Prospective Evaluation of Urine Dipstick for Detection of Significant Hemolysis in Outpatients on CF-LVAD Support

Purpose: The mechanism of left ventricular assist device (LVAD) thrombosis initiation and propagation is unknown. Correctly identifying the thrombi components could aid in directing therapy for patients with suspected LVAD thrombosis. Methods: H&E staining was used for histologic analysis of thrombi removed from HeartMate II (HMII) devices explanted at the University of Louisville. Immunohistochemistry identified platelets and neutrophils using antibodies against CD42b (glycoprotein Ib) and myeloperoxidase, respectively. Age of fibrin was assessed by Martius, Scarlet, Blue staining. Results: 28 thrombi from 17 LVADs were analyzed. Four pumps only had an inlet bearing thrombus, 3 pumps only had a rotor vein thrombus, and 2 pumps only contained an outlet bearing thrombus. Seven pumps had clots in multiple locations. In total, 72% of the thrombi (20/28) were either located around the inlet bearing (9), the rotor veins (5), or the outlet bearing (6). The laminated fibrin rings of the inlet stator thrombi were 150 -2618 microns thick. The inner rings had crosshatched fibrin followed by dense fibrin rings (Figure). Outer rings had mixed fibrin with less organized structure. Rings with higher densities of platelets and neutrophils were more commonly seen in the outer rings of rotor thrombi (Figure). Outlet bearing thrombi varied histologically, but most were similar to the rotor and inlet thrombi with increased areas of nuclear material. Three thrombi from the inlet conduit and three from outlet elbow were similarly structured and composed of loose meshwork with white blood cells and areas of layered fibrin. Platelets were present in dense areas. Conclusion: The fibrin density varied in clots formed in different parts of the HMII. Fibrin of different ages in the inlet bearing thrombi suggests development over time and reinforces the necessity of anticoagulation. The increased frequency of platelets in the outer rings of the inlet bearing thrombi would support further investigation into their role in thrombus propagation.