Development of a nonthrombogenic collagenous blood-prosthetic interface.

Investigations to develop an implantable assist pump for prolonged circulatory support have been impeded by accumulation of friable thrombus on the prosthetic interface, with subsequent embolization. To circumvent this problem, the textured, fibril surface of a polyurethane pump chamber (mat thickness 430 microns) was inoculated with cultured bovine fetal fibroblasts (labelled with thymidine-14C) prior to animal implantation. The pneumatically actuated device (stroke volume 75 ml), maintained a pulsatile blood flow throughout each study. In 20 calf experiments, extending up to 335 days, 30 X 10(6) fibroblasts (in 50 ml media) derived from a single Holstein fetus were distributed on the urethane surface (360 +/- 50 cells/mm2) by rotation of a sealed device for three hours (12 revolutions/hour). Following connection to the circulation, cell washout was minimal. Resultant biologic linings, examined after animal sacrifice, were densely adherent to the underlying polymer matrix, and varied in thickness from 250 micron-1.5 mm. Microscopically, fibroblasts were identified from the surface to base, accompanied by numerous collagen bundles and abundant ground substance. Amino acid analysis in 10/20 pumps implanted for 31--335 days, revealed 50 +/- 5 Hydroxyproline residues/1000 residues (50% collagen) and scant elastin. Donor fibroblasts were identified by radioautography and karyotyping. Lack of immunologic response in 12 Hereford pump recipients as confirmed by serial fibroblast cytotoxicity assays. In conclusion, an induced collagenous-blood interface permitted prolonged mechanical circulatory support in animals without thromboembolic complications.

Development of collagenous linings on impermeable prosthetic surfaces.

In an effort to accelerate development of a biologic lining on the fibrillar surface of a left ventricular assist pump, the blood-contacting interface was covered with bovine fetal fibroblasts immediately prior to implantation into the animal. Selection of these syngeneic cells was based on their demonstrated prolificacy and abundant collagen production. Comparative studies, carried out in 17 Holstein calves, indicated that an adherent, thin, collagenous lining developed on the fibroblast-seeded polyurethane pump chamber in nine animals. Similar implantations of eight non-cell-seeded (control) devices resulted in formation of a predominantly acellular, fibrinous membrane, varying in thickness from 1 to 8 mm. Pump chamber compliance was significantly reduced when the histologic surface exceeded 3 mm in thickness, resulting in impaired filling and an inadequate stroke volume. The use of 14C-thymidine-labeled fibroblasts permitted later identification of the donor cells in the collagenous linings by radioautography. Serial immunologic studies undertaken to detect evidence of rejection in recipient Holstein calves were negative.

Temporary left ventricular bypass: factors affecting patient survival.

Circulatory support (range, 2 hours-8 days) was undertaken in eight cardiac surgical patients (with two survivors) exhibiting intractable cardiogenic shock. A paracorporeal, pneumatic, xenograft-valve pump was interposed between the left ventricular apex and ascending aorta. Pumping lowered left atrial and ventricular pressure while maintaining cardiac output (1.8--2.6 l/min/m2). Following implantation, plasma hemoglobin and erythrocyte mechanical fragility values were elevated but decreased to normal when renal function was not impaired. Mild thrombocytopenia was noted in three patients and was severe in five others with persistent hemorrhage. Anticoagulation agents were used during tapering of pump flow (three patients) after 100, 105 and 120 hours of bypass. Otherwise, for the major portion of the interval of mechanical circulatory support, anticoagulants were not administered. Despite this fact, no systemic embolization was detected in any of the patients. It appears that assist pump support can be life-saving in acute left ventricular failure in patients following cardiac surgery.