Transient Loss of Consciousness - Investigations

Electrocardiogram - ECG

• Essential in all cases of syncope.
• Often normal, particularly in younger patients with vasovagal faints.
• Diagnostic changes may be present in some patients:
  • High grade atrioventricular block, atrial fibrillation with a very slow ventricular response rate or marked sinus pauses - all indicate a bradycardic cause for syncope.
  • A long QT interval - indicates likely polymorphic ventricular tachycardia as a cause of syncope
  • ECG fetures of Wolf-Parkinson-White syndrome - indicates likely supraventricular tachycardia or rapidly conducted atrial fibrillation as the cause of syncope.
• Bi-fascicular or Tri-fascicular blocks in elderly patients (eg RBBB + left hemiblock + first degree block or LBBB + first degree block) are strong indicators of a bradycardic cause for syncope and empiric pacing is often warranted.
• Features of underlying structural heart disease including LVH/strain, Q waves of prior myocardial infarction and LBBB.
  • Echocardiography is recommended in these cases and the possibility of a ventricular tachyarrhythmia is heightened.

Holter Monitor

• This investigation is grossly overused and of little value in patients with infrequent symptoms, particularly younger patients or if the ECG is normal.
• Recommended mainly in patients with frequent symptoms, ie. occurring daily or at least multiple times per week.
• Occasionally helpful in detection of silent features of disease, eg QT abnormalities, chronotropic incompetence, asymptomatic sinus pauses.

External Event (Loop) Monitor

• These store less information than Holter Monitors but allow up to a week monitoring.
  • therefore useful in patients with frequent symptoms where Holter has been unrewarding.
  • more useful for pre-syncope/dizzy spells rather than complete loss of consciousness.

Echocardiography

• Echocardiography is recommended particularly if the ECG or cardiac auscultation are abnormal.
• It can be diagnostic in some cases
  • aortic stenosis,
  • HOCM.
• The finding of substantially impaired left ventricular (or right ventricular) systolic function or wall motion changes consistent with prior myocardial infarction should raise suspicion of ventricular tachyarrhythmias.

Tilt Table Testing

• Performed in cases of suspected neurally mediated syncope
  • a positive test which exactly reproduces patient symptoms is virtually diagnostic, but a negative test does not exclude this diagnosis.
• Protocols vary but in general tilt testing is performed as either a 40-minute passive tilt or a 10-minunte passive tilt followed by provocation with either then isoprenaline or sublingual nitroglycerine
  • provocation improves sensitivity but at the cost of some false positive results.

Implantable Loop Recorder

• A small metal device implanted subcutaneously with a battery life of >1yr, which continually records the patients ECG. Information is 'frozen' and stored for later retrieval by patient activation using an external activator soon after the episode of syncope.
  • Autoactivation parameters can also be set to improve sensitivity.
  • Once information is downloaded the device can be reset to store future events.
• A very useful tool particularly in patients with infrequent but recurrent syncope without diagnosis after conventional investigations.

Exercise Stress Testing

• May be helpful if symptoms typically occur during exertion.
• Can be combined with thallium perfusion imaging or echocardiography for better predictive accuracy or if cardiac structural abnormalities suspected.

Invasive Investigations

• Coronary angiography may be indicated if other tests suggest possible ischaemic heart disease.
• Electrophysiological Testing may be required if tachyarrhythmias are identified or suspected.

Neurological Investigations

• Cerebral CT or MRI are recommended when
  • the event was a first seizure event
  • focal neurological signs are present
  • head injury occured due to the loss of consciousness
• Electroencephalograms (EEG's) are most helpful when performed within 24 hours of a suspected seizure
  • If unremarkable and a seizure is suspected then a sleep deprived EEG can increase yield
  • Longer EEG monitoring with video telemetry can also be performed.
• Carotid dopplers are not a useful investigation in the assessment of patients with transient loss of consciousness.

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