All cardiac disease patients who participated in the monitoring exercises at the cardiac rehabilitation clinic from January 2000 to December 2009 were included in the study. Out of a total of 975 patients, 663 patients (67.5%) were male, with a mean age of 58.9±10.6 years. Among them, 731 patients (75.0%) had received a percutaneous transluminal coronary angioplasty (PTCA), while 57 patients (5.8%) had received conservative therapy including medication after a coronary angiography, 129 patients (13.2%) had undergone coronary artery bypass graft (CABG) and 41 patients (4.2%) had had other cardiac operations such as valvular surgery. Eight patients (0.8%) out of the other 17 were under medical treatment for cardiomyopathy, 6 patients (0.6%) for peripheral artery disease, and 3 patients (0.3%) for arrhythmia (Table 1). Intercurrent patients with stroke, cancer or neuromuscular skeletal system diseases for whom faithful implementation of cardiac rehabilitation would be difficult were excluded from the study.

Through a prior graded exercise test, the risk stratification of cardiac attack was investigated, and follow-up measures were examined retrospectively through clinical records for patients in whom cardiovascular-related complications, abnormal hemodynamic responses and symptoms, electrocardiogram abnormalities or any other cardiovascular-related abnormalities had occurred.

Risk assessments of cardiac attack resulting from exercise were performed on the patients participating in cardiac rehabilitation by a prior graded exercise test. The monitoring exercises in the hospital were done under ECG monitoring and were carried out according to exercise prescriptions that included strict management instructions on risk factors for the initial 6 to 8 weeks. Before starting the monitoring exercises, all patients received a symptom-limited graded exercise test using the modified Bruce protocol. For the graded exercise testing, 12-channel real-time ECG tester for exercise load testing Q4500 (Quinton Instrument Co., Boston, USA), automatic blood pressure and pulse measuring instrument Model 412 (Quinton Instrument Co., Boston, USA), and treadmill for graded exercise testing Medtrack ST 55 (Quinton Instrument Co., Boston, USA) were employed. Exercise prescriptions were issued based on the results of the initial graded exercise test. The exercise time for each session consisted of 10 minutes for the preparatory exercise, 30 minutes for the main exercise, and 10 minutes for the cooling down exercise for a total of 50 minutes. The exercise intensity in terms of the target heart rate increased stepwise from 40% to 85% of the heart rate reserve values as calculated from the graded exercise test results. The rate of perceived exertion (RPE) during the monitoring exercises was maintained at 13-14 (a little difficult). Throughout the monitoring exercise, real-time ECG, heart rate, and blood pressure were monitored, the patient's perceived symptoms frequently checked, and the indices recorded.

Not a single incident of fatal cardiovascular-related complication such as death, cardiac arrest, or acute myocardial infarction occurred during the monitoring exercises (0/13,934 exercise hours). However, there were 70 cases of cardiovascular-related abnormal events in 59 patients (1/199 exercise hours), of which 17 cases (1/820 exercise hours) were angina pectoris only without ECG abnormality. There were 31 cases of ECG abnormality without a symptom (1/449 exercise hours), 12 cases of both angina pectoris and ECG abnormality (1/1,161 exercise hours), and 10 cases of abnormal hemodynamic response (1/1,393 exercise hours) (Table 2).

Among 59 patients for whom cardiovascular-related abnormalities were observed during exercise, 41 patients (69. 5%) were male with a mean age of 56.5±12.4 years. Prior to initiation of the cardiac rehabilitation, 53 patients (89.8%) had received a PTCA, with an average remaining stenosis rate of 23.5±8.4%, and an average ejection fraction of the left ventricle of 46.3±21.2%; 34 patients (57.6%) had lesions of the left anterior descending artery, and 6 patients (10.2%) had CABG (Table 3). Classification of these 59 patients according to exercise risk stratification9,10 showed 45 patients (76.3%) belonged to the high risk group, 8 patients (13.5%) to the middle risk group, and 6 patients (10.2%) to the low risk group (Table 4).

Out of the 59 patients who had problems during monitoring exercise, 36 had their problems resolved through confirmation angiography and adjustment of cardiovascular-related medications. On angiography, 20 patients showed restenosis and received PTCA for reperfusion. One patient who exhibited atrial fibrillation and ventricular tachycardia received internal defibrillator insertion, and another patient showing bradycardia and syncope underwent coronary artery bypass graft. The patient with ventricular tachycardia was prescribed Verapamil injection intravenously and a dosage of a calcium channel blocker (Table 5). All 59 patients were able to participate in the monitoring exercises again, and have been receiving regular follow-up while continuously participating in cardiac rehabilitation programs of their local communities.