Postural Response of Low-Frequency Component of Heart Rate Variability: Materials and Methods

Patients
We studied retrospectively a cohort of 250 consecutive patients (181 men and 69 women) who were admitted to the Nagoya City University Hospital for elective cardiac catheterization and coronary angiography between November 1987 and February 1991. During the hospital admission, we had assessed short-term HRV during HUTT during previous studies on the relationships between autonomic functions and coronary atherosclerosis. All patients had CAD documented by positive results of exercise testing with thallium myocardial scintigraphy, previous angiographic evidence of coronary artery stenosis, or a history of myocardial infarction. None of the patients, however, had any of the following conditions at baseline: (1) valvular heart disease or congenital heart disease; (2) congestive heart failure of New York Heart Association class III or IV; (3) myocardial infarction, stroke, or major surgical procedure within the previous 6 months; (4) high-grade heart block or pacemaker therapy; (5) frequent ectopic beats or atrial fibrillation; and (6) insulin-dependent diabetes melli-tus, COPD, uncontrolled hypertension, severe renal or hepatic disease, malignancy, or other life-threatening disease.
At baseline, the mean (± SD) age of the patients was 57 ± 9 years (age range, 40 to 75 years). Ninety-eight patients (39%) had a history of myocardial infarction, but none had a history of coronary angioplasty or bypass graft surgery, 52 (21%) had non-insulin-dependent diabetes mellitus, and 136 (54%) were smokers. The mean left-ventricular ejection fraction was 64 ± 11%. The protocol of this study was approved by the Nagoya City University Medical School Institutional Review Board.

Baseline Measurements and Follow-up
Baseline clinical characteristics including medical history, lifestyle, plasma lipid concentration, and glucose concentration after a 14-h fast were available for all patients from their medical records during the index hospital admission. The number of patients with coronary artery stenosis (which was defined as a luminal narrowing of > 75% in a major coronary artery or branch) and the values for left ventricular ejection fraction and end-diastolic pressure were obtained from the cardiac catheterization data recorded at baseline. For the purposes of the autonomic assessment, treatment with all medications but sublingual nitroglycerin had been discontinued for at least 1 week before hospital admission. None of the patients had been receiving a long-acting P-blocker during the preceding month. Additionally, no patients developed any symptoms of syncope or presyncope during the HUTT.

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