The Journal of Thoracic and Cardiovascular Surgery, Vol 99, 107-112, Copyright © 1990 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. II. Modification of early changes by platelet inhibition with aspirin and dipyridamole
LE Boerboom, GN Olinger, TZ Liu, ER Rodriguez, VJ Ferrans and AH Kissebah
Department of Cardiothoracic Surgery, Medical College of Wisconsin, Milwaukee.
The objective of this study was to determine the early influence of
platelet inhibition on the histologic, morphometric, and biochemical
evolution of vein bypass grafts in a nonhuman primate model. Cephalic vein
grafts were interposed bilaterally in the femoral arteries of 15
stump-tailed macaque monkeys fed a diet that sustains plasma cholesterol
levels of approximately 225 mg/dl. All animals received in combination
aspirin, 80 mg/day, and dipyridamole, 50 mg/day. Grafts were excised from
five animals for analysis on each of postoperative days 3, 7, 14, 30, 60,
and 90. In animals subjected to platelet inhibition, cholesterol content in
the graft was 170 +/- 52 micrograms/100 mg at 90 days, 205% of the level in
ungrafted vein (p less than 0.01). This change was small in comparison with
the increase to 686% of ungrafted vein observed in our study of control
animals. In stepwise regression analysis, cholesterol content of grafts was
best predicted by prevalence of foam cells (r2 = 0.82), and the proportion
of intima as a fraction of total wall area was best predicted by the
presence of macrophages (r2 = 0.69). Platelet inhibition did not decrease
the extent of intimal hyperplasia. The prevalence of adherent platelets (r
= -0.72) and the amount of fibrin (r = -0.78) correlated inversely with the
amount of endothelium present during the first 14 days. The strength of
these correlations declined with time, despite persistent lack of
endothelium in some areas. Medial fibrosis occurred to the same extent as
in control grafts, as did the early appearance of platelet factor VIII and
fibronectin and the lack of vasa vasorum at 3 days followed by reappearance
at 7 days. These data demonstrate that platelet inhibition dramatically
reduces lipid uptake by grafts in the first 90 days but has less influence
over histologic or morphometric changes.
