Digital implantable loop recorders in the investigation of syncope in children: Benefits and limitations

BACKGROUND Conventional diagnostic methods for detecting arrhythmogenic causes of syncope in children are poor. Digital implantable loop recorders are of proven value in adults. OBJECTIVES The purpose of this study was to evaluate digital implantable loop recorders in the investigation of syncope in children. METHODS We reviewed the clinical and technical records of 18 consecutive patients (6 female and 12 male; age <= 16 years) who received an implantable loop recorder from 1999 to 2005. RESULTS Median age at implantation was 11.3 years (range 4.6-16.5 years). Median duration of the device in situ was 18 months (range 5-36 months). Median time to diagnosis was 6 months (range 1 day to 17 months). Two patients had a congenital heart defect. Ten children (56%) had an event, 9 (50%) of whom had diagnostic information; 5 (28%) had profound bradycardia or asystole; 2 (11%) had polymorphic ventricular tachycardia (VT); and 1 child had supraventricular tachycardia. One patient died, but the automatically activated recording was recorded over again after death. One child had sinus rhythm during syncope. One child with polymorphic VT had no auto-activation on two occasions, and the third activation was triggered by asystole after VT terminated. Sixteen patients (89%) had false-positive activations as a result of either artifact or sinus tachycardia. CONCLUSION The digital implantable loop recorder is a useful diagnostic modality in children with unexplained syncope. However, the automatic detection algorithm is imperfect, missing genuine polymorphic VT and frequently interpreting muscle tremors as VT. Because of continuous overwriting by automatic detection, genuine arrhythmias may be over-recorded by artifact.