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Left Internal Mammary Artery Usage in Coronary Artery Bypass Grafting: A Measure of Quality Control

S Karthik and BM Fabri
Ann R Coll Surg Engl 2008; 85(4):367-69.

Over the last two decades, many studies have shown better long-term patency rates and survival in patients undergoing coronary artery bypass grafting (CABG) with left internal mammary artery (LIMA) to the left anterior descending artery (LAD).
Although the current focus in the UK is on mortality rates, we believe that it will not be long before this will also include the incidence of major morbidity after CABG such as stroke, myocardial infarction (MI), renal failure and sternal wound problems. We also believe that we should now consider LIMA usage as a marker of quality control in CABG. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1964611/

This study very clearly demonstrated that:

1. Approximately 4% of all patients undergoing first-time CABG do not need a graft to the LAD.
2. Of the rest, about 92% receive LIMA to LAD.

Six sub-groups of patients in whom LIMA usage was significantly less were:

(i) the elderly (> 70 years of age);

(ii) females;

(iii) diabetics;

(iv) patients having emergency CABG;

(v) poor left ventricular (LV) function (ejection fraction [EF] < 30%); and

(vi) respiratory disease.

LIMA usage was also reduced in patients undergoing combined CABG and valve procedures.

Multiple arterial grafts improve late survival of patients undergoing CABG

BACKGROUND: Use of the left internal mammary artery (LIMA) in multivessel coronary artery disease improves survival after coronary artery bypass graft surgery; however, the survival benefit of multiple arterial (MultArt) grafts is debated. (Perhaps not without reason. One problem is the small size of the left circumflex artery, and where does the right coronary artery have a place?)
METHODS : We reviewed 8622 Mayo Clinic patients who had isolated primary coronary artery bypass graft surgery for multivessel coronary artery disease from 1993 to 2009. Patients were stratified by number of arterial grafts into the LIMA plus saphenous veins (LIMA/SV) group (n=7435) or the MultArt group (n=1187). Propensity score analysis matched 1153 patients.
RESULTS: Operative mortality was 0.8% (n=10) in the MultArt and 2.1% (n=154) in the LIMA/SV (P=0.005) group.This result was not statistically different (P=0.996) in multivariate analysis or the propensity-matched analysis (P=0.818).
Late survival was greater for MultArt versus LIMA/SV (10- and 15-year survival rates were 84% and 71% versus 61% and 36%, respectively [P<0.001], in unmatched groups and 83% and 70% versus 80% and 60%, respectively [P=0.0025], in matched groups). The large difference between the MultiArt versus the LIMA/SV appears to be the 61% and 36% in unmatched and 80% and 60% in matched, evident at 15-years, favorable for the MultiArt group.
MultArt subgroups with bilateral internal mammary artery/SV (n=589) and

• bilateral internal mammary artery only (n=271) had improved 15-year survival (86% and 76%; 82% and 75% at 10 and 15 years [P<0.001]), and
• bilateral internal mammary artery/radial artery (n=147) and LIMA/radial artery (n=169) had greater 10-year survival (84% and 78%; P<0.001) versus LIMA/SV.

In multivariate analysis, MultArt grafts remained a strong independent predictor of survival (hazard ratio, 0.79; 95% confidence interval, 0.66-0.94; P=0.007).

CONCLUSIONS:

In patients undergoing isolated coronary artery bypass graft surgery with LIMA to left anterior descending artery,

• arterial grafting of the non-left anterior descending vessels conferred a survival advantage at 15 years compared with Saphenous Venous (SV) grafting.

It is still unproven whether these results apply to higher-risk subgroups of patients.