2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: Executive summary: A report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society

Abstract

Glenn N. Levine, MD, FACC, FAHA, Chair Patrick T. O’Gara, MD, FACC, FAHA, Chair-Elect Jonathan L. Halperin, MD, FACC, FAHA, Immediate Past Chair #Former Task Force member; current member during the writing effort. Sana M. Al-Khatib, MD, MHS, FACC, FAHA Kim K. Birtcher, MS, PharmD, AACC Biykem Bozkurt, MD, PhD, FACC, FAHA Ralph G. Brindis, MD, MPH, MACC# Joaquin E. Cigarroa, MD, FACC Lesley H. Curtis, PhD, FAHA Lee A. Fleisher, MD, FACC, FAHA Federico Gentile, MD, FACC Samuel Gidding, MD, FAHA Mark A. Hlatky, MD, FACC John Ikonomidis, MD, PhD, FAHA José Joglar, MD, FACC, FAHA Susan J. Pressler, PhD, RN, FAHA Duminda N. Wijeysundera, MD, PhD Preamble ............................................................e2191.Introduction .....................................................e2211.1.Methodology and Evidence Review ...........e2211.2.Organization of the Writing Committee .....e2221.3.Document Review and Approval ..............e2221.4.Scope of the Guideline ................................e2222.General Principles ..............................................e2222.1.Definitions: Terms and Classification ...........e2232.2.Epidemiology and Demographics .................e2242.3.Initial Evaluation of Patients With Syncope: Recommendations ..........................................e2252.3.1.History and Physical Examination ........e2252.3.2.Electrocardiography ...........................e2252.3.3.Risk Assessment ............................e2252.3.4.Disposition After Initial Evaluation ...e2273.Additional Evaluation and Diagnosis ...................e2283.1.Blood Testing: Recommendations ...............e2283.2.Cardiovascular Testing: Recommendations.....e2283.2.1.Cardiac Imaging .............................e2283.2.2.Stress Testing ..................................e2293.2.3.Cardiac Monitoring .........................e2293.2.4.In-Hospital Telemetry .......................e2303.2.5.Electrophysiological Study ...............e2303.2.6.Tilt-Table Testing .............................e2303.3.Neurological Testing: Recommendations ....e2313.3.1.Autonomic Evaluation ......................e2313.3.2.Neurological and Imaging Diagnostics .... e2314.Management of Cardiovascular Conditions .........e2314.1.Arrhythmic Conditions: Recommendations.....e2314.1.1.Bradycardia .....................................e2314.1.2.Supraventricular Tachycardia ...........e2314.1.3.Ventricular Arrhythmia .....................e2314.2.Structural Conditions: Recommendations .......e2314.2.1.Ischemic and Nonischemic Cardiomyopathy.... e2314.2.2.Valvular Heart Disease ......................e2314.2.3.Hypertrophic Cardiomyopathy .........e2314.2.4.Arrhythmogenic Right Ventricular Cardiomyopathy ...............................e2324.2.5.Cardiac Sarcoidosis .........................e2324.3.Inheritable Arrhythmic Conditions: Recommendations .....................................e2324.3.1.Brugada Syndrome .........................e2324.3.2.Short-QT Syndrome ........................e2324.3.3.Long-QT Syndrome ........................e2324.3.4.Catecholaminergic Polymorphic Ventricular Tachycardia ..................e2324.3.5.Early Repolarization Pattern ............e2335.Reflex Conditions: Recommendations ...............e2335.1.Vasovagal Syncope ....................................e2335.2.Pacemakers in Vasovagal Syncope ..............e2345.3.Carotid Sinus Syndrome ............................e2345.4.Other Reflex Conditions .............................e2346.Orthostatic Hypotension: Recommendations .......e2346.1.Neurogenic Orthostatic Hypotension ...........e2346.2.Dehydration and Drugs ..............................e2357.Orthostatic Intolerance .......................................e2358.Pseudosyncope: Recommendations .....................e2369.Uncommon Conditions Associated With Syncope .... e23610.Age, Lifestyle, and Special Populations: Recommendations ...........................................e23610.1.Pediatric Syncope ...................................e23610.2.Adult Congenital Heart Disease .............e23610.3.Geriatric Patients ....................................e23610.4.Driving and Syncope ..............................e23710.5.Athletes ..................................................e23711.Quality of Life and Healthcare Cost of Syncope ....e23811.1.Impact of Syncope on Quality of Life ......e23811.2.Healthcare Costs Associated With Syncope......e23812.Emerging Technology, Evidence Gaps, and Future Directions .........................................................e23812.1.Definition, Classification, and Epidemiology.........e23812.2.Risk Stratification and Clinical Outcomes .... e23812.3.Evaluation and Diagnosis .......................e23812.4.Management