Polypropylene small-diameter vascular grafts.

Polypropylene's physical properties (e.g., high tensile strength) and relatively inert behavior suggest that fabrication into an arterial substitute may result in an efficacious prosthesis. Grafts were woven from polypropylene yarn into conduits 4 mm I.D. x 50 mm in length. Control grafts were Dacron and ePTFE. Baseline platelet aggregometry on all dogs was performed with 10(-5) M ADP. Aspirin and dipyridamole were given for three days preoperatively and maintained for 2 weeks after surgery. Fifty-four grafts were placed into the aortoiliac position, two different graft materials per dog. The grafts were explanted at intervals of 2 weeks through 16 months; photographed for thrombus-free surface area determinations; and preserved for light, scanning, and transmission electron microscopy. Late (4-16 month) patency was 81% (13/16) for polypropylene, 69% (9/13) for Dacron, and 20% (1/5) for ePTFE. These data include one year patencies of 11/12 (92%) for polypropylene and 7/10 (70%) for Dacron. Late patency for polypropylene grafts was better than for PTFE (p less than 0.05). Platelet aggregation status did not predict graft patency. Light microscopy of 2-week polypropylene explants showed inner capsules composed of myofibroblasts and macrophages, with patchy areas of endothelial cells lining the lumen. By 1 month, a confluent endothelialized surface was seen in all polypropylene explants. Progressive thickening of inner capsules with myofibroblasts and collagen continued through 4 months, reaching a mean thickness of 142 +/- 50 microns (compared to 150 +/- 30 microns for Dacron). These findings suggest potential clinical efficacy for polypropylene as an arterial substitute.

Partially bioresorbable vascular grafts in dogs.

Previous studies have shown the effectiveness of partially resorbable arterial prostheses in the rabbit. This study compares these same compound prostheses with commercial graft materials in the dog. Conduits 4 mm inner diameter X 50 mm in length were woven from composite yarns containing 69% polyglactin 910 (PG910)/31% polypropylene or containing 70% polydioxanone/30% polypropylene. Nonresorbable controls were woven Dacron and expanded polytetrafluoroethylene (ePTFE). Baseline platelet aggregometry to 10(-5) mol/L adenosine diphosphate was performed. Seventy prostheses were implanted into the aorto-ilac positions, and the prosthesis/tissue complexes were harvested serially from 2 weeks to 1 year. Explanted specimens were photographed and fixed for light microscopy and for scanning and transmission electron microscopy. Results showed no aneurysms or perigraft hematomas. Overall patency for the PG910/polypropylene grafts was 18 of 20 (90%) and for polydioxanone/polypropylene was 19 of 22 (86%). For Dacron and ePTFE, 13 of 19 (68%) and 6 of 11 (54%) remained patent at time of explantation. The partially resorbable grafts, as a group, had significantly greater patency than the control grafts (p less than 0.03). Platelet aggregometry was not predictive of graft patency. Histologic analysis of the partially bioresorbable groups showed inner capsules (IC) composed of myofibroblasts and collagen beneath confluent endothelialized surfaces by 1 month. Kinetics of IC formation paralleled the rates of resorption of the resorbable components. IC cellularity and thickness were greater than those within Dacron or ePTFE. This study suggests an enhanced transinterstitial endothelial cell and myofibroblast ingrowth into the ICs of partially resorbable grafts and shows the effectiveness of these prostheses in the dog.

The validity of canine platelet aggregometry in predicting vascular graft patency.

Several laboratories have found canine platelet aggregometry predictive of thrombotic potential in vascular grafts. Adenosine diphosphate (ADP) is a frequently used agonist, often at unspecified or differing concentrations. This study was designed to evaluate the predictive value of ADP-induced platelet aggregometry and the validity of the methodology. Platelet aggregometry in response to 2 x 10(-5) M ADP was assayed in 70 dogs. Twenty-six percent were aggregators, 51% were non-aggregators, and 20% were indeterminant. All dogs were then treated with aspirin and dipyridamole. Vascular prostheses were implanted bilaterally (aorto-iliac) and anti-platelet therapy continued for two weeks. Dose-response to ADP was studied at three concentrations in 20 dogs. At 2 x 10(-5) 1/20 aggregated, at 4 x 10(-5) 3/19 aggregated and at 2 x 10(-4) 15/20 aggregated. Time between samples and study was evaluated in 11 dogs, with 2/11 changing from non-aggregator to aggregator at two or three hours. Daily reproducibility was studied in 70 dogs, 14 of which changed aggregation status between days. Patency was 58/68 (85%) for non-aggregators, 23/34 (68%) for aggregators (p = 0.038). Platelet aggregometry has significant predictive value for graft patency but methodology must be specified and standardized.

Platelet interactions with heparin binding growth factor and fibronectin.

A fibronectin (Fn)/heparin/heparin binding growth factor (HBGF)/heparin (FHHH) complex can be affixed to vascular grafts. This study examines the effect of HBGF, Fn, and FHHH on platelet adhesion and aggregation. Expanded polytetrafluoroethylene (PTFE) grafts (5 cm X 4 mm) were treated with Fn (n = 9), FHHH (n = 9), or neither (n = 10) and interposed into canine aortoiliac systems, using each dog as its own control. Autogenous radiolabeled (111In oxine-650 muCi) platelets were injected IV prior to re-establishment of circulation. Blood flow was determined by electromagnetic flowmetry and perfusion maintained for 30 min. Grafts were removed with native aorta and ipsilateral iliac arteries (IIA). Specimens, excluding anastomoses, were sectioned for gamma counting and computerized planimetry. Results showed that FHHH and Fn treated grafts contained significantly more radioactivity than control segments, when normalized to their IIA. FHHH treated grafts contained 27 +/- 16 times more radioactivity per mm2 than IIA, Fn treated prostheses 12 +/- 8 times more, and untreated PTFE 4 +/- 3 times more. FHHH was significantly more radioactive than Fn alone (p less than or equal to 0.03). Platelet aggregation in response to either Fn or HBGF was studied in vitro. Aggregation was not activated by either Fn (1-100 micrograms/100 microliters) or HBGF (25-2,500 ng/100 microliters). These data suggest that Fn and HBGF promote platelet adhesion but not aggregation.