Reduced baroreflex sensitivity in patients with vasovagal syncope

The evidence is conflicting regarding the role of baroreflex in patients with vasovagal syncope. The aim of the study was to measure baroreflex sensitivity (BRS) and hemodynamic parameters during head up tilt test (HUT) with nitroglycerine stimulation.

Nitroglycerine stimulated HUT was performed in 51 patients with the history of recurrent syncope (mean age 46±19 years, 18 men, 23 women). Cardiac output (CO), stroke volume (SV), left-ventricular ejection time (LVET) and total peripheral resistance (TPR) were assessed during HUT by volume-clamp method using a beat-to-beat photopletysmography. Spontaneous BRS sensitivity was computed using a sequential BRS calculation.

HUT was positive after nitroglycerine administration in 28 patients and negative in 23 patients. BRS was lower at the time of syncope in HUT positive group compared to end-test values in HUT negative group (0.54±0.27 vs 0.72±0.35, p=0.03). At the time of syncope, CO was significantly lower in HUT positive patients compared to HUT negative patients (2.6±1.4 vs 4.3±1.4 l/min, p<0.0001), similarly as SV (34.7±14.7 vs 49.2±19 ml, p=0.005). LVET was significantly higher in syncopal patients (282.27±26.2 vs 240.5±58.8 ms, p=0.002) and TPR did not differ between two groups.

Reduced BRS may contribute to the development of the vasovagal syncope by inability to adequately counteract hypotension resulting from decreased cardiac output at the time of syncope (Tab. 3, Ref. 18).