Adoption and effectiveness of internal mammary artery grafting in coronary artery bypass surgery among Medicare beneficiaries.
OBJECTIVE
The aim of this study was to assess the pattern of the adoption of internal mammary artery (IMA) grafting in the United States, test its association with clinical outcomes, and assess whether its effectiveness differs in key clinical subgroups.


BACKGROUND
The effect of IMA grafting on major clinical outcomes has never been tested in a large randomized trial, yet it is now a quality standard for coronary artery bypass graft (CABG) surgery.


METHODS
We identified Medicare beneficiaries ≥66 years of age who underwent isolated multivessel CABG between 1988 and 2008, and we documented patterns of IMA use over time. We used a multivariable propensity score to match patients with and without an IMA and compared rates of death, myocardial infarction (MI), and repeat revascularization. We tested for variations in IMA effectiveness with treatment × covariate interaction tests.


RESULTS
The IMA use in CABG rose slowly from 31% in 1988 to 91% in 2008, with persistent wide geographic variations. Among 60,896 propensity score-matched patients over a median 6.8-year follow-up, IMA use was associated with lower all-cause mortality (adjusted hazard ratio: 0.77, p < 0.001), lower death or MI (adjusted hazard ratio: 0.77, p < 0.001), and fewer repeat revascularizations over 5 years (8% vs. 9%, p < 0.001). The association between IMA use and lower mortality was significantly weaker (p ≤ 0.008) for older patients, women, and patients with diabetes or peripheral arterial disease.


CONCLUSIONS
Internal mammary artery grafting was adopted slowly and still shows substantial geographic variation. IMA use is associated with lower rates of death, MI, and repeat coronary revascularization.
Stanford University School of Medicine, Stanford, California. Electronic address: hlatky@stanford.edu.
Mark A
MA
Hlatky
Stanford University School of Medicine, Stanford, California.
Derek B
DB
Boothroyd
Stanford University School of Medicine, Stanford, California.
Bruce A
BA
Reitz
Stanford University School of Medicine, Stanford, California.
David A
DA
Shilane
Stanford University School of Medicine, Stanford, California; National Bureau of Economic Research, Cambridge, Massachusetts.
Laurence C
LC
Baker
Division of Research, Kaiser Permanente Northern California, Oakland, California.
Alan S
AS
Go
D000368:Aged; D000369:Aged, 80 and over; D001026:Coronary Artery Bypass / Q000191:economics* / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008323:Mammary Arteries / Q000637:transplantation*; D006278:Medicare / Q000191:economics*; D009203:Myocardial Infarction / Q000191:economics / Q000601:surgery*; D012189:Retrospective Studies; D015996:Survival Rate / Q000639:trends; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology
CABG; CI; DES; HR; ICD9-CM; IMA; International Classification of Diseases, Ninth Revision-Clinical Modification; MI; PAD; PCI; comparative effectiveness research; confidence interval; coronary artery bypass graft surgery; drug-eluting stent(s); hazard ratio; internal mammary artery; internal mammary-coronary artery anastomosis; myocardial infarction; outcomes research; p value for the treatment × covariate interaction test; p(int); percutaneous coronary intervention; peripheral arterial disease