Left Ventricular Hypercontractility Immediately after Tilting Triggers a Disregulated Cardioinhibitory Reaction in Vasovagal Syncope: Echocardiographic Evaluation during the Head-Up Tilt Test

OBJECTIVES: Vasovagal syncope (VVS) has been believed to occur when mechanoreceptors are discharged by vigorous ventricular contraction. However, previous investigators have reported divergent observations regarding the presence of left ventricular (LV) hypercontractility in VVS. Because the autonomic nervous system can be promptly activated after certain stimuli, we postulated that instantaneously increased LV contractility at the time of venous pooling may trigger the disregulated vasovagal reaction in VVS. METHODS: Forty-seven patients (31 males, mean age 41 ± 18 years) with unexplained syncope were enrolled. Echocardiography was performed during the head-up tilt test (HUTT) as follows: baseline, passive tilting (0 and 20 min), and tilting with isoproterenol administration (5 and 10 min). Patients were divided into 2 groups according to the results of the HUTT; group 1 (n = 12) had a positive result and group 2 had a negative response. RESULTS: LV ejection fraction (LVEF), determined immediately after tilting, increased in group 1, whereas LVEF decreased in group 2 (p = 0.032). Although left atrial and LV volumes decreased similarly during the test, group 1 showed a progressive reduction in LVEF, while LVEF progressively increased in group 2 (p = 0.007). CONCLUSION: Patients with HUTT-induced VVS presented LV hypercontractions immediately after tilting and a subsequent decrease in LV contractility. An instantaneous activation of the sympathetic nervous system at the time of venous pooling may trigger an early disregulated vasovagal reflex via an increase in LV contractility in VVS.