of Specific Conditions .......e23812.5.Special Populations ................................e238References ..........................................................e239Appendix 1Author Relationships With Industry and Other Entities (Relevant) ..................................e247Appendix 2Reviewer Relationships With Industry and Other Entities (Comprehensive) .......................e249Appendix 3Abbreviations .................................................e254 Since 1980, the American College of Cardiology (ACC) and American Heart Association (AHA) have translated scientific evidence into clinical practice guidelines (guidelines) with recommendations to improve cardiovascular health. These guidelines, which are based on systematic methods to evaluate and classify evidence, provide a cornerstone for quality cardiovascular care. The ACC and AHA sponsor the development and publication of guidelines without commercial support, and members of each organization volunteer their time to the writing and review efforts. Guidelines are official policy of the ACC and AHA. Practice guidelines provide recommendations applicable to patients with or at risk of developing cardiovascular disease. The focus is on medical practice in the United States, but guidelines developed in collaboration with other organizations may have a global impact. Although guidelines may be used to inform regulatory or payer decisions, their intent is to improve patients’ quality of care and align with patients’ interests. Guidelines are intended to define practices meeting the needs of patients in most, but not all, circumstances and should not replace clinical judgment. Guideline-recommended management is effective only when followed by healthcare providers and patients. Adherence to recommendations can be enhanced by shared decision making between healthcare providers and patients, with patient engagement in selecting interventions based on individual values, preferences, and associated conditions and comorbidities. The ACC/AHA Task Force on Clinical Practice Guidelines (Task Force) continuously reviews, updates, and modifies guideline methodology on the basis of published standards from organizations including the Institute of Medicine1Committee on Standards for Developing Trustworthy Clinical Practice Guidelines, Institute of Medicine (U.S.)Clinical Practice Guidelines We Can Trust.ed. National Academies Press, Washington, DC2011Google Scholar, 2Committee on Standards for Systematic Reviews of Comparative Effectiveness Research, Institute of Medicine (U.S.)Finding What Works in Health Care: Standards for Systematic Reviews. National Academies Press, Washington, DC2011Google Scholar and on the basis of internal reevaluation. Similarly, the presentation and delivery of guidelines are reevaluated and modified on the basis of evolving technologies and other factors to facilitate optimal dissemination of information at the point of care to healthcare professionals. Given time constraints of busy healthcare providers and the need to limit text, the current guideline format delineates that each recommendation be supported by limited text (ideally, <250 words) and hyperlinks to supportive evidence summary tables. Ongoing efforts to further limit text are underway. Recognizing the importance of cost–value considerations in certain guidelines, when appropriate and feasible, an analysis of the value of a drug, device, or intervention may be performed in accordance with the ACC/AHA methodology.3Anderson J.L. Heidenreich P.A. Barnett P.G. et al.ACC/AHA statement on cost/value methodology in clinical practice guidelines and performance measures: a report of the American College of Cardiology/American Heart Association Task Force on Performance Measures and Task Force on Practice Guidelines.J Am Coll Cardiol. 2014; 63: 2304-2322Crossref PubMed Scopus (125) Google Scholar To ensure that guideline recommendations remain current, new data are reviewed on an ongoing basis, with full guideline revisions commissioned in approximately 6-year cycles. Publication of new, potentially practice-changing study results that are relevant to an existing or new drug, device, or management strategy will prompt evaluation by the Task Force, in consultation with the relevant guideline writing committee, to determine whether a focused update should be commissioned. For additional information and policies regarding guideline development, we encourage readers to consult the ACC/AHA guideline methodology manual4ACCF/AHA Task Force on Practice Guidelines. Methodology Manual and Policies From the ACCF/AHA Task Force on Practice Guidelines. American College of Cardiology and American Heart Association, 2010. Available at: http://assets.cardiosource.com/Methodology_Manual_for_ACC_AHA_Writing_Committees.pdf. Accessed January 23, 2015.Google Scholar and other methodology articles.5Halperin J.L. Levine G.N. Al-Khatib S.M. et al.Further evolution of the ACC/AHA clinical practice guideline recommendation classification system: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Clinical Practice Guidelines.J Am Coll Cardiol. 