Evaluating the relative contributions of vasodepression and cardioinhibition to the blood pressure (BP) decrease in tilt-induced vasovagal syncope (T-VVS) requires methods that reflect BP physiology accurately. In order to assess the relative contributions of vasodepression and cardioinhibition to T-VVS using novel methods.

The parameters determining BP, i.e., total peripheral resistance (TPR), heart rate (HR), and stroke volume (SV), in 163 patients with T-VSS documented by continuous EEG and ECG monitoring. Cardioinhibition was defined as the start of an HR decrease (HR) before syncope and used logarithms of SV, HR, and TPR ratios to quantify the multiplicative relation BP=SV·HR·TPR. Cardioinhibition initially only represented a reduction of the corrective HR increase but was accompanied by an immediate acceleration of the ongoing BP decrease. The two significant factors lowering BP in T-VVS were reduced cardioinhibition and SV. The term vasodepression in reflex syncope should not be limited to reduced arterial vasoconstriction, reflected in TPR, but should also encompass venous pooling, reflected in SV.

T-VVS is the result of 3 overlapping processes. The least important process is decreased TPR, the likely result of diminished arteriolar vasoconstriction. The cardioinhibition, starting late but gaining strength quickly has its effect on BP at syncope was similar in size to that of SV’s fall.

Ref: https://www.ahajournals.org/doi/10.1161/CIRCRESAHA.120.316662