Program: Oral and Poster Abstracts
Session: 331. Pathophysiology of Thrombosis: Poster I
Methods: Blood samples were collected peri-operatively and long-term post-operatively (until transplant or expiration) during normal clinic visits from 13 consented patients who were implanted with a HeartMate II LVAD (Thoratec, Pleasanton, CA). Fresh whole blood collected in 3.2% sodium citrate was centrifuged for platelet poor plasma then ultracentrifuged (20,000 g, 90 min) to pellet MPs. Aliquots of the MP rich samples were stained with the dye PKH67 (to identify biological membranes) then separated into five tubes containing either: Tyrode’s buffer (control), CD41-PE (platelets), CD45-PE [leukocytes (WBC]), CD146-PE [endothelium (EC)], or CD235-PE [erythrocytes (RBCs)]. Samples were analyzed on an EPICS XL flow cytometer (Beckman-Coulter, Miami, FL) to determine the presence and quantity of cellular MPs using an in-house assay. MPs were identified as PKH67(+) events with a size < 1µm based on size-defined polystyrene beads. Blood samples from 12 healthy individuals were processed in the same manner to establish normal MP levels. A database of clinical events in the LVAD patients was created from medical chart review and included LDH, platelet count, aPTT, D-dimer, fibrinogen and assessment of warfarin by INR. For each patient, clinical and MP data were graphed on a linear time scale; the day that the MP and the clinical values exceeded their ULN was identified and related to time of a clinical adverse event.
Results: MP levels in patients without adverse events during the follow-up period (2/13) remained below the ULN of 500 microparticles. Patients with thrombotic episodes (11/13) had elevated levels (2000 to 9000 microparticles) a median 50 days (range 35-391 days) prior to LDH elevation; MP levels reverted to normal following resolution of the event. Platelet and RBC MPs were elevated earlier and to a greater extent than MPs from WBCs and ECs. Some patients (2/11) only had an elevation of RBC MPs. Platelet counts were elevated up to 50 days post-surgery (12/13 patients), but levels were normal at time of the thrombotic event. There was no obvious association with adverse events for INR time out of therapeutic range or any other clinical parameter.
Discussion: Microparticle levels in VAD patients with thrombotic events were shown to cross the normal threshold weeks prior to the time when common clinical parameters indicated an abnormality, suggesting that changes in microparticle levels may be useful in predicting thrombotic events. Hypercoagulability in VAD patients can be influenced by a number of factors including exposure of blood to foreign surfaces, altered shear stresses, inflammation and infection. Data from this investigation warrants further study for the incorporation of microparticles into the clinical management of patients with implanted VADs and to determine whether the pattern of change in microparticle subtypes can identify the stimulus for pump thrombosis, leading to more effective prophylactic measures.
Disclosures: No relevant conflicts of interest to declare.
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