Nonarrhythmic syncope documented by an implantable loop recorder (an ISSUE substudy)

Owing to the episodic behavior of syncope, the correlation of spontaneous syncopal episodes with an abnormal finding can be regarded as a reference standard. In the International Study on Syncope of Uncertain Etiology (ISSUE),(1,2) the most frequent finding observed during syncopal recurrences was severe bradycardia or an asystolic pause, thus establishing the mechanism of syncope. In the other cases, normal sinus rhythm was frequently recorded at the time of syncope. Although not diagnostic, this finding allows us to definitely exclude an arrhythmia as the cause of syncope. In this substudy from ISSUE, we analyzed in detail the characteristics of patients who had an electrocardiographically documented nonarrhythmic syncope.