Introduction:
Autologous saphenous vein (SV) and internal mammary artery (IMA) are used as bypass conduits during coronary artery bypass graft surgery. Vasospasm of the arterial and venous grafts may constitute a significant clinical problem. Pretreatment with a vasodilator drug of the graft ex vivo or intraluminal injection before implantation may be used for spasm prophylaxis. This in-vitro study was designed to assess the vasoactive effects and time-dependent changes of botulinum toxin A (BTX-A) and papaverine pretreatment on vasospasm of human SV and IMA grafts. Also histomorphology of the vessels were assessed.

Material and methods:
SV and IMA segments were suspended in organ baths and isometric contraction responses to two different concentrationsof 5-hydroxytryptamine (5-HT) and endothelin-1 (ET-1) were recorded after incubation with two different concentrations of BTX-A and papaverine at two time points (0 hours and 2nd hour).

Results:
The results suggest that; 1) incubation with BTX-A and papaverine relaxes both SV and IMA rings contracted with 5-HT and ET-1, 2) duration of the relaxant effect of BTX-A lasts longer than papaverine, 3) no apparent histomorphologic changes are observed in the grafts under light microscopy.

Conclusions:
This study demonstrates that in human SV and IMA grafts, pretreatment with both BTX-A and papaverine are safe and have a potent inhibitory effect depending on the vessel and vasoconstrictor agent. Long lasting vasodilatory effect of BTX-A on vascular smooth muscle may provide promising results for preventing venous and arterial graft spasm.