Eastern Cardiothoracic Surgical Society

Higher Rates of Graft Failure with Use of Free Versus In-Situ Internal Mammary Artery Bypass Grafts: Insights from the PREVENT-IV Trial
David Ranney1, Judson B. Williams1, Hillary Mulder2, Daniel Wojdyla2, Morgan L. Cox2, C. Michael Gibson2, Michael J. Mack2, Mani A. Daneshmand2, John H. Alexander2, Renato D. Lopes2 , 1WakeMed Physicians Practices, Raleigh, NC, 2 Duke University Medical Center, Durham, NC

OBJECTIVE: While in-situ internal mammary artery (i-IMA) grafting remains the most frequent conduit in CABG, circumstances may necessitate free grafting of the IMA (f-IMA), though differences in outcomes have not been fully characterized. The purpose of this study was to compare clinical and angiographic outcomes of i-IMA versus f-IMA coronary bypass grafts.

METHODS: Among the angiographic cohort of PREVENT IV, N=34 had at least one f-IMA graft and N=1,538 received at least one i-IMA graft. Characteristics of patients, procedure, and grafts/targets were compared between cohorts. Primary endpoints included death, MI, and revascularization, and incidence of graft failure (stenosis >75%) on angiography at 12-18 months post-operatively.

RESULTS: Patient receiving i-IMA grafts were more often of white race and higher weight. Distribution of elective versus urgent/emergent cases were similar between groups. Aortic cross clamp time was shorter in the f-IMA cohort (39.5 vs 57.0 min, p=0.04) but duration of bypass was similar (93.5 vs 100.0 minutes, p=0.793). Of the in-situ grafts, 97.3% were LIMA, 86.6% were of good quality, and the LAD was bypassed in 88.2%. This compares to free grafts which were LIMA in 68.0%, of good quality in 96.1%, and bypassed the LAD in 58.8% and OM1 in 23.5%. Rates of death, MI, and revascularization, and graft failure are reported in the Table.

CONCLUSIONS: Although clinical outcomes are similar with use of free versus in-situ IMA grafts, higher rates of graft failure are encountered with use of the f-IMA graft. In-situ grafts should thus remain the preferred conduit when permitted.

Association between IMA type and outcomes

Outcome Free IMA
Rate* (Count)
In Situ IMA
Rate (Count)
(95% CI)
Death 3.32 (5) 2.27 (166) 1.46 (0.60 – 3.54) 0.41
Myocardial Infarction 1.35 (2) 0.49 (35) 2.71 (0.65 – 11.25) 0.17
Revascularization 5.74 (7) 3.43 (224) 1.61 (0.76 – 3.41) 0.22






Odds Ratio

(95% CI)


Graft Failure (stenosis >75%) 23.33 (7/30) 8.51 (118/1387) 3.27 (1.38 – 7.79) <0.01

*Rate per 100 patient-years of follow-up. **Rate computed as raw frequency at the end of follow-up (1.5 years) of those who had an angiography.