SAN FRANCISCO — Intensive glycemic control — dropping glycated hemoglobin (HbA1c) levels below 6% — appears to be associated with an increased risk for heart failure in diabetes patients, as does poor control (HbA1c levels of 7% or greater), new data from a case-control study show. The results suggest that glycemic control is an independent risk factor for incident chronic heart failure in type 2 diabetes patients, said Helen Parry, MD, from the University of Dundee, Scotland, who presented her findings at the American College of Cardiology 2013 Scientific Sessions here today.
"Type 2 diabetic patients should aim for tight glycemic control, keeping an HbA1c in the range of 6% to 6.9% if they want to reduce their risk of heart failure," she said. But she acknowledged: "Aiming for such a tight range of glycemic control is not clinically very easy."
Asked how she thought glycemic control contributed to HF risk, she replied, "It's probably multifactorial. First, there's a possibility these people are on a lot of antihyperglycemics — they are on insulin and sulfonylureas — and we know that these are associated with development of heart failure. Aside from the drug effects, we know that hyperglycemia is bad for the heart and increases mortality, so it may be that even in those whose [mean] HbA1c is around 5.5%, these are also the people who are more susceptible to acute hyperglycemic events."
Diabetics at Much Higher Risk of Heart Failure
Dr. Parry explained that type 2 diabetes is a "major" risk factor for heart failure, with data from the Framingham study showing that men have a 6-fold and women an 8-fold higher risk of HF development if they also have diabetes, as opposed to their nondiabetes counterparts.
Some of this increased risk is explained by the fact that diabetes increases coronary artery disease (CAD) risk, hypertension, and obesity, all of which contribute to heart failure. But even accounting for these, there remains a proportion of HF unexplained among diabetics, something that has been termed "diabetic cardiomyopathy," she noted.
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Dr. Helen Parry
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If diabetes does directly promote HF, it should follow that improved glycemic control would be protective, Dr. Parry hypothesized. She noted that a number of prior observational studies, including most recently the Swedish National Diabetes registry, have shown an association between HbA1c measurement of greater than 7% and an increased risk of HF hospitalization in patients with type 2 diabetes.
Unfortunately, 3 randomized controlled trials assigning diabetic patients to intensive or standard glycemic control, ACCORD , ADVANCE and VADT, were "underpowered" to look at whether glycemic control affected the risk of HF, she noted.
Poor and Intensive Glycemic Control More Than Double HF Risk
She and her colleagues set out to determine whether glycemic control reflected by multiple HbA1cmeasurements was associated with HF in type 2 diabetes, whether this association occurs independently of CAD, and whether glycemic control predicts time to HF development.
They studied the diabetic population of Go-DARTS (n=8890). Chronic HF was defined as either a hospital discharge code for CHF or systolic dysfunction requiring a loop diuretic. They matched HF cases with controls for gender and age at diabetes diagnosis.
Using multiple HbA1c measures, they calculated a mean. CHF incidence was determined during the study period, October 1999 to August 2011, and Cox regression analysis was used to examine the link between the mean HbA1c and time to CHF, accounting for all possible confounders.
Heart failure is common in patients with type 2 diabetes, and glycemic control is associated with HF in both CAD sufferers and those free of CAD.
Of 8890 diabetics, 759 developed HF during the study period, and those with poor glycemic control were twice as likely to develop it — the odds ratio (OR) of developing CHF with updated mean HbA1cgreater than 6.9% was 2.26 (P < .01).
But intensive glycemic control (less than 6%) also appeared to increase the risk for CHF (OR, 2.48 P < .01).
The researchers also found that CAD frequency and myocardial infarction (MI) were increased when the mean HbA1c was outside the range of 6% to 7%, Dr. Parry noted.
"Heart failure is common in patients with type 2 diabetes, and glycemic control is associated with HF in both CAD sufferers and those free of CAD," she concluded, adding that both overly strict glycemic control and hyperglycemia appear to hasten CHF onset.
Dr. Parry has disclosed no relevant financial relationships.
American College of Cardiology Scientific Sessions. Abstract 905-7. Presented March 9, 2013.
