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Enhanced reflex response to baroreceptor deactivation in subjects with tilt-induced syncope

, : Enhanced reflex response to baroreceptor deactivation in subjects with tilt-induced syncope. Journal of the American College of Cardiology 41(7): 1167-1173, April 2

OBJECTIVES: We sought to evaluate whether changes in resting baroreflex control of heart rate are a distinctive feature of healthy subjects with a history of syncope prone to a positive tilt-test response. BACKGROUND: The mechanisms involved in the pathogenesis of vasovagal syncope (VVS) are still poorly understood; in particular, the contribution of arterial baroreflex control of heart rate is matter of discussion. METHODS: A passive tilt-table test was performed in 312 consecutive, otherwise healthy subjects (age 36+-15 years) with unexplained syncope and 100 control subjects. At baseline, spontaneous baroreflex sensitivity (BRS; ms/mm Hg) and the baroreflex effectiveness index (BEI) were assessed using the sequence method. RESULTS: The study population showed normal baroreflex function. Tilt-induced VVS in 94 subjects who were younger than both the tilt-negative and control subjects (30+-14, 38+-15, and 37+-14 years, respectively; p=0.00005) showed greater BRS (17.4+-9.8, 13.2+-7.9, and 12.8+-8.2 ms/mm Hg, respectively; p=0.0001), but had a similar BEI (0.59+-0.18, 0.56+-0.19, and 0.58+-0.2, respectively; p=NS). On Cox multivariate analysis, the occurrence of VVS during tilt was inversely related to age (hazard ratio 0.97; p=0.0004) and directly related to the BRS slope of sequences, implying a baroreceptor deactivation (hazard ratio 1.05; p=0.02), but not of sequences characterized by arterial baroreceptor stimulation. CONCLUSIONS: Subjects with tilt-induced VVS showed greater resting BRS but had a normal BEI. The enhanced reflex tachycardic response to arterial baroreceptor deactivation at rest may represent a characteristic feature of subjects prone to tilt-induced VVS.


PMID: 12679218

DOI: 10.1016/s0735-1097(03)00050-0

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