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
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Figure 1 Heart rate and blood pressure changes during the control and saline tilt sequences. Heart rate increased markedly (A) and blood pressure (B) decreased early during the control tilt. A significant decrease in blood pressure presaged syncope; this occurred first and was subsequently accompanied by a significant decrease in heart rate. The hemodynamic changes were comparatively attenuated during the saline tilt. A small increase in heart rate between the early tilt and late tilt period was observed. #p < 0.05, early tilt or midtilt vs. supine. *p < 0.05, midtilt or late tilt vs. early tilt. +p < 0.05 faint/late tilt vs. midtilt.
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Figure 2 Power spectral density during control tilt (A) and saline tilt (B). During the control tilt, upon assumption of the upright position, there was a significant increase in low frequency power (0.03 to 0.15 Hz) with a decrease in high frequency power (0.16 to 0.50 Hz). Despite continued upright positioning, there was a progressive decline in low frequency power. After the administration of normal saline, low frequency power progressively increased during the remainder of upright positioning.
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Figure 3 Low frequency (LF) power during control and saline tilt: A, LF power, B, peak LF power, and C, LF/high frequency (HF) ratio. With upright tilt during the control state, there was a rapid and early peak in LF power. With continued upright positioning, a progressive decrease in LF power was observed. However, after saline administration, LF power remained constant throughout the duration of upright tilt. Solid line = control tilt; dashed line = saline tilt. #p < 0.05, early tilt vs. supine. *p < 0.05, faint/late tilt vs. early tilt.
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