Reduced baroreflex sensitivity in patients with vasovagal syncope

Area of Science:

• Cardiology
• Autonomic Nervous System Function
• Syncope Pathophysiology

Background:

• Conflicting evidence exists on the baroreflex sensitivity's role in vasovagal syncope.
• Understanding baroreflex function is crucial for diagnosing and managing syncope.

Purpose of the Study:

• To measure baroreflex sensitivity (BRS) and hemodynamic parameters.
• To investigate these parameters during a head-up tilt test (HUT) with nitroglycerine stimulation in patients with recurrent syncope.

Main Methods:

• 51 patients with recurrent syncope underwent nitroglycerine-stimulated HUT.
• Beat-to-beat photopletysmography assessed cardiac output (CO), stroke volume (SV), left-ventricular ejection time (LVET), and total peripheral resistance (TPR).
• Spontaneous BRS was calculated using sequential analysis.

Main Results:

• The head-up tilt test was positive in 28 patients and negative in 23.
• Reduced BRS was observed at syncope in the HUT-positive group compared to the HUT-negative group (0.54±0.27 vs 0.72±0.35, p=0.03).
• At syncope, HUT-positive patients showed significantly lower CO (2.6±1.4 vs 4.3±1.4 l/min, p<0.0001) and SV (34.7±14.7 vs 49.2±19 ml, p=0.005), with higher LVET (282.27±26.2 vs 240.5±58.8 ms, p=0.002).

Conclusions:

• Reduced BRS may contribute to vasovagal syncope.
• This occurs due to an impaired ability to counteract hypotension caused by decreased cardiac output during syncope.