High speed detection of R-R intervals for universal Holter recordings.

Abstract

Heart rate variability (HRV) has been gaining popularity for its potential to estimate the autonomic nerve function and prognosis of patients with cardiovascular diseases. Holter recordings have been used for the measurement of R-R intervals in out-patients and for the estimation of circadian variations of HRV. However, when the manufacturer of the Holter tape recorder is not the same as that of the Holter analyzer a correction of the tape speed error for the accurate measurement of the R-R intervals is abandoned. The simultaneous assessment of additional physical parameters recorded on the Holter recorder and R-R interval is not possible with commercial software. To overcome these problems, we developed a system to detect R-R intervals at the playback speed of a Holter analyzer 500 times real-time with the correction of tape speed error from a system clock recorded on the Holter tape. High- and low-pass filter processed ECG signals and a comparator provided digital signals representing the R-R intervals. The R-R intervals and system clock intervals (tape speed) were measured simultaneously by interrupt-driven software, using timer-counters in a personal computer. The measured R-R intervals were corrected with the system clock intervals. The power spectra of the tape speed error showed that tape speed error significantly affects the power spectra of HRV, if not corrected. This method is applicable to Holter tape recorders of any manufacturer. This system also enables the simultaneous measurement of HRV and other physical parameters to evaluate their relations.