Background: Injury to the smooth muscle cells of the media affects the remodeling process of vein grafts. The purpose of this study was to determine whether different techniques of surgical preparation influence the degree of medial smooth muscle injury.
Methods: Carotid-saphenous vein interposition grafting was performed in crossbred pigs (n = 32), using distended (n = 16) or nondistended (n = 16) conduits. After 3 to 90 days, the media was evaluated for the presence of smooth muscle cells (desmin stains), myofibroblast formation (transient alpha-SM actin expression), and apoptosis (TdT-mediated dUTP nick end-labeling [TUNEL]).
Results: Smooth muscle loss was uniformly severe; only 5% +/- 5% (p < 0.01) and 14% +/- 9% (p < 0.01) of the medial area of distended and nondistended veins were desmin positive in comparison with 80% +/- 9% of controls. Apoptosis appeared to contribute to medial smooth muscle loss (5.7% +/- 4.3% in vein grafts versus 0.0% +/- 0.0% of TUNEL-positive cells in controls; p = 0.05). There was a time dependent increase in medial myofibroblast formation (p < 0.05).
Conclusions: Severe medial smooth muscle loss occurs in vein grafts, even when prepared without distension. Apoptosis contributes to the early disappearance of smooth muscle cells. Adjunctive measures, in addition to ideal surgical techniques, should be developed to prevent medial muscle loss.