We found that over the last decade, there was a significant absolute rise of 12% in the prevalence of DM among patients hospitalized for AMI in the United States. The rise occurred in the setting of an eight percent decrease in the number of overall AMI hospitalizations in 2006 (versus 1997) and a 51 percent increase in actual numbers of AMI hospitalizations with coexisting diabetes in 2006 (versus 1997). Although it is widely recognized that several countries around the world are in the midst of a diabetes epidemic [7
], and a major city in the US reported a recent sharp increase in diabetic patients hospitalized for myocardial infarction [8
], this recent nationwide boost in prevalence among patients experiencing incident coronary heart disease, the major killer of individuals with DM [9
], may be of major public health concern especially if it threatens the declining national trend in coronary artery disease events.
Prevalence data for DM among AMI patients across countries and populations from prior studies conducted in the 1980s and 1990s ranged from 10 to 24% [9
]. In the general US adult population, the prevalence of diagnosed diabetes rose from 5.1% in 1988–1994 to 7.7% in 2005-2006 [2
]. In comparison, our study showed that in the US, prevalence of DM among AMI patients has increased to a greater degree than in the general population and is now four times more frequent in AMI patients. The precise reasons for the rise in patients hospitalized for AMI with comorbid DM cannot be readily garnered from this study based on an administrative dataset. However, based on prior data [10
], recent information [14
], and some speculation, the increasingly higher DM prevalence rates noted in this nationwide study of AMI patients likely reflect a combination of factors including the higher risk of AMI in patients with DM, a true rise in the prevalence of DM in the setting of higher rates of obesity and sedentary lifestyle [16
], better diagnostic techniques, improved documentation (heightened awareness of diabetes as a coronary risk factor may have resulted in increased testing for diabetes and more complete reporting of diabetes), and prolonged survival. A recent meta-analysis suggests that DM imparts a doubling of the AMI risk, independent of other vascular risk factors [17
]. The exact contributions of each of these factors may be hard to determine, but to the extent that there has probably been a real increase in diabetes among these high-vascular risk patients, policy makers at all levels may want to intensify efforts to prevent and optimally control diabetes, especially in the AMI patients we identified as being at higher odds of having comorbid DM.
One such group of patients as noted in our study may be young and middle-aged women. We found a higher prevalence of DM among women with AMI compared to their aged-matched male counterparts, a difference which lessened with increasing age, but which was most apparent among AMI patients <55 years. Furthermore, the rate of increase in DM prevalence over the decade appeared to be slightly greater in women aged <65 years compared to similarly aged men. A disproportionate burden of coronary risk factors and comorbidities among younger women versus their male counterparts has been previously reported [18
], but we are unaware of data explicitly presenting the magnitude of differences in DM prevalence among AMI patients for successive age groups after the age of 55 years. Such a major difference in DM prevalence may in part contribute to the well-known higher rates of in-hospital mortality seen in women versus men aged <60 years [19
It was interesting to note that hypertension and renal disease diagnoses have also risen substantially over the decade. Again these increases likely have a multifactorial basis but conceivably also represent some degree of real increase. Both these medical conditions are of course strongly related to presence of diabetes [22
] and indeed were among the strongest independent predictors of DM diagnosis in our study. Other factors independently linking co-existent DM with incident AMI in our multivariable analyses were female sex, non-White race, and comorbid systemic vascular damage have been noted in other studies [23
Consistent with other studies, there was an overall decline in the absolute number of AMI hospitalizations during the study period [27
]. In recent study, the annual AMI hospitalization rate in the fee-for-service population fell from 1131 per 100 000 beneficiary-years in 2002 to 866 in 2007, a relative 23.4% decline. The apparent reduction in AMI hospitalization may be attributed to decrease in certain CV risk factors, greater use of cardiovascular protective medications, and improvements in coronary revascularization. However, had there not been such a large temporal increase in the prevalence of DM, the reduction in AMI hospitalizations during this time period may have been even more pronounced.
This study has limitations. First, we cannot exclude possible inaccurate reporting of ICD codes. However, the ICD-9
diagnosis-coded case definitions have been consistently well validated in previous studies using the same or similar hospitalization data [29
]. Further, any potential reporting errors in this large database were unlikely to have been systematic. Second, detailed patient-level data, such as glucose levels, HbA1c, vascular biomarkers, and medications were not available for our analysis. Third, since up to one-fourth of all persons with diabetes may actually be undiagnosed [30
], we may have missed patients with DM who did not have a premorbid history and were not screened during their hospitalization. Fourth, we could not count out hospital AMIs which did not result in hospitalization. While an increase in out-of-hospital sudden cardiac death can potentially explain a decline in AMI hospitalizations, it would not explain the rising prevalence of DM. Finally, the observed rise in DM prevalence may also have been impacted by lowering of the fasting plasma glucose range for diagnosing impaired fasting glucose in 2003 [31
], but between years 1997 and 2006, the rate of increase in DM prevalence among AMI patients was relatively constant, suggesting that the change in diagnostic criteria had a minimal effect on DM rates in this population. In addition, the substantially higher rise in DM prevalence among AMI patients versus general population during this time period suggests that this was probably not a major factor. The study benefited from its nationwide scope, standardized methodology, and clinician diagnosed incidence data.
In conclusion, overall risk factor reduction and better treatment of AMI patients has decreased incidence of AMI rates, but we observed a recent steep rise in the number of patients hospitalized for AMI with coexisting DM the United States, a boost that suggests that the population health burden of diabetic coronary heart disease (CHD) remains considerable and might be increasing. Future studies are warranted to confirm these results and explore ways to mitigate this mounting problem, which could exponentially worsen in the years to come, in the face of the growing obesity epidemic.