Phys · cardiovascular
Syncope
Also known as fainting · vasovagal syncope · neurocardiogenic syncope · carotid sinus hypersensitivity · carotid sinus syndrome · orthostatic hypotension · postural hypotension · cardiogenic syncope · arrhythmic syncope · situational syncope · micturition syncope · cough syncope
Consultant-physician-depth guide to syncope — the transient loss of consciousness from global cerebral hypoperfusion — using the 2018 ESC classification of reflex, orthostatic, and cardiac causes, with a directed investigation pathway from ECG to implantable loop recorder, risk stratification, and evidence-based management including physical counter-pressure manoeuvres, fludrocortisone, midodrine, and pacemaker therapy for selected patients.
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Target exams
Red flags
- Syncope during exertion — exclude aortic stenosis, HCM, arrhythmia, pulmonary hypertension until proven otherwise
- Syncope without prodrome, while supine, or with palpitations — likely arrhythmic, requires urgent cardiac workup
- Abnormal ECG — bifascicular block, Mobitz II, complete heart block, long QT, Brugada pattern, epsilon waves, sustained VT
- Family history of sudden cardiac death under 50 years — suspect inherited channelopathy or cardiomyopathy
- Severe structural heart disease — heart failure, low LVEF, previous MI — high one-year mortality
- Syncope causing major injury — fracture, head injury, motor vehicle accident — warrants admission
- Recurrent unexplained syncope in older patient — consider carotid sinus hypersensitivity and orthostatic hypotension from polypharmacy
Syncope
The answer first
Syncope is a transient loss of consciousness caused by global cerebral hypoperfusion, characterised by rapid onset, short duration, and spontaneous complete recovery [1]. The mechanism is always the same: cerebral blood flow falls below the minimum needed to sustain consciousness. What varies is why.
The 2018 ESC guidelines classify syncope into three categories, and this classification governs every decision below [1]:
- Is it reflex (neurocardiogenic) syncope? The most common cause. A triggered autonomic reflex produces vasodilation and/or bradycardia — vasovagal, situational, or carotid sinus hypersensitivity. The heart and vasculature are structurally normal; the problem is the reflex.
- Is it orthostatic hypotension? The autonomic system or medications fail to maintain blood pressure on standing. The mechanism is a failure of vasoconstriction — not a reflex, but an inability to compensate for gravity.
- Is it cardiac syncope? The most dangerous. An arrhythmia or structural lesion prevents the heart from maintaining cardiac output. This category carries the highest mortality and demands urgent investigation. [1]
The two pivotal questions at the bedside:
- Was it truly syncope? Exclude seizure, concussion, psychogenic pseudosyncope, and metabolic causes of transient loss of consciousness. A careful history alone establishes the diagnosis in 23 to 50 per cent of cases [1].
- Is there a high-risk feature? Exertional syncope, no prodrome, structural heart disease, abnormal ECG, or family history of sudden death demand admission and expedited workup. Everything else can be investigated as an outpatient.
DWE high-yield: Every patient with syncope gets a 12-lead ECG. It is non-negotiable, cheap, and identifies the highest-risk causes. If you remember one rule, remember this — the ECG is mandatory for all syncope, regardless of how typical the story sounds. [1]
References9ShowHide
- [1]Brignole M 'Ten Commandments' of ESC Syncope Guidelines 2018: The new European Society of Cardiology (ESC) Clinical Practice Guidelines for the diagnosis and management of syncope were launched 19 March 2018 at EHRA 2018 in Barcelona Eur Heart J, 2018.PMID 29860370
- [2]Brignole M, Moya A, de Lange FJ, et al. Practical Instructions for the 2018 ESC Guidelines for the diagnosis and management of syncope Eur Heart J, 2018.PMID 29562291
- [3]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.PMID 28280231
- [4]van Dijk N, Quartieri F, Blanc JJ, et al. Effectiveness of physical counterpressure maneuvers in preventing vasovagal syncope: the Physical Counterpressure Manoeuvres Trial (PC-Trial) J Am Coll Cardiol, 2006.PMID 17045903
- [5]Sheldon R, Raj SR, Rose MS, et al. Fludrocortisone for the Prevention of Vasovagal Syncope: A Randomized, Placebo-Controlled Trial J Am Coll Cardiol, 2016.PMID 27364043
- [6]Sheldon R, Faris P, Tang A, et al. Midodrine for the Prevention of Vasovagal Syncope : A Randomized Clinical Trial Ann Intern Med, 2021.PMID 34339231
- [7]Brignole M, Menozzi C, Moya A, et al. Pacemaker therapy in patients with neurally mediated syncope and documented asystole: Third International Study on Syncope of Uncertain Etiology (ISSUE-3): a randomized trial Circulation, 2012.PMID 22565936
- [8]Parry SW, Steen N, Bexton RS, Tynan M, Kenny RA. Pacing in elderly recurrent fallers with carotid sinus hypersensitivity: a randomised, double-blind, placebo controlled crossover trial Heart, 2009.PMID 19124530
- [9]Kenny RA, Richardson DA, Steen N, et al. Carotid sinus syndrome: a modifiable risk factor for nonaccidental falls in older adults (SAFE PACE) J Am Coll Cardiol, 2001.PMID 11691528