2016; 67: 1572-1574Crossref PubMed Google Scholar, 6Jacobs A.K. Kushner F.G. Ettinger S.M. et al.ACCF/AHA clinical practice guideline methodology summit report: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.J Am Coll Cardiol. 2013; 61: 213-265Crossref PubMed Scopus (0) Google Scholar, 7Jacobs A.K. Anderson J.L. Halperin J.L. The evolution and future of ACC/AHA clinical practice guidelines: a 30-year journey: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.J Am Coll Cardiol. 2014; 64: 1373-1384Crossref PubMed Scopus (67) Google Scholar, 8Arnett D.K. Goodman R.A. Halperin J.L. et al.AHA/ACC/HHS strategies to enhance application of clinical practice guidelines in patients with cardiovascular disease and comorbid conditions: from the American Heart Association, American College of Cardiology, and U.S. Department of Health and Human Services.J Am Coll Cardiol. 2014; 64: 1851-1856Crossref PubMed Scopus (0) Google Scholar The Task Force strives to avoid bias by selecting experts from a broad array of backgrounds. Writing committee members represent different geographic regions, sexes, ethnicities, races, intellectual perspectives/biases, and scopes of clinical practice. The Task Force may also invite organizations and professional societies with related interests and expertise to participate as partners, collaborators, or endorsers. The ACC and AHA have rigorous policies and methods to ensure that guidelines are developed without bias or improper influence. The complete relationships with industry and other entities (RWI) policy can be found online. Appendix 1 of the current document lists writing committee members’ relevant RWI. For the purposes of full transparency, writing committee members’ comprehensive disclosure information is available online, as is comprehensive disclosure information for the Task Force. When developing recommendations, the writing committee uses evidence-based methodologies that are based on all available data.4ACCF/AHA Task Force on Practice Guidelines. Methodology Manual and Policies From the ACCF/AHA Task Force on Practice Guidelines. American College of Cardiology and American Heart Association, 2010. Available at: http://assets.cardiosource.com/Methodology_Manual_for_ACC_AHA_Writing_Committees.pdf. Accessed January 23, 2015.Google Scholar, 5Halperin J.L. Levine G.N. Al-Khatib S.M. et al.Further evolution of the ACC/AHA clinical practice guideline recommendation classification system: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Clinical Practice Guidelines.J Am Coll Cardiol. 2016; 67: 1572-1574Crossref PubMed Google Scholar, 6Jacobs A.K. Kushner F.G. Ettinger S.M. et al.ACCF/AHA clinical practice guideline methodology summit report: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.J Am Coll Cardiol. 2013; 61: 213-265Crossref PubMed Scopus (0) Google Scholar, 7Jacobs A.K. Anderson J.L. Halperin J.L. The evolution and future of ACC/AHA clinical practice guidelines: a 30-year journey: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.J Am Coll Cardiol. 2014; 64: 1373-1384Crossref PubMed Scopus (67) Google Scholar Literature searches focus on randomized controlled trials (RCTs) but also include registries, nonrandomized comparative and descriptive studies, case series, cohort studies, systematic reviews, and expert opinion. Only key references are cited. An independent evidence review committee (ERC) is commissioned when there are 1 or more questions deemed of utmost clinical importance that merit formal systematic review. This systematic review will determine which patients are most likely to benefit from a drug, device, or treatment strategy and to what degree. Criteria for commissioning an ERC and formal systematic review include: a) the absence of a current authoritative systematic review; b) the feasibility of defining the benefit and risk in a time frame consistent with the writing of a guideline; c) the relevance to a substantial number of patients; and d) the likelihood that the findings can be translated into actionable recommendations. ERC members may include methodologists, epidemiologists, healthcare providers, and biostatisticians. The recommendations developed by the writing committee on the basis of the systematic review are marked with “SR”. The term guideline-directed management and therapy (GDMT) encompasses clinical evaluation, diagnostic testing, and pharmacological and procedural treatments. For these and all recommended drug treatment regimens, the reader should confirm the dosage by