Autonomic modulation and cardiac contractility in vasovagal syncope

Area of Science:

• Cardiology
• Autonomic Nervous System Research
• Physiology

Background:

• Neurally mediated syncope may involve ventricular mechanoreceptor stimulation triggering vagal discharge.
• Previous hypotheses suggest increased cardiac contractility precedes vasovagal syncope.

Purpose of the Study:

• To investigate if sympathetic activity increases cardiac contractility before vasovagal syncope.
• To explore the role of cardiac contractility in the pathogenesis of syncope.

Main Methods:

• Studied 23 patients with recurrent syncope undergoing a 60° tilt test with nitrate challenge.
• Assessed autonomic activity via heart rate variability analysis.
• Quantified cardiac contractility using tissue-Doppler echocardiography, measuring peak systolic (Sw) and diastolic (Aw) myocardial velocities.

Main Results:

• Tilt-induced syncope showed increased low-frequency and decreased high-frequency heart rate variability components, indicating sympathetic activation.
• Ventricular contractility (Sw) increased similarly in syncopal and non-syncopal patients.
• Atrial contractility (Aw) significantly decreased in syncopal patients.

Conclusions:

• Findings do not support increased ventricular contractility preceding tilt-induced syncope.
• A reduction in atrial contractility is observed, potentially contributing to vasovagal syncope.
• This challenges the proposed mechanism of ventricular mechanoreceptor stimulation as the primary trigger.