Left ventricular hypercontractility immediately after tilting triggers a disregulated cardioinhibitory reaction in vasovagal syncope: echocardiographic evaluation during the head-up tilt test.
OBJECTIVE
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).


CONCLUSIONS
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.
Divisions of Cardiology, Yonsei Cardiovascular Center, Yonsei University College of Medicine, Seoul, Republic of Korea.
Jeonggeun
J
Moon
Hyunsu
H
Kim
Jong-Youn
JY
Kim
Soreen
S
Chung
Eui-Young
EY
Choi
Pil-Ki
PK
Min
Byoung Kwon
BK
Lee
Bum-Kee
BK
Hong
Hyuck Moon
HM
Kwon
Se-Joong
SJ
Rim
D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology; D002306:Cardiac Volume / Q000502:physiology; D004452:Echocardiography; D005260:Female; D006321:Heart / Q000294:innervation / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D011187:Posture / Q000502:physiology; D012021:Reflex, Abnormal / Q000502:physiology; D019462:Syncope, Vasovagal / Q000150:complications* / Q000503:physiopathology*; D018667:Tilt-Table Test; D018487:Ventricular Dysfunction, Left / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology*; D055815:Young Adult