reviewing product insert material and evaluate the treatment regimen for contraindications and interactions. The recommendations are limited to drugs, devices, and treatments approved for clinical use in the United States. The Class of Recommendation (COR) indicates the strength of the recommendation, encompassing the estimated magnitude and certainty of benefit in proportion to risk. The Level of Evidence (LOE) rates the quality of scientific evidence that supports the intervention on the basis of the type, quantity, and consistency of data from clinical trials and other sources (Table 1).4ACCF/AHA Task Force on Practice Guidelines. Methodology Manual and Policies From the ACCF/AHA Task Force on Practice Guidelines. American College of Cardiology and American Heart Association, 2010. Available at: http://assets.cardiosource.com/Methodology_Manual_for_ACC_AHA_Writing_Committees.pdf. Accessed January 23, 2015.Google Scholar, 5Halperin J.L. Levine G.N. Al-Khatib S.M. et al.Further evolution of the ACC/AHA clinical practice guideline recommendation classification system: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Clinical Practice Guidelines.J Am Coll Cardiol. 2016; 67: 1572-1574Crossref PubMed Google Scholar, 6Jacobs A.K. Kushner F.G. Ettinger S.M. et al.ACCF/AHA clinical practice guideline methodology summit report: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines.J Am Coll Cardiol. 2013; 61: 213-265Crossref PubMed Scopus (0) Google Scholar The reader is encouraged to consult the full-text guideline9Shen W.-K. Sheldon R.S. Benditt D.G. et al.2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society.Heart Rhythm. 2017; 14: e155-e217Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar for additional guidance and details with regard to syncope because this executive summary contains limited information. Glenn N. Levine, MD, FACC, FAHA Chair, ACC/AHA Task Force on Clinical Practice GuidelinesTable 1Applying Class of Recommendation and Level of Evidence to Clinical Strategies, Interventions, Treatments, or Diagnostic Testing in Patient Care* (Updated August 2015) Open table in a new tab The recommendations listed in this guideline are, whenever possible, evidence based. An initial extensive evidence review, which included literature derived from research involving human subjects, published in English, and indexed in MEDLINE (through PubMed), EMBASE, the Cochrane Library, the Agency for Healthcare Research and Quality, and other selected databases relevant to this guideline, was conducted from July to October 2015. Key search words included but were not limited to the following: athletes, autonomic neuropathy, bradycardia, carotid sinus hypersensitivity, carotid sinus syndrome, children, death, dehydration, diagnosis, driving, electrocardiogram, electrophysiological study, epidemiology, falls, implantable loop recorder, mortality, older populations, orthostatic hypotension, pediatrics, psychogenic pseudosyncope, recurrent syncope, risk stratification, supraventricular tachycardia, syncope unit, syncope, tilt-table test, vasovagal syncope, and ventricular arrhythmia. Additional relevant studies published through October 2016, during the guideline writing process, were also considered by the writing committee, and added to the evidence tables when appropriate. The finalized evidence tables, included in the Online Data Supplement, summarize the evidence used by the writing committee to formulate recommendations. Lastly, the writing committee reviewed documents related to syncope previously published by the ACC and AHA and other organizations and societies. References selected and published in this document are representative and not all inclusive. An independent ERC was commissioned to perform a systematic review of clinical questions, the results of which were considered by the writing committee for incorporation into this guideline. The systematic review report “Pacing as a Treatment for Reflex-Mediated (Vasovagal, Situational, or Carotid Sinus Hypersensitivity) Syncope” is published in conjunction with this guideline.10Varosy P.D. Chen L.Y. Miller A.L. et al.Pacing as a treatment for reflex-mediated (vasovagal, situational, or carotid sinus hypersensitivity) syncope: a systematic review for the 2017 ACC/AHA/HRS guideline for the evaluation and management of syncope: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society.Heart Rhythm. 