Ms. Houle et Ge. Billman, Low-frequency component of the heart rate variability spectrum: a poor marker of sympathetic activity, AM J P-HEAR, 45(1), 1999, pp. H215-H223
Citations number
32
Categorie Soggetti
Cardiovascular & Hematology Research
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
The low-frequency component of the heart rate variability spectrum (0.06-0.
10 Hz) is often used as an accurate reflection of sympathetic activity. The
refore, interventions that enhance cardiac sympathetic drive, e.g., exercis
e and myocardial ischemia, should elicit increases in the low-frequency pow
er. Furthermore, because an enhanced sympathetic activation has been linked
to an increased propensity for malignant arrhythmias, one might also predi
ct a greater low-frequency power in animals that are susceptible to ventric
ular fibrillation than in resistant animals. To test these hypotheses, a 2-
min coronary occlusion was made during the last minute of exercise in 71 do
gs with healed myocardial infarctions: 43 had ventricular fibrillation (sus
ceptible) and 28 did not experience arrhythmias (resistant). Exercise or is
chemia alone provoked significant heart rate increases in both groups of an
imals, with the largest increase in the susceptible animals. These heart ra
te increases were attenuated by beta-adrenergic receptor blockade. Despite
the sympathetically mediated increases in heart rate, the low-frequency pow
er decreased, rather than increased, in both groups, with the largest decre
ase again in the susceptible animals: 4.0 +/- 0.2 (susceptible) vs. 4.1 +/-
0.2 In ms(2) (resistant) in preexercise control and 2.2 +/- 0.2 (susceptib
le) vs. 2.9 +/- 0.2 In ms(2) (resistant) at highest exercise level. In a si
milar manner the parasympathetic antagonist atropine sulfate elicited signi
ficant reductions in the low-frequency power. Although sympathetic nerve ac
tivity was not directly recorded, these data suggest that the low-frequency
component of the heart rate power spectrum probably results from an intera
ction of the sympathetic and parasympathetic nervous systems and, as such,
does not accurately reflect changes in the sympathetic activity.