Invasive electrophysiologic testing is considered if noninvasive testing does not identify arrhythmia in patients with any of the following: Unexplained recurrent syncope Unexplained red flag findings Ischemic cardiomyopathy, non-ischemic cardiomyopathy, and adult congenital disease, or unexplained syncope that does not otherwise meet criteria for an ICD used for primary prevention A negative response defines a low-risk subgroup with a high rate of remission of syncope.