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Neurally mediated cardiac syncope: autonomic modulation after normal saline infusion
T R Burklow1, J P Moak, J J Bailey
1Department of Cardiology, Children's National Medical Center, Washington, DC 20010, USA.
Journal of the American College of Cardiology
|June 11, 1999
Summary
Normal saline administration prevented syncope in adolescents by altering autonomic nervous system responses during tilt table testing. This intervention blunted low-frequency power changes, suggesting a modified sympathetic withdrawal.
Area of Science:
- Cardiology
- Autonomic Nervous System Physiology
- Pediatric Medicine
Background:
- Neurally mediated syncope treatment often involves intravascular volume expansion.
- The impact of volume expansion on autonomic nervous system activity in syncope has not been thoroughly evaluated.
Purpose of the Study:
- To assess heart rate variability (HRV) response to orthostatic stress during tilt table testing.
- To determine the effect of normal saline administration on HRV in adolescents with syncope.
Main Methods:
- 12 adolescents with syncope history underwent tilt table testing (80 degrees for 30 min).
- HRV analysis was conducted before and after normal saline infusion.
- Data were analyzed using an autoregression model (Burg method).
Main Results:
- All subjects experienced syncope during control testing; normal saline prevented syncope in all participants.
- Control tilt showed an initial increase then decrease in low-frequency (LF) power until syncope.
- Normal saline blunted the initial LF power increase and prevented LF power decrease during tilt.
Conclusions:
- Normal saline administration altered autonomic responses during orthostatic stress.
- This intervention prevented paradoxical sympathetic withdrawal and syncope.
- Increasing intravascular volume may modify autonomic reflexes triggering neurally mediated syncope.