Cardiac Arrhythmia and Syncope Center, Department of Medicine (Cardiovascular Division), University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
Heart Rhythm. 2012 Nov;9(11):1847-52. doi: 10.1016/j.hrthm.2012.07.028. Epub 2012 Aug 1.
Although vasovagal syncope (VVS) is preceded by a surge of circulating catecholamines (epinephrine [Epi] and norepinephrine [NE]) of adrenal/renal and synaptic origin, prevention of VVS with β-adrenergic blockade has been ineffective except in "older" VVS patients.
We hypothesized that age-related differences of β-blocker effect may be due in part to differences in the relative magnitudes of Epi and NE release during an evolving faint, specifically, greater Epi/NE ratio in younger fainters compared to older patients. To assess this hypothesis, we measured changes in Epi/NE ratios in younger (<40 years) vs older (≥40 years) patients during head-up tilt-table test-induced VVS.
The study comprised 29 patients (12 patients ≥40 years [mean 56 ± 10.7 years] and 17 patients <40 years mean 25 ± 5.7 years]) with recurrent suspected VVS in whom 70° head-up tilt testing reproduced symptoms. Arterial Epi and NE concentrations were measured at baseline (supine), 2 minutes of head-up tilt, and syncope.
Baseline Epi and NE concentrations and the Epi/NE ratio did not differ in younger and older groups (Epi: 90 ± 65 pg/mL vs 70 ± 32 pg/mL; NE: 226 ± 122 pg/mL vs 244 ± 183 pg/mL). However, Epi/NE ratio increased to a greater extent in younger fainters during head-up tilt and tended to be greater in younger patients at both 2 minutes (<40: 1.02 ± 1.29 vs ≥40: 0.40 ± 0.27, P = .11) and at symptoms (<40: 2.6 ± 1.26 vs ≥40: 1.6 ± 0.71, P = .03). At symptoms, Epi/NE ratio ≥2.5 was observed in 9 of 17 younger patients vs 1 of 12 older patients (P = .02).
Epi/NE ratios tend to be greater in younger fainters, a finding that may account in part for the observation that β-blocker therapy is less effective in reducing VVS susceptibility in younger individuals.
虽然血管迷走性晕厥（VVS）是由肾上腺/肾源性和突触源性循环儿茶酚胺（肾上腺素[Epi]和去甲肾上腺素[NE]）激增引起的，但β-肾上腺素能阻滞剂预防 VVS 除了在“较年长”的 VVS 患者中之外，效果并不理想。
我们假设β阻滞剂效果的年龄相关差异部分可能是由于在逐渐出现晕厥时 Epi 和 NE 释放的相对幅度不同，具体来说，年轻晕厥者的 Epi/NE 比值大于年长患者。为了评估这一假设，我们在倾斜试验诱发的 VVS 中测量了年轻（<40 岁）和年长（≥40 岁）患者之间 Epi/NE 比值的变化。
该研究包括 29 例反复疑似 VVS 的患者（12 例≥40 岁[平均 56±10.7 岁]和 17 例<40 岁[平均 25±5.7 岁]），70°头高位倾斜试验可重现症状。在基线（仰卧位）、头高位倾斜 2 分钟和晕厥时测量动脉内 Epi 和 NE 浓度。
年轻和年长组之间的基础 Epi 和 NE 浓度和 Epi/NE 比值没有差异（Epi：90±65 pg/mL 与 70±32 pg/mL；NE：226±122 pg/mL 与 244±183 pg/mL）。然而，年轻晕厥者在头高位倾斜时 Epi/NE 比值增加幅度更大，且在 2 分钟时（<40：1.02±1.29 与≥40：0.40±0.27，P=0.11）和症状时（<40：2.6±1.26 与≥40：1.6±0.71，P=0.03）年轻患者中更倾向于更大。在症状时，17 例年轻患者中有 9 例（9/17）的 Epi/NE 比值≥2.5，而 12 例年长患者中只有 1 例（1/12）（P=0.02）。
年轻晕厥者的 Epi/NE 比值倾向于更大，这一发现部分解释了β-阻滞剂治疗减少年轻个体 VVS 易感性效果较差的原因。
