Is vitamin C superior to diltiazem for radial artery vasodilation in patients awaiting coronary artery bypass grafting?

Abstract

Objectives: We aimed to measure the vasodilating effects of vitamin C on the radial arteries of healthy subjects and to assess whether vitamin C is superior in this regard to diltiazem, a commonly used vasodilator in coronary artery bypass using radial conduits. Methods: In a case-control study (study 1) oral single-dose vitamin C (2 g) was given to 15 healthy nonsmokers and 15 matched otherwise healthy smokers. In a randomized double-blind study (study 2) oral single-dose vitamin C (2 g, n = 15) and diltiazem (180 mg, n = 15) were compared in preoperative patients with coronary artery disease. We examined the dilation of the radial artery with highresolution ultrasonography and measurement of the lumen surface and color Doppler images of the nondominant radial artery just before and 2 hours after drug administration. Results: In study 1 both smokers and nonsmokers showed a significant increase in the lumen surface at 2 hours compared with at baseline (P < .001 and P = .013, respectively). The increase was larger in smokers (median, 37.5% vs 14.3%; P = .004). In study 2 both groups showed statistically significant increases in the lumen surface at 2 hours compared with at baseline (P < .001 and P = .008 for vitamin C and diltiazem, respectively). Vitamin C achieved a larger increase than diltiazem (median, 33.3% vs 18.2%; P = .016). In multivariate modeling the increase in lumen surface was independently predicted by use of vitamin C over diltiazem (+21.2%, P = .007), diabetes mellitus (+14.5%, P = .085), increased cholesterol (+26.2%, P = .001), and smoking history (+20.8%, P = .017). Conclusions: Vitamin C is a potent acute vasodilator in both smokers and nonsmokers and is superior to diltiazem in preoperative coronary patients who need protection from vasospasm of the radial conduit.