Urgent considerations
See Differentials for more details
It is critical to identify patients with a high risk of death. The presence of structural heart disease or abnormal ECG findings indicate that a patient may be at high risk of death.[16] Causes of syncope that need to be excluded urgently include those listed below.
Myocardial infarction and ischaemia
An acute myocardial infarction or a remote myocardial infarction, especially with left ventricular dysfunction, can result in syncope due to ventricular arrhythmia, which can be life-threatening. Patients may have a history of known coronary artery disease (CAD) and preceding chest pain. ECG should be performed immediately to look for signs of infarction such as ST-segment elevation, new left bundle branch block, and arrhythmias.
Cardiac arrhythmias
Bradyarrhythmia and tachyarrhythmia are potentially life-threatening conditions that present with syncope. A history of CAD, medicines that promote AV block or torsades de pointes, and increased age increase the likelihood of arrhythmias. Less common causes of cardiac arrhythmias associated with sudden death, such as Wolff-Parkinson-White syndrome and inherited cardiac ion channel abnormalities (such as long QT syndrome and Brugada syndrome), should be excluded.
Occult haemorrhage
Significant haemorrhage from gastrointestinal bleeding, tissue trauma, ruptured aortic aneurysm, ruptured ovarian cyst, ruptured ectopic pregnancy, retroperitoneal haemorrhage, or ruptured spleen may present with syncope.
Aortic dissection
Needs to be considered in patients with chest and back pain. ECG may be abnormal if the dissection involves the coronary vessels, and chest x-ray may show a widened mediastinum; however, definitive testing with trans-oesophageal echocardiogram (TOE) or contrast computed tomography (CT) chest is urgently required to show the intimal flap and false lumen of aortic dissection.
Cardiac tamponade
May be caused by acute myocardial infarction, aortic dissection, trauma, hypothyroidism, or pericarditis. Immediate pericardiocentesis is required.
Severe hypoglycaemia
Severe hypoglycaemia due to excessive administration of insulin, hepatic disease, or islet of Langerhans tumour may cause syncope. All patients presenting acutely with syncope should have blood glucose level measured as part of the initial assessment.
Hypoglycaemia and associated loss of consciousness is generally not transient unless treated, and thus hypoglycaemia is often excluded from studies of syncope.
Addison's disease
Acute, life-threatening addisonian crisis can present with syncope, nausea and vomiting, fever, hypotension, hyperpigmentation, and electrolyte abnormalities. Presumptive treatment with hydrocortisone is required to correct hypotension.[17]
Massive pulmonary embolism
Saddle pulmonary embolus produces cardiac outflow obstruction, resulting in decreased cerebral perfusion and syncope.[18] Prospective studies report pulmonary embolism in between 2.3% and 25.3% of patients hospitalised with syncope.[19]
The history needs to include possible thromboembolic (TE) risk factors, such as previous TE disease, prolonged immobilisation (e.g., flight >4 hours), smoking, oral contraceptive pill or hormone replacement therapy use, known malignancy, or family history of TE.
Urgent evaluation with a CT pulmonary angiogram, ventilation/perfusion scan, D-dimer, or TOE (showing right heart failure or extension of thrombus in pulmonary artery) can help to make the diagnosis, and ECG changes of S1Q3T3 or right bundle branch block may also be seen. Arterial blood gases can quantify the degree of hypoxia.[20]
Thrombolysis should be considered for patients with massive pulmonary embolism causing cardiogenic shock.[21]
Subarachnoid haemorrhage
Headache, particularly when "thunderclap" in nature, or the appearance of focal neurological signs in a patient with syncope, should raise subarachnoid haemorrhage as a potential cause.
There is no utility in routinely obtaining a head CT scan in patients with syncope because lack of either a headache or abnormal neurological examination adequately rules out subarachnoid haemorrhage as the cause aetiology of the syncopal event.
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