmodified before evaluation in bovine experiments. Orthotopic implantation of the TAHs was performed with cardiopulmonary bypass (CPB) using tip-to-tip heparin surface coated perfusion equipment and very low systemic heparinization (50 IU/kg bodyweight). After weaning from CPB and stabilizing hemodynamics, circulating heparin was neutralized with protamine (1:1). All animals were totally supported for 24 hours before elective sacrifice. No heparin was added at any time during support. Mean activated coagulation time (ACT) was 167+/-24 s at baseline before heparinization for CPB, 330+/-45 s at the end of CPB, 181+/-25 s after 1 hour of support, 180+/-31 s after 6 hours, and 185+/-28 s after 18 hours. After explantation, the TAHs perfused without anticoagulation were carefully analyzed. Atrial cuff coverage with red clot was 30+/-21% for artificial surfaces modified by biomembrane mimicry versus 100+/-0% for standard control surfaces (p<0.01). The number of macroscopic deposits found on the inflow valves was 1.33+/-0.47 for surfaces modified by biomembrane mimicry versus 3.83+/-1.86 for standard control surfaces (p<0.05). Likewise, on the outflow valves the number of macroscopic deposits was 0.00+/-0.00 for surfaces modified by biomembrane mimicry versus 1.00+/-0.81 for standard control surfaces (p<0.05). We conclude that presence and distribution of red clots and other macroscopic deposits are significantly different for artificial surfaces with biomembrane mimicry versus standard control surfaces. Application of the biomembrane mimicry concept has the potential to provide improved TAHs.

Heparin surface coated hard shell venous reservoirs: experimental evaluation ex vivo.

The present study was designed for ex vivo evaluation of a heparin coated hard shell venous reservoir in comparison to uncoated control reservoirs. An open chest bovine right heart bypass model (n=9, bodyweight 72 ± 6 kg) with passive blood drainage from the right atrium into the venous reservoir and active retransfusion into the pulmonary artery (roller pump) was selected for this purpose. Clear priming was used for the open perfusion circuit. No heparin was given before or during the evaluation period which was scheduled for 6 hours. Reservoir blood flow was at the beginning 3.5 ± 0.6 I/min for coated versus 3.4 ± 0.3 l/min for uncoated (NS). After 6 hours, blood flow was 3.3 ± 0.1 I/min for coated versus 2.7 ± 0.4 l/min for uncoated (p<0.05). Hematocrit moved from a baseline level of 30 ± 2% for coated versus 28 ± 3% for uncoated (NS) to 28 ± 3% for coated versus 27 ± 5% for uncoated (NS) after 6 hours. Prebypass platelet levels of 100% in both groups moved to 84 ± 3% for coated versus 78± 23% for uncoated (NS) after 6 hours. Activated coagulation time (ACT) before bypass was 148 ± 12 s for coated and 153 ± 6 s for uncoated (NS). After 6 hours, ACT was 160 ± 9 s for coated versus 152 ± 5 s for uncoated (NS). Thrombin time before bypass was 15 ± 2 s for coated versus 16 ± 2 s for uncoated (NS). After 6 hours, thrombin time was 17 ± 2 s for coated versus 18 ± 4 s for uncoated (NS). Baseline antithrombin III levels were 91 ± 25% for coated versus 96 ± 17% for uncoated (NS). After 6 hours antithrombin III levels were 95 ± 23% for coated versus 93 ± 19% for uncoated (NS). Baseline fibrinopeptide A levels were 2.6 ± 0.4 ng/ml for coated versus 2.6 ± 0.8 ng/ml for uncoated (NS). After 10 minutes of perfusion fibrinopeptide A moved to 4.8 ± 0.9 ng/ml for coated versus 8.8 ± 3.2 ng/ml for uncoated and reached 10.7 ± 2.6 ng/ml after 2 hours for coated versus 15.3 ± 0.1 for uncoated (p<0.01). We conclude, that despite the open perfusion mode, the tested heparin surface coated venous hard shell reservoirs have improved thromboresistance. Heparin surface coating increases the reservoir flows and reduces fibrinopeptide A production.