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A Method for Automatic Identification of Reliable Heart Rates Calculated from ECG and PPG Waveforms

Affiliations of the authors: Bioinformatics Cell, Telemedicine and Advanced Technology Research Center, US Army Medical Research and Materiel Command, Fort Detrick, MD (CY, ZL, TM, JR); Department of Emergency Medicine, Massachusetts General Hospital, Boston, MA (ATR); Dr. Liu is currently with the Division of Biostatistics, Greenebaum Cancer Center and Department of Epidemiology and Preventive Medicine, University of Maryland Medical Center.

Correspondence and reprints: Jaques Reifman, PhD, U.S. Army Medical Research and Materiel Command MRMC/TATRC, 504 Scott Street, Ft. Detrick, MD 21702-5012; e-mail: <jaques.reifman{at}us.army.mil>.

Received for publication: 08/01/05; accepted for publication: 01/16/06.

Objective: The development and application of data-driven decision-support systems for medical triage, diagnostics, and prognostics pose special requirements on physiologic data. In particular, that data are reliable in order to produce meaningful results. The authors describe a method that automatically estimates the reliability of reference heart rates (HRr) derived from electrocardiogram (ECG) waveforms and photoplethysmogram (PPG) waveforms recorded by vital-signs monitors. The reliability is quantitatively expressed through a quality index (QI) for each HRr.

Design: The proposed method estimates the reliability of heart rates from vital-signs monitors by (1) assessing the quality of the ECG and PPG waveforms, (2) separately computing heart rates from these waveforms, and (3) concisely combining this information into a QI that considers the physical redundancy of the signal sources and independence of heart rate calculations. The assessment of the waveforms is performed by a Support Vector Machine classifier and the independent computation of heart rate from the waveforms is performed by an adaptive peak identification technique, termed ADAPIT, which is designed to filter out motion-induced noise.

Results: The authors evaluated the method against 158 randomly selected data samples of trauma patients collected during helicopter transport, each sample consisting of 7-second ECG and PPG waveform segments and their associated HRr. They compared the results of the algorithm against manual analysis performed by human experts and found that in 92% of the cases, the algorithm either matches or is more conservative than the human's QI qualification. In the remaining 8% of the cases, the algorithm infers a less conservative QI, though in most cases this was because of algorithm/human disagreement over ambiguous waveform quality. If these ambiguous waveforms were relabeled, the misclassification rate would drop from 8% to 3%.

Conclusion: This method provides a robust approach for automatically assessing the reliability of large quantities of heart rate data and the waveforms from which they are derived.