MEASUREMENT OF PARASYMPATHETIC ACTIVITY FROM 24-HOUR AMBULATORY ELECTROCARDIOGRAMS AND ITS REPRODUCIBILITY AND SENSITIVITY IN NORMAL SUBJECTS, PATIENTS WITH SYMPTOMATIC MYOCARDIAL-ISCHEMIA, AND PATIENTS WITH DIABETES-MELLITUS

The parasympathetic nervous system plays a major role in the pathophys iology of many cardiovascular diseases, particularly in modulating myo cardial electrical stability. Measurements of heart rate variability h ave been widely used to assess parasympathetic activity. The reproduci bility of measurements obtained from 24-hour ambulatory electrocardiog rams has not been well documented. We have developed a technique for m easuring parasympathetic activity from clinical quality 24-hour ambula tory electrocardiograms by counting beat-to-beat increases in RR inter val that are >50 ms. To determine the reproducibility and sensitivity of our technique, we analyzed repeated 24-hour electrocardiograms of 1 73 subjects (19 normal subjects, 67 patients with ischemic heart disea se, and 87 diabetics) followed up over periods of 2 to 16 weeks. In al l subject groups, mean valves for repeated measurements were virtually identical, Measurements were stable in all 3 groups throughout the co urse of the study, as assessed by intraclass correlation coefficients. This technique is sensitive enough to detect relatively small changes in parasympathetic activity in subjects, as demonstrated by the In ca lculated Bland and Altman coefficients of repeatability. Reproducibili ty and sensitivity of our technique are particularly good in normal su bjects and in patients with ischemic heart disease. The results obtain ed with this technique imply that other related measurements of parasy mpathetic activity will show similar excellent short- and long-term re producibility and sensitivity.