Nitroglycerin is preferable to diltiazem for prevention of coronary bypass conduit spasm. 
Diltiazem is widely used to prevent radial artery spasm after coronary bypass grafting (CABG).  However, recent in vitro and in vivo studies have shown that nitroglycerin is a superior conduit vasodilator compared to diltiazem.  A clinical comparison of these agents in patients undergoing CABG has not been previously performed.  One hundred sixty-one consecutive patients undergoing isolated CABG with the radial artery were prospectively randomized to 24-hour intravenous infusion of nitroglycerin or diltiazem followed by 6-month treatment with a daily dose of isosorbide mononitrate (n = 84) or diltiazem CD (n = 77).  Analyses were performed on "intention-to-treat" basis.  Crossovers because of low cardiac output, complete heart block, or sinus bradycardia occurred in 5 patients in the diltiazem group and none in the nitroglycerin group (p = 0.05).  Operative mortality (nitroglycerin, 1.2% versus diltiazem, 1.3%), major morbidity (14% versus 16%), perioperative myocardial infarction (1.2% versus 0%), peak serum creatinine phosphokinase MB fraction levels (27 versus 21 U), intensive care unit stay (34+/-19 versus 38+/-30 hours) and total hospital length of stay (4.7+/-1.4 versus 4.7+/-1.3 days) were similar (p = not significant for all).  Cardiac pacing was required more often in the diltiazem group (28% versus 13%, p = 0.01).  Follow-up longer than 2 months was available in 145 patients (90%).  Follow-up mortality (nitroglycerin, 1.2%; diltiazem, 1.3%), myocardial infarction (6%, versus 5%), and reintervention (8% versus 6%) rates and average angina class (1.3+/-0.7 versus 1.1+/-0.4) were similar (p = not significant for all).  Thallium stress test obtained in 117 patients showed abnormal perfusion in the radial artery territory in only 4 patients (3%), 2 in each group (p = not significant).  Treatment with diltiazem was more costly ($16,340 versus $1,096).  Nitroglycerin is preferable to diltiazem for prevention of conduit spasm.  Nitroglycerin is safe, effective, better tolerated, and less costly than diltiazem, and therefore, should be the agent of choice.