晕厥是一种由于短暂性全脑灌注不足引起的短暂意识丧失，特点是发作快、持续时间短、自发性完全恢复。[1]Brignole M, Moya A, de Lange FJ, et al. 2018 ESC guidelines for the diagnosis and management of syncope. Eur Heart J. 2018 Jun 1;39(21):1883-948.https://academic.oup.com/eurheartj/article/39/21/1883/4939241http://www.ncbi.nlm.nih.gov/pubmed/29562304?tool=bestpractice.com 伴有不能维持姿势性张力。[2]Shen WK, Sheldon RS, Benditt DG, et al. 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, and the Heart Rhythm Society. Circulation. 2017 Aug 1;136(5):e60-122.https://www.ahajournals.org/doi/abs/10.1161/CIR.0000000000000499http://www.ncbi.nlm.nih.gov/pubmed/28280231?tool=bestpractice.com 晕厥有许多原因，它不同于眩晕、癫痫发作、昏迷、跌倒、精神性假性晕厥、跌倒发作、短暂性脑缺血发作 (transient ischaemic attack, TIA) 和意识改变状态。[3]Strickberger SA, Benson DW, Biaggioni I, et al. AHA/ACCF scientific statement on the evaluation of syncope: from the American Heart Association Councils on Clinical Cardiology, Cardiovascular Nursing, Cardiovascular Disease in the Young, and Stroke, and the Quality of Care and Outcomes Research Interdisciplinary Working Group; and the American College of Cardiology Foundation In Collaboration With the Heart Rhythm Society. Circulation. 2006 Jan 17;113(2):316-27.http://circ.ahajournals.org/cgi/content/full/113/2/316http://www.ncbi.nlm.nih.gov/pubmed/16418451?tool=bestpractice.com
阅读更多发病率各不相同，取决于所研究人群的特征。由于不同研究之间，使用的方法和定义不一致，在解读流行病学估计值时也有一些困难。
在一项针对 305,932 例患者的横断面研究中，调整后的晕厥发病率在 0.80 至 0.93/1000 人年之间，从 2000 年到 2005 年，没有发生改变。估计总死亡率也一直保持在 0.28% 左右。[4]Alshekhlee A, Shen WK, Mackall J. et al. Incidence and mortality rates of syncope in the United States. Am J Med. 2009 Feb;122(2):181-8.http://www.ncbi.nlm.nih.gov/pubmed/19100958?tool=bestpractice.com 55%-82% 的晕厥患者可以确定病因。[5]Kapoor WN, Hanusa BH. Is syncope a risk factor for poor outcomes? Comparison of patients with and without syncope. Am J Med. 1996 Jun;100(6):646-55.http://www.ncbi.nlm.nih.gov/pubmed/8678086?tool=bestpractice.com[6]Alboni P, Brignole M, Menozzi C, et al. Diagnostic value of history in patients with syncope with or without heart disease. J Am Coll Cardiol. 2001 Jun 1;37(7):1921-8.https://www.sciencedirect.com/science/article/pii/S0735109701012414?via%3Dihubhttp://www.ncbi.nlm.nih.gov/pubmed/11401133?tool=bestpractice.com[7]Linzer M, Yang EH, Estes NA 3rd, et al. Diagnosing syncope. Part 1: Value of history, physical examination, and electrocardiography. Clinical Efficacy Assessment Project of the American College of Physicians. Ann Intern Med. 1997 Jun 15;126(12):989-96.http://www.ncbi.nlm.nih.gov/pubmed/9182479?tool=bestpractice.com 老年晕厥住院患者中，非心血管因素的比例（例如血管迷走神经性或直立性发作）是心血管因素的两倍（例如心律失常或心肌缺血）。[8]Getchell WS, Larsen GC, Morris CD, et al. Epidemiology of syncope in hospitalized patients. J Gen Intern Med. 1999 Nov;14(11):677-87.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1496762/http://www.ncbi.nlm.nih.gov/pubmed/10571716?tool=bestpractice.com
危险因素识别是评估晕厥患者中最重要的一步。识别有高死亡风险的患者也是至关重要的（例如：有结构性心脏病或心电图异常的患者）。[9]Martin TP, Hanusa BH, Kapoor WN. Risk stratification of patients with syncope. Ann Emerg Med. 1997 Apr;29(4):459-66.http://www.ncbi.nlm.nih.gov/pubmed/9095005?tool=bestpractice.com
