HeartMate II Explants Due to Hemolysis Show Acute on Chronic Laminar Fibrin Layering at Stators

Purpose The progression of hemolysis to LVAD thrombosis is incompletely understood. Despite antiplatelet therapy and anticoagulation with coumadin, clot formation within LVADS occurs at a variable rate, leading to LVAD dysfunction and ultimately failure. Clot progression and anatomy is poorly defined. Understanding the location and structure of clot may help in its treatment and target prevention. Methods and Materials 266 Patients had HM2s placed between 2007-2012. Six devices were explanted and preserved specifically for pathologic analysis. HM2 were evaluated in 3 areas (inlet stator [IS], outlet stator [OS], rotor assembly [RA]). Tissues were with hematoxylin and eosin. Microscopic evaluation for cells including fibroblasts, macrophages, red cell and bacteria were performed. Results The average support time was 292±533 (34-1377) days. LDH prior to explant was 4434±3511 (703-8884). No cells were found at the core of any of the clots. All patients had both coumadin and aspirin therapy. [Table 1] [ figure 1 ] Conclusions Stator build-up occurs within 30 days of HM2 implantation. The microscopic structure is the same at the stator bearings, whether it was 34 days or 1377 days. This appears to be an interaction of heat and blood components as cells are absent at the core. RA clot has a similar concentric chronic layering found in the stator, suggesting that RA clot may be extension of the process on the stator bearing vs acute thrombus. Medical therapy targeting fibrin formation may lead to reduced fibrin load on the bearing and decease pump dysfunction. CLOT Support(Days) Inlet Stator Rotor Outlet Stator Fibrin Layering Pump 1 1377 Y N Y Y Pump 2 127 Y N Y Y Pump 3 66 Y Y N Y Pump 4 34 Y Y Y Y Pump 5 57 Y Y Y Y Pump 6 88 N N Y Y