CLINICAL STUDIES
Neurally mediated cardiac syncope: autonomic modulation after normal saline infusion
Thomas R. Burklow, MD, FACC*,
Jeffrey P. Moak, MD, FACC*,
James J. Bailey, MD, MSc and
Fairouz T. Makhlouf, MS
* Department of Cardiology, Children’s National Medical Center, Washington, DC, USA
Center for Information Technology, National Institutes of Health, Bethesda, Maryland, USA
Department of Statistics, American University, Washington, DC, USA. The opinions and assertions in this article are those of the author (T.R.B.) and do not necessarily represent those of the Department of the Army or Department of Defense
Manuscript received April 15, 1997;
revised manuscript received January 25, 1999,
accepted February 24, 1999.
Reprint requests and correspondence: Dr. Jeffrey P. Moak, Department of Cardiology, Children’s National Medical Center, 111 Michigan Ave, N.W., Washington, DC 20010
jmoak{at}cnmc.org
OBJECTIVES
This study assessed the heart variability response to orthostatic stress during tilt table testing before and after normal saline administration.
BACKGROUND
The efficacy of sodium chloride and mineralocortoid in the treatment of neurally mediated cardiac syncope is attributed to intravascular volume expansion; however, their modulation of autonomic nervous system activity has not been evaluated.
METHODS
Heart rate variability analysis was performed on 12 adolescents with a history of syncope or presyncope (mean age 15.2 ± 0.7 years) during tilt table testing. Subjects were upright 80° for 30 min or until syncope. After normal saline administration, the patient was returned upright for 30 min. Heart rate variability analysis data were analyzed by an autoregression model (Burg method).
RESULTS
All subjects reproducibly developed syncope during control tilt table testing; median time to syncope was 9.4 ± 2.1 min. After normal saline infusion, none of the subjects developed syncope after 30 min upright. In the control tilt, there was an initial increase followed by a progressive decrease in low frequency power until syncope. Repeat tilt after normal saline administration demonstrates that low frequency power increased but the magnitude of initial change was blunted when compared with control. In addition, low frequency power increased during normal saline tilt sequence compared with the control tilt, during which it decreased.
CONCLUSIONS
Normal saline blunted low frequency power stimulation and prevented paradoxical low frequency power (sympathetic) withdrawal. Increasing intravascular volume with normal saline alters autonomic responses that may trigger neurally mediated syncope reflexes.
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Abbreviations and Acronyms
| | HF | = high frequency | | HRV | = heart rate variability | | HUT | = head-up tilt | | LF | = low frequency |
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