During the six-year follow-up, the incidence of cardiovascular events after myocardial infarction was 24%. Smoking and 2-h PG were two independent predictors of CV in patients with myocardial infarction. Our research group has previously reported that the prevalence of IGT and unknown DM is high in patients with ischemic heart disease [1
]. This study confirms the results from previous studies [12
] and highlights the clinical relevance of hyperglycemia 2-h post glucose challenge as independent risk factors for CV events in patients with ischemic heart disease. Several epidemiological studies have indicated that patients with pre-diabetic conditions, below the threshold for diabetes, are at higher risk for cardiovascular disease [14
]. Thus, previous studies have shown that IGT and newly detected diabetes were risk factors for increased CV events after AMI [16
]. However, it's still unclear whether patients with 2-h postchallenge glucose below the threshold for DM after MI are at a higher risk of CV events. This study also suggests, in line with previous reports [18
] that 2-h PG is a better risk predictor of CV events than FPG.
Concurring with our study, Schinner et al. [20
] found a high prevalence of impaired glucose metabolism in patients with coronary heart disease (CHD) assessed by coronary angiography. They found a continuous increased risk of CHD with blood glucose levels even in the subdiabetic range. However, as in our study, they found that post-prandial hyperglycaemia contributed more to CHD than fasting hyperglycemia.
The pathophysiological mechanism behind the relationship between 2-h plasma glucose and CV events is not fully understood. Previous studies have shown that there is a correlation between 2-h plasma glucose with higher levels of plasminogen activator inhibitor (PAI) [21
] and high sensitive C-reactive protein as a marker for low grade inflammation [4
]. In line with our study, Chu et al. [22
] showed that postchallenge hyperglycemia, increased levels of pro-inflammatory markers such as tumor necrosis factor alpha (TNF-α) and nitrotyrosone time-dependently, and that these levels were associated with coronary artery disease (CAD) in patients without previous recognized diabetes.
Disturbed glucose metabolism is associated with left ventricular dysfunction and increased intima media thickness of the carotid artery [23
]. Patients with IGT often develop metabolic syndrome with increased obesity. Thus the pathophysiological relationship between 2-h plasma glucose and CV events may be explained by different mechanisms.
Other investigators have suggested age, left ventricular ejection fraction, use of beta-blockers, aspirin and statins as potential predictors for long-term CV inpatients with AMI [24
] But even after adjustment for pharmacological therapy, age and other proposed predictors, we found that 2-h post load PG and smoking were independent predictors of CV events following AMI. The observation that smoking predicts CV disease is in line with previous studies [28
Smoking is an independent risk factor for all-cause mortality and cardiovascular death and is also associated with impaired glucose tolerance and increased risk of type 2 diabetes [30
]. The pathophysiological mechanism by which smoking effects glucose intolerance and worsens clinical outcomes in diabetic patients is not fully understood. According to previous studies, smoking leads to increased insulin resistance, beta cell dysfunction, endothelial dysfunction and low-grade chronic inflammation [32
Systolic blood pressure was also associated with the CV events; however, the relationship was significant only in univariate analysis. Previous studies have shown a correlation between high blood pressure and metabolic changes, such as impaired glucose tolerance and postchallenge hyperglycemia. The exact mechanism of this correlation remains somewhat unclear. It has been demonstrated that postprandial hyperglycemia is associated with increased oxidative stress [33
] and endothelial dysfunction [35
] and this would promote the development of atherosclerosis [36
] and hypertension [36
]. Furthermore, hyperglycemia is related to decreased blood flow to skeletal muscle, resulting in decreased glucose utilization [38
This study consisted of a small number of patients in a single center. Thus, despite a seemingly convincing message, our results may not reflect the real world population.
In conclusion, we show that in this study population with previous MI without known DM, 2-h plasma glucose and smoking were significant predictors of CV death, recurrent MI, stroke and unstable angina pectoris, independent of baseline characteristics and medical treatment.
Our results suggest that 2-h PG and smoking could be linked to an increased risk of CV events in patients with previous MI. An OGTTcould be added to the standard risk evaluation procedures in a hospital settings, as a potential method for preventing CV events it could be the focus of future clinical investigations.