Investigations
1st investigations to order
12-lead ECG
Test
Should be obtained in all patients.
Patients with recurrent syncope, or those who have experienced trauma due to syncope, warrant further evaluation with an ambulatory ECG monitor (i.e., Holter monitor).
Result
rules out atrioventricular block, bradycardia, asystole, long QT, bundle branch block
serum haemoglobin
Test
Obtained to rule out syncope caused by anaemia.
Result
normal; low in anaemia
plasma blood glucose
Test
Obtained to rule out syncope caused by hypoglycaemia.
Result
normal; low in hypoglycaemia
serum beta-hCG (human chorionic gonadotrophin)
Test
Obtained to rule out syncope caused by pregnancy.
Result
negative; positive in pregnancy
cardiac enzymes
Test
Obtained to rule out myocardial infarction if there is clinical suspicion.
Result
normal; elevated in myocardial infarction
D-dimer level
Test
Obtained to rule out pulmonary embolism if there is clinical suspicion.
Result
normal; elevated in pulmonary embolism
serum cortisol
Test
Obtained to rule out syncope caused by adrenal insufficiency.
Result
normal or decreased
urea or serum creatinine
Test
Obtained to rule out syncope caused by dehydration.
Result
normal or elevated
Investigations to consider
echocardiogram
Test
Should be obtained if there is any concern that structural heart disease is present or needs to be excluded.
Result
rules out hypertrophic cardiomyopathy, aortic stenosis, poor ventricular function
tilt-table test
Test
Used only if there is suspicion of vasovagal syncope (VS) but the medical history is not convincing on its own. May be used to teach patients about premonitory symptoms in VS syndrome or to assure a patient that the physician has had an opportunity to witness an event.
Detailed discussion of tilt-table testing protocols can be found in the American College of Cardiology (ACC) expert consensus report and guideline documents from the European Society of Cardiology and the ACC/American Heart Association/Heart Rhythm Society.[1][2][34]
The first step is passive head-up tilt at 60° to 70°, during which the patient is supported by a footplate and gently applied body straps, for 20-45 minutes (protocols vary).
If needed, tilt testing is repeated with a drug challenge. Until recently, the most frequently used provocative drug was isoprenaline, usually given in escalating doses. However, intravenous or sublingual glyceryl trinitrate has gained favour, in part because it expedites the procedure without adversely affecting diagnostic use.
The so-called Italian protocol, in which a 20-minute passive tilt is followed if necessary by sublingual glyceryl trinitrate, has become the most popular protocol as a result of its relatively short duration with well-preserved specificity and sensitivity.
Result
reproduction of symptoms/syncope, bradycardia, hypotension
carotid sinus massage (CSM)
Test
Used to diagnose carotid sinus syndrome (CSS) in patients with a history of syncope.
CSS may be diagnosed when CSM reproduces symptoms as a result of ≥1 of the following being induced: >3 seconds of asystole, paroxysmal atrioventricular (AV) block, a marked decrease in systemic arterial pressure (usually a drop in systolic BP ≥50 mmHg), or a combination of these.[1][2][48] CSM should be performed in both upright and supine positions, with pressure applied for 5 seconds in each position.[1] The European Society of Cardiology recommends applying pressure for 10 seconds to allow time for symptoms to develop.[48]
Abnormal responses can also be frequently observed in patients without syncope. The diagnosis may be missed in about one third of cases if only supine CSM is performed.
CSM should not be performed in patients who have experienced transient ischaemic attack or stroke within the past 3 months or in patients with carotid bruits (unless carotid Doppler studies convincingly exclude significant carotid artery narrowing).[2]
Result
reproduction of symptoms and at least one of the following: >3 seconds of asystole, paroxysmal AV block, or a marked decrease in systemic arterial pressure (usually a drop in systolic BP ≥50 mmHg)
insertable loop recorder
Test
Used if events are relatively infrequent (<1 or 2 per month) and an arrhythmia is suspected.
Result
rules out brady- or tachyarrhythmia
electrophysiological study
Test
Infrequently indicated.[1] May be used if structural heart disease is present and a tachyarrhythmia is suspected or in patients who may be experiencing intermittent high-grade conduction block. It is also warranted if there is suspicion of paroxysmal supraventricular tachycardia as the cause of symptoms, especially if the patient describes palpitations prior to syncope.
Result
rules out long sinus node recovery time, infrahisian conduction disease, inducible ventricular tachycardia
Valsalva manoeuvre
Test
The Valsalva manoeuvre is used to assess the integrity of the arterial baroreceptor reflex arc and may indicate the presence of autonomic failure that can cause syncope through orthostatic hypotension.[2] In itself, however, the Valsalva manoeuvre does not directly implicate a mechanism for syncope.
The Valsalva response is typically tested under continuous ECG and BP monitoring in addition to monitoring the patient for clinical symptoms.
Result
normal in NMRS; may indicate the presence of autonomic failure that can cause syncope through orthostatic hypotension
active standing test
Test
The active standing test assesses patient response to active movement from supine to upright posture. Active muscle movement is expected to propel more blood towards the central circulation to provide the increase in cardiac output required for upright posture. The initial hypotension occurs on active standing but not on tilting. To detect the pressure decrease, beat-to-beat pressure monitoring (usually non-invasive) is essential. A ≥3-minute period of active upright standing may also demonstrate later diminution of BP indicative of classic orthostatic hypotension (delayed orthostatic hypotension).[1][48]
Result
to rule out orthostatic hypotension
cold pressor test
Test
The cold pressor test is performed by immersing the hand into a container of ice-cold water, usually for 1 minute. Any changes in blood pressure and heart rate are recorded. It has not been used to identify a specific diagnosis.
Result
may provide insight into autonomic reflex integrity
cough test
Test
Induced cough may help assess susceptibility to cough (tussive) syncope, but few data are available.[52] As with carotid sinus massage, it may be best undertaken with the patient in the upright posture.
Diagnostic criteria for haemodynamic response to induced cough have yet to be determined.
Result
to rule out susceptibility to cough syncope
Emerging tests
adenosine triphosphate (ATP) test
Test
The value of bolus administration of ATP remains controversial.[2] The ATP test may be useful to identify a form of syncope associated with neurally mediated paroxysmal atrioventricular (AV) block in certain older people in whom other causes have been excluded, and may guide a decision to initiate permanent pacing by unmasking occult AV nodal disease in susceptible people.[1] The diagnostic and predictive value of the test remains to be confirmed by prospective studies. In the absence of sufficient data, the test may be considered at the end of the diagnostic work-up.
The most thoroughly tested protocol involves injection of a 20-mg bolus of ATP into a brachial vein in a supine patient who is undergoing continuous ECG monitoring.[49] BP is monitored non-invasively.
The outcome of the test (positive or negative) depends on the duration of the ATP-induced cardiac pause. A pause >10 seconds, even if interrupted by escape beats, is defined as abnormal. Some reports suggest that a pause >6 seconds is sufficient to declare the test abnormal.[50] For patients with abnormal responses, reproducibility is approximately 80% both in the short and the long term.
Because of the possibility of bronchospastic reactions, the ATP test is contraindicated in patients with known asthma.
Result
identifies form of syncope associated with presumed neurally mediated paroxysmal AV block in certain older people
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