This study was a prospective, multicenter registry-based study performed from March 1999 to December 2005. The KCAR (Korean Coronary Artery disease Registry) Study was initiated in 1999 to determine and record the clinical characteristics of ischemic heart disease in the Korean population. Nationwide, seven university hospitals in Korea (Yeungnam University Hospital, Daegu: Chungnam University Hospital, Daejeon: Kyunghee University Hospital, Seoul: Chungbuk University Hospital, Cheongju: Chonnam University Hospital, Gwangju: Hanrim University Hospital, Seoul: Donga University Hospital, Busan) participated in this study. Research coordinators registered all patients, evaluated at the cardiac catheterization laboratory for the purpose of assessment or treatment of ischemic heart disease. This registry included all consecutive patients who had coronary angiography with one of the following: 1) evidence of myocardial ischemia on exercise electrocardiography (ECG) and myocardial perfusion scanning ; 2) induced coronary spasm with the ergonovine or acetylcholine provocation test 3) clinical evidence of myocardial infarction based on clinical symptoms, cardiac enzymes and ECG. The different patient diagnoses included syndrome X, variant angina, stable angina, unstable angina, ST-elevated MI (STEMI), and non-ST elevated MI (NSTEMI). All diagnoses were determined by expert consensus after review of the available clinical data. Patients with atypical chest pain and normal angiographic findings, without evidence of myocardial ischemia, were excluded from this study. On the day after admission, a detailed medical history was obtained from subjects and doctors and study coordinators performed a physical examination. The physical examination included height and weight recorded according to standard methods; the body mass index was calculated by weight (kg)/height (m)². The total serum cholesterol and triglyceride levels were measured by enzymatic calorimetric testing after overnight fasting on the day after admission. The low-density lipoprotein cholesterol was calculated using the Friedewald formula. A coordinator at each hospital entered data collected from each institution into a standardized computerized database provided by the KCAR committee. The data coordinators attended meetings four times a year; at the meetings, the study protocol was reviewed and discussed. From March 1999 to December 2005, 6,549 patients were registered into the database. All patients were divided into three groups according to age: young patients, ≤40 (n=134), middle-aged patients, 41-70 (n=4451) and older patients, ≥71 (n=1778). We compared the baseline clinical characteristics and angiographic findings among these groups.

Based on the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC) VII guidelines, hypertension was defined as known hypertension or a blood pressure (BP) ≥140/90 mmHg5). The diagnosis of diabetes mellitus was based on fasting plasma glucose levels ≥126 mg per dL (7.0 mmol per L) or two-hour postprandial plasma glucose (2hrPPG) readings ≥200 mg per dL (11.1 mmol per L)6). The metabolic syndrome was defined according to a modification of the Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III)7). Since the cutoff values for the definition of obesity in Asian populations have been revised, the criteria for the metabolic syndrome was modified8). The metabolic syndrome was diagnosed if three or more of the following were present: (a) Obesity defined by a body mass index >25 kg/m² (b) hypertriglyceridemia if the TG ≥150 mg/dL (c) low HDL-C : HDL-C<40 mg/dL in men or <50 mg/dL in women (d) hypertension as known hypertension or a BP ≥130/85 mmHg and (e) dysglycemia was defined as known diabetes (DM) or a fasting plasma glucose ≥110 mg/dL. Cardiac syndrome X was present in patients with typical exertional chest pain, a positive response to stress testing and normal coronary angiograms.

All data were described as means and standard deviation. To compare variables at three intervals, we performed one-way ANOVA and Scheffe's post-hoc test using the SPSS-PC 12.0 statistical package. A p-value less than 0.05 was considered significant.

Of the 6,349 patients enrolled: 70% of the patients were in the 41-70 age group 2.1% in the ≤40 age group, and 27.9% in the ≥71 age group (Figure 1). The ≤40 age group had a higher number of males than the 41-70 and ≥71 age groups (85.1%, 68.9% and 50.1%, respectively, p<0.01). Furthermore, the 40 age group had a higher frequency of smoking and family history of ischemic heart disease than did the other groups (p<0.01, respectively). However, the over 41 age groups had a higher frequency of age-related risk factors such as diabetes mellitus, hypertension and stroke than did the ≤40 age group (p<0.01, respectively) (Table 1) (Figure 2).

Hypercholesterolemia defined as a serum total cholesterol 200 mg/dL or more was more common in the ≤40 age group than in the 41-70 and ≥71 age groups (49.4%, 37.3% and 31.5%, respectively, p<0.01). The levels of total cholesterol, triglycerides and LDL-C were significantly higher in younger patients than in the older patients. However, the HDL-C was not significantly different among the three groups (Table 2). To determine the frequency and contributing factors for the metabolic syndrome, all risk factors were identified and compared in the different groups; the metabolic syndrome for the total study population was identified in 55% of the ≤40, 66% of the 41-70 and 57% of the ≥71. The highest prevalence of the metabolic syndrome was in the middle age group (p<0.001) (Table 3). The frequency of contributing factors for the metabolic syndrome, according to age group was analyzed. In the ≤40 age group, obesity (79%) and hypertension (79%) were the most common contributing factors identified for the metabolic syndrome; hypertension and high fasting glucose were the most common contributing factors in the older age groups (Table 3).

Coronary angiography showed normal or minimal stenosis in 37% and one vessel disease in 48% in the ≤40 age group. The prevalence of multivessel disease was dramatically increased with advancing age; 51% of the patients had more than two vessel disease in the ≥71 age group (Figure 3). Young patients frequently presented with a myocardial infarction (MI), non-ST elevated MI (23%) and ST elevated MI (22%). However, older patients were most frequently admitted with unstable or stable angina (Figure 4). The treatment modalities were not different among the different age groups. About 13~14% of patients were treated by medication only. Percutaneous coronary intervention (PCI) was performed in more than 80% of the patients in each group. Coronary artery bypass graft surgery (CABG) was performed in 1.7% of all patients (Figure 5).