The effects of botulinum toxin A and papaverine on human saphenous vein and internal mammary artery grafts: an in vitro study

Introduction: Autologous saphenous vein (SV) and internal mammary ar-tery (IMA) are used as bypass conduits during coronary artery bypass graft surgery. Vasospasm of the arterial and venous grafts may constitute a sig-nificant 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 ef-fects and time-dependent changes of botulinum toxin A (BTX-A) and pa-paverine pretreatment on vasospasm of human SV and IMA grafts. Also, histomorphology of the vessels was assessed.Material and methods: SV and IMA segments were suspended in organ baths, and isometric contraction responses to 2 different concentrations of 5-hydroxytryptamine (5-HT) and endothelin-1 (ET-1) were recorded after in-cubation with 2 different concentrations of BTX-A and papaverine at 2 time points (0 h and 2 h).Results: The results revealed the following: 1) incubation with BTX-A and papaverine relaxes both SV and IMA rings contracted with 5-HT and ET-1; 2) the duration of the relaxant effect of BTX-A lasts longer than papaverine; and 3) no apparent histomorphological changes were 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. The long-lasting vasodilatory effect of BTX-A on vascular smooth muscle may provide promising results in the prevention of venous and arterial graft spasm.