Off-Pump CABG Reduces AKI Risk—But No Difference in Later Kidney Function

Patients assigned to off-pump coronary artery bypass grafting (CABG) have a lower risk of acute kidney injury (AKI) but no reduction in the rate of reduced kidney function 1 year later, reports a study in the Journal of the American Medical Association.

In the international randomized trial, 4752 patients undergoing their first isolated CABG procedure were assigned to the off-pump (beating-heart) technique or to on-pump cardiopulmonary bypass. A kidney function substudy analyzed serum creatinine data during the postoperative period and at 1-year follow-up in 2932 patients. The two groups were compared for their risk of AKI at 30 days, defined as a 50 percent or greater increase in serum creatinine level. The 1-year rate of loss of kidney function—a 20 percent or greater reduction in estimated GFR—was also compared between groups.

The 30-day AKI risk was 17.5 percent in patients assigned to off-pump CABG versus 20.8 percent in the on-pump group: adjusted relative risk (RR) 0.83. However, the reduction in AKI did not lead to a reduced risk of kidney function loss at 1 year: 17.1 and 15.3 percent, respectively.

A subgroup analysis of patients who had chronic kidney disease at baseline showed an even greater reduction in AKI risk with off-pump CABG: 19.2 versus 30.2 percent, RR 0.63. In both analyses, the results were similar when different definitions of AKI were used.

Cardiac surgery is associated with a substantial risk of mild to moderate AKI, but the implications for long-term kidney function are unclear. No intervention that lowers the risk of AKI has been proved to protect long-term kidney function.

The new trial shows a lower 30-day risk of AKI in patients undergoing off-pump CABG rather than the on-pump procedure. However, this does not lead to any difference in the rate of reduced kidney function at 1-year follow-up. The researchers write, “[T]he findings emphasize proof is needed to claim an intervention that reduces the risk of mild acute kidney injury better preserves long-term kidney function for the group that received it” [Garg AX, et al. Kidney function after off-pump or on-pump coronary artery bypass graft surgery: a randomized clinical trial. JAMA 2014; 311:2191–2198].