6 2 Methods 2.1 Data source COPD patients admitted to the three hospitals (People's Liberation Army General Hospital; Beijing Union Medical College Hospital and Beijing Hospital of Ministry of Health) from 2000/01/01 to 2010/03/03 were enrolled in the study. The three hospitals, which are managed by the government, registered 99% of the health data for people living in Beijing. 2.2 Study population Selected patients had to meet the following criteria. First, the discharge diagnosis had to be in accordance with the 9/10th Revision of the International Classification of Diseases (ICD-9/10). Patients were diagnosed as having chronic bronchitis, emphysema or COPD. Secondly, patients should have a history of using anticholinergics and β-receptor agonists, or theophylline, either long-term or temporarily. Thirdly, patients had to be 40 years of age or older. Fourthly, the time-span from hospitalization to an outpatient (or the time-span for which hospital records were available) was more than six months. Lastly, the patients need to be Han Chinese. A total of 4960 patients with a mean age of 72.2 ± 10.4 years and COPD were enrolled. There were 3570 males (mean age, 72.2 ± 10.5 years), and 1390 females (mean age, 72.0 ± 10.4 years), (Table 1). 2.3 Validation of hospital discharge codes We used the case management system based on the International Classification of Diseases (ICD) code in the three hospitals to search for the basic information on COPD patients. The tenth revision (ICD-10) was carried out by PUMC Hospital, Beijing and Hospital Ministry of Health. While the Chinese PLA General Hospital used the ninth revision (ICD-9) from January 2003 to July 2008. We then referred to the relevant content from their medical records. Differences in the ICD versions were corrected by referring to Tables ICD-9~ICD-10 from the Military Hospital Diagnosis Code. Disease codes were retrieved according to sub-orders (Table 2). Table 1. Age and sex distribution of chronic obstructive pulmonary disease patients. Age group (yr) < 50.0 50.0~59.9 60.0~69.9 70.0~79.9 ≥ 80.0 Males n (%) 141 (3.9) 324 (9.1) 758 (21.2) 1508 (42.2) 839 (23.6) Females n (%) 59 (4.2) 108 (7.8) 304 (21.9) 602 (43.3) 317 (22.8) Total n (%) 200 (4.0) 432 (8.7) 1062 (21.4) 2110 (42.5) 1156 (23.4) Cui H et al. Cardiovascular diseases in COPD Table 2. Codes of cardiovascular disease. Diseases Ischemic heart disease Arrhythmia Heart failure Hypertension ICD–9 code 410.x–414.x 427.x 428.x, 402.x 401.9x, 402.901 or 403.907 ICD: international classification of diseases. ICD–10 code I20.x–I25.x I44.x–I49.x I50.x I10.x–I15.x The prevalence of the target disease was defined as the percentage of patients with the target disease compared to all enrolled patients during the study period. 2.4 Statistical analyses The continuous variables were tested for normal distribution by the Kolmogorov-Smirnov test. The normal distributed continuous variables were shown as mean ± SD. The categorical variables were presented as frequencies (percentages). Comparisons of the groups for continuous variables were performed with the unpaired t-test. Comparisons of the groups for categorical variables were performed with Pearson chi-square test. P < 0.05 (two-sided) was considered significant. SPSS 18.0 statistical software (SPSS, Chicago, IL, USA) was used for data analysis in the study. 3 3.1 Results Prevalence of CVD in COPD patients The total prevalence of CVD in COPD patients was 51.7%, specifically 2562 cases out of all cases with COPD had CVD. The prevalence of ischemic heart disease among COPD patients was 28.9%, of heart failure was 19.6% and of arrhythmia was 12.6%. 3.2 Background of patients with COPD A total of 96.7% of 4960 patients with COPD were from the Beijing district. Social and commercial insurance paid for the primary medical treatment in of 60.8% of patients. The professional background of the patients varied (Table 3). 3.3 Age prevalence of CVD in COPD patients The prevalence of various types of CVD (ischemic heart disease, angina, acute myocardial infarction, arrhythmia, atrial fibrillation/atrial flutter, heart failure, hypertension) in COPD patients increased with age (Figure 1). 3.4 Sex prevalence of CVD in COPD patients The prevalence of CVD complications in COPD patients differed according to sex. The prevalence of CVD was 49.3% in male COPD patients and 47.6% in female COPD Journal of Geriatric Cardiology | jgc@jgc301.com; http://www.jgc301.com