Glucose levels as a prognostic marker in patients with ST-segment elevation myocardial infarction: a case–control study
The current findings are consistent with the results of previous registries, suggesting 14.3 – 40.9 % prevalence of DM in patients with acute myocardial infarction according to the national population characteristics [6, 7]. However, all registries show a significant increase in the in-hospital mortality rate in diabetic patients with myocardial infarction, compared with patients without carbohydrate metabolism disorders. The GRACE registry reported that patients with ST-segment elevation myocardial infarction and previously diagnosed diabetes demonstrated 11.7 % in-hospital mortality, whereas patients without carbohydrate metabolism disorders had 6.4 % mortality rate [6]. The results of the GulfRACE register also indicated a significant increase in the in-hospital mortality rate among diabetic patients with acute coronary syndrome compared with patients without diabetes (4.4 % vs. 3.4 %, respectively, p??0.01) [7, 8].
The present study showed different relationships between blood glucose levels at admission and in-hospital mortality in MI patients with and without diabetes. Therefore, blood glucose levels 7.0 mmol/L at admission in MI patients without diabetes were associated with the lowest in-hospital mortality rate, and linearly increased with increased blood glucose levels. The lowest rate of in-hospital mortality was found in patients with moderate hyperglycemia. A higher rate of in-hospital mortality in this group of patients was associated with severe hyperglycemia and euglycemia. Notably, severe hyperglycemia on admission was associated with increased in-hospital mortality in MI patients with and without DM.
When analyzing the association between diabetic patients with MI and euglycemia on admission to hospital and high in-hospital mortality, there is a negative effect of hypoglycemia on the prognosis in these patients [9]. However, patients with diabetes tend to adapt better to higher blood glucose levels than to normal levels. Therefore, euglycemia (diagnosed on admission) may be regarded as relative hypoglycemia affecting the prognosis. Consequently, chronic hyperglycemia (estimated on admission and on days 10–14 of the in-hospital period) could be an important marker of poor prognosis in MI patients with and without DM.
Comparative assessment of the effect of glycemic status on the prognosis in patients with MI should consider postprandial glucose levels, which play an important role in the development of adverse cardiovascular events [10, 11]. The DECODE study [12], which assessed the risk of death under different variants of hyperglycemia, showed that the postprandial glucose level is an independent risk factor, with higher prognostic significance than glycated hemoglobin levels. Several studies have suggested that after-meal high blood glucose levels are more important for the risk assessment of cardiovascular complications in diabetic patients than fasting glucose levels [12]. Therefore, assessment of the effects of acute and chronic hyperglycemia on induction of oxidative stress in patients with DM suggests that its main triggering mechanism is acute deviations in blood glucose levels, but not long-term chronic hyperglycemia (or small fluctuations in postprandial blood glucose) [13]. Postprandial hyperglycemia in patients with DM is associated with reduced myocardial perfusion caused by microvascular abnormalities. We have previously shown a positive effect of adequate glycemic control [14].
In general, hyperglycemia on admission in ACS patients is a major predictor of survival and increased risk of development of cardiovascular events, regardless of diabetic status [1]. Moreover, the present study showed that hyperglycemia on admission to hospital, as an indicator reflecting the degree of oxidative stress in acute coronary events, significantly affects immediate and long-term prognosis in patients with MI. However, the majority (74.2 %) of patients with DM had high levels of postprandial and fasting glucose (i.e., presence of chronic hyperglycemia), which affected the prognosis during the in-hospital period. Notably, the prognostic value of hyperglycemia did not change during the whole in-hospital period [15]. Nevertheless, previous studies have shown an increase in the mortality rate in patients with hypoglycemia and MI [15–17].
Taking into consideration the adverse effect of hypoglycemic episodes on the long-term prognosis in MI patients with DM, spontaneous hypoglycemia might be a marker of the severity of disease and adverse outcomes or an independent predictor of a poor prognosis. Further studies are required to determine the role of hypoglycemia as a mediator of adverse outcomes in MI patients.