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J Thorac Cardiovasc Surg 2006;131:1021-1028
© 2006 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

How many arterial grafts are enough? A population-based study of midterm outcomes

^a Division of Cardiovascular Surgery, University of Toronto, Toronto, Ontario, Canada
^b Division of General Internal Medicine, Sunnybrook and Women's College Health Sciences Centre, and the Institute for Clinical Evaluative Sciences, University of Toronto, Toronto, Ontario, Canada

Received for publication June 18, 2005; revisions received September 12, 2005; accepted for publication September 15, 2005.

^_* Address for reprints: Veena Guru, MD, Institute For Clinical Evaluative Sciences, 2075 Bayview Ave, G106, Toronto, Ontario M4N 3M5, Canada (Email: veena.guru{at}utoronto.ca).

OBJECTIVE: Current evidence suggests arterial grafting improves freedom from cardiac events after coronary artery bypass graft surgery. It has been shown that 2 arterial grafts provide improved outcome compared with 1 arterial graft. This population study seeks to understand trends in arterial graft use and midterm outcomes of patients receiving 1, 2, or 3 arterial grafts.

METHODS: This study is a retrospective population-based cohort of 53,727 patients (47,214 with 1 arterial graft, 5466 with 2 arterial grafts, and 1047 with 3 arterial grafts) undergoing isolated coronary artery bypass graft surgery in Ontario (1991-2001). The patients were followed by using linked clinical and administrative data, with complete follow-up until December 31, 2003 (average patient years of follow-up: 6 years for those with 1 arterial graft, 5 years for those with 2 arterial grafts, and 4 years for those with 3 arterial grafts). Propensity matching was used to compare outcomes between patients receiving 1 versus 2 arterial grafts, 2 versus 3 arterial grafts, and 1 versus 2 or 3 arterial grafts. The outcomes included death, repeat revascularization (angioplasty or coronary artery bypass grafting), cardiac readmission (readmission for angina, heart failure, and myocardial infarction), and a composite comprising all of these outcomes. Cox proportional hazards models were used to compare outcomes for propensity-matched patients. Subgroup analyses of various patient risk categories defined by the tercile of predicted 30-day mortality risk were conducted between propensity-matched individuals.

RESULTS: The use of multiple arterial grafts (defined as >1 arterial graft) increased mainly in the latter part of the study, from 4% in 1991 to 27% in 2001. Four thousand nine hundred sixty-eight patients were propensity matched (91% of patients receiving 2 arterial grafts) to compare outcomes with those of patients receiving 1 arterial graft. One thousand twenty-eight patients were propensity matched (98% of those receiving 3 arterial grafts) to compare outcomes with those of patients receiving 2 arterial grafts. Five thousand four hundred ninety-one patients were propensity matched (84% of those receiving 2 or 3 arterial grafts) to compare outcomes with those of patients receiving 1 arterial graft. Two arterial grafts were shown to be protective for cardiac readmission (0.8; 95% confidence interval, 0.76-0.92) and a composite outcome (0.9; 95% confidence interval, 0.72-0.95) compared with 1 arterial graft. Two or 3 arterial grafts were further found to improve survival (0.8; 95% confidence interval, 0.72-0.99). In all patient operative risk categories, 2 or 3 arterial grafts were protective for cardiac readmission (hazard ratio, 0.7-0.8) and the composite outcome (hazard ratio, 0.8). There was no difference in the Cox hazard ratios of propensity-matched patients in the comparison of the groups receiving 3 versus 2 arterial grafts.

CONCLUSIONS: Few patients received more that 1 arterial graft in our region. There was a survival benefit in receiving 2 or 3 arterial grafts. Patients with low, moderate, and high operative risk receiving 2 or 3 arterial grafts had lower rates of cardiac readmission compared with patients receiving only 1 arterial graft. This suggests that the standard of care should include the use of at least 2 arterial bypasses in all categories of operative risk to allow for optimal midterm outcomes.

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