Urgent considerations
See Differentials for more details
It is critical to identify patients with a high risk of death. The presence of factors such as structural heart disease, heart failure, cerebrovascular disease, family history of sudden cardiac death, trauma, or abnormal ECG findings indicate that a patient may be at high risk of death.[12][19] Causes of syncope that need to be excluded urgently include those listed below.
Myocardial infarction (MI) and ischemia
An acute MI or a remote MI, 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 or dyspnea. An 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, medications 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 should be excluded, such as Wolff-Parkinson-White syndrome and inherited cardiac ion channel abnormalities (e.g., long QT syndrome and Brugada syndrome).
Occult hemorrhage
Significant hemorrhage from gastrointestinal bleeding, tissue trauma, ruptured aortic aneurysm, ruptured ovarian cyst, ruptured ectopic pregnancy, retroperitoneal hemorrhage, or ruptured spleen may present with syncope.
Aortic dissection
Needs to be considered in patients with chest and back pain. Oxygen/advanced life support protocol and hemodynamic support should be instituted without delay if dissection is suspected. ECG may be abnormal if the dissection involves the coronary vessels, and chest x-ray (if the patient’s clinical status allows) may show a widened mediastinum. If available, immediate investigation with transthoracic echocardiogram is recommended.[20][21] However, an urgent contrast computed tomography (CT) chest is required for definitive diagnosis (transesophageal echocardiography [TEE] and magnetic resonance imaging are alternatives).
Cardiac tamponade
May be caused by acute MI, aortic dissection, trauma, hypothyroidism, or pericarditis. Immediate pericardiocentesis is required.
Severe hypoglycemia
Severe hypoglycemia due to excessive administration of insulin, hepatic disease, or islet of Langerhans tumor may cause syncope. All patients presenting acutely with syncope should have blood glucose level measured as part of the initial assessment.
Hypoglycemia and associated loss of consciousness is generally not transient unless treated, and thus hypoglycemia is often excluded from studies of syncope.
Addison 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.[22]
Massive pulmonary embolism
Saddle pulmonary embolus produces cardiac outflow obstruction, resulting in decreased cerebral perfusion and syncope.[23] Prospective studies report pulmonary embolism in between 2.3% and 25.3% of patients hospitalized with syncope.[24] Reports on the prevalence of pulmonary embolism in patients hospitalized with syncope vary widely from <1.0% to 17.3%.[24][25]
The history needs to include assessment of possible thromboembolic (TE) risk factors, such as previous TE disease, prolonged immobilization (e.g., flight >4 hours), recent surgery, smoking, oral contraceptive pill or hormone replacement therapy, known malignancy, or family history of TE.[26]
Urgent evaluation with a CT pulmonary angiogram, ventilation/perfusion scan, D-dimer, or TEE (showing right heart failure or extension of thrombus in pulmonary artery) can help 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.[27]
Thrombolysis should be considered for patients with massive pulmonary embolism causing cardiogenic shock.[28]
Subarachnoid hemorrhage
Headache, particularly when ''thunderclap'' in nature, or the appearance of focal neurologic signs in a patient with syncope, should raise subarachnoid hemorrhage as a potential cause. If subarachnoid hemorrhage is suspected, an urgent noncontrast head CT scan should be ordered as soon as possible.
There is no utility in routinely obtaining a head CT scan in patients with syncope, because lack of either a headache or abnormal neurologic examination adequately rules out subarachnoid hemorrhage as the cause of the syncopal event.[29][30][31]
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