This retrospective cohort study was conducted in Tawam hospital, Al Ain City, which is the fourth largest city in the UAE, with a population of 650,000 of which approximately 30% are UAE nationals. Tawam hospital, is one of the largest tertiary care hospitals in Al Ain, providing health care services to UAE nationals and the expatriate community.
The United Arab Emirates University and Tawam Hospital Review Boards (CRD 239/13) granted ethical approval for this study. The Cerner©electronic medical record (EMR) management system was utilized to obtain patient data retrospectively. Patient information was anonymized to protect patient identity. Informed consent was waived, as identifying data was not collected from the EMR.
The original study population enrolled all patients who visited the outpatient clinics of Tawam Hospital between April 1, 2008 and December 31, 2008 and were followed-up until the end of the study period, July 31, 2018. All patients who were ≥18 years old and had an established diagnosis of CAD, cerebrovascular disease, or peripheral vascular disease (PVD) were included in this study. Established CAD was defined as a documented history of stable angina, unstable angina, percutaneous coronary intervention, coronary artery bypass graft surgery, or myocardial infarction. Cerebrovascular disease was defined as a documented diagnosis of transient ischemic attack (TIA) or stroke; PVD, as a documented diagnosis of peripheral artery disease. Patients were followed from the time of the first diagnosis of CVD until a recurrent CVD event, death, or the end of the study period on July 31, 2018.
The study’s sample size was calculated using a formula for a study designed to estimate incidence in a population [Rosner B. Fundamentals of biostatistics. 7th ed. Boston: Cengage Learning, Inc; 2010.]. A sample size of 194 was determined based on an anticipated 60% incidence of recurrent CVD  and utilizing 80% power at a 2-sided level of significance of 0.05.
Data retrieved from the EMR included sociodemographic parameters, such as age, sex, body mass index (BMI); traditional CVD risk factors, included smoking, history of HTN, blood pressure (BP), history of diabetes mellitus, total cholesterol, and low-density lipoprotein (LDL); other parameters, such as anti-hypertensive medications, lipid-lowering medications, and antiplatelet therapy. Smokers were defined as current smokers or having a history of smoking. BMI was calculated as weight in kilograms divided by the square of the height in meters. Commonly accepted BMI ranges are those recommended by the World Health Organization as follows: overweight (BMI 25–29.99 kg/m2), obese class I (BMI 30–34.99 kg/m2), obese class II (BMI 36–40 kg/m2), and obese class III (≥ 41 kg/m2) . Diabetes was defined as receiving oral hypoglycemic medications; HTN, as receiving anti-hypertensive medications or having a SBP ≥140 mm Hg or DBP ≥ 90 mm Hg, blood pressure was categorized as follows: normal (SBP <140 or DBP <90); grade 1 HTN (SBP 140–159 or DBP 90–99); grade 2 (SBP 160–179 or DBP 100–109); and grade 3 (SBP ≥180 or DBP ≥110) . Based on Adult Treatment Panel III guidelines, LDL level ≥ 2.6 mmol/L (≥100 mg/dL) is suboptimal, and total cholesterol >5.17 mmol/L (> 200 mg/dL) is suboptimal .
Recurrent CVD events
The outcome of our study included recurrent CVD events and/or death. Recurrent CVD events included stable angina, unstable angina, percutaneous coronary intervention, myocardial infarction, TIA, and cerebral infarction confirmed by computed tomography scan, magnetic resonance imaging, or ankle-brachial index <0.9. Death was defined as death due to myocardial infarction, stroke, and/or sudden death. The data for comorbidities and CVD events were collected using the definitions in the documented history in the EMR. Those with missing data were excluded.
The overall incidence rate of recurrent CVD events, the incidence rates in males and females, and the incidence rates according to different age categories were calculated by dividing the number of study participants with recurrent CVD event by the total patient-years of follow-up for the study population and for each subgroup accordingly.
Baseline variables were tested for association between males and females using independent-samples t-test for continuous variables and Fisher’s exact test (two-tailed) for categorical variables. Continuous variables are presented as means (±standard deviation (SD)), while categorical variables are presented as proportions. The patient-years at risk for recurrent CVD events were calculated for each subject from the baseline visit until the occurrence of a recurrent CVD, death, or the last outpatient clinic visit, whichever occurred first. Univariable and multivariable-adjusted Cox proportional hazard regression models were used to evaluate the risk factors for recurrent CVD events. The independent predictors included in the multivariable-adjusted Cox regression model were age (continuous), sex, smoking, HTN, diabetes mellitus, LDL (continuous), and BMI (continuous). Proportional hazards assumption was assessed by log-log plots, while multi-collinearity was evaluated by examining the tolerance value. The results are expressed as hazard ratios and 95% confidence intervals (CIs). A p value <0.05 (two-sided) was considered statistically significant for all tests. All statistical analyses were performed using IBM SPSS software, version 25 (IBM Corporation, Armonk, NY, USA).