2017; 14: e255-e269PubMed Google Scholar The writing committee was composed of clinicians with expertise in caring for patients with syncope, including cardiologists, electrophysiologists, an emergency physician, and a pediatric cardiologist. The writing committee included representatives from the ACC, AHA, Heart Rhythm Society (HRS), American Academy of Neurology, American College of Emergency Physicians, and Society for Academic Emergency Medicine. This document was reviewed by 2 official reviewers each nominated by the ACC, AHA, and HRS; 1 reviewer each from the American Academy of Neurology, American College of Emergency Physicians and Society for Academic Emergency Medicine, and Pediatric and Congenital Electrophysiology Society; a lay/patient representative; and 25 individual content reviewers. Reviewers’ RWI information was distributed to the writing committee and is published in this document (Appendix 2). This document was approved for publication by the governing bodies of the ACC, AHA, and HRS and endorsed by the American College of Emergency Physicians, Society for Academic Emergency Medicine, and the Pediatric and Congenital Electrophysiology Society. The purpose of this ACC/AHA/HRS guideline is to provide contemporary, accessible, and succinct guidance on the management of adult and pediatric patients with suspected syncope. This guideline is intended to be a practical document for cardiologists, arrhythmia specialists, neurologists, emergency physicians, general internists, geriatric specialists, sports medicine specialists, and other healthcare professionals involved in the care of this very large and heterogeneous population. It is not a review of physiology, pathophysiology, or mechanisms of underlying conditions associated with syncope. The nature of syncope as a symptom required that the writing committee consider numerous conditions for which it can be a symptom, and as much as possible, we have addressed the involvement of syncope only as a presenting symptom. Because of the plausible association of syncope and sudden cardiac death (SCD) in selected populations, this document discusses risk stratification and prevention of SCD when appropriate. The use of the terms selected populations and selected patients in this document is intended to direct healthcare providers to exercise clinical judgment, which is often required during the evaluation and management of patients with syncope. When a recommendation is made to refer a patient to a specialist with expertise for further evaluation, such as in the case of autonomic neurology, adult congenital heart disease (ACHD), older populations, or athletes, the writing committee agreed to make Class IIa recommendations because of the paucity of outcome data. The definition of older populations has been evolving. Age >75 years is used to define older populations or older adults in this document, unless otherwise specified. If a study has defined older adults by a different age cutoff, the relevant age is noted in those specific cases. Finally, the guideline addresses the management of syncope with the patient as a focus, rather than larger aspects of health services, such as syncope management units. The goals of the present guideline are:•To define syncope as a symptom, with different causes, in different populations and circumstances.•To provide guidance and recommendations on the evaluation and management of patients with suspected syncope in the context of different clinical settings, specific causes, or selected circumstances.•To identify key areas in which knowledge is lacking, to foster future collaborative research opportunities and efforts. In developing this guideline, the writing committee reviewed the evidence to support recommendations in the relevant ACC/AHA guidelines noted in Table 2 (in the full-text guideline) and affirms the ongoing validity of the related recommendations in the context of syncope, thus obviating the need to repeat existing guideline recommendations in the present guideline when applicable or when appropriate. For the purpose of this guideline, definitions of syncope and relevant terms are provided in Table 2. See Table 3 for historical characteristics associated with, although not diagnostic, cardiac and noncardiac syncope; Table 4 for short- and long-term risk factors; Table 5 for the type of events, event rates, and study durations from investigations that estimate risk scores; Table 6 for examples of serious conditions associated with syncope which may require inpatient evaluation and “treatment”; Figure 1 for the algorithm on initial evaluation for syncope; and Figure 2 for patient disposition after initial evaluation for syncope. See Online Data Supplements 1 through 4 for data supporting Section 2.Table 3Historical Characteristics Associated With Increased Probability of Cardiac and Noncardiac Causes of Syncope40Berecki-Gisolf J. Sheldon A. Wieling W. et al.Identifying cardiac syncope based on clinical history: a literature-based model tested in four independent datasets.PLoS ONE. 2013; 8: e75255Crossref PubMed Scopus (0) Google Scholar, 47Colivicchi F. Ammirati F. Melina D. et al.Development and prospective validation of a risk stratification system for patients with syncope in the emergency department: the OESIL risk score.Eur Heart J. 2003; 24: 811-819Crossref PubMed Scopus (242) Google Scholar, 48Costantino G. Perego F. Dipaola F. et al.Short- and long-term prognosis of syncope, risk factors, and role of hospital admission: results from the STePS (Short-Term Prognosis of Syncope) study.J Am Coll Cardiol. 