Evaluation of the Reynolds Pathfinder II system for 24 h heart rate variability analysis

Heart rate variability (HRV) in 24-h Holter recordings is normallydetermined using commercially available Holter equipment. However,short-term speed variations in tape-based Holter systems havenot been thoroughly investigated and recommendations for speedcontrol are vague. In this study, overall accuracy and precisionof RR interval measurement was assessed for two types of taperecorder replayed on the same Reynolds Pathfinder II system.Artificial QRS complexes spaced at exact intervals were recordedsimultaneously by the two recorders. In addition, records of118 healthy subjects were evaluated for false-positive normal-normalintervals. During replay, digital output from the pathfinderwas processed by a locally developed personal computer-basedHR V system. Using the recorded crystal generated timing track (TT)for speedcontrol and the TT dependent speed surveyor (SS), set to allowspeed errors up to±3·1% mean RR per 5min. h^h–1.24 h^h–1,for test tapes, corresponded exactly to true RR,forboth recorders. Beat-to-beat variation, for 1000 ms test intervals,calculated as standard deviation (SD) and root mean square ofsuccessive differences (RMSSD) was 3 ms, 3 ms versus 5 ins,and 8 ms for Oxford and Tracker tapes respectively. No differencebetween sequential intervals exceeded±10 ms versus ±20ms for Oxford and Tracker respectively. Reproducibility of meanRR and HRV parameters for patient records, expressed as a coefficientof variation, was 0·1–1·7%. False positivenormal-normal intervals>2·3 s, due to artifacts, werefound in 99 of 118 records, and these increased mean SD andRMSSD values significantly, whereas percent successive RR intervaldifferences>50 ms were unaffected. A crystal generated TT (60/16 Hz) and an SS allowing a maximumerror of±31%, together correct speed during recordingand replay to a degree that is acceptable for HRV analysis.A simple estimate of HRV counts of successive RR interval differences>50ms is a reliable param eter as it is relatively insensitiveto artifact.