Implanted cardiac monitors provide continu- ous rhythm monitoring and stored recordings of electrograms based on patient activation or pre- set parameters, allowing a prolonged monitor- ing period of a few years. These devices require a minor invasive procedure with local anesthesia for implantation. In patients with sporadic symp- toms, including syncope, implantable recorders are useful in diagnosing serious tachyarrhythmias (including VA) and bradyarrhythmias.S4.2.3-2 S4.2.3-4 They are generally reserved for patients in whom other ambulatory monitoring is nonrevealing due to the infrequency of events. A 25% added yield in diagnosis has been described after an unreveal- ing external ambulatory monitor.S4.2.3-5 In a study of patients with syncope, the implantable moni- tor had a greater diagnostic yield than conven- tional testing with external monitoring, tilt table testing and electrophysiological study.S4.2.3-2 A systematic review in patients with syncope con- cluded that use of these devices provide a higher rate of diagnosis and a trend toward reduction in syncope relapse after diagnosis, as compared with conventional management.S4.2.3-3 A prospec- tive study of patients after MI, with LVEF <40%, demonstrated NSVT (>16 beats long) in 13%, VT (>30 s) in 3% and VF in 3% of patients.S4.2.3-1 It is important to accurately correlate the symptoms with the arrhythmias detected by implanted car- diac monitors. 4.2.4. Noninvasive Cardiac Imaging Recommendations for Noninvasive Cardiac Imaging Referenced studies that support the recommendations are summarized in Online Data Supplement 6. 