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Impaired arterial baroreceptor sensitivity before tilt-induced syncope.
1Centro de Estudos da Função Autonómica, Hospital de São João, Porto, Portugal.
Summary
Autonomic dysfunction in neurocardiogenic syncope (NCS) is linked to reduced baroreceptor gain and high-frequency heart rate variability during tilt tests. These changes occur before syncope, indicating transient autonomic dysfunction.
Area of Science:
- Cardiology
- Autonomic Neuroscience
- Physiology
Background:
- Neurocardiogenic syncope (NCS) pathophysiology is debated, with autonomic dysfunction implicated.
- Conflicting data exist regarding autonomic nervous system (ANS) involvement in NCS.
- Understanding ANS and hemodynamic changes during NCS is crucial for diagnosis and management.
Purpose of the Study:
- To evaluate autonomic nervous system (ANS) function and non-invasive hemodynamics in patients with neurocardiogenic syncope (NCS).
- To analyze changes in heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreceptor gain (BRG) during head-up tilt testing in NCS patients.
- To determine if baseline autonomic and hemodynamic parameters can predict tilt-induced syncope.
Main Methods:
- Retrospective and prospective evaluation of NCS patients, non-NCS syncope patients, and normal controls undergoing head-up tilt tests.
- Assessment of HRV and SBPV using Fast Fourier Transforms (FFT).
- Measurement of spontaneous baroreceptor gain (BRG) and non-invasive hemodynamics (cardiac output, total peripheral resistance) using Modelflow.
Main Results:
- No significant baseline differences in autonomic or hemodynamic parameters were observed between groups, except for higher baseline systolic blood pressure in controls.
- During tilt testing in NCS patients, heart rate increased, systolic blood pressure decreased, arterial baroreceptor gain reduced, and high-frequency HRV decreased before syncope.
- Low-frequency HRV, SBPV, cardiac output, and total peripheral resistance remained unchanged throughout the tilt test.
Conclusions:
- A decrease in arterial baroreceptor gain and high-frequency HRV may be early indicators of the transient autonomic dysfunction characterizing NCS.
- Baseline autonomic and hemodynamic assessments are insufficient to predict tilt-induced syncope.
- Further research into the dynamic changes of ANS function during tilt testing is warranted for a comprehensive understanding of NCS pathophysiology.