Transient Loss of Consciousness (TLoC)
Overview
Transient loss of consciousness (TLoC) is a sudden, brief episode of unresponsiveness with rapid onset and spontaneous complete recovery.
It is a common ED presentation (≈3-5% of attendances) and includes syncope (transient global cerebral hypoperfusion), epileptic seizures, transient ischaemic attacks, subarachnoid haemorrhage presenting with collapse, psychogenic non‑epileptic events and rarer causes.
The ED aim is to identify immediately life‑threatening causes (especially cardiac syncope and intracranial haemorrhage), make a working diagnosis, and triage for observation, admission or safe discharge (see NICE CG109).
Basic physiology
Syncope follows transient global cerebral hypoperfusion. Mean arterial pressure reflects cardiac output and peripheral resistance: BP = HR × SV × TPR A fall in blood pressure may result from reduced heart rate (HR) or stroke volume (SV), or reduced total peripheral resistance (TPR).
Major categories
- Reflex (neurally mediated) syncope: vasovagal (most common), situational (e.g., micturition, coughing), carotid sinus hypersensitivity.
- Orthostatic hypotension: drug‑induced, dehydration, autonomic failure, postural orthostatic tachycardia syndrome (POTS).
- Cardiac syncope: arrhythmic (bradyarrhythmias or tachyarrhythmias) or structural (severe valvular disease, hypertrophic cardiomyopathy, obstructive lesions). This category carries the highest immediate mortality risk.
- Neurological mimics: epileptic seizure and intracranial pathology such as subarachnoid haemorrhage. TIA is not a typical cause of isolated transient loss of consciousness; carotid-territory TIA usually causes focal neurological symptoms without loss of consciousness. Vertebrobasilar ischaemia can...