Introduction
Statistics show a global increase in the elderly population, which is faster in some countries such as Iran [1, 2]. On the other hand, the prevalence and occurrence of acute and chronic diseases such as diabetes and heart diseases increases in old age [4] such that 75% of deaths caused by coronary artery diseases occur in the elderly [8]. Considering that limited research has been done in Iran on the prevalence of risk factors in diabetic and non-diabetic elderly suffering from heart attack, this study aims to compare the prevalence of risk factors, the type of reperfusion treatment, and the mortality of older patients with myocardial infarction in two diabetic and non-diabetic groups.

Methods
This is a cohort study. The statistical population consists of all older adults (age ≥60 years), whose information were available in the ST‐segment elevation myocardial infarction (STEMI) registry system of Imam Ali hospital in Kermanshah, Iran between July 2016 and January 2020. Of these, 1460 older people suffering from STEMI were selected based on the inclusion criteria and divided into two diabetic and non-diabetic groups. Data collection was done using a checklist including demographic information, medical records, cardiovascular disease risk factors, clinical examinations, diagnostic tests, treatment performed during at the time of admission, hospitalization and discharge. After receiving the phone numbers of the patients for follow-up, their condition was monitored for a period of one year after discharge. During the follow-up, the information of all patients was recorded in terms of disease status and mortality, as well as the date and cause of death. Information including age, sex, place of residence, history of blood pressure, history of smoking, history of cardiovascular disease and coronary interventions, creatinine level, glomerular filtration rate (GFR), and blood lipid level were also recorded. Their blood lipid profile was recorded on the first day of admission to the hospital.
In terms of reperfusion treatment type, they were divided into groups of primary PCI, clot dissolving treatment, coronary surgery, and no treatment. Based on BMI, they were divided into four groups: Thin (≥23), normal (23-25), overweight (25-29.9) and obese (≤30) (38). HDL less than 55 mg/dL in women and less than 45 mg/dL in men was considered as low HDL. The GFR of patients was calculated using the CKD-EPT formula and divided into two groups: GFR >60 and GFR <60 [39, 40]. In the statistical analysis, the assumption of the normality of data distribution for the HDL, LDL and GFR variables was not rejected using the kurtosis and skewness tests. Hence, independent t-test was used to compare them between diabetic and non-diabetic patients. Mann-Whitney U test was used for triglyceride and cholesterol levels variables due to abnormal data distribution. Chi-square test was used for all nominal variables except for the BMI where Fisher’s test was used. Data analysis was done in Stata software, version 14. The significance level was set at 0.05.

Results
The majority of participants were male and illiterate. There was a significant difference in BMI between the two groups (P<0.001); there were 14.68 and 28.29% thin people; 22.32 and 23.81% with normal weight, 43.43 and 36.57% overweight, and 19.57 and 11.33% obese in diabetic and non-diabetic groups, respectively. In overall, 13.7% of the elderly had a history of myocardial infarction (P=0.012), which was more in diabetic patients (17.8%) than in non-diabetic patients (12.3%). Moreover, 54.1% in the diabetic group and 16.9% in the non-diabetic group had high blood fat. In addition, 67.7% of diabetics had a history of hypertension, which was higher compared to non-diabetics (50.5%). The difference in blood lipids and blood pressure between the two groups was significant (P<0.001).
The mean LDL was 97.82±30.79 in the diabetic group and 103.58±30.63 in the non-diabetic group (P=0.003). The prevalence of high LDL in diabetics was lower than in non-diabetics (16.6% vs. 18%) (P<0.001). The prevalence of low HDL in diabetics was higher than in non-diabetic elderly (63.1% vs. 52.8%) (P=0.001). The mean cholesterol level was 168.99±43.52 in diabetics and 173.34±39.99 in non-diabetics (P<0.014). The prevalence of low GFR (GFR<60) in diabetic patients was 56.10% which was significantly higher in non-diabetic patients (49.07%). The type of reperfusion treatment performed for the two groups was not significantly different (P=0.692). In diabetic and non-diabetic groups, 20.81 and 18.30% of the participants, respectively, did not receive any of the usual treatments. Although the mortality rate in diabetic elderly was higher than in the non-diabetic group, this difference was not statistically significant (P=0.692). In the diabetic and non-diabetic groups, 81.58 and 84.62% of the patients, respectively, were still alive.

Conclusion
The analysis of risk factors in high-risk and vulnerable groups such as the elderly with diabetes provides valuable information to healthcare centers to plan for preventing and improving the quality of treatment measures and reducing the adverse effects of the disease in high-risk people. The results of this study showed that the most important risk factors that should be considered and controlled in diabetic elderly with myocardial infarction were BMI≥30, history of heart attack, blood lipid profile, blood pressure level, triglyceride level, and GFR<60. The most important risk factors in non-diabetic elderly with myocardial infarction were high LDL and high cholesterol level.

Ethical Considerations
Compliance with ethical guidelines
The Vice President of Research and Technology of Kermanshah University of Medical Sciences approved the study protocol (Code: KUMS.REC.1395.252).

Funding
This study was financially supported by Department of Research and Technology, Kermanshah University of Medical Sciences.

Authors' contributions
All authors equally contributed in preparing this article.

Conflicts of interest
The authors declared no conflict of interes.

Acknowledgements
The authors would like to thank Vice-Chancellor of Kermanshah University of Medical Sciences, for financiall support. We gratitude Imam Ali Hospital's staff, especially the staff of the Heart Research Center; Hossein Siabani, Leila Zamzam, Elaha Mohammadi and others. We highly gratitude Haniyeh Charjo for collecting the data.


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