Introduction

Introduction

This guideline is about the assessment, diagnosis and specialist referral of adults and young people (aged 16 and older) who have experienced a blackout (the medical term for this is 'transient loss of consciousness' or TLoC for short).

TLoC is very common: it affects up to half the population in the UK at some point in their lives. TLoC may be defined as spontaneous loss of consciousness with complete recovery. In this context, complete recovery would involve full recovery of consciousness without any residual neurological deficit. An episode of TLoC is often described as a 'blackout' or a 'collapse', but some people collapse without TLoC and this guideline does not cover that situation. There are various causes of TLoC, including cardiovascular disorders (which are the most common), neurological conditions such as epilepsy, and psychogenic attacks.

The diagnosis of the underlying cause of TLoC is often inaccurate, inefficient and delayed. There is huge variation in the management of TLoC. A substantial proportion of people initially diagnosed with, and treated for, epilepsy have a cardiovascular cause for their TLoC. Some people have expensive and inappropriate tests or inappropriate specialist referral (unnecessary referral or referral to the wrong specialty); others with potentially dangerous conditions may not receive appropriate assessment, diagnosis and treatment.

There is some existing NICE guidance that relates to TLoC, including that on epilepsy[1], falls[2], dual chamber pacemakers[3] and implantable cardioverter defibrillators[4]. Although related guidance on conditions that may contribute to TLoC exist (particularly chapter 8 of the 'National service framework for coronary heart disease'[5], and the European Society of Cardiology guidelines on syncope[6]), there is no NICE guidance that addresses the crucial aspects of initial assessment, diagnosis and specialist referral of people who have had TLoC. People experiencing TLoC may come under the care of a range of clinicians, and the lack of a clear pathway may contribute to misdiagnosis and inappropriate treatment.

In considering the assessment and treatment of people who have experienced TLoC, it is important to distinguish terms that describe the circumstances or nature of the episode from those that define the mechanism for loss of consciousness. Descriptive terms tend to guide further aspects of assessment, whereas the mechanism of TLoC will determine treatment. For example, 'exercise-induced syncope' describes the circumstances in which TLoC has occurred but does not indicate whether it was due to the mechanical effect of structural heart disease (such as severe aortic stenosis requiring valve surgery), a cardiac arrhythmia complicating structural heart disease (requiring treatment of the structural heart disease and of the arrhythmia), or a cardiac arrhythmia that requires treatment but is either not associated with any other heart disease or is associated with other heart disease that does not in itself require treatment. Furthermore, syncope that is exercise-induced but occurs shortly after stopping exercise rather than during exercise is most likely to be vasovagal in origin. The appropriate choice of investigation will be determined by the fact that TLoC was exercise-induced and by findings from the initial clinical assessment and electrocardiogram (ECG). The mechanism for TLoC established by these investigations will determine what treatment may be needed.

Clinical reasoning forms an important part of the process of ensuring that people who experience TLoC receive assessment, advice and treatment that is appropriate for each individual. Determination of the mechanism for TLoC in an individual requires collection of evidence (from a detailed history, from clinical assessment and from appropriate investigations), and interpretation of each piece of evidence in overall clinical context. For example, in one person a piece of evidence such as witnessed seizure activity and/or urinary incontinence may point to a diagnosis of epilepsy, but in another may be entirely consistent with 'convulsive syncope', where other features of the episode indicate clearly that it was an episode of vasovagal syncope.

This guideline aims to define the appropriate pathways for the initial assessment, diagnosis and specialist referral of people who have had TLoC, so that they receive the correct diagnosis quickly, efficiently and cost effectively, leading to a suitable management plan. The approach of the Guideline Development Group was to produce a guideline in the form of an algorithm, pointing clinicians and patients towards those areas where guidance already exists (such as the guidance on epilepsy [NICE guideline CG20]; replaced by Epilepsies: diagnosis and management [NICE guideline CG137]), and providing new guidance in other areas, namely for people with syncope.

  • National Institute for Health and Care Excellence (NICE)