Patients with type 1 diabetes whose HbA1c levels exceeded 9.1% before coronary artery bypass grafting were significantly more likely to die or suffer major coronary adverse events over the next 5 years than were those with better glycemic control, researchers reported.

And patients with the worst glycemic control had more than double the risk of death or major coronary adverse events (MACE) as those who were adequately controlled before surgery, Dr. Thomas Nyström at the Karolinska Institutet in Stockholm, Sweden and his associates reported July 27 in the Journal of the American College of Cardiology.

Diabetes affects about one in four patients who undergo revascularization for multivessel coronary artery disease. To understand the links between preoperative hemoglobin A1c (HbA1c) levels and adverse postoperative outcomes, the researchers conducted a nationwide, population-based study of 764 type 1 diabetes mellitus patients who underwent coronary artery bypass grafting in Sweden between 1997 and 2012 (J. Am. Coll. Cardiol. 2015; 66: 535-43 [doi: 10.1016/j.jacc.2015.05.054]).

After a median of 4.7 years of follow-up, 44% of patients had died or had experienced MACE, for an incidence rate of 82 events per 1,000 person years, according to the investigators. Risk of death or MACE in the 5 years after surgery was significantly higher when preoperative HbA1c levels were 10% ore more compared with 7% or less, they said (hazard ratio, 2.25; 95% confidence interval, 1.29 to 3.94).

Risk of death or MACE also was significantly elevated for patients with levels of 9.1% to 10.0%.

“Interventions to achieve better control of blood glucose concentrations and other cardiovascular risk factors in patients with [type I diabetes mellitus] should be evaluated in prospective trials,” the investigators wrote.

The study was supported by the Swedish Society of Medicine, Karolinska Institutet Foundations and Funds, the Mats Kleberg Foundation, and the Swedish Heart and Lung Foundation. The researchers reported having no relevant financial disclosures.