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CLINICAL RESEARCH: ELECTROPHYSIOLOGY

Dissection of long-range heart rate variability

Controlled induction of prognostic measures by activity in the laboratory

^* Cardiovascular Research Group, University of Calgary, Calgary, Alberta, Canada

Manuscript received July 17, 2003; revised manuscript received January 7, 2004, accepted January 12, 2004.

^* Reprint requests and correspondence: Dr. Robert Sheldon, University of Calgary, Faculty of Medicine, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
sheldon{at}ucalgary.ca

OBJECTIVES: We sought to determine whether the long-range measures of heart rate variability (HRV)—the standard deviation of sequential 5-min heart period mean values (SDANN) and the heart period spectral amplitude in the ultra-low frequency band <0.0033 Hz (ULF)—had their origins partly in physical activity.

BACKGROUND: The SDANN and ULF are prognostic HRV factors whose physiologic origins are obscure. Their discontinuous presence throughout the day suggested that they arise from changes in heart period due to activity.

METHODS: Heart period sequences were recorded from 14 patients with left ventricular dysfunction and 14 control subjects during an unrestricted 24-h day, 4-h supine rest, and 4-h epoch with scripted activities.

RESULTS: The SDANN was higher during activity than during rest (74 ± 23 ms vs. 43 ± 17 ms, p < 0.0001), as were ULF magnitudes (p < 0.0001). The increase in SDANN was due to specific activities that contributed heavily (p < 0.0001 by analysis of variance); for example, a 10-min walk and 90-min rest each contributed 22% of total SDANN. Patients with heart disease had a lower SDANN and ULF and a higher mean heart rate than control subjects during all recordings. The proportional ranges in heart period were the same in the two groups during controlled, scripted activities but were wider in control subjects than in patients during ambulatory recordings, suggesting decreased activity by patients.

CONCLUSIONS: Activity increases SDANN by increasing the range of heart periods. Patients with diminished ventricular function have a reduced SDANN on ambulatory electrocardiograms, possibly and partly because of a higher mean heart rate and reduced variations in physical activity.

Abbreviations and Acronyms   ACE = angiotensin-converting enzyme   ANOVA = analysis of variance   ECG = electrocardiogram   HRV = heart rate variability   LV = left ventricular   SDANN = standard deviation of sequential 5-min heart period mean values   SDNN = standard deviation of all heart periods   ULF = ultra-low frequency band <0.0033 Hz

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