Human intraperitoneal response to a left ventricular assist device with a Ti-6AI-4V alloy surface

The soft tissue reaction to long-term implantation of an intraperitoneal left ventricular assist device (LVAD) was investigated. The HeartMate 1000 (Thermo Cardiosystems, Inc., Woburn, MA) is a pneumatically driven blood pump with smooth titanium alloy (Ti-6AI-4V) outer surfaces that is placed intraperitoneally in the left upper quadrant and sutured to the anterior abdominal wall. It is being used currently as a bridge to cardiac transplant, which sometimes requires extended support times. We examined the tissue capsule that formed around the rigid circular pump housing of four LVADs (duration of implant: 61, 86, 128, and 153 days) for gross, histologic, immunohistochemical, and ultrastructural analysis. Immunostaining was performed using monoclonal and polyclonal antibodies against cytoskeletal tissue markers (vimentin, desmin, alpha-smooth muscle actin), T and B lymphocytes, carcinoembryonic antigen, factor VIII, and cytokeratins (CAM 5.2 AE1/AE3, 34 beta E12, and 35 beta H11). Direct fluorescent immunolabeling for fibrinogen was also performed to characterize cell and tissue type. Histologic analysis of the 3 to 4 mm thick capsule with white, glistening inner surfaces showed fibrovascular tissue with multipotential subserosal cells (MSCs), capillary endothelium, collagen, and a few mononuclear infiltrates. The immunohistochemical profile of the MSCs differed from myofibroblasts despite a morphologic similarity. Transmission electron microscopy revealed abundant rough endoplasmic reticulum and peripherally arranged myofilaments within the spindle shaped cells. It was hypothesized that capsule formation was initiated by fibrin deposition, followed by proliferation of MSCs and subsequent formation of fibrovascular tissue.(ABSTRACT TRUNCATED AT 250 WORDS)