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Circulation. 2017;136:e60–e122. DOI: 10.1161/CIR.0000000000000499 August 1, 2017 e79 CLINICAL STATEMENTS AND GUIDELINES

patients with syncope and heart disease would include treating the immediate cause of syncope and further assessing long-term management strategies to improve prognosis. The recommendations stated in this section focus on syncope relevant to and within the context of the specific stated cardiac condition.

4.1 Arrhythmic Conditions: Recommendations

Cardiac arrhythmia is a common cause of syncope, and the prompt identification of an arrhythmic etiology has diagnostic and prognostic implications. When bradyar- rhythmias and tachyarrhythmias are discovered in patients with syncope, determining their causal relationship to syncope often poses challenges for the practitioner. The baseline presence of an arrhythmia does not necessarily represent the etiology of syncope (eg, marked resting bradycardia in a young patient with syncope). Furthermore, determining the significance of atrial tachyarrhythmias and VT—which are often paroxysmal and occult on initial evaluation—poses additional challenges and may warrant a more extensive evaluation (Section 3.2). Section 4.1 broadly outlines strategies to guide the practitioner when evaluating patients with bradycardia, supraventricular arrhythmias (including AF), and VT.

4.1.1 Bradycardia: Recommendation

Recommendation for Bradycardia

COR LOE Recommendation

I C-EO In patients with syncope associated with bradycardia, GDMT is recommended.12

N/A A search and review of papers on syncope and bradycardia has been performed since the last updated guidelines were published in 2012.12 The writing committee supports the previous recommendations pertaining to syncope in patients with sinus node dysfunction and AV conduction diseases. In adult patients presenting with syncope and chronic bifascicular block but without documented high-degree AV block, for whom other causes have been excluded, an RCT265 showed that a dual-chamber pacemaker reduced recurrent syncope. The evidence continues to support, without change from the previous recommendation, the notion that permanent pacemaker implantation is reasonable for syncope in patients with chronic bifascicular block when other causes have been excluded.

The use of adenosine triphosphate in the evaluation of syncope in older patients continues to evolve. In a small, single-blind trial of older patients (mean age 75 years) randomized to active pacing or back-up pacing with documented adenosine triphosphate– sensitive sinoatrial or AV block, there was a 75% risk reduction in syncope recurrence with dual-chamber pacing.266 Adenosine triphosphate is not available in the United States. The writing committee has reached a consensus not to make a new recommendation on its use for syncope evaluation because of the limited data at this time.

4.1.2 Supraventricular Tachycardia: Recommendations

Recommendations for Supraventricular Tachycardia (SVT)

COR LOE Recommendations

I C-EO In patients with syncope and SVT, GDMT is recommended.10

N/A Although patients with SVT frequently manifest palpitations and lightheadedness, syncope is uncommon. Of note, older patients with paroxysmal SVT are more prone to syncope or near-syncope than are younger patients; these symptoms appear to be independent of the rate of tachycardia, which is generally slower in older adult patients than in younger patients.267,268 Younger patients with SVT causing syncope generally have a very rapid tachycardia. Evaluation of syncope in patients with Wolff-Parkinson-White syndrome with preexcitation on ECG requires a thorough history to differentiate an arrhythmic syncope from a nonarrhythmic syncope, such as V VS, in younger patients.269 When a patient with syncope reports antecedent palpitations and lightheadedness, VT should be more strongly suspected than SVT. EPS may be useful to distinguish a VT from an SVT responsible for syncope associated with these antecedent symptoms. It should be noted that palpitations can also precede vasovagal faints due to sinus tachycardia, so not all palpitations are necessarily due to paroxysmal SVT or VT. I C-EO In patients with AF, GDMT is recommended.16

N/A AF can be associated with syncope. As with other forms of SVT, syncope from a rapid ventricular response (in the absence of preexcitation) is relatively unusual. Patients with chronic AF merit control of the ventricular response or maintenance of sinus rhythm with appropriate antiarrhythmic therapy (in carefully selected patients).16 Patients with paroxysmal AF are predisposed to an abnormal neural response during both sinus rhythm and arrhythmia, and the onset of AF may trigger V VS.270 In patients with sinus node dysfunction, syncope could occur upon termination of AF when prolonged pauses are present.

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