Results of an analysis of data from a healthcare database including nearly 70,000 patients with diabetes revealed that elevated HbA1c is a significant risk factor for acute myocardial infarction (AMI) and the need for coronary artery bypass graft surgery (CABG).

Introducing the analysis, Joseph E. Thomas, MD, Yale University School of Medicine, Connecticut, United States, said that while tight glycemic control has been associated with improved cardiovascular outcomes in both type 1 and type 2 diabetes, the relationship between glycemic control and cardiovascular outcomes in clinical practice is not well understood. Thomas and colleagues conducted a retrospective chart analysis of data from 69,418 patients with diabetes from the Integrated Health Care Information System (IHCIS).

For purposes of the analysis, patients were stratified into four index HbA1c groups: <6%, 6–7%, 7–9%, ≥9%. Mean patient age was ∼57 years (∼54% male), with prior AMI in 1.0–1.5% and prior CABG surgery in 0.1–0.5%. Mean follow-up was 27 months. In the HbA1c ≥9% group at baseline, total cholesterol, LDL-cholesterol, and triglycerides were higher, and HDL-cholesterol was lower than in the other groups. About a third of patients were receiving ACE inhibitors or angiotensin receptor blockers. As expected, use of oral antidiabetic agents and insulin was higher in patients with poorer glycemic control.

The unadjusted incidence rate for AMI, CABG, stroke, and their combination increased generally with increasing HbA1c with the exception of stroke (Table 1). “We were unable to explain the lower stroke incidence,” Dr. Thomas said, although he commented that TIAs had been excluded.

After adjusting for baseline characteristics (gender, age, baseline hypertension, AMI, congestive heart failure, peripheral vascular disease, and cardiovascular disease), hazard ratios for survival and AMI increased with worsening glycemic control (HR=1.57 for HbA1c ≥9%, p<0.001) when compared with the baseline <6% HbA1c group. The same pattern persisted for survival and CABG (HR=1.19 for index HbA1c 6–7, HR=1.56 for index HbA1c 7–9, HR=1.38 for index HbA1c ≥9). With adjusted survival and stroke, however, differences were not significant.

Dr. Thomas concluded, “Elevated index HbA1c is a significant risk factor for AMI, CABG and poorer survival. Glycemic control is associated with real-world, long-term macrovascular outcomes.” The data suggest, he added, that “early intervention with intensive diabetes treatment may reduce macrovascular risks.” Finally, he noted that ongoing trials (ORIGIN, ACCORD, VADT) are addressing the potential benefits of insulin therapy in patients with cardiovascular disease.

Limitations of this study include the fact that it was an observational study with short follow-up and that because the data were taken from the IHCIS managed care employee database, the population was likely to have been healthier and younger than the usual diabetes database.