Nitroglycerin is superior to diltiazem as a coronary bypass conduit vasodilator

Background: Recent reports of improved radial artery patency have been attr ibuted, in part, to routine use of diltiazem to prevent vasospasm, However, diltiazem is costly, and its use may be associated with negative inotropic and chronotropic side effects, This study compares the vasodilatory proper ties of diltiazem to those of nitroglycerin. Methods: In vitro, with the us e of organ chambers, the vasodilatory properties of diltiazem and nitroglyc erin were compared in matched segments of radial artery, internal thoracic artery, and saphenous vein that were harvested from the same patients (n = 11), The vasodilatory response of the radial artery to intravenous diltiaze m or nitroglycerin was compared in vivo (n = 10) with the use of ultrasonog raphic measurements of radial artery diameter. Results: The maximum relaxat ion of radial artery (100% +/- 4%), internal thoracic artery (96% +/- 4%), and saphenous vein (100% +/- 3%) to nitroglycerin were significantly greate r than the response to diltiazem (33% +/- 6%, 22% +/- 7%, and 34% +/- 5%, r espectively; P <.001), The thromboxane mimetic, U46619, induced radial arte ry spasm with a median effective concentration of 3.7 +/- 0.8 nmol/L, Physi ologic concentrations of nitroglycerin (0.1 mu mol/L) significantly inhibit ed the radial artery response to U46619 (median effective concentration, 6. 2 +/- 1.1 nmol/L; P =.046), whereas diltiazem (1 mu mol/L) did not (median effective concentration, 3.7 +/- 0.8 nmol/L; P =.64), In vivo, nitroglyceri n increased radial artery diameter 22% +/- 3%, which was significantly grea ter than diltiazem (3% +/- 0.5%; P =.001). Conclusion: Nitroglycerin is a s uperior conduit vasodilator and is more effective in preventing graft spasm than diltiazem, Nitroglycerin should be strongly considered as the drug of choice to prevent conduit spasm after coronary bypass grafting.