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(Circulation. 1998;98:1587-1590.)
© 1998 American Heart Association, Inc.

Correspondence

Heart Rate Variability Standards

Cheng-Deng Kuo, MD, PhD; ; Gau-Yang Chen, MD, MS

Cardiopulmonary Laboratory, Respiratory Therapy Department, Veterans General Hospital-Taipei and Institute of Clinical Medicine, National Yang-Ming University School of Medicine, Taipei, Taiwan, Republic of China

To the Editor:

The special report on heart rate variability by the European Society of Cardiology and North American Society of Pacing and Electrophysiology¹ presented important standards of measurement for heart rate variability analysis. In the report, the frequency range of the total power was defined as 0.04 to 0.4 Hz, the low-frequency (LF) component as 0.04 to 0.15 Hz, and the high-frequency (HF) component as 0.15 to 0.4 Hz. There are several problems in the calculation of specific spectral powers using these standards of measurement in heart rate variability analysis.

As stated in the report, the HF component is respiration related, and the distribution of the power and the central frequency of LF and HF components are not fixed but vary in relation to changes in autonomic modulations of heart period in the short-term recordings. Therefore, integrating the HF power within the all-frequency range of 0.15 to 0.4 Hz might have inherent error, especially when the respiration rate does not fall within this range for patients who have tachypnea or are under controlled respiration. Because the maximum frequency in the spectrum is the Nyquist frequency (half the sampling frequency),^{2 3} it might be better to use the Nyquist frequency as the upper limit of both HF power and total power.

When the direct current is excluded by baseline or trend removal in the calculation of spectral powers, the nonharmonic components in the very-low-frequency (VLF) region (<0.04 Hz) can be removed. In this case, it is not necessary to set a . . . [Full Text of this Article]

Marek Malik, MD, PhD

Department of Cardiological Sciences, St. George's Hospital Medical School, London, UK on behalf of the ESC/NASPE Task Force