2008; 51: 276-283Crossref PubMed Scopus (146) Google Scholar, 49Del Rosso A. Ungar A. Maggi R. et al.Clinical predictors of cardiac syncope at initial evaluation in patients referred urgently to a general hospital: the EGSYS score.Heart. 2008; 94: 1620-1626Crossref PubMed Scopus (187) Google Scholar, 50Grossman S.A. Fischer C. Lipsitz L.A. et al.Predicting adverse outcomes in syncope.J Emerg Med. 2007; 33: 233-239Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar, 51Martin G.J. Adams S.L. Martin H.G. et al.Prospective evaluation of syncope.Ann Emerg Med. 1984; 13: 499-504Abstract Full Text PDF PubMed Scopus (195) Google Scholar, 52Quinn J.V. Stiell I.G. McDermott D.A. et al.Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes.Ann Emerg Med. 2004; 43: 224-232Abstract Full Text Full Text PDF PubMed Scopus (245) Google Scholar, 53Reed M.J. Newby D.E. Coull A.J. et al.The ROSE (Risk Stratification of Syncope in the Emergency Department) study.J Am Coll Cardiol. 2010; 55: 713-721Crossref PubMed Scopus (135) Google Scholar, 54Sarasin F.P. Hanusa B.H. Perneger T. et al.A risk score to predict arrhythmias in patients with unexplained syncope.Acad Emerg Med. 2003; 10: 1312-1317Crossref PubMed Google Scholar, 55Sun B.C. Derose S.F. Liang L.J. et al.Predictors of 30-day serious events in older patients with syncope.Ann Emerg Med. 2009; 54: 769-778Abstract Full Text Full Text PDF PubMed Scopus (53) Google ScholarMore Often Associated With Cardiac Causes of Syncope•Older age (>60 y)•Male sex•Presence of known ischemic heart disease, structural heart disease, previous arrhythmias, or reduced ventricular function•Brief prodrome, such as palpitations, or sudden loss of consciousness without prodrome•Syncope during exertion•Syncope in the supine position•Low number of syncope episodes (1 or 2)•Abnormal cardiac examination•Family history of inheritable conditions or premature SCD (<50 y of age)•Presence of known congenital heart diseaseMore Often Associated With Noncardiac Causes of Syncope•Younger age•No known cardiac disease•Syncope only in the standing position•Positional change from supine or sitting to standing•Presence of prodrome: nausea, vomiting, feeling warmth•Presence of specific triggers: dehydration, pain, distressful stimulus, medical environment•Situational triggers: cough, laugh, micturition, defecation, deglutition•Frequent recurrence and prolonged history of syncope with similar characteristicsSCD indicates sudden cardiac death. Open table in a new tab SCD indicates sudden cardiac death. Table 2Relevant Terms and Definitions∗These definitions are derived from previously published definitions from scientific investigations, guidelines, expert consensus statements, and Webster dictionary after obtaining consensus from the WC.TermDefinition/Comments and ReferencesSyncopeA symptom that presents with an abrupt, transient, complete loss of consciousness, associated with inability to maintain postural tone, with rapid and spontaneous recovery. The presumed mechanism is cerebral hypoperfusion.11Moya A. Sutton R. Ammirati F. et al.Guidelines for the diagnosis and management of syncope (version 2009).Eur Heart J. 2009; 30: 2631-2671Crossref PubMed Scopus (6) Google Scholar, 12Sheldon R.S. Grubb B.P. Olshansky B. et al.2015 Heart Rhythm Society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope.Heart Rhythm. 2015; 12: e41-e63Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar There should not be clinical features of other nonsyncope causes of loss of consciousness, such as seizure, antecedent head trauma, or apparent loss of consciousness (i.e., pseudosyncope).11Moya A. Sutton R. Ammirati F. et al.Guidelines for the diagnosis and management of syncope (version 2009).Eur Heart J. 2009; 30: 2631-2671Crossref PubMed Scopus (6) Google Scholar, 12Sheldon R.S. Grubb B.P. Olshansky B. et al.2015 Heart Rhythm Society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome, inappropriate sinus tachycardia, and vasovagal syncope.Heart Rhythm. 2015; 12: e41-e63Abstract Full Text Full Text PDF PubMed Scopus (120) Google ScholarLoss of consciousnessA cognitive state in which one lacks awareness of oneself and one’s situation, with an inability to respond to stimuli.Transient loss of consciousnessSelf-limited loss of consciousness11Moya A. Sutton R. Ammirati F. et al.Guidelines for the diagnosis and management of syncope (version 2009).Eur Heart J. 2009; 30: 2631-2671Crossref PubMed Scopus (6) Google Scholar can be divided