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Circulation. 2017;136:e60–e122. DOI: 10.1161/CIR.0000000000000499 August 1, 2017 e71 CLINICAL STATEMENTS AND GUIDELINES

IIb C-LD Usefulness of brain natriuretic peptide and high-sensitivity troponin measurement is uncertain in patients for whom a cardiac cause of syncope is suspected.125,127,129,130

See Online Data Supplements 7 and 8. Although data to support biomarker testing are in general relatively weak, there are sufficient data to suggest that natriuretic peptide is elevated in patients whose subsequent cause for syncope is determined to be cardiac. A systematic review of biomarkers found little value in contemporary troponin measurement unless acute myocardial infarction is suspected, and there is modest predictive value for high-sensitivity troponin and natriuretic peptides for major adverse cardiovascular events. The ability of troponin and natriuretic peptide measurement to influence clinical decision making or patient outcome is unknown.129 III: No Benefit B-NR Routine and comprehensive laboratory testing is not useful in the evaluation of patients with syncope.126,131

See Online Data Supplements 7 and 8. There are no data on the utility of a standardized broad panel of laboratory testing in patients with syncope. Specific cardiac biomarkers may play a limited role when directed by clinical suspicion from the baseline assessment. There is little biological plausibility linking the remaining elements of broad-panel laboratory testing to the presentation or mechanism of syncope.

Recommendations for Blood Testing (Continued)

COR LOE Recommendations

Recommendations for Cardiac Imaging

COR LOE Recommendations IIa B-NR Transthoracic echocardiography can be useful in selected patients presenting with syncope if structural heart disease is suspected.80,99,124

See Online Data Supplement 9. Cardiac imaging is often used to identify a structural cardiac abnormality, and imaging with transthoracic echocardiography is widely used for this purpose because it is noninvasive and low risk. Transthoracic echocardiography can be useful when healthcare providers are concerned about the presence of valvular disease (eg, aortic stenosis), HCM, or LV dysfunction.124,133 In a retrospective study of patients presenting with syncope and suspected cardiac disease after history, physical examination, or ECG, the echocardiogram suggested a diagnosis of cardiac syncope in 48% of the study cohort.99 In a prospective evaluation of 650 patients referred for syncope of unknown origin, 88 patients had an abnormal history or ECG; an echocardiogram showed systolic dysfunction (LV ejection fraction ≥40%) in 24 patients80; and 50% of patients with LV systolic dysfunction had manifest arrhythmias, compared with 9% with minor, incidental abnormalities (P<0.01). Although an echocardiogram may not be able to establish the immediate cause of syncope, it provides information for a potential disease substrate related to prognosis.

IIb B-NR Computed tomography (CT) or magnetic resonance imaging (MRI) may be useful in selected patients presenting with syncope of suspected cardiac etiology.134

See Online Data Supplement 9. Imaging modalities, including CT and MRI, are usually reserved for selected patients presenting with syncope, especially when other noninvasive means are inadequate or inconclusive. These modalities offer superior spatial resolution in delineating cardiovascular anatomy (eg, in patients with structural, infiltrative, or congenital heart disease [CHD]).135,136 The use of CT and MRI in contemporary cardiology is increasing.137,138 Their role in the evaluation of syncope has been investigated.139 The use of CT or MRI increased from 21% in 2001 to 45% in 2010, as reported in a series of patients evaluated for syncope in the ED.134 MRI is useful when there is a suspicion of ARVC or cardiac sarcoidosis.140,141 When pulmonary embolism is suspected in patients presenting with syncope to the hospital, CT can confirm the diagnosis in selected patients.128 CT or MRI may not provide answers about the cause of syncope. They provide information on the structural disease substrate relevant to the overall diagnosis and subsequent evaluation and follow-up in selected patients presenting with syncope. III: No Benefit B-NR Routine cardiac imaging is not useful in the evaluation of patients with syncope unless cardiac etiology is suspected on the basis of an initial evaluation, including history, physical examination, or ECG.77,99

See Online Data Supplement 9. Although some investigators have advocated for cardiac imaging—particularly transthoracic echocardiography—as a routine screening examination for patients with syncope who lack clear signs or symptoms of cardiovascular disease,133 clinical evidence does not support such practice. Unexpected findings on echocardiograms to explain syncope are uncommon; a “screening” echocardiogram is of low utility.142 In 1 evaluation of 2106 inpatients with syncope, a battery of testing, including cardiac enzymes, CT scans, echocardiography, carotid ultrasonography, and electroencephalography, contributed to the diagnosis or management in <5% of cases and helped determine the etiology of syncope <2% of the time.77 Similarly, in another retrospective series of 128 inpatients with syncope, it was found that echocardiograms in patients with no clinical evidence of heart disease according to history, physical examination, or ECG either were normal (63%) or provided no useful additional information for arriving at a diagnosis (37%).99 Finally, radionuclide imaging and cardiac catheterization have little role in the evaluation of syncope.

3.2.1 Cardiac Imaging: Recommendations

3.2 Cardiovascular Testing: Recommendations

Cardiovascular causes of syncope are common. The presence of significant cardiovascular diseases, often associated with the cardiovascular causes of syncope, portends a poor prognosis.35,132 As such, cardiovascular testing can be a critical element in the evaluation and management of selected patients with syncope. It is important also to recognize that the abnormalities found during cardiovascular testing may not have a causal relationship to syncope itself. Determining the significance of such abnormalities, their causality, and whether subsequent treatment is merited requires clinical judgment and appropriate selection of cardiovascular testing.

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