The measures of persistent hyperglycemia during acute MI are better predictors of mortality than admission glucose, and mean hospitalization glucose appears to be the most practical metric of hyperglycemia associated risk, according to a study in the Feb. 25 issue of Circulation.
While elevated admission glucose is associated with an increased risk of mortality for acute MI patients, it is only the measurement of a single time-point and does not reflect the overall exposure to hyperglycemia.
An important unanswered question is whether persistent hyperglycemia during hospitalization has a greater impact on adverse outcomes in AMI than a single, random glucose measure. If it does, a second key question is how best to measure persistent hyperglycemia during AMI hospitalization
To answer these questions, Mikhail Kosiborod, MD, from the Mid America Heart Institute of Saint Luke’s Hospital, Kansas City, Mo., and colleagues analyzed data from 16,871 patients in Cerner Corporation’s Health Facts database, a database of patients hospitalized with AMI in 40 hospitals across the United States from 2000 to 2005.
They compared admission glucose with three alternatives: mean glucose (a simple average of each patient’s glucose levels over time), time-averaged glucose, or TAG (derived as the area under the curve of all glucose values during a specified time period divided by the length of that observation period), and the hyperglycemic index, or HGI (accounts only for the area under the curve of hyperglycemic glucose values over the length of stay, ignoring hypoglycemia).
These measurements were taken over three time windows during AMI hospitalization: the first 24 hours, the first 48 hours, and the entire length of hospitalization. Overall, 10 different glucose metric–time window combinations were evaluated.
Researchers found that C indexes (a method to evaluate the yield of medical tests) for all nine alternative metrics of persistent hyperglycemia were significantly higher than that of admission hyperglycemia.
They also noted a gradual, statistically significant increase in the prognostic importance of glucose metrics as the time window increased so that the C index for any summary measure over the entire hospitalization was higher than the C indexes for glucose metrics over 48 and 24 hours.
Although the differences between the C indexes for mean glucose, TAG, and HGI were statistically significant, they were small compared with the differences between all of the summary measures and the admission glucose value, according to the study.
Given the ease of clinical implementation and calculation, mean glucose appears to be the most practical summary measure of glucose control in the setting of AMI, the authors concluded.
They added that mean hospitalization glucose also is a powerful predictor of in-hospital mortality independent of other demographic and clinical patient factors and potential confounders.
“Such a ‘running average’ of glucose values in individual patients, nursing units, and entire hospitals could be used for prognosis and performance assessment and, if an intervention is demonstrated to be prognostically beneficial, as a modifiable target for quality improvement,” researchers said.
While the exact mechanisms behind the association of persistent hyperglycemia and higher in-hospital mortality have not been definitively established, the authors noted that prior physiological studies showed higher glucose levels in patients with AMI are associated with higher free fatty acid concentrations (which may induce cardiac arrhythmias), insulin resistance, and impaired myocardial glucose use, thus increasing the consumption of oxygen and potentially worsening ischemia.
Whether intensive glucose control in patients with AMI will result in improved survival remains to be tested in prospective randomized trials.