After discharge from the hospital, all patients were observed and medically treated by cardiologists in the Nagoya City University Hospital or by their family doctors. In 1999, the medical records were reviewed for cardiovascular events, intervention therapies, and medications. Furthermore, after obtaining written informed consent, the patients or their families were interviewed by telephone about cardiovascular and noncardiovascular events by a cardiologist who was blinded to the baseline HRV measurements. The interview was not possible in 7 of 250 patients (2.8%) for whom the follow-up period terminated at the last date on their available medical records. The mean follow-up period duration for the seven patients was 29 ± 9 months (range, 14 to 47 months).
We used only death as the end point of the present study. The causes of death were classified as follows: (1) cardiac death (ie, death from myocardial infarction, heart failure, fatal arrhythmia, or sudden cardiac death, which was defined as death within 1 h after the onset of a new symptom); and (2) noncardiac death.
To estimate the normal ranges for stationary-state levels of HRV and the responses of patients to the HUTT, we studied an age-matched and gender-matched group of 90 healthy subjects (65 men and 25 women; mean age, 58 ± 10 years; range, 45 to 70 years). The subjects had been screened for latent disorders through medical history, physical examinations, laboratory examinations, and ECG. Elderly subjects (ie, those subjects > 65 years old) also had been screened for occult cardiovascular disease by exercise tolerance testing. None of the subjects had received any medications for > 2 weeks preceding the study, but 32 subjects (35%) were smokers. These subjects underwent HUTT with the same protocol as that used in the patients, although they did not undergo coronary angiography.