Background: Syncope in apparently healthy subjects is usually attributed to a vasovagal reaction. However, a vagal cardio-inhibitory component is not always associated with a vasodepressor component in causing syncope: in fact, increases in heart rate, arterial pressure and plasmatic levels of catecholamines frequently precede loss of consciousness.
Methods: Prolonged 60 degrees head-up tilt table test (HUTT) was performed in 50 healthy subjects (27 male, 23 female - mean age 37.2 years) with recurrent syncope of vasodepressor or unknown origin. The upright-tilt test lasted 45 minutes: every minute of HUTT we measured heart rate (HR) and systolic (SBP) and diastolic blood pressure (DBP); at set intervals we took a blood sample to determine epinephrine (EP) and norepinephrine (NEP) levels.
Results: In patients with positive HUTT (42%) we observed a vaso-vagal response (10 patients) characterized by a sharp drop in SBP and DBP (> 50% of the basal values) and bradycardia (< 40 bpm) and/or sinus node arrests, and a hyperchronotropic-vasodepressor response (11 patients) characterized by a considerable increase in HR (> 60%) and simultaneous drop in SBP and DBP (> 30% of the basal values), and a large increase in plasmal EP (+881.9%).
Conclusions: According to the Authors, vasovagal response is mainly due to a reflex reaction originating from the cardiac stretch-receptors, whereas hyperchronotropic-vasodepressor response is mainly due to psychic stress and anxiety provoked by prolonged and forced posture during HUTT. The high levels of adrenergic activity and plasmal EP cause the excessive chronotropic response and the vasal effects of the syndrome. Due to the induction of a state of anxiety and its postural effects, HUTT is a useful provocative tool for complete evaluation of young patients with syncope of vasodepressor origin. We treated the patients differently, depending on how they responded to HUTT. Those with a vaso-vagal response were treated with alpha-sympathomimetic agents (ethylephrine or mydodrine) and those with a hyperchronotropic-vasodepressor response received non-selective beta-blockers. None of our patients had syncope recurrences during a mean follow-up of 12.3 months. Only two patients complained of dizziness; in one of them, symptomatology was abolished by an alpha-sympathomimetic beta-blocker association.