The influence of recording length on time and frequency domain analysis of heart rate variability

Analysis of Heart Rate Variability (HRV) is used to assess autonomic control of the heart. Many technical aspects may influence the outcome of HRV analysis. One of these aspects is recording length. Ambulatory monitoring recordings are frequently used as a data source. Because of their mathematical properties, some HRV variables are influenced by recording length. Further more, recording length may play a role, since, in clinical practice, hook-up times of ambulatory monitoring are not randomly distributed over time. In order to test recording-length related changes of HRV the authors tested three groups: 1. healthy subjects (n=24); 2. congestive heart failure patients (n=24); and 3. patients with coronary artery disease (n=21). Results revealed that although the average normal to normal interval already changed after 1 hour reduction, most time domain variables differed statistically significantly after 4 hours reduction in length. Frequency domain variables proved to be less sensitive to recording-length changes. The extent of length related changes of HRV was shown to vary in different patient categories. It is concluded that ambulatory monitoring recordings less than 20 hours long should not be used for HRV analysis